Design, Synthesis And Property Of Lanthanide/Transition Metal-Organic Coordination Polymers

Metal-organic coordination polymers or metal-organic frameworks(MOFs), with unique property or multi-functionalities, have been closely related to materials, physics, life sciences and chemistry. The study of lanthanide-contained coordination polymers has important significance in the fields of constructing of intriguing topological nets and synthesizing new materials with unique luminescent, electronic, magnetic and gas separate. Moreover, improving the hydrophobic of MOFs is of great important to the realize industrial applications of MOF materials. According to the theory of molecular engineering, we have focused our study on the reactions of rigid azacyclo-carboxylic acid with lanthanide (4f)/transition (4d) metals. A series of novel coordination polymers containing the 4f or 4d-4f mixed metals were successfully synthesized. The unique luminescent, gas adsorption and sensing properties of these polymers were systematically studied. The main research works of this thesis are as follow:In chapter 1, the backgrounds of this study were briefly introduced, including the research progresses of 4d-, 4f- and 4d-4f-contained functional coordination polymers with unique luminescent, magnetic, electric, gas adsorption, separation and sensing propertyes. Finally, the research aims and contents of this thesis were proposed.In chapter 2, the in situ decarboxylation and dehydration coupling of fumaric acid and isonicotinic acid under hydrothermal conditions and the luminescent property of an unprecedented two-dimensional coordination polymer containing in situ formed new ligands, 3-(4-pyridinecarboxylate)propionic acid (inpro) and oxalate (ox) moieties were explored. Electrophilic addition of fumaric acid to form unstable 2-hydroxysuccinic acid, which could get decarboxylated with trace quantity of nitric acid under certain temperature and pressure to form CO₂ and 3-hydroxypropionic acid: the in situ reductive coupling of CO₂ generated oxalate anion; the condensation reaction between 3-hydroxypropionic acid and 4-carboxypyridinium moiety through dehydration led to the formation of the Hinpro acid which then coordinated with the Eu(III) ion along with the oxalate anion leading to the formation of the coordition polymer 1, {[Eu(C₉H₈NO₄)(C₂O₄)]·2H₂O}n. 1 displays a two-dimensional layered network constructed by Eu-oxalate chanins and inpor. Upon excitation at 359 nm 1 emited the red fluorescent and shown lifetimes of 368.5?s at room temperature.In chapter 3, four new 4d-4f coordination polymers based on 2,6-pyridinedicarboxylate or isonicotinic acid as bridging ligands were obtained, [AgLn(pydc))₂(H₂O)3]·x(H₂O) [Ln = Eu, x = 1.25 (2); Ln = Tb, x = 1.25 (3)],and LnAg(OX)(IN)₂·H₂O (Ln = Nd (4); Eu (5)). The results shown that four 4d-4f coordination polymers emited characteristic fluorescence of lanthanide ions in UV-Visible (UV-Vis) region. The luminescent lifetimes of solid 2, 3 and 5 were measured to be 431.8, 886.8, and 756.6?s, respectively.In chapter 4, hydrothermal reaction of 5-methylpyrazine-2-carboxylic acid with trace amount of nitric acid as both oxidant and acidity modifier produced a novel microporous europium-conatining metal-organic framework [Eu2(?2-pzdc)(?4-pzdc)(?2-ox)(H₂O)₄]·8H₂O (6), which contained in situ oxidation of methyl and decarboxylation formed new ligands, 2,5-pyrazinedicarboxylate (H2pzdc) and oxalate (ox) moieties. It was found that in-situ synthesis of ligands from an organic precursor not only simplified the synthesis, but also led to enhanced crystal size and purity. 6 contained one hydrophilic channel within the three-dimensional structure and was able to host molecules with kinetic radii as big as 2.1 ?. The intensity of luminescence of guest-free MOF 6a exhibited solvent-dependent effects, which has the potential applications as a luminescent receptor for reversible and selective molecular sensing.In chapter 5, the self-assembly of terephthalic acid and 2,2'-dimethyl-4,4'-bipyridine/3,3'-dimethyl-4,4'-bipyridine with transition metal salt under solvothermal conditions obtained two new microporous metal-organic frameworks, [Zn₂(BDC)₂(P²)]·(DMF)₂·(H₂O) (SCUTC-18) and [Zn2(BDC)2(P3)]·(DMF)·(H₂O)2 (SCUTC-19), which both featured the same three-dimensional coordination network with 1D open channles. The results indicated that the incorporation of methyl groups enhanced the stability of MOF-508 which constructed by 4,4'-bipyridine, terephthalic acid and Zn²⁺ under standard atmospheric conditions. Furthermore, the moisture stability of the MOFs depended strongly on the positions of the methyl substitutes on the 4,4'-bipyridine linkers. The hydrophobic groups closer to the Zn centers, the hydrophobicity of MOFs was stronger. The combination of high stability in air and hydrophobicity as well as high adsorption capacity for toluene implies that SCUTC-18 has potential capabilities for air-cleaning applications.