Theoretical Studies On Halogen Bond-an Important Intermolecular Interaction

The intermolecular interaction is a general interaction which was widely used in thecrystal engineering, molecular recognition, materials chemistry and so on. Intermolecularinteraction has been widely studied not only in the chemical area, but also the biological.In this work, several typical intermolecular interactions, such as halogen bond, hydrogenbond, and anion π interactions, were used as the object of study. The perturbation theory,density function theory and the quantum theory of “Atoms in Molecules” were carried out onthe intermolecular interactions. We summarized the influence factors of the intermolecularinteractions. There are mainly contained three sections:1. The second-order M ller Plesset perturbation theory (MP2) calculations, andquantum theory of “atoms in molecules”(QTAIM) and non-covalent interaction (NCI)studies were carried out on a series of X···N halogen bonds in the YC6F4X···C2H8N2(X=Cl,Br, I; Y=F, CN, NO2, LiNC+, NaNC+) complexes. The electron-withdrawing substituentsproduce an enhancement effect on the size of the σ-hole and the maximum positiveelectrostatic potentials (VS,max), which further strengthens the halogen bonding. The metallicion M+(M+=Li+, Na+) has the ability to enhance the size of both the σ-hole and VS,maxvaluewith the formation of [MNCC6F4X]+, resulting in more electronic charge transfer away fromthe halogen atom X and an increase in the strength of the halogen bond. It is found that thevalues of VS,maxat the σ-holes are linear in relation to the halogen-bonded interaction energiesand the halogen bonding interaction distance, indicating that the electrostatic interaction playsa key role in the halogen bonding interactions.2. The influence of halogen bond acceptors on a series of N···I halogen bonding in theY-C6-nH6-nNn···C6F5I (n=1,2,3; Y=Cl, Br, I) complexes were studied under the densityfunctional M06-2X level. For the halogen bond acceptors C6-nH6-nNn(n=1,2,3), with thedecreasing number of nitrogen atom in the aromatic ring, the most negative electrostaticpotentials (VS,min) outside the nitrogen atom becomes more negative and the halogen-bondedinteraction energies become greater. With the addition of halogen anions to the halogen bondacceptor, the XB become more covalent, more electronic charge transfer from the XBacceptors to donors, the XB acceptors become more energetic stabilization and XB donorsbecome more destabilization. The XB interaction in the Y-C6-nH6-nNn···C6F5I (n=1,2,3; Y=Cl, Br, I) complexes display the characteristics of “closed-shell” noncovalent interactions.From the view of the Laplacian of electron density function, the halogen bonding interactioncan be classified as lump-hole interaction. 3. The intermolecular interactions in the complexes of tetraoxacalix[2]arene[2]triazinewith the four typical polyatomic anions(SCN, NO3, BF4,and PF6) were studied at theM06-2X/aug-cc-pVDZ level. The region of the positive electrostatic potentials is focused onthe central region of tetraoxacalix[2]arene[2]triazine. The anions points to the positiveelectrostatic potential region of tetraoxacalix[2]arene[2]triazine formation of complexes. Theintermolecular interaction in the complexes has hydrogen bonding and anion π interactions.For the complexes, the electron density (ρb) at the BCP of hydrogen bonding are greater thanthe ρbat the BCP of anion π interactions, indicating that the hydrogen-bond interactions arestronger anion π interactions in the complexes. The interactions in complexes display thecharacteristics of “closed-shell” noncovalent interactions.The innovation in this thesis:1. The XB donor of substituted haloperfluoroarenes C6F4XY (X=Cl, Br, I; Y=F, CN,NO2) as bond donors, which was widely used in crystal engineering. We studied herelationship between the molecular electrostatic potentials and the strength of halogen-bondinteraction in the complexes. We sum analysis of the topological parameters of electrondensity and the topological parameters of the Lacplacian of electron density, indicating thatthe electron-withdrawing substituents and the metallic ion have the ability to enhance thehalogen-bond interaction. Visualize of the information of halogen-bond at BCP as regions ofreal space and distinguish of the types of interactions.2. Assessment of the influence of XB acceptors on the halogen-bond interactions isstudied firstly. The topological parameters of the Lacplacian of electron density was used tostudy the region of valence shell charge concentration in the Y-C6-nH6-nNn···C6F5I (n=1,2,3;Y=Cl, Br, I) complexes.3. The interaction in the complexes of tetraoxacalix[2]arene[2]triazine with the anionswere theoretical studies. The QTAIM studies have shown that these interaction of complexeswere the “closed-shell” noncovalent interactions and the hydrogen-bond interactions arestronger anion π interactions in the complexes.