Correlation of EPR-parameters with thermodynamic stability constants for copper(II) complexes Cu(II)-EPR as a probe for the surface complexation at the water/oxide interface

Abstract

The Cu 2+(aq) forms inner sphere type complexes with surface functional groups of hydrous δ-Al 3O 3, TiO 2 and some silicas. EPR-parameters indicate that a pseudo square geometry around the Cu(II)-center is retained. The complexes formed are suggested to be of the type ( MeO) 4- n Cu(H 2O) n + 2? n = 2 for δ-Al 3O 3, one type of SiO 2; ( MeO) 4-Cu(H 2O) for TiO 2 (Anatase), and one type of SiO 3. A model is established which enables the estimation of thermodynamic stability constants of the surface complexes from the EPR-parameter g #. The potential of the model is demonstrated in a series of ternary complexes on δ-Al 3O 3 of the type ( AlO) 3 CuL 1 L 2(H 2O) 2. (L 1L 3 = bidentate ligand): Speciation of Cu(II) and stability constants can be obtained. The model opens new possibilities for the interpretation of the behaviour or Cu(II) in biological systems. A major revision of the current conception of cation adsorption in layer silicates and some catalytic systems (e.g. zeolites) is presented.