Symmetric bifurcated halogen bonds: substituent and cooperative effects

ABSTRACT

The aim of this study is to investigate the geometries, interaction energies and bonding properties of the symmetrical bifurcated halogen bond interactions (BXBs) by means of ab initio calculations. For this purpose, the NCX (X = Cl, Br) molecule is paired with a series of N-formyl formamide (NFF) derivatives (NFF-Z, Z = H, CN, CCH, OH, CH₃ and Li), and the properties of the resulting complexes are studied by molecular electrostatic potential, quantum theory of atoms in molecules, noncovalent interaction index and natural bond orbital analyses. For a fixed NCX molecule, interaction energies increase in the order of Z = Li > CH₃ > H > OH > CCH > CN. We found a strong correlation between the interaction energies of NCX:NFF-Z complexes and molecular electrostatic potential minimum values associated with NFF-Z monomers. Moreover, cooperative effects between BXB and XċċċN halogen bond interactions are studied in the ternary NCX:NCX:NFF-Z systems. Our results indicate that the strength of BXB interactions in the ternary complexes is enhanced by the presence of XċċċN bonds. Besides, cooperativity effects tend to increase the covalency of BXBs in these systems.

KEYWORDS:

• Halogen bond
• MEP
• NBO
• ab initio
• cooperativity

Disclosure statement

No potential conflict of interest was reported by the authors.