Phase Transitions in Tetramethylammonium Hexachloroplatinate(IV), -tellurate(IV), and -stannate(IV) as Studied by 35Cl NQR and Powder X-Ray Diffraction

Abstract

Abstract The 35Cl NQR spectra of [(CH3)4N]2PtCl6, [(CH3)4N]2TeCl6, and [(CH3)4N]2SnCl6 were recorded in a temperature range between 77 and ca. 350 K. Below room temperature, the temperature dependence measurements of NQR frequencies for all of these complexes confirmed the presence of structural phase transitions reported very recently. From the experiments of DTA carried out above room temperature, structural phase transitions were located at 385, 351, and 365 K in the same order of the above complexes. The X-ray powder patterns taken in the highest-temperature phase of these complexes (at ca. 390 K) were well interpreted as arising from the K2PtCl6-type cubic structure with the lattice constant a0=12.828, 13.053, and 12.975 Å for the Pt, Te, and Sn complexes, respectively. In this phase of each complex, however, no NQR spectra were observed. The mechanism of the phase transitions detected is discussed in connection with the structure of these complexes.