Potentiometric and spectroscopic study of mixed-ligand copper(II) complexes with N,N,N′,N",N"-pentamethyldiethylenetriamine and α- (or β-) alaninehydroxamic acids in water solution

Stabilities of the mixed-ligand complexes of Cu2+ ion with N,N,N'.N''.N''-pentamethyldiethylenetriamine [N,N,N',N'',N''-pentamethyl- bis(2-aminoethyl)amine}, Me(5)dien] as a primary ligand and alpha-alaninehydroxamic acid [2-amino-N-hydroxypropanamid, alpha-Alaha] or beta-alaninehydroxamic acid [3-amino-N-hydroxypropanamid, beta-Alaha] as a secondary ligand L and their absorption and EPR spectra at various pH values are reported. The visible spectra exhibit a characteristic red shift and a shoulder at lower energies indicating a five-coordinate structure of the formed complexes. The change of the EPR spectral parameters as a function of pH reflects two modes of an equatorial-axial chelation by the aminohydroxamic acid ligand L in the [CU(Me(5)dien)(HL)](2+) and [Cu(Me(5)dien)(L)](+) species. (C) 2002 Elsevier Science Ltd. All rights reserved.