Yan-Qing Jiao

Assembly of organic–inorganic hybrid materials constructed from polyoxometalate and metal–1,2,4-triazole units: synthesis, structures, magnetic, electrochemical and photocatalytic properties

A series of organic–inorganic hybrid compounds built from Keggin and Wells–Dawson polyoxometalates and TM-trz complexes (Htrz = 1,2,4-triazole) were obtained at different pH values under hydrothermal conditions, namely, [Co2(H2O)2(Htrz)5][SiW12O40]·2.5H2O (1), [Zn5(Htrz)8(trz)2(H2O)8][SiW12O40]2·10H2O (2), [CuI2CuII4(Htrz)4(trz)4Cl2][GeW12O40]·15H2O (3), [CuI2CuII4(Htrz)4(trz)4Cl2][SiW12O40]·15H2O (4), K2Na2(H2O)2[Co11(trz)14(H2O)14][P2W18O62]2·29H2O (5) and [Cu12(trz)10(Htrz)2(OH)4(SO4)2(H2O)6][P2W18O62]·28H2O (6). All of the compounds were characterized using single-crystal X-ray diffraction, TG analysis and powder X-ray diffraction. Compound 1 contains a kind of bimetallic–organic segment [Co2(Htrz)5]4+, which could be regarded as a quasi-sinusoid-like chain. 2 is a dimer constructed from two [SiW12O40]4− units linked by a [Zn5(trz)2(Htrz)8]8+ motif. In 3 and 4, the 2D wall-like layers constructed by the Cu(II) ions and Htrz ligands are extended into 3D frameworks by polyanions. 5 shows a complicated three-dimensional (3D) framework with a {412·612·84}{46}2 topology. Compound 6 is also a complicated 3D structure based on a triangular trinuclear Cu-trz unit and [P2W18O62] polyanions. To the best of our knowledge, 6 represents the largest copper cluster linked by amines in a POM system. Structural diversities reveal that the pH value of the reaction system plays a crucial role in the assembly of POM-based hybrids. Moreover, the optical band gaps, electrochemical properties, magnetic properties and the photocatalytic properties of the compounds have been investigated.

pH-controlled and sulfite anion-directed assembly of a family of cerium(III)-containing polyoxotungstates clusters.

A versatile one-pot strategy was employed to synthesize five cerium(III)-containing polyoxotungstate nanoclusters through pH-controlled and sulfite anion-directed assembly: [C2H8N]3Na7[Ce2(H2O)6W22O72(OH)4]·20H2O (1) at pH 5.0; [C2H8N]8Na16[Ce4(H2O)12W44O144(OH)12]·23H2O (2) at pH 4.5; [C2H8N]2Na4Ce2[Ce2(H2O)10W28O92(OH)2]·27H2O (3) at pH 2.8-3.3; [C2H8N]2Na7[{α-SW7O28}{Ce2(H2O)6}(W3O6){α-SW9O32}{α-SW9O31(OH)}]·18H2O (4) at pH 2.5; [C2H8N]2Na18[Ce2(H2O)9W36O110(OH)12]2·30H2O (5) at pH 1.5. These compounds were characterized by single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric (TG) analysis, X-ray photoelectron spectroscopy (XPS), and electrospray ionization mass spectrometry (ESI-MS). Moreover, their electrochemical properties were investigated. Single-crystal X-ray structure analysis revealed that 1 and 2 were di- and tetra-cerium(III)-bridged polyoxotungstates, constructed from two different types of lacunary {W11} units. 3 composed of the well-known cerium(III)-stabilized {W28} unit and organic amine-sodium-cerium cations, was isolated in the pH range 2.8-3.3. In this reaction system, the SO3(2-) anion acted as a heteroanion template at a lower pH 2.5. 4 was isolated by the combination of cerium(III) centers and SO3(2-) heteroanion template, which is the first lanthanide-containing polyoxotungstates with sulfur heteroatoms, and the 4f metal cerium(III) centers in 4 both have eight-coordinated modes and the SO3(2-) heteroanion templates display μ7 and μ9 coordination modes. At a much lower pH 1.5, the polyanion of 5 was obtained, two triangular-shaped {W36} subunits were bridged by the cerium(III) ions, resulting in the largest lanthanide-containing iso-polyoxotungstates known to date.

Three cobalt(II)-linked {P8W48} network assemblies: syntheses, structures, and magnetic and photocatalysis properties.

Three cobalt(II)-containing tungstophosphate compounds, Na8Li8Co5[Co5.5(H2O)19P8W48.5O184]⋅60 H2O (1), K2Na4Li11Co5[Co7(H2O)28P8W48O184]Cl⋅ 59 H2O (2), and K2Na4LiCo11[Co8(H2O)32P8W48O184](CH3COO)4Cl⋅47 H2O (3), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, elemental analyses, and magnetic measurements. The pH value impacts the formation of distinct cobalt-linked frameworks. The cyclic cavity of the polyanion accommodates 5.5, 7, and 8 cobalt ions in 1, 2, and 3, respectively. In compounds 1 and 2, each {Co5.5P8W48} and {Co7P8W48} fragment links to four others through multiple {Co-O-W} coordination bonds to generate a two-dimensional network. Compound 3 can be considered as a 3D network based on the {Co-O-W} coordination bonds and the {Co3(CH3COO)2(H2O)10} linkers between the {P8W48} fragments. Interestingly, acetate ligands have been employed to form the {Co3(CH3COO)2(H2O)10} unit, thereby inducing the construction of a 12-connected framework. To the best of our knowledge, compound 3 contains the largest-ever number of cobalt ions in a {P8W48}-based polyoxometalate when counterions are taken into account and the {P8W48} unit shows the highest number of connections thanks to the carboxyl bridges. The UV/Vis diffuse reflectance spectra of these powder samples indicate that the corresponding well-defined optical absorption associated with Eg can be assessed at 2.58, 2.48, and 2.73 eV and reveal the presence of an optical band gap. The photocatalytic H2 evolution activities of these {P8W48}-based compounds are evaluated.