Characterization of σ-hole interactions in 1:1 and 1:2 complexes of YOF2X (X = F, Cl, Br, I; Y = P, As) with ammonia: competition between halogen and pnicogen bonds

Abstract

Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to examine 1:1 and 1:2 complexes of YOF2X (X = F, Cl, Br, I; Y = P, As) with ammonia. The YOF2X:NH3 complexes are formed through the interaction of the lone pair of the ammonia with the σ-hole region associated with the X or Y atom of YOF2X molecule. The calculated interaction energies of halogen-bonded complexes are between −1.06 kcal/mol in the POF3···NH3 and −6.21 kcal/mol in the AsOF2I···NH3 one. For a given Y atom, the largest pnicogen bond interaction energy is found for the YOF3, while the smallest for the YOF2I one. Almost a strong linear relationship is evident between the interaction energies and the magnitudes of the positive electrostatic potentials on the X and Y atoms. The results indicate that the interaction energies of halogen and pnicogen bonds in the ternary H3N:YOF2X:NH3 systems are less negative relative to the respective binary systems. The interaction energy of Y···N bond is decreased by 1–22 %, whereas that of X···N bond by about 5–61 %. That is, both Y···N and X···N interactions exhibit anticooperativity or diminutive effects in the ternary complexes.