Di-μ-acetato-bis­[(acetato-κ(2) O,O′)bis­(iso­nicotinamide-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 inter­actions.