Assembly And Properties Of Polyoxometalates-Based Functional Complexes With Semi-rigid Bis–pyridyl/Bis-imidazolyl–bis–amide Ligands

In this paper, twelve polyoxometalates （POMs）-directed （including Keggin-type, Anderson-type POMs and isopolymolybdates） metal-organic complexes based on bis-pyridyl/bis-imidazolyl-bis-amide ligands have been synthesized under hydrothermal or solvothermal conditions and structurally characterized by single-crystal X-ray diffraction, powder XRD, IR spectroscopy, and TG analysis. The photocatalytic properties and electrocatalytic properties of the title compounds have been investigated.1. Through tuning different types of polyoxometalates （POMs） and using l,4-bis（3-pyridinecarboxamido）benzene as an organic ligand, four POM-based inorganic-organic hybrid compounds with different dimensionalities have been synthesized under hydrothermal conditions. The effect of different types of polyanions and pH value on the assembly and various structures of the title compounds has been discussed.[（H₂L¹ï¼‰₂(Mo₈O₂₆)] （1）[Cu^â…¡2 L¹6(P₂W₂₄O79)·4H₂O]·7H₂O （2）{Cu^â…¡2 L¹2（μ2-OH）[CrMo6（OH）₆O₁₈]·4H₂O}·4H₂O （3）{CuΓCuΔ2L¹2（μ₃-OH）₂[CrMo6（OH）₅O19]·6H₂O}·4H₂O （4）L¹=1,4-bis（3-pyridinecarboxamido）benzeneSingle-crystal X-ray analyses reveal that compound 1 exhibits a two-dimensional （2D） supramolecular network, which is constructed from protonated L ligands and [Mo₈O₂₆]4- anions through hydrogen bonding interaction. Compound 2 is a 1D hybrid chain based on an uncommon inorganic [P₂W₂₄O79]4-chain and "Y"-like （CuL3）₂+ subunits. Compound 3 shows a 2D network constructed from 1D inorganic Cu2-CrMo6 chains and bidentate L ligands, which is obtained at pH=4.1. When the pH was adjusted to 4.8, compound 4 is obtained and exhibits a 4-connected {66} 3D framework. The CrMo6 anions are connected by adjacent [Cuâ… 2Cu^â…¡2（μ₃-OH）₂（H₂O）6]4+ subunits to form 1D Cu4-CrMo6 inorganic chains, which are further extended by L ligands to construct the 3D network. The effect of different types of polyanions and pH value on the assembly and various structures of the title compounds has been discussed.Compounds 1 and 2 show good electrocatalytic activity toward the reduction of H₂O2. Compounds 2 and 3 exhibit remarkable photocatalytic activity for the degradation of MB under sunlight and UV irradiation.2. By using the isopolymolybdates as buiding blocks, and semi-rigid 1,4-bis（3-pyridinecarboxamido）benzene as an organic ligand to assemble with Mnâ…¡, Znâ…¡ and Coâ…¡ ions, through changing the ratio of H₂O and CH3OH, three transition metal organopolymolybdate hybrid compounds have been synthesized under solvothermal conditions. The effect of solvent on the assembly of the title compounds and formation of Mo-N bond, as well as the role of metal-organic moieties on the construction of diverse organopolymolybdate compounds have been discussed in detail.H₂[Mn（H₂O）4 L¹3(γ-Mo₈O₂₆)]·8H₂O （5）H[Zn2（CH3O）（H₂O）6 L¹3(γ-Mo₈O₂₆)] （6）H[CO2（CH3O）（H₂O）6 L¹3(γ-Mo₈O₂₆)] （7）L¹=1,4-bis（3-pyridinecarboxamido）benzeneIn compound 5, the γ-Mo₈ anions connected with pyridine groups of ligand L by Mo-N bond, forming an uncommon 1D γ-Mo₈-L chain. The adjacent chains were connected by [MnL¹/2（H₂O）4]2+ moieties through hydrogen bonding interaction to construct a 2D supramolecular network. Compounds 6 and 7 are isostructural, which show a 3D 2,4,6-connected {44·62}{44·66·84·10}{6} framework. The γ-Mo₈ anions were connected by [M（H₂O）₂（CH3O）]+[M=Zn （6） and Co （7）] subunits forming 1D M-Mo₈ chains, which were connected by [ML¹2（H₂O）4]2+ moieties to construct a 2D layer. In compounds 6 and 7, there also exist the same 1D γ-Mo₈-L chains as in 1, which extended the 2D networks to 3D frameworks. The Mo-N bond with pyridyl group was formed under the solvothermal conditions, which is scarcely reported to our knowledge.Compounds 5-7 show good electrocatalytic activity toward the reduction of H₂O2 and exhibit photocatalytic activity for the degradation of MB under UV irradiation.3. The Keggin-type and isopolymolybdates were used as buiding block, and semi-rigid 1,2-bis（1H-imidazole-4-carboxamido）hexamethylene was used as organic ligand to assemble with different metal ions, five three-dimensional POM-based supramolecules frameworks have been hydrothermally synthesized.L2= 1,2-bis（1H-imidazole-4-carboxamido）hexamethylene[Coâ…¡L2(Mo₈O₂₆)0.5（H₂O）]·H₂O（8）[Znâ…¡L2 (Mo₈O₂₆)0.5（H₂O）]·H₂O （9）[Cu^â…¡2L22（H₂O）](Mo₈O₂₆)·4H₂O （10）[Cu^â…¡L2 （H₂O）₂]·(Mo₈O₂₆)0.5 （11）Cu^â…¡2L22（PMoâ…¥9Moâ…¤3O39）·5H₂O （12）Single-crystal X-ray analyses reveal that compounds 8 and 9 are isostructural, and both compounds exhibit 3D supramolecular frameworks based on [M2L22]4+ subunits, [Mo₈O₂₆]4 anions and water molecules which connect through hydrogen bonding interaction. In compound 10, the 1D [Cu^â…¡2L2（H₂O）]4+ chains link Mos anions by three kinds of hydrogen bonds which make contributions to construct 3D supramolecular frameworks. Compound 11 exhibits a 3D supramolecular framework based on 1D [Cu^â…¡L22（H₂O）₂]2+ chains containing and the 1D chains connect with [Mo₈O₂₆]4- anions by two kinds of hydrogen bonds forming a 3D structure. Compound 12 is also a 3D supramolecular structure based on two types of infinite chains which is 1D inorganic [PMoâ…¥9 Moâ…¤3O39]4- chains and 1D [Cu^â…¡2L22]4+ chains. Both 1D chains connect each other by two kinds of hydrogen bonds forming a 3D supramolecular framework. Among the structure of these compounds, the hydrogen bonding interaction between N and O affects stability of the supramolecules.Compounds 8 and 12 show good electrocatalytic activity toward the reduction of H₂O2, NO2- and bromate. However compounds 9 and 12 exhibit photocatalytic activity for the degradation of MB under UV and visible light irradiation.