The crystal structures were determined by means of Rietveld analysis of X-ray powder diffraction data. They belonged to a tetragonal system in which both the Al and Cu atoms were surrounded tetrahedrally by 4 halogen atoms. The Al-Cl(Br) and Cu-Cl(Br) bond lengths were 0.210 (0.226)nm and 0.239 (0.245)nm, respectively. Nuclear magnetic resonance studies of monocrystals, using 63Cu, suggested that the principal axis of the e2Qg/h tensor was parallel to the c-axis. The quadrupole coupling constants were estimated to be 0.89 and 0.35MHz for the Cl and Br analogues, respectively. The temperature dependences of line-widths and line-shapes indicated that the activation energies for Cu+ diffusion were 48.5 and 46.4kJ/mol for CuAlCl4 and CuAlBr4, respectively. The spin-lattice relaxation times of the 35Cl and 81Br NQR signals were also affected by Cu+ diffusion.

K.Yamada, Y.Tomita, T.Okuda: Journal of Molecular Structure, 1995, 345, 219-27