TEMPERATURE-DEPENDENCE OF THE CRYSTAL-STRUCTURE AND EPR-SPECTRUM OF BIS(1,3,5-TRIHYDROXYCYCLOHEXANE)COPPER(II) TOSYLATE - A UNIFIED INTERPRETATION USING A MODEL OF DYNAMIC VIBRONIC COUPLING

The crystal structure of bis(1,3,5-trihydroxycyclohexane)copper(II) to sylate is reported at temperatures of 293, 233, 188, 163, and 93 K, as are the structures of the Zn(II) and Ni(II) analogues at room tempera ture for comparison. The isomorphous compounds are triclinic, space gr oup P (1) over bar, with one formula unit in the unit cell. The unit c ell parameters of the Cu compound at 293 K are a = 6.456(5) Angstrom, b = 9.505(3) Angstrom, c = 12.544(3) Angstrom, alpha = 76.57(2)degrees , beta = 87.48(4)degrees, gamma = 76.65(4)degrees. The centrosymmetric ZnO6 and NiO6 octahedra are tetragonally compressed with a slight ort horhombic distortion. The Cu-2+ polyhedra exhibit similar geometries, but with considerably larger deviations from a regular octahedron. Two of the three independent Cu-O bond lengths and two of the g-values ch ange significantly as a function of temperature. A model of dynamic vi bronic coupling is presented which explains both the EPR and structura l data. Vibronic wave functions associated with a Jahn-Teller potentia l energy surface modified by an orthorhombic lattice ''strain'' are gi ven. The temperature dependence of the structures is calculated from t he nuclear parts and that of the g-values from the electronic parts of the wave functions. The temperature dependence of the structures and g-values is also interpreted using a simpler model involving an equili brium between two forms of the complex which differ solely in their or ientation in the crystal lattice, and the results of the two approache s are compared.