Abstract:

The title centrosymmetric bimetallic complex, [Cu2(C 2H3O2)4(C6H 6N2O)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 CuO4 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.