Assembly And Properties Of Functional Complexes Based On Polyoxometalates And Pyrazine Carboxylic Acid/Aminopyridine And Their Amide Derivatives

In this paper, sixteen polyoxometalates(POMs)-directed(including Keggin-type and Anderson-type POMs, octamolybdate) functional complexes based on carboxylic acid/aminopyridine and their amide derivatives have been synthesized under hydrothermal or solvothermal conditions and characterized by IR, TGA, PXRD and single crystal X-ray diffractions. The electrochemical properties and photocatalysis degradation of methylene blue dye processes of compounds under different light have been studied.1. The 2-pyrazine carboxylic acid and 3-aminopyridine are selected as the organic ligands to react with different transition metal salts and different POMs under hydrotheramal conditions, five metal-organic complexes based on different types of Anderson-type POMs or octamolybdate have been synthesized.{H2[K(H2O)5]2[Cu(pzca)(H2O)3]2(Te Mo6O24)}(1){H[Cu(pzca)(H2O)2]2[Al Mo6(OH)6O18]}·17H2O(2)H6[Cu(C5H5N2)2(Mo8O27)(H2O)2]·2(C5H6N2)·2H2O(3)H6[Co(C5H5N2)2(Mo8O27)(H2O)2]·2(C5H6N2)·2H2O(4)H4[(C5H6N2)2{Ni(OH)6Mo6O18}]·4H2O(5)[C5H6N2=3-aminopyridine; Hpzca= 2-pyrazine carboxylic acid]Compound 1 is a 0D architecture, in which the A-type Anderson anion [Te Mo6O24]6-(Te Mo6) is modified by two [Cu(pzca)(H2O)3]+ cations and two [K(H2O)5]+ cations. The adjacent {[K(H2O)5]2[Cu(pzca)(H2O)3]2(Te Mo6O24)} clusters are connected by hydrogen-bonding interactions, resulting in a 3D supramolecular framework. When B-type Anderson anion [Al Mo6(OH)6O18]3-(Al Mo6) was used in compound 2, a 2D wave-like network was obtained, in which the adjacent 1D [Cu(pzca)]n n+ chains are linked by Al Mo6 anions with two terminal oxygen atoms. Compounds 3 and 4 are isostructural 3D metal-organic frameworks with a Cd SO4-type topology, which are constructed from infinite Mo8O276- inorganic chains in uncommon ABAB linking mode. Compound 3 exhibits a 1D supramolecular chain derived from in-situ formed Anderson-type [Ni(OH)6Mo6O18]4– anions and 3-aminopyridine via hydrogen-bonding interactions. The influence of different types of Anderson anions, metal ions and p H on tuning the structures and the formation of crystals have been explored and discussed. The electrochemical properties have been studied with compounds 1–3 as representatives.2. By introducing the symmetric pyrazine carboxylic acid amide derivatives ligands(flexible bis-pyrazine-bis-amide) into polyoxometalates(POMs) system, five POMs-based metal-organic complexes were synthesized under hydrothermal conditions.{Cu3(L1)2[Cr Mo6(OH)6O18]2(H2O)2}·10H2O(6)[Cu L1(Mo8O26)0.5]·H2O(7)[Cu2(L1)2(HPMoVI10MoV2O40)(H2O)2]·2H2O(8)[Cu2(L1)2(Si Mo12O40)(H2O)2]·2H2O(9)[Cu2(L2)2-(Si Mo12O40)]·2H2O(10)[L1=N,N’-bis(2-pyrazinecarboxamide)-1,3-propane,L2=N,N’-bis(2-pyrizinecarboxamide)-1,6-hexane]Compound 6 is a 1D infinite ribbon-like chain with Anderson type polyanions [Cr Mo6(OH)6O18]3- as building blocks. Compound 7 is a 2D layer constructed from 1D helical [Cu-L1]n2n+ chains and [Mo8O26]4- anions, in which the octamolybdates also act as inorganic building blocks. Compounds 8 and 9 are isostructural, and display 2D supramolecular networks based on the 1D [Cu-L1]n2n+ chains, in which the Keggin polyanions are serving as noncoordinated templates. Compound 10 is a 3D supramolecular framework constructed from the 2D [Cu-L2]n2n+ layers and the Keggin [Si Mo12O40]4- polyanion templates. In compounds 6–9, the L1 ligands display same symmetric coordination mode with two chelating sites. When lengthening the spacer of ligand, L2 exhibits a asymmetric coordination mode in compound 10. The structural diversities of 6–10 show that the different polyoxoanions and spacer lengths of the ligands play key roles in the construction of various architectures. The compounds 6–10 represent the first examples of introducing flexible bis-pyrazine-bis-amide ligands into the POMs system. The electrochemical properties and photocatalysis degradation of methylene blue dye processes of compounds have been studied.3. By introducing asymmetric aminopyridine amide derivatives ligands into polyoxometalates(POMs) system, six POMs-based metal-organic complexes were synthesized under hydrothermal or solvothermal conditions.H2{[Cu3(PCAP)4(H2O)2](β-Mo8O26)}·10H2O(11)H{[Cu(PCAP)(H2O)](β-Mo8O26)0.5}(12)H2[Co(H2O)6][Co2(PCAP)4(γ-Mo8O26)(H2O)2]·10H2O(13)H4[Cu2(TAAP)4(H2O)](Mo8O26)2·20H2O(14)H2[Co(TAAP)2(H2O)2](Mo8O26)·11H2O(15)H2[Ag4(TAAP)4(H2O)2](PMo12O40)2·4H2O(16)[HPCAP=3-(2-pyridinecarboxylic acid)amido pyridine;TAAP=3-(1H-Tetrazole-1-acetic acid amido) pyridine]Compound 11 is a 2D layer based on the infinite 1D [Cu3(PCAP)4]n2n+ chains and the bidentate β-Mo8O264- anions. In compound 12, 1D “thin centipede” [Cu2(PCAP)2]n2n+ chains were connected by tetradentate β-Mo8O264- anions through Cu-O bond to form a 2D network. In compound 13, the γ-Mo8O264- anions were connected by adjacent [Co2(PCAP)4(H2O)2] moieties through Co–O and Mo–N bonds forming an uncommon 1D “fat centipede” chain. The adjacent chains were futher extended to a 2D supramolecular network through hydrogen bonding interaction. Compounds 14 and 15 are isostructural, and they exhibit a 3D structure based on a 3D metal-organic framework and [Mo8O26]4-polyanions templates. Compound 16 exhibits a dimeric structure constructed from two Keggin [PMo12O40]3-anions and a tetranuclear [Ag4(TAAP)2(H2O)2]4+ subunit. The dimeric structures connected via hydrogen-bonding interactions to form a 2D supramolecular structure. The two asymmetric pyridyl-containing amide ligands used in this paper are first introduced to construct POMs-base compounds. Different ligands, metal ions, solvent and polyoxometalates play key roles in the construction of final architectures. The electrochemical properties and photocatalysis degradation of methylene blue dye processes of compounds under different light have been studied.