A new three-dimensional cobalt(II) coordination polymer with a 4-connected CdSO₄-like topology

The title cobalt(II) coordination polymer, poly[[diaqua­cobalt(II)]-μ₄-3,3′-(p-phenyl­ene)diacrylato], [Co(C₁₂H₈O₄)(H₂O)₂]_n, was obtained by reaction of Co(NO₃)₂·6H₂O and 3,3′-(p-phenyl­ene)diacrylic acid (H₂L) under hydro­thermal conditions. Each Co^II cation sits on a centre of inversion and is hexa­coordinated by six O-atom donors in an octa­hedral geometry. The Co^II centres are connected by four centrosymmetric L²⁻ anions, resulting in a three-dimensional framework structure. The coordinated water mol­ecules and carboxyl­ate O atoms form hydrogen-bond inter­actions, stabilizing the structure of the three-dimensional framework. Topologically, the framework represents a rare example of the three-dimensional 4-connected CdSO₄ network type. The metal cations and the organic ligand both show in-plane coordination with respect to the extended structure.

S1. Comment

Current interest in polymeric coordination networks is expanding rapidly, not only due to their potential applications in host–guest chemistry, ion exchange, gas storage and nonlinear optics, but also for their intriguing variety of topologies (Batten & Robson, 1998; Batten, 2001; Wu et al., 2005; Spencer et al., 2006). The construction of coordination networks with different topological characteristics has attracted significant attention from chemists (Barbour, 2001). It is well known that product topology can often be controlled and modified by selecting the coordination geometry preferred by the metal ion and the chemical structure of the organic ligand. The use of aromatic carboxylic acids in the synthesis of coordination polymers has aroused enormous interest due to their versatile coordination modes and variety of structural conformations (Yang et al., 2008). Aromatic multicarboxylate ligands, such as benzene-1,2-dicarboxylic acid, 1,3-benzenedicarboxylic acid and benzene-1,4-dicarboxylic acid, are widely used to construct coordination polymers with interesting properties (Zhang et al., 2005). In this regard, p-phenylenediacrylic acid (H₂L) is also a good ligand in coordination chemistry due to its strong coordination ability and versatile coordination modes, so much attention has been paid to it in recent years (Fang et al. 2007). In this contribution, H₂L was selected as a bridging ligand, and the title new cobalt(II) coordination polymer, [Co(C₁₂H₈O₄)(H₂O)₂]_n, (I), was obtained under hydrothermal conditions. Compound (I) represents a rare example of a three-dimensional framework with a 4-connected CdSO₄-like topology based solely upon square-planar nodes.

Selected bond distances and angles are listed in Table 1. As shown in Fig. 1, the asymmetric unit of (I) contains one-half of a Co^II cation, one-half of an L anion and one water molecule. Each Co^II cation has an octahedral coordination environment and is coordinated by four carboxylate O atoms from four different L anions [O1, O1ⁱ, O2ⁱⁱ and O2ⁱⁱⁱ; symmetry codes: (i) ?; (ii) ?; (iii) ? Please complete], which make up the basal plane, while the axial positions are occupied by two water O atoms (O1W and O1Wⁱ). Each L anion coordinates to four Co^II centres in a tetradentate mode (see scheme). This tetradentate coordination forms a three-dimensional framework structure of (I) (Fig. 2), stabilized by hydrogen-bonding interactions between the coordinated water molecules and carboxylate O atoms (Table 2).

A better insight into the structure of (I) can be achieved by application of the topological approach, i.e. reducing multidimensional structures to simple node-and-linker nets. As discussed above, the Co^II centre is defined as a square-planar 4-connected node. Each carboxylate O atom of L in (I) is coordinated to one Co^II ion in a monodentate manner; hence each L ligand bridges four adjacent Co^II ions. The mean deviation of atoms C1–C6, C1^iv–C6^iv, O1, O2, O1^iv and O2^iv from their plane is 0.2215 Å. Thus, the ligand L can also be regarded as a square-planar 4-connected node (Fig. 3). Both the Co^II and L nodes are equivalent. According to the simplification principle, the resulting structure of (I) is a 4-connected three-dimensional net. The topology of a single framework can be rationalized by considering that the shortest circuits starting and ending at each Co^II cation and L ligand are hexagons and octagons, forming an overall 6⁵.8 CdSO₄-like (cds) net (Wells, 1979).

So far, numerous fascinating archetypal topological structures, including NbO (nbo), Pt₃O₄ (pto), pyrite (pyr), quartz (qtz), rutile (rto), sodalite (sod), diamond (dia), SrSi₂ (10³-a) (srs), α-ThSi₂ (10³-b) (ths) and PtS (4².8⁴) (pts), have provided experimental examples. In this regard, 4-connected networks are particularly interesting (Zhang et al., 2005; Abrahams et al., 1999; Carlucci et al., 2002). The majority of 4-connected nets are constructed by tetrahedral or square-planar nodes. Typical 4-connected nets such as 6⁶, 6⁴.8², 4².8⁴ and 7⁵.9 have been well documented (Wells, 1984; Hawkins et al., 1993; Qi et al., 2008; Long et al., 2004; Fang et al., 2008; Bhogala et al., 2004; Carlucci et al., 1998). So far, although CdSO₄-like nets have been widely reported, those based on both a planar 4-connected organic ligand and a metal cation are relatively rare (Zhang et al., 2006).

S2. Experimental

A mixture of Co(NO₃)₂.6H₂O (29.1 mg, 0.10 mmol), H₂L (21.8 mg, 0.10 mmol) and water (12 ml) was sealed in a Teflon reactor (15 ml), which was heated at 413 K for 3 d and then gradually cooled to room temperature. Purple crystals of (I) were isolated (yield 58% based on Co).

S3. Refinement

H atoms bonded to C atoms were positioned geometrically (C—H = 0.93 Å) and refined as riding, with U_iso(H) = 1.2U_eq(C). Water H atoms were located in a difference Fourier map and refined freely.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART (Bruker, 1997); data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. A view of the local coordination of the Co^II cations in (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) 2 - x, -y, 2 - z; (ii) 2 - x, y + 1/2, 5/2 - z; (iii) x, -1/2 - y, z - 1/2; (iv) 1 - x, -1 - y, 3 - z.]
	Fig. 2. The three-dimensional framework structure of (I).
	Fig. 3. The shortest circuits of (I). Larger circles represent Co^II atoms and smaller circles represent L ligands. Both nodes are equivalent.
	Fig. 4. Schematic representation of the CdSO4-like net of (I).

poly[[diaquacobalt(II)]-µ₄-p-phenylenediacrylato]

Crystal data

[Co(C12H8O4)(H2O)2]	F(000) = 318
Mr = 311.15	Dx = 1.691 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1241 reflections
a = 12.9638 (5) Å	θ = 3.0–26.4°
b = 6.4039 (2) Å	µ = 1.42 mm^−1
c = 7.3594 (2) Å	T = 293 K
β = 90.561 (3)°	Block, purple
V = 610.94 (3) Å^3	0.21 × 0.18 × 0.12 mm
Z = 2

Data collection

Bruker APEX diffractometer	1241 independent reflections
Radiation source: fine-focus sealed tube	989 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
ϕ and ω scans	θmax = 26.4°, θmin = 4.2°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −16→11
Tmin = 0.733, Tmax = 0.841	k = −6→8
2788 measured reflections	l = −9→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)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.060	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0318P)^2] where P = (Fo^2 + 2Fc^2)/3
1241 reflections	(Δ/σ)max < 0.001
96 parameters	Δρmax = 0.27 e Å^−3
0 restraints	Δρmin = −0.31 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
C1	0.85690 (15)	−0.2552 (3)	1.2476 (2)	0.0168 (4)
C2	0.74851 (16)	−0.2688 (3)	1.3065 (2)	0.0248 (5)
H2	0.7070	−0.1509	1.2954	0.030*
C3	0.70774 (16)	−0.4420 (3)	1.3746 (2)	0.0244 (5)
H3	0.7508	−0.5577	1.3841	0.029*
C4	0.60116 (16)	−0.4680 (3)	1.4362 (2)	0.0232 (5)
C5	0.57415 (16)	−0.6520 (4)	1.5271 (3)	0.0295 (5)
H5	0.6237	−0.7551	1.5459	0.035*
C6	0.47522 (16)	−0.6826 (4)	1.5892 (3)	0.0309 (5)
H6	0.4592	−0.8061	1.6491	0.037*
O1	0.88488 (10)	−0.0847 (2)	1.17963 (17)	0.0226 (3)
O2	0.91616 (10)	−0.4125 (2)	1.26536 (16)	0.0216 (3)
O1W	1.07684 (12)	−0.2865 (2)	1.0108 (2)	0.0264 (4)
Co1	1.0000	0.0000	1.0000	0.01647 (13)
HW11	1.0843 (17)	−0.365 (4)	0.925 (3)	0.033 (7)*
HW12	1.067 (2)	−0.361 (5)	1.094 (4)	0.054 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0156 (10)	0.0213 (11)	0.0136 (8)	−0.0011 (9)	0.0024 (7)	0.0005 (7)
C2	0.0154 (11)	0.0273 (12)	0.0317 (10)	0.0018 (9)	0.0053 (8)	0.0059 (8)
C3	0.0177 (11)	0.0304 (12)	0.0252 (10)	−0.0028 (9)	0.0018 (8)	0.0034 (8)
C4	0.0165 (10)	0.0288 (12)	0.0243 (9)	−0.0062 (9)	0.0009 (8)	0.0058 (8)
C5	0.0186 (11)	0.0335 (13)	0.0364 (11)	0.0000 (10)	0.0025 (9)	0.0102 (9)
C6	0.0230 (12)	0.0332 (13)	0.0365 (11)	−0.0084 (11)	0.0051 (9)	0.0140 (10)
O1	0.0185 (7)	0.0193 (7)	0.0302 (7)	−0.0026 (6)	0.0079 (6)	0.0050 (6)
O2	0.0199 (8)	0.0220 (7)	0.0231 (6)	0.0028 (7)	0.0030 (5)	0.0037 (6)
O1W	0.0393 (10)	0.0182 (8)	0.0219 (7)	0.0031 (7)	0.0066 (7)	0.0011 (7)
Co1	0.0151 (2)	0.0155 (2)	0.01890 (19)	−0.00111 (18)	0.00467 (13)	−0.00020 (14)

Geometric parameters (Å, º)

C1—O1	1.256 (2)	C6—C4^i	1.393 (3)
C1—O2	1.273 (2)	C6—H6	0.9300
C1—C2	1.477 (3)	O1W—HW11	0.81 (3)
C2—C3	1.329 (3)	O1W—HW12	0.78 (3)
C2—H2	0.9300	Co1—O1	2.0754 (12)
C3—C4	1.468 (3)	Co1—O1^ii	2.0754 (12)
C3—H3	0.9300	O1W—Co1	2.0890 (15)
C4—C6^i	1.393 (3)	Co1—O1W^ii	2.0890 (15)
C4—C5	1.402 (3)	Co1—O2^iii	2.1072 (13)
C5—C6	1.380 (3)	Co1—O2^iv	2.1072 (13)
C5—H5	0.9300
O1—C1—O2	123.54 (17)	C1—O2—Co1^v	126.91 (11)
O1—C1—C2	116.55 (17)	Co1—O1W—HW11	125.0 (16)
O2—C1—C2	119.90 (16)	Co1—O1W—HW12	119 (2)
C3—C2—C1	122.86 (19)	HW11—O1W—HW12	104 (3)
C3—C2—H2	118.6	O1^ii—Co1—O1	180.0
C1—C2—H2	118.6	O1^ii—Co1—O1W^ii	95.27 (6)
C2—C3—C4	126.2 (2)	O1—Co1—O1W^ii	84.73 (6)
C2—C3—H3	116.9	O1^ii—Co1—O1W	84.73 (6)
C4—C3—H3	116.9	O1—Co1—O1W	95.27 (6)
C6^i—C4—C5	117.74 (18)	O1W^ii—Co1—O1W	180.0
C6^i—C4—C3	123.36 (17)	O1^ii—Co1—O2^iii	94.83 (5)
C5—C4—C3	118.89 (19)	O1—Co1—O2^iii	85.17 (5)
C6—C5—C4	121.0 (2)	O1W^ii—Co1—O2^iii	92.27 (6)
C6—C5—H5	119.5	O1W—Co1—O2^iii	87.73 (6)
C4—C5—H5	119.5	O1^ii—Co1—O2^iv	85.17 (5)
C5—C6—C4^i	121.26 (19)	O1—Co1—O2^iv	94.83 (5)
C5—C6—H6	119.4	O1W^ii—Co1—O2^iv	87.73 (6)
C4^i—C6—H6	119.4	O1W—Co1—O2^iv	92.27 (6)
C1—O1—Co1	133.87 (12)	O2^iii—Co1—O2^iv	180.0

Symmetry codes: (i) −x+1, −y−1, −z+3; (ii) −x+2, −y, −z+2; (iii) −x+2, y+1/2, −z+5/2; (iv) x, −y−1/2, z−1/2; (v) −x+2, y−1/2, −z+5/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—HW11···O2^vi	0.81 (3)	2.00 (3)	2.803 (2)	170 (2)
O1W—HW12···O1^v	0.78 (3)	2.28 (3)	3.010 (2)	155 (3)

Symmetry codes: (v) −x+2, y−1/2, −z+5/2; (vi) −x+2, −y−1, −z+2.