A Study of Anonic Motions in Solid Rubidiumand Cesium Tetrachloroaurates(III)by Measuring the Temperature Dependence of Chlorine Nuclear Quadrupolar Relaxation Times

Abstract

Abstract The temperature dependences of 35Cl NQR frequencies and 35Cl nuclear quadrupolar relaxation times T1Q and T2Q were determined above 82K for Rb[AuCl4] and CsfAuClJ up to ca. 340 and 320 K, respectively. Below these temperatures two 35Cl NQR frequencies were observed for each complex whereas no resonance could be detected above the respective temperatures. For both complexes, T1Q observed below ca. 270 K was interpreted as mainly determined by the rotary lattice vibration around the pseudo-C4(C4) axis and each Cl-Au-Cl diagonal axis of the square planar complex anion, whereas T1q observed above ca. 270 K was definitely shown to be determined through the reorientation of the anions about their C′4 axis. The activation energies for the C′4 reorientation of the anions was evaluated to be 71 and 53 kJ mol-1 for the rubidium and cesium salts, respectively. The anionic dynamics are discussed by assuming the motion of the anions within and out of the C4 potential wells at lower and higher temperatures, respectively.