Macrocyclic ligand design. Interaction of a series of successively N-benzylated derivatives of 1,4,8,11-tetraazacyclotetradecane (cyclam) with copper(II) and nickel(II)

The interaction of a series of N-benzylated cyclam ligand derivatives incorporating from one to four benzyl groups with nickel(II) and copper(II) is reported. The isolation of a selection of 1 : 1 (metal : ligand) complexes of both metals has been carried out and visible spectral, EPR, electrochemical and X-ray determinations have been employed to probe the nature of the respective complexes in both the solid state and in solution. Emphasis has been given to investigating the effect of the successive N-benzylation along this ligand series on the properties of the above complexes. The UV-VIS spectra obtained for each series of metal complexes indicate that the sequential introduction of N-benzyl substituents produces a change to lower ligand fields of the corresponding macrocyclic tetramines. Cyclic voltammograms of both the nickel(II) (low-spin) and copper(II) complexes both yield evidence for M(III)/M(II) as well as M(II)/M(I) couples in acetonitrile.