Structural analysis of low melting organic salts: perspectives on ionic liquids

Abstract

Ionic liquid-forming salts often display low melting points (a lack of crystallisation at ambient temperature and pressure) as a result of decreased lattice energies in the crystalline state. Intermolecular interactions between the anion and cation, and the conformational states of each component of the salt, are of significant interest as many of the distinctive properties ascribed to ionic liquids are determined to a large extent by these interactions. Crystallographic analysis provides a direct insight into the spatial relationship between the cations and anions and provides a basis for an enhanced understanding of the physico-chemical relationship of the ionic liquids. This perspective article examines the crystallographic studies of relevance to ionic liquid-forming organic salts as a basis for the rational design and synthesis of novel ionic liquids.

Transformation of acidic poorly water soluble drugs into ionic liquids

“…The interaction among the solute molecules in solid state correlates with the crystallinity of the solid substance. For all tested APIs, the bulky TBP counterion with its voluminous alkyl side chains reduced the melting points as compared to the free acids and the sodium salts, suggesting a reduced packing efficiency and lattice enthalpy, respectively [9,35]. In addition to these basic qualitative and thermodynamic considerations, the frequency of API detachment from the solid state has been correlated to the activation energy for detachment, which can be indirectly derived from relating the activation energy for attachment of dissolved API to the solid form and the work required for the formation of the drug-drug cluster under isobaric and isothermal conditions.…”

Synthesis and Structure of Ionic Liquids Containing the ­[Al(OC6H4CN)4]– Anion

“…The thermal behavior, especially the melting point, is closely related to the crystal structure and accordingly to the overall ionic interaction 33. An admissible quantity to cover this interaction is the lattice potential energy U POT .…”

Characterization of hexacationic imidazolium ionic liquids as effective and highly stable gas chromatography stationary phases

“…Organic cations such as imidazolium, pyridinium, ammonium and phosphonium can be easily combined with a variety of anions (halides, PF 6 À , BF 4 À , SbF 6 À , etc. ), leading to a myriad of possibilities for the modification of their physicochemical properties, a feature not possible for organic compounds [14].…”