Magnetic and electrochemical studies on binuclear copper(II) complexes derived from 2,6-diacetyl-4-methylphenol: the X-ray and molecular structure of an acyclic, binuclear Schiff-base complex

Abstract

The syntheses of binuclear copper(II) complexes derived from 2,6-diacetyl-4-methylphenol are reported. Magnetic susceptibility measurements in the temperature range 6–300 K establish that the two Cu²⁺ in bis(2,6-diacetyl-4-methylphenolato)dicopper(II) diperchlorate (3) and µ-[2,6-bis(5′-amino-1′-methyl-2′-azapent-1′-enyl)-4-methylphenolato]-µ-hydroxo-diperchloratodi-copper(II)(4) are antiferromagnetically coupled with the singlet–triplet separation 2J=–460 and –493 cm^–1, respectively. In bis[4-methyl-2,6-bis(1′-oxido-3′-oxobut-1′-enyl)phenol]dicopper(II)(5), on the other hand, the two Cu²⁺ are magnetically independent. Electrochemical studies of the three compounds in dimethyl sulphoxide solutions reveal highly irreversible behaviours due to chemical and/or stereochemical changes subsequent to electron transfer. Upon reduction, (3) and (4) give stable copper(I) species, but (5) is reduced directly to copper metal. The crystal structure of complex (4) is triclinic, R= 0.0605, for 3 074 reflections. The molecule comprises a binuclear copper(II) cation in which the metals are separated by 2.9571(15)Å and asymmetrically bridged by an endogenous phenoxy-bridge and an exogenous hydroxy-bridge.