Recent advances in transition-metal-containing Keggin-type polyoxometalate-based coordination polymers

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.

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

We utilised the rich coordination character of Wells–Dawson polyoxometalates (POMs) to explore the higher-level helical conformation of hybrids. Herein, two compounds, [Ag26(Trz)16(OH)4][P2W18O62] (1) and Na[Ag16(Trz)9(H2O)4][P2W18O62]·H2O (2) (Trz = 1,2,3 triazole), with multi-fold meso-helices were successfully isolated. Both 1 and 2 displayed two different types of four-fold meso-helices, which are composed of POMs and organic–metal subunits. The interesting thing is that the four-fold helixes of 2 sequentially evolve into the most complex eight-fold meso-helices by sharing the building blocks. In addition, the multi-chelate patterns of Wells–Dawson POMs in 2 represent the highest coordination numbers to date, which dominates the evolution from four-fold to eight-fold meso-helices. For the first time, the Wells–Dawson POMs-based hybrids 1 and 2 have been used as anode materials in lithium-ion batteries (LIBs). The initial specific capacities of 1077 mA h g−1 for 1 and 1094 mA h g−1 for 2 were much higher than those of (NBu4)6[P2W18O62] and commercial graphite as reference anodes at a current density of 100 mA cm−2. Also, both of them showed stable performance after 100 cycles.

Self-organization towards complex multi-fold meso-helices in the structures of Wells–Dawson polyoxometalate-based hybrid materials for lithium-ion batteries

Improving the photocatalytic H2 evolution activity of Keggin polyoxometalates anchoring copper-azole complexes

Polyoxometalate-based coordination frameworks (POMCFs) extend the families of material chemistry and structural chemistry due to their diverse properties and fascinating architectures. In the architectural field of POMCFs, the choice of organic ligand usually plays a key role in the self-assembling process. To date, plenty of organic ligands, such as carboxylates and N-donor ligands, have been designed and utilized in the construction of porous, multinuclear and polythreaded architectures. As far as N-donor ligands are concerned, their flexible and rigid nature can show important influences on the formation of various architectures. This perspective highlights the recent developments in polythreaded/penetrating, multinuclear, helical architectural chemistry of POMCFs constructed from flexible N-donor ligands, including bis-imidazole, bis-triazole, bis-pyridine, bi-mercaptotetrazole, bi-pyridyl-bis-amide and bis-pyridyltetrazole ligands. Here, we will describe the influence of different space lengths and coordination groups on flexible N-donor ligands, as well as the influence of pH and polyoxometalates on the architectural structures of POMCFs, which may offer some possible synthetic strategies for constructing functional POMCFs with novel architectures.

Architectural chemistry of polyoxometalate-based coordination frameworks constructed from flexible N-donor ligands

Self-assembly of multiple components into well-defined and predictable structures remains one of the foremost challenges in chemistry. Here, upon subtle ligand variation, we reported on the assembly of three new polyoxometalate-based organic–inorganic hybrid compounds with different helical channel, [Ag3(H2pyttz-I)2][PMo12O40] (1), [Ag6(H2pyttz-II)4][CoW12O40]·2H2O (2), and [Ag7(Hpyttz-II)3(H2pyttz-II)][GeW12O40]·7H2O (3) (H2pyttz-I/II = 4-/3-pyrid-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, POM = polyoxometalates). X-ray diffraction analysis shows that compound 1 is constructed by “butterfly-like” Ag5(H2pyttz-I)2 subunits and POMs clusters, which are assembled into close helical channels impregnated with the components selves. Both compounds 2 and 3 are constructed by “paddle-wheel like” Ag4(H2pyttz-II)4 motifs and POMs clusters, which bring into being the larger helical channels (10.5% and 12.5% of the cell volume, respectively). Note that the only difference in compounds 2 and 3 is that the former conta...

Liang Li

Papers

Assembly of Polyoxometalate-Based Hybrids with Different Helical Channels upon Subtle Ligand Variation