Polyoxometalates (POMs) of Nb and Ta are greatly different from those of Mo, W, and V that have been studied extensively and developed well. The latter can be formed simply by acidification of their aqueous monomeric oxoanions and has found application areas from catalysis to magnetism, materials science, medicine, and nanotechnology. Even now the polyoxoniobate (PONb) chemistry has accelerated dramatically over the last 15 years, and a vast expansion of available PONbs has been reported. However, after nearly 200 years of POM research, Ta-based POM chemistry is still at its infant stage and only dominated by the isopolyoxotantalate ions (Ta and Ta) and transition-metal-capped Ta species, along with two Ti-substituted polyoxotantalates [TiTaO] and [TiTaO] reported very recently. In this study, we discover two novel peroxotantalophosphate clusters [P(TaO)O] (1) and [P(TaO)O] (2) by incorporating phosphorus heteroatom into Ta-oxo framework, which represent the first two examples of heteropolytantalate. Interestingly, two PTa half-units are cis- and trans-condensed in 1 and 2, leading to "open" and "closed" configurations, respectively. These two chemically and structurally related clusters can be isolated in a controlled manner, and the yields are relatively high. Both compounds were characterized in the solid state by single-crystal X-ray diffraction, P MAS NMR, FT-IR, TGA, and elemental analysis as well as byP NMR in solution. The results presented here provide a strategy to be applicable to other heteroatom-incorporated polyoxotantalates and further expand the phase space for polyoxotantalate chemistry.
Two novel octamolybdate-based tricarbonyl metal derivatives have been successfully synthesized and characterized, which represent the first two examples of tricarbonyl metal groups attached to a new {Mo(8)O(30)} building block.
A hexanuclear CdII metal–organic framework (1) based on 4‐(1H‐pyrazole‐4‐carboxamido)benzoic acid (H2L) and featuring a three‐dimensional microporous framework was synthesized. Notably, 1 shows a unique fluorescence‐quenching response toward Fe3+ ions with high selectivity and sensitivity (Stern–Volmer constant KSV = 2.07 × 104 m–1). The response is attributable to the coaction of absorption competition and energy‐transfer (ET) mechanism. Furthermore, spectral analysis indicates that the energy‐transfer mechanism makes the dominant contribution to the fluorescence quenching of 1.
Niobium tungsten oxide is a potential replacement for graphite in fast‐charge lithium‐ion batteries due to its high rate performance and high stability. Herein, Nb14W3O44 anode was synthesized by hydrothermal reaction of niobium oxalate and ammonium tungstate and sequent calcination of niobium tungsten oxide precursors. Compared with the traditional solid‐state method, the particle size and calcination time of Nb14W3O44 obtained by the modified method are greatly reduced. Through orthogonal experiments, the optimal synthesis conditions were determined, and it was found that hydrothermal conditions have an important influence on the particle size of the final product, while the calcination temperature and time greatly affect the purity of the product and thus influence its specific capacity during cycles.
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