Complexes of transition metals with Schiff bases and the factors influencing their redox properties. Part I. Nickel and copper complexes of some diketone bisthiosemicarbazones

Abstract

A series of nickel complexes, containing a planar NiN₂S₂ co-ordination unit, where the ligand is a tricyclic tetradentate Schiff base derived from R¹CO·COR²(R¹= R²= H or Me; R¹= H, R²= Me), cyclohexane-1,2-dione, camphorquinone, hexane-2,5-dione, hexene-2,5-dione and phthaladehyde and either thiosemicarbazide or 4-methylthiosemicarbazide {NH₂·NH·C(:S)·NHMe}, have been prepared and characterised. Diacetylbis-(thiosemicarbazonato) copper(II), and its 3-ethoxybutane-1,2-dione bis-(4-methylthiosemicarbazonato) analogue, have also been prepared. A polarographic and cyclic voltammetric examination of these complexes has revealed that they undergo an ill defined, irreversible oxidation process, at ca.+1·0 V, but that they may be reduced in two, reversible, one-electron steps. The half-wave potentials for the reduction waves depend on the substituents attached to the periphery of the tricyclic ligand framework, on the central metal atom, and on the extent of the conjugation around the ligand. A macrocyclic complex, obtained by treatment of hexane-2,5-dione bis-(4-methylthiosemicarbazonato) nickel with αα′-o-dibromoxylene, has been prepared, and is believed to contain octahedrally co-ordinated nickel(II)(axial Br).