Quantum Chemical Studies of Weakly Coordinated Ionic Systems: Predictions of Chemical and Physical Properties

Strongly bonded systems can be treated by quantum chemistry in a quick and satisfying manner; however, weak bonds, as found in weakly coordinating anions (WCAs) and ionic liquids (ILs) - compound classes of increasing preparative and theoretical interest - are much harder to describe. The predictive screening of possible new WCAs revealed compounds with interesting properties as possible targets for future syntheses in order to stabilize very reactive and/or strongly coordinating cations. Regarding ILs, it was demonstrated that in the cases in which a weak bond cannot be completely neglected, a purely statistical treatment often suffices to describe bulk physical properties. The chemical nature of the single ions and their specific interactions possess rather little significance since the most important ordering parameter seems to be the molecular size. These studies may prove not only a valuable tool in themselves, but may also provide insight in fundamental thermodynamical principles that become apparent in complex molecules.