The influence of high hydrostatic pressure on the crystal structure of cesium gold chloride (Cs₂Au^IAu^IIICl₆) in the pressure range up to 52 × 10⁸ Pa

Using a gasketed diamond-anvil high-pressure cell, which has been adapted to the automatic four-circle diffractometer, we have studied the structural changes of single crystals of the mixed-valence compound Cs₂Au^IAu^IIICl₆ under high hydrostatic pressure. Measurements with a modified measuring procedure at different pressures show a continuous decrease in the lattice constants. The changes in the relative volume are about 19% in the pressure range up to 52 x 10⁸ Pa while the a/c ratio remains constant. The Cl atoms, which coordinate with the different gold atoms in the form of strongly distorted octahedra, move towards the symmetrical position between the Au^I and Au^III atoms as the pressure increases. At about 52 x 10⁸ Pa the gold atoms become indistinguishable, this means only formal Au²⁺ atoms are present.