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

A series of binuclear macrocyclic copper(II) complexes [Cu₂L^m,n](ClO₄)₂·xH ₂O 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: Cu^IICu^II Cu^ICu^II and Cu^IICu^I Cu^ICu^I. The comproportionation constants, K_com, for the mixed valence Cu^ICu^II complexes have been determined electrochemically. The K_com value increases in the order of the macrocycles: (L^2,2)^2- < (L^2,3)^2- < (L^2,4)^2- < (L^2,5)^2- and (L^3,3)^2- < (L^3,4)^2- < (L^3,5)^2-. Cryomagnetic investigations (80-300 K) reveal a moderately strong antiferromagnetic spin exchange between the copper(II) ions within each complex (J = -210 to -390 cm^-1).