Constructions And Properties Of Coordination Polymers Of Tetradentate Nitrogen-based Ligands

The coordination polymers（CPs）, which are constructed of metal ions and multitopic ligands, have shown intriguing structural topologies and broad applications as functional materials in adsorption, release, fluorescence, catalysis and nonlinear optics. Thus the design and synthesis of CPs have attracted considerable attention in recent years. Multiple N-donor ligands and polycarboxylates are usually used in the assembly of CPs, while the dinitrogen ligands are the most common investigated. However, study from the tetra- or multi- dentate N-donor ligands are rare up to now. We have been interested in the construction of CPs derived from tetratopic N-containing ligands and polycarboxylates and their physical and chemical properties as well. In this thesis, we selected two tetrapyridyl ligands tetrakis（4-pyridyl）cyclobutane（tpcb） and tetrakis[4-（1-imidazolyl）phenyl]methane（tipm） and carried their reaction with polycarboxylates and metal ions. A number of coordination polymers were obtained. Based on the structural characters of the corresponding complexes, we invested their adsorption, release, photoluminescence properties and photocatalytic degradation properties. These results were briefly described as follows:1. The reactions of Cd SO4 or Cd（NO3）2 with tetrakis（4-pyridyl）cyclobutane（tpcb） under hydrothermal conditions or at ambient temperature resulted in four Cd（II） coordination polymers, formulated as {[Cd3（tpcb）2)（η-η-μ-SO4）2（H₂O）6]SO4·16H₂O}n（1）, {[Cd（tpcb）0.75（OH）（H₂O）2]（NO3）}n（2）, {[Cd2（tpcb）（SO4）2（H₂O）6]·2Me OH·3H₂O}n（3） and {[Cd（tpcb）（NO3）（H₂O）2]（NO3）}n（4）. Compounds 1, 2, and 4 possess complicated 3D frameworks, while 3 presents a 1D chain structure. In the four compounds, tpcb ligands take different coordination modes. In 1 and 2, the tpcb ligands take an up-down-up-down（rtct-） mode. While, in 3 and 4, the tpcb ligands take an up-up-down-down（rctt-） mode. The four compounds have good absorption in the UV-Vis diffuse reflectance spectra. Their energy gaps are less than 3.4 e V, indicating that they could be used as photocatalysts for the photocatalytic reactions. Their photocatalytic activities toward the degradation of three organic dyes（MO, MB and Rh B） in aqueous solutions were studied under the UV light. Among them, 2 and 4 processed better catalytic performances.The hydrothermal reactions of 1,3-H₂ BDC or 5-NO₂-1,3-H₂ BDC, Cd（II） and tpcb produced two coordination polymers [Cd（tpcb）0.5（1,3-BDC）]n（5） and {[Cd2（tpcb）（5-NO₂-1,3-BDC）2（OH₂）2]·4H₂O}n（6）, respectively. Compound 5 exhibits a 3D（4,4）-connected net while 6 possess a 3D（3,4,5）-connected net. The analogous reactions led to the formation of the different 3D frameworks in 5 and 6 despite NO₂ group in the 5-position of 5-NO₂-1,3-H₂ BDC binds neither with Cd（II） centers nor with water molecules. Although the latter has one more NO₂ group in the 5 position than 1,3-H₂ BDC, and this NO₂ group binds neither Cd（II） centers nor water molecules. The two dicarboxylates in 5 and 6 take different coordination modes, which lead to the significant difference in luminescent properties.2. The ligand tipm was effectively synthesized by the microwave-assisted reaction. Two isostructural CPs [Zn2（tipm）（1,3-BDC）2]n（7） and {[Co2（tipm）（1,3-BDC）2]?0.5CH₃CN}n（8） were obtained by the reactions of Zn（NO3）2 or Co（NO3）2 with tipm and 1,3-H₂ BDC under solvothermal conditions. When cobalt ions were incorporated into the Zn-based framework of 7 during solvothermal process, two isostructural CPs {[Zn（2-2x）Co2x（tipm）（1,3-BDC）2]?b H₂O}n（x = 2.4%, b = 0 for 9, x = 23%, b = 1 for 10） were produced. Compounds 7 and 8 exhibited good catalytic activity toward the photodegradation of Rh B under the UV irradiation. Compared to 7 and 8, the doped CPs 9 and 10 showed better photocatalytic activities.Solvothermal reactions of H₂ BPDB with tipm and Cd（II） salts produced two isostructural 3D coordination polymers {[Co（tipm）（H₂O）2]（BPDB）·2（CH₃CN）}n（11） and {[Ni（tipm）（H₂O）2]（BPDB）·2（CH₃CN）}n（12）. 11 and 12 exhibited similar activity in catalyzing the photodegradation of MO and Rh B.3. Solvothermal reactions of Ni（II） salts, tpcb and 5-R-1,3-H₂BDC（R = CH₃, NH₂, HSO3） gave rise to three porous polymers {[Ni₂（μ2-OH₂）（tpcb）（5-R-1,3-BDC）2]·x H₂O}n（R = CH₃（13）, NH₂（14）, HSO3（15）, x=10（13, 14）, 9（15））. CP 13 was the most stable and might lose the solvent molecules upon heating and formed a porous [Ni₂（μ2-OH₂）（tpcb）（5-CH₃-1,3-BDC）2]n（16）. The crystal of 16 could absorb the I2 molecules to get {[Ni₂（μ2-OH₂）（tpcb）（5-CH₃-1,3-BDC）2]·x I2}n（x I2@16）. The sorption research on 16 showed that each molecule could absorb three I2 molecules（x = 3）. A complete I2 release from x I2@16 needs 12 hours and follows the zero order kinetics in the first half hour. The release rate is about 2 × 10^-6 mol·L^-1·min（-1）. The crystals of 16 could also absorb organic molecules p-benzoquinone（Q） to obtain Q@16.When 1,4-H₂ NDC was introduced to the Ni（II）/Co（II）/tpcb system as the second ligand, two 3D coordination polymers {[Ni₂（μ2-OH₂）（tpcb）（1,4-NDC）2]·8H₂O}n（17） {[Co2（μ2-OH₂）（tpcb）（1,4-NDC）2]·8H₂O}n（18） were seperated. Their strctures are similar to those of 13-15; and they possess good stabilities.