Theoretical Study Of Chalcogen Bonding Interaction Among Small Molecules

In this paper, Ab initio calculation have been carried out to investigate the structures, stabilities and bonding of FH2 S and CSF₂ systems（1） HOCl and SHX（ X= F, CN, NC, Cl, Br, NO₂, CCH, CH3, H）.（2） F₂CX（X = S and Se）???HM（X = S and Se）（3） SHNO₂ S:N-base, for nitrogen bases NC-, NCF, NCCl, NCBr, NCH, NCLi,NCNa. We performed the Natural Bond Orbital（NBO） analysis to study the nature of interactions in the systems. The “atoms in molecules ”（AIM） theory was also applied to find the bond critical points（BCPs） and to analyze the nature of bonding in terms of electron densities（ρBCP）, Laplacians（?2ρBCP）, the total electron energy density H（H=G+V） and its components（the local kinetic energy density G and the local potential energy density V） at BCPs. Based on the NBO and AIM analysis, we obtained the binding energies of different structures.The mains contents are as following:1 Ab initio quantum chemistry methods were used to analyze the noncovalent interactions between HOCl and SHX（X = F, CN, NC, Cl, Br, NO₂, CCH, CH3, H）.Three energetic minimal configurations have been characterized for each case, where the S center acts as a Lewis acid interacting with O to form a chalcogen bond, as well as a Lewis base interacting with Cl or H of HOCl respectively to form halogen bond and hydrogen bond. An electronegative substituent such as F, CN, NC and NO₂ tends to form a stronger chalcogen bond, while an electropositive substituent such as CCH,CH3 and H is inclined to form a more stable H-bonded complex. The chalcogenbonded, halogen-bonded and H-bonded complexes are stabilized by the charge transfers from Lp（O） to σ*（SX）, from Lp（S） to σ*（ClO）, and from Lp（S） to σ*（HO）,respectively. As a result, the SHF unit becomes positively charged in halogen-bonded and hydrogen-bonded complexes but negatively charged in chalcogen-bonded complexes. Theory of atoms in molecules, natural bond orbital analysis, molecular electrostatic potential and localized molecular orbital energy decomposition analysiswere applied to investigate these noncovalent bonds.2 Complexes F₂CX（ X = S and Se）???HM（ X = S and Se） have been studied by quantum chemical calculations at the MP₂/aug-cc-pVTZ level to investigate the competition between Ï€-hole interaction and chalcogen bond F₂CX（ X = S and Se）has a dual role of a Lewis acid and base with the Ï€-hole on the X atom and the H atom to participate in the Ï€-hole interaction and chalcogen bond with HM, respectively.Both types of interactions become stronger for X = Se, and the Ï€-hole interaction is much stronger than the chalcogen bond. The C-X???H hydrogen bond is dominated by the electrostatic interaction, and this conclusion holds for the Ï€-hole interaction in F₂CX???HM complex, but the electrostatic and polarization contributions are similar in F₂CX???HM complex. Theory of atoms in molecules, natural bond orbital analysis,molecular electrostatic potential and localized molecular orbital energy decomposition analysis were applied to investigate these noncovalent bonds.3 Ab initio MP₂/aug-cc-pVDZ calculations have been carried out on the chalcogen-bonded complexes SHNO₂ S:N-base, for nitrogen bases NC-, NCF, NCCl,NCBr, NCH, NCLi, NCNa. S-N distances and interaction energies vary dramatically in these complexes. For a fixed acid, interaction energies decrease in the order NCNa > NCLi > NCBr > NCCl> NCH > NCF. In contrast, for a fixed base, there is no single pattern for the variations in distances and interaction energies as a function of the acid. This suggests that there are multiple factors that influence these properties.The electron-donating ability of the base is also a factor in determining the structures and interaction energies of these complexes. Charge transfer from the N lone pair to the σ*S-N orbital stabilizes SHNO₂ S:N-base complexes. The total charge-transfer energies correlate with the interaction energies of these complexes.Decomposition of the total interaction energy reveals that the induction energy constitutes more than half of the total attraction.