An unconventional halogen bond with carbene as an electron donor: An ab initio study

Abstract An unconventional halogen bond has been proved to exist in H 2 C–BrH complex. The halogen bond energy of H 2 C–BrH complex is calculated at four levels of theory [MP2, MP4, CCSD, and CCSD(T)]. The result shows that the carbene is a better electron donor. The substitution effect is prominent in this interaction. For example, the interaction energy in H 2 C–BrCN complex is increased by more than 300% relative to H 2 C–BrH complex. The analyses of NBO, AIM, and energy components were used to unveil the nature of the interaction. The results show that this novel halogen bond has similar characteristics to hydrogen bonds.