Interpretation of the temperature dependent g values of the Cu(H2O)2+6 ion in several host lattices using a dynamic vibronic coupling model

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Abstract
The causes of the previously reported temperature dependence of the g values of the Cu(H2O)2+6 ions in Cu2+ doped Zn(H2O)6(GeF6) and the Tutton’s salts M2Zn(H2O)6(SO4)2, where M=K+, Rb+, NH+4, and Cs+, supplemented by new experimental measurements on the K+ salt, have been investigated. The ground state dynamics of the complexes have been modeled on the cubic E×ε Jahn–Teller Hamiltonian perturbed by an orthorhombic lattice strain. For each compound, the vibronic energy levels and associated wave functions were calculated numerically, the overall g values at any temperature being given by a thermal average of the g values of the individual vibronic energy levels, because of rapid exchange between the levels. For the Tutton’s salts it was found that the low temperature g values are strongly influenced by the tetragonal component of the lattice strain, with this corresponding to an axial compression of the ligand field. The temperature dependence of the g tensors, on the other hand, was found to depend largely on the orthorhombic component of the lattice strain. For the K+ and NH+4 salts, where structural data are available, the strain parameters derived using the model are in good agreement with the geometries reported for the Zn(H2O)2+6 host complexes. For Cu2+ doped Zn(H2O)6(GeF6) the model implies a lattice strain of tetragonal symmetry corresponding to a slight elongation of the axial metal–ligand bonds. The results are compared with those reported previously by Silver and Getz, and other workers, who used a simple model involving temperature dependent equilibria between energy levels corresponding to different orientations of the Cu(H2O)2+6 ions in the host lattices to interpret the temperature dependence of the g tensors.