Synthesis, electrochemical and magnetic properties of a series of new unsymmetrical macrocyclic binuclear copper(II) complexes

Abstract

A series of binuclear macrocyclic copper(II) complexes [Cu₂L][ClO₄]₂ have been prepared in which the two copper(II) ions are placed in two geometrically distinct co-ordination environments, comprising saturated and unsaturated nitrogen-donor sets. Cyclic voltammetry has revealed two reduction couples, Cu^IICu^II→ Cu^IICu^I and Cu^IICu^I→ Cu^ICu^I. The first is sensitive to the macrocyclic structure as well as to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials as the macrocycle size increases. The comproportionation constants K_com for the mixed-valence Cu^ICu^II complexes have been determined electrochemically. Cryomagnetic investigations (80–300 K) reveal a weak antiferromagnetic spin exchange between the copper(II) ions within each complex (J=–85 to –195 cm ^–1).