Effect of confinement on structure, energy and vibrational spectra of (HF)n, n=1-4

Interaction energy, enthalpy and Gibbs free energy for (HF)(n)@C-60, n = 1-4 were calculated using the density functional theoretic method (DFT(MN15)/aug-cc-pVTZ//aug-cc-pVDZ). The interaction energy was found to be - 14.9 kcal/mol for HF@C-60 and - 5.1 kcal/mol for (HF)(2)@C-60. The HF dimer has the two HF molecules forming an L-shaped structure with an extremely short hydrogen bond. While the trimer retains its hydrogen bonded triangular shape inside the cage, the tetramer has the fluorine atoms arranged in a pyramidal shape. There is an elongation of the HF bond length and a significant red shift in the H-F vibrational frequency in all cases.