Tetrakis(μ-2-phenylacetato-κ2 O:O′)bis{[4-(dimethylamino)pyridine-κN 1]cobalt(II)}

The title compound, [Co2(C8H7O2)4(C7H10N2)2], crystallizes as a centrosymmetric dimer containing two CoII atoms bridged by four bidentate phenylacetate ligands in syn–syn bridging modes. Each CoII atom is five-coordinated by four O atoms from four different carboxylate ligands and the ring N atom of a 4-(dimethylamino)pyridine unit, generating a distorted square-pyramidal geometry in which the four O atoms form the basal plane and the N atom occupies the axial position. In the crystal, C—H⋯O interactions link the dinuclear complex molecules into a three-dimensional network.

The title compound, [Co 2 (C 8 H 7 O 2 ) 4 (C 7 H 10 N 2 ) 2 ], crystallizes as a centrosymmetric dimer containing two Co II atoms bridged by four bidentate phenylacetate ligands in syn-syn bridging modes. Each Co II atom is five-coordinated by four O atoms from four different carboxylate ligands and the ring N atom of a 4-(dimethylamino)pyridine unit, generating a distorted square-pyramidal geometry in which the four O atoms form the basal plane and the N atom occupies the axial position. In the crystal, C-HÁ Á ÁO interactions link the dinuclear complex molecules into a three-dimensional network.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LR2113).

Comment
The N-heteroaromatic ligand 4-(dimethylamino)pyridine (DMAP) finds use as a homogeneous catalyst in cellulose acylation in the synthesis of biodegradable plastics (Satgé et al., 2004). DMAP is also known to form transition metal complexes which exhibit luminescence properties (Araki et al., 2005). Our interest in cobalt(II) carboxylates with DMAP evolves from their catalytic activity. Moreover, carboxylic acid complexes of cobalt(II) have properties of special interest in the fields of biology and magnetism (Cotton et al., 1999). The coordination chemistry of centrosymmetric dinuclear Co 2+ complexes bridged by carboxylates has been investigated (Cui et al., 1999, Catterick et al., 1977. In order to explore further the coordination behaviour of the Co 2+ ion, the title complex, incorporating phenylacetate and DMAP as co-ligand has been prepared and its crystal structure is reported here. The title molecule is a centrosymmetric dimer with four bidentate phenylacetate groups as bridging ligands between two Co II centres, to each of which a DMAP group is also coordinated, as shown in Fig (Cui et al., 1999) and benzoate (Catterick et al., 1977). The Co(II) atom is 0.2286 (2) Å from the mean plane formed by the four equatorial O atoms. On the other hand, the coordinated N2 atom also lies in the same direction, at a distance of 2.2643 (13) Å from the plane. The dihedral angles between the mean planes through the C10-C15 and C18-C23 benzene rings and the DMPA plane are 7.46 (9)° and 72.08 (9)°, respectively. The dihedral angle between the 87.22 (4)°, which is close to the ideal value of 90°. Nonclassical C-H···O hydrogen bonds (Table 1)

Experimental
CoCl 2. 2H 2 O (0.116 g,1 mmol) was dissolved in methanol (10 ml). To this solution, phenyacetic acid (C 6 H 5 CH 2 COOH; 0.136 g, 1 mmol) was added and the mixture was stirred for ca 10 min to obtain a bleu solution. 4-(Dimethylamino)pyridine (0.122 g, 1 mmol) was added and the mixture was stirred for an additional 2 h. Single crystals suitable for X-ray diffraction were obtained from a methanol solution of the title complex by slow evaporation.

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Symmetry code, (i):1 -x, -y, -z.

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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.