Inverse Halogen Bonds Interactions Involving Br Atom in the Electronic Deficiency Systems of CH₃^⊕ … Br-Y (Y=H, CCH, CN, NC)

Inverse halogen bonds interactions involving Br in the electronic deficiency sys-tems of CH₃^⊕…Br-Y (Y=H, CCH, CN, NC) have been investigated by B3LYP/6-311++G(d, p) and MP2/6-311++G(d, p) methods. The calculated interaction energies with basis set super-position error correction of the four IXBs com-plexes are 218.87, 219.48, 159.18, and 143.05 kJ/mol (MP2/6-311++G(d, p)), re-spectively. The relative stabilities of the four complexes increased in the order:CH₃^⊕…BrCN3^⊕…BrNC3^⊕…BrH≈CH₃^⊕…BrCCH. Natural bond orbital theory analysis and the chemical shifts calculation of the related atoms revealed that the charges flow from Br-Y to CH₃^⊕. Here, the Br of Br-Y acts as both a halogen bond donor and an electron donor. Therefore, compared with conventional halogen bonds, the IXBs complexes formed between Br-Y and CH₃^⊕. Atoms-in-molecules theory has been used to investigate the topological properties of the critical points of the four IXBs structures which have more covalent content.