The Network Structure [SbHg2]GaCl4: An X‐Ray Study of a Temperature Driven Phase Transition

Abstract

Abstract[SbHg2]GaCl4 is a new compound forming red, transparent, air sensitive crystals with a cationic network [SbHg2]+ topologically related to cristobalite. Tetrahedral (GaCl4)− groups are located in suitable cavities. The title compound is the first example of this formula type with antimony and exists in a low (LT) and a high‐temperature (HT) modification (Tc = 277 K). The HT‐modification crystallizes in space group Pbcn (no. 60) with the lattice constants a = 1200.23(4) pm, b = 876.15(4) pm, c = 1750.83(6) pm (Z = 8, T = 293 K) whereas the LT‐modification crystallizes in Pna21 (no. 33) with a = 1743.30(6) pm, b = 874.36(5) pm, c = 1196.92(4) pm (T = 170 K). The phase transition is partially of first order and is investigated by a series of temperature dependent X‐ray single crystal measurements. The origin of the phase transition is most likely a significant librational disorder of the GaCl4 tetrahedra at higher temperatures which is frozen out in the LT‐modification. This becomes obvious from only one type of GaCl4 tetrahedra with unusual large anisotropic thermal parameters for the Cl atoms in the HT‐modification. In the LT‐modification two types of GaCl4 groups with significantly reduced thermal parameters and slightly different orientations are found. A comparison of the interatomic distances between the Cl atoms of the GaCl4 groups and atoms in the first coordination sphere gives evidence that in one orientation the interaction between Cl and Sb and in the other the interaction between Cl and Hg is optimized.