Charge templates in ionic liquids + aromatics systems revisited by NMR and MD simulations

F. VACA CHAVEZ; N. DIAS; K. SHIMIZU; P. MORGADO; E. FILIPE; J. N. CANONGIA LOPES

Congreso; 9TH LIQUID MATTER CONFERENCE; 2014

In recent years experimental and theoretical works have been focused to investigate the mutual solubility of different molecular species (MS) and ionic liquids (ILs). One of our first studies centered on the phase behavior of mixtures of ILs plus benzene and its fluorinated derivatives [1]. By changing the amount and position of the fluorine atoms around the aromatic ring of the solute molecules we were able to prove, using Molecular Dynamics (MD)-based spatial distribution functions, that the ions of the ionic liquid acted as charge templates for the dipole and/or quadrupole moments of the aromatic molecules. Such studies were then extended to other classes of molecular compounds in order to interpret at a molecular level the fluid phase behavior of the corresponding IL+MS systems. It was found that in most cases the ion-molecule interactions that define the complex behavior of such systems can be correlated to i) the electronic density makeup of the molecular species; ii) the conformational flexibity of the molecular ions that compose the ionic liquid and the concomitant mobility of the polar network formed by them; iii) the presence of any functional groups. NMR studies have been conducted [2,3] to probe the interactions between ionic liquid ions and molecular species dissolved in them. These studies involved multinuclear 1D and 2D NMR spectroscopy. One of the advantages of such methods is that information about each interaction center in the ions or the molecular species can be monitored individually as the composition of the (IL+MS) is changed. In this work we have decided to revisit the original IL + aromatic systems in order to corroborate and extend the initial MD simulation findings: we have used NMR spectroscopy on the same systems to obtain information on the interactions between individual atoms on the ions and in the molecular species and how these match the original averaged-out spatial distribution functions and also newly MD-based pair radial distribution functions between selected interaction centers in the mixture´s components. [1] K. Shimizu, M. F. Costa Gomes, A. A. Pádua, L. P. Rebelo, J. N. Canongia Lopes, J. Phys. Chem. B, 113(29), 9894-9900 (2009). [2] G. Avent, P. A. Chaloner, M. P. Day, K. R. Seddon and T. Welton, J. Chem. Soc. Dalton Trans., 3405?3413 (1994). [3] A. Mele, G. Romano, M. Giannone, E. Ragg, G. Fronza, G. Raos and V. Marcon, Angew. Chem. Int. Ed., 45, 1123?1126 (2006).