Structures and phase transitions in piperazinium hexachlorometallates, (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn. A X‐ray diffraction and 35Cl NQR study

Abstract

AbstractCrystal structures and the nature of the chemical bond in piperazinium hexachlorometallates (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn, were studied by X‐ray diffraction and 35Cl NQR spectroscopy. Piperazinium hexachlorostannate trihydrate shows a solid‐solid phase transition at Tc = 256 K. A disorder of the piperazinium ring and of one of the three water molecules appears in the high temperature phase (space group D122h‐Pnnm, a = 1147.5 pm, b = 959.9 pm, c = 719.4 pm, Z = 2). The disorder affects the 35Cl NQR spectrum. The low temperature phase of (C4H12N2)[SnCl6] · 3H2O reveals two 35Cl NQR lines, whereas in the high temperature phase only one resonance line was observed besides the existence of two crystallographically different chlorine atoms in the unit cell. — Piperazinium hexachlorotellurate crystallizes with space group D162h‐Pnma (a = 1398.5 pm, b = 1203.1 pm, c = 822.2 pm, Z = 4). The TeCl6 octahedra is strongly distorted, with the Te‐Cl bond lenghts differing by about 15%. This distortion is reflected in the 35Cl NQR spectra; the resonance lines are spread over a wide frequency range. — The crystal structure of piperazinium hexachloroplatinate (space group C32h‐C2/m, a = 1016.0 pm, b = 1184.7 pm, c = 695.2 pm, β = 130.227°, Z = 2) shows only small distortions in the PtCl6 octahedra. The two line 35Cl NQR spectrum at lower temperature is in agreement with the crystal structure. — Piperazinium hexachloroplumbate reveals a three 35Cl NQR lines at lower temperature. At Tc = 310 K a phase transition occurs and a one line 35Cl NQR spectrum appears. A hysteresis, about 5 K wide, is connected with the transition.