Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 339  Indian Academy of Sciences

How to make boron harder than diamond? M M BALAKRISHNARAJAN and ELUVATHINGAL D JEMMIS School of Chemistry, University of Hyderabad, Central Univ. P.O., Hyderabad 500 046, India With its electron-precise covalent bonding, the extreme hardness of diamond is not surprising. On a scale of 1–15 (the modified Mohr’s Scale of Hardness), diamond is at the top. Despite its widely discussed electron deficiency, the beta-rhombohedral polymorph of elemental boron has a hardness value of 11. This is to be compared to the hardness parameter of metal aluminum which stands at 3. While it is difficult to increase the hardness of diamond, it may be possible to do so for boron. We have analysed the structure of elemental boron with respect to its electron deficiency. Though the betarhombohedral boron is electron deficient, the extent of electron deficiency is not nearly as much as is anticipated. The schematic decomposition of the distinct structural fragments from the unit cell of elemental boron, the comparison of their electronic structures with molecules that can be constructed from these fragments, and the translation of the individual electronic structure requirements to the elemental boron polymorph are presented in detail. These studies have led, among others, to the formulation of a series of electron counting rules for polycondensed boranes and to encapsulated polyhedral structures. We also predict the precise number of electrons required per unit cell to make the beta-rhombohedral boron electron sufficient without changing its structure.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 340  Indian Academy of Sciences

The bis(m-thiolato) di-copper centre in cytochrome oxidase: A novel conformational switch for electron transfer SAYAN GUPTA and SHYAMALAVA MAZUMDAR Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India Cytochrome oxidase is a ubiquitous membrane-bound enzyme involved in the terminal stage of the respiratory electron transfer chain in cellular respiration. The enzyme consists of three metal active centres namely, the binuclear copper (CuA) site, sixcoordinated heme a(Fe: a) site and the binuclear iron–copper catalytic site (Fe: a3-CuB). We are interested in the understanding of the structural and mechanistic aspects of the biochemical functions of cytochrome oxidase and have been involved in detailed spectroscopic and kinetic studies of the enzyme and its analogues. The binuclear copper (CuA) site forms the first electron entry point in the enzyme. It is located in sub-unit II of the enzyme exposed to the matrix side of the membrane. This CuA site consists of a novel bis(m-thiolato) bridging by two cysteine (C220 & C216) residues. The other ligands to the copper centres are His181, His224, Glu218 and Met227. The native enzyme has been shown to consist of mixed valence coppers at this site with an average charge of 1⋅5 units on each copper. The mechanism of electron transfer to and from the CuA site in cytochrome oxidase is a subject of immense interest. The soluble fraction of the sub-unit II cloned and over-expressed in E. coli has been studied as a model of the electron entry site (CuA) of cytochrome oxidase. The CuA site in the sub-unit II was found to exist in a pH induced conformational equilibrium with a high pH conformer being preferred at elevated temperatures. Such conformational fluctuations can provide a gating mechanism for the electron transfer process. We discuss some of our recent results on this conformational equilibrium in the dicopper site in the light of understanding of the functional properties of the intact enzyme.

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Formation, spectroscopy and reactivity of the [L3CuII2CuIIIO2]3+ core: A new structural motif in copper dioxygen chemistry PULAKESH MUKHERJEE 1, TIM MACHONKIN 1, JENNIFER L DUBOIS 1, ADAM P COLE 1, BRITT HEDMAN 1,2, KEITH O HODGSON 1,2, EDWARD I SOLOMON 1 and T D P STACK 1 1 Department of Chemistry, Stanford University, Stanford, CA 94305, USA 2 Stanford Synchrotron Radiation Laboratory, SLAC, Stanford, CA 94309 USA Interaction of copper with dioxygen is of importance in both industrial oxidation processes and biological systems. Thus discrete complexes resulting from reactions of Cu(I) complexes and dioxygen are of great interest. Mononuclear and binuclear copper dioxygen complexes have been known for some time. Herein we report the characterization of a novel class of trinuclear complexes generated using simple diamine ligands and Cu(I). A 3:1 LCu(I):O2 stoichiometry leads to complete 4 e– reduction of O2. Crystallographic, spectroscopic, and theoretical investigations are consistent with the formation of a localized mixed-valence [CuIICuIICuIII] core. This 3:1 metal:O2 stoichiometry is unprecedented not only for copper but for any transition metal. A complete spectroscopic characterization and the reactivity of these complexes towards exogenous substrates will be presented.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 342  Indian Academy of Sciences

Organometallic fluorides of main group and transition elements HERBERT W ROESKY University of Gottingen, Gottingen, Germany Me3SnF, Ph2PbF2 and Ph3BiF2 are used for the preparation of organometallic fluorides. Their different properties in fluorination reactions are discussed. The application of organometallic fluorides as catalysts and matrices for trapping reactive intermediates is given (e.g. MeZnF). Moreover, the syntheses of difluoroorganometallic anions such as [Me2AlF2] are reported. In this paper, the reactions of titanium and zirconium fluorides with aluminium alkyls are described and the application of these systems in polymerization reactions is mentioned. In addition the recent chemistry on aluminium hydrides is reported.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 343  Indian Academy of Sciences

Interesting properties of some iron(II), copper(I) and copper(II) complexes with tridentate ligands P T MANOHARAN RSIC, Indian Institute of Technology, Chennai 600 036, India Tridendate ligands with nitrogen centers, generally well-known as the tripod ligands, have been of considerable interest to inorganic chemists dealing with the preparation of model compounds for hemocyanin, tyrosinase etc. We have found that such ligands when complexed with iron(II) and copper(II) and copper(I) ions produce not only structurally interesting molecules but also those with interesting magnetic and phase transition properties. Most of them exhibit molecular dynamics mainly because of the inherent ligand structure. Furthermore, the relative conformations of the ligands when two such ligands are added to the same metal have temperature dependent properties. There is a beautiful example of exchange coupling with both the ground and excited states involved, as proven by a combination of EPR and magnetic susceptibility. Similarly a combination of Mössbauer, magnetism and NMR spectroscopy – all temperature dependent – prove beyond doubt the nature of the structure-based phase transitions. All these and much more go to prove the versatility and usefulness of such ligands. These are discussed with suitable examples.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 344  Indian Academy of Sciences

Diastereoisomeric homo- and heterobimetallic Ru and Os complexes: Manifestation of properties due to electron and proton transfers SUJOY BAITALIK and KAMALAKSHA NAG Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700 032, India Intramolecular electronic communication in bi- and polynuclear ruthenium(II) and osmium(II) complexes with appropriate bridging and terminal oligopyridine ligands have received considerable attention. However, stereoisomeric complexity of such systems due to the chirality of each tris-chelate unit complicates the issue. We report here a series of RuIIRuII, OsIIOsII, and RuIIOsII complexes based on pyrazole-3,5-bis(benzimidazole) as the bridging ligand and 2,2′ -bipyridine or 1,10-phenanthroline as the terminal ligand. For each complex, either the meso (∧ ∆) and rac (∧ ∧ , ∆∆) forms or the two enantiomeric pairs (∧ ∆, ∆∧ ) and (∧ ∧ , ∆∆) have been isolated and characterized by NMR spectroscopy and X-ray crystallography. Since these complexes contain dissociable NH protons, physicochemical studies involving symbiotic electron and proton transfers have been carried out. The remarkable influence of protons on the extent of metal–metal interaction has been observed in terms of profound shifts of redox potentials, metal-to-ligand charge transfer and intervalence transfer transition energies and also the on/off effect of spectral emission.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 345  Indian Academy of Sciences

Modelling non-redox enzymes: Anaerobic and aerobic acetylene hydratase SABYASACHI SARKAR Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India Acetaldehyde is the first metabolite produced during acetylene degradation by bacteria either aerobically or anaerobically. Conversion of acetylene into acetaldehyde, ethanol, acetate, and biomass occurs in anaerobic cultures of Palobacter acetylinicus or aerobically with Mycobacterium lacticola, Nocardia rhodochrous, Rhodococcus Al, Bacillus sp and also with strains like MoAcy 1, MoAcy 2, TueAcy 1, and TueAcy 3 1. The first step of the fermentation pathway, the hydration of acetylene to acetaldehyde, is catalyzed by the enzyme, acetylene hydratase. A detailed biochemical assay on these systems showed that the anaerobic strain, WoAcy 1, from Palobacter acetylinicus possesses a tungsten-containing acetylene hydratase but the dependency on either molybdenum or tungsten of the aerobic strains could not be biochemically established. Among these, strains like MoAcy 1, and Tue Acy 1, though isolated from aerobic bacteria, require anaerobic conditions and strong reductants to catalyze the hydration of acetylene. In contrast, strains like MoAcy 2 and TueAcy 3 perform similar activity even under oxidising conditions without involving any reducing agent 1. Based on the biochemical report on the presence of tungsten-pterin enedithiolate ligation in the acetylene hydratase of Palobacter actylinicus 2, we have revealed the relevant chemistry prevalent in such enzymatic reactions involving synthetic model compounds 3. In continuation of our work related to the chemistry of meaningful analogue reactions of pterin containing molybdo- and tungsto-enzymes 4, the present work focuses on the essential difference in reactivity between the isolates from the aerobic and anaerobic strains of native systems by model reactions. References 1. Rosner, B M, Rainey F A, Kroppenstedt R M and Schink B 1997 FEMS Microbiol. Lett. 148 175 2. Rosener B M and Schink B 1995 J. Bacteriol. 177 5767 3. Yadav J, Das S K and Sarkar S 1997 J. Am. Chem. Soc. 119 4315 4. Das S K, Biswas D, Maiti R and Sarkar S 1996 J. Am. Chem. Soc. 118 1387

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Properties of extended inorganic solids predicted/rationalized by First Principles electronic structure calculations RAM SESHADRI and CLAUDIA FELSER 1 Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India 1 Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Mainz D-55099, Germany Due to the vastly complex nature of the problem, guidelines for the preparation of extended inorganic solids with specific electronic properties remain meagre. Here we present the use of First Principles LMTO band structure calculations for the rationalization of the properties of a number of interesting extended solids. These include metallic or semiconducting behaviour in some delafossite oxides 1 and the paraelectric to antiferroelectronic transition in an elpasolite associated with the localization of the lone pair on Pb 2. Through an analysis of the electronic structures of a number of superconductors 3–5, we find certain crucial features that permit us to propose candidate systems that might display this phenomenon. Through a related analysis of magnetic systems (isostructural with the superconductors) using spin-polarised calculations 3,6, we rationalize and predict the phenomenon of giant (or colossal) magnetoresistance (GMR) in a number of compounds. Some of these predictions have already borne fruit 7. References 1. 2. 3. 4. 5. 6.

Seshadri R, Felser C, Thieme K and Tremel W 1998 Chem. Mater. 10 2189 Seshadri R, Baldinozzi G, Felser C and Tremel W 1999 J. Mater. Chem. 9 2463 Felser C, Seshadri R, Leist A and Tremel W 1998 J. Mater. Chem. 8 787 Felser C, Thieme K and Seshadri R 1999 J. Mater. Chem. 9 451 Felser C and Seshadri R 1999 J. Mater. Chem. 9 459 Lang O, Felser C, Seshadri R, Renz F, Kiat J-M, Ensling J, Gutlich P and Tremel W 2000 Adv. Mater. 12 65 7. Felser C, Ahn K, Kremer R K, Seshadri R and Simon A 1999 J. Solid State Chem. 147 19

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The new world of phospha-organometallic chemistry JOHN F NIXON School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton BN1 9QJ, England The past few years have seen the development of a rich new area of organometallic chemistry in which phosphorus atoms have replaced CH-fragments in the more familiar unsaturated organic ligands. There is now an extensive range of phospha-organometallic compounds containing phospha-alkynes, phospha-alkenes, phospha-dienes, phosphaallyls, phosphacyclobutadienes, phosphacyclopentadienyls and phospha-arenes as well as tetraphosphacubanes and tetraphospha-barrelenes. The area has recently been reviewed in the book Phosphorus: The Carbon Copy by K B Dillon, F Mathey and J F Nixon (Wiley, 1998). This work discusses the key role of the phospha-alkyne, ButCP in the generation of a wide variety of novel phospha-organometallic compounds containing 1,3diphosphacyclobutadiene, 1,2,4-triphosphacyclopentadienyl, 1,3-diphosphacyclopentadienyl, 1,3,5-triphosphabenzene, and 1,3,5,7-tetraphosphabarrelene ring systems. Examples will be drawn from main group, transition metal, lanthanide and actinide elements. Sandwich, half-sandwich and triple decker sandwich compounds will be presented and discussed, as well as the synthetic utility of the technique of metal vapour synthesis. An additional feature of the phospha-organometallic compounds not available to conventional organometallic compounds, is their potential as ligands in view of the availability of the P-lone pair electrons and this aspect will also be covered.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 348  Indian Academy of Sciences

De novo design and synthesis of water-soluble gold(I) compounds: Structure–antitumor activity considerations KATTESH V KATTI 1,3, NAGAVARAKISHORE PILLARSETTY 1,2 and HIDEO KAMEI 4 Radiopharmaceutical Sciences Institute, Departments of 1Radiology, 2Chemistry and 3Research Reactor, University of Missouri, Columbia, MO 65211, USA 4 Department of Surgery, Aichi-Gakuin University Hospital, Nagoya, Japan Research in fundamental main group chemistry (and their coordination chemistry with specific transition metal precursors) is central to the design and development of transition metal-based compounds that meet certain structure–catalytic/biological activity relationships. Our recent studies have demonstrated that hydroxymethyl phosphine ligands (HMP) possess unique ligating characteristics in that they transmit several desirable properties to the coordinated transition metal compounds. Their coordination also brings about kinetic inertness, over a wide range of pH, in aqueous media 1,2. Gold compounds have been implicated for potential use in cancer therapy. However, there is no gold compound yet available for clinical use because of the pronounced kinetic instability of these compounds under physiological conditions. In the quest for designing therapeutically useful gold compounds, we have succeeded in the design and development of a series of gold(I) compounds via coordination with HMP ligands. As shown in structures A and B, subtle changes in ligand environments induce dramatic changes in the geometry around the Au(I) center. In vitro and in vivo studies using A have provided conclusive evidence that it inhibits growth of tumour cells derived from human colon, gastric and prostate carcinomas. New strategies in ligand design, coordination chemistry with coinage metals (Au and Ag) and structure-biological activity considerations are presented.

References 1. Katti K V, Gali H, Smith C J and Berning D E 1999 Acc. Chem. Res. 32 9 2. Gali H, Karra S R, Reddy V S and Katti K V 1999 Angew. Chem. Int. Ed. 38 2020

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Chemistry of peroxo-vanadium(V) and fluorochromates(VI): Development of newer reagents and methodologies UPASANA BORA, MIHIR K CHAUDHURI, SIDHARTHA S DHAR and DIPAK KALITA Department of Chemistry, Indian Institute of Technology, Guwahati 781 001, India Dioxygen activated through coordination to the metal center of a metalloenzyme catalyses a variety of biochemical oxidation reactions. Based on the knowledge of the activity of one such enzyme, vanadium bromoperoxidase (VBrPO), and the information that emerged out of our investigation of reactivity of peroxovanadium(V) systems, environmentally benign synthetic protocols have been developed for the synthesis of brominating agents as well as for bromination of organic substrates leading to bromoorganics which have garnered a significant amount of commercial importance. Elicited strategies of the present investigation are highlighted with reference to tetrabutylammonium tribromide (TBATB) and cetyltrimethylammonium tribromide (CTMATB) as the reagents, and V2O5–H2O2 promoted regioselective bromination of organic substrates by tertrabutylammonium bromide (TBAB) as a methodology. TBAB  or  CTMAB 

TBATB or CTMATB

V2O5, H2O2

Org

OrgBr

Sustained interest in the reaction chemistry of fluorochromates(VI) has now afforded a new reagent, 3,5-dimethylpyrazolium fluorochromate(VI), C5H8N2H[CrO3F] (DmpzFC), with the desired physical properties. The reagent is highly soluble in organic solvents and is far less acidic than its companion reagents. DmpzFC is capable of very efficiently oxidizing polycyclic hydrocarbons and primary, secondary and allylic alcohols to the corresponding carbonyl compounds under mild conditions. Several applications and advantages of the reagent including its efficacy in readily transforming ∆5-steroids to ∆5keto steroids are highlighted.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 350  Indian Academy of Sciences

Some interesting structural features and metallated hypervalent/electron deficient molecules B N ANAND Department of Chemistry, Panjab University, Chandigarh 160 014, India The metallation of hypervalent species/electron deficient molecules 1 of main group elements with transition metals through nucleophilic substitution reactions has resulted in the isolation of some novel products 2. These synthetic species have some interesting structural features. An overview of our experience in this field is highlighted. References 1. Anand B N, Rajwant B and Venugopalan P Indian J. Chem. (in press) 2. Anand B N, Krossing I and Nöth H 1997 Inorg. Chem. 36 1979

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 351  Indian Academy of Sciences

Influence of organic cations on the crystal packing of decavanadate containing solids A RAMANAN, PRASUN ROY, T DURAISAMY, SANJEEV SHARMA and P AYYAPPAN Department of Chemistry, Indian Institute of Technology, New Delhi 110 016, India Polyoxometallates form a rich class of inorganic materials which exhibit a range of molecular and electronic structural versatility, reactivity and relevance to catalysis, biology, medicine, geochemistry, material science, and topology 1,2. The metal oxide clusters invariably contain highly symmetrical core assemblies of MOn units which often adopt quasi-spherical structures based on Archimedean and Platonic solids, of considerable topological interest. Particularly interesting are the polyoxovanadates with hollow spheres, which exhibit many different types of surface organization owing to a variety of metal macropolyhedra and macropolyhedral fragments built of VO4, VO5 and VO6 in addition to variable oxidation states V(IV) and V(V). Polyoxovanadates frequently show interesting host–guest interaction. Understanding the driving force for the formation of such clusters still remains a formidable challenge. In this talk, we will present our results on the synthesis and structural chemistry of decavanadate clusters exhibiting zero- and two-dimensional networks. The talk also addresses the chemistry of formation of such clusters in terms of the influence of organic cations.

References 1. Muller A, Peters F, Pope M T and Gatteschi D 1998 Chem. Rev. 1 1 2. Muller A, Syed Q N, Bogge H and Schmidtmann M 1999 Nature 397 48

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 352  Indian Academy of Sciences

Homolytic displacements at two reactive centres: Organobridged dicobaloximes and organodisulphonyl chloride B D GUPTA, V VIJAI KANTH and VEENA SINGH Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India Recent work has shown that organocobaloximes, RCo(dmgH)2Py, undergo very facile radical chain reactions (SH2 and SH2′ ) and provide an excellent handle in the form of the reactive Co–C bond for the functionalisation of the organic group by a variety of C, S and N centred radicals 1. RCoIII(dmgH)2Py + XY

R′ Y + X CoIII(dmgH)2Py

R = allyl, allenyl, benzyl, butenyl, hexenyl; R′= rearranged organic group XY = BrCCl3, CCl3CN, ArSO2Cl, PhSSPh, PhSeSePh. The reactions are free radical in nature and the yield of the products depend upon various factors like the nature of the organocobalt substrate, nature of the free radical and reaction conditions. It is envisaged that the utility of these reactions if extended to two reactive centres, either in the organometallic substrate or in the free radical substrate, will open-up ways for the synthesis of many new organic products. In this paper we report (a) the reactions of organobridged dicobaloximes (having two reactive Co–C bonds) with sulphur-centred radicals (TsCl, PhSSPh, PhSeSePh), (b) the reactions of diorganosulphonyl dichloride (having two reactive S–Cl bonds) with organocobaloximes. CoIIICH2ArCH2CoIII + XY → Products XY = TsCl, PhSSPh, PhSeSePh, Co = Co(dmgH)2Py hn RCo(dmgH)2Py + ClSO2 –– Ar ––SO2Cl ––––→ Products 0–5°C References 1. Gupta B D, Veena Singh, Qanungo K, Vijai Kanth V and Sengar R S 1999 J. Organometal. Chem. 582 279

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 353  Indian Academy of Sciences

Design of novel supramolecular self-assembly creating noninterpenetrating rectangular grid with a neutral cavity ERINGATHODI SURESH, KAMLA BOOPALAN, RAKSH VIR JASRA and MOHAN MADHAV BHADBHADE Silicates and Catalysis Division, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India Metal–organic composite materials with appropriate building blocks which can assemble into structures with specific and desired frameworks are challenging both for their solid state technology and for their chemical architecture. Of special interest is the construction of a microporous network that can exhibit reversible guest exchange and selective catalytic activities. The major problem encountered in the synthesis of molecular based microporous coordination polymers is the collapse of the structure upon removal of the included guest molecule in the cavity or interpenetration. Much less is known about extended two-dimensional systems based on molecular square sheets in general and rectangular grids in particular. By a judicious choice of the building units it is possible to design extended cationic, anionic and neutral frameworks with varied pore characteristics. The results reported herein illustrate the utility of using the process of self-assembly for the construction of neutral rectangular architecture. By selecting appropriate metal (Co+2, Cd+2) coordination and different edge-sharing ligands (4,4¢ -bpy, phth), we have developed a synthetic strategy to construct two neutral, noninterpenetrating rectangular grids which are structurally characterized. To the best of our knowledge this is the third structure reported in the area of neutral rectangular assembly. The staggered stacking between the 2D sheets makes the structure less intriguing and reducing the cavity size which accommodates two water molecules by O–H… O interaction.

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Monodentate behaviour of 2,2¢-bipyridine and 1,10-phenanthroline in cyclometallated rhodium(III) complexes – 1H and 13C NMR evidence G A NAGANAGOWDA 1, K V RAMANATHAN 1, V GAYATHRI 2 and N M NANJE GOWDA 1 1 Sophisticated Instruments Facility, Indian Institute of Science, Bangalore 560 012, India 2 Department of Chemistry, Central College Campus, Bangalore University, Bangalore 560 001, India Binuclear cyclometallated complex (I) [RhCl(m-Cl)(bBzlH2bz)]2 [bBzlH2bzH = 1,3bis(benzimidazolyl)benzene] undergoes dichlorobridge cleavage reaction with monobidentate ligands to produce mononuclear and heterocycle bridged binuclear complexes of the types RhCl(bBzlH2bz)(OClO3)(L/N-N) (L = AsPh3; N-N = 2,2¢ -bipyridine (bipy) or 1,10-phenanthroline (phen)) and [RhCl2(bBzlH2bz)]2(m-N-N) (N-N = pyrazine or 4,4¢ bibyridine), respectively. In the former complex (II), the bidentate chelating Nheterocycles show a monodentate coordination as evidenced by 2-D 1H-1H correlated and NOE experiments (DQF-COSY and ROESY), 1H-13C single- and multiple-bond correlated 2-D NMR experiments (PFG-HSQC and PFG-HMBC) and 1H, 13C spin lattice relaxation time measurements. The non-coordination of the pendant nitrogen of the heterocycle, bipy or phen is evidenced by the observation of two sets of signals together with the presence of interligand NOEs only between the coordinated part of the heterocycle and the bisbenzimidazole as seen in the corresponding ROESY spectrum. Further, the 1H and 13C spin lattice relaxation times are lower for the nuclei in the coordinated part of the heterocycle, bipy or phen than those for the uncoordinated part supporting the fact that only one of the two nitrogens of the heterocycle is coordinated to the metal. I

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A study of ruthenium complexes of some biologically relevant aN-heterocyclic carboxylic acids P SENGUPTA and S GHOSH Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700 032, India a-N-heterocyclic acids like pyridine-2-carboxylic acids, pyridine 2,6-, 2,5-, 2,3- dicarboxylic acids, imidazole-4,5-dicarboxylic acid and pyrazine-2-carboxylic acid exhibit diverse biological activities and also display a variety of coordination modes towards transition metal ions. The present study reports on the preparation, properties and biological activities (antibacterial action) of several ruthenium complexes involving these ligands. All the complexes are synthesized by following a general procedure via the Agcomplex of the appropriate a-N-heterocyclic carboxylic acid ligand. Ag+ ion has a very high affinity for Cl– to form AgCl and, thus free L is released in the reaction medium for coordination to M. Ag+ + 2LH → Ag(LH)2+ MeOH

Ru(PPh3)3Cl2 + Ag(LH)2+

Ru(PPh3)2(L)2. Reflux

Ligands used are pyridine 2,3-, 2,5-, and 2,6-dicarboxylic acids, imidazole-4,5dicarboxylic acid, pyridine-2-carboxylic acid and pyrazine-2-carboxylic acid. All the complexes are characterised by elemental analysis, various spectroscopic techniques and cyclic voltammetric studies. Coordination geometry around the Ru(II) acceptor center is established and structure of one representative complex [Ru(PPh3)2(L)2] (LH = pyridine2,3-dicarboxylic acid) is solved by single crystal X-ray diffraction technique. Antibacterial activities of the complexes are evaluated by determining their capacity to inhibit the growth of E. coli 10536 (MIC) in a nutrient broth.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 356  Indian Academy of Sciences

Metal-coordinated phenoxyl radicals: Models for the enzyme galactose oxidase MANISH BHATTACHARJEE, SHAMAYITA SEN GUPTA and RIYA DATTA Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India In recent years, studies on metal coordinated phenoxyl radicals have gained importance due to their biochemical significance. Such radicals are involved in the action of various enzymes like galactose oxidase, ribonucleotide reductase etc. The present report deals with the synthesis and characterization of new ligand systems containing phenoxide donor centres and their metal complexes and the generation of stable metal coordinated phenoxyl radicals in solution.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 357  Indian Academy of Sciences

Synthesis and DNA-interactions of new Co(III), Fe(II), Ni(II), Ru(II) and Os(II) complexes of modified phenanthroline ligands C V SASTRI, D EASWARAMOORTHY #, ATHILAKSHMI #, L GIRIBABU and B G MAIYA School of Chemistry, University of Hyderabad, Hyderabad 500 046, India # Present address: Crescent Engineering College, Vandalur, Chennai 600 048, India Metal complexes of the type [M(LL)3]n+, where LL is either 1,10-phenanthroline (phen) or a modified phen, are particularly attractive species for developing new diagnostic and therapeutic agents that can recognise and cleave DNA. The ligands or the metal in these complexes can be varied in an easily controlled manner to facilitate an individual application thus providing easy access to the understanding of details involved in DNAbinding and cleavage. Previously, we have reported the design, synthesis and DNA interactions of a few mixed-ligand complexes of the type [M(phen)2(LL)n+ 1. In this paper, we present results of analogous studies carried out with new complexes, the structures of which are shown below.

References 1. Arounaguiri S and Maiya B G 1999 Inorg. Chem. 38 842

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 358  Indian Academy of Sciences

Stability and thermodynamics of Zn(II)-cysteinemethylester and histidinemethylester system – Relevance to zinc core in transcription factor IIIA P RABINDRA REDDY, M RADHIKA and K FLORENCE NIGHTINGALE Department of Chemistry, Osmania University, Hyderabad 500 007, India Recently, much attention has been paid to a novel property of zinc in the putative formation of ‘zinc fingers’. The requirements for zinc in the regulation of gene expression is exemplified by transcription factor IIIA (TF IIIA). TF IIIA is a zinccysteine protein, which contains ‘zinc fingers’ that bind to DNA. ‘Zinc fingers’ are regions of protein containing four residues of histidine and/or cysteine that are coordinated to zinc in a tetrahedral configuration and form a loop that can take part in protein nucleic acid interactions 1,2. Thus the zinc-core, consisting of Zn-cysteinehistidine residues, has an important role in the stabilization of these ‘zinc fingers’. Given the ubiquitous occurrence of ‘zinc fingers’ in biological function, the stability and thermodynamic parameters associated with the interaction of zinc with cysteinemethylester and histidinemethylester as a model for zinc core were assessed. The various factors responsible for the formation and stabilization of the core were identified. References 1. Berg J M and Shi Y 1996 Science 271 2. Michael J B, Greggory W, David M and David R S 1998 J. Mol. Biol. 284 1307

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Chemically distinct coupled Cu(II) dimers: Structure and physicochemical properties R SRINIVASAN, R VENKATESAN, T M RAJENDIRAN and P SAMBASIVA RAO Department of Chemistry, Pondicherry University, Pondicherry 604 014, India Tridentate Schiff’s base prepared from 4-methyl-2-amino pyridine and salicylaldehyde acts as binucleating ligand, coordinating as bidentate with one metal ion and monodentate with the second metal ion. The binuclear Cu(II) complex with a m-acetato group has been prepared as the mono perchlorato salt. Electron paramagnetic resonance spectra at room temperature show strong coupling with zero field splitting, D = 134⋅5 mT, g = 2⋅353 and 2⋅159. Frozen dilute solutions show the characteristic patterns. Detailed analysis and simulation are presented. Electrochemical analysis also confirm strong interaction. Cyclic voltammetric studies show two successive one-electron transfer kinetics. Cu(II)Cu(II) ↔ Cu(I)Cu(II) ↔ Cu(I)Cu(I). The notable feature of the structure is that the Schiff base acts as a bidentate ligand (phenolic O- and imine –N=) towards one of the copper ions and binds to the other copper ion through the hetero N–atom.

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Perbrominated 2-nitro-tetraphenylporphyrins: Synthesis, characterisation and properties P BHAVANA and P BHYRAPPA Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India A new class of perbrominated 2-nitro-tetraphenylporphyrins [2-nitro-7,8,12,13,17,18hexabromo- and 2-nitro-3,7,8,12,13,17,18-heptabromo-5,10,15,20-tetraphenylporphinato copper(II) [CuTPP(NO2)(Br)6 and CuTPP(NO2)(Br)7] and their free bases and Zn(II) complexes were synthesized in good yields by the reaction of 2-nitro-5,10,15,20tetraphenylporphinato copper(II), CuTPP(NO2) with liquid bromine followed by acid demetallation reactions. These porphyrins were characterised by UV-Visible, 1H NMR, and mass spectroscopic techniques. Ligation of nitrogenous bases with ZnTPP(NO2)(Br)7 complex exhibits enhanced equilibrium constant (Keq) values relative to ZnTPP(Br)8 complexes.

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Synthesis and photophysical study of unsymmetrical porphyrin arrays M RAVIKANTH Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India Porphyrin-based dimers, trimers and oligomers have received considerable attention as models for the study of electron transfer and energy transfer processes in photosynthesis. Multiporphyrin arrays are also attractive because of their potential use in nonlinear optics, molecular devices and photodynamic therapy of cancer. An unsymmetrical porphyrin array with two different porphyrin units is an ideal model to study photoinduced processes. Core-modified porphyrins in which one or two pyrrole rings are replaced by five-membered heterocycles like thiophene and furan exhibited novel physico-chemical properties which are quite different from N4 porphyrin systems. Connecting the core-modified porphyrins with N4 porphyrins would result in unsymmetrical porphyrin arrays and study of their photodynamics would be helpful in understanding the factors that govern the photoinduced processes. In this paper, we report the synthesis and characterization of unsymmetrical porphyrin arrays comprising of heterosubstituted porphyrin (N3S and N2S2) and N4 porphyrin subunits. Phenyl and diphenyl ethynyl groups are used as links which provide rigidity to the arrays and thereby allow strong interaction between the porphyrin units. Steady state fluorescence data indicate that the energy transfer between the porphyrin units depends on the link.

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Hydrogen-bonding patterns involving a cyclic phosphate SUDHA KUMARASWAMY, PRAVEEN KOMMANA, G PADMAJA and K C KUMARA SWAMY School of Chemistry, University of Hyderabad, Hyderabad 500 046, India Hydrogen bonding as a structure-determinant is well-known in biology and chemistry. Phosphates, which always have electronegative oxygen atoms, bear no exception in their involvement in hydrogen bonding interactions. In biosystems the ubiquitous presence of water makes the study of structural patterns due to H-bonding much too complicated. We have been interested in the structure and reactivity of cyclic phosphorus systems, and in this connection have made an attempt to study H-bonding patterns associated with the cyclic phosphate 1. Compound 1 itself exists in two crystallographic modifications. Its complexes with imidazole, methanol (as a solvate) and the amino acid L-proline have been structurally characterized. In a novel reaction of 1 with KF/18-crown-6 in tetrahydrofuran, the complex 2 is isolated. H-bonding features found in all the above compounds are discussed.

Acknowledgements We thank the Council of Scientific and Industrial Research (CSIR, New Delhi) for financial support and the Department of Science and Technology (DST, New Delhi) for setting up a Single Crystal X-ray Diffractometer Facility at the University of Hyderabad.

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Development of a new class of ruthenium polypyridine photo-redox assemblies B MONDAL, S CHAKRABORTY and G K LAHIRI Department of Chemistry, Indian Institute of Technology, Bombay, Mumbai 400 076, India A new class of ruthenium terpyridine complexes incorporating imine functionalities, [RuII/III/IV(trpy)(L)Cl] (L = o-OC6H3(R)-C(R¢ )=N-CH2-Ar or o-OC6H3(R)-C(R¢ )=N-NHAr) have been developed as possible effective photo-redox assemblies. The imine functions incorporating NH spacer have undergone imine to azo tautomerism on coordination to the ruthenium terpyridine moiety whereas the imine functions (L) having CH2 spacer remain unaltered on coordination. A significant shift in MLCT band energy has been observed depending on the field strength of coordinated L. The complexes display reversible RuIII–RuII and quasireversible RuIV–RuIII couples. The effect of internal imine to azo transformation of L has been well-reflected in the redox behaviour of the metal complexes. The complexes exhibit moderately strong emissions from the lowest energy MLCT bands in the range 661–690 nm in EtOH-MeOH (4:1 v/v) at 77 K. The quantum yields of the complexes are found to vary significantly depending on the nature of L as well as the substituents present in the framework of L. Electronic structures of the trivalent complexes indicate the presence of high degree of rhombicity in the complexes. In the presence of Ag+ ion, the replacement of Cl– ion takes place with concomitant metal oxidation followed by antiferromagnetically coupled m-oxo dimer formation, (trpy)(L)RIII (m-O)RuIII(L)(trpy).

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Mechanistic studies of the decay of a group of nonheme diiron(III)-peroxo complexes MANABENDRA RAYa and LAWRENCE QUE JRb a Department of Chemistry, Indian Institute of Technology, Guwahati 781 001, India b Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA The investigation of dioxygen binding and activation in dinuclear iron complexes has attracted recent interest because of the presence of carboxylate bridged dinuclear iron sites in several biologically important proteins, such as the R2 protein of ribonucleotide reductase, the hydroxylase component of methane monooxygenase and fatty acid desaturases 1. In the first step of oxygen activation, the diiron(II) centre binds oxygen to form a diiron(III)-peroxo adduct which then undergoes O–O bond cleavage to form different active intermediates depending upon the protein. The lifetime of the peroxo intermediate varies widely from protein to protein. Structures for three diiron(III)-peroxo complexes have been reported in recent years. Although the structures and related studies have greatly enhanced our understanding about the formation of the peroxide intermediate in the proteins, the process of breaking the O–O bond and interaction with substrate is far from understood. In this report we present kinetic studies of the decomposition of a group of closely related diiron(III)peroxo complexes and their interaction with triphenylphosphine as a substrate. Kinetic studies of the decomposition of [FeIII2(O2)(hptp)(O2CR)n]2+/1+ (hptp = anion of N, N, N¢ , N¢ -tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-diaminopropane; RCO2– = various substituted benzoic acid; n = 1 or 2) at low temperature shows a pseudo first order rate of decay. The rate of decay depends both on the pKa of the bridging benzoate and the concentration of PPh3 present in the solution. Our data show the formation of a 1:1 adduct between the peroxo complex and PPh3 before decomposition. The major finding of this work is the remarkable stability of the peroxo complex generated from [FeIII2(O2)(hptp)(O2CPh)2]+ which decomposes roughly two orders of magnitude slower than the corresponding mono benzoate complex. This is in contrast with an earlier finding from this group which showed that increased electron donation to the core facilitates cleavage of the peroxo species. The present report discusses the effect of coordination site saturation compared to the electronic effect on extending the lifetime of the peroxo species. References 1. Que Jr L 1997 J. Chem. Soc., Dalton Trans. 3933

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Titanium-catalysed dehydrocoupling of chiral carbosilanes ANUBHAV SAXENA, N SAMPRIYA, A S BRAR and RAVI SHANKAR Department of Chemistry, Indian Institute of Technology, New Delhi 110 016, India Transition metal-catalysed dehydrocoupling of organosilanes containing primary, secondary and tertiary SiH groups has been developed as an effective route to short chain oligosilanes 1. Studies have been extended using NMR spectroscopy 2 to understand the underlying stereochemistry of these oligomers. In the present studies, some hitherto unknown carbosilanes containing SiH groups have been prepared via hydrosilylation method. (i) H2PtCl6/70º/8 h

CH2CHSiCl2R + PhR¢ SiH2

RH2SiCH2CH2SiHR¢ Ph + (ii) LiAlH4

bisomer

RH2SiCH(CH3)SiHR¢ Ph a isomer

where [R = H; R¢= Me(1); R = R¢= Me(2); R = H, R¢= Ph(3)]. The CpTiCl2/BuLi catalysed dehydropolymerization of these monomers afford Si–Si bonded oligomers with chiral functional groups. The microstructure of the oligosilanes have been elucidated by one- and two-dimensional [1H, 13C{1H}DEPT–135º, 29Si{1H} DEPT–135º, TOCSY, HSQC] NMR studies.

References 1. Doumaev V K and Harrod J F 1996 Organometallics 15 3859 2. Doumaev V K, Rahimian K, Gauvin F and Harrod J F 1999 Organometallics 18 2249

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Synthesis of novel metalloflavoporphyrins and their 1e/2e transfer studies B B SAHOO, G PANDAY, A AWASTHI and S M S CHAUHAN Department of Chemistry, University of Delhi, Delhi 110 007, India In cytochrome P450 reductase, the flavin accepts electrons from NADH and transfers them to the porphyrin-Fe of native cytochrome P450 in biomembranes. Synthesis of a new set of covalently linked flavoporphyrins by an ester linkage between flavin and porphyrin moieties and their characterization by FAB mass, 1H NMR, IR, optical absorption and emission spectroscopies are reported in order to understand the 2e/1e transfer from flavin to iron porphyrin in flavohemeproteins in membranes. The proximate conformations of flavin and porphyrin rings are demonstrated by 1H NMR and computer modelling studies. The porphyrin and flavin rings of ortho linked flavoporphyrins are in close proximity to each other, whereas flavin moieties are remote from the porphyrin ring in the meta and para linked flavoporphyrins. Manganese(III) complexes of these flavoporphyrins have been prepared and their cyclic voltammetric studies reveal that the flavin reduction potentials, Flox + e– = Fl– and Fl– + e– = Fl2– have been anodically shifted by the proximity of the linked porphyrin moiety.

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Reactions of iron(III) porphyrins with peroxides and hydrogen peroxide: Mechanistic insights PARVESH WADHWANI and DEBKUMAR BANDYOPADHYAY Department of Chemistry, Indian Institute of Technology, New Delhi 110 016, India Iron(III) porphyrin catalysed oxidations of different substrates by hydroperoxides and hydrogen peroxides have been the choice of many research groups in the recent years, the reasons being their easy availability and the eco-friendly by-products. Intermediates in such oxidation reactions have been the subject of intensive debate 1. Various research groups have adduced evidence in favour of homolytic and hetrolytic cleavage of the peroxo-bond; there are also reports suggesting a unified mechanism for all oxidants 2,3.

Reactive   → [PFe(III)- O x]  rds  → intermedia [PFe(III)]+ + Ox  fast te    S [PFe(III)]+ + SO

(1)

Thus a generalized equation for such a oxidation reaction shown in (1) where P is the porphyrin dianion, Ox is the oxidant, S is the substrate and SO is the oxidized product. Recent studies in our laboratory have indicated that formation of such intermediate(s) in solution is highly dependent on the choice of the solvent and the catalyst involved. Generation, identification and reactivity of such intermediate(s) and the protocol for the activation of the catalyst are discussed. References 1. Traylor T G, Tsuchiya S, Byun Y-S and Kim C 1993 J. Am. Chem. Soc. 115 2775 2. Traylor T G, Fann W-P and Bandyopadhyay D 1989 J. Am. Chem. Soc. 111 8009, and references therein 3. Traylor T G, Kim C, Fann W-P and Perin C L 1998 Tetrahedron 54 7977

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Oxygen-rich molybdenum and chromium complexes: Synthesis, structure and catalysis RATNA BANDYOPADHYAY, SUDEB BISWAS and RAMGOPAL BHATTACHARYYA Department of Chemistry, Jadavpur University, Calcutta 700 032, India A hitherto unknown 1 pentagonal bipyramidal complex, [MoO(O2)2(QO)2] (1) (QOH = 8quinolinol) very efficiently (almost quantitative yield and high turnover number) catalyses homogeneous liquid phase oxidation of methyl benzenes, viz., toluene and o- and p-xylenes to benzoic acid, phthalic acid and p-toluic acid respectively, using H2O2 and O2 as oxidants. [MoO(O2)2·2QOH] (2) on attempted crystallization from CH3CN affords (1). Again (1) when treated with H2O2 affords (2) and hence these observations suggest that (1) is the catalyst precursor and (2) the active species. [CrO3(OH)]– (3) obtained by crystallizing [CrO(O2)2(OH)]– from acetonitrile is an astonishingly potential catalyst in selective oxidation of cinnamaldehyde to cinnamic acid with high turnover, but this apart, (3) catalytically reduces water present in organic solvent to dihydrogen while oxidising benzaldehyde and cinnamaldehyde to the respective acids. The same catalyst shows catalase type behaviour bringing out dioxygen from hydrogen peroxide. Reference 1. Bandyopadhyay R, Biswas S, Guha S, Mukherjee A K and Bhattacharyya R 1999 J. Chem. Soc., Chem. Commun. 1627

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Complete suppression of back-reaction in strongly acidic media for photochemically active Ru(bp)32+-O2 system VISHWAS JOHISb, DILIP KOTKARb, VINIT S PATHAKb, V SWAYAMBHUNATHANb, PRASHANT KAMATc, AMITAVA DASa and PUSHPITO K GHOSHa,b a Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India b ICI India Research & Technology Centre, Thane 400 601, India c Radiation Chemistry Laboratory, University of Notre Dame, Notre Dame, USA Oxygen is one of the few molecules which effectively quench Ru(bp)32+ (bp: 2,2¢ bipyridyl; kq = 3·4 ´ 10–9 M–1 s–1 = kCT + keT where CT is charge transfer and eT is energy transfer). In this paper, we describe a non-sacrificial system, Ru(bp)32+ and H2O2 formation. This is achieved by efficient suppression of the back reaction between Ru(bp)33+ and O2*–, using a proton trap for O2*–-Ru(bp)32+–Ru(bp)33+ cycle in 7 or 9 M H2SO4, which is found to be completely reversible when photooxidation is followed by electrolytic reduction. Luminescence studies show that presence of O2 causes 30% quenching of luminescence intensity in 9M H2SO4. Quantum yield measurements reveal that ~27 molecules of Ru(bp)32+ are formed for every 100 photons absorbed. This suggests that almost 100% of the forward reaction leads to irreversible product formation, i.e. Ru(bp)32+ and H2O2, following the mechanistic path 1 and 2. Ru(bp) 32+ + O2 + H+ → Ru(bp) 33+ + HO2*–

(1)

2HO2* → H2O2 + O2

(2)

–

Transient difference absorption spectra were also recorded for this system and the results correspond nicely to our steady-state luminescence data, i.e. disappearance of *Ru(bp)32+ is practically equal to the chemical quantum yield for Ru(bp)33+ formation. The back reaction for this system was also studied in dark and the equilibrium constant for (3) was calculated to be 0·21 in 7 M H2SO4. 2Ru(bp) 32+ + O2 → 2Ru(bp) 32+ + H2O2

(3)

This equilibrium is shifted entirely to the left at pH 7, suggestive of very pronounced cell potential change at low pH which remains to be fully understood.

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Effect of chelate-ring over the stabilization of copper-dioxygen adducts RAJEEV GUPTA and RABINDRANATH MUKHERJEE Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India Copper-dioxygen adducts are very important in biological systems as well as in synthetic oxidation chemistry. Very few such intermediates have been characterized, and the structural factors responsible for catalytic effectiveness of the copper catalysts remain ambiguous. The oxidation chemistry of well-characterized copper-dioxygen adducts is thus expected to provide the basis for designing and developing new catalytic oxidation systems. Chelate-ring size makes considerable difference in the reactivity of such complexes. Systematic variation of chelate-rings can lead to better understanding of the factors responsible for occurrence of such copper-dioxygen adducts. In this presentation, two ligands, MeL and MeL*, have been used to demonstrate the effect of chelate-rings over the stabilization of the copper-dioxygen intermediate species. One such species with ligand MeL has been used to show the oxidation of externally added substrates. Final end products of both ligands are discussed in detail to throw some light on the difference in the behaviour of chelate-rings.

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Molecular phosphates and siloxanes M G WALAWALKAR Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India There has been immense interest and enthusiasm recently among chemists to develop materials at low temperatures through molecular routes. Especially interesting are the studies carried out on molecular phosphonates 1 and siloxanes 2,3 by Roesky, Tilley, Mason, Feher and others. This presentation focuses on the structural correlation between the molecular siloxanes/phosphonates and the material silicates/phosphates. It also deals with the generalisations of the synthetic efforts employed in the preparation of molecules which represent the building units in zeolites and molecular sieves. The similarities and the variations in these molecules which could lead to the formation of the materials and the presence of plausible reactive groups which make the compounds susceptible to various reaction conditions are discussed. References 1. Walawalkar M G, Roesky H W and Murugavel R 1999 Acc. Chem. Res. 32 170 2. Feher F J and Budzichowski T A 1995 Polyhedron 14 3239 3. Murugavel R, Voigt A, Walawalkar M G and Roesky H W 1996 Chem. Rev. 96 2205

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Alternative motifs for nonlinear optics SUSHANTA K PAL, ANU KRISHNAN, A G SAMUELSON and PUSPENDU K DAS Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India The search for new materials with large nonlinear optical properties is of considerable interest. It is well-established that molecules containing electron-donating and electronwithdrawing groups interacting through a conjugated system show large hyperpolarizabilities. The second-order hyperpolariability of donor–acceptor (D–A) substituted benzene and stilbene derivatives have demonstrated that with increasing donor–acceptor strength and conjugation path length, an enhancement of second-order hyperpolarizability occurs. Other motifs with alternative donor–acceptor–donor (D–A–D) units have been less explored.

Herein we report the synthesis and characterization of Schiff base complexes having an electron-donating ferrocene centre and an electron acceptor like anthraquinone or dicyanoethylene. These complexes have interesting spectroscopic and electrochemical properties. The electrochemical properties of the complexes were investigated by cyclic voltammetry. The bis-ferrocene complex linked through an anthraquinone spacer shows electronic communication between the two iron centres. The quadratic hyperpolarizability b in solution was measured by the hyper-Rayleigh scattering technique. The ferrocenyl Schiff base complexes attached to anthraquinone have high hyperpolarizablities.

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Bulky aryloxo organotitanium chlorides G ANANTHARAMAN, KANHAYALAL BAHETI and R MURUGAVEL Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India The last few years have witnessed a sudden interest in the chemistry of titanium aryloxides due to their use as Diels–Alder 1 and cross coupling/oligomerization catalysts 2. There have also been reports on the use of [(ArO)(C5H5)TiCl2] for the preparation of cationic alkyl derivatives of titanium 3. In view of the proven ability of C5Me5 ligand (Cp*) in stabilizing organotitanium compounds, it is of interest to generate bulky aryloxide derivatives of Cp*TiCl3. Thus, the reaction of Cp*TiCl3 with various phenols in a 1:1 ratio in the presence of Et3N affords the aryloxides of the formula [(ArO)Cp*TiCl2] (Ar = 4-MeC6H4, 2,6-Me2C6H3, 2,6-iPr2C6H3, 2,6-tBu2-4-MeCl6H2) in nearly quantitative yields. The details of this investigation are discussed in this presentation. References 1. Santora B P, White P S and Gagne M R 1999 Organometallics 18 2557 2. Waratuke S A, Thorn M G, Fanwick P E, Rothwell A P and Rothwell I P 1999 J. Am. Chem. Soc. 121 9111 3. Thorn M G, Vilarado J S, Fanwick P E and Rothwell I P 1999 Chem. Commun. 2427

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Phase relations in Ag–Ni–Zn–S and Cu–Si–Ni–Sn–S systems GUNJAN GARG and ASHOK K GANGULI Department of Chemistry, Indian Institute of Technology, Haus Khas, New Delhi 110 016, India Starting with pure metals and sulphur in evacuated silica tubes and heating up to 900ºC led to several copper- and silver-based compounds in Ag–Ni–Zn–S, Cu–Si–Ni–Sn–S systems. Powder diffraction studies showed either a thiospinel-related structure (cubic, a ~ 10·3 Å, sp.gp. Fd3m) or sphalerite related structure (cubic, a ~ 5·41 Å, sp.gp. F43m). The possibility of a tetragonal superstructure in some of the silver-based compounds is also investigated. The spinel-related phases were found to crystallize from melts in the temperature range of 670–850ºC while sphalerite-related phases crystallized between 850 and 900ºC. Single crystals have been obtained by slow cooling. Structural studies of these crystals will be discussed. These materials are interesting with respect to their ion exchange/intercalation of the monovalent ions suitable for use as cathode materials and some of these compounds have interesting electro-optical properties.

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Synthesis of lanthanum and neodymium dititanates from homogeneous hydroxide precipitation M SURESH and A V PRASADARAO Department of Inorganic and Analytical Chemistry, Andhra University, Visakhapatnam 530 003, India The need for electroceramics that can operate at high temperatures is rapidly increasing. Compounds with pervoskite layer structure (PLS) such as La2Ti2O7 and Nd2Ti2O7 are known to exhibit not only very high Curie temperatures of the order of 1500ºC but also show excellent piezoelectric properties that are suitable for high temperature transducer applications. Syntheses of La2Ti2O7 and Nd2Ti2O7 in polycrystalline form have already been reported in terms of mixed amorphous hydroxides, liquid mix techniques and sol– gel methods apart from conventional solid-state reactions of the oxides. Since chemical methods give good control over stoichiometry and yield phase-pure final products at relatively lower temperatures compared to conventional ceramic methods, an attempt has been made in this study to obtain coprecipitated precursors for lanthanum/neodymium and titanium starting from corresponding water-soluble salts. Use of potassium titanyl oxalate led to selective precipitation of lanthanum oxalate at all pH values thus precluding the formation of any complexes with TiO2+ ion. However, use of titanium tetrachloride with lanthanum nitrate facilitated formation of coprecipitated hydroxides which on thermolysis yielded phase-pure La2Ti2O7 at 950ºC. Precipitates obtained from 1:1 equimolar aqueous solutions of La/Nd nitrate and potassium titanyl oxalate at different pH values were studied by TG and DTA methods while the phase identification of heat-treated samples was performed by XRD.

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Synthesis of a 4-membered ring zinc phosphate monomer and its condensation self-assembly into an open-framework structure S NEERAJ, SRINIVASAN NATARAJAN and C N R RAO Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India In recent years there has been a tremendous surge in the synthesis of open-framework metal phosphates, with the objective of rendering them porous for potential application in catalysis and sorption processes. These materials are generally prepared hydrothermally in the presence of organic amines. One of the crucial aspects of these materials that needs to be understood is the pathway which leads to the evolution of these hierarchial structures with varying degrees of complexity. In the case of aluminophosphates, it has been proposed that a linear chain precursor transforms to a ladder-type structure, followed by layer and 3-dimensional structures. The chain and ladder structures themselves contain 4-membered metal phosphate rings which clearly constitute the fundamental building unit of these open-framework structures. Our objective was to see if we could isolate this monomeric 4-membered ring basic building unit and examine its transformation, if any, to open-framework structures. Our studies in this direction have resulted in isolation of a monomeric 4-membered ring zinc phosphate, which on further heating at 50ºC transforms to a layered open-framework structure. The isolation of this monomeric unit is of fundamental significance.

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Effect of cation size and disorder on the properties of the rare earth cobaltates, Ln0·5A0·5CoO3 (Ln = rare earth, A = alkaline earth) P V VANITHA, P N SANTHOSH and C N R RAO Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India The ferromagnetic Curie temperature TC, of the rare earth cobaltates, Ln0·5A0·5CoO3 increases with the average size of the A-site cation up to an 〈rA〉 of 1·40 Å and decreases thereafter due to size mismatch. Disorder due to size mismatch has been investigated by studying the properties of two series of cobaltates with fixed 〈rA〉 and differing size variance, s2. It is found that TC decreases linearly with s2, according to the relation, TC = T0C – ps2. When s2 is large (> 0·012 Å2), the material becomes insulating, providing evidence for a metal–insulator transition caused by size-disorder. Thus, Gd0·5Ba0·5CoO3 with a large s2 is a charge-ordered insulator below 340 K. The study demonstrates that both average radius, 〈rA〉, and size-disorder play a role in determining the magnetic and transport properties of the rare earth cobaltates.

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Electrochemical investigations related to solid state magnesium batteries G GIRISH KUMAR and N MUNICHANDRAIAH Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Investigations leading to the understanding and development of solid state magnesium batteries are considered important, as Mg is free from hazards and is also highly stable and abundant. A gel polymer electrolyte (GPE) of about 100 mm thickness is investigated for electrochemical reversibility of the Mg/Mg2+ couple and for characterization of Mg/GPE/MnO2 solid state cells. The GPE consists of polyacrylonitrile, propylene carbonate, ethylene carbonate and magnesium triflate. The composition is optimized in view of the minimum liquid constituent required for gel formation and the maximum specific conductivity (s). The s of the GPE films follows Arrhenius behaviour and the energy of activation for ionic conduction is in the range 0·13 and 0·16 eV. The a.c. impedance data of the Mg/GPE/Mg symmetrical cells are analysed by fitting the data to the equivalent circuit. The value of the interfacial resistance (Ri) of the Mg/GPE interface which is contributed by the surface passive film resistance (Rf) on the Mg metal and charge-transfer resistance (Rct) of the Mg/Mg2+ electrochemical reaction are evaluated. Ri decreases with increase of the cell temperature, while on the other hand, it increases with the ageing of the cell at ambient temperature. Several Mg/GPE/MnO2 cells are assembled and their discharge behaviour studied. Cyclic voltammetric experiments qualitatively suggest reversible behaviour of the MnO2 electrode in GPE medium. The cells are subjected to about 20 charge/discharge cycles. Progressive surface passivation of the Mg negative electrode and poor rechargeability of the MnO2 positive electrode limit cycle life.

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Synthesis and reactions of ferrocene derived hydroxymethyl phosphines, [Fe(o-C5H5)-{o-C5H4CH(R)P(CH2OH)2}] R = H, CH3 T V V RAMAKRISHNAa, ANIL J ELIASa and ASHWANI VIJb a Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India b Single Crystal X-ray Diffraction Laboratory, University of Idaho, Moscow, ID 83843, USA The relevance of ferrocene-based phosphines stems from the fact that a large number of chiral aminoethyl and phosphinoethyl ferrocenes have been found to be highly efficient chiral ligands for homogeneous catalysts in asymmetric transformations 1. Many of these have been derived primarily from [1-(N,N-dimethylamino)ethyl/methyl] ferrocene with further substitution by a phosphine moiety on the substituted cyclopentadienyl group. Such compounds possess a planar chirality in addition to the central element of chirality resulting from a chiral carbon. Further, ferrocenyl diphosphines as well as substituted phosphaferrocene ligands belonging to this category have been synthesized and their metal complexes prepared. In this paper we discuss the synthesis of ferrocene derived racemic phosphines and their sulphides having hydroxymethyl and morpholinomethyl substituents on the phosphorus. Use of ferrocene-derived hydroxymethyl phosphine sulphide as a potential precursor for making organometallic spirocyclic compounds with inorganic heterocycles is studied.

Reference 1. Goodwin N J, Henderson W, Nicholson B K, Sarfo J K, Fawcett J and Russel D R 1999 J. Chem. Soc., Dalton Trans. 1785

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Structure and properties of a family of sugar vanadates incorporating VO3+ KAJAL KRISHNA RAJAKa and SANKAR PRASAD RATHb a Department of Chemistry, Jadavpur University, Calcutta 700 032, India b Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India Protected carbohydrates, having two free cis hydroxyl groups, (general abbreviation H2SUG) have been synthesized and their reactions with VO(L-Asal)(OMe) (OHMe)/VOL(L-Asal)(H2O) in dichloromethane/methanol have afforded mononuclear esters of type VO(HSUG)(Asal) as dark-coloured solids (red in solution). Here, L-Asal2– is the deprotonated salicylaldimine of L-alanine (A = a), L-valine (A = v) and Lphenylalanine (A = p). The X-ray structures of representative cases (e.g. VO(b-DHMe3GP)(Lvsal), where b-D-H2Me3GP is methyl-2,6-dimethoxy-b-D-galactopyranoside) show that the carbohydrates bind to the metal site as a five-membered O,O-chelate ring in a monoionized state, the undissociated hydroxyl group lying trans to the oxo-oxygen atom. The X-ray structures also show that the chiral configuration of the metal site corresponds exclusively to the endo disposition of the V=O and the amino acid C–R bonds. Solution studies (1H and 51V NMR) show that the molecular structures observed in the solid state are grossly preserved in solution.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 381  Indian Academy of Sciences

Synthesis and structure of ruthenium(II) ternary complexes involving N-2-(aminopyridyl)-2-carbamoylpyridine SUJIT DUTTA and P K BHATTACHARYA Department of Chemistry, Faculty of Science, MS University of Baroda, Baroda 390 002, India The ligand, N-(2-aminopyridyl)-2-carbamoylpyridine (L) has been synthesized by reacting pyridine-2-carboxylicacid with 2-aminopyridine and has been characterised by elemental analysis, 1H NMR, IR and mass spectral studies. The complex [Ru(PPh3)2(L)Cl2] has been synthesized by reacting [Ru(PPh3)3Cl2] with L. Further reaction of [Ru(PPh3)2(L)Cl2] with bidentate chelating ligands L¢(L¢= 2,2¢ -bipyridine, 1,10-phenathroline, 2-(2-aminoethyl)pyridine and ethylenediamine) yield complexes of general formula [Ru(PPh3)2(L)(L¢ )]ClO4. All the complexes are diamagnetic (low spin d6, S = 0) and show intense bands corresponding to metal to ligand charge-transfer transitions and inter-ligand transitions in the UV-Vis spectra. All the complexes show one reversible oxidation due to ruthenium(II)–ruthenium(III) in the anodic region of the cyclic voltammogram. The ruthenium(II)–ruthenium(III) impulses are found to be sensitive to the nature of the donor sites of the bidentate ligand L¢ . Further characterization of the complexes have been achieved by IR and electrospray mass spectral studies.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 382  Indian Academy of Sciences

Photooxidation of nickel(II) macrocyclic complexes from the charge-transfer-to-solvent excited states P NATARAJAN, P PAUL#, T DHANASEKARAN and H PRAKASH Department of Inorganic Chemistry and National Centre for Ultrafast Processes, University of Madras, Chennai 600 025, India # Catalysis Division, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India Nickel(II) macrocyclic systems with saturated and unsaturated tetraaza type ligands show intense absorption bands in the ultraviolet region and the excited states exhibit the characteristics of charge-transfer-to-solvent transitions. Investigations of the photochemical pathways in acetonitrile, dichloromethane, and water using flash kinetic spectroscopic techniques reveal different reaction products. The primary photochemical reaction involves oxidation of the metal centre leaving the ligand unaffected in most cases. The role of the solvent and dissolved oxygen primarily determine the nature of the products. Flash photolysis investigations have shown details of the reactions of the oxidised nickel(III) complex with the transient species present in the solution. Photoproduced nickel(III) macrocyclic complexes have been isolated in a few cases and the structures elucidated. Structural information and results of the flash photolysis studies are presented.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 383  Indian Academy of Sciences

Synthesis and X-ray structural characterization of first trinuclear ruthenium(II) Schiff-base phenolate complex of tripodal ligand with trigonal symmetry N MANGAYARKARASI and P S ZACHARIAS School of Chemistry, University of Hyderabad, Hyderabad 500 046, India The antitumour properties of cis and trans RuL(dmso)nCl2 and their pattern of interaction with nitrogen bases of DNA have stimulated interest in the synthesis of haloruthenium(II) sulphoxide complexes. The trinuclear ruthenium(II) Schiff base complex Ru3H3L¢ (dmso)6Cl6 has been synthesized from preformed acyclic tripodal ligand H3L¢1. The X-ray crystal structure of the complex, Ru3H3L¢ (dmso)6Cl6 shows that each ruthenium atom is coordinated by phenolic and carbonyl oxygens of ligand, sulphur atoms of two dmso moieties in the equatorial plane, and two chloride ions in axial positions and has distorted octahedral geometry.

H3L′

X-ray structural characterization of H3L¢shows the presence of free formyl group instead of formation of acetal group as reported earlier 2. H3L¢shows carry over of molecular trigonal symmetry into the crystal and formation of a trigonal network due to intermolecular interactions of the aminomethylene (N–CH2) proton and formyl (CH=O) oxygen (see figure). CSD analysis shows that this N–C–H… O=CH interaction is unique. References 1. Smith C A, Sunderland-Smith A J, Kwpplwe B K, Kratz F and Baker E N 1996 J. Biol. Inorg. Chem. 1 424 2. Archibald S J, Blake A J, Schroder M and Winpenny R E P 1994 J. Chem. Soc., Chem. Commun. 1669

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 384  Indian Academy of Sciences

Characterization of normal and inverted sapphyrins and rubyrins A SRINIVASAN, SIMI K PUSHPAN, V G ANAND and T K CHANDRASHEKAR Department of Chemistry, Indian Institute of Technology, Kanpur 208 016 India Research on the development of easy and efficient methods for the synthesis of expanded porphyrins, particularly sapphyrins and rubyrins, is receiving attention in view of their diverse applications in Photodynamic Therapy (PDT), as contrasting agents for Magnetic Resonance Imaging (MRI) and as anion receptors. Both sapphyrins and rubyrins show diverse structures 1. An inverted structure of sapphyrin is characterized by rotation of the heterocyclic ring opposite to bipyrrole/bithiophene/biselenophene unit 1, while an inverted rubyrin structure shows rotation of both heterocyclic rings connected to two bipyrrole units. The normal structures of sapphyrins and rubyrins do not show any ring inversion. An example of normal rubyrin is shown in 2. In this work, an attempt has been made to rationalize this structural diversity on the basis of X-ray crystal structural data of both sapphyrins and rubyrins.

1

2

Reference 1. Srinivasan A, Anand V G, Narayanan S J P, Pushpan S K, Kumar M R, Chandrashekar T K, Sugiura K-I and Sakata Y 1999 J. Org. Chem. 64 8693

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 385  Indian Academy of Sciences

Functionalization of a heteroditopic cryptand: Exocyclic coordination with iron(III) PUNAM TRIPATHI, ABHIGYAN SOM and PARIMAL K BHARADWAJ Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India Catecholate ligands with first-row transition metal ions as well as many heavier transition and post-transition metal ions have received enormous attention in recent years. Fe(III) forms a tris-catecholate complex with the highest formation constant (logKf » 52) of any iron chelate ever determined. A heteroditopic cryptand is derivatized with a catechol unit to have a novel receptor. The high binding ability of catechol units to Fe(III) has been utilized to bring together three such receptors. The integrity of the complex is maintained in dilute solution at room temperature. Thus, it provides a robust system for further complexation. The cavity of each cryptand unit can include a metal ion like Cu(II) to form hetero-metallic systems. This allows the study of electronic interactions between different metal ions. Besides, with exocyclic receptors appended to cryptands and preferential binding of the exoreceptors to metal ions, giant metal-driven assembly can be realized. In a cryptand based assembly, the cavities of the cryptands can be tailored to obtain systems with novel structures and bonding as well as new materials.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 386  Indian Academy of Sciences

Dependence of the cone angles of phosphorus-containing ligands in the chemistry of hydride and dihydrogen complexes of ruthenium NISHA MATHEW and BALAJI R JAGIRDAR Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India A series of new hydride complexes of ruthenium of the type trans[(dppe)2Ru(H)(L)][BF4], dppe = Ph2CH2CH2Ph2, L = P(OMe)3, P(OEt)3, PMe2Ph, P(OiPr)3 have been prepared and characterized using a procedure similar to the one reported earlier. It was found that the binding ability of the ligand decreases in the order P(OMe)3 @ P(OEt)3 > PMe2Ph > P(OiPr)3 with an increase in the cone angle of the phosphorus ligand,. The protonation reactions of the precursor hydride complexes, trans[(dppe)2Ru(H)(L)][BF4] result in a mixture of the dihydrogen complex and the homolysis reaction product, the dihydride species for L = P(OMe)3 and P(OEt)3. There is strong dependence on the concentration of the acid used for the isolation of either the dihydrogen or the dihydride complex. Similar protonation reactions in the cases of PMe2Ph and P(OiPr)3 yielded unidentifiable species having a hydride and dihydrogen ligand. P(OiPr)3 ligand in trans-[(dppe)2Ru(H)P(OiPr)3][BF4] was found to be extremely labile and was readily substituted by H2 as a consequence of its high cone angle (131º). The syntheses, characterization, and chemistry of these species are presented.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 387  Indian Academy of Sciences

Two-dimensional NMR studies of allyl palladium complexes of diphosphazanes SWADHIN K MANDALa, G A NAGANAGOWDAb and SETHARAMPATTU S KRISHNAMURTHYa a Department of Inorganic and Physical Chemistry and bSophisticated Instruments Facility, Indian Institute of Science, Bangalore 560 012, India h3-Allyl complexes are intermediates in organic synthetic reactions such as allylic alkylation and amination. There is growing interest in understanding the structures of chiral h3-allyl intermediates as this would help to unravel the mechanism of enantioselective C–C bond forming reactions. Two-dimensional NMR study is a powerful tool to elucidate the structures of such complexes. Here we present the synthesis of 1,3-diphenylallyl complexes of diphosphazanes of the type X2PN(R)PY2 and the monosulphide Ph2PN(CHMe2)P(S)Ph2. NMR studies show the presence of only one isomer (e.g. A or B) in solution except for those diphosphazanes bearing C2-symmetric binaphthylenedioxy moiety, in which case two isomers are observed (e.g. C and D). Allylic arrangement in these complexes has been determined by 2-D NOESY and ROESY spectra. These complexes are found to be active for C–C bond formation when they are treated with the sodium salt of dimethylmalonate.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 388  Indian Academy of Sciences

Synthesis and molecular structure of manganese complexes with hindered N3 ligand UDAI P SINGHa, R SINGHa, S HIKICHIb and Y MORO-OKAb a Department of Chemistry, University of Roorkee, Roorkee 247 667, India b Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226 8503, Japan Manganese-dioxygen complexes are assumed to play significant roles in physiologically important enzymatic reactions including superoxide dismutation, decomposition of hydrogen peroxide and dioxygen evolution from water catalysed by manganese containing proteins 1. Accordingly, the characterization of structurally well-defined manganese-dioxygen complexes are important from bioinorganic viewpoints. Here, we report the synthesis and molecular structure of manganese(II)-chloro, hydroxo, manganese(III)-oxo complexes of the hydrotris(3,5-diisopropyl-1-pyrazolyl)borate ligand and oxidation behaviour of the Mn(II)-hydroxo complexes. When bis(m-hydroxo)dimanganese(II,II) complex was reacted with excess amount of H2O2 in the presence of 3,5-diisopropylpyrazole (3,5-iPr2pzH) (2 equiv.) at room temperature for 30 min, a colour change was observed and the resultant complex was found to be the intramolecular hydrogen bonded peroxo complex Mn(O2)(3,5-iPr2pzH)(HB(3,5-iPr2pz)3). This complex is not stable and decomposes slowly in solution at room temperature. The reaction of a bis(m-oxo)dimanganese(III,III) with excess amount of H2O2 in the presence of 2methylimidazole (2-MeIM) resulted in the isolation of intermolecular hydrogen bonded monomeric side-on peroxo manganese(III) complex, Mn(O2)(2-MeIM)(HB(3,5-iPr2pz)3). The O–N distances in this complex are shorter (011-N82, 2·76(1) Å) than the range of distances expected for a hydrogen bond between the peroxide and the imidazole proton. The complex is stable at room temperature and is unable to oxidize triphenylphosphine and ethyl vinyl ether.

Reference 1. Pecoraro V L, Baldwin M J and Gelasco A 1994 Chem. Rev. 94 807

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 389  Indian Academy of Sciences

Copper(II) nickel(II), cobalt(II) and oxovanadium(IV) complexes of substituted b-hydroxyiminoanilides S SEVAGAPANDIAN, K NEHRU and P R ATHAPPAN Department of Inorganic Chemistry, Madurai Kamaraj University, Madurai 625 021, India Complexes of the general formula, ML2 [where M = copper(II), nickel(II), cobalt(II) and oxovanadium(IV); L = 1,2,3,5,6,7,8,8a-octahydro-3-hydroxyimino-N-(4-X-phenyl)1-phenyl-5-(phenyl-methylene)-2-naphthalenecarboxamide (X = H, CH3, OCH3 Cl)] have been prepared and characterized on the basis of elemental analysis, magnetic moments, i.e., EPR and electronic spectra. These metal complexes contain N4 chromophore with the ligand coordinating through the nitrogens of the azomethine and deprotonated anilide functions. Cyclic voltammogram indicates that the copper(II) complexes are reduced quasi-reversibly in acetonitrile solution. Square planar and square pyramidal structures are assigned to the copper(II) and oxovanadium(IV) respectively complexes while tetrahedral geometry is assigned to the nickel(II) and cobalt(II) complexes. Deprotonated anilide nitrogen is involved in coordination and the presence of an electron-donating group at the p-position of the anilide function decreases the ∆E values of the d-d transitions while the values increase when an electron-withdrawing group is substituted. Line spacing in the EPR spectra of the copper(II) and oxovanadium(IV) complexes increases when CH3 group is present in the p-position of the anilide group and decreases when CH3 group is replaced with OCH3 or Cl. The n(C–N) of the anilide group and the n(C=N) of the azomethine function of the oxime metal complexes are metal-sensitive.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 390  Indian Academy of Sciences

Synthesis, structure and spectral and electrochemical properties of new mixed ligand monomeric Ru(II) complexes of bis(pyrid-2-yl)- and bis(benzimidazol-2-yl)-dithioether ligands MARIAPPAN MURALI and MALLAYAN PALANIANDAVAR Department of Chemistry, Bharathidasan University, Tiruchirapalli 620 024, India Two novel binuclear Ru(II) complexes [Ru(pdto)(m-Cl)]2(ClO4)2 1 [pdto = 1,8-bis(pyrid2-yl)-3,6-dithiaoctane] and [Ru(bbdo)(m-Cl)]2(ClO4)2 2 [bbdo = 1,8-bis(benzimidazol-2yl)-3,6-dithiaoctane] have been prepared to elucidate the effect of Ru–S bond on the electronic properties of Ru(II) centres. The complex 1 has been shown to be a binuclear species in which two Ru(II) octahedra are bridged by two chloride ions constituting a common edge between the octahedra. The facile symmetrical bridge cleavage reaction of 1 and 2 with the diimine ligand 2,2¢ -bipyridine or 1,10-phenanthroline has been employed to obtain the mononuclear Ru(II) complexes [Ru(pdto)(bipy)](ClO4)2 3, [Ru(bbdo)(bipy)](ClO4)2 4, [Ru(pdto)(phen)](ClO4)2 5 and [Ru(bbdo)(phen)](ClO4)2 6. The crystal structures of 3, 4, 5 and 6 contain a distorted Ru(II) octahedra composed of two nitrogen atoms of 2,2¢ -bipyridine (3 and 4) or 1,10-phenanthroline (5 and 6) and two thioether sulphurs and two pyridine or benzimidazole nitrogen atoms of the pdto or bbdo ligand. The 1H NMR spectra of the complexes are helpful in assessing their solution geometry. Electronic spectra of all the complexes in MeCN solution exhibit two MLCT bands. Electrochemical measurements on the complexes in MeCN solution reveal that the lower redox potential of Ru(II)/Ru(III) couple in 4 and 6, compared to 3 and 5 respectively, is due to the enhanced s-donor capacity of benzimidazole nitrogen atoms in 4 and 6, which leads to an increase in negative charge on ruthenium; this is reflected in the energies of the MLCT bands. The mononuclear dicationic species are more difficult to oxidise than the corresponding binuclear dicationic species, which is in line with the observation of the dp ® p*2 MLCT band at lower energies. The redox properties of the complexes are illustrated with the help of the Lever parameters. The coordinated thioethers raise the Ru(II)/Ru(III) redox potentials by stabilising Ru(II) oxidation state.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 391  Indian Academy of Sciences

A novel tetranuclear maze type network having assembly of copper(II), 2,2¢-dicarboxydiphenylthioether and pyridine: [Cu4(C5H5N)8{S(C6H4CO2)2}4(H2O)]⋅3H2O RAJKUMAR BHUBON SINGHa and SAMIRAN MITRAb a Department of Chemistry, Nagaland University, Lumani Campus, Mokokchung 798 601, India b Department of Chemistry, Jadavpur University, Calcutta 700 032, India Transition metal complexes having supramolecular architecture become very important for the study of metal–metal interaction through suitable bridging ligands. For the synthesis of polymeric compounds in the self-assembly of the transition metal ions with appropriate bridging and chelating ligands were mostly focussed on oligopyridines and its derivatives as connector ligands. Here, we have synthesized a novel macrocyclic copper(II) tetranuclear assembly with 2,2¢ -dicarboxydiphenylthioether as bridging ligand along with pyridine. It has an interesting supramolecular architecture having a twodimensional steric maze-type network. The complex has a distorted macrocycle which is composed of four copper(II) ions and four 2,2¢ -dicarboxydiphenylthioether ligands for every copper(II) ion; two pyridine molecules are coordinated in the trans position as shown in the figure. The tetranuclear macrocyclic structure is centrosymmetric at Cu(1), Cu(2), CU(1)* and Cu(2)* and extends to infinity along the C-axis with the carbonyl group O(6)[C=O] occupying the apical position of Cu(1)* of another macromolecule and O(6)* similarly bonded to Cu(1).

Figure 1. Crystal structure of [Cu4(C5H5N)8{S(C6H4CO2)2}4(H2O)]⋅3H2O

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 392  Indian Academy of Sciences

A copper complex (2,2¢-bipyridine)(salicyclideneglycinato) copper(II) as a model for the active site structure of amine oxidase PATTUBALA A N REDDY, RIYA DATTA and AKHIL R CHAKRAVARTY Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Copper-containing amine oxidases are one of the most widely distributed classes of type 2 copper enzymes 1,2. They catalyse the oxidative deamination of primary amines: RCH2NH2 + O2 + H2O ® RCHO + H2O2 + NH3. Based on spectroscopic studies, the active site of amine oxidase in its oxidised form is postulated to have one CuII site coordinated to 3 histidine residues in the equatorial position and two water molecules giving a CuN3O2 coordination sphere. In this paper, we report a copper(II) complex having a CuN3O2 coordination geometry which is found to be catalytically active in oxidising ascorbic acid in air. In aqueous–methanol, ascorbic acid reduces the copper(II) complex to form a brown copper(I) species which readily converts to the green precursor copper(II) complex in the presense of dioxygen. The proposed catalytic cycle for this conversion in air is shown below. The copper(II) complex is also catalytically active in the oxidation of benzylamine as an organic substrate. This mimics the functional property of amine oxidase.

References 1. Knowles P F and Dooley D M 1993 In Metal ions in biological systems (ed.) H Siegel (New York: Dekker) 2. McIntire W S and Hartman C 1993 In Principles and applications of quinoproteins (ed.) V L Davidson, Dekker (New York: Dekker) p 173

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 393  Indian Academy of Sciences

Polymeric coordination compounds SAILAJA SUNKARI and M V RAJASEKHARAN School of Chemistry, University of Hyderabad, Hyderabad 500 046, India Metal coordination polymers with one- and two-dimensional structures are of current interest due to their possible relevance to material science 1. In continuation of our previous studies 2,3, several new polymeric compounds are reported here. Among the complexes of silver with aminomethyl pyridine (amp) Ag(2-amp)ClO4 (1) forms 1-D chains, whereas in Ag(4-amp)ClO4 (2) there is an hexagonal arrangement of polymer chains. On the other hand, Ag(3-amp)ClO4 (3) is a tunnel-forming polymer. Ce(dipic)3Sr(dipicH2)(OH2)3·5H2O (4) (dipicH2 – dipicolinic acid) exhibits 1-D polymeric chain structure, built up of alternating nine coordinate Ce and eight coordinate Sr polyhedra. The analogous Ce–Ba compound (5) exhibits a polymeric chain built up of nine coordinate Ba units only, arranged in a hexagonal lattice.

(2)

(4)

(3)

(5)

References 1. Chen C T and Suslick K S 1993 Coord. Chem. Rev. 128 293 2. Swarnabala G and Rajasekharan M V 1997 Polyhedron 16 921 3. Swarnabala G and Rajasekharan M V 1998 Inorg. Chem. 37 1483

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 394  Indian Academy of Sciences

b-Cyclodextrin-assisted intervalence charge transfer in mixedvalent [2]rotaxane complexes having metal centres linked by interrupted p-electron systems ATINDRA D SHUKLA, H C BAJAJ and AMITAVA DAS Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India The study of intramolecular electron transfer in redox active binuclear transition metal complexes is of great fundamental importance and is an area of contemporary research interest. Though there are many reports on the role of bridging ligands (BL) in tuning metal–metal interactions and intramolecular electron transfers in bi/polynuclear metal complexes, till date very little is known about the role of bridging ligands (BL) trapped in cyclodextrin cavities. With proper design it is possible to synthesise supramolecular species in which a cyclic molecular head, e.g. cyclodextrin, is threaded by a linear hydrocarbon chain bearing bulky metal complexes of different oxidation states as stoppers that prevent the complex from dissociating into cyclic and linear molecular components. This approach can enable us to investigate the effect of cyclodextrin inclusion of BL and thus the effect of nonbonding interaction on Intervalence Charge Transfer (IVCT) and metal–metal coupling. In this paper, we report syntheses of [2]rotaxane containing FeII and RuIII complexes as stoppers, b-CD as cyclic molecular head and 4,4¢ -bipyridyl derivatives (1,2-bis(4-pyridyl)ethane (bpe) and 1,3-bis(4pyridyl)propane (tmbp)) as BL. It is possible to synthesise [2]rotaxane by self-assembly route (scheme 1). Inclusion of a bridging ligand in the b-CD cavity has initiated optical electron transfer from Fe(II) to Ru(III), a feature not observed in the absence of inclusion.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 395  Indian Academy of Sciences

Coordination polymers of divalent metal ions based on 1,2,4,5-benzenetetracarboxylic acid: Synthesis and structure DIVYA KRISHNAMURTHY, M SATHIYENDIRAN and R MURUGAVEL Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076, India There is considerable interest in assembling extended metal–ligand polymeric networks using an organic molecule as the basic building block 1,2. In recent years, a number of such metal–organic frameworks have been constructed and their molecular structures established by diffraction studies. Interest in such polymeric frameworks stems from the rigidity and stability of these structures and also from their possessing pores of sizes and shapes, unobserved as yet, in zeolites and molecular sieves, which allow selective inclusion of guest molecules. We have recently constructed several metal(II)-1,2,4,5-benzenetetracarboxylate networks starting from 1,2,4,5-benzenetetracarboxylic acid as the ligand (metal = Co, Ni, Zn and Ca). The products have been identified by elemental analyses and the usual spectroscopic methods; in addition, molecular structures of a few representative examples have been established by single crystal X-ray diffraction studies. Thermal behaviour was verified by both TGA and DTA studies. Further, we are also investigating the possibility of utilizing these compounds for modifying the 2-D and 3-D extended frameworks exhibiting unusual ion-exchange, neutral guest exchange and selective absorptive behaviour. Preliminary results of these investigations along with structural correlations are reported. References 1. Yaghi O M, Li H and Groy T L 1996 J. Am. Chem. Soc. 118 9096 2. Yaghi O M, Li G and Li H 1995 Nature (London) 378 703

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 396  Indian Academy of Sciences

Activation of the pentamethylcyclopentadienyl group bound to nickel group metals towards Diels–Alder addition K MOHAN RAOa and N M BOAGb a Department of Chemistry, North Eastern Hill University, Shillong 793 003, India b Department of Chemistry and Applied Chemistry, University of Salford, Salford, UK, M5 4WT Cyclopentadienyl complexes of the type [M(h5-C5R5)L2] (M = Co, Rh, Ir, Ni; L = 2e– or 1e– donor) are well-known to exhibit two types of distortion arising from loss of degeneracy of the e¢orbitals of the cyclopentadienyl group on interaction with the frontier orbitals of the ML2 fragment 1. We have studied this distortion in pentamethylcyclopentadienyl complexes of platinum and have found that neutral systems of the type [(h5-C5Me5)PtLX] (L = CO, PR3; X = halide, alkyl) where the distortion is large, the pentamethylcyclopentadienyl ring is activated towards the Diels–Alder addition of a variety of dienophiles including dioxygen and we are able to isolate complexes containing the bound adduct. This process is inherently face-selective. We describe the effect of metal ligand substitution on the syn/anti-isomer ratio of the complexes produced. All these complexes were characterized by various spectroscopic techniques. In addition, complexes of dioxygen adduct and ethyl vinyl ketone adduct were characterized by single crystal X-ray crystallography. Reference 1. Lichtenberger D L, Blevins II C H and Ortega R B 1984 Organometallics 3 1614

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 397  Indian Academy of Sciences

Cyclopalladates of naphthylazobenzenes: Synthesis, isomerism, metaloxylation and photochemical behaviour D N NEOGI, R BHAWMICK and P BANDYOPADHYAY Department of Chemistry, University of North Bengal, Darjeeling 734 430, India A group of 2¢ -substituted phenylazo-1-naphthalenes react with palladium(II) to give cyclopalladated species, in which palladium–carbon bond formation occurs at the naphthyl ring. In ethanolic medium, 2¢ -alkylthio-phenylazo-1-naphthalene reacts with palladium(II) and yields an isomeric mixture of compounds (1) and (2). The structures of both (1) and (2) have been determined by X-ray crystallography. Both the compounds are cyclopalladated species having Pd-C(naphthyl) bond. Cyclometallation occurs at C(8) of the naphthyl ring in compound (1) whereas compound (2) contains Pd–C bond at C(2) of the naphthyl ring. Spectral and microanalytical characterization of (1) and (2) are also reported. At room temperature compound (2) undergoes selective metaloxylation reaction (oxygen atom insertion into metal–carbon bond) with m-chloroperbenzoic acid but compound (1) fails to react. In solution, the photochemical conversion of (1) to (2) has been observed.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 398  Indian Academy of Sciences

Modelling the active site properties of dopamine b-hydroxylase A M THOMAS, G C MANDAL, S K TIWARY and A R CHAKRAVARTY Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Dopamine b-hydroxylase (DbH) is a copper-containing glycoprotein that hydroxylates dopamine to norepinephrine 1,2. Based on spectroscopic studies the active site of the metalloenzyme is proposed to have two copper centres. The enzyme in the oxidized dicopper(II) form gets reduced to the dicopper(I) unit by ascorbate and, in the following step, dopamine and dioxygen bind to the enzyme to form a ternary complex resulting in the oxidation of dopamine and the formation of the oxidised form of the enzyme. In this paper, we report a dicopper(II) complex that has been found to be catalytically active in oxidising the ascorbic acid. The reduced complex reacts with dioxygen and benzylamine to form a ternary complex, followed by the oxidation of the amine. The catalytic process models the functional properties of dopamine b-hydroxylase. The reaction of the dicopper(II) complex with ascorbic acid in aqueous–methanol forms an intermediate brown species, which on exposure to air converts to a blue species that has been isolated and structurally characterized. The proposed catalytic cycle for the conversion of the reduced species to the oxidized complex in air is shown below. The oxalate anion in the catalytically active complex is generated from the dehydroascorbic acid by hydrolytic ring rupture followed by oxidation of 2,3-diketo-1-gluconic acid.

References 1. Abolmaali B, Taylor H V and Weser U 1998 Struct. Bonding 91 91 2. Klinmann J P 1996 Chem. Rev. 96 2541

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 399  Indian Academy of Sciences

N-, S-glycosides: Some organic and inorganic aspects of a few glycosides AJAY KUMAR SAHa, T MOHAN DASa, E K WEGELIUSb, E KOLEHMAINENb, P K SAARENKETOb, K RISSANENb and CHEBROLU P RAOa a Bioinorganic Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India b Department of Chemistry, University of Jyvaskyla, Jyvaskyla 40351, Finland Glycosides are of biological and pharmaceutical interest. To understand the genesis of glycosidic bond formation and the influence of metal ions on this, we have taken up a systematic study both with N- and S-glycosides. A few glycosylamines of a biologically active molecule, 3,6-ethylidene-D-glucopyranose, which acts as a reversible inhibitor of human erythrocyte transporter, have been prepared using different aryl amines. These glycosidic products are characterized by simple analytical, spectral and crystallographic techniques. Role of different metal ions on the glycosidic bond formation has also been studied. Several metal complexes have been synthesized with one of the glycosylamine and the products have been characterized based on spectral and analytical techniques in order to establish their structures. Biologically important S-glycosides, which are of use in Wilson and Menkes diseases, are also prepared from different saccharides. One of these S-glycosides, Dglucobenzothiazoline, has been subjected to complexation studies with transition metal ions. Several complexes have been synthesized, isolated, purified and characterized by a number of analytical, spectral and electrochemical techniques. All these compounds have been found to be compositionally and structurally different from each other. 1H, 13 C NMR and EPR spectra have been found to be crucial in establishing the structures of these molecules. Acknowledgement AKS, TMD and CPR are grateful to Professor K Rissanen and his group at Jyvaskyla University, Finland for the crystallographic facilities.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 400  Indian Academy of Sciences

Co(II), Ni(II) and Cu(II) complexes of bis(1,2-diphenyl-1-hydroxyimino-2-ethylidene)1,5-carbohydrazone and bis(1,2-dimethyl-1-hydroxyimino-2ethylidene)-1,5-carbodihydrazone N4-macrocycles as precursors for vitamin B12 and coenzyme B12 models D U WARAD, C D SATISH and CHANDRASEKHAR S BAJGUR Department of Chemistry, Gulbarga University, Gulbarga 585 106, India A series of novel N4-macrocyclic ligands (HL) have been synthesized by the condensation of carbohydrazide, H2N–NH–CO–NH–NH2 with 1,2-diphenyl-1hydroxyiminoethane-2-one and 1,2-butane-3-hydroxyiminoethane-2-one in 1:2 molar ratio. These ligands upon reaction with Co(II), Ni(II), and Cu(II) chlorides in 1:1 molar ratio have yielded mononuclear metal complexes of the type M(HL)Cl(H2O). Also, the reactions of the ligand with the corresponding metal salts in 1:2 molar ratio have yielded binuclear complexes of the type M2LCl2(H2O)2. The mononuclear Co(II), Ni(II) and Cu(II) complexes were also prepared by template synthesis. The isolated complexes have been characterized by elemental analysis and spectroscopic methods. The biological activities of the complexes have been studied by screening the compounds against E. coli, S. aureus, A. niger and C. albicans.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 401  Indian Academy of Sciences

Synthesis of copper and nickel complexes using compartmental ligands: X-ray, electrochemical and magnetic studies J MANONMANI, V NARAYANAN and M KANDASWAMY Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India The search for several synthetic routes leading to mononuclear or polynuclear complexes have been stimulated by the potential relevance of these compounds in bioinorganic chemistry. One of them consists of the synthesis of compartmental ligands, which are organic molecules able to bind with one or more metal ions. In the present work, we have synthesized acyclic dicompartmental ligand suitable for the complexation of transition metal ions which can form mononuclear, homo- or heterodinuclear complexes. Mononuclear complexes ML1 (M = Cu, Ni) where, L1 = N,N¢ -bis[2-hydroxy-3(morpholino-1-ylmethyl)-5-methylbenzyl]alkyldiimine (alkyl = (CH2)n, n = 2, 3 or 4) and ML2 where, L2 = N,N¢ -bis[2-hydroxy-3-(morpholino-1-ylmethyl)-5-bromobenzyl]alkyldiimine, (alkyl = (CH2)n, n = 2, 3 or 4) have been synthesized and characterized by electronic and ESR spectra. Electrochemical and magnetic studies were carried out. The complexes CuL1a (1), CuL1e (3), NiL1a (7) and NiL1d (10) (a = en, c = bn, d = trien) have been analysed by X-ray crystallography. Complexes 1 and 3 have square pyramidal geometry. The co-ordination geometry around the metal ion in complex 7 is square planar and that in complex 10 is octahedral. The electrochemical property of the complexes was studied using cyclic voltammetry. A single quasi-reversible electron transfer process occurs at the negative potential region (Epc = –80 to –1·0 V). Copper complexes show a normal magnetic moment (meff = 1·68–1·75 BM) and are ESR active. Square planar nickel complexes are diamagnetic whereas nickel complex (10) has a magnetic moment value of 3·12 BM characteristic of octahedral structures.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 402  Indian Academy of Sciences

Tris(catecholato)silicates of nickel: Synthesis, characterization and first observation of inter-ion ligand transfer J VIJEYAKUMAR KINGSTON, G S M SUNDARAM and M N SUDHEENDRA RAO Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India Catecholato complexes of transition metals have evoked interest for long and have also been the subject of recent studies due to their importance as useful model compounds for the study of microbial uptake and transport of iron. With regard to the constitutional and structural issues of nickel catecholates, many contradictory reports have appeared in literature. Only in 1998, Reymond et al have clarified through X-ray crystallographic studies, some of the compositions and behaviour of nickel catecholates. Recently, hypervalent silicates namely tris(catecholato)silicates (SICAT) with different organic counter ions (R+)2[Si(cat)3], have been made in our laboratory. These show potential to incorporate transition metal ions in place of organic counter ion by a facile ion-exchange process. Using this strategy, we have now obtained different nickel containing tris(catecholato) silicates, viz. [Ni(H2O)6][Si(cat)3], [Ni(NH3)6][Si(cat)3], [Ni(en)3][Si(cat)3], [Ni(dien)2][Si(cat)3] etc. and have characterized them by analytical and spectroscopic methods. Contrary to expected behaviour, some of these compounds are found to undergo a slow but definite colour change in the solid state at room temperature. By probing this, we find that through a ligand exchange process, the catechol moiety of the hypervalent anion has moved to the nickel centre signifying the preference of the 1,2dihydroxybenzene moiety for the transition metal centre.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 403  Indian Academy of Sciences

Synthesis, electrochemical and magnetic properties of new acylic ‘end-off’binuclear copper(II) complexes T M RAJENDIRAN, R KANNAPPAN, R VENKATESAN and P SAMBASIVA RAO Department of Chemistry, Pondicherry University, R.V. Nagar, Kalapet, Pondicherry 605 014, India A series of nonbridged nitrito binuclear copper(II) complexes [Cu2L(NO2)2(H2O)] ClO4·H2O of ‘end-off’ Mannich base ligands have been synthesized. Cyclic voltammetry of these complexes revealed that the reduction process involved two successive oneelectron transfer steps at different potentials. CuIICuII → CuIICuI → CuICuI The conproportion constants Kcon for the mixed valence CuIICuI complex has been determined electrochemically. Cryomagnetic investigations (77–300 K) indicate an antiferromagnetic spin exchange between the copper(II) ions within the complex. Crystal structure analysis shows that the ligand is pentadentate, donating two nitrogens as well as a bridging oxygen to each copper. The most notable feature of the structure is that neither of the nitrito groups are bridging between the Cu ions but are bonded in an O-bonded, nonlinear arrangement to each copper resulting in an open m-phenolate structure. Perchlorates occupy the interstitial positions.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 404  Indian Academy of Sciences

Dinuclear ruthenium(II) and/or osmium(II) complexes of bipyridyl ligands bridged by rigid spacers: Synthesis, electrochemical behaviour, absorption spectra and luminescence properties ANVARHUSEN K BILAKHIYA, BEENA TYAGI and PARIMAL PAUL Discipline of Silicates and Catalysis, Central Salt & Marine Chemicals Research Institute, G.B. Marg, Bhavnagar 364 002, India Supramolecular Ru(II) and Os(II) polypyridyl chemistry gained considerable interest due to their rich electrochemical and photophysical properties and potential use in a variety of energy/electron transfer processes. Such systems can be developed by covalent linking of prefabricated molecular components (building blocks) with spacers having bidentate donor sets. Suitable choice of the building blocks and appropriate designing of the structure can, in fact, allow the occurrence of energy/electron transfer along the supramolecular array. With a view to develop such systems, new bridging ligands, 1,4-bis[4-(4¢ -methyl)-2,2¢ -bipyridyl)imine]benzene (BL1) and 4,4¢ -bis[4-(4¢ -methyl)2,2¢ -bipyridyl)imine]benzene (BL2) and their dinuclear complexes of the type [(bpy)2Ru–BL1/BL2-Ru(bpy)2]4+, [(bpy)2Os–BL1/BL2-Os(bpy)2]4+ and [(bpy)2RuBL1/BL2-Os(bpy)2]4+ have been synthesized. For the synthesis of heterodinuclear complexes a new strategy has been adopted, which eliminates the possibility of the presence of homodinuclear complexes as impurity. Mononuclear model complexes [(bpy)2RuL1]2+, [(bpy)2OsL1]2+ and [(bpy)2RuL2]2+, where L1 = [4-(4¢ -methyl)-2,2¢ bipyridyl)imine]-4-aminobenzene and L2 = [4-(4¢ -methyl)-2,2¢ -bipyridyl)imine]-4aminodiphenylene, have been prepared. Ligands and metal complexes were characterized on the basis of elemental analysis, FAB mass, IR, and 1H NMR data. All metal complexes exhibit characteristic MLCT absorption bands in the visible region. They also show luminescence bands at room temperature. Cyclic and square wave voltammograms of all complexes exhibit metal-based oxidations (M(II)/(III)) in the potential ranges +1·20 to +1·23 V for Ru(II) and +0·75 to +0·82 V for Os(II). Ligand-based reductions occurred in the potential range –1·28 to –1·90 V. Mixed-valence species of the dinuclear complexes were generated by the addition of standard solution of ammonium cerium(IV) nitrate, and the properties of the mixed valence species have been studied. The emission state lifetimes of all complexes were measured at room temperature. The homodinuclear complexes exhibit significantly long lifetimes due to delocalization of the excited electron on the conjugated bridging unit. In heterodinuclear complexes the Ru-based emission lifetimes decreased significantly due to energy transfer from the Ru-unit to the Os-based unit.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 405  Indian Academy of Sciences

Peroxometal-mediated oxidation of bromine leading to environmentally favourable protocol for selective bromination of organic substrates: Implications for vanadium bromo peroxidase (VBrPO) SIDDHARTHA D DHAR and MIHIR K CHAUDHURI Department of Chemistry, Indian Institute of Technology, Guwahati 781 001, India Tribromide (Br3–) appears to be the ultimate product of a peroxo-metal mediated oxidation reaction, e.g. V2O5, H2O2 or

Bu4NBr

Bu4NBr3. H2MoO4, H2O, H2O2, H+

The identity of Bu4NBr3 was ascertained by isolation followed by spectroscopic and Xray crystallographic characterization. Taking clues from the knowledge derived from the aforementioned reaction as well as from that of the activity of VBrPO, it has been shown that V2O5 very effectively catalyses the bromination of organic substrates, including selective bromination of aromatics by Bu4NBr in presence of hydrogen peroxide. V2O5 (cat)

3Bu4NBr + H2O2

[Bu4NBr3] + 2Bu4NOH,

Ar---H + [Bu4NBr3]

Ar---Br + Bu4NBr + HBr.

For instance:

Versatility of this environmentally benign reaction protocol involving a variety of substrates has also been demonstrated by other collaborators. Implications of this investigation with reference to VBrPO activity are discussed. 405

Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 406  Indian Academy of Sciences

Catalytic carboxyester hydrolysis by diaminodiphenols TAMAL GHOSH and RUPENDRANATH BANERJEE Department of Chemistry, Jadavpur University, Calcutta 700 032, India Two diaminodiphenols, 1 and 2, have been examined as catalysts for the hydrolysis of 4nitrophenyl acetate (NA) and 4-nitrophenylphosphate (NP) in aqueous-acetonitrile (25% acetonitrile v/v) media at 35ºC, I = 1·0 mol dm–3. The compound 1 enhances the hydrolysis rate of NA more than 105 times. Its catalytic efficiency is only 80 times less than that of the OH– ion. Somewhat unexpectedly, addition of Cu2+ and Zn2+ strongly inhibit hydrolysis because the metal ions scavenge 1 by way of complex formation. In contrast to 1, 2 shows poor catalytic activity towards the hydrolysis of NA. Neither 1 nor 2 catalyses the hydrolysis of NP. The reasons for the specificity of 1 as a hydrolytic catalyst for NA is under investigation through kinetic and equilibrium measurements in solution.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 407  Indian Academy of Sciences

Chiral Ru(II) Schiff base complex-catalysed enantioselective epoxidation of styrene derivatives R I KURESHY, N H KHAN, S H R ABDI, S T PATEL, P IYER and R V JASRA Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India Ruthenium(II) chiral Schiff base complexes 1–5 and their precursor ligands derived from L-histidine with salicylaldehyde, 3-tert-butyl-, 3,5-ditert-butyl-, 3,5 dichloro- and 3,5dinitrosalicylaldehyde are reported. Characterisation of the ligands and complexes was accomplished by various appropriate physico-chemical studies namely, microanalysis, IR-, UV-Vis-, 1H, 31P{1H} NMR, CD spectroscopy, optical rotation, conductance measurement, and cyclic voltammetry. Complexes thus synthesised were used as catalysts for enantioselective epoxidation of styrene, 4-chloro-, 4-nitro, and 4-methyl styrene. Efficiency of the catalytic system was explored by varying the substituents on the ligand moiety of the catalysts and their effect on substituted styrenes was also studied. Iodosyl benzene turned out to be the oxidant of choice. Interestingly, catalyst 5 gave best results with 4-nitrostyrene suggesting that the higher electron density on the catalyst works better with electronically deficient substrates. The enantiomeric excess of the resulting epoxide was evaluated by gas chromatographic analysis.

1 2 3 4 5

: : : : :

R1 = R2 = NO2 R1 = R2 = Cl R1 = R2 = H R1 = C(OH3)3, R2 = H R1 = R2 =C(CH3)3 R3 = Histidine

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 408  Indian Academy of Sciences

Selective oxo-functionalisation of C–H bond with t-BuOOH catalysed by [RuIII(amp)(bipy)Cl] complex DEBABRATA CHATTERJEE, ANANNYA MITRA and SANGHAMITRA MUKHERJEE Chemistry Section, Central Mechanical Engineering Research Institute, Durgapur 713 209, India [RuIII(amp)(bipy)Cl] complex (1) (H2amp = N-(hydroxyphenyl)salicyldimine, bipy = 2,2¢ -(bipyridyl)) has been synthesised and characterised by physico-chemical methods. Complex (1) is found to be an effective catalyst 1 in the oxidation of cyclohexene to cyclohexene-1-ol, cyclohexane to cyclohexanol and cyclohexanone using tert-butylhydroperoxide (t-BuOOH). A high-valent Ru(V)-oxo species as catalytic intermediate formed in the reaction of complex (1) with t-BuOOH is proposed as the source of oxygen atom in the oxidised product. Kinetic data suggest that the formation of Ru(V)-oxo species is substitution-controlled. The results of the product distribution in the present investigation clearly indicate the highly electrophilic nature of Ru=O bond in the [RuV(amp)(bipy)O]+ intermediate complex which leads to the high affinity for hydrogen atom/hydride abstraction.

Acknowledgement We gratefully acknowledge the financial support from the Department of Science & Technology, Government of India. We are thankful to Shri Hardyal Singh for his encouragement. Reference 1.

408

Chatterjee D, Mitra A and Mukherjee S 1999 Polyhedron (accepted)

Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 409  Indian Academy of Sciences

Electrocatalytic oxidation of hydrogen peroxide by poly(NiII-teta) complex modified electrodes V GANESAN and R RAMARAJ School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India Electrochemical methods based on the direct reduction or oxidation of substrate molecules at bare electrodes are often not suitable for analytical applications because the electrode reactions are subjected to large over-voltage. Modifying the surface of an electrode with a redox mediator is a well-established strategy for achieving wider applicability of electroanalytical methodology. In the past few years, there has been an increasing interest in the study of electrocatalytic properties of tetra-azamacrocyclic metal complexes of cobalt and nickel. Ni(II) and Co(III) with tetra-azamacrocyclic ligands have been reported as exceptionally efficient and selective electro- and photocatalysts for the reduction of CO2, nitrate, nitrite and O2. The determination of H2O2 and organic peroxides is rapidly gaining practical importance in clinical industries and environmental fields. Conventional methods for the determination of peroxides such as spectrophotometry, colorimetry and chemiluminescence involve complicated methods and suffer from various interferences. The need for simple, sensitive and rapid detection schemes for monitoring peroxides has promoted much of the research in the development of sensors for these applications. In this paper, we report the electrocatalytic behaviour of NiII-teta (teta = C-meso-(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)), polymerized on an electrode surface, towards the oxidation of hydrogen peroxide. To prepare poly(NiII-teta) incorporated Nafion modified electrode, Nafion coated glassy carbon electrode was used. These poly(NiII-teta) modified electrodes electrocatalysed the oxidation of hydrogen peroxide. The mechanism of the hydrogen peroxide oxidation at the modified electrodes and the influence of Nafion film are discussed.

409

Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 410  Indian Academy of Sciences

Excited state reaction of [(2-carboxypyridinato)bis(2,2¢bipyridine)ruthenium(II)] ion with phenolate ions T SHUNMUGASUNDARI, P THANASEKARAN and S RAJAGOPAL School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India Photoinduced electron transfer (PET) reaction of homoleptic tris-chelated polypyridine ruthenium(II) complexes with phenolate ions is sensitive to the structure of the ligand of the Ru(II) complex as well as of the phenolate ions 1. In recent years 2 the photophysical and photochemical properties of Ru(II) complexes based on ligands that include coordinating atoms other than nitrogen have been generally explored. When picolinic acid (PA) is used as the ligand, it is coordinated to the metal via the carboxylate ion and the nitrogen atom. In the present study we have synthesised [(2-carboxypyridinato)bis(2,2¢ -bipyridine)ruthenium(II) ion [RuII(PA)(bpy)2]+ and studied the photophysics and PET reaction of tris-chelated heteroleptic ruthenium(II) complex with several phenolate ions and compared the results with those observed for the parent complex, Ru(bpy)32+. The wavelength (lmax) of absorption (477 nm) and emission (645 nm) maxima of [RuII(PA)(bpy)2]+ are red-shifted compared to Ru(bpy)32+ and emission lifetime (t) is less (120 ns) at room temperature. Phenolate ions containing electron-releasing groups form a ground-state complex with [RuII(PA)(bpy)2]+ but quench the emission by electron transfer mechanism. The luminescence quenching of *[RuII(PA)(bpy)2]+ with ArO– is less efficient compared to that of *Ru(bpy)32+. The excited-state reduction potentials of [RuII(PA)(bpy)2]+ and Ru(bpy)32+ are 0⋅57 V and 0⋅80 V respectively. The excited state reaction of [RuII(PA)(bpy)2]+ with ArO– is explained using a scheme involving complex formation between the reactants in the ground state. References 1. 2.

410

Rajagopal S et al 1998 J. Chem. Soc., Faraday Trans. 94 3339 Norrby T et al 1997 Inorg. Chem. 36 5850

Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 411  Indian Academy of Sciences

Aluminium(III) alkoxides as unique synthons for heterocyclic derivatives containing aluminium(III) atoms in different coordination states R BOHRA, NIKITA SHARMA and S NAGAR Department of Chemistry, University of Rajasthan, Jaipur 302 004, India Facile reactivity of aluminium(III) alkoxides with organic protic reagents with alcohol as the only side product provides a convenient method for the synthesis of a variety of products which may not be synthesized by any other route. The possibility of removal of alcohol azeotropically with solvent benzene makes it possible to prepare mixed ligand derivatives in interesting coordination states depending upon the uni/polydentate nature of the reagent: 2Al(OPri)3 + 2CH3COCH2COCH3 → [(CH3COCHCOCH3)2Al(m-OPri)2Al(OPri2)] + 2PriOH [(CH3COCHCOCH3)2Al(m-OPri)2Al(OPri)2] + xC9H8NOH → [(CH3COCHCOCH3)2Al(m-OPri)2Al(OPri)2–x(ONH6C9)x] + xPriOH (x = 1 or 2; C9H6NOH = 8-hydroxyquinoline) The 27Al NMR spectra of a representative derivative [(CH3COCHCOCH3)2Al(mOPri)2Al(OPri)(ONH6C9), exhibit signals at d11⋅22 and 0⋅81 ppm indicating the presence of both penta- and hexa-coordinated aluminium(III) atoms.

Similarly reactions of the following types yield interesting derivatives containing aluminium(III) atoms at different coordination states. (acac)2Al(m-OPri)2Al(OPri)2 + HSP(S)(OR)2 → (acac)2Al(m-OPri)2Al(OPri)[SP(S)(OR)2] + PriOHbenzene

(acac)2Al(m-OPri)2Al(OPri)2 + 2HO-G-OH –––––––→ (acac)2Al(m-O-G-O)Al(O-G-O) + 4PriOH (where hacac = acetylacetone, ester, HO-G-OH = glycols and HSP(S)(OR)2 = dithiophosphoric acid).

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 412  Indian Academy of Sciences

Synthesis and transition metal chemistry of novel phosphorus(III)-containing inorganic heterocycles RASHMISHREE PANDA and M S BALAKRISHNA Department of Chemistry, Indian Institute of Technology Bombay, Powai Mumbai 400 076, India Synthesis of phosphorus containing macrocycles and cryptands has evoked much interest in recent years and provided exciting and novel chemistry. The introduction of trivalent phosphorus atoms or phosphoryl and thiophosphoryl groups into a ring enhances the versatility of the macrocyclic ligands in forming complexes with both hard and soft metals. Tri-coordinated phosphorus-containing macrocycles can easily bind transition metals while alkali and alkaline earth metal ions can be trapped with P = O or P = S groups. Our interest in this area and the above observations prompted us to pursue a systematic synthetic and structural investigation of some phosphorus(III)-containing inorganic heterocycles of the type I. We have also made a series of analogous acyclic phosphines of the type II.

Synthesis, reactivity, spectroscopic and structural aspects, and transition metal chemistry of the above compounds are presented.

412

Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 413  Indian Academy of Sciences

New open-framework yttrium oxalates with structure-directing amines R VAIDHYANATHAN, S NATARAJAN and C N R RAO Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064, India Microporous open-framework solids have gained importance on account of their potential utility in catalysis and ion-exchange studies. A large number of metal phosphates as well as a few metal oxalates are known to form such open-framework structures. Here we report the synthesis of two entirely new open-framework oxalate structures formed in the presence of structure-directing organic amines. The compound I, [Y(C2O4)2][C5H11N2], has an eight-coordinated yttrium. The yttrium and oxalate linkages give rise to a threedimensional structure with 12-membered (6Y and 6 oxalates) honeycomb-like apertures along both x- and z-axes. Another 8-membered (4Y and 4 oxalates) channel is seen along the y-axis. The amine molecules are located in the 12-membered channel. In compound II, [Y2(C2O4)4(H2O)2][C3H12N2].4H2O, yttrium is nine-coordinated. The yttrium and oxalate ions are so connected as to form a three-dimensional structure with 12-membered (6Y and 6 oxalates) channels along x-, y- and z-axes, within which the amine and water molecules reside. Both the structures I and II are stabilized by extensive hydrogen bonding between the amine, the water and the framework. The compound II may adsorb water reversibly. Further work in this direction is in progress.

413

Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 414  Indian Academy of Sciences

Hydrothermal synthesis and structure of framework cobalt phosphates AMITAVA CHOUDHURY a,b, SRINIVASAN NATARAJAN a and C N R RAO a,b a Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore 560 064, India b Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India Open-framework phosphates investigated in the last few years, specially those of transition metals, are of particular interest because of their potential applications in catalysis, sorption and separation techniques. Amongst the transition metals, cobalt phosphate occupies a prime position because of its interesting magnetic properties. The compound [C2N2H10]2[Co4(PO4)4]+H2O (I), has a structure constructed from alternating CoO4 and PO4 tetrahedra. The connectivity leads to the formation of 8-membered channels in all the crystallographic directions resembling the aluminosilicate zeolite, merlinoite. The compound is unique in the sense that it is the first pure transition metal phosphate which has zeolitic structure. The compound [Co3⋅5(PO4)3][C2N2H10] (II), has several noteworthy features. The structure is constructed using CoO4, CoO5, CoO6 and PO4 polyhedra. It shows an unusual structural transformation on cooling. A sheet-like Co-O-Co connectivity at room temperature extends in three dimensions at 140 K as is observed by single crystal structure determination at both room temperature and at 140 K. Magnetic studies reveal that the compound shows ferromagnetic interactions at low temperature.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 416  Indian Academy of Sciences

Morphological control of aragonitic calcium carbonate systems: Syntheses, characterisation and their phase transformation behaviour DEBOJIT CHAKRABARTY and SAMIRAN MAHAPATRA Hindustan Lever Research Centre, ICT Link Road, Chakala, Andheri (East), Mumbai 400 099, India The three crystalline forms of calcium carbonate, viz. calcite, aragonite and vaterite, exhibit rhombohedral, ‘needle-like’ and spheroidal morphologies respectively. Studies in recent years have shown that the shape/morphology of calcite crystals can be modified using various methods. However, there has been no report of habit modification of aragonite crystals before the present study 1. The morphological control of both these polymorphs have widespread implications in calcium carbonate biomineralisation processes. Aragonite crystals with novel morphologies like, ‘cauliflower’ and ‘flake’ have been synthesised by combining aq. solutions of CaCl2 and Na2CO3 under ambient conditions. These aragonites represent the first examples of their kind, and have been unambiguously characterized by their powder X-ray diffraction (XRD) patterns, Raman and FTIR spectra, and Scanning Electron Micrographs (SEM). These morphologically modified aragonite samples are stable at room temperature in their solid states, but can be thermally transformed to their thermodynamically stabler congener, calcite. This phase transformation behaviour has been systematically investigated using temperature dependent XRD and SEM imaging studies. Thermally transformed calcite crystals exhibit surface features and topography similar to those found for their parent aragonites. Kinetic and thermodynamic parameters for this phase transformation process have been determined.

Reference 1. Chakrabarty D and Mahapatra S 1999 J. Mater. Chem. 9 2953

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Solid state chemistry of new polysulphides in A/Sn/S (A = Na, K, Rb) systems M SUSEELA DEVI and K VIDYASAGAR Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India Ternary polychalcogenides containing chalocogen–chalcogen bonds are metastable compounds that have been reported to be isolated by only low temperature synthetic routes 1 such as the molten salt flux method, the solvothermal method etc. These compounds possess novel, low and three-dimensional structural frameworks and also unique physical properties. Synthetic and structural solid state chemistry of the polychalcogenides has been an active area of research for the last ten years. In this work, we present the results of our synthetic and structural investigations of polysulphides, in A/Sn/S (A = Na, K, Rb) systems possessing novel structures as determined by single crystal X-ray diffraction. Reference 1. Kanatzidis M G and Sutorik A C 1995 Prog. Inorg. Chem. 43 151

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Microwave-assisted rapid synthesis of Si-MCM-41 HARESH M MODY 1, PRITI PANDYA 1, PRASHANT BHATT 2 and RAKSH VIR JASRA 1 1 Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India 2 Department of Chemistry, Bhavnagar University, Bhavnagar 364 002, India Synthesis of mesoporous molecular sieves of uniform pore size in the range of 15 to 100 Å has elicited considerable interest for their potential applications in catalysis and selective adsorption of gases and liquids. MCM-41, a hexagonal array of unidimensional parallel channels with diameters 15 to 100 Å, is prepared hydrothermally using a broad spectrum of surfactants as templates under a wide range of synthetic conditions (temperature, pH, reaction time and gel compositions). Hydrothermal synthesis of MCM41 is mostly reported to take several days for completion. The use of microwaves for the synthesis of inorganic porous solids like zeolites has been reported to reduce the synthesis time significantly. Recently, Chen-Guey Wu and Thomas Bein have reported the synthesis of Al-MCM-41 using temperature control microwave ovens within about 1 h with tetramethylammonium silicate and Hi Sil T600 as a source of silica and C16H33N(CH3)3 Cl/OH (60% of OH anion) as templating agent. We report, in the present study, rapid synthesis of hexagonal mesoporous silica MCM-41 by irradiating precursor gels with microwaves for different time intervals (10– 60 min). The samples were characterized by powder X-ray diffraction (XRD) and BET by nitrogen adsorption at 77 K. Properties of these samples were compared with the MCM-41 prepared by the conventional hydrothermal method (100°C for 144 h). No significant difference was observed in the specific surface area of samples prepared under either microwave or conventional hydrothermal conditions. X-ray diffraction data revealed that samples prepared by the conventional hydrothermal method showed maximum value of net integral intensity of d(100) reflection and minimum value of full width at half maximum (FWHM). However a sample prepared with 40 min microwave irradiation time yielded maximum crystallinity amongst samples prepared under microwave irradiation.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 418  Indian Academy of Sciences

Structurally deformed metalloporphyrins on polymer support by anchoring at porphyrin periphery M PADMANABHAN and TESSYMOL MATHEW School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills, Kottayam 686 560, India Porphyrins with nonplanar geometry and having distorted p-framework are compounds of considerable interest as they are known to show interesting and highly specific catalytic and enzymatic properties. Metalloporphyrins grafted on solid polymer support have several advantages over their unsupported species in their chemical and industrial applicability. In this paper, functionalised tetraphenylporphyrin (H2TPP) moiety grafted on divinylbenzene cross-linked polystyrene support was developed by interacting (5aniline,10,15,20-triphenyl)porphyrins with Merrifield resin. Characterisation of these compounds and determining the extent of grafting of the porphyrins were done by spectral methods. It was found that depending on the position of the amino group on the aniline moiety the grafted porphyrins undergo varying extents of molecular distortions. Various Cu(II) derivatives of these porphyrins were also supported on the polymer support and their electronic and ESR spectral properties measured. The extent of distortion of the porphyrins was found to vary with the position of grafting as ortho > meta > para.

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Design, syntheses, characterization and single crystal X-ray diffraction studies of multicomponent Zn-tetraphenylporphyrins: Novel building blocks for microporous crystalline solids ATINDRA D SHUKLA 1, PARESH C DAVE 1, ERINGATHODI SURESH 1, GOPAL PATHAK 2, AMITAVA DAS 1 and PARTHASARATHI DASTIDAR 1 1 Silicates & Catalysis Division, Central Salt & Marine Chemicals Research Institute, Bhavnagar 364 002, India 2 National Chemical Laboratory, Pune 411 008, India Two multicomponent Zn-tetraphenylporphyrin (ZnTPP) based building blocks, have been synthesized for designing microporous crystalline solids. Reactions between ZnTPP and 4,4¢ -bipyridine (4,4¢ -bpy) in two different molar ratios gave complexes [{ZnTPP)3{m-4,4¢ bpy}2] (1) and [{ZnTPP)2{m-4,4¢ -bpy}] (II). Complexes I and II were characterized by different spectroscopic and analytical methods. In order to study their supramolecular array, inclusion complexes of I and II with toluene as guest (namely Ia and IIa respectively) have been prepared and their structures determined by single crystal X-ray crystallographic techniques.

Packing arrangements of these building blocks in their inclusion complexes are found to be quite similar to the gross packing mode of TPP based materials. Interestingly, in Ia, an extra channel is formed around the central porphyrin core of the trimer because of its unprecedented tilt with respect to the terminal porphyrin core of the trimer. Thermogravimetric analysis (TGA) of IIa corresponds well with the stoichiometry found in the crystal structure. To the best of our knowledge, complex I is the second example of crystallographically characterized hexacoordinated ZnTPP complex with N donor heterocyclic ligand.

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Cyclometallation in calixarenes: Synthesis and structural characterization of a novel cyclopalladated calix[4]arene bisphosphite L MAHALAKSHMI, S S KRISHNAMURTHY and M NETHAJI Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Calixarenes 1, a class of phenolic macrocycles, continue to find applications in diverse fields, especially in catalysis and solvent extraction of metal ions. Phosphorus containing calixarenes 2 with P(III) centres (notably phosphanes, phosphites or phosphinites) provide an attractive platform for anchoring transition metal-based catalysts which would have several distinct advantages over the conventional transition metal homogeneous catalysts. Recent reports on calixarenes have explored this aspect 3. In this context, our present report on a novel cyclopalladated calixarene bisphorphite unfolds a new facet of calixarene chemistry. The novel symmetrically bridged calix[4]arene bisphosphite-I has been isolated from the reaction of p-tert-butylcalix[4]arene with ROPCl2 (R = 2,6-But2, 4-ME–C6H2–) in the presence of NaH, followed by column chromatography over silica gel. Reaction of I with PdCl2(NCPh)2 or PdCl2(COD) gives the cyclopalladated p-tert-butylcalix[4]arene bisphosphite-II, unprecedented in calixarene chemistry. Structural studies reveal that the aryl rings of the phenolic substituents in the cyclopalladated complex-II are oriented perpendicular to each other unlike in the case of the calixarene bisphosphite ligand-I although in both the compounds the calixarene framework adopts a distorted cone conformation.

References 1. Böhmer V 1995 Angew. Chem., Int. Ed. Engl. 34 713 2. Wieser-Jeunesse C, Matt D, Yaftian M R, Burgard M and Harrowfield J M 1998 C.R. Acad. Sci. Paris, T. 1, Ser. II 479 3. Wieser C, Dieleman C B and Matt D 1977 Coord. Chem. Rev. 165 93

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Synthesis and characterization of ruthenium complexes bearing tris(pyrazol-1-yl)methane ligand NIBEDITA RATH 1, NISHA MATHEW 1, BALAJI R JAGIRDHAR 1, R SRINIVASA GOPALAN 2 and G U KULKARNI 2 1 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India 2 Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India Tripodal nitrogen donor ligands, in particular, tris(pyrazol-1-yl)borate (Tp), have been employed in organometallic chemistry due to their unique properties. Complexes containing tris(pyrazol-1-yl)methane (TPM) have barely been explored. The isoelectronic as well as similar structural features of TPM and Tp provides an opportunity to compare the electronic as well as steric properties of these ligands upon complexation with metal centres. We have synthesized three new ruthenium complexes containing TPM ligand. Reaction between RuCl2(PPh3)3 and TPM in THF gives a yellow product which we believe is (TPM)RuCl2(PPh3). Enroute, a green [(TPM)RuCl(PPh3)2]Cl is obtained in small yields. We have isolated and structurally characterized this green [(TPM)RuCl(PPh3)2]Cl complex. Reaction of RuHCl(PPh3)3 with TPM and NH4PF6 in THF gives a yellow [(TPM)RuH(PPh3)2]PF6. THF, r.t

THF

RuCl 2 (PPh 3 ) 3 + TPM    → [(TPM)Ru (PPh 3 ) 2 Cl]Cl  –PPh  → [(TPM)Ru(PPh3)Cl2] –PPh3

3

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 422  Indian Academy of Sciences

First examples of metal derivatives of modified corrole and expanded corrole S SRIDEVI, JEYAPRAKASH NARAYANAN and T K CHANDRASHEKAR Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India In recent years, though the importance of expanded porphyrins has been highlighted, there are only a few reports on contracted porphyrins (corroles) and their expanded derivatives. This difficulty has been attributed to the non-availability of easy and efficient methodologies to synthesise them in gram quantities 1,2. Very recently, we were able to synthesise modified corroles as well as their expanded derivatives by a novel method involving a-a coupling reactions. In this presentation, the details of the synthetic methodology, spectral and structural data are discussed in terms of their electronic structure and coordination behaviour. Specifically, Ni(II) and Cu(II) bind oxa corrole(1) with the participation of all the heteroatoms while the Rh(I) complex binds only to one imino and one amino nitrogens. On the other hand, Rh(I) complex of expanded corrole(2) shows a square planar coordination with three heteroatoms still available for coordination.

1

2

References 1. Narayanan S J, Sridevi B, Chandrashekar T K, Vij A and Roy R 1999 J. Am. Chem. Soc. 121 9053 2. Narayanan S J, Sridevi B, Chandrashekar T K, Englisch U and Senge K R 1999 Org. Lett. 1 587

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 423  Indian Academy of Sciences

Metal mediated amination of aromatic rings following carbon-nitrogen bond formation and the coordination chemistry thereof AMRITA SAHA, AMIT K GHOSH, PARTHA MAJUMDAR and SREEBRATA GOSWAMI Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India Metal-mediated reactions which result in addition of [NR]2– fragments belong to a reaction class of fundamental importance in chemistry in connection with carbonnitrogen bond formation processes. In this presentation we wish to report our results on aromatic ring amination of a pendant phenyl ring of coordinated 2-(phenylazo)pyridine, pap. Upon coordination, both ortho and para-C–H of the pendant phenyl group of the diaza ligand are activated. As a result, amination processes occurring both at ortho- and para- are observed. These chemical transformations of the coordinated pap ligand are schematically shown below. A rationale for the site selectivity for this amination process depending on the availability of coordination site is presented.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 424  Indian Academy of Sciences

Platinum metal chemistry of bisphosphines derived from N,N¢-substituted ethylenediamine derivatives RITA M ABHYANKAR and M S BALAKRISHNA Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India The role of chelate complexes containing bisphosphine ligands in homogeneous catalysis for various organic transformations is well documented. However, binuclear complexes with bridging bisphosphines can promote both homogeneous and heterogeneous catalysis depending upon the nature of the metals and their oxidation states. Binuclear palladium (I) and platinum (I) complexes, co-ordinate small molecules across the metal–metal bond to form ‘A-frame’ complexes and are considered to be possible models for catalytic intermediates generated on the metal surface. In heterobimetallic systems selective transformation of each metal centre can generate a whole new range of systems. The chemistry of platinum metal complexes containing bis-(diphenylphosphino)methane(dppm) has been extensively studied in this regard whereas similar types of reports concerning bisphosphines wherein the phosphorus atoms are separated by more than two atoms/heteroatoms are limited. We report here the synthesis of new complexes of the type [MX2(h1-L)2]{M = Pd, Pt; L = Ph2PN(R)CH2CH2N(R)-PPh2; R = CH3, CH2C6H5, C6H5} containing two dangling bisphosphines which can be used as precursors, to prepare a series of homo- and hetero-binuclear complexes. Also, synthesis and spectroscopic studies of M(0) and M(I) (M = Pd, Pt) complexes are presented.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 425  Indian Academy of Sciences

Steric control of the coordination mode of thiosemicarbazone ligands, synthesis, structure and redox properties of ruthenium and osmium complexes FALGUNI BASULI and SAMARESH BHATTACHARYA Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Calcutta 700 032, India An unusual coordination mode (1) of benzaldehydethiosemicarbazone (Hbztsc-R) has been observed in a series of complexes of type [M(PPh3)2(bztsc-R)2] (M = Ru, Os) obtained from the reaction of the ligands with [M(PPh3)2X2] (X = Cl, Br). Assuming the bulk of PPh3 to be responsible for such a coordination mode, another family of mixedligand complexes of type [M(bpy)2(bztsc-R)]+ have been prepared where 2,2¢ -bipyridine, which is of much smaller size, has been used as the co-ligand. However, similar fourmembered chelate ring formation by benzaldehydethiosemicarbazone (1) has been observed. Modelling studies have showed that this mode of coordination of the benzaldehydethiosemicarbazone ligand depends on the steric bulk of the aryl group. This has been authenticated by preparing similar complexes of acetonethiosemicarbazone (Hactsc), viz. [M(bpy)2(actsc)]+, where the actsc ligand forms a five-membered chelate ring (2). Structures of a selected benzaldehydethiosemicarbazone ligand and three representative complexes have been determined. Spectral and electrochemical properties of the complexes have been investigated.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 426  Indian Academy of Sciences

Crystal structure and magnetic behaviour of the two-dimensional complex [Cu(dmen)]2[Fe(CN)6] (dmen = 2-dimethylaminoethylamine) with an exceptional cyano-bridging N MONDAL, M K SAHA, B BAG and S MITRA Department of Chemistry, Jadavpur University, Calcutta 700 032, India The chemistry of several bimetallic assemblies has developed recently due to their variable magnetic properties 1. Among them a cyanide system based on prussian blue and its analogues is particularly useful and has drawn considerable interest. The cyanide bridged bimetallic assemblies of [Cu(dmen)]2[Fe(CN)6] (dmen = 2-dimethylaminoethylamine) have been prepared and characterized by elemental analysis, infrared, ESR and electronic spectroscopy. The crystal structure of the compound showed a monoclinic system of space group P21/c with a = 11⋅11(2), b = 8⋅969(10), c = 10⋅73(2) Å, a = g= 90, b= 112⋅48(11)° and Z = 2. The polymeric two-dimensional sheet of the compound consists of two different rings; one is a four-membered square ring and another a twelvemembered hexagonal ring. In the crystal, all the Fe(II) ions have two free cyanide groups, two linearly bridging cyanide groups and two end-on bridging cyanide groups, which is exceptional. Each Cu(II) ion shows distorted square pyramidal geometry. From the variable temperature magnetic susceptibility measurements, the complex was found to exhibit a weak ferromagnetic interaction between the nearest copper (II) through the diamagnetic iron(II) atoms.

Reference 1. Fukita N, Ohba H, Okawa H, Matsuda K and Iwamura H 1998 Inorg. Chem. 37 842

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Copper(II) activated transformation of azomethine to imidate SATYANARAYAN PAL, NIMMA RAJAIAH SANGEETHA and SAMUDRANIL PAL School of Chemistry, University of Hyderabad, Hyderabad 500 046, India Tridentate Schiff bases are excellent ligands in forming dinuclear complexes of metal ions which prefer square-planar geometry. Deprotonated monobasic arylhydrazones of 2pyridine-carboxaldehyde can coordinate a metal ion via the pyridine-N, the imine-N and the amide-O atoms. We are interested in amide-O bridged dinuclear complexes in order to study the influence of amide proton on the interaction between the two metal ions. In developing a dinuclear copper(II) complex we have reacted 4-dimethylaminobenzoylhydrazone of 2-pyridine-carboxaldehyde (HL) with Cu(O2CCH3)2×H2O in methanol. The product obtained is a dinuclear complex, [Cu2L2¢ (m-O2CCH3)2]×2H2O, in which the azomethine group of HL has been transformed to imidate. The syntheses and X-ray structures of the free hydrazone and the dinuclear copper(II) complex of the transformed ligand are described in this work.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 428  Indian Academy of Sciences

Transition metal chemistry of hydroxy(–OH)-rich molecules: Syntheses, crystal structures and solution reactivity studies MISHTU DEY 1, P K SAARENKETO 2, E KOLEHMAINEN 2, K RISSANEN 2 and CHEBROLU P RAO 1 1 Bioinorganic Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India 2 Department of Chemistry, University of Jyvaskyla, Jyvaskyla 40351, Finland Appropriately designed hydroxy(–OH) containing Schiff’s base and Mannich base molecules have been recently found to be important for development of the coordination chemistry of a number of metal ions in the biomimetic chemistry of metalloenzymes. In this context, our group has studied the coordination role of these molecules with oxoV(V), oxo-Mo(VI), oxo-U(VI) and Ti(IV) 1,2. Reactions of hydroxy(-OH)- rich salicylidene moieties with late transition metal ions such as Co(II), Ni(II), Cu(II) and Zn(II) led to the formation of a variety of mononuclear, dinuclear and tetranuclear complexes bound to alkoxo, phenolate and imine groups. These complexes have been characterized by analytical, spectral and electrochemical methods including single crystal X-ray diffraction studies. A unique feature of some of these complexes is that the –CH2OH function of the hydroxy-rich molecule does not coordinate with the metal ions. This feature is in contrast with that observed in the complexes of oxo-V(V), oxo-Mo(VI), oxo-U(VI) and Ti(IV). The complexes have been subjected to reactivity studies. These complexes exhibit core-conversion properties. Conversion of the mononuclear complex to the corresponding tetranuclear counterpart and vice versa is observed in the case of copper complexes. These interconversion reactions have been studied with other complexes as well. These complexes undergo trans-metallation reactions. Acknowledgements MD and CPR are grateful to Professor K Rissanen and his group at Jyvaskyla University for the crystallographic facilities. References 1. Asgedom G, Sreedhara A, Kivikoski J, Valkonen J, Kolehmainen E and Rao C P 1996 Inorg. Chem. 35 5674 2. Rao C P, Sreedhara A, Rao P V, Verghese B M, Rissanen K, Kolehmainen E, Lokanath N K, Sridhar M A and Prasad J S 1998 J. Chem. Soc., Dalton Trans. 2383

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Rectangular grids formed by hydrogen-bonding interactions between successive chains of linear polymers [Co(II)-4,4¢-bpy-Co(II)]n and their inclusion properties: Synthesis and single crystal investigations E SURESH 1 and MOHAN M BHADBHADE 2 1 Silicates and Catalysis Division, Central Salt & Marine Chemicals Research Institute, GB Marg, Bhavnagar 364 002, India 2 Physical Chemistry Division, National Chemical Laboratory, Pune 411 008, India Three cobalt(II) coordination polymers [Com-(4,4¢ -bpy)(H2O)2(ClO4)2].4,4¢ -bpy.H2O 1, [Com-(4,4¢ -bpy)(H2O)4](ClO4)2. 4,4¢ -bpy. H2O 2 and [Com-(4,4¢ -bpy)(H2O)4](succinate). 2H2O linking the metal centres via exobidendate ligand 4,4¢ -bipyridyl have been synthesized and structurally characterized. The crystal structures of all these complexes have in common a one-dimensional linear polymer linking the Co centres by 4,4¢ -bpy; 1 is a neutral complex, with the perchlorate ion coordinated to the metal, whereas 2 and 3 are cationic with perchlorate and butanedioate anions present respectively in the lattice. The interesting feature of all the polymeric networks is the presence of strong O– H...N interactions between the included 4,4¢ -bpy moieties in 1 and 2 with the coordinated water molecules and O–H...O interaction of the succinate dianion with the coordinated water in 3 forming an H-bonded rectangular sheet structure which crosslinks the adjacent layers. All the structures have non-interpenetrating cavities of rhombic shape (as shown in the figure) which are occupied either by water molecules or counter anions involved in strong H-bonding with the coordinated water molecules. Consequently, a rational approach to achieve higher dimensional network structures has been attempted using appropriate ligands.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 430  Indian Academy of Sciences

Electronic structure of hexanitroferrates K2M[Fe(NO2)6] where M = Pb, Sr, Zn, Ca K PADMAKUMAR 1 and P T MANOHARAN 2 1 School of Chemical Sciences, M. G. University, Kottayam 686 560, India 2 Department of Chemistry and Regional Sophisticated Instrumentation Centre, Indian Institute of Technology Madras, Chennai 600 036, India Detailed variable temperature Mössbauer, infrared, EXAFS spectroscopic measurements and variable temperature magnetic susceptibility experiments were carried out on K2PbFe(NO2)6 to investigate the electronic structure and correlate it to the observed unusual magnetic hyperfine interaction in the system. All these results have then been further extended to the other systems where lead has been substituted with strontium, zinc and calcium because of the structural similarity of these systems with the lead compound. This has been further confirmed by detailed variable temperature Mössbauer spectral measurements on the above mentioned systems. The transition temperature in all these systems was found to be 45 K. All these results exactly match the results for K2BaFe(NO2)6 reported earlier by the same authors 1 and clearly indicate that the Fe atom in these lattices is in the high spin + 2 oxidation state which is quite contrary to the earlier reports on low spin states. Reference 1. Padmakumar K and Manoharan P T Spectrochim. Acta A56 905

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 431  Indian Academy of Sciences

Ligational behaviour of thiometallate [(MS4)2–, (M = Mo, W)] ligands towards Ni(II) in the presence of aliphatic diamines BEENA VERNEKAR and B R SRINIVASAN Department of Chemistry, Goa University PO, Goa 403 206, India Thioanions of the group VI metals are unusual ligands as they are purely inorganic in nature and have been extensively used in inorganic synthesis. These efforts have resulted in the synthesis and the structural characterization of a variety of sulphur-bridged homo and hetero bi, tri, tetra and multimetallic complexes 1. The continuing research in this area is mainly due to the importance of such complexes in materials science and in hydrodesulphurization (HDS) catalysis 2,3. It has been observed that HDS activity is enhanced when Ni or Co is added to Mo or W based catalysts and also that the active phase contains M¢ -Mo-S (M¢= Ni or Co) units. We have studied the complex formation reactions of Ni(II) with thiometallates in the presence of aliphatic diamines like 1,2diaminoethane, 1,2-diaminopropane and 1,3-diaminopropane. Herein, we wish to report the synthesis and characterization of neutral hexacoordinated mixed ligand Ni complexes of the general formula [L2Ni(MS4)] 1 (L = aliphatic diamine, M = Mo, W) and another series of complexes [L3Ni][MS4] 2 (L = aliphatic diamine, M = Mo, W). These complexes can be thermally decomposed to provide mixed metal sulphides. The details of the synthetic methodology and the procedures employed for characterization of 1 and 2 as well as the thermal decomposition pathways are discussed. References 1. Muller A, Diemann E, Jostes R and Bogge H 1981 Angew. Chem., Int. Ed. Engl. 20 934 2. Muller A 1986 Polyhedron 5 251 3. Diemann E, Weber Th and Muller A 1994 J. Catal. 148 288

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Spectroelectrochemistry Y2K: An analytical approach K RAMESH Sinsil International, 165, Parishram Park, Gorwa, Baroda 390 016, India A simple spectroelectrochemical system has been designed to carry out cyclic voltammetry, square wave voltammetry, bulk electrolysis with coulometry and recording spectroscopy experiments on oxidised/reduced species in a single shot. The cell is made with standard joints for Schlenk line operations and provision for spectroscopic measurements. Optical fibre technology has been used in the world for the first time to carry out experiments on in situ spectroscopy of the solution before and after the coulometry. Electrochemical systems (CH instruments, USA), CCD array spectrometer (Ocean Optics, USA) and home-made electrodes have been used to establish the techniques. The spectroscopy and electrochemistry systems are connected by optical fibre 10 mm path length dip probes. Spectroscopic signals and data are processed separately by hand held CCD array spectrometer connected to PC which eliminates the need for a separate spectrophotometer and allows connection to existing electrochemical system for spectral measurements. In the year 2000, two days of student labour may be reduced to two hours, that too without transferring the air-sensitive solution.

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Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 112, No. 3, June 2000, p. 433  Indian Academy of Sciences

Synthesis, structure and reactivity of a water-soluble copper(I) complex D SARAVANA BHARATHI 1, ASHOKA G SAMUELSON 2, N K LOKANATH 2, M A SHRIDHAR 2 and SASHIDARA PRASAD 2 1 Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India 2 Department of Physics, University of Mysore, Manasagangotri, Mysore 570 006, India Water-soluble phosphines and their complexes have attracted a great deal of interest because of their potential use in aqueous catalytic organometallic chemistry and biomedical applications. Tris(hydroxymethyl)phosphine (THP) is moderately air-stable and water-soluble. While the coordination chemistry of this ligand with Pt, Pd, Ni and Rh has been widely studied, complexes of group 11 transition elements are practically unknown. We report the synthesis and characterization of the first copper(I) complex of THP.

On treatment of [Cu(CH3CN)4]ClO4 with THP in a suitable solvent, a white precipitate of the complex [Cu(THP)3(P(CH2OH)2(CH2O))] 1 results which is very water-soluble. Interestingly, compound 1 has the counter anion in the starting material (perchlorate) replaced by an alkoxide arm of the ligand. The same result is obtained while using other copper(I) precursors such as [Cu(CH3CN)4]BF4. The loss of HX (X = ClO4/BF4) is presumably the result of very efficient crystallographic packing of the nearly spherical molecule in the lattice. The synthesis, structure, and reactivity of complex 1 is presented.

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Magnetism in intercalated compounds of layered manganese thiophosphate N V VENKATRAMAN and S VASUDEVAN Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Layered manganese thiophosphate MnPS3 undergoes an unusual ion-exchange intercalation reaction in which solvated cation G+ (solv) can be inserted into the galleries with loss of Mn2+ from the layers to give Mn1–xPS3 G2x+ (solv). Intercalation occurs with dilation of the lattice. The host MnPS3 is a two-dimensional antiferromagnet. The intercalated compounds, however, show weak ferromagnetism at low temperatures. When the guest cations are hydrated ions, the intercalates are unstable, losing water to give Mn1–xG2xPS3. In order to keep the guest cations within the galleries, we have exchanged the water of hydration in the intercalated compounds, Mn0⋅75PS3K0⋅5(H2O) and Mn0⋅75PS3Mn0⋅25(H2O), with a crown-ether (18-crown-6-ether). The stronger chelating action of the crown-ether prevents the guest cations from slipping into the layer. The magnetic properties of these compounds have been investigated in order to understand the origin of weak ferromagnetism in intercalated compounds of MnPS3.

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Tailoring the particulate properties of aluminates prepared by combustion method T MIMANI and K C PATIL Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Aluminium based spinels constitute an interesting class of oxide ceramics with technological applications such as abrasives, pigments, catalysts, phosphors etc. The nano-structured ceramics display improved properties over the bulk materials 1. Nanocrystalline aluminate spinels MAl2O4, M = Zn and Mn, have been prepared by the combustion of aqueous solutions containing the corresponding metal acetate, aluminium nitrate and various fuels like urea, carbohydrazide, oxalyl hydrazide, hexamethylene tetramine and glycine. Interestingly spinels prepared by using metal acetate precursors yield nanosize (10–100 nm) oxides having very large surface area (40–180 m2/g) compared to the nitrate precursor 2. The products have been characterised by powder XRD. The particulate properties have been investigated using TEM. The particle size is found to vary from 10 to 100 nm depending upon the fuel. References 1. Meyer F, Hemplemann R, Mathur S and Veith M 1999 J. Mater. Chem. 9 1755 2. Kingsley J J, Suresh K and Patil K C 1990 J. Mater. Sci. 25 1305

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Construction of a pulsed nozzle fourier transform microwave spectrometer to study the lithium bond A P TIWARI 1, B J MUKKADA 1, E ARUNAN 1 and P C MATHIAS 2 1 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India 2 Sophisticated Instruments Facility, Indian Institute of Science, Bangalore 560 012, India Hydrogen bond is ubiquitous in chemistry and biology. Several chemists have considered the existence of an analogous lithium bond 1,2, though experimental verification has been scarce 2. Pulsed nozzle fourier transform microwave (PNFTMW) spectrometer is ideal for forming and observing the lithium bond. It employs supersonic expansion to form weakly bound complexes such as hydrogen-bonded or van der Waals complexes. By introducing a hot nozzle, one could form complexes of lithium halides. In principle, one could study any complex formed by atoms, molecules, radicals and ions. From the microwave spectrum of the complex, moments of inertia and equilibrium geometry can be determined. This is the first step towards obtaining the ‘intermolecular’ potential, which is important in understanding intermolecular interactions. The construction of PNFTMW spectrometer is quite involved 3,4. References 1. 2. 3. 4.

Kollman P A, Liebman J F and Allen L C 1970 J. Am. Chem. Soc. 92 1142 Szczesniak M M, Ratajczak K, Agarwal U P and Rao C N R 1983 Chem. Phys. Lett. 44 465 Ault B S and Pimentel G C 1975 J. Phys. Chem. 79 621 Balle T J and Flygare W H 1981 Rev. Sci. Instrum. 52 33

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Resonance Raman spectroscopic investigation of MLCT character in Schiff base ferrocenyl complexes B ABRAHAM, B KARTHIKEYAN, SUSHANTA K PAL, A G SAMUELSON and S UMAPATHY Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Resonance Raman spectroscopy, because of its utility in understanding resonant state dynamics and structure, is an ideal tool to investigate MLCT states of inorganic complexes. In particular, the tunability of the excitation wavelength and thus the resulting resonance Raman intensities provide information on the nuclear displacements of vibrational modes that are Franck–Condon active in the resonant state. In this preliminary report, we present the recent results on the investigation of MLCT character of series of Schiff base complexes (see figure) with substituents of varying electron-withdrawing ability. The wavelength-dependent resonance Raman response has been observed and characterized with a view to understand the nature of MLCT states due to the presence of these substituents. This aspect is of considerable interest since the extent of charge transfer on MLCT excitation has direct correlation to its photochemical properties and nonlinear optical response.

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Studies on meso-substituted free-base octamethoxyporphyrins PRADEEPTA K PANDA and V KRISHNAN Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India Octamethoxyporphyrin, with eight electron-donating methoxy groups, is the most electron-rich porphyrin and shows interesting photophysical and electrochemical properties. Here, we report the synthesis of various meso-substituted free-base octamethoxyporphyrins (figure)

X = –H, –NO2, –CHO, –CH2OH

Structure of meso-substituted free-base octamethoxyporphyrins.

These are characterized by 1H NMR and other spectroscopic methods. The optical absorption spectra of these meso-substituted free-base porphyrin derivatives exhibit a hypsochromic shift compared to the unsubstituted octamethoxy free-base derivative. The emission data of these meso-substituted free-base derivatives reveal a marginal red shift of the transitions with reduced quantum yield compared to the unsubstituted free-base porphyrin. These data are discussed in terms of electronic structure calculations. Acknowledgement The authors are thankful to the Council of Scientific and Industrial Research, New Delhi for financial support.

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