Spectroscopic and electrochemical aspects of copper(II) chelates containing 1,2-diamines and β-ketoenols

Abstract

The IR and electronic excitation spectra of a series of new copper(II) chelates containing the anion of a β-ketoenol (β-dione) and N,N-dimethyl- N′-ethyl-ethylenediamine (dmeen) were obtained in the solid state and in solution. Electrochemical measurements indicate enhanced stability of the ternary chelates. Their spectra suggest, in conjunction with other physicochemical measurements, that the chelate rings in the [Cu(β-dionato)(dmeen)] + entity are coplanar. The substituents within the β-ketoenolato moiety induce electronic effects that affect the energy levels of the molecules, influence the extent of covalent interactions between the metal centre and bulky weakly coordinating anions, change the ligand field strength and may alter the course of the reaction. Solvatochromic shifts demonstrate the Lewis acidity inherent in these chelates and the tendency of the copper(II) ion to achieve coordination saturation. As good linear correlation between the donor number of a series of solvents and the energy of ligand field transitions pertains, such ternary chelates may be employed to assess the Lewis basicity of liquids.