Effect of the Lattice Field on the Electronic Structure and Dynamics of Copper-Hexahydrate in Tutton Salts

Previous structural and electron paramagnetic resonance (EPR) results are combined with new theoretical chemistry calculations on a series of copper-containing Tutton salts to investigate the influence of the host crystal electric field on the copper unpaired wave function and dynamics. Density functional theory (DFT) computations were performed on clusters centered on the host structure metal-hexahydrate complex to provide a model of atomic charges, which in turn were used to determine the electric fields and potentials at points along coordinate bonds of the complex. A significantly higher electric potential at the metal-water bonds is found for those Tutton salt systems having a greater copper EPR temperature dependency. Such a dependency has long been interpreted to arise from the averaging of tensor coupling parameters of the copper-hexahydrate complex due to a dynamic Jahn-Teller effect. However, the correlation found here reinforces a recent view that the coupling of the copper complex to the surrounding crystal lattice is the major determinant of these dynamics. The lattice potentials lack any significant temperature dependency and thus do not appear to be responsible for changes in the EPR patterns. A trend also appears between unbalanced spin in the compressed d-orbital lobe of the unpaired wave function and the magnitude of the potential. Hence, the lattice field is an important factor in defining both the electronic and dynamic characteristics of the copper-hexahydrate complex in these systems.