Cooperative effects of noncovalent bonds to the Br atom of halogen-bonded H ₃NBrZ and HCNBrZ (Z F, Br) complexes

A series of complexes formed between halogen-bonded H ₃NHCNBrZ (Z Br, F) dimers and H ₃NHCNBrZXY (XY HF, ClF, BeH ₂, LiF) trimers were investigated at the MP2 and B3LYP levels of theory using a 6-31G(d,p) basis set. Optimized structures, interaction energies, and other properties of interest were obtained. The addition of XY to the H ₃NHCNBrZ dyad leads to enhanced intermolecular binding with respect to the isolated monomers. This enhanced binding receives contributions from the electrostatic and inductive forces between the constituent pairs, with, in some instances, substantial three-body non-additive contributions to the binding energy. It was found that the XY LiF interaction causes the greatest distortion of the H ₃NHCNBrZ halogen bond from the preferred linear orientation and also provides the strongest binding energy via the nonadditive energy.