Design, Syntheses And Properties Of Nitrogen Rich Dicarboxylic Keggin Type Polyoxometalates Based Coordination Polymer

Polyoxometalate (POM)-based metal-organic framework (MOF) materials combining the advantages of both POM units and MOFs have a potential application in absorption, separation, catalysis and medical chemistry. They have good prospects in catalysis owing to the electronic and physical properties of POMs that are tunable by varying constituent elements. On the other hand, POM anions represent a well-defined library of inorganic building blocks with Lewis and Bronsted acidity that can be utilized as efficient solid-acid catalysts for a series of organic reactions.In this paper three series of twelve metal-organic polymer have been obtained by the reaction of three different length rigid multifunctional azoles/carboxylic ligands: l,2,3-triazole-4,5-dicarboxylic acid (H3tda),5-tetrazolylisophthalic acid (H3TZI) and 4’-(1H-tetrazol-5-yl)biphenyl-3,5-dicarboxylic acid (H3L) with d10 metal ions and polyoxometalates, respectively. The molecular structures of complexes were characterized by single-crystal X-ray diffraction. In addtion, the catalysis properties, dyes absorption, nitrobenzene detection have been studied systemically. The results are listed as following:1. A series of three remarkable complexes have been isolated by using simple one-step solvothermal reaction of copper chloride,5-tetrazolylisophthalic acid (H3TZI), and various Keggin-type polyoxometalates (POMs), respectively. Crystal analysis of HLJU 1-3 (denoted as HLJU, HLJU= Heilongjiang University) reveals that Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1 (MOF: metal-organic framework) with large cell volume:[PMo12040]@[Cu60(TZI)3(H20)9]4·OH·31H2O (HLJU-1)[SiMo12O40]@[Cu6O(TZI)3(H2O)9]4·32H2O (HLJU-2)[PW12O40]@[Cu6O(TZI)3(H2O)6]4·OH·31H2O (HLJU-3)To the best of our knowledge, the verified structure of HLJU 1-3 is the third type of porous POM@MOF defined by crystal structure after POM@HKUST-1 and POM@MIL-101 series. Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1. The molecular structures of HLJU 1-3 have been determined and characterized by single-crystal X-ray diffraction, IR, TG-DSC, PXRD and EPR spectrum. HLJU 1-3 exhibit unique catalytic selectivity and reactivity in the oxidation of alkylbenzene with environmental benign oxidant under mild condition in aqueous phase as well as the uptake capacity towards organic pollutants in aqueous solution. They possess the following excellent characteristics, which are comparable to the conventional, POM-supported catalysts:unambiguous X-ray crystallography, which confirms their texture; good dispersion of POMs at the molecular level, which prohibits conglomeration; high immobilization of POMs, which overcomes catalyst leaching and deactivation; and their highly stable crystalline framework, which allows for catalyst recycling. In addition, the dyes absorption experiment further confirm that there are an additive synergism between POMs and MOFs.2. To investigate the influence of POM species, temperature and counterions on the structures of POM-MOFs containing Cu-tda second building blocks (SBUs), six new complexes with various dimensionalities, were isolated depending on the reaction conditions. These complexes possess similar building blocks facilitate to explore the reaction course of "black box"-like self-assembly process:[Cu(H2tda)(H20)2]4·[SiW12O40]·9H2O (4)[Cu2(H2tda)2(H2O)3]·[Cu(H2tda)(H2O)2]·[PMo12O40] · 5H2O (5)[Cu(H2tda)(H20)2]3·[PMo12O40]·[Cu(Htda)(H2O)3]·8H2O (6)[Cu2(H2tda)2(H2O)4]2·[Cu2(tda)2(H2O)4]·[HPW12O40]·18H2O (7)[Cu2(H2tda)2(H20)4]·[SiW12O40]·(TMA)2·3H2O (8)[Cu(H2tda)(H20)3]·[SiW12O40]·(TMA)3·H2O (9)Isolation of six new POM-MOF complexes with various dimensionalities and topologies demonstrates that the POM species, temperature and counterions dominate the structural variety of these POM-MOF complexes. E. g. the charges of POM polyoxoanions play a key role in controlling the coordination numbers of POMs; The high temperature facilitate to form high dimensionalities by forming more covalent bonds; the counterions efficiently hinder building blocks to assembly, which lead to the formation of lower dimensionalities. This approach provides step by step understanding on the assembly processes in terms of the influences of POM clusters, temperature and counterions. The photocatalysis degrade RhB experiment illustrates that the formation of a POM-based complex can improve the photocatalytic performance of POMs.3. A series of three porous MOF materials have been solvothermally isolated by employing d10 metal cations (Zn cation and Cu cation),5-tetrazolylisophthalic acid (H3TZI) and 4’-(1H-tetrazol-5-yl)biphenyl-3,5-dicarboxylic acid (H3L) ligands, respectively:[Zn6(OH)2(TZI)3·6H2O]·40H2O (10)[Zn2(OH)(L)·2H2O]·6H2O (11)[Cu2(TZI)(OH)(DMF)]2·(DMF)2 (12)By modulate the length of ligands, the complexes 10 and 11 possess the same topology(4,64,8)(43,64,83)(62,8). By adjust the species of metal cation, the complex 12 was isolated, which display a high connected bcu topology. Furthermore, complexes 10 and 11 were employed as the sensor for the detection of nitrobenzene through fluorescence quenching. The stability of the complexes 10 and 11 were investigated that the quenching efficiency without decrease even after six turn.