HYDROSTATIC-PRESSURE EFFECTS ON THE PHASE-TRANSITIONS IN [Z(CH3)(4)](2)CUCL4 (Z=N, P)

X-ray diffraction studies of [Z(CH3)(4)](2)CuCl4 (Z = N, P) single cry stals have been carried out under hydrostatic pressure at room tempera ture. In [N(CH3)(4)](2)CuCl4, phase transitions take place successivel y, to a monoclinic phase with a unique axis along b (space group, C-2h (5)-P12(1)/c1) at 1.4 GPa, to another monoclinic phase with a unique a xis along c (C-2h(5)-P112(1)/n) at 1.7 GPa, and then to an orthorhombi c phase (D-2(4)-P2(1)2(1)2(1)) at 3.4 GPa, accompanied by a discontinu ous change in the crystal color from light yellow to dark green. By co ntrast, in [P(CH3)(4)](2)CuCl4 no pressure-induced phase transition wa s detected, and its crystal color continuously changes from light yell ow to light yellow green with pressure. The color changes of both crys tals are considered to be a result of changes in CuCl42- anion geometr y.