A novel one-dimensional coordination polymer, catena-poly[[diaquacobalt(II)]-[mu]-(2,2'-bipyridyl-3,3'-dicarboxylato-[kappa]⁴N,N':O,O')]

The title compound, [Co(C₁₂H₆N₂O₄)(H₂O)₂]_n, has been hydro­thermally synthesized and structurally characterized. It consists of polymeric chains of [Co{[mu]-(2,2'-bipyridyl-3,3'-di­carboxyl­ato-[kappa]⁴N,N':O,O')}(H₂O)₂] units, in which each Co^II cation is octahedrally coordinated by two chelating pyridyl N atoms, two chelating carboxyl O atoms from different carboxylate groups of another bipyridyl ligand, and two water mol­ecules as terminal ligands. A crystallographic twofold axis parallel to the chain axis, passes through the Co atom.

S1. Comment

Transition metal coordination polymers of one-, two- and three-dimensional infinite frameworks have been an attractive research area because of their diverse structures and useful properties (Davis, 2002; Hagrman et al., 1999). Polydentate ligands, which are used as bridges in the construction of coordination polymers, are quite important in the crystal engineering of supramolecular architectures organized by coordinate covalent or hydrogen bonding (Moulton & Zaworotko, 2001).

2,2'-Bipyridyl-3,3'-dicarboxylate (bpdc) is a potential bridging ligand in view of its functional groups. However, it usually acts as an N,N'-bidentate ligand, forming a chelate with one metal centre in the corresponding discrete complex molecules (Goddard et al., 1990; Ravikumar et al., 1997; Yoo et al., 1997; Menon et al., 1997). Only a few metal coordination polymers bridged by bpdc have been reported to date. For example, bpdc acts as an O,O'-bidentate µ₂ ligand to bridge two metal centres via one O atom of its two carboxyl groups in the polymer [Mn(bpdc)(H₂O)₄]_n (Swamy et al., 1998). The monoprotonated bpdc in [Ag(µ₃-Hbpdc)(H₂O)]_n (Tong et al., 2000) coordinates as an N,N',O-tridentate µ₃ ligand to form three bridges, N—Ag, N'-Ag and O—Ag. Furthermore, in [Cu(µ₂-bpdc)(H₂O)₂]_n, bpdc also coordinates in an N,N',O-tridentate fashion, but as a µ₂ ligand to bridge two Cu^II ions through one N—Cu—N' chelating system and one O—Cu coordinate bond (Zhuang et al., 1994; Ravikumar et al., 1995). The title complex, [Co(µ₂-bpdc)(H₂O)₂]_n, (I), reported here is another one-dimensional coordination polymer, in which bpdc acts as a µ₂ ligand in the N,N':O,O'-tetradentate fashion to form two chelate bridges. \sch

In complex (I), the bpdc chelates one Co^II cation, which lies on a twofold axis, via its two pyridyl N atoms (N and N'), and another Co^II cation via its two carboxyl O atoms (O1 and O1'). Each Co^II cation is octahedrally coordinated, where the equatorial plane comprises the two N atoms of one bpdc ligand on one side and two carboxyl O atoms from different carboxyl groups of a second bpdc ligand on the other side. The apical positions are occupied by the O atoms of the two coordinated water molecules (Fig 1). This octahedron is distorted (Table 1).

The crystal structure of (I) consists of linear polymeric chains of [Co(µ₂-bpdc)(H₂O)₂] units. The chains incorporate a twofold axis along the chain direction, which is parallel to b. The chains are interconnected by hydrogen bonding involving atom H1 between adjacent chains, via the coordinated H₂O molecules of one chain and the non-coordinated carboxyl O atoms of the adjacent chain, forming a layer parallel to (001). There is one intrachain hydrogen bond involving atom H2 (Fig. 2 and Table 2). These layers stack along the c axis to build up the whole crystal structure.

Complex (I) has the same chemical components as [Cu(µ-bpdc)(H₂O)₂]_n, but it has a totally different crystal structure to that reported for the latter. The different structures are a result of bpdc acting as a tetradentate ligand in the Co complex and as a tridentate ligand in the Cu complex.

In order to explore the conductivity of (I), the Kubelka-Munk function, F = (1-R_inf)²/2R_inf, was converted from the recorded diffuse reflectance data for (I), where R_inf is the relative diffuse reflectance of an infinitely thick layer (Wendlandt & Hecht, 1966). The plot of the Kubelka-Munk function versus energy (eV) displayed a steep absorption edge in the UV-vis region, from which a band gap of about 2.7 eV was estimated (McCarthy et al., 1993). This suggests that the crystal of (I) is possibly a semiconductor.

S2. Experimental

All chemicals and solvents were of reagent grade, and were used without further purification. 2,2'-Bipyridyl-3,3'-dicarboxylic acid (2,2'-binicotinic acid, H₂bpdc) was prepared according to the literature method of Wimmer & Wimmer (1983). A mixture of CoCl₂ (0.1298 g, 1.0 mmol) and H₂bpdc (0.2560 g, 1.0 mmol) in a mole ratio of 1:1 was sealed in a 25 ml Teflon-lined stainless steel Parr bomb containing methanol (11.2 ml) and water (2.8 ml), heated at 433 K for 3 d, and then cooled to room temperature. Orange sheet-like crystals of (I) were isolated and washed in turn with water, ethanol and anhydrous ether. The reflectance spectrum of the compound was taken on a UV-3100 recording spectrophotometer from 250 to 2500 nm.

S3. Refinement

The H atoms on the water molecule were refined in fixed positions, while the others were refined in riding mode.

Computing details

Data collection: SMART (Bruker, 1997-2000); cell refinement: SMART; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1990); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The coordination environment of Co^II in (I), with the atomic labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. One layer of the structure of (I), showing the [Co(µ-bpdc)(H2O)2]n chains lying parallel to b. Hydrogen bonds are shown as dashed lines. The a axis is approximately vertical in the diagram.

catena-poly-[[diaquacobalt(II)]-µ-(2,2'-bipyridyl-3,3'-dicarboxylato- κ⁴N,N':O,O')]

Crystal data

[Co(C12H6N2O4)(H2O)2]	F(000) = 684
Mr = 337.15	Dx = 1.938 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 1437 reflections
a = 11.373 (2) Å	θ = 3.2–31.2°
b = 7.8632 (16) Å	µ = 1.52 mm^−1
c = 13.162 (3) Å	T = 293 K
β = 100.92 (3)°	Sheet, orange
V = 1155.8 (4) Å^3	0.2 × 0.1 × 0.05 mm
Z = 4

Data collection

Make Model CCD area-detector diffractometer	2133 independent reflections
Radiation source: fine-focus sealed tube	1563 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.046
Detector resolution: 15 x 15 microns pixels mm^-1	θmax = 33.5°, θmin = 3.2°
ϕ and ω scans	h = −17→17
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick 1996)	k = −7→11
Tmin = 0.764, Tmax = 0.927	l = −20→19
5330 measured reflections

Refinement

Refinement on F^2	Primary atom site location: patt
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.054	Hydrogen site location: difference Fourier map
wR(F^2) = 0.132	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0624P)^2 + 0.0074P] where P = (Fo^2 + 2Fc^2)/3
2133 reflections	(Δ/σ)max < 0.001
96 parameters	Δρmax = 0.69 e Å^−3
2 restraints	Δρmin = −0.40 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
Co	0.0000	0.70340 (7)	0.2500	0.01833 (16)
O1	−0.03905 (17)	1.5087 (2)	0.13819 (15)	0.0217 (4)
O2	0.13384 (17)	1.3653 (3)	0.17289 (16)	0.0252 (4)
O3	−0.17466 (17)	0.6908 (3)	0.28347 (16)	0.0258 (4)
H1	−0.2314	0.7276	0.2450	0.031*
H2	−0.1760	0.5889	0.2943	0.031*
N	−0.06589 (19)	0.9130 (3)	0.15830 (17)	0.0181 (4)
C1	−0.0290 (2)	1.0679 (3)	0.19373 (18)	0.0147 (5)
C2	−0.0425 (2)	1.2080 (3)	0.12723 (19)	0.0157 (4)
C3	−0.1105 (2)	1.1878 (4)	0.0281 (2)	0.0203 (5)
H3	−0.1250	1.2807	−0.0162	0.024*
C4	−0.1562 (2)	1.0300 (4)	−0.0043 (2)	0.0224 (5)
H4	−0.2051	1.0159	−0.0688	0.027*
C5	−0.1275 (2)	0.8947 (4)	0.0615 (2)	0.0216 (5)
H5	−0.1515	0.7863	0.0381	0.026*
C6	0.0224 (2)	1.3746 (3)	0.14944 (18)	0.0174 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co	0.0193 (3)	0.0105 (2)	0.0242 (3)	0.000	0.00149 (18)	0.000
O1	0.0247 (9)	0.0127 (9)	0.0256 (10)	0.0034 (7)	−0.0003 (7)	−0.0004 (8)
O2	0.0193 (9)	0.0164 (10)	0.0381 (11)	0.0010 (8)	0.0006 (8)	0.0004 (9)
O3	0.0210 (9)	0.0188 (10)	0.0374 (12)	0.0024 (8)	0.0048 (8)	0.0059 (9)
N	0.0188 (10)	0.0114 (10)	0.0230 (11)	−0.0009 (8)	0.0013 (8)	−0.0021 (9)
C1	0.0154 (11)	0.0111 (11)	0.0175 (11)	0.0006 (8)	0.0030 (8)	−0.0034 (9)
C2	0.0173 (10)	0.0103 (10)	0.0194 (11)	0.0015 (9)	0.0029 (8)	−0.0009 (10)
C3	0.0243 (12)	0.0170 (12)	0.0180 (12)	0.0028 (10)	−0.0004 (9)	0.0034 (10)
C4	0.0213 (12)	0.0238 (14)	0.0204 (12)	−0.0010 (11)	−0.0009 (9)	−0.0027 (11)
C5	0.0216 (12)	0.0160 (12)	0.0257 (13)	−0.0029 (10)	0.0008 (10)	−0.0038 (11)
C6	0.0245 (12)	0.0140 (12)	0.0135 (10)	−0.0017 (10)	0.0026 (9)	0.0002 (9)

Geometric parameters (Å, º)

Co—N	2.096 (2)	C1—C2	1.398 (3)
Co—O1^i	2.112 (2)	C1—C1^ii	1.504 (5)
Co—O3	2.116 (2)	C2—C3	1.395 (4)
O1—C6	1.258 (3)	C2—C6	1.505 (4)
O2—C6	1.249 (3)	C3—C4	1.382 (4)
O3—H1	0.7959	C3—H3	0.9300
O3—H2	0.815	C4—C5	1.372 (4)
N—C5	1.342 (3)	C4—H4	0.9300
N—C1	1.343 (3)	C5—H5	0.9300
N^ii—Co—N	76.35 (12)	N—C1—C1^ii	113.12 (15)
N—Co—O1^i	99.38 (8)	C2—C1—C1^ii	126.37 (15)
N—Co—O1^iii	167.59 (8)	C3—C2—C1	118.2 (2)
O1^i—Co—O1^iii	87.09 (11)	C3—C2—C6	116.5 (2)
N—Co—O3^ii	99.49 (9)	C1—C2—C6	124.9 (2)
N—Co—O3	84.75 (8)	C4—C3—C2	120.1 (2)
O1^i—Co—O3	91.63 (8)	C4—C3—H3	120.0
O1^iii—Co—O3	84.49 (8)	C2—C3—H3	120.0
O3^ii—Co—O3	174.65 (12)	C5—C4—C3	118.1 (2)
C6—O1—Co^iv	119.07 (16)	C5—C4—H4	121.0
Co—O3—H1	122.14	C3—C4—H4	121.0
Co—O3—H2	97.55	N—C5—C4	122.4 (3)
H1—O3—H2	115.4	N—C5—H5	118.8
C5—N—C1	120.0 (2)	C4—C5—H5	118.8
C5—N—Co	121.93 (18)	O2—C6—O1	126.4 (2)
C1—N—Co	117.28 (16)	O2—C6—C2	115.8 (2)
N—C1—C2	120.5 (2)	O1—C6—C2	117.7 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H1···O2^v	0.80	1.97	2.748 (3)	166
O3—H2···O2^iii	0.82	1.85	2.645 (3)	164

Symmetry codes: (iii) −x, y−1, −z+1/2; (v) x−1/2, y−1/2, z.