Abstract
Understanding the behavior of a chemical compound at a molecular level is fundamental, not only to explain its macroscopic properties, but also to enable the control and optimization of these properties. The present work aims to characterize a set of systems based on the ionic liquids [Aliquat][Cl] and [Aliquat][FeCl] and on mixtures of these with different concentrations of DMSO by means of H NMR relaxometry, diffusometry and X-ray diffractometry. Without DMSO, the compounds reveal locally ordered domains, which are large enough to induce order fluctuation as a significant relaxation pathway, and present paramagnetic relaxation enhancement for the [Aliquat][Cl] and [Aliquat][FeCl] mixture. The addition of DMSO provides a way of tuning both the local order of these systems and the relaxation enhancement produced by the tetrachloroferrate anion. Very small DMSO volume concentrations (at least up to 1%) lead to enhanced paramagnetic relaxation without compromising the locally ordered domains. Larger DMSO concentrations gradually destroy these domains and reduce the effect of paramagnetic relaxation, while solvating the ions present in the mixtures. The paramagnetic relaxation was explained as a correlated combination of inner and outer-sphere mechanisms, in line with the size and structure differences between cation and anion. This study presents a robust method of characterizing paramagnetic ionic systems and obtaining a consistent analysis for a large set of samples having different co-solvent concentrations.
Highlights
In 1914, Paul Walden was able to synthezise ethylammonium nitrate and produced the first ever report mentioning a room temperature liquid composed entirely of ions [1].Ionic Liquids (ILs) have only recently experienced a surge in academic and technological interest and became an ever-growing class of chemical compounds
The present study aimed to investigate the local order and molecular dynamics of magnetic and non-magnetic ionic liquids mixed with DMSO
DMSO affects the local order of these systems and the paramagnetic relaxation enhancement produced by the presence of iron in the magnetic compounds
Summary
In 1914, Paul Walden was able to synthezise ethylammonium nitrate and produced the first ever report mentioning a room temperature liquid composed entirely of ions [1].Ionic Liquids (ILs) have only recently experienced a surge in academic and technological interest and became an ever-growing class of chemical compounds. Optimized for different applications that range from catalysis [3,4] to separation processes [5], gas storage and batteries [6,7]. These molten salts, generally composed of organic cations and organic or inorganic anions, are recognized for their wide liquid range, negligible vapor pressure, high thermal and chemical stability and high conductivity, among other properties. It is possible to make the properties of ionic liquids, namely viscosity and the diffusion coefficient, dependent on external magnetic fields by incorporating a metal-based ion into their structure, making these systems a part of a subclass referred to as magnetic ionic liquids (MILs). The presence of a paramagnetic metal in MILs induces an effective
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