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

The Cu2+(aq) forms inner sphere type complexes with surface functional groups of hydrous δ-Al3O3, TiO2 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-nCu(H2O)n + 2?n = 2 for δ-Al3O3, one type of SiO2; ( MeO)4-Cu(H2O) for TiO2 (Anatase), and one type of SiO3. 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-Al3O3 of the type ( AlO)3 CuL1 L2(H2O)2. (L1L3 = 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.