Experimental evidence for the blue-shifted hydrogen-bonded complexes of CHF₃ with π-electron donors

Blue-shifted hydrogen-bonded complexes of fluoroform (CHF₃) with benzene (C₆H₆) and acetylene (C₂H₂) have been investigated using matrix isolation infrared spectroscopy and ab initio computations. For CHF₃-C₆H₆ complex, calculations performed at the B3LYP and MP2 levels of theory using 6-311++G (d,p) and aug-cc-pVDZ basis sets discerned two minima corresponding to a 1:1 hydrogen-bonded complex. The global minimum correlated to a structure, where the interaction is between the hydrogen of CHF₃ and the π-electrons of C₆H₆ and a weak local minimum was stabilized through H…F interaction. For the CHF₃-C₂H₂ complex, computation performed at MP2/aug-cc-pVDZ level of theory yielded two minima, corresponding to the cyclic C-H…π complex A (global) and a linear C-H…F (n-σ) complex B (local). Experimentally a blue-shift of 32.3cm^-1 and 7.7cm^-1 was observed in the ν₁ C-H stretching mode of CHF₃ sub-molecule in Ar matrix for the 1:1 C-H…π complexes of CHF₃ with C₆H₆ and C₂H₂ respectively. Natural bond orbital (NBO), Atoms-in-molecule (AIM) and energy decomposition (EDA) analyses were carried out to explain the blue-shifting and the nature of the interaction in these complexes.