| The research of coordination polymer (metal-organic frameworks, MOFs) remains an extremely active field of material chemistry, coordination chemistry and crystal chemistry in recent years. The construction of metal-organic frameworks is of great interest due to their intriguing network topologies and their potential applications as catalysts, ion exchange, gas storage, fluorescence and magnetism. Crystal engineering based on organic linkers and metal centers with specific coordination geometries is an important approach in the preparation of coordination materials with desired functions. In addition to coordinative covalent bonding which is most important in constructing coordination polymer, hydrogen bonding,π-πstacking interaction and other weak intermolecular interactions have attracted considerable interest in the construction of supramolecular coordination framework.As one kind of five-numbered nitrogen-containing heterocycles, triazole (Htrz) is an attractive ligand, in which each individual nitrogen atom is a very strong N-ligating donor for metal ion. The trz ligand can bridge metal ions with diversity bridging fashions (μ1,2,μ2,4 andμ1,2,4) in the neutral and anionic ligand forms, respectively. Using the trz as the bridging ligand, a series of high-dimensional MOFs with multiple metal sites has been rationally designed and constructed, which have promising applications in fields of ion-exchange, gas storage, fluorescence and photoluminescent properties. On the base of the inner characters of trz ligand, we designed and tuned different conditions to attain a series of MOFs containing trz.At the same time, we selected another type of nitrogen-containing heterocyclic ligands, 1,10-phenanthroline (phen) to construct the coordination network in the hydrothermal condition. The ligand phen is a suitable hydrogen bond donor and can lead to interesting supramolecular architectures through aromatic-aromatic (π-π) interactions. The effect of the phen ligand on the polymeric topology provides some value experimental facts for crystal engineering of the weak intermolecular interactions.1. In chapter two, we chose the aromatic carboxylate ligands, i.e. the 1,3-benzenedicarboxylic acid (1,3-H2bdc), two derivatives of 1,3-H2bdc (5-hydroxyisophthalic acid: H2hip, 5-nitroisophthalic acid: H2nip), 1,3,5-benzenetricarboxylic acid (H3btc) and 1,2,4,5-benzenetetracarboxylic acid (H4btec) as the starting materials together with Zn salt and Htrz ligand. Utilizing the hydrothermal technique, a series of coordination polymers was synthesized successfully, namely {[Zn7(trz)6(1,3-bdc)4(H2O)2]·2H2O}n (1), {[Zn7(trz)6(hip)4(H2O)2]·8H2O}n (2), [Zn4(trz)4(Hnip)2(nip)]n (3), [Zn5(trz)2(Hbtc)4(H2O)4]n (4) and [Zn(H4btec)0.5(trz)2]n (5). Compounds 1 to 4 exhibit 3D pillared frameworks with polynuclear Zn(II) clusters. There also exist some distinct features in the frameworks of compounds 1 to 4. Compounds 1 and 2 have intersecting ring channels as viewed from b and c directions. Compound 3 has the 2D {[Zn4(trz)4]4+}n layers with (4, 82) topological network held together in the–ABAB– stacking sequence along a direction, and these adjacent layers are further linked by nip ligands to generate a 3D framework. The 2D layers in 4 are built up by octahedra [ZnO6] and building blocks [Zn2(trz)2]2+, which are quite different from two-component Zn/trz layers in compounds 1 to 3. As the increase in steric hindrance of coexistence groups (-OH, 2; -NO2, 3; -COOH, 4), compounds 1 to 4 show the tendency to form the dense structures. The high-dimensional structures with multiple metal sites of compound 1 to 4 show the characteristics of MOFs containing trz ligand. Different from 1 to 4, compound 5 is a 1D polymeric chain which enrichs the family of coordination polymer constructed from trz ligand.The synthesis conditions of compounds 2 are also discussed, the experimental data show that the reaction temperature, time and the introduction of NaOH or organic amines to reaction system will have profound impact on the production, and compound 2 is stable. All the compounds 1-5 exhibit strong emission at room temperature, which suggest that it may be an efficient solid emitting material.2. In chapter three, we chose the aliphatic carboxylate ligands, i.e. the succinic acid (H2suc), tartaric acid (H2tar) and adipic acid (H2adi) as the starting materials together with Zn salt and Htrz ligand. Utilizing the hydrothermal technique, three new coordination polymers were synthesized successfully, namely [Zn(trz)(Hsuc)]n (6), [Zn2(trz)2(tar)]n (7), [Zn7(H2O)2(OH)2(trz)4(adi)4]n (8). Both compounds 6 and 7 consist of 2D {[Zn4(trz)4]4+}n layer motifs, although the 2D layer structures possess different arrangements (–AAA– fashion in 6,–ABAB– fashion in 7). The aliphatic carboxylate ligands play a key role in controlling the whole molecular architecture. Compound 6 displays a 2D layered structure in which the layers are decorated by Hsuc at the both sides. In 7, the 2D {[Zn4(trz)4]4+}n layers are connected by the tartrate, resulting in the 3,4-connected 3D framework. The Zn metal sites in 8 show a variety of coordination polyhedra: tetrahedron, square pyramidal and octahedron, the adi ligands also exhibit three different coordinated modes. Through the linkage of trz and adi ligands between Zn(II) centers, the 3D network with heptanuclear cluster units [Zn7(trz)4]10+ is formed in 8.The TGA studies demonstrate that 7 is more stable compared with 6, which is relative to the structure of compounds. The luminescence properties of the compounds 6 and 7 indicate that they may be good candidates for potential photoactive materials.3. In chapter four, we extend our research by using phen as ligand and synthesize five supramolecular coordination polymers(9-13) and one coordination polymers with 2D layer structure(14): [Zn(nba)2(phen)(H2O)] (9), [Zn(nip)(phen)]n (10), [Cd(nip)(phen)2]n (11), [Cd2(nip)2(phen)2]n (12), [Cd(tar)(phen)]n (13) and [Cd(fum)(phen)]n (14) (Hnba = 4-nitrobenzoic acid;H2fum = fumaric acid). Compound 9 consists of mononuclear Zn(II) molecules which forms a 2D supramolecular structure based on hydrogen bonding, Compound 10-13 displays 1D chains with the linear, zigzag and ladder 1D motifs, which are assembled into the 3D supramolecular framework through hydrogen bonds. Theπ-πstacking between the phen ligands of the adjacent chains can also be found in compounds 10, 12 and 13. The possible source of the fum ligand in 14 is the decomposed product of the malic acid, which is not common in the hydrothermal reaction.We found that the adequate addition of ethanol is favored to the formation of 11 and the applied metal source Cd(phen)2(NO3)2 is suitable for the high quality of product crystals. TGA result shows that 10 is stable below 418°C, unusually high for coordination polymers, which indicates its good thermal stability. In addition, compound 12 show good fluorescence in the solid state at room tenperature.In conclusion, we report the preparations, crystal structures and properties of a series of coordination polymers constructed from nitrogen-containing heterocyclic ligands (trz and phen) in this paper. We also study the effect factors (reaction time, temperature, pH value, and mole ratio etc.) of the reactions and summarize the rules of synthesis. |
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