Comparison of hydrogen- and halogen-bonding interactions in the complexes of the substituted carbonyl compounds with hypohalous acids and monohaloamines

Abstract

An ab initio study of the complexes formed by hypohalous acids and monohaloamines (designated as HAX where A = O or NH and X = Cl, Br, or I) with RCHO (R = H, CH3, OCH3, and NH2) carbonyl compounds has been carried out at the MP2/aug-cc-pVTZ computational level for comparative study on hydrogen bonds with halogen bonds. Two types of complexes are formed by their combination –RCHO···HAX and RCHO···XAH (A = O or NH) named as hydrogen-bonded and halogen-bonded, respectively, although other weak interactions also coexist in both types of complexes. Analysis of the BSSE-corrected interaction energies reveals that hydrogen bond strength decreases with an increase in size of X atom (i.e., HACl > HABr > HAI) while reverse trend is indicated for halogen-bonded complexes (HACl < HABr < HAI). For the carbonyl compounds, the interaction energies for both hydrogen- and halogen-bonded complexes follow the same order of HCHO < CH3CHO < (CH3O)CHO < (H2N)CHO. Vibrational frequency analysis suggests that both the H-O and H-N bonds are red-shifted while C–H bonds are blue-shifted in hydrogen-bonded complexes. Similarly, the X-O/X-N and C-H bonds are red- and blue-shifted respectively in halogen-bonded; however, the magnitude of red shift for X-O and X-N bonds in halogen-bonded complexes is much smaller than that of H-O and H-N bonds in hydrogen-bonded complexes. The MEP, NBO, and AIMALL methods have been utilized to understand structure, properties, and nature of the interaction stabilizing these two types of the complexes. Relationship of the interaction energies with MEP, charge transfer (CT), and change in % s character obtained from NBO analysis is also drawn for both complexes.