title: Competitive pi interactions and hydrogen bonding within imidazolium ionic liquids.
abstract: In this paper we have explored the structural and energetic landscape of potential π(+)-π(+) stacked motifs, hydrogen-bonding arrangements and anion-π(+) interactions for gas-phase ion pair (IP) conformers and IP-dimers of 1,3-dimethylimidazolium chloride, [C1C1im]Cl. We classify cation-cation ring stacking as an electron deficient π(+)-π(+) interaction, and a competitive anion on-top IP motif as an anion-donor π(+)-acceptor interaction. 21 stable IP-dimers have been obtained within an energy range of 0-126 kJ mol(-1). The structures have been found to exhibit a complex interplay of structural features. We have found that low energy IP-dimers are not necessarily formed from the lowest energy IP conformers. The sampled range of IP-dimers exhibits new structural forms that cannot be recovered by examining the ion-pairs alone, moreover the IP-dimers are recovering additional key features of the local liquid structure. Including dispersion is shown to impact both the relative energy ordering and the geometry of the IPs and IP-dimers, however the impact is found to be subtle and dependent on the underlying functional.
authors.affiliation: Department of Chemistry, Imperial College London, London, SW7 2AZ, UK. richard.matthews@imperial.ac.uk p.hunt@imperial.ac.uk.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Matthews
authors.forename: Tom
authors.initials: T
authors.lastname: Welton
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Hunt