Comparisons of the interactions of benzene, furan and thiophene with Lewis acids: the rotational spectrum of thiophene⋯HF

Rotational constants, centrifugal distortion constants and H(D)F nuclear hyperfine coupling constants were determined for the three isotopomers [32S]thiophene⋯HF, [34S]thiophene⋯HF and [32S]thiophene⋯DF by pulsed-nozzle, Fourier-transform microwave spectroscopy. Interpretation of the spectroscopic constants suggests that the complex has a planar geometry of CS symmetry, with a long, weak hydrogen bond formed by HF to the π-electron density in the region of S. Determined geometrical parameters are: r(S⋯H)=2.98(5) Å, φ=65(1)°, with a deviation θ=34(6)° of the S⋯H–F nuclei from collinearity. Differences and similarities among the angular geometries of thiophene⋯HF, its congener furan⋯HF and benzene⋯HF are discussed.