Tin and lead derivatives of a Schiff base – bis(orthoquinone) ligand

Abstract

The condensation of two molecules of 3,5-di-tert-butylcatechol (dbc) with ammonia under oxidizing conditions is believed to proceed via a keto-imine radical. Further condensation, and subsequent reaction with tin(II) or lead(II) halides, yields complexes of identical composition, M[dbqdi]2, where dbqdi is 3,5-di-tert-butyl-1,2-quinone-1-(2-hydroxy-3,5-di-tert-butylphenyl)imine anion; this name is used without prejudice as to the actual structure of the ligand. The two compounds differ in crystallographic and magnetic properties, and ESR measurements show that the tin compound has a triplet ground state. Both involve six-coordination of the metal in a distorted environment; tin is in the +IV state, but lead is +II, and there are corresponding differences in the form of the ligand. For SnIV(dbqdi)2, the crystal parameters are orthorhombic, space group C2221, a = 19.597(4), b = 24.375(4), c = 23.755(6) Å, Z = 8, and R = 0.073 for 1405 unique reflections. For PbII(dbqdi)2, monoclinic, space group P21/n, a = 14.56(1), b = 25.967(9), c = 15.13(1) Å, β = 99.81(7)°, Z = 4, R = 0.065 for 4911 unique reflections. The different complexation behaviour is shown to be a consequence of the redox properties of the two metallic elements. Keywords: tin, lead, ESR, coordination chemistry, electron transfer.