An electron spin resonance study of the copper(II) chelates of cyclobutane-1,1-dicarboxylic acid and their mixed ligand chelates

Abstract

The X-band e.s.r. spectra of the copper(II) chelate of cyclobutane-1,1-dicarboxylic acid formed in dimethylformamide, dimethyl sulphoxide, or trimethyl phosphate show that dimeric species are formed which give rise to magnetic dipole–dipole coupling in dimethylformamide or dimethyl sulphoxide and predominantly exchange coupling when trimethyl phosphate is used as the solvent. The introduction of salicyclic, mandelic, benzilic, malic, or citric acid results in the formation of monomeric mixed ligand complexes though minor amounts of dimeric species are present. The ‘triplet’ state spectra have been used to extract structural and magnetic parameters of the copper(II) dimeric chelates.