COOPERATIVITY BETWEEN HYDROGEN BOND AND HALOGEN BOND INHBr⋯BrX⋯HBr (X = F, Cl, Br)

Abstract

An ab initio study has been carried out to investigate the structures, binding energies and atomic charge of the binary complexes HBr⋯BrX and ternary complexes HBr⋯BrX⋯HBr (X = F, Cl, Br) at the MP2/aug-cc-pvdz theoretical level. Four types of interactions are observed among these systems: hydrogen bond, halogen bond, unusual hydrogen bond and unusual halogen bond. Two types of stable structures existed in the trimers: acyclic and monocyclic. The stabilities of the complexes may be decided by three factors: the strength of the halogen bond, the nature of halogen or hydrogen bond of intermolecular interaction and the type of the trimer's structure. The absolute value of the cooperativity contribution in these triads is in range of 0.77 ∼ 21.59%, which shows that the cooperative energy is of importance in them. The nature of the intermolecular interactions has been also investigated through the electrostatic potential and the theory of atoms in molecules (AIM). The values of ∇2ρ at BCPs are positive in all complexes, indicating that the interactions are closed-shell. The ratio |Vc|∕Gcof all complexes ranges from 0.782 to 0.935 (satisfy the condition |Vc|∕Gc< 1) along with Hc> 0, revealing that these complexes are predominantly electrostatic in character.