Comparison Of The Directionality Of The Various Non-covalent Interactions

The intermolecular interactions take a very important role in supramolecular chemistry, molecular physics, materials science and other related fields. It also has a great impact on the structures of the gas, liquid and solid phase compounds and the mechanism of the reaction process. The scientists have already researched the experiment and theory of intermolecular interaction extensively and in-depthly for many years. Mulliken pointed out that the most common intermolecular interaction is the supplying electron for electron density arid area by the dense area. The typical intermolecular interactions are hydrogen, halogen, lithium and chalcogen bonds.This work divided into three parts, compared of the directionality of the various non-covalent interactions with electron density topological analysis of the theory of atoms in the molecule, localized molecular orbital energy decomposition and natural bond orbital（NBO） analysis. The main research method is molecular electrostatic potential analysis.The first part of this work, the HOOOH···XF（X = Cl, Br, H, Li） complexes were constructed and studied based on the M06-2X/aug-cc-pVTZ method. Detailed electrostatic potential（ESP） analyses were performed to compare the directionality of halogen bonds with those of hydrogen bonds and lithium bonds. To do this, the interactions of HOOOH with the molecules XF（X?=?Cl, Br, H, Li） were investigated. For each molecule, the percentage of the van der Waals（vdW） molecular surface that intersected with the ESP surface was used to roughly quantify the directionality of the halogen, hydrogen, lithium bond associated with the molecule. The size of the region of intersection was found to increase in the following order: ClF?<?BrF?<?HF?<?LiF. The maximum ESP in the region of intersection, V S, max, was observed to become more positive according to the sequence ClF?<?BrF?<?HF?<?LiF. For ClF and BrF, the positive electrostatic potential was concentrated in a very small region of the vdW molecular surface. On the other hand, for HF and LiF, the positive electrostatic potential was more diffusely scattered across the vdW surface than for ClF and BrF. Also, the optimized geometries of the dipolymers HOOOH···?XF（X?=?Cl, Br, H, Li） indicated that halogen bonds are more directional than hydrogen bonds and lithium bonds, consistent with the results of ESP analyses.The second part of this work, MOn···R（M=O, S, Se; n=2, 4; R=NCH, NH₃, OH₂, FCl） complexes were constructed based on the MP2/aug-cc-pVTZ method. According to the molecular electrostatic potential analysis, the chal-bond interactions were predicted between the ESP maximum of MOn（σ-hole） to the ESP minimum of molecule R. The geometries and the frequencies were performed and the chal-bonds formed. Based on the electron density topological analysis of the theory of atoms in the molecules, localized molecular orbital energy decomposition and natural bond orbital（NBO） analysis, the following conclusions could be drawn: According to the order of O<S<Se、MO2<MO4（M=S, Se） the chal-bond strength increased; the formation of chal-bond was affected by the σ-hole in electrostatic potential: the larger electrostatic potential value of M（σ-hole） is, the more electron MOn transfered to molecule R; For the three compounds SeO₄···OH₂, SeO₂···NH₃, and SeO₄···NH₃, the chal-bond is partially covalent in character, the rest chal-bonds belong to the characteristics of closed-shell and weak interaction.HF method and 6-31G（d,p） basis set were used to study the halogen-bonding interaction of C₄H₄N₂···2ClF, and to explore the enhancing effect of halogen anions on the N···Cl halogen bond. By analyzing the molecular surface electrostatic potentials, the geometries of the complexes were constructed and optimized, and frequency analyses were carried out to confirm the stable complexes at their ground levels. Topological analyses of electron density were carried out to character the nature of the N···Cl halogen bond.（1） Two N···Cl halogen bonds can be formed through the two negative electrostatic potentials regions outside the nitrogen atoms of C₄H₄N₂ and the positive electrostatic potentials region outside the chlorine atom of ClF. Two hydrogen bonds can be formed between the halogen anions and two of the hydrogen atoms of C₄H₄N₂. The hydrogen bonds have enhancing effects on the N···Cl halogen bonds along the increasing sequence of Br^-, Cl^-, F^-.（2） Topological analyses of electron density on the halogen bond indicate that the N···Cl halogen bond becomes stronger in sequence of C₄H₄N₂-2ClF 、 C₄H₄N₂-2FCl-F-、C₄H₄N₂-2FCl-Cl-, and C₄H₄N₂-2ClF-Br-. The N···Cl halogen bonds in these complexes belong to closed-shell interactions.The innovations in this thesis:1. For each molecule, with the molecular electrostatic potential（ESP） analysis as the main research methods, the percentage of the van der Waals（vdW） molecular surface that intersected with the ESP surface was defined and used to roughly quantify the directionality of the halogen, hydrogen, lithium bond associated with the molecule. The conclusion is that halogen bonds are more directional than hydrogen bonds and lithium bonds.2. The σ-hole regions of the molecule MOn（M=O, S, Se; n=2, 4） were discovered, and the chalcogen bonds have been studied..