Structure and Dynamics of the 1-Hydroxyethyl-4-amino-1,2,4-triazolium Nitrate High-Energy Ionic Liquid System

Abstract

An investigation of the structure and dynamics of the high-energy ionic liquid, 1-hydroxyethyl-4-amino-1,2,4-triazolium nitrate (HEATN), was undertaken. Both experimental and computational methods were employed to understand the fundamental properties, characteristics, and behavior of HEATN. The charge separation, according to the electrostatic potential derived charges, was assessed. The MP2 (second-order perturbation theory) geometry optimizations find six dimer and five tetramer structures and allow one to see the significant highly hydrogen bonded network predicted within the HEATN system. Due to the prohibitive scaling of ab initio methods, the fragment molecular orbital (FMO) method was employed and assessed for feasibility with highly energetic ionic liquids using HEATN as a model system. The FMO method was found to adequately treat the HEATN ionic liquid system as evidenced by the small relative error obtained. The experimental studies involved the investigation of the solvation dynamics of the HEATN system via the coumarin 153 (C153) probe at five different temperatures. The rotational dynamics through the HEATN liquid were also measured using C153. Comparisons with previously studied imidazolium and phosphonium ionic liquids show surprising similarity. To the authors' knowledge, this is the first experimental study of solvation dynamics in a triazolium-based ionic liquid. Disciplines Chemistry CommentsThis article is from Journal of Physical Chemistry B 116 (2012): 503, doi:10.1021/jp207840q. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. There has been a steeper than exponential growth in the number of publications related to ionic liquids since the year 2000. Authors1 The interest in ionic liquids reflects their versatility and their environmentally friendly properties in comparison to commonly used compounds.2À4 Ionic liquids are molten salts, commonly composed of an organic cation and an inorganic anion that can often be liquid at room temperature. These low-melting salts are considered to be green solvents, in contrast to volatile organic compounds, due to their high chemical and thermal stabilities, negligible vapor pressure, 5 and high recoverability and reusability.6,7 Ionic liquids can be customized by varying the identity of the substituents on the cation or by adapting the moiety of the anion.8 This versatility and these unique properties have piqued the interest of the scientific community, and a variety of fundamental studies 9À16 have been performed on ionic liquids to obtain a better understanding of their characteristics.One interesting application of ionic liquids is in the highenergy density matter (HEDM) community, where many different molten salts have been explored and reported. 17 It is important to understand what characteristics make ionic liquids suited to HEDM applications. This very problem was explored computationally in a series of studies,...

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