Vibrational spectroscopy at very high pressures. Part 28. Raman and far-infrared spectra of some complex chlorides A2MCl6 under hydrostatic pressure

Raman and far‐IR mode frequency shifts with pressure have been observed under hydrostatic conditions in a gasketed diamond anvil cell (d.a.c.). Using compressibilities calculated from unit cell constants and lattice energies, Gruneisen parameters γi have been obtained for all observed modes. Where previous data exist for comparison, it is shown that use of a d.a.c. without gaskets (i.e., applying a shear stress to the sample) greatly underestimates the true shifts of IR modes in particular. The Gruneisen parameter γ1 for a1g ν1 of the complex ions is always greater than γ2. It is shown that this is due to the greater value of anharmonicity of ν1, as is the increase in γ1, γ2, and γ3 in the series A2MCl6, where A=Cs, Rb, K. Gruneisen parameters for K2SnCl6 and Rb2TeCl6 are greater than for non‐transition metal complexes. Anomalies in the νi versus pressure curves for K2SnCl6 and [(CH3)4N]2MCl6 (M=Sn, Te, Pt) are discussed in relation to their structures. Shifts of νi with temperature for K2ReCl6 and K2...