J Inorg Organomet Polym (2010) 20:313–319 DOI 10.1007/s10904-010-9346-9

Synthesis and Structures of Two Ba(II) Metal–Organic Frameworks Based on Pyridine-2,6-Dicarboxylic Acid N-Oxide Li-Li Wen • Fang-Ming Wang • Xiao-Ke Leng Miao-Miao Wang • Qing-Jin Meng • Hui-Zhen Zhu

•

Received: 5 January 2010 / Accepted: 10 March 2010 / Published online: 20 March 2010 Ó Springer Science+Business Media, LLC 2010

Abstract Hydrothermal and solution reactions of pyridine-2,6-dicarboxylic acid N-oxide (2,6-PDCO) and BaCl2
2H2O yield two metal–organic frameworks; namely [Ba(2,6-PDCO)]n (1) and [Ba(2,6-PDCO)
H2O]n (2), respectively. Single-crystal X-ray analyses reveal that compound 1 is a dense framework whereas compound 2 is a porous one, though both compounds have an infinite twodimensional (2D) layer structure. Compounds 1 and 2 are the first examples of pyridine dicarboxylic acid N-oxide introduced into the alkaline earth metal–organic framework. Keywords Barium(II)-metal–organic frameworks
Crystal structure

1 Introduction Metal–organic frameworks (MOFs) are a relatively new class of crystalline coordination polymers, which have potential in a myriad of applications, including gas storage, chemical separation, heterogeneous catalysis and optical, electronic, magnetic materials [1–7]. In order to design and synthesize new MOFs with specific structures and

L.-L. Wen
F.-M. Wang
Q.-J. Meng (&)
H.-Z. Zhu Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, 210093 Nanjing, People’s Republic of China e-mail: [email protected] L.-L. Wen (&)
X.-K. Leng
M.-M. Wang Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, 430079 Wuhan, People’s Republic of China e-mail: [email protected]

properties, much work is being focused on choosing the favored geometry and function of metal ions and organic ligands [8–14]. As an important member of aromatic polycarboxylate acid, pyridine dicarboxylic acid N-oxide, which can offer possibilities to form MOFs through both the carboxylate and N-oxide bridge, has been systematically studied in our previous work [15–17]. A series of extended coordination networks from pyridine-2,6-dicarboxylic acid N-oxide (2,6-PDCO) and d-block metal centers have been constructed and display distinct architectures varying from 1D helix, 2D brick-wall and herringbone to 3D interpenetration in the presence of different N-containing auxiliary ligands. Owing to their higher coordination number and more flexible coordination geometry, alkaline earth metals should produce novel structures with charming topologies different from transition metals. In addition, the alkaline earth metals, which are distributed in most cells and tissues, often in considerable concentrations, play an important role in the biochemistry of virtually all living organisms. A constant supply is indispensable for unrestricted performance of biological functions [18]; e.g., barium metal is known as an antagonist for potassium [19–21]. In the process of binding to various sites, the ions compete with other common metal ions, some of which are antagonists through a different specificity. This specificity is predominantly governed by the charge and size of the cation as well as the ion’s resulting effective coordination number and geometry. Thus, an improved understanding of the function of biological cations is expected from a detailed study of the coordinating properties of the metals that compete with various ligating groups. Research on MOFs has generally centered on the assembly of organic linkers with d-block metal ions. The

123

314

chemistry of alkaline earth metals has been a largely undeveloped area of coordination chemistry [22–26]. As a continuation of our research on the coordination chemistry of 2,6-PDCO and heavy alkaline earth metals (i.e., barium), we have targeted a new class of high-dimensional MOFs prepared from 2,6-PDCO and barium under different synthetic conditions. Two new MOFs [Ba(2,6-PDCO)]n (1) and [Ba(2,6-PDCO)
H2O]n (2) were obtained.

J Inorg Organomet Polym (2010) 20:313–319

amount of white precipitation formed. After filtration, the solution was left to evaporate at room temperature. One month later, colorless block crystals of 2 suitable for X-ray diffraction were obtained (yield: 26% based on Ba). Anal. Calcd. for C7H5BaNO6 (%): C, 24.99; H, 1.50; N, 4.16%; found: C, 24.95; H, 1.54; N, 4.13. IR (KBr, cm-1): 3419m, 3109w, 1651s, 1610s, 1575s, 1505w, 1455w, 1409s, 1371s, 1240m, 1229m, 1215m, 1194w, 1154w, 917m, 857m, 821m, 805m, 788m, 766m, 702s, 659w, 594m, 545m, 516s, 459w, 429w.

2 Experimental 2.1 Materials and Measurements

2.3 X-ray Crystallography

The reagents and solvents employed were commercially available and used as received without further purification. 2,6-PDCO was synthesized as reported previously [27]. The C, H, and N microanalyses were carried out with a Perkin-Elmer 240 elemental analyzer. The IR spectra were recorded on KBr discs with a Bruker Vector 22 spectrophotometer in the 4,000–400 cm-1 region. Luminescence spectra for the solid samples were recorded with a Hitachi 850 fluorescence spectrophotometer. Thermogravimetric (TGA) analyses were performed on a simultaneous SDT 2960 thermal analyzer under flowing N2 at a heating rate of 10 °C min-1 between ambient temperature and 800 °C. Powder X-ray diffraction patterns were recorded on a RigakuD/max-RA rotating anode X-ray diffractometer ˚ ) radiawith graphitemonochromatic Cu Ka (k = 1.542 A tion at room temperature.

Suitable single crystals of 1 and 2 were selected and mounted in air onto thin glass fibers. X-ray intensity data were measured at 293 K on a Bruker SMART APEX CCD-based diffractometer with graphite-monochromatic ˚ ). Data reductions and MoKa radiation (k = 0.71073 A absorption corrections were performed with the SAINT and SADABS software packages, respectively [28]. All structures were solved by a combination of direct methods and difference Fourier syntheses and refined against F2 by the full-matrix least-squares technique [29, 30]. Crystallographic data and other pertinent information for 1 and 2 are summarized in Table 1. Selected bond lengths and bond angles with their estimated standard deviations are listed in Table 2.

Table 1 Crystal data and structure refinement for 1–2

2.2 Syntheses of Complexes 2.2.1 [Ba(2,6-PDCO)]n (1) A mixture of BaCl2
2H2O (50.4 mg, 0.2 mmol), 2,6-PDCO (37.1 mg, 0.2 mmol), NaOH (15.6 mg, 0.4 mmol) and H2O (3 mL) was placed in a Parr Teflon-lined stainless steel vessel (25 cm3). The vessel was sealed and heated at 120 °C for 3-d. After the mixture was slowly cooled to room temperature, colorless block crystals of 1 were obtained (yield: 32% based on Ba). Anal. calcd for C7H3BaNO5 (%): C 26.40, H 0.95, N 4.40; found: C 26.46, H 1.09, N 4.42. IR (KBr, cm-1): 3419m, 3061w, 1604s, 1407s, 1373s, 1242m, 1227s, 1191w, 913m, 859s, 828m, 814w, 793m, 785m, 771w, 758w, 707s, 644w, 591m, 555m, 571m, 451m, 422w. 2.2.2 [Ba(2,6-PDCO)
H2O]n (2) A mixture of BaCl2
2H2O (50.8 mg, 0.2 mmol), 2,6PDCO (37.6 mg, 0.2 mmol), NaOH (15.7 mg, 0.4 mmol) and H2O (10 mL) was placed in a breaker; a small

123

1

2

Formula

C7H3BaNO5

C7H5BaNO6

Formula weight

318.43

336.46

Crystal system

Orthorhombic

Triclinic

Space group ˚ a/A

Pbca

P-1

7.8328(11)

4.449(3)

˚ b/A ˚ c/A

9.5185(14)

9.583(6)

21.456(3)

12.124(8)

a/°

90

97.645(10)

b/°

90

98.778(11)

c/° ˚3 V/A

90

98.436(11)

1599.7(4)

498.9(6)

Z

8

2

qcalcd/g cm-3

2.644

2.240

l/mm-1 Collected reflections

4.958 7831

3.989 4616

Unique reflections

1572

1965

R(int)

0.0328

0.0314

Final R indices [I [ 2r(I)]

0.0914

0.0617

Goodness-of-fit on F2

1.12

1.03

J Inorg Organomet Polym (2010) 20:313–319

315

˚ ) and bond angles (°) for 1–2 Table 2 Selected bond lengths (A 1a Ba1–O1

2.997(3)

Ba1–O5

2.660(3)

Ba1–O1#4

2.886(3)

Ba1–O3#2

2.715(3)

Ba1–O5#2

2.732(3)

Ba1–O2#5

2.800(3)

Ba1–O4#3

2.694(3)

Ba1–O1#1

3.012(3)

Ba1–O2#1

2.950(3)

O1–Ba1–O5

62.94(9)

O1–Ba1–O1#4

133.40(9)

O1–Ba1–O3#2

O1–Ba1–O5#2

68.01(9)

O1–Ba1–O2#5

91.97(8)

O1–Ba1–O4#3

155.36(9)

O1–Ba1–O1#1

105.56(8)

O1–Ba1–O2#1

61.71(8)

O1#4–Ba1–O5

70.62(9)

O3#2–Ba1–O5

124.10(10)

O5–Ba1–O5#2

124.80(9)

O2#5–Ba1–O5

65.94(9)

O4#3–Ba1–O5

141.66(9)

O1#1–Ba1–O5

93.04(9)

O2#1–Ba1–O5

72.40(9)

O1#4–Ba1–O3#2

125.24(9)

O1#4–Ba1–O5#2

152.39(8)

O1#4–Ba1–O2#5

64.87(8)

O1#4–Ba1–O4#3

71.24(9)

O1#4–Ba1–O1#1

79.74(8)

O1#4–Ba1–O2#1

108.17(8)

O3#2–Ba1–O5#2

68.36(9)

O2#5–Ba1–O3#2

74.88(9)

O3#2–Ba1–O4#3

O1#1–Ba1–O3#2

139.16(9)

O2#1–Ba1–O3#2

126.56(8)

O2#5–Ba1–O5#2

O4#3–Ba1–O5#2

89.09(9)

O1#1–Ba1–O5#2

76.84(9)

O2#1–Ba1–O5#2

62.99(8)

O2#5–Ba1–O4#3 O1#1–Ba1–O4#3

100.81(9) 76.45(9)

O1#1–Ba1–O2#5 O2#1–Ba1–O4#3

142.94(8) 116.78(9)

O2#5–Ba1–O2#1 O1#1–Ba1–O2#1

137.68(8) 43.88(8)

80.96(10)

82.16(10) 140.17(8)

2b Ba1–O1

3.009(4)

Ba1–O2

3.011(4)

Ba1–O2#1

2.850(4)

Ba1–O4#2

2.955(4)

Ba1–O3#3

2.839(4)

Ba1–O1#4

2.816(4)

Ba1–O5#4

2.709(4)

Ba1–O4#5

2.828(4)

Ba1–O5#5

O1–Ba1–O2

43.52(9)

O1–Ba1–O2#1

69.15(10)

O1–Ba1–O4#2

158.02(10)

O1–Ba1–O3#3

101.32(10)

O1–Ba1–O1#4

60.51(9)

O1–Ba1–O5#4

108.97(10)

O1–Ba1–O4#5

141.04(10)

O1–Ba1–O5#5

83.93(10)

O2–Ba1–O2#1

98.73(10)

O2–Ba1–O4#2

125.75(10)

O2–Ba1–O3#3

58.24(10)

O1#4–Ba1–O2

91.80(10)

O2–Ba1–O5#4

151.70(11)

O2–Ba1–O4#5

126.31(10)

O2–Ba1–O5#5

67.15(10)

2.725(4)

O2#1–Ba1–O4#2

98.81(10)

O2#1–Ba1–O3#3

123.41(10)

O1#4–Ba1–O2#1

88.09(10)

O2#1–Ba1–O5#4

69.74(10)

O2#1–Ba1–O4#5

134.78(10)

O2#1–Ba1–O5#5

150.42(11)

O3#3–Ba1–O4#2

69.26(10)

O1#4–Ba1–O4#2

139.63(10)

O4#2–Ba1–O5#4

82.25(11)

O4#2–Ba1–O4#5

60.32(10)

O4#2–Ba1–O5#5

110.57(11)

O1#4–Ba1–O3#3

137.23(10)

O3#3–Ba1–O5#4

149.71(11)

O3#3–Ba1–O4#5

88.40(11)

O3#3–Ba1–O5#5

72.60(10)

O1#4–Ba1–O5#4 O4#5–Ba1–O5#4

62.87(10) 68.02(11)

O1#4–Ba1–O4#5 O5#4–Ba1–O5#5

86.76(10) 109.92(10)

O1#4–Ba1–O5#5 O4#5–Ba1–O5#5

67.43(10) 62.94(11)

a

Symmetry codes for 1: (#1) 1/2 - x, 1/2 ? y, z; (#2) 1/2 ? x, 3/2 - y, 1 - z; (#3) -x, 2 - y, 1 - z; (#4) -1/2 ? x, 3/2 - y, 1 - z; (#5) -x, 1 - y, 1 - z. b Symmetry codes for 2: (#1) -1 ? x, y, z; (#2) -1 ? x, 1 ? y, z; (#3) x, 1 ? y, z; (#4) -x, 2 - y, -z; (#5) 1 - x, 2 - y, -z

3 Results and Discussion 3.1 Crystal Structures of 1 and 2 In 1, the asymmetry unit contains one barium center and one 2,6-PDCO2- anion. Ba1 is coordinated by nine atoms to show a distorted single capped square-antiprism geometry: two oxygen atoms (O1#1, O2#1) of one chelating carboxylate group from one anion, two N-oxide moieties (O5, O5#2) and two monodentate carboxylate oxygen atoms (O1, O3#2) from two nonequivalent anions, three carboxylate oxygen atoms (O4#3, O1#4, O2#5), respectively, from three different anions (Fig. 1a). In 2, the asymmetry unit includes one barium center, one 2,6-PDCO2- anion and one lattice water. Figure 1b

depicts a molecular structure showing the arrangement about the Ba center, in which Ba1 is also coordinated to nine-oxygen atoms to form a similar environment to that of 1. In 1, the average Ba–O bond length for the carboxylate ˚ , and is obviously longer than groups amounts to 2.865 A ˚ ). This obserthose involving N-oxide moieties (2.696 A vation is similar to those reported in the literature [31–33]. The two carboxylate groups are out of the plane of the corresponding linking pyridine rings with the dihedral angles between them ca. 61° and 93°, respectively. These angles are distinct from those observed for free H2PDCO in which the carboxylate groups are found to be essentially coplanar with the pyridine rings [34]. In addition, the two carboxylate groups are twisted by 66°.

123

316

J Inorg Organomet Polym (2010) 20:313–319

Fig. 1 Coordination environments of Ba atoms (hydrogen atoms omitted for clarity) for compounds 1 and 2

In 2, the average Ba–O(carboxylate) distance is ˚ , while the average Ba–O (N-oxide) length is 2.901 A ˚ ; these are slightly longer compared to those in 1. 2.717 A The dihedral angles between the COO- groups and pyridine rings range from ca. 65° to 119° while the distortion angle between the two carboxylate moieties is 75°. For both compounds, the fully deprotonated 2,6PDCO2- anions act as effective hexadentate bridging ligands linking the Ba metal centers, but in different modes. In 1, two carboxylate groups adopt a l2–g1:g1 (i.e., each oxygen atom coordinates to one metal atom and the carboxylic group coordinates to two metal atoms) mode and one adopts a l4–g2:g2 (i.e., each oxygen atom coordinates to two metal atoms, and the carboxylic group

123

coordinates to four metal atoms) mode. Additionally, the N-oxide moiety acts as l2-bridge connecting two metal centers. This is which is similar to that of pyridine monocarboxylate N-oxide compound, [Gd(NNO)(H2O)2 (SO4)]n [35]. In 2, two carboxylate groups adopt a l3–g1:g2 mode and one adopts a l3–g2:g2 mode. The N-oxide also adopts a l2-bridge. Compared to the previously reported MOFs containing 2,6-PDCO, the anions in these two compounds display quite different coordination (Fig. 2). For 1, the 2, 6-PDCO ligand links the Ba ions to form a 2D dense layer structure in the ab plane (Fig. 3a). This 2D layer is undulating rather than planar. The hydrogen-bonded interaction between the carbon atom (C4) and the carboxylate oxygen atom (O4#6) has a distance of 3.307(5)

J Inorg Organomet Polym (2010) 20:313–319

317

Fig. 3 The 2D dense layer structure of compound 1 (a) and the 2D porous layer structure of compound 2 (b) Fig. 2 Coordination modes of 2,6-PDCO in compounds 1 and 2

˚ (Symmetry code: #6 -x, -1/2 ? y, 3/2 - z) and serves A to increase the order of the adjacent layers from a two- to a three-dimensional network, which increases the structural stability. For better insight into the nature of this framework, the simplified framework is given in Fig. 4a, where the carbon and nitrogen atoms are omitted. Clearly, the O ˚ is dinuclear Ba O Ba unit with Ba


Ba distance of 4.4 A O

bridged by O1, O2 and O5 atoms, which are connected to each other and result in the final 2D layer (Fig. 5). By contrast, in 2, the Ba ions are bridged by the 2,6-PDCO ligand to generate a 2D porous layer structure in the ab plane (Fig. 3b). This structure retains an effective ˚ 3 per unit cell, which is 19.5% of the void volume of 97.5 A crystal volume [36]. Free water molecules are located at the cavities and are hydrogen-bonded to the coordinated carboxylate oxygen atoms of the host network [O


O ˚ ]. Similar to 1, the simplified structure 2.962(5)–2.970(5) A of 2 is presented in Fig. 4b. There exist three types of O ˚ dinuclear Ba Ba units with Ba


Ba distances of 5.033 A O

˚ (bridged by two symmetry-related O1 atoms), 4.449 A ˚ (bridged by O2 and O5 atoms) and 4.999 A (bridged

Fig. 4 Simplified frameworks for 1 (a) and 2 (b)

123

J Inorg Organomet Polym (2010) 20:313–319

Intensity (a. u.)

318

(a) (b)

10

20

30

40

50

2 theta (deg.) Fig. 6 X-ray power diffraction diagram of compound 1: simulated spectra (a); single crystal data (b)

by two symmetry-related O4 atoms), respectively. The dinuclear units are connected by Ba atoms to form the final framework. Apparently, the formation of MOFs depends on the combination of several factors, such as the coordination geometry of metal ions, the nature of ligands, the ratio between metal salt and ligand, and reaction conditions such as solvent and templates [37–40]. In general, only small pores or even no pores were produced for those species synthesized under hydrothermal conditions (high temperature, high pressure and water as the solvent). In contrast, mild reaction conditions at low temperature/pressure are favorable for more porous MOFs. Actually, in our study, by using the same metal and organic ligand source, densely packed 1 was prepared under solvothermal conditions while porous 2 was prepared under a conventional solution reaction at room temperature. In both compound, the larger alkaline earth metal cation, Ba2?, prefers a higher coordination number (nine), which is attributed to the larger of metal radii. 3.2 Thermal Stability and Powder XRD Compound 1 is stable up to 400 °C at which point the framework structure begins to collapse. For compound 2, the first weight-loss is 5.42% (calcd: 5.35%) 20–76 °C and corresponds to the loss of one free water molecules per formula unit. A plateau is observed from 80 to 370 °C indicating no further weight loss. Above 370 °C the framework starts to decompose rapidly. Guest water molecules are removed by heating 2 at 150 °C for 2 h under N2. Powder X-ray diffraction of 2 before and after water expulsion shows only minor changes in pattern, which indicates that 2 is intact after removal of the guest. It is worth noting that after the evacuated solids

123

Intensity (a. u.)

Fig. 5 TG curve of compounds 1 and 2

(d) (c) (b) (a)

10

20

30

40

50

2 theta (deg.) Fig. 7 X-ray power diffraction diagram of compound 2: simulated spectra (a); evacuated compound 2 (b); compound 2 (c); rehydrated and evacuated compound 2 (d)

of 2 are immersed in H2O at room temperature overnight, the PXRD pattern is the same as the original; i.e., 2 rehydrates. To substantiate the phase purity of 1 and 2, powder XRD experiments were performed. The powder XRD patterns are in good agreement with the simulated pattern except for the relative intensity variation, which are a result of the preferred orientations of the crystals (Figs. 6, 7).

4 Conclusion In summary, two metal–organic frameworks, 1 and 2, were constructed from H2PDCO ligand and a heavy alkaline earth metal (barium) under different synthetic conditions. They are the first examples of pyridine dicarboxylic acid N-oxide being introduced into the alkaline earth metal coordination polymeric framework. The present study not only demonstrates that the nature of ligands and geometric

J Inorg Organomet Polym (2010) 20:313–319

needs of metal atoms play an important role in the crystal packing of MOFs, but also that the synthetic conditions affect the formation of the supramolecular architecture.

5 Supplementary Material Crystallographic data (CIF file) have been deposited at the Cambridge Crystallographic Data Center, CCDC Nos. 746752 for 1 and 746753 for 2. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax: ?/441223-336033; email: [email protected] or http://www. ccdc.cam.ac.uk). Acknowledgments This work was financially supported by the National Nature Science Foundation of China (Grant 20771056 and 20801021), China Postdoctoral Science Foundation (20070420985), and Jiangsu Planned Projects for Postdoctoral Research Funds (0702021C).

References 1. B. Moulton, M.J. Zaworotko, Chem. Rev. 101, 1629 (2001) 2. K. Uemura, S. Kitagawa, K. Fukui, K. Saito, J. Am. Chem. Soc. 126, 3817 (2004) 3. G. Fe´rey, C. Mellot-Draznieks, C. Serre, F. Millange, Acc. Chem. Res. 38, 217 (2005) 4. N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300, 1127 (2003) 5. J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y. Jeon, K. Kim, Nature 404, 982 (2000) 6. S.L. James, Chem. Soc. Rev. 32, 276 (2003) 7. M. Higuchi, D. Tanaka, S. Horike, H. Sakamoto, K. Nakamura, Y. Takashima, Y. Hijikata, N. Yanai, J. Kim, K. Kato, Y. Kubota, M. Takata, S. Kitagawa, J. Am. Chem. Soc. 131, 10336 (2009) 8. S.K. Henninger, H.A. Habib, C. Janiak, J. Am. Chem. Soc. 131, 2776 (2009) 9. H.A. Habib, A. Hoffmann, H.A. Hoppe, C. Janiak, Dalton Trans. 1742 (2009) 10. H.A. Habib, J. Sanchiz, C. Janiak, Dalton Trans. 4877 (2008) 11. A.N. Khlobystov, A.J. Blake, N.R. Champness, D.A. Lemenovskii, A.G. Majouga, N.V. Zyk, M. Schro¨er, Coord. Chem. Rev. 222, 155 (2001) 12. M. Eddaoudi, D.B. Moler, B. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Rev. 34, 319 (2001)

319 13. L. Pan, B. Parker, X. Huang, D.H. Olson, J.Y. Lee, J. Li, J. Am. Chem. Soc. 128, 4180 (2006) 14. D. Fiedler, D.H. Leung, R.G. Bergman, K.N. Raymond, Acc. Chem. Soc. 38, 349 (2005) 15. L.L. Wen, D.B. Dang, C.Y. Duan, Y.Z. Li, Q.J. Meng, Inorg. Chem. 44, 7161 (2005) 16. L.L. Wen, Z.F. Tian, D.B. Dang, Z.P. Ni, Q.J. Meng, Z. Anorg. Allg. Chem. 632, 689 (2006) 17. L.L. Wen, Z.D. Lu, X.M. Ren, C.Y. Duan, Q.J. Meng, S. Gao, Cryst. Growth Des. 9, 227 (2009) 18. H.C. Freeman, in Inorganic Biochemistry, vol. 1, ed. by J. Eichhorn (Marcel Dekker, New York, 1979), p. 129 19. H. Schmidbau, I. Bach, D.L. Wilkinson, G. Mu¨ller, Chem. Ber. 123, 1599 (1990) 20. D.J. Jenden, J.F. Reger, J. Physiol. (Lond.) 169, 889 (1963) 21. R.B. Martin, in Metal Ions in Biological Systems, vol. 20, ed. by H. Sigel (Marcel Dekker, New York, 1986), p. 43 22. E.H.L. Falcao, Naraso, R.K. Feller, G. Wu, F. Wudl, A.K. Cheetham, Inorg. Chem. 47, 8336 (2008) 23. K.M. Fromm, Coord. Chem. Rev. 252, 856 (2008) 24. A.Y. O’Brien, J. Hitzbleck, A. Torvisco, G.B. Deacon, K. Ruhlandt-Senge, Eur. J. Inorg. Chem. 172 (2008) 25. K.M. Fromm, Dalton Trans. 43, 5103 (2006) 26. R.G. Harrison, O.D. Fox, M.O. Meng, N.K. Dalley, L.J. Barbour, Inorg. Chem. 41, 838 (2002) 27. D.L. Heywood, J.T. Dunn, J. Org. Chem. 24, 1569 (1959) 28. Bruker AXS, SAINT Software Reference Manual (Madison, 1998) 29. Software Packages SMART and SAINT (Siemens Analytical X-ray Instrument Inc., Madison, 1996) 30. SHELXTL, Version 5.1 (Bruker AXS, Inc., Madison, 1997) 31. X.Y. Duan, J.G. Lin, Y.Z. Li, C.J. Zhu, Q.J. Meng, CrystEngComm 10, 207 (2008) 32. Y. Yang, G.Q. Jiang, Y.Z. Li, J.F. Bai, Y. Pan, X.Z. You, Inorg. Chim. Acta 359, 3257 (2006) 33. H.F. Zhu, Z.H. Zhang, W.Y. Sun, T. Okamura, N. Ueyama, Cryst. Growth Des. 5, 177 (2005) 34. L.C. Nathan, C.A. Doyle, A.M. Mooring, D.C. Zapien, S.K. Larsen, C.G. Pierpont, Inorg. Chem. 24, 2763 (1985) 35. Z. He, Z.M. Wang, C.H. Yan, CrystEngComm 7, 143 (2005) 36. A.L. Spek, PLATON, Version 1.62 (University of Utrecht, Utrecht, The Netherlands, 1999) 37. R. Kitaura, K. Fujimoto, S. Noro, M. Kondo, S. Kitagawa, Angew. Chem., Int. Ed. 41, 133 (2002) 38. R. Kitaura, K. Seki, G. Akiyama, S. Kitagawa, Angew. Chem., Int. Ed. 42, 428 (2003) 39. L. Carlucci, G. Ciani, D.W. Gudenberg, D.M. Proserpio, A. Sironi, Chem. Commun. 631 (1997) 40. S.K. Ghosh, P.K. Bharadwaj, Inorg. Chem. 43, 2293 (2004)

123