trans-Di­aqua­bis(5-carboxy-1H-imidazole-4-carboxyl­ato-κ²N³,O⁴)­cobalt(II) 4,4′-bi­pyridine solvate

In the title compound, [Co(C₅H₃N₂O₄)₂(H₂O)₂]·C₁₀H₈N₂, the Co atom is trans-coordinated by two pairs of N and O atoms from two monoanionic 4,5-di­carboxy­imidazole ligands, and by two O atoms from two coordinated water mol­ecules, in a distorted octahedral geometry. The 4,4′-bi­pyridine solvent molecule is not involved in coordination but is linked by an N—H...N hydrogen bond to the neutral [Co(C₅H₃N₂O₄)₂(H₂O)₂] mol­ecule. Both mol­ecules are located on inversion centers. The crystal packing is stabilized by N—H...N and O—H...O hydrogen bonds, which produce a three-dimensional hydrogen-bonded network. Offset π–π stacking interactions between the pyridine rings of adjacent 4,4′-bi­pyridine molecules were observed, with a face-to-face distance of 3.345 (1) Å.

S1. Comment

The chemistry of α-N carboxyheterocycle ligands, such as 2-carboxypyindine, 2-carboxypyrazine, 4,5-dicarboxyimidazole and 2,3-dicarboxypyrazine, is attracting increasing attention because of their diversely efficient N and O donors in different coordination environments (Chatterjee et al., 1998; Elliot et al., 1987; Dougherty et al., 1984). Numerous metal complexes containing α-N carboxyheterocycle ligands have been reported in recent years (Lannon et al., 1984; Chatterjee et al., 1997), but the metal complexes of the 4,5-dicarboxyimidazole ligand (H₃dcbi) are relatively rare. In this field, five manganese complexes of the H₃dcbi ligand have been reported for the simulation of relevant manganese enzymes (Caudle et al., 1997; Rajendiran et al., 2003; Ma et al., 2003; Huang et al., 2001; Zhang et al., 2004). In addition, five other metal H₃dcbi complexes have been reported to date (Net et al., 1989; Sengupta et al., 2001; Bayon et al., 1987; Smith et al., 2000; Wang et al., 2004). Among these, there is only one example of a cobalt complex containing H₃dcbi ligands (Wang et al., 2004). We report here the crystal structure of a novel example of a cobalt complex with 4,5-dicarboxyimidazole ligands, which act as N,O-bidentate donors.

The structure of the title compound, (I), consists of two independent fragments (Fig. 1), namely the neutral mononuclear [Co(C₅H₃N₂O₄)₂(H₂O)₂] molecule and the 4,4'-bipyridine molecule, both located at two inversion centers. The asymmetric unit of (I) contains half of the complex molecule. In the [Co(C₅H₃N₂O₄)₂(H₂O)₂] fragment, the other equivalent half is related by a center of symmetry at the Co atom. The Co atom is six-coordinated by two pairs of N and O atoms from two symmetry-related H₂dcbi⁻ ligands and two O atoms from two symmetry-related coordinated water molecules. The CoN₂O₄ group adopts a distorted octahedral configuration. The Co1/N1/C1/C4/O1 basal plane exhibits a mean deviation of 0.0027 Å.

The two H₂dcbi⁻ ligands are situated trans to one another. Each H₂dcbi⁻ ligand behaves as an N,O-bidentate ligand and the second carboxy group of the ligand is protonated [C5—O3 = 1.325 (3) Å and C5—O4 = 1.214 (3) Å]; ?the structure of (I) thus differs from those of the ? related compounds Na₂[Co₄(dcbi)₄(bipy)₄] (Wang et al., 2004) and [Mn(salen)₂(H₂dcbi)₂(H₂O)] (Huang et al., 2000). The H₂dcbi⁻ ligands are planar (the mean deviation is 0.0069 Å), the maximum deviation, of 0.0214 Å for O2, being the result of hydrogen bonds involving atoms O2 and O3. The two coordinated water molecules occupy the apical sites. The linear O5/Co/O5ⁱ group is nearly perpendicular to the N1/O1/N1ⁱ/O1ⁱ basal plane, as indicated by the basal angles subtended at atom Co1 [Table 1; symmetry code: (i) −x + 2, −y, −z + 1]. The Co1—N1 and Co1—O1 distances [2.108 (2) and 2.116 (1) Å, respectively] are comparable to those reported in related Co complexes (Cheng et al., 2002; Kumagai et al., 2002). The Co1—O5 distance [2.108 (2) Å] is identical to the Co1—N1 distance. The similar cobalt–ligand bond lengths and highly octahedral ligand arrangement are indicative of there being no Jahn–Teller effect in the Co²⁺ (d⁷) ion.

It is noteworthy that the 4,4'-bipyridine ligand is not coordinated to the Co atom but acts as an independent ligand. The two independent fragments are linked by an N2—H2···N3 hydrogen bond (Table 2). All non-H atoms in the 4,4'-bipyridine ligand are nearly coplanar, with a mean deviation of 0.0048 Å. Interestingly, the 4,4'-bipyridine ring is nearly coplanar with the H₂dcbi⁻ ligand, with a dihedral angel of 2.4°. There are strong face-to-face π–π interactions involving the pyridine rings of adjacent 4,4'-bipyridine ligands, in an offset fashion with a face-to-face stacking distance of 3.3451 Å.

In the asymmetric unit, atom O2 of the deprotonated carboxy group links atom O3 of the protonated carboxy group of the H₂dcbi⁻ ligand through an O3—H3···O2 hydrogen bond (Table 2). The molecules in the crystal structure are linked by N2—H2···N3 and O5—H5B···O1ⁱⁱ hydrogen bonds (for symmetry codes see Table 2), which produce a two-dimensional network in the (−112) crystallographic plane (Fig. 2). In the two-dimensional network, the molecules are further linked to one another via O5—H5A···O2ⁱⁱⁱ hydrogen bonds (for symmetry codes see Table 2), which produce a three-dimensional supramolecular framework (Fig. 3).

S2. Experimental

The title compound was synthesized by a hydrothermal method under autogenous pressure. A mixture of Co(NO₃)₂·6H₂O (291 mg, 1 mmol), 4,5-dicarboxyimidazole (312 mg, 2 mmol), 4,4'-bipyridine (156 mg, 1 mmol) and distilled water (15 ml) was stirred under ambient conditions, and then triethylamine (0.25 ml) was added slowly to the suspension. The mixture was sealed in a 25 ml Teflon-lined steel autoclave, heated at 358 K for 3 d and then cooled to room temperature. The resulting prism-like crystals were recovered by filtration, washed with distilled water and dried in air (yield 59%). Analysis calculated for C₂₀H₁₈CoN₆O₁₀: C 42.78, H 3.21, N 14.97%; found: C 42.72, H 3.11, N 14.92%.

S3. Refinement

Aromatic H atoms and carboxylic acid H atoms were placed in calculated positions and treated using a riding-model approximation (C—H = 0.93 Å, N—H = 0.86 Å and O—H = 0.82 Å). Water H atoms were visible in difference maps and refined with a distance restraint of O—H = 0.82 (1) Å.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. ORTEP drawing of the title compound. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Packing diagrams of (I), showing (a) part of the two-dimensional hydrogen-bonded network and (b) the hydrogen-bonded three-dimensional supramolecular framework.

trans-Diaquabis(5-carboxy-1H-imidazole-4-carboxylato-κ²N³,O⁴)cobalt(II) 4,4'-bipyridine solvate

Crystal data

[Co(C5H3N2O4)2(H2O)2]·C10H8N2	Z = 1
Mr = 561.33	F(000) = 287
Triclinic, P1	Dx = 1.741 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 4.971 (2) Å	Cell parameters from 1479 reflections
b = 6.558 (3) Å	θ = 3.3–27.5°
c = 17.274 (8) Å	µ = 0.88 mm^−1
α = 86.009 (9)°	T = 293 K
β = 86.729 (8)°	Prism, red
γ = 72.526 (8)°	0.48 × 0.20 × 0.04 mm
V = 535.5 (4) Å^3

Data collection

Siemens SMART CCD area-detector diffractometer	2417 independent reflections
Radiation source: fine-focus sealed tube	2299 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.022
ϕ and ω scans	θmax = 27.5°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −6→6
Tmin = 0.816, Tmax = 0.966	k = −6→8
4137 measured reflections	l = −21→22

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.086	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0304P)^2 + 0.7039P] where P = (Fo^2 + 2Fc^2)/3
2417 reflections	(Δ/σ)max < 0.001
176 parameters	Δρmax = 0.42 e Å^−3
2 restraints	Δρmin = −0.47 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Co1	1.0000	0.0000	0.5000	0.01269 (11)
O1	1.1678 (3)	0.2574 (2)	0.47074 (7)	0.0144 (3)
O2	1.1972 (3)	0.5000 (2)	0.37558 (8)	0.0174 (3)
O3	1.0052 (4)	0.6103 (3)	0.24106 (10)	0.0317 (4)
H3	1.0707	0.5722	0.2840	0.048*
O4	0.7490 (4)	0.5018 (3)	0.16078 (9)	0.0290 (4)
O5	1.3627 (3)	−0.2120 (2)	0.44900 (8)	0.0154 (3)
H5A	1.328 (5)	−0.313 (3)	0.4298 (13)	0.023*
H5B	1.505 (3)	−0.257 (4)	0.4745 (13)	0.023*
N1	0.8467 (3)	0.0931 (2)	0.38764 (9)	0.0125 (3)
N2	0.6859 (3)	0.1800 (3)	0.26968 (9)	0.0147 (3)
H2	0.6005	0.1776	0.2280	0.018*
N3	0.3902 (4)	0.1334 (3)	0.14451 (10)	0.0197 (4)
C1	0.9344 (4)	0.2619 (3)	0.35663 (10)	0.0126 (3)
C2	0.8345 (4)	0.3175 (3)	0.28306 (11)	0.0144 (4)
C3	0.6974 (4)	0.0489 (3)	0.33359 (11)	0.0147 (4)
H3A	0.6112	−0.0593	0.3391	0.018*
C4	1.1117 (4)	0.3475 (3)	0.40403 (10)	0.0127 (3)
C5	0.8589 (5)	0.4827 (3)	0.22293 (12)	0.0223 (4)
C6	0.3439 (4)	0.2468 (3)	0.07646 (12)	0.0203 (4)
H6	0.4170	0.3617	0.0676	0.024*
C7	0.1920 (4)	0.2010 (3)	0.01843 (11)	0.0185 (4)
H7	0.1649	0.2842	−0.0280	0.022*
C8	0.0809 (4)	0.0300 (3)	0.03024 (11)	0.0158 (4)
C9	0.1281 (4)	−0.0870 (3)	0.10128 (11)	0.0209 (4)
H9	0.0567	−0.2022	0.1120	0.025*
C10	0.2822 (4)	−0.0302 (3)	0.15569 (11)	0.0211 (4)
H10	0.3122	−0.1104	0.2027	0.025*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.01383 (19)	0.01535 (19)	0.01107 (18)	−0.00713 (14)	−0.00499 (13)	0.00070 (12)
O1	0.0150 (6)	0.0171 (6)	0.0135 (6)	−0.0077 (5)	−0.0054 (5)	−0.0001 (5)
O2	0.0237 (7)	0.0185 (7)	0.0148 (7)	−0.0131 (6)	−0.0029 (5)	−0.0008 (5)
O3	0.0482 (10)	0.0302 (9)	0.0238 (8)	−0.0223 (8)	−0.0087 (7)	0.0055 (6)
O4	0.0362 (9)	0.0320 (9)	0.0194 (8)	−0.0114 (7)	−0.0075 (7)	0.0053 (6)
O5	0.0140 (6)	0.0173 (7)	0.0177 (7)	−0.0076 (5)	−0.0064 (5)	−0.0016 (5)
N1	0.0136 (7)	0.0150 (7)	0.0109 (7)	−0.0071 (6)	−0.0028 (6)	0.0001 (6)
N2	0.0152 (7)	0.0196 (8)	0.0113 (7)	−0.0073 (6)	−0.0048 (6)	−0.0016 (6)
N3	0.0174 (8)	0.0272 (9)	0.0152 (8)	−0.0063 (7)	−0.0057 (6)	−0.0036 (7)
C1	0.0129 (8)	0.0137 (8)	0.0124 (8)	−0.0054 (7)	−0.0018 (7)	−0.0018 (6)
C2	0.0144 (8)	0.0162 (9)	0.0137 (9)	−0.0060 (7)	−0.0026 (7)	−0.0012 (7)
C3	0.0146 (9)	0.0175 (9)	0.0142 (8)	−0.0074 (7)	−0.0039 (7)	−0.0009 (7)
C4	0.0109 (8)	0.0142 (8)	0.0140 (8)	−0.0046 (7)	−0.0014 (6)	−0.0030 (6)
C5	0.0253 (10)	0.0227 (10)	0.0188 (10)	−0.0068 (8)	−0.0033 (8)	−0.0003 (8)
C6	0.0210 (10)	0.0237 (10)	0.0193 (10)	−0.0105 (8)	−0.0043 (8)	−0.0020 (8)
C7	0.0208 (10)	0.0214 (10)	0.0142 (9)	−0.0072 (8)	−0.0047 (7)	−0.0002 (7)
C8	0.0138 (8)	0.0218 (9)	0.0121 (9)	−0.0048 (7)	−0.0023 (7)	−0.0032 (7)
C9	0.0247 (10)	0.0268 (10)	0.0150 (9)	−0.0132 (9)	−0.0062 (8)	0.0023 (8)
C10	0.0247 (10)	0.0275 (11)	0.0123 (9)	−0.0090 (8)	−0.0069 (8)	0.0017 (7)

Geometric parameters (Å, º)

Co1—O5^i	2.108 (2)	N2—H2	0.86
Co1—O5	2.108 (2)	N3—C10	1.335 (3)
Co1—N1	2.108 (2)	N3—C6	1.340 (3)
Co1—N1^i	2.108 (2)	C1—C2	1.376 (3)
Co1—O1	2.116 (1)	C1—C4	1.486 (2)
Co1—O1^i	2.116 (1)	C2—C5	1.475 (3)
O1—C4	1.264 (2)	C3—H3A	0.93
O2—C4	1.259 (2)	C6—C7	1.389 (3)
O3—C5	1.325 (3)	C6—H6	0.93
O3—H3	0.82	C7—C8	1.390 (3)
O4—C5	1.214 (3)	C7—H7	0.93
O5—H5A	0.82 (1)	C8—C9	1.394 (3)
O5—H5B	0.82 (1)	C8—C8^ii	1.495 (4)
N1—C3	1.324 (2)	C9—C10	1.382 (3)
N1—C1	1.372 (2)	C9—H9	0.93
N2—C3	1.344 (2)	C10—H10	0.93
N2—C2	1.364 (2)
O5^i—Co1—O5	180.00 (7)	C2—C1—C4	132.32 (17)
O5^i—Co1—N1	91.61 (6)	N2—C2—C1	106.05 (16)
O5—Co1—N1	88.39 (6)	N2—C2—C5	120.12 (17)
O5^i—Co1—N1^i	88.39 (6)	C1—C2—C5	133.83 (18)
O5—Co1—N1^i	91.61 (6)	N1—C3—N2	111.55 (17)
N1—Co1—N1^i	180.00 (3)	N1—C3—H3A	124.2
O5^i—Co1—O1	90.26 (6)	N2—C3—H3A	124.2
O5—Co1—O1	89.74 (6)	O2—C4—O1	124.90 (17)
N1—Co1—O1	79.38 (6)	O2—C4—C1	118.87 (16)
N1^i—Co1—O1	100.62 (6)	O1—C4—C1	116.23 (16)
O5^i—Co1—O1^i	89.74 (6)	O4—C5—O3	122.0 (2)
O5—Co1—O1^i	90.26 (6)	O4—C5—C2	121.9 (2)
N1—Co1—O1^i	100.62 (6)	O3—C5—C2	116.06 (18)
N1^i—Co1—O1^i	79.38 (5)	N3—C6—C7	123.14 (19)
O1—Co1—O1^i	180.00 (7)	N3—C6—H6	118.4
C4—O1—Co1	115.49 (11)	C7—C6—H6	118.4
C5—O3—H3	109.5	C6—C7—C8	119.47 (18)
Co1—O5—H5A	112.5 (17)	C6—C7—H7	120.3
Co1—O5—H5B	118.5 (18)	C8—C7—H7	120.3
H5A—O5—H5B	110 (2)	C7—C8—C9	117.25 (17)
C3—N1—C1	105.66 (15)	C7—C8—C8^ii	122.2 (2)
C3—N1—Co1	143.83 (13)	C9—C8—C8^ii	120.5 (2)
C1—N1—Co1	110.50 (11)	C10—C9—C8	119.36 (19)
C3—N2—C2	107.47 (16)	C10—C9—H9	120.3
C3—N2—H2	126.3	C8—C9—H9	120.3
C2—N2—H2	126.3	N3—C10—C9	123.61 (18)
C10—N3—C6	117.16 (17)	N3—C10—H10	118.2
N1—C1—C2	109.28 (16)	C9—C10—H10	118.2
N1—C1—C4	118.40 (15)
O5^i—Co1—O1—C4	−92.20 (13)	C1—N1—C3—N2	0.2 (2)
O5—Co1—O1—C4	87.80 (13)	Co1—N1—C3—N2	−178.62 (15)
N1—Co1—O1—C4	−0.61 (13)	C2—N2—C3—N1	−0.3 (2)
N1^i—Co1—O1—C4	179.39 (13)	Co1—O1—C4—O2	−178.46 (14)
O5^i—Co1—N1—C3	−90.9 (2)	Co1—O1—C4—C1	0.7 (2)
O5—Co1—N1—C3	89.1 (2)	N1—C1—C4—O2	178.82 (16)
O1—Co1—N1—C3	179.1 (2)	C2—C1—C4—O2	−0.4 (3)
O1^i—Co1—N1—C3	−0.9 (2)	N1—C1—C4—O1	−0.4 (2)
O5^i—Co1—N1—C1	90.31 (12)	C2—C1—C4—O1	−179.61 (19)
O5—Co1—N1—C1	−89.69 (12)	N2—C2—C5—O4	0.2 (3)
O1—Co1—N1—C1	0.35 (11)	C1—C2—C5—O4	−179.9 (2)
O1^i—Co1—N1—C1	−179.65 (11)	N2—C2—C5—O3	179.53 (18)
C3—N1—C1—C2	0.0 (2)	C1—C2—C5—O3	−0.5 (3)
Co1—N1—C1—C2	179.26 (12)	C10—N3—C6—C7	−0.2 (3)
C3—N1—C1—C4	−179.37 (16)	N3—C6—C7—C8	0.0 (3)
Co1—N1—C1—C4	−0.11 (19)	C6—C7—C8—C9	0.4 (3)
C3—N2—C2—C1	0.3 (2)	C6—C7—C8—C8^ii	−179.0 (2)
C3—N2—C2—C5	−179.73 (17)	C7—C8—C9—C10	−0.5 (3)
N1—C1—C2—N2	−0.2 (2)	C8^ii—C8—C9—C10	179.0 (2)
C4—C1—C2—N2	179.06 (18)	C6—N3—C10—C9	0.1 (3)
N1—C1—C2—C5	179.8 (2)	C8—C9—C10—N3	0.2 (3)
C4—C1—C2—C5	−0.9 (4)

Symmetry codes: (i) −x+2, −y, −z+1; (ii) −x, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O2	0.82	1.72	2.537 (2)	178
N2—H2···N3	0.86	1.92	2.767 (2)	170
O5—H5A···O2^iii	0.82 (2)	1.88 (2)	2.691 (2)	169 (2)
O5—H5B···O1^iv	0.82 (2)	1.93 (2)	2.711 (2)	160 (2)

Symmetry codes: (iii) x, y−1, z; (iv) −x+3, −y, −z+1.