Synthesis, Crystal Structures And Electrochemical Properties Of Metal-organic Frameworks Compounds Based On Dipyridinyl Triazole

Hofmann-type compounds are chosen as the subject of the dissertation, and threenovel3D coordination polymers [Mn(bpytz)Ni(CN)4, Mn(bpytz)Pd(CN)4andFe(bpytz)Pd(CN)4] with regular pore structures were constructed by Mn(II) or Fe(II)ions,[Ni(CN)4]2-or [Pd(CN)4]2-, and3,5-bis(4-pyridyl)-1,2,4-triazole)(bpytz).Composition and structures for the three compounds were characterized by X-raysingle crystal diffraction, powder X-ray diffraction, FT-IR spectra and N2adsorptionexperiments. The effects of metal ions, cyanometallate anions and ligands oncoordination polymer’s structures and properties were discussed. In addition, theelectrochemical properties for a few Hofmann-like compounds with definitestructures were studied as cathode materials for lithium-ion batteries. The effects ofmetal ions, cyanometallate anions and ligand on their electrochemical properties werediscussed. The research results are as follows:1. The crystal structures of the three novel coordination polymers[Mn(bpytz)Ni(CN)4, Mn(bpytz)Pd(CN)4and Fe(bpytz)Pd(CN)4] were determined. Inthe three complexes, four cyano groups of Ni(CN)4]2-and [Pd(CN)4]2-took part incoordination as the bridged ligands, linking the Mn(II) ions and Ni(II) ions, Mn(II)ions and Pd(II) ions or Fe(II) ions and Pd(II) ions alternately to form2D layerstructures [MnNi(CN)4]∞/MnPd(CN)4]∞/[FePd(CN)4]∞. These2D sheets were linkedby bpytz as auxiliary bridge ligand, resulting in3D framework structures. However,the bpytz took on in different connected ways in the three complexes. In the complexMn(bpytz)Ni(CN)4, two N atoms of pyridine for bpytz don’t link the same metal ionsof adjacent layers. It is interesting that one N atom of the pyridine coordinated toMn(II) ion, while the other N atom of pyridine coordinated to Ni(II) ion of adjacentlayers, leading to tetragonal pyramid structure for Ni(II) ions with five coordination.The coordination environment of Mn(II) ions is a six-coordinated, distortedoctahedron. N atoms from four cyanos define a equatorial plane, nitrogen atom frombpytz and oxygen atom from ethanol occupies the axial positions, respectively. C atoms for methyls in coordinated ethanol molecules are disordered. Moreover, eachasymmetric unit of the complex contains three water molecules. The O atom in one ofthe water molecules is disorder. While complexes Mn(bpytz)Pd(CN)4andFe(bpytz)Pd(CN)4belong to classic3D Hofmann compounds, in which bpytz act asthe pillar ligand, bridging Mn(II) or Fe(II) ions of adjacent layers. The analysis of N2sorption shows that the two compounds can reversibly ab-and desorption behaviors.2. Six Hofmann-type compounds (Fe-pz-Ni, Fe-pz-Pd, Fe-pz-Pt, Cd-pz-Ni,Cd-bipy-Ni and Fe-tvp-Pt) have similar structures, in which pz, bipy and tvp only actas pillar bridge ligands. Two non-Hofmann-type compounds (Fe-bipy-Ni andMn-bipy-Ni) also have similar structures, in which bipy not only acts as the bridgeligand but also the terminal ligand. The electrochemical properties for eightcompounds were investigated as cathode materials for lithium-ion batteries by cyclicvoltammograms, impedance spectra, charge/discharge profiles and so on.Electrochemical results indicate that the eight compounds exhibit reversibleinsertion/extraction for lithium-ion. Furthermore, they have unprecedented long cyclelife and high rate performance. The effects of cyanometallate anions, metal ions andligand on their structures and electrochemical properties were discussed in detail. Wefound that the electrodes made of Fe-pz-Ni exhibited a high reversible specificcapacity of221.8mAh g-1after10cycles and218.2mAh g-1after100cycles atcurrent density of100mA g-1at ambient temperature. The specific capacity is higherthan the theory specific capacity of NiFe-PBA (70mAh g-1). What’s more, theelectrodes for Cd-pz-Ni and Fe-tvp-Pt, whose specific capacity have a tendency toincrease with the increase of cycle numbers.