Cooperative effects of noncovalent bonds to the Br atom of halogen-bonded H3N…BrZ and HCN…BrZ (Z = F, Br) complexes

Charge Displacement Analysis-A Tool to Theoretically Characterize the Charge Transfer Contribution of Halogen Bonds

Theoretical bonding analysis is of prime importance for the deep understanding of the various chemical interactions, covalent or not. Among the various methods that have been developed in the last decades, the analysis of the Charge Displacement function (CD) demonstrated to be useful to reveal the charge transfer effects in many contexts, from weak hydrogen bonds, to the characterization of σ hole interactions, as halogen, chalcogen and pnictogen bonding or even in the decomposition of the metal-ligand bond. Quite often, the CD analysis has also been coupled with experimental techniques, in order to give a complete description of the system under study. In this review, we focus on the use of CD analysis on halogen bonded systems, describing the most relevant literature examples about gas phase and condensed phase systems. Chemical insights will be drawn about the nature of halogen bond, its cooperativity and its influence on metal-ligand bond components.

Theoretical investigation on the interplay of hydrogen bond and halogen bond in HX⋯(BrCl)n (X = F, Cl, Br and n = 1, 2) complexes

Quantum chemical calculations at the MP2 level with the aug-cc-pVTZ basis set were used to investigate the HX ⋯( BrCl )n ( X = F , Cl , Br and n = 1, 2) complexes. They are connected via hydrogen bond or halogen bond in dimers and together in trimers. Molecular geometries, interaction energies, cooperative energies and atomic charge of dyads and triads have been studied at the Mp2/aug-cc-pVTZ computational level. All studied trimers show cooperativity with the simultaneous presence of a hydrogen and one or two halogen bond. The molecular electrostatic potential has been employed to explore the formation mechanisms of these molecular complexes. The AIM analysis has been performed at the Mp2/aug-cc-pVTZ level to examine the topological characteristics, confirming the coexistence of hydrogen bonds and one or two halogen bond for each complex.

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

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|∕Gc of 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.