Aggregation and Conformations in Dimethyl, Diethyl, and Dipropyl Sulfides at Low Temperature and High Pressure

The interplay between molecular aggregation and conformations of the three simplest dialkyl sulfides, S(CnH2n+1)2, dimethyl (DMS), diethyl (DES), and dipropyl (DPS) sulfide, has been investigated by in situ single-crystal X-ray diffraction and Raman spectroscopy as a function of temperature and pressure. Chalcogen bonds S···S are clearly favored in the structures of DMS and DPS polymorphs, but not in the exceptionally stable DES monomorph, whereas hydrogen bonds CH···S are present in all of the structures. DMS forms two new polymorphs at high pressure: a triclinic phase β up to 2.5 GPa and a monoclinic phase γ above. Under pressure, DES crystallizes in the same atmospheric monoclinic space group P21/n, maintaining an all-trans conformation up to ca. 15 GPa at least. In contrast, DPS exhibits conformational flexibility, crystallizing at low temperature in a monoclinic TGGT phase α of space group Cc, and, under compression, into a triclinic TTGT phase β of space group P1̅. At higher pressure, a transition toward the all-trans TTTT form occurs above 7 GPa, as indicated by Raman spectroscopy and supported by DFT calculations. These results highlight the unique conformational adaptability of sulfides under pressure and provide new insights into their crystal packing and intermolecular interactions.