Study On Synthesis And Properties Of Metal Complexes With N-Heterocyclic Carboxylic Acid Ligands

Molecule-based materials have attracted intense attention in coordination chemistry because of their potential applications such as gas storage, ion exchange, heterogeneous catalysis, and special magnetic properties. It is still a challenge to theoretically forecast the structures of complexes with desired functions by design and selection of suitable ligands, metal ions and other factors.The N-heterocyclic carboxylic acid ligands containing both N and 0 donors, which are strong electron donating atoms, have been demonstrated to be good bridging ligands due to their diverse coordination modes. In this dissertation, to design and synthesize multifunctional molecule-based materials with finely tuned structures and properties, twenty-nine complexes with eight N-heterocyclic carboxylic acid ligands exhibiting various structures and topologies have been synthesized and characterized. The nature of the properties of ligands, metal ions, solvent conditions and other factors were found to greatly influence the structures of the complexes. Furthermore, magnetic properties, reversible guest molecule adsorption and crystal structure transition properties of some complexes have been studied. The main contents are summarized as follows:1. Five metal-azide complexes with nicotinate, isonicotinate and pyrazine ligands have been synthesized and structurally characterized. Among them there is the nicotinate complex with rare 3D Kagome framework; the isonicotinate complex exhibiting reversible guest molecule adsorption properties explored by single-crystal-to-single-crystal transformations; and the pyrazine complex showing an unusual single chain magnet with pentacoordinated Co" ions.2. Two imidazole-containing acetic acid ligands and their nine complexes have been synthesized and structurally characterized. Some short bridge ligands with rich coordination modes and efficient magnetic exchange pathways, such as azide and formate, have been introduced to this system, and a 3,6-connected three-nodal unprecedented topology with Schlafli notation (42·6)2(47·66·82) was obtained. In addition, magnetic properties of some complexes have also been studied. These results probably provide the evidence for the origin of spin canting.3. Ten complexes with two triazole-containing acetic acid ligands have been synthesized and characterized. The effects of some factors such as the properties of ligands and co-ligands, the nature of metal ions, anionic hydrogen bonding, as well as the solvent on the structures of the complexes have been discussed, and the magnetic properties of some complexes were investigated. The results indicate that the triazole-containing acetic acid ligands could act as three-connected node to build three-connected topologies.4. Five complexes with tetrazole-1-acetic acid ligand were synthesized and characterized. The weak interactions in these complexes, such asπ-πand C-H…πinteractions, greatly affect the coordination modes of ligands and packing modes of the molecules in the crystal, and stabilize the solid structures of these complexes. In addition, magnetic properties of some complexes have also been studied. The results demonstrate that coordination configuration of metal ions and co-ligands have important effect on the magnetic properties of such complexes.