We report here on the synthesis, crystal structure, optoelectronic and vibrational properties, as well as the DFT calculations of the novel trimethylsulfonium tin trichloride (CH3)3SSnCl3. The air-stable compound is prepared by reacting the (CH3)3SCl and SnCl2 solid precursors in evacuated silica tubes at 100 °C. According to powder X-ray diffraction and Rietveld refinement, it crystallizes at room temperature in the orthorhombic space group Pbca (No. 61) with isolated pyramids of [SnCl3]- and (CH3)3S+ units. UV-vis reflectance and photoluminescence spectroscopies reveal a direct energy band gap of 3.85 eV, accompanied by a broad Stokes-shifted luminescence signal. Photoexcitation of the compound at room temperature and at -196 °C results in broadband luminescence with weak magenta emission centered at 400 nm using an excitation at 250 nm. First principal calculations provide insight into the physical properties through the electron and phonon density of states. Multitemperature Raman spectroscopy and differential scanning calorimetry reveal a reversible phase transition at ca. 70 °C that affects the vibrational modes of the [SnCl3]-. By dissolving (CH3)3SSnCl3 in dimethylformamide in ambient air for a week, oxidation of tin occurs in the "defect" perovskite ((CH3)3S)2SnCl6. The crystal structure of ((CH3)3S)2SnCl6 is also determined with high accuracy via single-crystal X-ray diffraction (cubic space group Pa-3 (No. 205)) and compared with (CH3)3SSnCl3 via Hirshfeld surface analysis.