Structural characterization of a series of new Cu-dipeptide complexes in solid state and in solution

Abstract

Four new Cu(II)-dipeptide complexes were studied in solid state and in solution. They were synthesised and characterised by infrared, electronic and EPR spectroscopic techniques. The crystal structure of [ Cu ( gly - val ) ] · 1 2 H 2 O , [Cu(val-gly)], [Cu(val-phe)] and [Cu(phe-phe)] was determined by X-ray diffraction methods. In all the complexes the Cu(II) ion is in a pyramidal-square based environment, equatorially coordinated to a terminal NH 2 group, the deprotonated amide group and one of the oxygen atoms of the carboxylate group. The fourth equatorial ligand is a carboxylate oxygen of a second dipeptide molecule and the fifth coordination position is occupied by the oxygen of an amide group belonging to a third dipeptide molecule. The structural study of the complexes in solution by EPR and electronic spectroscopy suggests that in the frozen solutions the complexes exist mostly as polymeric species while the monomer moiety becomes significant at the lowest concentrations studied. It can also be concluded that, at room temperature, the solutions mainly contain monomeric species.