New dimeric copper(II) complex [Cu(5-MeOsal)2(μ-nia)(H2O)]2 with magnetic exchange interactions through H-bonds

The synthesis and characterization (elemental analysis, IR, electronic and EPR spectra as well as magnetization measurements over the temperature range 1.8 K-300 K) of solid complex [Cu(5-MeOSal)(2)(mu-nia)(H2O)](2) (1; 5-MeOsal = 5-methoxysalicylate, nia = nicotinamide) is reported together with the crystal structure. In blue-green complex 1, two Cu(5-MeOsal)(2)(H2O) units are held together by a pair of biclentate nonchelating nicotinamide ligands, which form a (CuNC3O)(2) ring. Each Cu atom adopts a distorted square-pyramidal geometry. The oxygen atoms from two unidentate 5-MeOsal anions occupy the trans position, a water molecule and the pyridine N atom of nicotinamide build the basal plane and a carboxamide O atom occupies the apical position. The separation between two Cu atoms within the centrosymmetric dimer is 6.940(2) angstrom. The dimeric units are self-assembled across a centre of symmetry by the formation of two pairs of strong hydrogen bonds, which create a one-dimensional polymeric structure with the interdimer Cu center dot center dot center dot Cu separation 4.901(2) angstrom. It is believed that these hydrogen bonds between the copper(II) atoms are responsible for the unique magnetic properties of compound 1. The magnetic susceptibility of complex 1 exhibits a maximum at 6 K. A satisfactory explanation was found with the Bleaney-Bowers equation for Cu-Cu interaction through carboxylato groups and H-bond bridges (2J = -6.83 cm(-1)). An additional molecular field correction that was used to characterize the interaction across the nia bridges is assumed to be extremely weak (zJ' = -0.28 cm(-1)).