| Metal-organic coordination polymers based on carboxylate ligands have diverse topology structures and potential applications in the areas of optical, electronic, magnetic and catalytic properties. In the research on construction of metal-carboxylate coordination polymers, great efforts have been focused on rigid ligands, the investigation of flexible ones in construction of metal-organic frameworks is comparatively lacking, since they may exhibit more conformation and coordination versatility in contrast to the rigid ligands, which result in the difficulties in predicting the resulted framework structures. However, these features of flexible ligands may also provide various possibilities for constructing frameworks with novel topologies and desired properties.In this paper, by treating (1,3,4-thiadiazole-2,5-diyldithio)diacetic acid (H2tzda) or [(4,6-dimethyl-2-pyrimidinyl)thio] acetic acid (Hdpmta) with some metal ions directly or under the help of some subsidiary ligands, two series of metal-organic polymers have been successfully obtained at room temperature or under hydrothermal conditions. Furthermore, their fluorescence properties, magnetic and electric properties were also investigated.Firstly, treatment of H2tzda with CuSO4·5H2O or Cd(NO3)3·4H2O afforded two coordination polymers 1 and 2; reaction of H2tzda with CuSO4·5H2O, Cd(NO3)3·4H2O or Zn(NO3)3·6H2O and a subsidiary ligand (2,2'-bipy or phen) produced coordination polymers 3～6. Furthermore, assembly of H2tzda with CaCl2·2H2O provided polymer 7. polymers 1 and 3～6 display one-dimensional chain structure, 2 possesses three-dimensional network, while 7 exhibits two-dimensional layered network. In these polymers, the tzda shows five different coordination modes, which make above polymers own various structures. Study on the fluorescent properties of 2, 3 and 5～7 reveals that the subsidiary ligand may influence the fluorescent emission. The electrochemical studies on 1 and 4 show that their redox processes in the potential range of -0.6～0.4V are quasi-reversible and controlled by the diffusion.Secondly, ten coordination polymers 8～17 were prepared by reaction of transition metal salts with H2tzda and a subsidiary ligand (4,4'-bipy or bpe). 8, 9 and 13～16 have two-dimensional layered architectures and the structures of 8 and 13～16 are very similar, which are all generated from [M(tzda)]n moiety with double-chain structure cross-linking 4,4'-bipy spacers. The structures of 10～12 seem more complicated, in which the [M(tzda)]n layered subunits are extended to unique 3D framework by the bridging 4,4'-bipy ligand. Interestingly, the [M(tzda)]n layers display a rare structural feature with 'the Great Wall' shape of China. 17 also displays three-dimensional network, however, different those of 10～12, it's structure is generated from one double-chain [Ni2(tzda)(H2O)]n structure cross-linking bpe spacers and features two-fold honeycomb-like framework. In 8～17, the ligand tzda shows four coordination modes which is different from those of 1～7. The study on luminescent property shows that 8, 9 and 13, 14 display strong blue fluorescent emissions. The magnetic studies of 10～12 and 15～17 suggest all of them display the characteristics of a weak antiferromagnetic coupling between metal ions in the system mediated by carboxylate bridges.Thirdly, hydrothermal reactions of rare earth ions(Ⅲ) with H2tzda lead to six novel coordination polymers 18～23 with 3D network structures. In the structure of 18, there are four crystallographically independent Ce(Ⅲ) ions and six crystallographically independent tzda ligands displaying four coordination modes. Polymers 19～23 have similar structure, in which tzda shows three different coordination modes. All of these coordination modes are not same as those of transition metal coordination polymers. Under the excitation of UV light, the solid samples of 22 emit intense green luminescence. The magnetic data analyses indicate that there exist ferromagnetic interactions among rare earth ions(Ⅲ) in 21～23.Finally, four metal-organic complexes 24～27 based on [(4,6-dimethyl-2-pyrimidinyl)thio] acetic acid (Hdpmta) have been produced. Among them, 24 displays one-dimensional chain structures, 26 owns two-dimensional layered network, while 24 and 27 show mononuclear and dinuclear structures, respectively. The study on the luminescent properties of these complexes revealed that all of luminescent emission bands are cause by intraligand transition and the intensity of these bands are influenced by center metal ions and the structures of complexes. The magnetic behaviors show that in 27 the occurrence of a strong antiferromagnetic coupling between the copper(Ⅱ) ions can be observed. Similar to 1 and 4, the electrochemical study on 27 displays that its redox process in the potential range of -0.4～+0.4V is also quasi-reversible and controlled by the diffusion.
|
PDF Full Text Request