Crystal preparation and properties of cesium tin(II) trihalides

Synthesis methods for cesium tin(II) trihalides via aqueous solution and from the melts of anhydrous halides, which ensure freedom from oxidation and the effects of traces of water, are described. The halide compounds CsSnCl ₃, CsSnBr ₂Cl, CsSnBr ₃, CsSnBr ₂I, CsSnBrI ₂, and CsSnI ₃ all have the cubic perovskite structure at elevated temperatures, and all but the first two are good electrical conductors in this form. The growth of single crystals from the melt, and by vapor transport, is outlined. The ³⁵Cl nuclear quadrupole resonance spectrum of monoclinic CsSnCl ₃ consists of three lines, with frequencies 9,799, 11.005, and 11.695 MHz at 25°C, confirming the presence of pyramidal SnCl ₃^- ions in this structure. In CsSnBr ₃, there is a single ⁸¹Br nuclear quadrupole resonance line, with frequency 63.073 MHz at 25°C, which splits into two lines on cooling the sample below 19°C. The low-temperature form of CsSnBr ₃ apparently has a tetragonally distorted perovskite structure, with a = 11.59 and c = 11.61 Å at 12°C. A single ¹²⁷I nuclear quadrupole resonance line was observed in the low temperature orthorhombic form of CsSnI ₃, with frequency 79.707 MHz at 25°C, and the variation of the frequency of this line with temperature may indicate a minor phase change in CsSnI ₃ at 35°C.