Chemical exchange reaction of glycinatocopper(II) complex in water: a theoretical study

The axial water exchange on glycinatocopper(II) complexes was theoretically investigated by using density functional theory (DFT) calculations. Glycinatocopper(II) complexes are well-known by the diffusion controlled exchange of axial ligands. Calculations using explicitly coordinating water molecules and solvent models showed that bis-glycinatocopper(II) complexes have a four-coordinate planar structure, in which waters are excluded from the axial positions of Cu(II) due to the Jahn-Teller effect. This may be because coordinating axial waters induce the discrepancy in the most stable ligand field splittings of inner 3d and outer 4d orbitals of the Cu(II) cation. To estimate the reactivity of the axial water exchange, we calculated the rate constant by calculating Gibbs free energies for the activation. As a result, we obtained the rate constant as k = 3.61 x 10(10) s(-1) in aqueous solution at T = 298.15 K. This rate constant is slightly larger than that of the diffusion controlled exchange of axial waters, which is experimentally observed in the order of 10(9) s(-1). Finally, we determined the structures of tris-glycinatocopper(II) complexes. It was consequently found that the third glycine is coordinated to Cu with the amino groups as experimentally observed.