Noncovalent interactions of aromatic heterocycles: rotational spectroscopy and theoretical calculations of the thiazole–CF4 and thiazole–SF6 complexes

Abstract

The complexes of thiazole with CF₄ and SF₆ have been investigated by Fourier transform microwave spectroscopy and quantum chemical calculations. One rotational spectrum was observed for the thiazole–CF₄ complex. Experiments and theoretical computations confirmed that the observed structure of thiazole–CF₄ is primarily formed due to N⋯C_CF4 interaction with the C atom of CF₄ located in the plane of the thiazole ring. The rotational transitions of thiazole–CF₄ exhibit A/E torsional splitting induced by the internal rotation of the –CF₃ top. The potential barrier of the –CF₃ internal rotation is 0.2411(1) kJ mol⁻¹, consistent with the calculated value (∼0.3 kJ mol⁻¹). For the thiazole–SF₆ complex, one conformer with SF₆ located above the thiazole ring is detected. The observed structure of thiazole–SF₆ is mainly stabilized by van der Waals interactions. The energy decomposition analysis reveals that the electrostatics and dispersion are the dominant attractive contributions to the formation of thiazole–CF₄ and thiazole–SF₆ dimers, whereas the weight of the dispersion term becomes more significant in the thiazole–SF₆ complex compared to that of the thiazole–CF₄ complex.