title: The addition of CO₂ to four superbase ionic liquids: a DFT study.
abstract: The addition of carbon dioxide to four superbase ionic liquids, [P3333][Benzim], [P3333][124Triz], [P3333][123Triz] and [P3333][Bentriz] was studied using a molecular DFT approach involving anions alone and individual ion pairs. Intermolecular bonding within the individual ion pairs is characterised by a number of weak hydrogen bonds, with the superbase anion geometrically arranged so as to maximize interactions between the heterocyclic N atoms and the cation. The pairing energies show no correlation to the observed CO2 adsorption capacity. Addition of CO2 to the anion alone clearly resulted in the formation of a covalently-bound carbamate function with the strength of binding correlated to experimental capacity. In the ion pair however the cation significantly alters the nature of the bonding such that the overall cohesive energy is reduced. Formation of a strong carbamate function occurs at the expense of weakening the interaction between anion and cation. In the more weakly absorbing ion pairs which contain [123Triz](-) and [Bentriz](-), the carbamate-functionalised systems are very close in energy to adducts in which CO2 is more weakly bound, suggesting an equilibrium between the chemi- and physisorbed CO2.
authors.affiliation: Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK. r.g.bell@ucl.ac.uk.
authors.forename: Maxime
authors.initials: M
authors.lastname: Mercy
authors.affiliation: QUILL, School of Chemistry and Chemical Engineering, Queen's University Belfast, Belfast, Northern Ireland BT9 5AG, UK.
authors.forename: S F Rebecca
authors.initials: SF
authors.lastname: Taylor
authors.affiliation: QUILL, School of Chemistry and Chemical Engineering, Queen's University Belfast, Belfast, Northern Ireland BT9 5AG, UK.
authors.forename: Johan
authors.initials: J
authors.lastname: Jacquemin
authors.affiliation: QUILL, School of Chemistry and Chemical Engineering, Queen's University Belfast, Belfast, Northern Ireland BT9 5AG, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Hardacre
authors.affiliation: Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK. r.g.bell@ucl.ac.uk.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Bell
authors.affiliation: Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK. r.g.bell@ucl.ac.uk and School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK. deleeuwn@cardiff.ac.uk.
authors.forename: Nora H
authors.initials: NH
authors.lastname: De Leeuw