Über Caesiumtrichloromercurat(II) CsHgCl3: Lösung einer komplexen Überstruktur und Verhalten unter hohen Drücken

About Cesium Trichloromercurate(II) CsHgCl₃: Solution of a Complex Superstructure and Behaviour under High Pressure By solving the crystal structure of CsHgCl₃ a new uncommon distortion variant of the cubic perovskite type with extremely (2 + 2 + 2)‐distorted HgCl₆ octahedra has been found. The trigonal superstructure with space group P3₂ and ninefold cell contents differs from the aristotype only so far, as 2/3 of the Cl‐atoms are moved away from their ideal positions leading to 3 pairs of different Hg–Cl distances with about 2.35 Å, 2.71 Å and 3.15 Å. The cations Cs⁺ and Hg²⁺ and the chloride ions with medium Hg–Cl distance keep the ideal positions of a cubic perovskite lattice. Due to the evenly distribution of the three different bonds in the three directions of cubic space the cell shows an almost perfect cubic metric. Raman spectra and powder diffraction experiments up to pressures of 5 GPa demonstrated that the ideal perovskite arrangement is stabilized with increasing pressure. The shift of the FT‐Raman bands show in agreement with spectra simulations that the Hg–Cl bonds are equalized, leading to a regular octahedral co‐ordination of the Hg atoms. The disappearance of the Raman spectrum at P > 3.4 GPa indicates that the high pressure phase forms an ideal cubic perovskite (a = 5.204(1) Å, Hg–Cl = 2.60 Å).