Synthesis,Crystal Structure And Properties Of Metal-organic Coordination Polymers Based On 4-(Benzimidazole-1-y1)benzoic Ligand

Metal-organic coordination polymers not only have potential applications in gas storage and separation, optical, electrical and magnetic functional materials,molecular recognition and detection, and catalysis, but also can display diverse structural topologies. The study of the metal-organic coordination polymers becomes one of the interdisciplinary areas of inorganic chemistry, physical chemistry and materials chemistry. There some factors to influence the structure and the physical property of the coordination polymers, while the organic ligand is a key factor. The N-containing heterocyclic aromatic carboxylic acids containing oxygen and nitrogen donors, which can exhibits various coordination modes when coordinate to the metal ions. Herewith we synthesized a large spatial ligand of 4-（benzimidazole-1-yl）benzoic acid（Hbmzbc）, which is a rigid ligand. The Hbmzbc ligand is suitable as a bridging ligand that can exhibit an adaptable conformation in a certain structure as a result of the free rotation of the C–N single bond between the benzene moiety and benzimidazole moiety. Such a character makes it is an effective components for construction of the metal-organic coordination polymers with diverse structures. On the other hand, the Co²⁺ can exhibit rich magnetic behavior due to its large magnetic anisotropy resulting from significant spin-orbit coupling. The Cu²⁺ ion is used to build a functional metal- organic coordination polymers as because it can displays four,five and six-coordinated coordination modes and variable valences.Reactions of the Co²⁺ or Cu²⁺ ions with Hbmzbc ligand under different conditions afforded six novel metal- organic coordination polymers: namely,{[Co（bmzbc）₂]?（DMF）₂}_n（1） 、 [Co（bmzbc）₂（Hbmzbc）]n（2） 、 {[Co（bmzbc）₂（1,2-etdio）]·（H₂O）}_n（3） 、 {[Cu₃IICu I（bmzbc）₆]（NO₃）}_n（4） 、{[Cu（bmzbc）₂]·（DMF）₂（H₂O）}n（5）, and [Cu（bmzbc）₂]_n（6）. These structures have been characterized by single-crystal X- ray diffraction, X- ray powder diffraction and infrared spectra. The gas adsorption and magnetic properties of some of the compound have also been characterized.Three chapters are presented in this thesis.The first chapter has mainly reviewed the concept of the metal-organiccoordination polymers, the latest research progress on metal-organic coordination polymers which were built with the N-containing heterocyclic aromatic carboxylic ligands.The second chapter described the syntheses, structures, thermal stability analyses of the aboved mentioned six coordination polymers. The Co（II） ions are bridged by the rod-like bmzbc- ligands to give a two-dimensional（2D） sheet. The 2D sheets are further stacked into a 3D framework with 1D channels occluded the guest DMF molecules. The microporous nature of 1 was established by measuring CO₂ sorption isotherms. The abrupt changes observed in the C₃H₈ and C₂H₆ adsorption isotherms indicate a structural transformation occurred in the gas-loading process. Detailed magnetic studies show that the individual octahedral Co（II） ions in 1 exhibit field-induced slow magnetic relaxation, which is characteristic behavior of single-ion magnets（SIMs）. The long connection between the magnetic metal centers in 1 meets the requirements for construction of porosity and SIM in a well-defined network,providing a good candidate of functional molecular materials exhibiting SIM and porosity harmoniously. Structure 2 is a 2D（4, 4） net. The 3D chiral structure 3 is a2-fold interpenetrating qtz topological net. Magnetic measurements on 2 and 3showed field-induced slow magnetic relaxation resulting from single-ion anisotropy of the individual Co（II） ions. Compounds 1–3 exhibit field-induced slow magnetic relaxation. This work demonstrates that slow magnetic relaxation can be observed in the high-dimensional Co（II） coordination networks wherein the highly anisotropic central Co（II） ions are in an isolated magnetic environment and behave as single-ion magnet（SIM） units. This approach will provide a new route to the design molecular magnetic material based on a mononuclear complex unit.Compound 4 contains mixed Cu II and CuI ions. It features a 2D Kagome structure formed by the 4-（benzimidazole-1-yl）benzoic bridging the paddle-wheel dinuclear Cu₂（COO）₄ units. It is interesting that each triangular moiety of the Kagome layer is capped by a CuI ion bridged by three 4-（benzimidazole-1-yl）benzoic ligands, which give a tetrahedral cage. Compounds 5 and 6 also are 2D structures. The gas adsorption properties of compounds 4 and 5 are also investigated.The last chapter of the thesis presents the summary of this work.