A Study Of Molecular Weak Interactions On Several Kinds Of Compounds

Because of the vital role in the crystal engineering,the molecular recognition, supramolecular chemistry,the supramolecular assembly,crystal packing and the structure-activity relationship in biological systems,the study on the molecular weak interactions has attracted the attention of researchers.In recent years,the molecular weak interactions are being paid more attention to the experimental and theoretical investigations.But it is seldom about the weak interactions by topological analysis methods.The purpose of this paper is to study the geometry configuration,bonding nature by quantum chemistry and topological analysis of the electronic density methods.The rules of the formation of molecular weak interactions were discussed in order to help the further research in this field.In this thesis,the four types of weak interactions such as conventional resonance-assisted hydrogen bond,non-conventional C—H…O hydrogen bond,C—H…πinteraction andπ…πstacking were studied.At the first part of the thesis,the wide application of weak interaction,quantum chemistry and topological analysis was summarized.Bonding characters and electronic structures are still the main area of quantum chemical research.Because the topological analysis of the electronic density method is a new method,many studies are needed to be done by the theory.In chapter two,the resonance-assisted N—H…O/O—H…N hydrogen bond in hydroxyl azobenzene were studied by crystal chemistry,quantum chemistry and topological analysis.The results lead us to the conclusion that the N—H…O hydrogen bond is stronger than O—H…N hydrogen bond in hydroxyl azobenzene,and this resonance-assisted hydrogen bond is best described as a 3-center,4-electron covalence bond.The structures of two azobenzene single crystals were also studied.The results show that the weak molecular interactions such as C—H…O,C—H…N,C—H…Cl hydrogen bond,π…πstacking and C—H…πinteraction play important role in crystal packing.The results of CSD(Cambridge Structural Database) searches also show thatπ…πstacking and C—H…πinteraction dominate the molecular assembly.π…πstacking and C—H…πinteractions are usually contacted by centrosymmetry,and C—H…O,C—H…N hydrogen bonds are noncentrosymmetric hydrogen bond.In chapter three,the multi-center C—H...O hydrogen bond was studied.The geometry configuration,quantum calculation and electronic density analysis made us sure that R₃¹(11) multi-center C—H...O hydrogen bond was existed for a certainty in 4,4'-chalcone compounds.It was also testified that the characteristic of O—H...O resonance-assisted hydrogen bond was a 3-center,4-electron covalence bond.Linear correlations of the interaction energies with the electronic density in the hydrogen bond and the lengths of hydrogen bond were discussed.In chapter four,the crystal structures of 27 stilbazolium salts were retrieved from CSD.The relationship among the characteristic ofπ…πstacking and C—H…πinteraction,crystal packing energies and formation of centrosymmetric crystal was discussed.The results indicated that when the stilbazolium salts have got the same cations,the large anions can provide strong electrostatic interactions to overcome the dipole-dipole interactions.In this condition,the connected methods of C—H…πandπ…πweak interactions will master the type of space group of crystal packing.If these weak interactions were connected by centrosymmetry,the compounds are accumulated in centrosymmetric space groups.The compounds will accumulated in centrosymmetric space groups if the volume of anions is not large enough to overcome dipole interactions.