Solution Equilibrium and EPR Study of the Dinuclear Copper(II) Complexes of Aminopolycarboxylic Acids with an Alcohol OH Group in the Alkyl Chain Linkage

Abstract

Abstract Dinuclear copper(II) complexes of 2-hydroxy-1,3-diaminopropane-, 2-hydroxy-1,4-diaminobutane-, and 3-hydroxy-1,5-diaminopentane-N,N,N′,N′-tetraacetic acids (AC3O, AC4O, and AC5O) have been investigated by potentiometric titration, EPR and other spectroscopies. It has been confirmed that two or three different kinds of dinuclear complex species are formed in every ligand system, depending on the pH. In the complexes formed in the low-pH region, the two copper ions are coordinated independently by the two iminocarboxyl groups and have a weak magnetic dipolar interaction. In all of the three ligand systems the dinuclear complexes deprotonate the alcohol OH groups at low pH values (below 6) to form μ-alkoxo between the two copper ions. For AC3O and AC4O systems, the formation of μ-alkoxo and μ-hydroxo-double bridged complexes follows as the pH increases, while the AC5O system forms a double-bridged complex at a step from the non-bridged complex at pH 5.8. These mono-μ-alkoxo bridged and double-bridged complexes have fairly strong spin exchange interactions between the paramagnetic centers through the bridges. The length of the methylene linkage plays a role in determining the complex structures and magnetic interactions between the paramagnetic centers.