Ab Initio Studies on the Interplay between Unconventional B•••X Halogen Bond and Lithium/Hydrogen/Halogen Bond in HB(CO)2•••XCN•••YF (X = Cl, Br; Y = Li, H, Cl) Complexes

In this paper, ab initio calculations were performed on the ternary complex formed by HB(CO)2, XCN (X = Cl, Br) and YF (Y = Li, H, Cl). In these complexes boron act as a non-classical electron donor to form a unconventional halogen bond. The cooperative effect between the B•••X halogen bond and lithium/hydrogen/halogen bond was investigated. The calculated results show that the B•••X and N•••Y interactions in the termolecular complexes are stronger compared with those in their corresponding bimolecular complexs. The cooperativity energies of these termolecular complexes span a range, from -1.06 to -2.75 kJ /mol and -1.63 to -4.34 kJ /mol for X = Cl and Br, respectively, which indicates the presence of the cooperativity effect. The nature of interactions is analyzed in terms of parameters derived from molecular electrostatic potential (MEP), natural bond orbital (NBO) and atoms in molecules (AIM) analyses. The amount of charge transfer in the termolecular complexes is stronger compared with those in their corresponding bimolecular complexs. The obtained results from AIM analyses demonstrate that B•••X bond and N•••Y bond in the termolecular complexes are amplified compared to the bimolecular complexs.