Theoretical Studies On Cooperativity Of Hydrogen Bond, Halogen Bond, And Lithium Bond Among Supermolecules

Intermolecular noncovalent interactions in microworld are of vital importance in thestructures and properties of biomacromolecules, the distribution of molecules in crystals, andthe chemical reaction process. Intermolecular interactions also play a key role in themolecular-recognition process, one of the most important processes in our life. Hydrogenbond, halogen bond, and lithium bond are important intermolecular noncovalent interactions,have aroused great concern, and have become a hot topic of experimental and theoreticalstudies.In this work, the cooperativity of weak bonds was studied systematically from respect oftheoretical calculation and the interplay among weak bond was described and analysed. Thecooperativity can be classified into two types: positive cooperativity and negativecooperativity. Theoretical studies of positive cooperativity between HOX···OH/SH halogenbond and YH···（H）OX hydrogen bond as well as, the negative cooperativity betweenH···π/X···π bond and Li···π bond were performed by means of the ab initio calculations andQTAIM theoretical method. The main researches are as follows:1The character of the cooperativity between the HOX···OH/SH halogen bond （XB） andthe Y―H···（H）OX hydrogen bond （HB） in OH/SH···HOX···HY （X=Cl, Br; Y=F, Cl, Br）complexes has been investigated by means of second-order M ller Plesset perturbationtheory （MP2） calculations and “quantum theory of atoms in molecules”（QTAIM） studies inpart one. The geometries of the complexes have been determined from the most negativeelectrostatic potentials （VS,min） and the most positive electrostatic potentials （VS,max） on theelectron density contours of the individual species. The greater the VS,maxvalues of HY, thelarger the interaction energies of halogen-bonded HOX···OH/SH in the termolecularcomplexes, indicating that the ability of cooperative effect of hydrogen bond on halogen bondare determined by VS,maxof HY. The interaction energies, binding distances, infraredvibrational frequencies, and electron densities ρ at the BCPs of the hydrogen bonds andhalogen bonds prove that there is positive cooperativity between these bonds. The potentiation of hydrogen bonds on halogen bonds is greater than that of halogen bonds onhydrogen bonds. QTAIM studies have shown that the halogen bonds and hydrogen bonds areclosed-shell noncovalent interactions, and both have greater electrostatic character in thetermolecular species compared with the bimolecular species.2The influence of the Li···π interaction of C_6H6···LiOH on the H···π interaction ofC_6H6···HOX （X=F, Cl, Br, I） and X···π interaction of C_6H6···XOH （X=Cl, Br, I） have beeninvestigated by means of full electronic second-order M ller Plesset perturbation theory（MP2（full）） calculations and “quantum theory of atoms in molecules”（QTAIM） studies inpart two. The binding energies, binding distances, infrared vibrational frequencies, andelectron densities ρ at the BCPs of the hydrogen bonds and halogen bonds prove that theaddition of Li···π lithium bond to benzene weakens the H···π interaction and X···π interaction,and the influence of Li···π bond on hydrogen bond is greater than that on halogen bond. Forthe HOLi···C_6H6···HOX complexes, the weaker the binding energies of hydrogen bond, thegreater Li···π lithium bond influence on the H···π hydrogen bond. For HOLi···C_6H6···XOHcomplexes, the opposite conclusion can be drawn. QTAIM studies have shown that theintermolecular interactions of C_6H6···HOX and C_6H6···XOH are mainly attributable to π-typeinteraction. The electron density at the bond critical points （BCPs） of hydrogen bonds andhalogen bonds decrease from dimers ρ（D） to trimers ρ（T）, and the π-electron density at BCPsshows the same pattern. Natural bond orbital analyses show that the Li···π bond make theelectron transfer from C_6H6to HOX and XOH less.3The properties of inorganic benzenes as well as the M···π （M=Be, Mg, Ca）interactions in the inorganic benzene-bontaining half sandwich complexes have beeninvestigated by means of second-order M ller Plesset perturbation theory （MP2） calculationsand “quantum theory of atoms in molecules”（QTAIM） studies in part three. For the boron,carbon, nitrogen, oxygen, and surfer atoms of the inorganic benzenes, the positions of theattractors of π-electron density are obviously different. For the different atoms in the sameperiod, the distances between the attractors and respective nucleus become shorter and shorterwith the atom number increasing; for the atoms in the same group, the distances becomelonger from oxygen to surfer. For the inorganic benzenes, nucleus-independent chemical shifts （NICS） analysis show that the closer the electronegativity of neighboring atoms resultsin the greater delocalization extent of π-electrons, and the aromaticity of inorganic benzeneswill be enhanced. The binding energies follow the sequence of Be···X₃Y₃Hn <Mg···X₃Y₃Hn<Ca···X₃Y₃Hn（X=B, C; Y=N, O, S; n=3,6）, indicating that the stronger metallicity of M（M=Be, Mg, Ca）, the greater binding energies between M and inorganic benzenes. QTAIMstudies show that the interactions between inorganic benzenes and metal atoms M are mainlyattributable to π-type interaction. By analyzing of electron localization function （ELF）, thereis a new basin generated between M and inorganic benzenes upon the complexes formation,and the basin become increasingly larger in sequence of Be <Mg <Ca.The innovations in this thesis:1In the complexes of OH/SH···HOX···HY （X=Cl, Br; Y=F, Cl, Br）, the greater the VS,maxvalues of HY, the larger the interaction energies of halogen-bonded HOX···OH/SH in thetermolecular complexes, indicating that the ability of cooperative effect of hydrogen bond onhalogen bond are determined by VS,maxof HY. The potentiation of hydrogen bonds on halogenbonds is greater than that of halogen bonds on hydrogen bonds.2After adding Li···π bond to the complexes of C_6H6···HOX（X=F, Cl, Br, I） andC_6H6···XOH （X=Cl, Br, I）, forming termolecular complex, the Li···π interaction weaken theoriginal H···π interaction and X···π interaction. The stronger the H···π interaction, the smallerthe Li···π interaction influence on the H···π interaction. For HOLi···C_6H6···XOH complexes,the opposite conclusion can be drawn.3For different atoms X and Y of the inorganic benzenes X₃Y₃Hn, the positions of theattractors of π-electron density are obviously different. For the atoms in the same period, thedistances between the attractors and respective nucleus become shorter and shorter with theatom number increasing; for the atoms in the same group, the distances become longer fromoxygen to surfer.4For the inorganic benzenes, the decrease of Δel of neighboring atoms results in thedelocalization of π-electron enhanced and the aromaticity of inorganic benzenes will beintensified.