In this work, a succession of Keggin-type polyoxometalate (POM)-based metal–bis­(pyridyl-tetrazole) complexes, {Cu2(3-bptzp)3(H2O)4[SiW12O40]}·H2O (1), {Cu2(3-bptzpe)2(H2O)8[SiW12O40]}·4H2O (2), and {Cu2(3-bptzh)3(H2O)6[SiW12O40]} (3) (3-bptzp = 1,4-bis­(5-(3-pyridyl)­tetrazolyl)-butane; 3-bptzpe = 1,4-bis­(5-(3-pyridyl)­tetrazolyl)-pentane; 3-bptzh = 1,4-bis­(5-(3-pyridyl)­tetrazolyl)-hexane), were prepared and structurally characterized, which exhibited different architectures. The title complexes were used directly as electrocatalysts for hydrogen evolution reaction in alkaline and acidic media. The electrocatalytic activity for generating hydrogen was reinforced by the introduction of POMs. Complex 1 possesses the highest electrocatalytic activity for hydrogen evolution reaction with a low overpotential of 59.4 mV, achieving the current density of 10 mA·cm–2 in 0.1 M KOH. The different structures of the title complexes showed effects on the hydrogen evolution performance. For 1, the insertion of POMs between the ordered 2D metal–organic layers induced the enhancement of electrocatalytic activity.

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Two novel Anderson-type polyoxometalates (POMs)-based metal-organic frameworks (MOFs), namely, H{Cu2(μ2-OH)2L(1)[CrMo6(OH)6O18]}·4H2O (), {Cu2L(2)[CrMo(VI)5Mo(V)(OH)6O18](H2O)4}·4H2O () (L(1) = N,N'-bis(3-pyridinecarboxamide)-piperazine, L(2) = N,N'-bis(4-pyridinecarboxamide)-piperazine), are hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex , the hexadentate [CrMo6(OH)6O18](3-) polyoxoanion bridges the Cu(II) ions to generate a 2D Cu-POM inorganic layer, which is further extended by the μ2-bridging L(1) ligands (via ligation of pyridyl nitrogen atoms) to form a 3D MOF with a 4,6-connected {4(4)·6(10)·8}{4(4)·6(2)} topology. Complex is also a 3D POM-based MOF exhibiting a {4(2)·8(4)} topology, which is constructed from the quadridentate [CrMo(VI)5Mo(V)(OH)6O18](4-) polyoxoanions and μ4-bridging L(2) ligands (via ligation of pyridyl nitrogen and carbonyl oxygen atoms). The different coordination modes of POM polyanions and the isomeric bis(pyridylformyl)piperazine ligands play key roles in the construction of the title complexes. In addition, the photocatalytic activities of the title complexes on the degradation of methylene blue (MB) under UV, visible light and sunlight irradiation have been investigated in detail.

Two new Keggin-type POM-based metal–organic complexes with different structures have been synthesized, which can be used as electrochemical sensors for the detection of trace Cr(vi) and as supercapacitor materials.

A Cd(II) metal–organic framework (MOF) [Cd3(L)(NTB)2(DMA)2]·2DMA (Cd-MOF) was solvothermally prepared in the presence of N-donor ligand L (L = (E)-4,4’-(ethene-1,2-diyl)bis[(N-pyridin-3-yl)benzamide]) and O-donor ligand H3NTB (H3NTB = 4,4',4''-nitrilotribenzoic acid). The Cd-MOF...