Competition and cooperativity between hydrogen bond and halogen bond in HNC⋯(HOBr)n and (HNC)n⋯HOBr (n = 1 and 2) systems

A computational study of the complexes formed between HNC and HOBr has been undertaken at the MP2/aug-cc-pVTZ theoretical level. Eight dyads and fourteen triads formed through hydrogen bonding and halogen bonding were studied. It was found that the halogen bond is weaker than the hydrogen bond in HNC–HOBr dyad. The C atom in HNC is found to be a better electron donor than the O atom in HOBr. The cooperative effect is present between the hydrogen bond and halogen bond in the triads. The most stable triad corresponds to the complex combined with OH⋯C and NH⋯C hydrogen bonds. However, the largest cooperative effect occurs in the complex combined with NH⋯O and OBr⋯C interactions, in which the cooperative energy is about 23% of the total interaction energy. The cooperative effect is negative when HOBr acts as the proton and halogen donors simultaneously.