Molecular structures of tetrabromothiophene and -selenophene as determined by gas-phase electron diffraction and high-level quantum chemical calculations

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The molecular structures of tetrabromothiophene and tetrabromoselenophene were studied by gas-phase electron diffraction and quantum chemical calculations. Calculations at the DFT/B3LYP and MP2 levels of theory confirm that the molecules possess a planar structure in the gas phase. MD simulations were performed for both molecules. Definitive gas-phase molecular structures of tetrabromothiophene and tetrabromoselenophene are reported, based on refinements of electron diffraction data starting from different input geometries. The single-crystal structure of tetrabromoselenophene is also reported. Geometries of all tetrabromochalcogenophenes, C4Br4X (X=O, S, Se, Te), were calculated and trends in the geometrical parameters along the series are discussed.