title: Nature of noncovalent carbon-bonding interactions derived from experimental charge-density analysis.
abstract: In an effort to better understand the nature of noncovalent carbon-bonding interactions, we undertook accurate high-resolution X-ray diffraction analysis of single crystals of 1,1,2,2-tetracyanocyclopropane. We selected this compound to study the fundamental characteristics of carbon-bonding interactions, because it provides accessible σ holes. The study required extremely accurate experimental diffraction data, because the interaction of interest is weak. The electron-density distribution around the carbon nuclei, as shown by the experimental maps of the electrophilic bowl defined by a (CN)2 CC(CN)2 unit, was assigned as the origin of the interaction. This fact was also evidenced by plotting the Δ(2) ρ(r) distribution. Taken together, the obtained results clearly indicate that noncovalent carbon bonding can be explained as an interaction between confronted oppositely polarized regions. The interaction is, thus electrophilic-nucleophilic (electrostatic) in nature and unambiguously considered as attractive.
authors.affiliation: X-Ray Diffraction Unit, Institute of Chemical Research of Catalonia (ICIQ), Avgda. Països Catalans 16, 43007 Tarragona (Spain).
authors.forename: Eduardo C
authors.initials: EC
authors.lastname: Escudero-Adán
authors.affiliation: Department of Chemistry, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma de Mallorca (Spain).
authors.forename: Antonio
authors.initials: A
authors.lastname: Bauzá
authors.affiliation: Department of Chemistry, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma de Mallorca (Spain). toni.frontera@uib.es.
authors.forename: Antonio
authors.initials: A
authors.lastname: Frontera
authors.affiliation: X-Ray Diffraction Unit, Institute of Chemical Research of Catalonia (ICIQ), Avgda. Països Catalans 16, 43007 Tarragona (Spain). pballester@iciq.es.|Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluís Companys 23, 08010 Barcelona (Spain). pballester@iciq.es.
authors.forename: Pablo
authors.initials: P
authors.lastname: Ballester
keywords: ab initio calculations; charge density; noncovalent carbon bonding; supramolecular chemistry; σ-hole interactions