The importance of noncovalent interactions cannot be overstated.Among the noncovalent interactions,there is new interesting example that is comparable with the hydrogen bond and halogen bond; the case of pnicogen bond.In this work,the substitution effect on the π pnicogen and halogen bonds in C2H2…PH2X and C2H2…BrX(X=H,CH3,OH,Br,Cl,F,CN,and NO2)complexes were investigated using a high level ab initio method.The quantum theory of atoms in molecules(QTAIM)and the method of natural bond orbital(NBO)analysis were employed to examine the nature of π…P and π…Br interactions.It was found that two types of interaction are hallmarks of “closed-shell” and noncovalent interactions.It is not only the electron-withdrawing substituents(CN,Br,Cl,NO2,and F)increase interaction forces but also the electron-donor substituents(CH3,OH)strengthen the interactions.The interaction forces,for π…P,climbs in the sequence X = H < CH3 < OH < CN < Br < Cl < NO2 < F.This pattern is variable to that of π…Br systems,particularly for the NO2 group.The π…P interactions are weaker than,and in some cases comparable to the analogous halogen bonds except for the NO2 group.