Sigma-hole cooperativity in anionic [FX•••CH3•••YF]- (X, Y = Cl, Br) complexes

A computational study of anionic complexes of general formula [F-X center dot center dot center dot CH3 center dot center dot center dot Y-F] (X, Y = Cl, Br) predicted minimum energy structures with unusual bonding features. The two F atoms, the halogens X and Y and the central C atom all lie on the same straight line, with the three H atoms forming covalent C-H bonds perpendicular to this straight line. The bonding analysis suggests that the extra negative charge is localized on the central C atom and interacts favourably with the sigma-holes originating from the adjacent F-X and Y-F molecular subunits. This unusual cooperative bonding results in energetically stable complexes. (C) 2014 Elsevier B.V. All rights reserved.