Intra-cluster proton transfer in anilide–(HF)n (n = 1–4): Can the size of HF cluster influence the N−⋯H–F → N–H⋯F− switching

The impact of the HF cluster size on the proton-transfer switch between N−⋯H–F and N–H⋯F− in the anilide–(HF)n = 1–4 complexes was investigated by means of the quantum chemical methods. The change in the H-bond strength due to variation of the HF cluster size was well monitored by change in the binding energy (BE), structural parameter, electron density topology, natural charge and charge transfer. For n = 1, our results at the MP2/6-311++G(2d,2p) level show that the minimum-energy structure corresponds to the H-bonded complex PhNH−⋯HF with excess negative charge localized on the N atom of the anilide anion. For n > 1, minimum energy structures correspond to PhNH2⋯F−(HF)1–3 ones, namely a solvated F− ion. This is a case in which the relative change in the acidity of the HF is observed in the ground state as the size of cluster increases. The nature of the weak interactions in the complexes was characterized by means of atoms in molecules (AIM) and the natural bond orbital (NBO) analyses.