Syntheses, Structures And Characterizations Of The Metal Complexes With Several Multidentate Ligands

Multidentate ligands play an important role in the development of coordination chemistry. It has been the essential issue of modern coordination chemistry to select or design suitable multidentate ligands, and then let them react with metal ions to synthesize metal-organic coordination compounds with desired structures and excellent properties. The structures of complexes may be affected by many factors, which make it difficult to forecast them exactly. Therefore, it is of important significance to form coordination architectures by purposefully selecting or designing proper multidentate ligand, and letting them react with metal ions under various reaction conditions to synthesize complexes, and to investigate their structures and properties systematically as well as the relationship between them.Multidentate carboxylic acid ligands have taken a significant position in coordination chemistry recently because of their stronger coordination capability and diverse coordination modes. In this dissertation, multidentate ligands 2,2’-oxydiacetic acid, nitrogen heterocyclic dicarboxylic acid (pyridine-2,5-dicarboxylic acid, pyrazine-2,3-dicarboxylic acid) and aromatic carboxylic acid (salicylic acid, 5-sulfosalicylic acid,1,3,5-benzene tricarboxylic acid) etc have been used and twenty-five new coordination compounds of them have been synthesized. The structures of these complexes are determined by X-ray single crystal diffraction analysis and they are relative to the following factors, the coordination number of metal ions, the properties of ligands themselves, different synthesizing methods and auxiliary ligands and so on. Besides, solid-state fluorescence, magnetism, electrochemistry, and electron paramagnetic resonance (EPR) properties of some complexes have also been studied.The main contents of the dissertation are as follows.1. Six 3d-4f heteronuclear bimetallic coordination polymers 1-6 are synthesized when 2,2’-oxydiacetic acid ligand reacts with different transition metal and lanthanide metal ions at the same time. The analysis of their structures shows that the ligand bonds to center metal ions by double bridging chelateμ3 (1-6) and bridging chelateμ2(6) coordination modes. The solid-state fluorescence spectra, magnetic properties and electron paramagnetic resonance (EPR) spectra of complexes 1-5 are obtained, and the solid-state fluorescence spectra indicates that complexes 1-5 have similar fluorescence emissions with free ligand. Complex 1 has no magnetic exchange between metal ions at room temperature. The magnetic interactions of 2 can not be explicitly characterized because of the strong spin-orbit coupling between center metal ions. Complexes 3,4 and 5 have weak antiferromagnetic exchange interactions at lower temperatures but no interactions at room temperature. These conclusions are in good agreement with their electron paramagnetic resonance (EPR) spectra. In addition, the investigation of the cyclic voltammetric properties of compound 5 reveals that it is much stable and hard to be oxidated or reduced.2. Six monometallic coordination compounds 7-12 are obtained when 2,2’-oxydiacetic acid reacts with transition metal ions. The characterization of their structures exhibits that the ligand links center metal ions via double bridging chelateμ3 (7,9,11), tridentate chelate (8,10,11) and bridgingμ7 (12) coordination manners. The influence of metal ions, synthesis conditions and auxiliary ligands on formation of them is discussed. The results of magnetic properties of Cuâ…¡compound 7 indicate that it has ferromagnetic interactions between adjacent Cuâ…¡ions in 0-300K. Moreover, the fluorescence spectra of 7,10,11 and 12 are also investigated. The results are that the emissions of 7,10,11 come fromÏ€*â†'Ï€electron transitions of ligand, while that of 12 is assigned to two kinds of Ag-Ag interactions.3. Five transition metal complexes 13-17 with nitrogen heterocyclic dicarboxylic acids ligands are synthesized. The analysis of their structures displays that the corresponding ligand joins center metal ions through bidentate chelate (13), double bridging chelateμ3 (14,15), bridging chelateμ2 (16) as well as triple bridging chelateμ4 (17) coordination patterns. The effects of different ligand, different metal ions and different experimental conditions on forming structurally different compounds are analyzed. Furthermore, the fluorescence emission properties of three d10 complexes 15,16,17 are characterized and the emissions of them all originate fromÏ€*â†'Ï€electron transitions of ligand. 4. Three metal complexes 18,19,20 with nitrogen heterocyclic bridging ligands are prepared. The characterization of their structures indicates that the corresponding ligand connects center metal ions by bidentate bridging (18,19,20) and tridentate bridging (18) coordination model. The influence of different ligand and different metal ions on obtaining them is discussed. The investigations of their fluorescent properties reveal that the much stronger emissions of 18,19 come fromÏ€*â†'Ï€electron transitions of the corresponding ligand; whereas that of 20 is attributed toÏ€*â†'Ï€electron transitions of its counteranions. The studies on the magnetic properties of Coâ…¡compound 20 indicates that Coâ…¡ions are in high-spin state and compound 20 has weak antiferromagnetic interactions in 0-300K.5. Three d10 metal complexes 21,22,23 with aromatic multidentate carboxylic acids ligands are synthesized. The analysis of their structures reveals that the corresponding ligand bonds center metal ions via bridgingμ3 (21), bidentate chelate (22) and bridging chelateμ3 (23) coordination modes. The effects of different ligands on the formation structurally different complexes are studied. The studies on the solid-state fluorescent spectrum of Ag1 complex 21 show that its emissions originate from theÏ€*â†'Ï€electron transitions of benzene ring in ligand.6. Two d10 metal complexes 24,25 with chiral phosphine ligand are synthesized. The characterization of their structures shows that the ligand links center metal ions by bismonodentate (24) and bridgingμ2 (25) coordination manners. The influence of different metal ions on forming them is discussed in detail. Morevoer, their UV-vis and fluorescence spectra are also characterized and the results show that they have different extent metal-to-ligand charge transfer (MLCT).