Structural Organization in Neat Ionic Liquids and in Their Mixtures

Room temperature ionic liquids (RTILs) represent a class of materials whose employment in several applications is considered as a green alternative to toxic chemicals. Their potentialities are deemed to grow the more we understand their chemical-physical behaviour. As a matter of fact properties as basic as structural organization or microscopic interactions turn out to play a major role in many of their chemical-physical features, such as diffusive properties or solvation capabilities. Their being complex solvent media is a direct consequence of the chemical composition that leads to as diverse interactions as dispersive, coulombic, H-bonding, just to mention the most commonly encountered in conventional RTILs. The degree of comprehension of the structure in neat and mixed RTILs is steadily growing thank to the use of several complementary techniques such as diffraction and spectroscopic techniques and the link between their chemical details and the structure at microscopic as well as mesoscopic level is being unravelled by these studies. That opens the way to the rationalisation not only of basic chemical-physical properties but also of their bulk performances as solvent media. In this contribution we present experimental results aiming provide a structural description of two classes of samples. A first selection of diffraction experiments will aim to address the now well-known issue of mesoscopic structural organization in medium chain length RTILs. We will report original diffraction data from the family of 1-alkyl,3-methylimidazolium tetrafluoroborate as a function of the side alkyl chain length, highlighting the role of this parameter in affecting the mesoscopic order in the neat RTIL. We will also show experimental data highlighting the role of polar versus apolar interactions in determining this phenomenology describing results from a sample whose side chain is not an alkyl one. In the second part of this contribution, experimental results will be reported on binary mixtures of selected tetrafluoroborate salts and water. By the use of complementary techniques such as Raman and infrared spectroscopies, X-Ray and neutron diffraction we will provide a detailed overview of the phase diagram, nature of interactions as well as structural properties of these binary mixtures, expanding the current level of description for these systems. Overall we aim to provide a description of how the proposed experimental techniques can be successfully used to provide useful information in exploring the exciting, complex issue of RTILs and their mixtures.