Structure of an imidazolate-bridged zinc dimer with tris(2-pyridyl)-methylamine ligand and magnetic properties of its copper dimer analogue

The compound [(tmpa)Zn(im)Zn(tmpa)](ClO4)(3) [where tmpa is tris(2-pyridyl)-methylamine and im is imidazolate anion] was synthesized, and its crystal structure was determined by X-ray diffraction methods. The structure consists of a dimeric complex bridged by the deprotonated imidazole. The geometry of the coordination polyhedron around the zinc(II) ions is very near to trigonal bipyramidal. The electronic spectrum indicates the corresponding copper(II) dimer has the same geometrical structure as the zinc(II) dimer. Its ESR powder X-band spectrum shows features typical of an S = 1 system. Variable-temperature (4.2-300 K) magnetic susceptibility data give the antiferromagnetic interaction parameter J = -32.0 cm(-1). This behaviour is best accounted for by a superexchange mechanism involving sigma-exchange pathways.