Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to examine 1:1 and 1:2 complexes of YOF 2 X (X = F, Cl, Br, I; Y = P, As) with ammonia. The YOF 2 X:NH 3 complexes are formed through the interaction of the lone pair of the ammonia with the r- hole region associated with the X or Y atom of YOF 2 X molecule. The calculated interaction energies of halogen- bonded complexes are between -1.06 kcal/mol in the POF 3 NH 3 and -6.21 kcal/mol in the AsOF 2 INH 3 one. For a given Y atom, the largest pnicogen bond interaction energy is found for the YOF 3 , while the smallest for the YOF 2 I 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 H 3 N:YOF 2 X:NH 3 systems are less negative relative to the respective binary systems. The interaction energy of YN bond is decreased by 1–22 %, whereas that of XN bond by about 5–61 %. That is, both YN and XN interactions exhibit antico- operativity or diminutive effects in the ternary complexes.
