Noncovalent interactions of aromatic heterocycles: rotational spectroscopy and theoretical calculations of the thiazole-CF 4 and thiazole-SF 6 complexes.

The complexes of thiazole with CF 4 and SF 6 have been investigated by Fourier transform microwave spectroscopy and quantum chemical calculations. One rotational spectrum was observed for the thiazole-CF 4 complex. Experiments and theoretical computations confirmed that the observed structure of thiazole-CF 4 is primarily formed due to N⋯C CF 4 interaction with the C atom of CF 4 located in the plane of the thiazole ring. The rotational transitions of thiazole-CF 4 exhibit A/E torsional splitting induced by the internal rotation of the -CF 3 top. The potential barrier of the -CF 3 internal rotation is 0.2411(1) kJ mol -1 , consistent with the calculated value (∼0.3 kJ mol -1 ). For the thiazole-SF 6 complex, one conformer with SF 6 located above the thiazole ring is detected. The observed structure of thiazole-SF 6 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-CF 4 and thiazole-SF 6 dimers, whereas the weight of the dispersion term becomes more significant in the thiazole-SF 6 complex compared to that of the thiazole-CF 4 complex.