Dual function of the boron center of BH(CO) 2 /BH(N 2 ) 2 in halogen- and triel-bonded complexes with hypervalent halogens.

The complexes between BH(CO)2 /BH(N2 )2 and XF3 /XF5 are stabilized by a halogen bond and a triel bond. The MEP analyses of BH(CO)2 /BH(N2 )2 indicate that there are both a region with negative MEPs on the B atom in the vertical direction of the molecular plane and a σ-hole at the B-H bond end. Therefore, the boron atom in BH(CO)2 /BH(N2 )2 plays a dual role of a Lewis base and an acid in the halogen bond and triel bond, respectively. The halogen and triel bonds are stronger in order of IF3 < BrF3 < ClF3 , IF5 < BrF5 < ClF5 , and BH(CO)2 < BH(N2 )2 in most complexes. These complexes have large stability since the interaction energy varies from -5 to -115 kcal/mol. The halogen bond belongs to a covalent interaction or a partially covalent interaction in most complexes. The subsystems in these complexes have prominent deformation, accompanied with big charge transfer and large polarization.