X-Ray Diffraction and Nuclear Quadrupole Resonance Studies of Chromium Trichloride

The infinite-layer compound CrCl3 is found to undergo a first-order phase transformation near 240°K. The crystal structures of the high- and low-temperature phases have been elucidated by detailed x-ray diffraction and 35Cl nuclear quadrupole resonance studies. The previously reported structure for CrCl3 is shown to be incorrect. The present single-crystal diffraction results at 298° and 225°K give monoclinic (C2/m: a0=5.959 Å, b0=10.321, c0=6.114 Å, β=108.49°) and rhombohedral (R3̄: a0=5.942 Å, c0=17.333 Å) structures, respectively. The 35Cl quadrupole resonance frequencies, measured in polycrystalline samples, have been compared with results of field-gradient calculations based on the ionic point-charge model. The ionic contribution accounts for a large fraction of the total gradient making it impossible to evaluate the covalency parameters of the Cr–Cl bonds from the measured quadrupole coupling constants.