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

Philip J. Carlson, Iowa State University
Sayantan Bose, Iowa State University
Daniel W. Armstrong, University of Texas at Arlington
Tommy Hawkins, Air Force Research Laboratory
Mark S. Gordon, Iowa State University
Jacob W. Petrich, Iowa State University

Reprinted (adapted) with permission from Journal of Physical Chemistry B 116 (2012): 503, doi: 10.1021/jp207840q. Copyright 2012 American Chemical Society.

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.