Synthesis, crystal structure and optoelectronic properties of [(CH₃)₃S]SnBr₃

We report on the preparation, crystal structure and spectral properties of the novel trimethylsulfonium tin tribromide, [(CH₃)₃S]SnBr₃. The compound was synthesized by the solid-state reaction of (CH₃)₃SBr and SnBr₂ in evacuated pyrex tubes at 150 °C. Single-crystal X-ray diffraction (SCXRD) studies at −173.15 °C show that it forms a 0D network of isolated pyramids of [SnBr₃]⁻ and (CH₃)₃S⁺ units in an orthorhombic structure (space group <i>P</i>2₁2₁2₁, No. 19, <i>a</i> = 9.4508(8) Å, <i>b</i> = 14.1691(12) Å, <i>c</i> = 15.4409(14) Å)). Powder X-ray diffraction (PXRD) and Le bail profile fit analysis reveals that [(CH₃)₃S]SnBr₃ adopts at room temperature a different crystal structure with space group (<i>P</i>mmm, No. 47). Moreover, the oxidation of the compound occurs gradually in ambient air, towards the formation of [(CH₃)₃S)]₂SnBr₆ (space group <i>P</i>a-3, No. 205). Multi-temperature Raman spectroscopy reveals that a fully reversible structural phase transition occurs for [(CH₃)₃S]SnBr₃ between −36 and −56 °C, as evidenced by the changes in the vibrational modes of the [SnBr₃]⁻ ions. A direct band gap of 3.38 eV at RT is determined <i>via</i> UV–vis diffuse reflectance spectroscopy. Photoluminescence spectroscopy at −196.15 °C and 25 °C shows a weak luminescence signal with an emission maximum at ca. 460 nm for both temperatures.