Assessing the Structure of Protic Ionic Liquids Based on Triethylammonium and Organic Acid Anions

• DOI: 10.1021/acs.jpcb.1c00249
• Publication Date: 2021-03-10T06:10:35Z
• Authors: Enrico Bodo; Matteo Bonomo; Alessandro Mariani
• Keywords: Technology; ddc:600; 0103 physical sciences; info:eu-repo/classification/ddc/600; 600; 540; 01 natural sciences; binding energy; gases; ionic liquids; ionization of gases; negative ions; organic acids; positive ions

We present a computational analysis of the short-range structure of three protic ionic liquids based on strong organic acids: trifluoracetate, methanesulfonate, and triflate of triethylammonium. Accurate ab initio computations carried out on the gas-phase dimers show that the protonation of triethylamine is spontaneous. We have identified the anion-cation binding motif that is due to the presence of a strong hydrogen bond and to electrostatic interactions. The strength of the hydrogen bond and the magnitude of the binding energy decrease in the order trifluoroacetate ≳ methanesulfonate > triflate. The corresponding simulations of the bulk phases, obtained using a semiempirical evaluation of the interatomic forces, reveal that on short timescales, the state of the three liquids remains highly ionized and that the gas-phase cation-/anion-binding motif is preserved while no other peculiar structural features seem to emerge.