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⋯CCF4 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.