Dihalogen Molecules With Several Electron Donor Halogen Bond Electron Density Topological Study

Halogen bond is known as a kind of non-covalent intermolecular interaction. By considering crystal packing results as the sum of many different contributions of directional and non-directional intermolecular interactions, it is important that different types of interactions be considered jointly in structure analysis. Although research has traditionally focused on the more well known hydrogen-bonded interactions, a growing body of experimental and theoretical evidences confirms that interactions such as -X...Y- (X=C1, Br and I;Y=N, O, S and Ï€) or -X...Y- (X=C1, Br and I;Y=C1, Br and I) similarly play important roles in crystal engineering, super-molecular chemistry, high-value materials and drug designing. The main features of the interaction have close similarity with the hydrogen bond. Such interactions are the so-called halogen bond. The application area of quantum chemistry is increasingly growing, bonding characters and electronic structures in molecule are still the main area of quantum chemical research work. In recent years, the theory of "atoms in molecules" (AIM) has been applied to the studies of bonding characters and reaction mechanism, and noteworthy achievements have been achieved.The purpose of this thesis is to study the structures and bonding nature of the intermolecular halogen bond by the methods of quantum chemistry and topological analysis of the electronic density. In this thesis, two types of halogen bonds named as n-type halogen bond and Ï€-type halogen bond were studied.B3LYP/6-311++G(d,p) and MP2/(full)6-311++G(d,p) methods were used to study the n-type halogen bonds between dihalogen molecules XY and H₂CO or H₂CS, Ï€-type halogen bonds between XY and C₂H₂ or C₂H₄, halogen bonds between XY and furan, thiophen and pyrrole. Based on the AIM theory, the nature of the halogen bonds was discussed with programs GTA-2000 and AIM-2000.The study on the n-type halogen bonds between XY and H₂CO or H₂CS gave stable complexes with O...X-Y or S...X-Y interaction. On the Ï€-type halogen bonds between XY and C₂H₂ orC₂H₄ there exists Y-X...Ï€ interaction in each halogen-bond complexes, which has a T-shaped structure with the halogen atom (X) of XY pointing toward the bond critical point (BCP) of the C-C bond. Topological properties, Ï€-electron integral and contour maps of Ï€-electronic density and relevant Laplacian confirmed the presence of Ï€-type halogen bond.In the study on halogen-bonded complexes formed by XY and furan, two stable structures with O...X-Y and Ï€...X-Y interaction were obtained. The interaction energyof halogen bond in the latter complex is larger than that of the former. The formation of halogen bond results in an elongation of X-Y bond, which is accompanied by a red shift of stretching frequency of the X-Y bond. In the study on halogen-bonded complexes formed by XY and thiophen, two stable structures with S...X-Y and n.. .X-Y interaction were obtained. The interaction energy is between -2.40—5.56kcal/mol and -2.61—5.56 kcal/mol in the complexes of S...X and 7t...X. The topological studies of the electronic density indicated the nature of halogen bond in the XY-thiophen complexes is mainly due to electrostatic effects and the chemical bond of halogen bond is between covalent bond and electrovalent bond. The study of a series of halogen-bonded complexes formed between XY and pyrrole showed that two stable geometry structures with N...X-Y and 7T...X-Y interaction. N...X-Y complex has Cs symmetry, and in 7T...X-Y complex the C1F axis is likely perpendicular to the C-C bond next to O atom of furan. Topological studies of the electron density of the complexes confirmed the existence of the 7r-type halogen bond.The new conclusion and ideas of this work are listed as following:1. Two types of halogen bonds of n-type halogen bond and re-type halogen bond were studied by topological analysis of the electronic density. Similarities in the topological electron density characteristics between the properties of the HB complexes were found. The differences correspond to the variation trend of the atomic properties calculated for the interacting halogens with the AIM methodology (charge, volume, energy, dipolar polarization) when going from the monomers to the complexes were observed.2. Program GTA2000 compiled by ourselves was used to deal with the 7t-electron separating from 7c-type halogen bond complexes, it could describe the contours of ji-electronic density and Laplacian, and make GTA2000 link to program AIM2000 to calculate the u-electron integral. All of the results gave a clear description of the nature of 7t-rype halogen bond.3. For the first time, the halogen bond in complexes of furan, thiophen, pyrrole and dihalogen molecules were studied. D...X-Y(D=O, S, N) were found in the complexes, which were not found in the in experiment. The halogen bond of 7Z...X-Y is stronger than that of O.. .X-Y, which explained that only the %.. .X-Y interaction was obtained in experiment of furan-XY. The relationships of the charge transfer and the strength of halogen bond were discussed.