Di-μ-acetato-bis-[(acetato-κO,O')bis-(iso-nicotinamide-κN)copper(II)]

The title centrosymmetric bimetallic complex, [Cu(2)(C(2)H(3)O(2))(4)(C(6)H(6)N(2)O)(4)], is composed of two copper(II) cations, four acetate anions and four isonicotinamide (INA) ligands. The asymmetric unit contains one copper cation to which two acetate units bind asymmetrically; one of the Cu-O distances is rather long [2.740 (2) Å], almost at the limit of coordination. These Cu-O bonds define an equatorial plane to which the Cu-N bonds to the INA ligands are almost perpendicular, the Cu-N vectors subtending angles of 2.4 (1) and 2.3 (1)° to the normal to the plane. The metal coordination geometry can be described as a slightly distorted trigonal bipyramid if the extremely weak Cu-O bond is disregarded, or as a highly distorted square bipyramid if it is not. The double acetate bridge between the copper ions is not coplanar with the CuO(4) equatorial planes, the dihedral angle between the (O-C-O)(2) and O-Cu-O groups being 34.3 (1)°, resulting in a sofa-like conformation for the 8-member bridging loop. In the crystal, N-H⋯O hydrogen bonds occur, some of which generate a head-to tail-linkage between INA units, giving raise to chains along [101]; the remaining ones make inter-chain contacts, defining a three-dimensional network. There are in addition a number of C-H⋯O bonds involving aromatic H atoms. Probably due to steric hindrance, the aromatic rings are not involved in significant π⋯π inter-actions.