Synthesis, electrochemical and magnetic properties of new macrocyclic copper(II) complexes derived from 2,6-diacetyl-4-4-methylphenol

Abstract

A series of binuclear macrocyclic copper(II) complexes [Cu2Lm,n](ClO4)2·xH2O have been prepared in which the two copper(II) ions are placed in two geometrically distinct co-ordination environments. The macrocycles with two 2,6-bis(iminomethyl)-4-methylphenol entities combined through two different lateral chains, –(–CH2–)–m and –(–CH2–)–n (m = 2 or 3, n = 2 to 5) were synthesized by stepwise cyclization. Cyclic voltammetry shows the presence of two reduction couples: CuIICuII CuICuII and CuIICuI CuICuI. The comproportionation constants, Kcom, for the mixed valence CuICuII complexes have been determined electrochemically. The Kcom value increases in the order of the macrocycles: (L2,2)2−<(L2,3)2−<(L2,4)2−<(L2,5)2− and (L3,3)2−<(L3,4)2−<(L3,5)2−. Cryomagnetic investigations (80–300K) reveal a moderately strong antiferromagnetic spin exchange between the copper(II) ions within each complex (J = −210 to −390 cm−1).