Synthesis, Structures And Properties Of Coordination Polymers Based On Triazole And Tetrazole Heterocyclic Ligands

Coordination polymers are involved with the behavior of crystal engineering. Recently, the research of coordination polymers has attracted much attention because of their flexible tailoring, various topologies and their potential applications, such as gas adsorption, ion-exchange, molecular recognization, catalysts, magnetism, optics and so on. Up to now, according to the principle of crystal engineering, the design and synthesis of coordination polymers are invested a great deal of effort based on appropriate metal ions and versatile bridging organic ligands.In this paper, we report the preparations, crystal structures and properties of coordination polymers constructed from 1,2,4-triazole (Htrz) and tetrazole-1-acetic acid (Htza). Triazoles and tetrazoles are aromatic five-membered heterocycles containing three and four nitrogen atoms, respectively. Htrz as a multifunctional ligand, exhibits a strong bridged bonding ability for metal ions. The Htrz ligand through five different coordination modes can bridge metal ions. The protonated trz ligand may function as a dinucleating ligand (μ1,2 andμ2,4 binding modes), while deprotonated trz ligand can coordinate two or three metal ions (μ1,2,μ1,4 andμ1,2,4 binding modes). Its interesting bridging modes can afford polynuclear clusters as secondary building units (SBUs), such as dinuclear, linear trinuclear, tetranuclear, pentanuclear, hexanuclear, heptanuclear clusters and so on. Coordination polymers using Htrz ligand show various topologies and their potential applications. Compared to triazole, tetrazole holds an additional nitrogen atom and exhibits more bridging coordination possibilities. Tetrazole-1-acetic acid is bifunctional ligand containing of tetrazolate and carboxylate groups. Htza with four nitrogen atoms and two oxygens potential binding centers can serve as a class of excellent polydentate ligands. On the other hand, the -CH2- group between the tetrazole ring and carboxylate group offers flexible orientations of the carboxylate arm, which have been employed in construction of coordination polymers with structure varieties and novel performance. The Htza ligand is a suitable hydrogen bond donor and can form interesting supramolecular architectures throughπ-πinteractions. So we choose Htrz and Htza as organic ligands to design and synthesize a series of coordination polymers. In the second chapters, under hydrothermal or solvothermal conditions, six compounds were synthesized successfully with the aromatic carboxylate ligands in zinc-trz system, namely, Zn4(μ4-O)(trz)2(4,4'-bpdc)2 (1), Zn2(trz)2(2,4'-bpdc) (2), [Zn5(trz)4(btc)2(DMF)2(H2O)2]·2H2O·DMF (3), Zn4(trz)3(btc)2(CH3CN)(H2O)]·5H2O·(Bu4N) (4), [Zn7(trz)6(H2btec)2(btec)]·H2O (5) and [Zn3(trz)2(btec)(H2O)4]·2H2O (6), [4,4'-H2bpdc= 4,4'-biphenyldicarboxylate, 2,4'-H2bpdc= 2,4'-biphenyldicarboxylate, H3btc=1,2,4-benzenetricarboxylate, Bu4N= tetrabutylammonium, H4btec= benzenetetracarboxylate]. Compounds 1,3,4,5 and 6 also exhibt three-dimensional frameworks based on rod-link secondary building units (SBUs). Compound 2 is two-dimensional structures. All compounds also contain polynuclear zinc clusters. There are some distinct features in the structures of compounds 1 to 6. Compound 1 is a 2-fold interpenetrating diamond topology constructed from {[Zn4(μ4-O)(trz)24+]}n SBUs. Compound 2 is a two-dimensional 6-connected hxl network based on {[Zn2(trz)2]2+}n SBUs. Both compounds 3 and 4 exhibit three-dimensional (3,8)-connected tfz-d nets with{43}2{46.618.84} topology symbol built from rod-shaped {[Zn5(trz)4]6+}n SBUs (3) and {[Zn4(trz)3]5+}n SBUs (4). In 3 and 4 compounds, rod-like units are connected by btc ligands via different modes. Compound 5 is a three-dimensional (4,12)-connected network with (32.44)(38.424.524.610) topology symbol built from rod-shaped {[Zn7(trz)6]8+}n. Compound 6 shows a (4,6)-connected three-dimensional structure with Schlafli symbol {44.610.8}{44.62}, containing infinite straight {[Zn2(trz)2][ZnO4]}n chain with dinuclear [Zn2(trz)2] and [ZnO4] unit. The structure of compounds 3,4 and 6 are all high-connected nodes networks built from polynuclear metal clusters. The synthesis conditions of compounds 3 and 4 are also discussed, the experimental data show that the structures of 3 and 4 depend closely on the addition of Na2CO3 or tetrabutylammonium hydroxide. At the same time, the effect of action conditions were discussed between compounds 5 and 6, too.In the third chapter, we choose metal lead react with tetrazole-1-acetic acid and gain two coordination polymers Pb(tza)2 (7) and PbCl(tza) (8) under hydrothermal condition. We discussed the effect of alkali metal and alkali-earth metal on the synthesized compounds 7 and 8. Compound 7 is a three-dimensional supramolecular architecture. The coordination geometry of Pb(1) will transfer from hemidirected to holodirected geometry through the potential weak Pb-O and Pb-N bonds in 7. Compound 8 consists of two-dimensional inorganic layers by Pb(II) andμ3-Cl-, which are further linked by tza ligand to generate a novel a three-dimensional structure. There are three different rings [Pb2Cl2], [Pb2O2] and [Pb4Cl4] within the two-dimensional inorganic layers of 8. Compared to the structure of 7, we omitted Cl-atom in 8.Under hydrothermal conditions, the self-assembly of Pb(NO3)2,2,2'-oxydiacetic acid and Htrz (additive) generates a three-dimensional lead(Ⅱ) framework [Pb(oda)] (9). Compound 9 contains a one-dimensional infinite Pb-O chain which is connected throughμ3-,μ4-,μ5-coordination modes of oda to form a new three-dimensional structure. Compound [Pb(sui)] (10) was synthesized with succinic acid as organic ligand and Htza as additive. The structure of 10 containing one-dimensional rod-like linked adjacent [Pb2O2] units through together lead, which are connected by succinic acid ligand to form a 3-connected two-dimensional framework. For 9 and 10 when the bonding limit of Pb-O extends from 2.76 to 2.90 A and Pb-Pb extends 4.3 A, the potential weak bonds of Pb-O and Pb-Pb can be found, which construct a more complicated structure. The effect of additives (Htrz and Htza) was discussed between compounds 9 and 10.In conclusion, we report the preparations, crystal structures and properties of a series of coordination polymers constructed from aromatic five-membered heterocycles ligands (Htrz and Htza) in this paper. We also study the effect factors of the reactions and summarize the rules of synthesis. All the compounds charactrized by single-crystal X-ray diffraction analyses, X-ray power diffraction, elemental analyses, infrared absorption spectra and thermogravimetric analyses. Additionally, solid state fluorescent emission spectra of 1-6 compounds show fluorescent properties at room temperature.