An EPR study of copper(II)-substituted biguanide complexes. Part III

The EPR and optical spectra of bis(diethylbiguanide)copper(II) base and its salts and mono(diethylbiguanide)copper(II) salts have been measured both in the solid state and in N,N-dimethylformamide (DMF) in order to elucidate the structure and nature of the bonding between the central metal atom and the ligand. From the spectral data the degree of covalency of σ- and π-bonds of the copper(II) ion with the nitrogen atoms of the ligands have been calculated. The σ-bonds present a moderate degree of covalence while the in-plane π-bonds possess a strong covalent character. The covalency of the biguanide complexes is attributed to the strong σ-interaction of the copper(II) ion with deprotonated imino ligand bonding sites and electron delocalization over the chelate ring. The superfine structure of some compounds may be ascribed to the interaction of the unpaired electron of the copper(II) ion with four equivalent or nearly equivalent nitrogen atoms of the ligands. The general properties of the complexes studied, which contain the equivalent CuN42− chromophore, are summarized.