Experimental Evidence for Blue-Shifted Hydrogen Bonding in the Fluoroform–Hydrogen Chloride Complex: A Matrix-Isolation Infrared and ab Initio Study

The 1:1 hydrogen-bonded complex of fluoroform and hydrogen chloride was studied using matrix-isolation infrared spectroscopy and ab initio computations. Using B3LYP and MP2 levels of theory with 6‑311++G(d,p) and aug‑cc‑pVDZ basis sets, the structures of the complexes and their energies were computed. For the 1:1 CHF3–HCl complexes, ab initio computations showed two minima, one cyclic and the other acyclic. The cyclic complex was found to have C–H···Cl and C–F···H interactions, where CHF3 and HCl sub-molecules act as proton donor and proton acceptor, respectively. The second minimum corresponded to an acyclic complex stabilized only by the C–F···H interaction, in which CHF3 is the proton acceptor. Experimentally, we could trap the 1:1 CHF3–HCl cyclic complex in an argon matrix, where a blue-shift in the C–H stretching mode of the CHF3 sub-molecule was observed. To understand the nature of the interactions, Atoms in Molecules and Natural Bond Orbital analyses were carried out to unravel the reasons for blue-shifting of the C–H stretching frequency in these complexes.