In situ crystallization of methanesulfonic acid, CH3SO3H, and serendipitous single crystal formation of its anhydride, (CH3)2S2O5

Methanesulfonic acid, CH3SO3H, has been crystallized using an in situ technique on a single crystal diffractometer. The crystal structure is monoclinic (P21/c, Z = 4, a = 842.07(4) pm, b = 582.20(3) pm, c = 820.38(4) pm, β = 106.459(2)°) and stamped by the presence of strong hydrogen bonds. Single crystals of the anhydride of methanesulfonic acid, (CH3)2S2O5, formed as a side product in the reaction of bis‐trimethylsilyl‐sulfate, [(CH3)3SiO]2SO2 with SO3 in a sealed glass ampoule. The monoclinic crystal structure (P21/n, Z = 12, a = 1794.5(2) pm, b = 831.75(7) pm, 1383.4(1) pm, β = 110.630(4)°) shows three crystallographically different (CH3)2S2O5 molecules in the unit cell. According to the orientation of the CH3 groups with respect to each other the (CH3)2S2O5 molecule appears as the so‐called trans‐conformer. The structure of both molecules is corroborated by quantum mechanical DFT calculations.