title: Cyclopropenium Cations Break the Rules of Attraction to Form Closely Bound Dimers.
abstract: The crystal structures of tris(ethylmethylamino)-cyclopropenium chloride and tris(diethylamino)-cyclopropenium iodide reveal the presence of closely bound dicationic dimers formed from two closed-shell monomer units. The distances between the C3 centroids of the staggered monomers are at the short end of those normally found in π-stacked neutral arenes, let alone charged aromatic rings. Computational analysis reveals that short-range interactions are dominated by strong dispersion forces, enabling metastable dicationic dimers to form without covalent intermolecular bonding. Surrounding counterions then provide a background source of charge balance, imparting strong thermodynamic stability to the system. Additionally, these counterions form a weak but attractive electrostatic bridge between the monomer units, contributing to the surprisingly short observed intermolecular C3-C3 centroid distance.
authors.affiliation: Department of Chemistry, University of Canterbury , Private Bag 4800, Christchurch 8041, New Zealand.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Wallace
authors.affiliation: Department of Chemistry, University of Canterbury , Private Bag 4800, Christchurch 8041, New Zealand.
authors.forename: Chaminda D
authors.initials: CD
authors.lastname: Jayasinghe
authors.affiliation: Department of Chemistry, University of Canterbury , Private Bag 4800, Christchurch 8041, New Zealand.
authors.forename: Matthew I J
authors.initials: MI
authors.lastname: Polson
authors.affiliation: Department of Chemistry, University of Canterbury , Private Bag 4800, Christchurch 8041, New Zealand.
authors.forename: Owen J
authors.initials: OJ
authors.lastname: Curnow
authors.affiliation: Department of Chemistry, University of Canterbury , Private Bag 4800, Christchurch 8041, New Zealand.
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Crittenden