Hydrothermal/Solvothermal Syntheses, Structures And Properties Of Polyoxometalates-based Complexes Decorated By Transition Metal-pyridine Tetrazole Derivatives Subunits

In this paper, seventeen polyoxometalates (POMs)-based complexes decorated by transition metal-rigid/flexible (pyridyl)-tetrazole (ptz) derivatives subunits have been synthesized under hydrothermal or solvothermal conditions and structurally characterized by elemental analyses, single crystal X-ray diffractions, IR, TG and PXRD. The electrochemical and photocatalytic properties of these compounds have been studied as well.1. The classical Keggin and Lindqvist type POM anions were used as inorganic building units and modified by Cu/Ag/Cd/Ni-rigid ptz subunits under hydrothermal and solvothermal conditions, resulting in nine new POM-based compounds containing multinuclear Cu clusters, multinuclear Ag belts, single Cd metal-organic unit and trinuclear Ni subunit. The influences of the synthetic methods, ptz ligands with different N-donor site and different transition metal ions on the construction of POM-based compounds have been discussed. [Cu7(2-ptz)8(OH)2(H2O)2(HPMoⅥ10MoⅤ2040)]·4H2O (1) [Cu5(2-ptz)6(HPMoⅥMoⅤ2O40)(H2O)4]·4H2O (2) [Cu2(2-ptz)2(Mo4014)0.5] (3) [Cu3(OH)2(3-ptz)4(γ-H4Mo8O26)(H2O)4]·10H2O (4) [Ag6(4-ptz)4(H2SiMo12O40)] (5) [Ag5(4-ptz)4(H2PMo12O40)]·5H2O (6) [Cd(3-ptz)4(CH3O)2](H7PMo12O40)·2H2O (7) [Cd(4-ptz)4(CH3O)2](H7PMo12O40)·2H2O (8) {[Ni3(4-ptz)4(H2O)2]2(HPMo12O40)2}·7H2O (9) (2-ptz= 5-(2-pyridyl)-tetrazole,3-ptz= 5-(3-pyridyl)-tetrazole,4-ptz= 5-(4-pyridyl)-tetrazole)Compound 1 owns two kinds of CuⅡ subunits:penta-nuclear cluster and mononuclear subunit, which connect each other to form a one dimension (1D) stair-like metal-organic chain. The adjacent 1D stair-like chains are further linked by tetradentate Keggin anions to construct a 2D layer. In compound 2, the tetra-nuclear CuⅡ clusters and mono-nuclear CuⅡ subunits construct a 2D metal-organic layer, which is further linked by bidentate Keggin anions to build a 3D framework. In compound 3, each [Mo4O14]4- cluster connected with six neighboring [Mo4O14]4- clusters through six bi-nuclear [Cu2(2-ptz)2]2+ subunits to yield a two dimensional (2D) layer. In compound 4, bi-dentate inorganic [Mo8O26]4- anions linked the tri-nuclear [Cu3(OH)2(3-ptz)4] clusters to construct a 1D chain. Adjacent chains connect with each other through Mo-N bonds between the [Mo8O26]4- anions and pyridyl groups from the tri-nuclear clusters to form a 2D layer. In compound 5, the 4-ptz ligand link AgⅠ ions with tetrozole groups to form ID infinite Ag-ptz chains, which are extended by the pyridyl group of 4-ptz and the tetrozole groups of other 4-ptz to construct a 2D layer. The adjacent 2D layers are further linked by 6-connected Keggin anions to build a 3D framework. In compound 6, the 4-ptz are fused by AgⅠ ions to form a 1D infinite Ag-ptz belts. The Keggin anions are linked by AgⅠ ions to construct another infinite inorganic chain, in which each Keggin anion provides six oxygen atoms to coordinate with the AgⅠ ions from the adjacent Ag-ptz belts to construct a 2D layer. Compounds 7 and 8 are isostructural. In 7, four 3-Hptz ligands and two methanol molecules coordinate with one Cdn ion to form a [Cd(3-Hptz)4(CH3O)2] metal-organic unit, which links the adjacent discrete PMo12O403- (PMo12) anions through hydrogen bonding interactions to construct a 2D supramolecular layer. In compound 9, the tetrazole groups from one 4-Hptz and two 4-ptz ligands coordinate with three Ni ions to form a flat trinuclear subunit, which is further covered by another 4-Hptz vertically, resulting in a {[Ni3(4-ptz)2(4-Hptz)2(μ3-O)(H2O)2]2+ cluster. Adjacent trinuclear clusters connect with each other through pyridyl group of 4-ptz ligands to form a 1D chain. The PMo12 anions hang on both sides of the 1D chain. The synthetic methods, ptz ligands with different N-donor site and different transition metal ions have great effect on the final structures of these compounds. Compounds 3-4 and 5-6 show good electrocatalytic activity toward the reduction of H2O2 and nitrite, and compounds 1,2,5,6 and 3,4,7,8,9 possess good photocatalytic activity and stability for the photodegradation of Rhb and MB under UV irradiation.2. By introducing the unprecedented and flexible bis(pyridyl-tetrazole) ligand and Ag ions into polyoxometalates (POMs) system, three POM-based compounds were synthesized under hydrothermal conditions. The influences of different coordination modes of the flexible bis(pyridyl-tetrazole) ligand under different pH on the construction of the whole structures were discussed. {Ag(3-bptzh)(H2PMo12040)}·H2O (10) [V(H2O)Ag2(3-bptzh)(SiMo12O40)] H2O (11) {V(H2O)[Ag2(3-bptzh)]2(PW12O40)2} 2H2O (12) 3-bptzh=1,6-bis(5-(3-pyridyl)-tetrazolyl)hexaneCompound 10 exhibits a helix structure constructed from a binuclear [Ag2(3-bptzh)] subunit and [PMo12O40]3- anions. Compounds 11 and 12 are isostructural. The Keggin anions are linked by two Ag1 ions to construct a infinite inorganic chain, in which every two Ag1 ions of the infinite inorganic chain coordinate with the flexible ligands construct a 2D metal-organic layer, the adjacent 2D metal-organic layer linked by Keggin anions and a 3D framework is built. The different coordination modes of the flexible bis(pyridyl-tetrazole) ligand under different pH have great effect on the final structures of these compounds. Compounds 10-12 show good electrocatalytic activity toward the reduction of H2O2, and possess good photocatalytic activity and stability for the photodegradation of MB under UV irradiation.3. By introducing three pyridyl-lH-tetrazole derivatives to Keggin-Ag-(1,10-phenanthroline) system, five new POM-based inorganic-organic hybrid compounds with different dimensionalities were synthesized under hydrothermal conditions. [Ag3(4-ptz)2Na(phen)(HPMo12O40)] 2H2O (13) [Ag4(3-ptz)2(phen)2(HPMo12O40)] (14) [Ag4(3-ptz)2(phen)2(HVW12O40)] (15) [Ag3(3-bptzb)(phen)2(PMo12O40)] (16) [Ag3(3-bptzb)(phen)2(VW12O40)] (17) phen=1,10-phenanthroline,3-ptzH=5-(3-pyridyl)-1H-tetrazole,4-ptzH = 5-(4-pyridyl)-1H-tetrazole,3-bptzb= 1,4-bis(5-(3-pyridyl)-tetrazolyl)butaneCompound 13 is a one dimension belt architecture constructed from an Ag-4-ptz metal-organic chain and two Ag-PMo12O40-Na-phen inorganic-organic chains. When the rigid ligand of 3-ptzH was introduced as secondary ligand instead of 4-ptzH, compounds 14 and 15 are isostructural, which contain a 1D zigzag Ag-3-ptz chain with terminal phen ligands hanging on both sides of the chain. The Keggin anions as tetradentate ligands connect adjacent Ag-3-ptz chains to construct 2D networks. When the flexible 3-bptzb was selected as secondary ligand, isostructural compounds 16 and 17 with 2D networks were obtained, which are constructed from the bi-nuclear [Ag2(3-bptzb)(phen)2] subunits and PMo12O40-Ag or VW12O40-Ag inorganic chains, respectively. The three pyridyl-1H-tetrazole derivatives as secondary ligands have great effect on the dimensitionality and architectures of these compounds. Compounds 13-17 possess good photocatalytic activity and stability for the photodegradation of MB under UV irradiation and compound 16 show good electrocatalytic activity toward the reduction of H2O2 and nitrite.