Search

With the aim to understand the relatively high solubility of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), an important energetic material with a high degree of inter- and intra-molecular hydrogen bonding, in fluoride anion containing ionic liquids (ILs), first principles molecular dynamics simulations in the isobaric-isothermal ensemble were carried out for a system using hydrous tetramethylammonium fluoride as the prototypical solvent. Simulations initiated from both molecular TATB and its Meisenheimer complex (i.e., a σ-complex of the fluoride and the electrophilic ring of TATB) yield a Zundel-type complex where a proton is shared between an amino group and an F(-) ion, whereas the Meisenheimer complex is found to be only transiently stable. An analysis of the electronic structure probing the Wannier function centers supports the finding of a proton-sharing complex with a three-center four-electron like bond. The Zundel-type complex also yields an electronic absorption spectrum consistent with the experimentally observed color change. This study provides evidence that the remarkable solubility of otherwise hard-to-dissolve molecular crystals in ILs can be aided by chemical modification of the solute.

Materials with a high-degree of inter- and intra-molecular hydrogen bonding generally have limited solubility in conventional organic solvents. This presents a problem for the dissolution, manipulation and purification of these materials. Using a state-of-the-art density-functional-theory based quantum chemical solvation model we systematically evaluated solvents for a known hydrogen-bonded molecular crystal. This, coupled with direct solubility measurements, uncovered a class of ionic liquids involving fluoride anions that possess more than two orders of magnitude higher solvation power as compared with the best conventional solvents. The crystal structure of one such ionic liquid, determined by X-ray diffraction spectroscopy, indicates that F- ions are stabilized through H-bonded chains with water. The presence of coordinating water in such ionic liquids seems to facilitate the dissolution process by keeping the chemical activity of the F- ions in check.