Five-co-ordination in molecular complexes of zinc, cadmium, and mercury(II) with potentially ter- or tetra-dendate ligands with nitrogen donor atoms

Abstract

Complexes of zinc, cadmium, and mercury(II) halides with several potentially ter- and tetra-dendate ligands with nitrogen donor atoms are assigned either five- or six-co-ordinate structures on the basis of physical measurements. The potentially tetra-dendate ligands may use either three or four of the donor nitrogen atoms in bonding, depending on the metal ion and the steric demands of the ligand. 1H N.m.r. spectra indicate rapid exchange between co-ordinated and unco-ordinated nitrogen atoms.The results show that with the type of ligand studied zinc and mercury(II) have comparable capacities for five-co-ordination. The incidence of six-co-ordination is Cd > Zn ≃ Hg.