Poly­[[di­aqua­cobalt(II)]-di-[mu]-4-cyano­benzoato-[kappa]⁴O:O']

The title compound, [Co(C₈H₄NO₂)₂(H₂O)₂]_n, which was obtained by the reaction of CoCl₂·6H₂O with 4-cyano­benzoic acid, is the first two-dimensional 4-cyano­benzoate cobalt(II) polymer. The Co atom lies on a centre of symmetry and its coordination polyhedron is a slightly distorted octahedron, defined by two water and four carboxyl­ate O atoms. The 4-cyano­benzoate (cba) anion is bridging in a syn-skew coordination mode, which ensures a two-dimensional architecture with the building block Co₄(cba)₄.

S1. Comment

The design and construction of frameworks in the field of coordination polymers have been extensively studied, due to their potential applications as functional materials (Alam, 2003; Liddle & Clegg, 2002; Seo et al., 2000). Recently, complexes with 4-cyanobenzoic acid (Hcba) have received considerable attention, due to their potential application as strongly fluorescent materials (Yuan et al., 2001) and their structural interest (Wang et al., 2003). However, all examples of 4-cyanobenzoate metal complexes reported to date are monomers [with Co^II (Xie et al., 2004; He & Zhu, 2003a) or Cu^II (Zhou et al., 2003; Wang et al., 2003)], dimers [with Rh^II (Schiavo et al., 2003)], or one-dimensional polymers [with Ca^II (Yuan et al., 2001), Cu^II (He & Zhu, 2003b) or Co^II (He et al., 2003)]. In this paper, we report the title compound, (I), which is the first two-dimensional compound constructed with the cba ligand. \sch

The Co atom in (I) lies on a centre of symmetry and the structure is two-dimensional, with the Co atom in a slightly distorted octahedral geometry defined by two O donors from two water molecules and four O atoms from four cba ligands (Fig. 1). Atoms O1, O1ⁱⁱ, O3 and O3ⁱⁱ occupy the basal plane, while atoms O2bⁱⁱⁱ and O2ⁱ occupy the apical positions [symmetry codes: (i) x, 1/2 − y, 1/2 + z; (ii) 1 − x, −y, 1 − z; (iii) 1 − x, y − 1/2, 1/2 − z]. The Co—OW bond distances [2.0913 (15) Å] in (I) are shorter than those in the analogous compounds [Co(cba)₂(phen)(H₂O)₂], (II) [2.114 (2) and 2.156 (2) Å; Xie et al., 2004], [Co(cba)₂(4,4'-bipy)(H₂O)₂]_n, (III) [2.155 (2) Å; He et al., 2003] and [Co(cba)₂(3-NH₂-py)₂(H₂O)₂]·2H₂O, (IV) [2.120 (2) Å; He & Zhu, 2003a]. In compounds (II)-(IV), the carboxylate groups are all in a syn-monodentate coordination mode and the Co—O(COO⁻) bond distances [2.071 (2)–2.110 (2) Å] are shorter than the Co—OW distances [2.114 (2)–2.156 (2) Å]. In (I), the carboxylate has a bridging mode and two kinds of Co—O(COO⁻) bond distances are observed, namely the Co1—O1 distance of 2.0527 (14) Å in the syn-coordination mode, which is shorter than the Co—OW distance, and the Co1—O2ⁱ distance of 2.1437 (14) Å in the skew-coordination mode.

In (I), the carboxylate group is not coplanar with the attached benzene ring, the dihedral angle being 15.2 (2)°. Moreover, the bridging mode of the 4-cyanobenzoate ligand is syn-skew, and the Co···Co separation bridged by the cba ligand is 4.9471 (4) Å. The bridging skew coordination of the cba ligand leads to a building unit of [Co₄(cba)₄], which is the basic unit in the two-dimensional framework (Fig. 2).

In most of the previously reported 4-cyanobenzoate complexes, there is an [M(cba)₂(H₂O)₂] motif. The two water molecules could be arranged in a cis or a trans pattern. In (II), the two water molecules are arranged cis. In (III)-(IV), the two water molecules are in trans positions. Although cis or trans-(OW, OW) types could be found in (II)-(IV), the [Co(cba)₂(H₂O)₂] structures in these three compounds are monomeric, with the cba ligands in a syn-monodentate mode. In the one-dimensional structure of [Ca(cba)₂(H₂O)₂] (Yuan et al., 2001), the cba ligand is in a syn-skew bridging mode and the two water molecules are cis. In contrast, the aqua ligands in (I) are trans. Therefore, the combination of the bridging coordination mode and the trans-arrangement of the aqua ligands leads to the two-dimensional architecture observed in (I).

In the crystal of (I), π–π interactions between cba ligands are observed. The shifts of atoms C2—C7 at (x, y, z) from the plane defined by C2—C7 at (x, 1/2 − y, 1/2 + z) are in the range 3.305 (4)–3.586 (3) Å. In the two-dimensional framework, these π–π interactions of the cyanophenyl groups are extended into one-dimensional stacking columns along the c axis. Moreover, hydrogen bonds (Table 2) are observed in the two-dimensional framework. The coordinated water molecule forms hydrogen bonds with neighbouring carboxylate groups. Therefore, π–π and hydrogen-bonding interactions enhance the stability of the crystal structure.

S2. Experimental

A solution of CoCl₂·6H₂O (0.0717 g, 0.3 mmol) in water (10 ml) was mixed with a previously prepared solution of 4-cyanobenzoic acid (0.0833 g, 0.57 mmol) and 4-aminopyridine (0.0536 g, 0.57 mmol) in dimethylformamide (10 ml). The resulting solution was put aside and evaporated slowly. After three months, dark-red crystals of (I) had formed and were collected.

S3. Refinement

H atoms bonded to C atoms were located geometrically and treated as riding, with C—H distances of 0.93 Å and with U_iso(H) = 1.2U_eq(C). The water H atoms were located from difference Fourier maps and refined, with restraints for the O—H distances (0.80 Å) and with U_iso(H) = 0.05 Ų.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SHELXTL (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A view of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) x, 1/2 − y, 1/2 + z; (ii) 1 − x, −y, 1 − z; (iii) 1 − x, y − 1/2, 1/2 − z].
	Fig. 2. A view of the two-dimensional framework of (I), projected along (1,0,1). H atoms have been omitted for clarity.
	Fig. 3. A view of the π–π interactions in (I).

Poly[[diaquacobalt(II)]-di-µ-4-cyanobenzoato-κ⁴O:O']

Crystal data

[Co(C8H4NO2)2(H2O)2]	F(000) = 394
Mr = 387.21	Dx = 1.707 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 15.5951 (18) Å	Cell parameters from 2419 reflections
b = 6.6087 (7) Å	θ = 5.3–56.4°
c = 7.3635 (8) Å	µ = 1.18 mm^−1
β = 96.979 (2)°	T = 293 K
V = 753.28 (14) Å^3	Block, dark red
Z = 2	0.48 × 0.32 × 0.18 mm

Data collection

Bruker SMART CCD area-detector diffractometer	1656 independent reflections
Radiation source: fine-focus sealed tube	1473 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.077
ϕ and ω scans	θmax = 27.1°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −19→19
Tmin = 0.639, Tmax = 0.809	k = −8→7
4306 measured reflections	l = −7→9

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)] = 0.035	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.097	H atoms treated by a mixture of independent and constrained refinement
S = 1.10	w = 1/[σ^2(Fo^2) + (0.0445P)^2 + 0.1431P] where P = (Fo^2 + 2Fc^2)/3
1656 reflections	(Δ/σ)max < 0.001
121 parameters	Δρmax = 0.49 e Å^−3
2 restraints	Δρmin = −0.38 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.

The calculation of the shifts of the atoms C2—C7 at (x, y, z) from the plane defined by C2—C7 at (x, 1/2 − y, 1/2 + z): * −0.0052 (0.0017) C2 * 0.0098 (0.0018) C3 * −0.0056 (0.0019) C4 * −0.0032 (0.0017) C5 * 0.0077 (0.0018) C6 * −0.0035 (0.0018) C7

−3.4564 (0.0022) C2_$4 − 3.3047 (0.0036) C3_$4 − 3.3151 (0.0040) C4_$4 − 3.4454 (0.0021) C5_$4 − 3.5718 (0.0031) C6_$4 − 3.5861 (0.0030) C7_$4

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	0.5000	0.0000	0.5000	0.02046 (16)
O1	0.40647 (9)	0.0898 (2)	0.2955 (2)	0.0276 (3)
O2	0.43076 (9)	0.4085 (2)	0.2205 (2)	0.0271 (3)
O3	0.43785 (10)	−0.2806 (2)	0.4963 (2)	0.0299 (4)
N1	−0.03135 (14)	0.2769 (4)	−0.2059 (4)	0.0516 (6)
C1	0.38325 (12)	0.2521 (3)	0.2183 (3)	0.0213 (4)
C2	0.29348 (12)	0.2601 (3)	0.1205 (3)	0.0233 (4)
C3	0.25493 (14)	0.4445 (4)	0.0693 (4)	0.0318 (5)
H3	0.2860	0.5639	0.0914	0.038*
C4	0.17131 (15)	0.4512 (4)	−0.0136 (4)	0.0365 (6)
H4	0.1452	0.5749	−0.0450	0.044*
C5	0.12597 (13)	0.2722 (4)	−0.0504 (3)	0.0306 (5)
C6	0.16418 (14)	0.0871 (4)	−0.0033 (3)	0.0362 (5)
H6	0.1339	−0.0326	−0.0297	0.043*
C7	0.24769 (14)	0.0829 (4)	0.0833 (3)	0.0317 (5)
H7	0.2735	−0.0406	0.1170	0.038*
C8	0.03780 (15)	0.2767 (4)	−0.1383 (3)	0.0379 (6)
H3A	0.4328 (19)	−0.364 (4)	0.402 (3)	0.050*
H3B	0.4553 (17)	−0.353 (4)	0.594 (3)	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0176 (2)	0.0203 (2)	0.0226 (2)	0.00134 (13)	−0.00087 (15)	−0.00080 (15)
O1	0.0223 (7)	0.0265 (8)	0.0320 (8)	0.0011 (6)	−0.0054 (6)	0.0049 (7)
O2	0.0241 (7)	0.0273 (8)	0.0293 (8)	−0.0044 (6)	0.0003 (6)	0.0023 (7)
O3	0.0361 (8)	0.0218 (8)	0.0308 (8)	−0.0032 (6)	−0.0002 (7)	0.0012 (6)
N1	0.0287 (11)	0.0624 (15)	0.0602 (15)	0.0034 (10)	−0.0090 (10)	−0.0005 (13)
C1	0.0186 (9)	0.0238 (10)	0.0219 (10)	0.0006 (7)	0.0042 (8)	−0.0011 (8)
C2	0.0187 (9)	0.0283 (11)	0.0227 (10)	0.0013 (7)	0.0021 (8)	0.0021 (8)
C3	0.0252 (11)	0.0270 (10)	0.0416 (14)	0.0001 (9)	−0.0024 (10)	0.0016 (10)
C4	0.0286 (12)	0.0347 (12)	0.0443 (15)	0.0092 (9)	−0.0026 (11)	0.0056 (11)
C5	0.0185 (10)	0.0456 (14)	0.0270 (11)	0.0016 (8)	0.0000 (9)	0.0011 (10)
C6	0.0256 (11)	0.0370 (13)	0.0434 (14)	−0.0068 (9)	−0.0054 (10)	−0.0010 (12)
C7	0.0251 (10)	0.0276 (11)	0.0405 (13)	0.0014 (9)	−0.0042 (9)	0.0046 (11)
C8	0.0264 (12)	0.0473 (14)	0.0385 (14)	0.0037 (10)	−0.0016 (10)	0.0015 (12)

Geometric parameters (Å, º)

Co1—O1^i	2.0527 (14)	C1—C2	1.495 (3)
Co1—O1	2.0527 (14)	C2—C7	1.382 (3)
Co1—O3	2.0913 (15)	C2—C3	1.391 (3)
Co1—O3^i	2.0913 (15)	C3—C4	1.372 (3)
Co1—O2^ii	2.1437 (14)	C3—H3	0.9300
Co1—O2^iii	2.1437 (14)	C4—C5	1.388 (4)
O1—C1	1.247 (2)	C4—H4	0.9300
O2—C1	1.270 (2)	C5—C6	1.386 (3)
O2—Co1^iv	2.1437 (14)	C5—C8	1.447 (3)
O3—H3A	0.884 (10)	C6—C7	1.379 (3)
O3—H3B	0.878 (10)	C6—H6	0.9300
N1—C8	1.132 (3)	C7—H7	0.9300
O1^i—Co1—O1	180.0	O1—C1—C2	116.93 (17)
O1^i—Co1—O3	92.30 (6)	O2—C1—C2	119.21 (17)
O1—Co1—O3	87.70 (6)	C7—C2—C3	119.54 (19)
O1^i—Co1—O3^i	87.70 (6)	C7—C2—C1	119.78 (18)
O1—Co1—O3^i	92.30 (6)	C3—C2—C1	120.67 (19)
O3—Co1—O3^i	180.0	C4—C3—C2	120.4 (2)
O1^i—Co1—O2^ii	84.51 (6)	C4—C3—H3	119.8
O1—Co1—O2^ii	95.49 (6)	C2—C3—H3	119.8
O3—Co1—O2^ii	89.13 (6)	C3—C4—C5	119.6 (2)
O3^i—Co1—O2^ii	90.87 (6)	C3—C4—H4	120.2
O1^i—Co1—O2^iii	95.49 (6)	C5—C4—H4	120.2
O1—Co1—O2^iii	84.51 (6)	C6—C5—C4	120.67 (19)
O3—Co1—O2^iii	90.87 (6)	C6—C5—C8	119.1 (2)
O3^i—Co1—O2^iii	89.13 (6)	C4—C5—C8	120.2 (2)
O2^ii—Co1—O2^iii	180.0	C7—C6—C5	119.1 (2)
C1—O1—Co1	136.41 (13)	C7—C6—H6	120.4
C1—O2—Co1^iv	124.48 (14)	C5—C6—H6	120.4
Co1—O3—H3A	124 (2)	C6—C7—C2	120.7 (2)
Co1—O3—H3B	112.0 (19)	C6—C7—H7	119.6
H3A—O3—H3B	107 (3)	C2—C7—H7	119.6
O1—C1—O2	123.85 (18)	N1—C8—C5	178.8 (3)
O3—Co1—O1—C1	169.5 (2)	O2—C1—C2—C3	−14.8 (3)
O3^i—Co1—O1—C1	−10.5 (2)	C7—C2—C3—C4	1.5 (4)
O2^ii—Co1—O1—C1	80.6 (2)	C1—C2—C3—C4	−177.3 (2)
O2^iii—Co1—O1—C1	−99.4 (2)	C2—C3—C4—C5	−1.6 (4)
Co1—O1—C1—O2	19.6 (3)	C3—C4—C5—C6	0.3 (4)
Co1—O1—C1—C2	−159.46 (15)	C3—C4—C5—C8	−179.8 (2)
Co1^iv—O2—C1—O1	100.8 (2)	C4—C5—C6—C7	0.9 (4)
Co1^iv—O2—C1—C2	−80.2 (2)	C8—C5—C6—C7	−178.9 (2)
O1—C1—C2—C7	−14.5 (3)	C5—C6—C7—C2	−1.0 (4)
O2—C1—C2—C7	166.4 (2)	C3—C2—C7—C6	−0.3 (4)
O1—C1—C2—C3	164.4 (2)	C1—C2—C7—C6	178.6 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3A···O2^v	0.88 (1)	2.01 (1)	2.881 (2)	170 (3)
O3—H3B···O2^i	0.88 (1)	2.14 (2)	2.867 (2)	140 (2)
O3—H3B···O1^vi	0.88 (1)	2.35 (2)	3.087 (2)	142 (2)

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