Tetrakis(μ-4-methylbenzoato-κ2 O:O′)bis[(isonicotinamide-κN)copper(II)]

In the title centrosymmetric binuclear complex, [Cu2(C8H7O2)4(C6H6N2O)2], the Cu atoms [Cu⋯Cu = 2.6375 (6) Å] are bridged by four 4-methylbenzoate (PMB) ligands. The four nearest O atoms around each CuII ion form a distorted square-planar arrangement, and the distorted square-pyramidal coordination is completed by the pyridine N atom of the isonicotinamide (INA) ligand. Each CuII ion is displaced by 0.2633 (1) Å from the plane of the four O atoms, with an average Cu—O distance of 1.974 (2) Å. The dihedral angles between carboxylate groups and the adjacent benzene rings are 7.88 (19) and 9.68 (10)°, while the benzene rings are oriented at a dihedral angle of 85.90 (9)°. The pyridine ring is oriented at dihedral angles of 8.59 (7) and 83.89 (9)° with respect to the benzene rings. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link the molecules into a three-dimensional network. π–π contacts between the benzene rings and between the pyridine and benzene rings, [centroid–centroid distances = 3.563 (2) and 3.484 (2) Å, respectively] may further stabilize the crystal structure.

In the title centrosymmetric binuclear complex, [Cu 2 (C 8 H 7 O 2 ) 4 (C 6 H 6 N 2 O) 2 ], the Cu atoms [CuÁ Á ÁCu = 2.6375 (6) Å ] are bridged by four 4-methylbenzoate (PMB) ligands. The four nearest O atoms around each Cu II ion form a distorted square-planar arrangement, and the distorted square-pyramidal coordination is completed by the pyridine N atom of the isonicotinamide (INA) ligand. Each Cu II ion is displaced by 0.2633 (1) Å from the plane of the four O atoms, with an average Cu-O distance of 1.974 (2) Å . The dihedral angles between carboxylate groups and the adjacent benzene rings are 7.88 (19) and 9.68 (10) , while the benzene rings are oriented at a dihedral angle of 85.90 (9) . The pyridine ring is oriented at dihedral angles of 8.59 (7) and 83.89 (9) with respect to the benzene rings. In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into a three-dimensional network.contacts between the benzene rings and between the pyridine and benzene rings, [centroid-centroid distances = 3.563 (2) and 3.484 (2) Å , respectively] may further stabilize the crystal structure.
In the crystal structure, intermolecular N-H···O hydrogen bonds (Table 2) link the molecules into a three-dimensional network, in which they may be effective in the stabilization of the structure. The π-π contacts between the benzene rings and benzene and pyridine rings, Cg1-Cg1 i and Cg3-Cg1 ii , [symmetry codes (i): 1 -x, -y, 1 -z; (ii) x, y, z -1, where Cg1 and Cg3 are centroids of the rings A (C2-C7) and C (N1/C17-C21)] may further stabilize the structure, with centroid-centroid distances of 3.563 (2) and 3.484 (2) Å, respectively.

Experimental
The title compound was prepared by the reaction of CuSO 4 .5H 2 O (1.25 g, 5 mmol) in H 2 O (50 ml) and isonicotinamide (1.22 g, 10 mmol) in H 2 O (20 ml) with sodium 4-methylbenzoate (1.58 g, 10 mmol) in H 2 O (150 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving green single crystals.
supplementary materials sup-2 Refinement Atoms H2A and H2B (for NH 2 ) were located in a difference Fourier map and refined isotropically. The remaining H atoms were positioned geometrically with C-H = 0.95 and 0.98 Å, for aromatic and methyl H atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and x = 1.2 for aromatic H atoms. Fig. 1. The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 20% probability level. Primed atoms are generated by the symmetry operator: (') 2-x, 2-y, 2-z.

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

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq