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-chloroanilinium) 8(Cd 1-xCu xCl 6)Cl 4 are measured as a function of temperature and x and analyzed with respect to the geometry and bonding properties of the CuCl 6 polyhedra. These undergo strong distortions due to vibronic 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 crystallographic a axis. This strain becomes apparent in the cadmium compound (x = 0), whose crystal structure is also reported [a = 8.701(2) Å, b = 13.975(2) Å, c = 14.173(2) Å, α = 81.62(1)°, β= 72.92(1)°, γ = 77.57(1)°, triclinic P1̄, 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), the CuCl 6 polyhedra are coupled elastically, with the long axes of neighboring polyhedra having perpendicular orientations. The elastic correlation presumably is not of the long-range antiferrodistortive type, however. Above about 55 K, the angular Jahn - Teller distortion component becomes dynamically averaged within the time scale of the EPR experiment, leading to local tetragonally compressed CuCl 6 octahedra.