In situ Crystallization of Methanesulfonic Acid, CH₃SO₃H, and Serendipitous Single Crystal Formation of its Anhydride, (CH₃)₂S₂O₅

Methanesulfonic acid, CH 3 SO 3 H, has been crystallized using an in situ technique on a single crystal diffractometer. The crystal structure is monoclinic ( P 2 1 / 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, (CH 3 ) 2 S 2 O 5 , formed as a side product in the reaction of bis ‐trimethylsilyl‐sulfate, [(CH 3 ) 3 SiO] 2 SO 2 with SO 3 in a sealed glass ampoule. The monoclinic crystal structure ( P 2 1 / 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 (CH 3 ) 2 S 2 O 5 molecules in the unit cell. According to the orientation of the CH 3 groups with respect to each other the (CH 3 ) 2 S 2 O 5 molecule appears as the so‐called trans ‐conformer. The structure of both molecules is corroborated by quantum mechanical DFT calculations.