Syntheses, Structures And Properties Of Coordination Polymers Constructed From Tetrazole Derivative Ligands

As an important branch in the field of supramolecular chemistry and crystalengineering, the design and assembly of coordination polymers （CPs） has become avery attractive research field over the past ten years, due to CPs’ fascinatingarchitectures and topologies as well as their potential application as functionalmaterials in many areas, such as gas separation and storage, ion-exchange, molecularand chiral recognition, catalysis optoelectronics, magnetism, luminescence, sensorsproperties, etc.. In recent years, the field of coordination polymers has madeconsiderable progress, more and more functional coordination polymers with novelarchitectures have been synthesized, but the design and synthesis of the targetstructure still can not be completely controlled. In order to be able to early achieve thetarget of directed synthesis, it is therefore critical at this stage to accumulate a largedatabase of synthetic data, explore the synthesis rules, and establish mature andrational theoretical system.At present, most researchers are focused on exploring new functional CPs byjudicious choice and design of organic moieties, and investigating the relationshipbetween the structures and properties. Constructing coordination polymers withtetrazole derivative ligands is a hot research topic. The tetrazole molecules possessstrong activity with four nitrogen atoms that similar to carboxylic, to give diversecoordination modes, which easy to form polynuclear metal clusters and/or chain building blocks. In this paper, we start to form the functional coordination polymerswith novel structures, using5-substituted tetrazole derivatives as the ligands, bychanging the metal centers, the concentration and the ratio of the reagents, and thetemperature, successfully synthesized eleven new compounds underhydro（solvo）thermal conditions. The topologies and properties of these compoundshave been discussed. The main contributions in this work are blow:1. Two novel lead（Ⅱ）-based tetrazole CPs,[Pb₄（OH）₄（BDT）₂]·2H₂O （1） and[Pb₄（OH）₄（BDT）]·BDT·2H₂O （2）, have been synthesized under hydrothermalconditions by using rigid bitetrazole ligand1,4-benzeneditetrazol-5-yl （H₂BDT） withPb（Ⅱ） ions. Due to ligand BDT2-adopts different coordination modes, these twocompounds possess the same cubane-shaped [Pb₄（OH）₄]⁴⁺inorganic building unitsbut exist great differences in the final3D supermolecular networks. In compound1,μ3-and μ4-bridging BDT2-connect [Pb₄（OH）₄]⁴⁺clusters to construct the3Dsupramolecular network via Pb-N weak bonds. When the μ3-bridged BDT2-areneglected, the connections between μ4-bridging BDT2-and [Pb₄（OH）₄]⁴⁺clustersform a2-fold interpenetrated （10,3）-d （or utp）3D network. Compound2exhibits a2D square grid with （4,4） topology and the adjacent2D networks are further linkedby Pb-O weak bonds to generate the3D supramolecular structure. It is worth pointingout that the coordination modes of BDT2-in1and2are observed for the first time inM-BDT networks. The structures of these compounds are highly influenced by theconcentration of the starting reagents, that is, a metal to ligand ratio of3:2at highconcentration of the starting reagents yields phase pure crystals of1, while compound2is formed at dilute conditions. In addition, the pH value of the reaction solution is akey factor in the formation of the [Pb₄（OH）₄]⁴⁺cluster. We also have used two-stepsynthesis method successfully constructed compounds1and2. Firstly, the precursorsof [Pb₄（OH）₄]⁴⁺clusters [Pb₄（OH）₄][NO₃]4were synthesized, then, we employedthem react with BDT2-ligands. Moreover, compounds1and2exhibit strongsolid-state fluorescent emission with millisecond luminescence lifetimes at roomtemperature. 2. Five new three-dimensional frameworks [Co₃（OH）₂（apt）4（H₂O）₂]2n（3）,[Zn（apt）₂]_n（4）,[Ag（apt）]_n（5）,[Co（cpt）（H₂O）]_n（6）, and [Pb（cpt）]_n（7）, have beenhydrothermally synthesized by employing4-substituted tetrazole-benzoate ligands,4-aminophenyl-1H-tetrazole （4-apt） and4-carboxyphenyl-1H-tetrazole （4-cpt）.Compounds3-5are built by amino substituent4-apt with Co（Ⅱ）, Zn（Ⅱ）, and Ag（I）ions. In comound3, the infinate1D metal-oxygen [Co₃（OH）₂（tz）] chains featuringzig-zag motif are connected by μ3-apt ligands to form a3D structure with binodal rtl（rutile） topology, while μ2-apt bridging ligand using two tetrazole nitrogen atomsbridges Co atoms in order to meet the six coordination mode of Co atoms. Compound4manifests a3D noninterpenetrated dia framework via μ2-apt ligands linked Zncenters, in which Zn-Zn-Zn angles are much the same to those in an idealizeddiamond network. Compound5shows a2D layer structure with3-connected4·82-festopology which is constructed from4-apt with novel coordination mode and Ag（I）ions. Compounds6and7are made of carboxyl substituent4-cpt organic ligands andCo （Ⅱ） and Pb （Ⅱ） ions, respectively. In compound6, the adjacent （L） left-and （R）right hand helices are formed by tetrazole bridging Co1atoms, which with oppositechirality are united alternately together through4-carboxyl of ligands to exhibit a2Dmetal-organic sheet. Such layers are further linked by the1-position of the tetrazolegroup to give a3D framework with PtS net. Compound7possesses a3D frameworkwith5-connected46·64-bnn topology if each Pb atom and4-cpt ligand can beconsidered as a five-connecting node, respectively.Luminescent studies show that compounds3-7exhibit good solvent-dependentproperties, and luminescent intensity obviously enhance in acetonitrile while sharplyquench in carbon tetrachloride and acetone. In addition, compounds3and6show thedominant antiferromagnetic interactions between the Co（Ⅱ） ions, and compound3exists the spin-canted behavior at low temperature.4. Using imidazole substituted organic ligand4-imidazolphenyl-1H-tetrazole（4-ipt） and different aromatic carboxylates as secondary ligands, four novel CPs[Zn（ipt）（1,4-bdc）_0.5]（8）,[Zn1.5（ipt）（2,5-pydc）]（9）,[Zn（Hipt）（1,2,4,5-btec）_0.5]（10）, and [Cd（Hipt）（1,2,4,5-btec）_0.5]（11） have been successfully synthesized and analyzed.Compound8,9, and11are3D pillared frameworks, and show some distinct featuresbetween them. Compound8has the2D [Znipt]nlayers built by μ3-ipt bridging ligandsand Zn（Ⅱ） ions, these adjacent layers are further linked by pillared1,4-BDC2-ions. Itfeatures a2-fold interpenetrating dmc framework. Contrary to compound8, the2Dlayers in9are connected by2,5-pydc with chelating and monodentate bridging modeand Zn（Ⅱ） ions. The final3D network is formed by4-ipt ligand pillared the2D[Zn₂（2,5-pydc）]nlayer motifs. It is worthy to point out the4-ipt ligand plays asupporting role due to the1,4-position nitrogen atoms of the tetrazole group.Compound9is simplified as a3D2-nodal （3,6）-connected topology. The same tocompound9, the2D layer in11is made of each aromatic carboxylic acid1,2,4,5-btecjoined six Cd（Ⅱ） ions which containing infinite Cd-O-Cd rods. These2D layers arepillared by4-ipt with terminal bidentate coordination mode liked BIMB ligand toform the final3D structure. Compound10exhibits a2D layer structure decoratedwith4-ipt ligands which is formed by1,2,4,5-btec linkers and Zn（Ⅱ） ions. Thesolid-state fluorescence spectroscopy shows compounds8-11display intensefluorescent emissions, which may be proposed to originate from the intraligandtransition of4-ipt modified by metal coordination.The results described herein summarize the synthesis, topological analysis andfluorescence and magnetism properties of an assortment of CPs constructed by5-substituted tetrazole derivatives as organic linkers. A general relationship betweenthe product and synthesis method has been established and we hope that thisaccumulation of experimental data will be valuable for the continuous developmentof functional CPs.