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.