Competitive pi interactions and hydrogen bonding within imidazolium ionic liquids

• Published in: Physical chemistry chemical physics : PCCP Vol. 16; no. 7; pp. 3238 - 3253
• Main Authors: Matthews, Richard P, Welton, Tom, Hunt, Patricia A
• Format: Journal Article
• Language: English
• Published: England 01.01.2014
• Subjects: Chlorides
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c3cp54672a

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.