The structure, redox properties, and reactions of some planar [MIIN4] chelate compounds of cobalt, nickel, and copper, and their oxidised products, including paramagnetic cobalt(III) species

Abstract

An investigation is reported of the structure and some reactions of the cobalt(II), nickel(II), and copper(II) compounds of several tricyclic quadridentate di-anionic Schiff's base ligands derived from o-aminobenzaldehyde and various diamines. The ligands are 1,2-bis-(o-iminobenzylideneamino)ethane (aben), 1,2-bis-(o-iminobenzyl-ideneamino)propane (abpn), 1,3-bis-(o-iminobenzylideneamino)propane (abtn), and 1,2-bis-(o-iminobenzylideneamino)phenylene (abphen). The physicochemical data presented are supplementary to that of two recent papers in proving a four co-planar co-ordination polyhedron in the metal(II) compounds. In addition, a polarographic study of the redox behaviour of these compounds indicates that all should have chemically accessible higher oxidation states. Attempts to prepare the nickel and copper oxidation products of the type [M(L)X](X= Br, I) gave only amorphous solids which have not been characterised. But the crystalline compounds [Co(L)X](X= Cl, Br, I) which were readily isolated, are unique examples of paramagnetic cobalt(III) compounds with nitrogen-donor ligands. A square-pyramidal five-co-ordinate structure is postulated. These compounds react in donor solvents such as pyridine to form six-co-ordinate diamagnetic species of the type [Co(L)(solvent)X]. The crystalline diamagnetic compound [Co(aben)(py)Cl] has been isolated, and evidence is given for an equilibrium in the solutions in donor solvents between the diamagnetic and paramagnetic species.