EPR AND ELECTRONIC-SPECTRA OF (3-CHLOROANILINIUM)8[CUCL6]CL4 - EVIDENCE FOR TETRAGONALLY ELONGATED CUCL6(4-) IONS WITH THE LONG AXIS DISORDERED IN 2-DIMENSIONS

The low-temperature electronic and electron paramagnetic resonance spe ctra of (3-chloroanilinium)8[CuCl6]Cl4 suggest that at the local level each CuCl64- ion has a tetragonally elongated octahedral coordination geometry, with a significant orthorhombic distortion, rather than the tetragonally compressed geometry suggested previously. However, the d irections of the long and intermediate Cu-Cl bonds are disordered, so that the bond lengths averaged over the unit cell correspond to a comp ressed tetragonal geometry. Magnetic susceptibility measurements sugge st coupling parameters similar to those reported previously, with weak antiferromagnetic interactions in the direction parallel to the short est Cu-Cl bond direction, and very weak ferromagnetic coupling in the plane normal to this direction, and it is shown that this is consisten t with the proposed disorder in the compound. A model describing the p otential surface and vibronic energy levels of the CuCl64- ion in term s of Jahn-Teller coupling and lattice strain interactions is presented , and correlated with the spectroscopic data and Cu-Cl bond lengths de rived from the X-ray thermal ellipsoids.