Cooperative interaction between π-hole and single-electron σ-hole interactions in O2S•••NCX•••CH3 and O2Se•••NCX•••CH3 complexes (X = F, Cl, Br and I)

Ab initio calculations are performed to analyse the cooperative effects between pi-hole and single-electron sigma-hole interactions in O2S center dot center dot center dot NCX center dot center dot center dot CH3 and O2Se center dot center dot center dot NCX center dot center dot center dot CH3 complexes, where X = F, Cl, Br and I. These effects are investigated in terms of geometric and energetic features of the complexes, which are computed by UMP2/aug-cc-pVTZ(-PP) method. Our results indicate that the shortening of the each pi-hole bond distance in the complexes is dependent on the strength of the sigma-hole interaction. The maximum and minimum energetic cooperativity values correspond to the most and least stable complexes studied in the present work. The cooperativity between both types of interaction is chiefly caused by the electrostatic effects. The topological analysis, based on the quantum theory of atoms in molecules, is used to characterise the interactions and analyse their enhancement with varying electron density at bond critical points.