Topic
Polyoxometalate
About: Polyoxometalate is a research topic. Over the lifetime, 3493 publications have been published within this topic receiving 94123 citations. The topic is also known as: POM.
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TL;DR: The first polyoxometalates incorporating uranyl hetero groups have been synthesized by reaction of Na9(A-PW9O34) with UO2(NO3)2 as discussed by the authors.
Abstract: The first examples of polyoxometalates incorporating uranyl hetero groups have been synthesized by reaction of Na9(A-PW9O34) with UO2(NO3)2. Sodium, ammonium, and potassium salts of (M2(UO2)2- (PW9O34)2) 12- (M ) Na, NH4, K) were characterized by P and W NMR spectroscopy and single-crystal structural analysis. The sodium salt (1) contains an anion of Ci symmetry in which two PW9O34 groups sandwich two UO2 2+ and two Na + cations. The uranium atoms have pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one PW9O34 and two bonds to the other. The sodium cations have approximate tetrahedral coordination geometry. Single-line P and five-line W NMR spectra confirm that the anion structure is maintained in solutions containing excess Na + . The ammonium and potassium salts contain anions in which the UO2 2+ cations (pentagonal bipyramids) are unsymmetrically sandwiched between the PW9O34 groups, as are two closely associated cations, one internal and one external. In solution both, salts give two-line P and nine-line W NMR spectra that are consistent with the solid-state structures. Solution equilibria are rapidly established between the two structure types and are dependent upon the concentrations and identities of the cations. Based on integrated P NMR spectra, the equilibrium constants for (Na2(UO2)2(PW9O34)2) 12- + 2M + T (M2(UO2)2(PW9O34)2) 12- + 2Na + are 128 ( 12 (M ) K + ) and 1.8 ( 0.8 (M ) NH4 + ). The requirement of the second cation in order to satisfy the mass-action expression for Keq, coupled with a W NMR spectrum that implies Cs symmetry, demonstrates that the external ion-paired cation undergoes rapid exchange between several surface sites of the heteropolyanion. Solutions of 1 are stable at pH 7 in the presence of excess sodium cations, and the anion is transferable into toluene by phase-transfer techniques. Addition of calcium ions to solutions of 1 generates a new one-line P NMR spectrum of a Ca derivative which is assumed to be isostructural with 1.
132 citations
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TL;DR: This work reports the spontaneous and rapid growth of micrometre-scale tubes from crystals of a metal oxide-based inorganic solid when they are immersed in an aqueous solution containing a low concentration of an organic cation.
Abstract: We report the spontaneous and rapid growth of micrometre-scale tubes from crystals of a metal oxide-based inorganic solid when they are immersed in an aqueous solution containing a low concentration of an organic cation. A membrane immediately forms around the crystal, and this membrane then forms micrometre-scale tubes that grow with vast aspect ratios at controllable rates along the surface on which the crystal is placed. The tubes are composed of an amorphous mixture of polyoxometalate-based anions and organic cations. It is possible for liquid to flow through the tubes, and for the direction of growth and the overall tube diameter to be controlled. We demonstrate that tube growth is driven by osmotic pressure within the membrane sack around the crystal, which ruptures to release the pressure. These robust, self-growing, micrometre-scale tubes offer opportunities in many areas, including the growth of microfluidic devices and the self-assembly of metal oxide-based semipermeable membranes for diverse applications.
131 citations
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TL;DR: In this article, Anderson-type polyoxomolybdates were functionalized with pendant pyridyl groups, and evidence for electronic communication between the polyoxometalate and the porphyrin was established by fluorescence spectroscopy.
Abstract: Two Anderson-type polyoxomolybdates [FeMo6O18{(OCH2)3CNHCO(4-C5H4N)}2]3– and [MnMo6O18{(OCH2)3CNHCO(4-C5H4N)}2]3– and two Lindqvist-type polyoxovanadates [V6O13{(OCH2)3CCH2OC(O)(4-C5H4N)}2]2– and [V6O13{(OCH2)3CNHCO(4-C5H4N)}2]2– were functionalized with pendant pyridyl groups. The electrochemical analysis revealed reversible redox processes at the heteroatom of the Anderson-type compounds and at the vanadium atoms in the Lindqvist series. Axial coordination of the polyoxometalate-grafted pyridyl groups to the metal ion in [Ru(CO)TPP] (TPP = tetraphenylporphyrin) and [ZnTPP] yielded polyoxometalate–porphyrin assemblies in solution. Evidence for electronic communication between the polyoxometalate and the porphyrin was established by fluorescence spectroscopy. Cyclic voltammetry showed the influence of the porphyrin on the redox process of the polyoxometalate and also nucleophilic attack at the porphyrin skeleton by the pendant pyridyl groups. Implications for the construction of supramolecular functional devices based on these components are discussed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
131 citations
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131 citations