Theoretical Investigations On The Weak Intermolecular Interactions Between Aromatic Heterocycles And Halogenated Benzenes

Weak intermolecular interactions between molecules play important roles in the fields of molecular recognition,crystal engineering,self-assembly of functional materials,chemical separation,catalysis,supramolecular chemistry and biomedical engineering.Therefore,understanding weak intermolecular interactions is significant for many fields of chemistry.In recent years,the research of weak interaction has attracted much attention by both experimental and theoretical researchers.In this thesis,bromopentafluorobenzene and iodopentafluorobenzene were selected as electron acceptors,aromatic heterocyclic furan,thiophene and pyridine were selected as electron donors.All of the monomers and dimers were optimized at the M06-2X/aug-cc-pVDZ level of theory using the Gaussian software package,these dimers were built based on the electrostatic potential distribution of the electron donor and acceptor according to the principle of the attraction between positive and negative regions.Three types?T-shape,face-to-face,head-to-head?of stable structures without imaginary frequency are screened out,basis set superposition error correction?BSSE?with counterpoise method is used for the optimization of the dimeric structures.In addition,single point energies of the stable dimers were calculated at the?B97X-D/aug-cc-pVDZ and CCSD?T?/aug-cc-pVDZ levels of theory for obtaining the interaction energies of the dimers.Quantum theory of atoms in molecules?QTAIM?analysis was performed for all dimers without imaginary frequencies,and the?3,-1?bond critical points in the dimers were analyzed to obtain the interaction type between atoms.Non-covalent interaction?NCI?analysis can obtain the types and regions of weak interactions between dimers.Finally,by employing energy decomposition analysis?EDA?,the interaction energy of each dimer is decomposed into electrostatic interaction(E_elst),exchange interaction(E_exch),repulsive interaction(E_rep),polarization interaction(E_pol),dispersion interaction(E_disp),and it can tell us the driving force of the formation of each dimer.The donor-acceptor orbital interaction in each dimer was explained by natural bond orbital?NBO?analyses.The main contents of each chapter in this thesis are as follows:Chapter 1,introduction.This chapter briefly introduces the research background and several common types of weak intermolecular interactions,and it also summarizes the research progress and applications of intermolecular interactions in recent years as well as the research purpose and significance of this thesis.Chapter 2,theoretical basis and analytical methods.In this chapter,the calculation methods of semiempirical,density functional theory and coupling cluster are introduced.In addition,some common analysis methods?electrostatic potential analysis,QTAIM,NCI,energy decomposition analysis,NBO?of weak intermolecular interactions are introduced and illustrated in detail.Chapter 3,studying the weak intermolecular interactions between bromopenta-fluorobenzene and pyridine.Bromopentafluorobenzene and pyridine were selected as the research materials,and the weak intermolecular interaction between them was calculated and analyzed.It was found that there were different types of binding modes via weak intermolecular interactions,and the energy decomposition analysis showed that the driving forces of weak intermolecular interactions are different,1)the binding mode of head to head weak intermolecular interaction is the halogen bond interaction,and the driving force mainly comes from the electrostatic interaction;2)the binding mode of T-shape weak intermolecular interaction is mainly van der Waals interaction,and the dispersion interaction is the main driving force;3)in the face-to-face mode,the?-?stacking is the main stabilizing factor,and the dispersion interaction is the main driving force.By comparing these dimers,it can be found that the most favorable binding mode is the?-?stacking,and the less stable structure is the T-shape structure.Chapter 4,exploring the weak intermolecular interaction between bromo-or iodo-pentafluorobenzene and furan as well as thiophene.In this chapter,the weak intermolecular interaction between bromo-or iodo-pentafluorobenzene and furan?or thiophene?was studied in detail.Three different binding patterns of dimer are also obtained,and the type and driving force of each weak intermolecular interactions are similar to that in chapter 3,but it is worth noting that the binding mode and interaction of dimers between bromo-and iodo-pentafluorobenzene and thiophene and furan can be influenced by the type of atoms.Since the region on iodine atom top in iodopentafluorobenzene has a larger a region of positive electrostatic potential,sulfur atom in thiophene can form stable dimer with it,but the similar structure is not found in dimers of bromopentafluorobenzene and thiophene.In other words,the binding mode and interaction energy can be adjusted by changing the type of atoms and the electronic effects of some groups.