Theoretical Studies on Cationic Chalcogen and Pnicogen Bonds in Binary and Ternary Complexes

The cationic chalcogen bonds and pnicogen bonds in binary complexes XH2S+ center dot center dot center dot NCH2P and ternary complexes NCH2P center dot center dot center dot PyX(X = NH2, CH3, H, CN, F, Cl, Br) with MP2/cc-pVDZ and cc-pVTZ were investigated theoretically. The effects of cationic chalcogen and pnicogen bond length, charge density rho and del(2 rho) at bond critical points, van der Waals' s surface penetrating distance, the second order stabilization energy and charge transfer on the complex interaction energy were discussed. The results show that cationic chalcogen bond becomes stronger when the substituting group X is an electron-withdrawing group and that pnicogen bond becomes stronger when X is electron-donating group. The possible reason of the abnormal effect of the substituting group CN on the stability of XH2S+ center dot center dot center dot NCH2P complex was investigated with the energy-decomposition method. Further, we investigated the synergistic effects of cationic chalcogen and pnicogen bonds in the H,S+center dot center dot center dot NCH,center dot center dot center dot PyX( X= NH2, CH,, H, CN, F, Cl, Br) complexes, and the influences of substituting group on the stability of these ternary complexes. By comparing the second-order stabilization energy and interaction energy of the monomers in these ternary and binary complexes, it is found that cationic chalcogen bond and pnicogen bond have positive synergistic effects on enhancing the stability of these ternary complexes.