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.
A novel 24-niobic-2-tellurite, [HTeNbO], was isolated by incorporating tellurite anions into a polyoxoniobate cage. The synthesized cluster represents the first example of a sandwich-type polyoxoniobate with the largest telluroniobate aggregate. Furthermore, the hybrid material acts as an efficient catalyst for the decolorization of basic fuchsin.
A novel octacobalt-containing polyoxoniobate, Na6 K12 [H2 Co8 O4 (Nb6 O19 )4 ]⋅39 H2 O, has been prepared by a combination of hydrothermal and diffusion methods. The polyanion [H2 Co8 O4 (Nb6 O19 )4 ](18-) incorporates a tetrameric assembly of Lindqvist-type [Nb6 O19 ](8-) fragments trapping a {Co(II) 4 Co(III) 4 } cluster which comprises a central {Co(III) 4 O4 } cubane core, surrounded by another four Co(II) ions linkers. Furthermore, magnetic measurements show that the compound exhibits antiferromagnetic interactions.
By deliberately using a metastable polyanion [(NbO2 )6 P2 W12 O56 ](12-) (1), which was formed in situ, we have discovered the unprecedented hexameric cluster {Mn15 (Nb6 P2 W12 O62 )6 } (2), in which the six polyanions [Nb6 P2 W12 O61 ](10-) are alternately connected by four intriguing trinuclear {Mn(III) 3 } moieties and four {Mn(II) } linkers. This discovery is the first in which the phosphoniobotungstate has been made accessible by using transition-metal ions; furthermore, polyanion 2 represents the largest niobotungstate cluster reported to date. Analysis by means of electrospray ionization mass spectrometry (ESI-MS) provides insight into the self-assembly process, and the peaks observed relate to the different charge states of the parent cluster, thus confirming the stability of 2. In addition, magnetic-susceptibility measurements reveal that each {Mn(III) 3 } subunit is a separate single-molecule magnet (SMM). This discovery results from the exploration of the reverse effect of metastable polyanion 1 possessing high reactivity, thereby turning a disadvantage into an advantage. This finding could define a new synthetic strategy for the design and synthesis of magnetic polyoxometalate (POM) clusters.
By
adopting different crystal growth methods, two novel organic–inorganic
hybrids, [{Cu(phen)}6(H2O)(Te5Nb15.5Cu0.5O57)]3.5– and
its dimer, have been successfully synthesized. These are fabricated
by simple compound reactions and directed by the tellurite anions,
which act as heteroanion templates and linkers, as well as a pendant
ligand. The compounds were characterized by IR spectra, UV/vis, thermogravimetric
analysis, and single crystal X-ray diffraction. Furthermore, the solution
behavior was also investigated.
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