Unusual cooperativity effects between halogen bond and donor-acceptor interactions: The role of orbital interaction

Abstract

Cooperative effects between halogen and donor-acceptor interactions are studied in C5H5B⋯NCX⋯NCY complexes, where X=F, Cl, Br, I and Y=H, CN, OH, Li. The B⋯N binding distances are found to be longer than those in C5H5B⋯NCX dimers, which means that the formation of the X⋯N interaction weakens the B⋯N bonds. This abnormal cooperativity effect is further investigated by means of molecular electrostatic potential, electron density and natural bond orbital analyses. It is found that the back-bonding π→π∗ orbital interaction between C5H5B and NCX moieties is responsible for the unusual cooperativity of B⋯N and X⋯N interactions.