A study on aromatic C–H⋯X (X = N, O) hydrogen bonds in 1,2,4,5-tetrafluorobenzene clusters using infrared spectroscopy and ab initio calculations

The (1:1) clusters of 1,2,4,5-tetrafluorobenzene (TFB) with CH3CN, CH3OCH3, and NH3 were studied both experimentally and computationally. Using fluorescence-detected infrared (FDIR) spectroscopy, the aromatic C–H⋯X (X = N, O) hydrogen bond formation in the clusters was directly evidenced by a low-frequency shift and intensity enhancement of the aromatic C–H stretching vibration in the TFB moiety. The molecular structures, stabilization energies, and vibrational frequencies of the clusters were computed at the MP2/6-31+G* level. The observed low-frequency shifts of the aromatic C–H stretch in the clusters correlate with the proton affinities of the acceptor molecules.