The Influence Of POM Types,Temperature And Ligand Types And Properties On The Construction Of POM-based Compounds

In this paper,under hydrothermal conditions,by using nitrogen heterocyclic ligands with five-membered and six-membered rings respectively as organic ligands,1,4-bis（1,2,4-triazole-1-yl）butane（btb）,4-butyl-1H-pyrazole（bpz）,2-[1,2,4]triazol-4-yl-ethylamine（tea）,2,3-naphthalenylphenazine（npz）,2,3-diphenylpyrazine（dpz）,pyrazine（pz）,through tuning the varieties of POMs,the reaction temperature,the synergistic effects of the mono-and mixed-ligands in differentreactionsystem,thirteencompoundsbasedon Keggin/Anderson/Lindqvist polyoxometalate（POM）were synthesized.Their structures were characterized by single crystal X–ray diffraction.Furthermore,the electrochemical and photocatalytic properties of these new POM-based compounds were also explored.1.Under hydrothermal conditions,by using 1,4-bis（1,2,4-triazole-1-yl）butane ligand（btb）and tuning different varieties of POMs,two compounds with different dimensionalities were synthetized:[Cu^II（btb）_1.5(γ-Mo₈O₂₆)_0.5（H₂O）]·2H₂O（1）,[Cu₂^II（btb）₄(PMo^VMo₁₁^VIO₄₀)]·2H₂O（2）（btb=1,4-bis（1,2,4-triazole-1-yl）butane）In compound 1,there exists a ladder-like metal-organic chain with the bi-dentate[γ-Mo₈O₂₆]^4-anions inserting into the grids.Adjacent chains share the same Cu-btb lines of the ladder to form a two dimensional（2D）layer.Compound 2also owns a ladder-like metal-organic chain.The tetra-dentate[PMo₁₂O₄₀]^3-anions embed the grids.The same Cu-btb line is shared by adjacent chains to build a 2D layer.The btb ligands link adjacent layers to form a three dimensional（3D）framework.2.The pendent organic ligands 4-butyl-1H-pyrazole（bpz）and2-[1,2,4]triazol-4-yl-ethylamine（tea）,were introduced to Anderson-Cu/Ag systems.Both pendent ligands,bpz and tea,have two successive potential N donors with strong coordination capacity.This feature conduces to aggregate metal ions to form multi-nuclear clusters.By tuning the reaction temperature,two Anderson-and two[?-Mo₈O₂₆]^4--based compounds decorated by pendent organic ligands have been hydrothermally synthesized:[Cu₉^II（bpz）₂（pz）₂（H₂O）₂₄][H₂(Cr（OH）₅Mo₆O₁₉)₄]·11H₂O（3）,[Cu^II（bpz）₂（H₂O）₂(γ-H₄Mo₈O₂₆)]·2H₂O（4）,[Cu₂^II（tea）₂（H₂O）₆(HCr（OH）₆Mo₆O₁₈)₂]·6H₂O（5）,[Ag^I（bpz）（H₂O）(γ-H₄Mo₈O₂₆)_0.5]（6）（bpz=4-butyl-1H-pyrazole,pz=1H-pyrazole,tea=2-[1,2,4]triazol-4-yl-ethylamine）In compound 3,there are two kinds of tri-nuclear Cu^II clusters induced by bpz and pz ligands,respectively.Four Anderson-type anions are linked by these tri-nuclear clusters to form a“W”-type subunit.In compound 4,the[Cu（bpz）₂（H₂O）₂]²⁺subunits connect theγ-Mo₈ anions to construct a chain.The remaining two non-coordinated N donors in[Cu（bpz）₂（H₂O）₂]²⁺further link two adjacentγ-Mo₈ anions through Mo-N bonds.In compound 5,there exists a bi-nuclear Cu^II cluster[Cu₂（tea）₂（H₂O）₆]⁴⁺.The discrete bi-nuclear Cu^II clusters and the CrMo₆ anions link each other through abundant hydrogen bonding interactions.In compound 6,the[Ag（bpz）（H₂O）]⁺subunits connectγ-Mo₈ anions to build a zigzag chain.The chains are further fused by other[Ag（bpz）（H₂O）]⁺cations to form a grid-like layer.There still exist Mo-N bonds in 6.3.By using POMs with different charges,seven compounds based on Lindqvist and Keggin anions have been hydrothermally synthesized.A single ligand or mixed-ligands modify anions in this series:[Ag₂^I（npz）₅(W₆O₁₉)]·（npz）（7）,[Ag₂^I（npz）₃(HPW₁₂O₄₀)]（8）,[Ag₃^I（npz）₄(PMo₁₂O₄₀)]（9）,[Ag₄^I（pz）₅(SiMo₁₂O₄₀)]（10）,[Ag₄^I（npz）₂（pz）(PMo^VMo₁₁^VIO₄₀)]（11）,[Ag₄^I（npz）₄（dpz）₂(SiW₁₂O₄₀)（H₂O）₂]（12）,{Ag₅^IK₂^I（npz）₄（dpz）₂[H(PW^VW₁₁^VIO₄₀)₂]}（13）（npz=2,3-naphthalenylphenazine,dpz=2,3-diphenylpyrazine,pz=pyrazine）In compound 7,there is a distorted“I”-type[Ag（npz）₂]⁺subunit with two npz arranging vertically.Two[Ag（npz）₂]⁺subunits support the[W₆O₁₉]^2-anion symmetrically.In compound 8,there are[Ag₂（npz）₃]²⁺clusters with one linking and two terminate npz,which are further linked by[PW₁₂O₄₀]^3-anions to form a“sunrise”-like chain.In compound 9,there exist a discrete[Ag₂（npz）₃]²⁺cluster and a mono-supporting anion[Ag^I（npz）(HPW₁₂O₄₀)]^-.In compound 10,there are two kinds of cycles in honeycomb-like Ag-pz layer:six-membered cycle I and eight-membered cycle II.An anion dimmer linked by a Ag^I ion embeds in bigger cycle II.In compound 11,one pz and two npz are connected by four Ag^I ions to build a linear[Ag₄（npz）₂（pz）]⁴⁺subunit.The PMo₁₂ anions link the linear subunits alternately and a 1D chain is formed.In compound 12,there exists discrete[Ag₂（npz）₂（dpz）（H₂O）]²⁺subunit and Keggin anion.In compound 13,the Keggin-K inorganic chains are connected by Ag^I-npz-dpz subunits to form a 2D layer.The adjacent layers are further linked by anions to build a 3D framework.