Spectroscopic Signatures of Hydrogen-Bonding Motifs in Protonic Ionic Liquid Systems: Insights from Diethylammonium Nitrate in the Solid State

Abstract

Diethylammonium nitrate, [N 0 0 2 2 ][NO 3 ], and its perdeuterated analogue, [N D D 2 2 ] [NO 3 ], were structurally characterized and studied by infrared, Raman, and inelastic neutron scattering (INS) spectroscopy. Using these experimental data along with state-of-the-art computational materials modeling, we report unambiguous spectroscopic signatures of hydrogen-bonding interactions between the two counterions. An exhaustive assignment of the spectral features observed with each technique has been provided, and a number of distinct modes related to NH···O dynamics have been identified. We put a particular emphasis on a detailed interpretation of the high-resolution, broadband INS experiments. In particular, the INS data highlight the importance of conformational degrees of freedom within the alkyl chains, a ubiquitous feature of ionic liquid (IL) systems. These findings also enable an in-depth physicochemical understanding of protonic IL systems, a first and necessary step to the tailoring of hydrogen-bonding networks in this important class of materials.

Protic ionic liquids for sustainable uses

“…19,20 The removal of solvent, residual water, and/or base is usually carried out under reduced pressure, but some authors advise freeze-drying to avoid unintentional removal of the basic component (and leaving an excess of acid). 18,21 This simple synthetic procedure yields ILs that are potentially very cheap, as exemplified by ILs based on sulfuric acid. Their price can be on par with common organic solvents, and their properties are vastly tuneable by altering amines and stoichiometry.…”

“…17 In many instances, however, at least one component tends to be dissolved in water, or an organic solvent, to manage the exothermic effect. 18 The reaction can be stoichiometric, or with base in excess; in the latter case, base is removed in the drying step. 19,20 The removal of solvent, residual water, and/or base is usually carried out under reduced pressure, but some authors advise freeze-drying to avoid unintentional removal of the basic component (and leaving an excess of acid).…”

“…19,20 The removal of solvent, residual water, and/or base is usually carried out under reduced pressure, but some authors advise freeze-drying to avoid unintentional removal of the basic component (and leaving an excess of acid). 18,21…”

ICE-MAN the Integrated Computational Environment for Modeling and Analysis for Neutrons at ORNL

“…Currently, there are two main components, OCLIMAX [2][3][4][5][6][7] and QClimax [8]. OCLIMAX is principally used on VISION (BL-16B) but can also be used to analyze phonon data from ARCS [9][10][11][12], CNCS, HySPEC [13], SEQUOIA [14][15][16][17], CORELLI, triple axes spectrometers (ORNL), LET, MAPS [18], MARI [19], MERLIN [20], TOSCA [18,[21][22][23], (ISIS), DCS (NIST), AMATERAS [19] (J-PARC), NERA [24] (Dubna) etc. OCLIMAX can calculate thermal neutron scattering cross-section of solids [4,16,17,25].…”