GEOMETRY AND ELECTRONIC-STRUCTURE OF CUCL64- POLYHEDRA DOPED INTO (3-CHLOROANILINIUM)(8)[CDCL6]CL-4 - AN EPR AND STRUCTURAL INVESTIGATION

The EPR single-crystal and powder spectra of mixed crystals of (3-chlo roanilinium)(8)(Cd1-xCuxCl6)C-4 are measured as a function of temperat ure and x and analyzed with respect to the geometry and bonding proper ties of the CuCl6 polyhedra. These undergo strong distortions due to v ibronic Jahn-Teller coupling, with the resulting tetragonal elongation being superimposed by a considerable orthorhombic symmetry component induced by a host site strain acting as a compression along the crysta llographic a axis. This strain becomes apparent in the cadmium compoun d (x = 0), whose crystal structure is also reported [a = 8.701(2) Angs trom, b = 13.975(2) Angstrom, c = 14.173(2) Angstrom, alpha = 81.62(1) degrees, beta = 72.92(1)degrees, gamma = 77.57(1)degrees, triclinic P1 , Z = 1]. A calculation of the ground state potential surface and its vibronic structure nicely reproduces the g values, Cu-Cl spacings, and ligand field data. At high copper concentrations (including x = 1), t he CuCl6 polyhedra are coupled elastically, with the long axes of neig hboring polyhedra having perpendicular orientations. antiferrodistorti ve type, however. Above about 55 K, the angular Jahn-Teller distortion component becomes dynamically averaged within the time scale of the E PR experiment, leading to local tetragonally compressed CuCl6 octahedr a.