J Chem Crystallogr (2013) 43:360–364 DOI 10.1007/s10870-013-0428-8

ORIGINAL PAPER

Structural Studies of the Hexakis(pyridazine)cobalt(II) and Hexakis(pyridazine)ruthenium(II) Ions as their Hexafluorophosphate and Tetraphenylborate Salts Yifan Shi • Atta M. Arif • Richard D. Ernst

Received: 5 May 2012 / Accepted: 28 May 2013 / Published online: 14 June 2013 Ó Springer Science+Business Media New York 2013

Abstract The new [Co(pydz)6]2? ion (pydz = pyridazine) has been prepared by a straightforward route in aqueous solution, and isolated as its hexafluorophosphate salt. The salt crystallizes in the monoclinic space group C2/c with a = ˚ , b = 10.6846(2) A ˚ , c = 16.3404(2) A ˚, b = 18.4796(3) A 3 ˚ 92.0518(11)8, V = 3224.30(9) A , Dcalc = 1.709 at 150(1) K. The dication has crystallographically imposed 2 symmetry. The analogous, previously reported ruthenium complex ion could be isolated as its tetraphenylborate salt following the reaction of [RuCl2(1,5-COD)]x(COD = cyclooctadiene) with pyridazine in the presence of hydrogen gas. This salt also crystallizes in the monoclinic space group C2/c, with a = ˚ , b = 19.8693(4) A ˚ , c = 38.4545(7) A ˚, b = 17.8441(3) A 3 ˚ 95.4231(6)8, V = 13573.0(4) A , Dcalc = 1.321 at 150(1) K. Keywords Crystal structure  Cobalt pyridazine  Ruthenium pyridazine

there is one case in which a tricyclic pyridazine does [2]. With regard to the bimetallic species, to date there have been no structural reports of any heterobimetallic complexes in which pyridazine bridges the two metal centers, which may be either due to a lack of attention devoted to preparing such species, or to the fact that the metal which is more acidic may sufficiently reduce the basicity of the uncharged pyridazine to the extent that coordination to the second metal becomes too weak. Herein we report synthetic routes to divalent cobalt and ruthenium complexes in which the metal ions are octahedrally coordinated by six pyridazine ligands. As a result, these species should have the potential for chelating to at least a second metal ion. Their solid state structures are presented, which appear to be the first for transition metal hexa(pyridazine) complexes.

Introduction

Experimental

Pyridazine (pydz, 1) has been found to be a very versatile ligand, due to its potential to either coordinate to a single metal as a monodentate ligand, or to coordinate to two metal centers [1]. While no structurally characterized examples have been reported in which pyridazine serves

All reactions and manipulations were carried out under an atmosphere of prepurified nitrogen in Schlenk apparatus or in a glovebox. Reagent grade solvents were deoxygenated by bubbling nitrogen through them for 2–3 min. [RuCl2(1,5-COD)]x (COD = cyclooctadiene) was prepared by a reported procedure [3].

as a bidentate ligand to a single metal center,

Y. Shi  A. M. Arif  R. D. Ernst (&) Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, UT 84112-0850, USA e-mail: [email protected]

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Hexakis(pyridazine)cobalt(II) hexafluorophosphate, [Co(pydz)6](PF6)2 (2) To 0.45 g (1.5 mmol) of Co(NO3)26H2O dissolved in 20 mL of deionized water were added 0.50 g (3.0 mmol) of NH4PF6 and 1.1 mL (15 mmol) of pyridazine under nitrogen. The solution was stirred for several hours, and then it was filtered through a coarse frit with a Celite pad to

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remove a white solid. The filtrate was concentrated to ca. 10 mL which led to a very viscous solution. An orange crystalline solid grew on the side of the flask during a 5 h period while the solvent was removed slowly using a nitrogen flow and mild heating in an oil bath. The product was washed with 8 mL of H2O, and two 8 mL aliquots of ethanol, and then was dried in vacuo to yield 1.1 g (86 %) of an orange-red solid. Crystals suitable for a diffraction study were obtained by running the reaction in a dilute solution and slowly evaporating the solvent. Anal. Calc. for C24H24F12N12P2Co (2): C, 34.72; H, 2.89; N, 20.26. Found: C, 34.53; H, 2.71; N, 20.27. Hexakis(pyridazine)ruthenium(II) tetraphenylborate, [Ru(pydz)6][B(C6H5)4]2 (3) To 0.40 g (1.4 mmol) of [Ru(1,5-COD)Cl2]x dissolved in 10 mL of methanol under nitrogen was added 0.90 mL (12 mmol) of pyridazine in a heavy-wall borosilicate glass tube. While the mixture was stirring, the glass tube was pressurized with hydrogen gas to three atmospheres and heated to 50 °C. After standing overnight, it had changed to a red solution, which was subsequently transferred to a Schlenk flask by syringe, after which the solvent was removed in vacuo and the remains were further dried under reduced pressure. The resulting oily mixture was redissolved in 15 mL of acetonitrile, and 0.52 g (1.5 mmol) of NaBPh4 was added to the flask. During 3 h of stirring, the bright yellow product precipitated out. All solvent was then removed in vacuo. The residue was collected on a frit, and washed with 10 mL of CH2Cl2 and then 10 mL of THF, although the THF did dissolve a bit of the product. After removal of the washings from the receiving flask, the yellow product remaining on the frit was dissolved in 30 mL of CH3NO2, and filtered through the frit. Removal of the solvent and subsequent drying of the compound were carried out in vacuo. Yield: 0.80 g, 47 %. Crystals suitable for an X-ray diffraction study were obtained by cooling a concentrated CH3NO2 solution to -30 °C overnight. This reaction also worked under nitrogen without the presence of any hydrogen, which led to a slightly lower yield. Anal. Calc. for C72H64B2N12Ru (3): C, 70.81; H, 5.24. Found: C, 70.08; H, 4.68. 1H NMR (300 MHz, CDCl3, ppm): 9.21 (d, 6H, J = 5.4 Hz, H1,5,9,13,17,21), 8.99 (d, 6H, J = 5.0 Hz, H4,8,12,16,20,24), 7.80 (dd, 6H, J = 8.3 Hz, 5.7 Hz, H2,6,10,14,18,22), 7.68 (dd, 6H, J = 7.3, 5.0 Hz, H3,7,11,15,19,23). X-Ray Crystallography A single crystal of complex 2 was mounted on a glass fiber and held in place with Paratone oil cooled by a 150(1) K nitrogen stream on a Nonius Kappa CCD

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diffractometer. The programs COLLECT, DENZO-SMN, and SCALEPAC [4] were used for data collection and processing. Axial photographs and systematic absences, in addition to the successful refinement of the structure, revealed the space group to be C2/c. The structure was solved by a combination of direct methods and Fourier methods using SIR 97 [5], and subjected to least-squares refinements with SHELXL97 [6] using published scattering factors [7]. The nonhydrogen atoms were refined anisotropically, while the hydrogen atoms were refined isotropically. The molecule was found to be located on a two fold rotational axis. Complex 3 was also found to crystallize in space group C2/c. Its structural study was entirely analogous to that of 2, except that in this case there is a rotational disorder of one of the pyridazine ligands, involving atoms N4, C5, C7, C8, and their attached hydrogen atoms, in addition to a disorder of one molecule of nitromethane involving atoms C75, N15, O5, O6, and the hydrogen atoms associated with C75. The latter disorder is such that C75 and O5 appear as composite images. The hydrogen atoms on the disordered C5, C7, C8, and C75 atoms were allowed to ride on their attached carbon atoms. There is a disorder involving N4 and N40 that correlates with the half-occupancy oxygen atoms O5 and O6. Were N4 and O6 to be present simul˚ . Thus, when taneously, they would be separated by 1.77 A ˚ , and N4 is present, so is O5, giving a contact of 3.98 A 0 ˚. when N4 is present, so is O6, giving a contact of 3.37 A One of the tetraphenylborate ligands resides on a general position, while the other two (with B2 and B3) each have crystallographically imposed two-fold rotational symmetry. Pertinent aspects of the data collection and refinement procedures are presented in Table 1, while selected bonding parameters are given in Tables 2 and 3. CCDC depositions 826983 (Ru) and 826984 (Co) contain the full crystallographic information for these structures. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: ?44-1223-336-033; or Mail: [email protected]).

Results and Discussion Synthesis The [Co(pydz)6]2? complex ion could readily be prepared in aqueous solution from the reaction of the cobaltous ion with an excess of pyridazine, and subsequently the complex could be isolated in good yield as its orange–red PF6salt. In order to prepare the ruthenium analogue, [RuCl2(1,5-COD)]x (COD = cyclooctadiene) was

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J Chem Crystallogr (2013) 43:360–364

Table 1 Crystal and experimental data

Table 2 Selected bond [Co(pydz)2? 6 ](PF6 )2

lengths

˚) (A

and

angles

(°)

for

Empirical Formula

C24H24 CoF12N12P2

C74.125H70.375 B2N14.125O4.25Ru

Formula weight

829.42

1349.76

Co–N1

2.1796 (11)

P–F1

1.6102 (9)

Temperature (K) ˚) Wavelength (A

150 (1)

150 (1)

Co–N2

2.1580 (11)

P–F2

1.5932 (10)

0.71073

0.71073

Co–N3

2.1694 (11)

P–F3

1.5887 (10)

Bond distances

Crystal system

Monoclinic

Monoclinic

N1–N2

1.3483 (16)

P–F4

1.5958 (10)

Space group

C2/c

C2/c

N3–N4

1.3407 (16)

P–F5

1.5914 (9)

N5–N6

1.3507 (15)

P–F6

1.6187 (9)

Unit cell dimensions a

18.4796 (3)

17.8441 (3)

Bond angles

b

10.6846 (2)

19.8693 (4)

Co–N1–N2

114.06 (8)

Co–N1–Cl

125.47 (9)

c

16.3404 (2)

38.4545 (7)

Co–N3-N4

115.92 (8)

Co–N3–C5

123.52 (9)

92.0518 (11) 3224.30 (9)

95.4231 (6) 13573.0 (4)

Co–N5–N6 N1–Co–N10

113.44 (8) 178.63 (6)

Co–N5–C9 N3–Co–N30

126.44 (9) 89.88 (6)

b (8) ˚ 3) Volume (A Z

4

8

N1–Co–N3

90.27 (4)

N3–Co–N5

179.79 (4)

Dcalcd (g cm-3)

1.709

1.321

N1–Co–N30

88.76 (4)

N3–Co–N50

90.16 (4)

l(MoKa) (mm-1)

0.741

0.293

N1–Co–N5

89.93 (4)

N5–Co–N50

89.81 (6)

F(000)

1668

5616

h range (8)

2.51–27.48

2.1–27.88

Limiting indices

-23 B h B 23

-23 B h B 23

-13 B k B 13

-25 B k B 20

-21 B ‘ B 21

-50 B ‘ B 50

Reflections collected/unique

6825/3677

27961/16134

Completeness (%)

99.5

99.5

Goodness of fit on F2

1.043

1.029

R indices [I [ 2r (I)]

R1 = 0.0260, wR2 = 0.0649

R indices (all data) (Dq)max,

min

R (int)

91.04 (4)

˚ ) and angles (°) for [Ru(pydz)2? Table 3 Selected bond lengths (A 6 ] ] [B(C6H5)4 2 Bond distances Ru–N1

2.086 (2)

N1–N2

1.354 (3)

Ru–N3

2.084 (2)

N3–N4

1.349 (3)

Ru–N5

2.072 (2)

N5–N6

1.352 (3)

R1 = 0.0526, wR2 = 0.0917

Ru–N7

2.086 (2)

N7–N8

1.350 (3)

R1 = 0.0305, wR2 = 0.0677

R1 = 0.1106, wR2 = 0.1098

Ru–N9

2.101 (2)

N9–N10

1.347 (3)

Ru–N11

2.086 (2)

N11–N12

1.346 (3)

0.284, -0.371

0.696, -1.037

B1–C25

1.645 (5)

B2–C49

1.641 (4)

0.0631

B1–C31

1.656 (4)

B2–C55

1.652 (4)

B1–C37

1.660 (4)

B3–C61

1.641 (4)

B1–C43 Bond angles

1.653 (4)

B3–C67

1.653 (4)

Ru–N1–N2

113.96 (16)

Ru–N1–C4

125.73 (19)

Ru–N3–N4

117.87 (17)

Ru–N3–C8

123.31 (20)

Ru–N5–N6

113.78 (16)

Ru–N5–C12

125.97 (18)

Ru–N7–N8

118.67 (16)

Ru–N7–C16

121.58 (18)

Ru–N9–N10

116.77 (16)

Ru–N9–C20

123.53 (18)

Ru–N11–N12

117.11 (16)

Ru–N11–C24

123.31 (18) 179.03 (8)

0.0149

hydrogenated at 50 °C so as to effect removal of the diene, in the presence of an excess of pydz. This procedure led to an unoptimized yield of 47 % for the complex, as its B(C6H5)4 salt. Structural Description The structural result and pertinent bonding parameters for 2 are presented in Fig. 1 and Table 1. Complex 2, containing a Co(II) ion with the expected octahedral coordination by its six pyridazine ligands, resides on a twofold rotational axis, which causes N1 to be positioned trans to its equivalent, while N3 and N5 are positioned cis to their equivalents. The Co–N distances range from 2.158(1) to 2.180(1) ˚ , which may be compared to values ranging from 2.099 to A ˚ in a bis(tripyridylamine) complex [8]. The N–N 2.152 A ˚, and P–F distances average 1.347(3) and 1.600(5) A n? respectively. No other M(pydz)6 complexes appear to

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N1–Co–N5

0

N1–Ru–N3

93.74 (9)

N3–Ru–N9

N1–Ru–N5

87.52 (8)

N3–Ru–N11

89.19 (8)

N1–Ru–N7

174.25 (9)

N5–Ru–N7

90.87 (8)

N1–Ru–N9

86.48 (9)

N5–Ru–N9

91.79 (8)

N1–Ru–N1

91.10 (8)

N5–Ru–N11

176.11 (9)

N3–Ru–N5

87.28 (8)

N7–Ru–N9

88.06 (9)

N3–Ru–N7

91.69 (9)

N7–Ru–N11

90.85 (8)

N9–Ru–N11

91.76 (8)

have been structurally characterized, although the related M(3,30 -bipyridazine)2? 3 complexes of iron and nickel have been [9].

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The pyridazine ligands adopt asymmetric orientations, analogous to those adopted in monodentate pyrazole and pyridazine complexes [10]. The asymmetry leads to a closer than

C2 C3 C1 C21

C4

C19 C20

C22

C18

N12 N2

N1 C23 N11

N9 C17

C24

Ru1

N4 C5

N10 N5

N6 C16

C12

N3

N7 C9

C11

C6 C8

C15 N8

C10

C7 C14 C13

otherwise expected approach of the N–N bonds to the metal center. The distortion can be appreciated through a comparison of the Co–N–N and Co–N–C angles, the former being smaller than the latter by ca. 10°. Conceivably this distortion may allow for the pyridazine coordination to switch from one nitrogen atom to the other. The structure of the analogous Ru(pydz)2? 6 complex may be seen in Fig. 2, while pertinent bonding parameters are listed in Table 3. In this case, there is no crystallographically C3

Fig. 2 Molecular structure of the dicationic 3. The 30 % probability ellipsoids are shown

imposed symmetry. The Ru–N distances range from ˚ , and are thus significantly shorter 2.072(2) to 2.101(2) A than those of 2, due to 3’s low spin configuration. Similar trends have been observed previously for Fe(II) and Ru(II) amine complexes [10]. As in the cobalt complex, the Ru–N– N angles are smaller than the Ru–N–C angles, though by a slightly lesser degree, ca. 7°–8°. The N–N bond lengths ˚ , similar to those in 2, while the B–C average 1.350(2) A ˚. bonds range in distance from 1.641(4) to 1.660(4) A

C2

C4

Conclusions C1 N2 N1 C10

C9 N5

N4

C11 C12

Co1 C8

N6

N3 C7 C5 C6

Previously [RuCl2(1,5-COD)]x has been shown to serve as a useful precursor for the preparations of [RuCl2(1,5COD)(tmeda)], [RuCl2(tmeda)2], [RuCl2(tmeda)(Hpyz)2], and Ru(naph)2? complexes (tmeda = N,N,N’,N’-tetra4 methylethylenediamine; Hpyz = pyrazole; naph = 1,8naphthyridine) [1, 10, 11]. Herein it also has been shown to be an effective precursor to the Ru(pydz)2? ion. The 6 related cobalt complex may readily be prepared from Co(II) salts in aqueous media as a result of the greater substitution lability of this ion. Acknowledgments The authors gratefully acknowledge partial support from the University of Utah and the US Department of Energy, Office of Fossil Fuel Energy, under contract number DE-FC26-05NT42456.

References Fig. 1 Molecular structure of the dicationic 2. The 30 % probability ellipsoids are shown

1. Harvey BG, Arif AM, Ernst RD (2004) Polyhedron 23: 2725–2731

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364 2. Klein H-F, Helwig M, Karnop M, Konig H, Hammerschmitt B, Cordier G, Florke U, Haupt H-J (1993) Z Naturforsch, B 48:785–793 3. Albers MO, Ashforth TV, Oosthuizen HE, Singleton E (1999) Inorg Synth 26:68–69 4. Otwinowski Z, Minor W (1997) Methods Enzymol 276:307–326 5. Altomare A, Burla MC, Camalli M, Cascarano GL, Giacovazzo C, Guagliardi A, Moliterni AGG, Polidori G, Spagna R (1999) J Appl Crystallogr 32:115–119 6. Sheldrick GM (1997) SHELXL97, programs for crystal structure analysis. University of Go¨ttingen, Germany

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J Chem Crystallogr (2013) 43:360–364 7. International Tables for Crystallography (1992), Vol. C. Kluwer Academic Publisher, Dordrecht, pp 206-222 and 476-516 8. Kucharski ES, McWhinnie WR, White AH (1978) Aust J Chem 31:2647–2650 9. Onggo D, Rae AD, Goodwin HA (1990) Inorg Chim Acta 178:151–163 10. Shi Y, Arif AM, Ernst RD (2010) J Chem Crystallogr 40: 235–240 11. Harvey BG, Shi Y, Peterson BK, Arif AM, Ernst RD (2006) Inorg Chim Acta 359:839–845