Polyoxometalate lacunary

Laurencin, D. Villanneau, R. Gerard, H. Proust, A. Experimental and Theoretical Study of the Regiospecific Coordination of Ru and Os Fragments on the Lacunary Polyoxometalate [a-PWnOjg]. J. Phys. Chem. A 2006, 110, 6345-6355. 

This complex is prepared by the addition of a water solution of Ni2 + to a solution of the lacunary polyoxometalate. 

THREE-DIMENSIONAL ORDERED MACROPOROUS HYBRID SILICA MATERIALS FUNCTIONALIZED WITH LACUNARY KEGGIN-TYPE POLYOXOMETALATES PREPARATION AND CHARACTERIZATION... 

Polyoxometalates have found applications in analytical and clinical chemistry, catalysis (including photocatalysis), biochemistry (electron transport inhibition), medicine (antitumoral, antiviral, and even anti-HIV activity), and solid-state device [19,20], Recently, three-dimensional ordered materials are modified by the incorporation of POM into wall structures using a direct synthesis approach [21,22], The motivation for the work lies in the novel properties that POM is introduced into silica networks [19,20], The incorporation is that the POM is linked to silica matrix by covalent grafting. A class of POM that are particularly attractive for the preparation of hybrid materials are the lacunary POM. Lacunary POMs include the mono and divacant unsaturated Keggin fragments [X" W,039]< ">- (X"+=B Ge P [22], [ Y -SiWioOgg] [21], Lacunary... 

Guo Y. H., Yang Y., Hu C. W., Ordered macroporous hybrid silica based on lacunary Keggin-type polyoxometalates preparation, characterization and photochemical behavior, Qn press). 

Figure 5.21 The one-dimensional chain in [Ce(H20)3(SiWn039)] [67b], (Reproduced with permission from M. Sadakane, et ai, Controlled assembly of polyoxometalate chains from lacunary building blocks and lanthanide-cation linkers, Angewandte Chemie International Edition, 2000, 39, no.l6, 2914-2916 (Figure 1). Wiley-VCH Verlag GmbH Co. KGaA.)...

Figure 5.24 The two-dimensional layer structure of [Ln2(H20)9(a2-P2 Vi706i)]" [36]. (Reprinted with permission fromY. Lu, etal., New polyoxometalate compounds built up of lacunary Wells-Dawson anions and trivalent lanthanide cations, Inorganic Chemistry, 45, no. 5, 2055-2060 (Figure 3), 2006. 2006 American Chemical Society.)...

By far the largest number of actinide POMs are polytungstates, and exploration of this field has been closely linked and often inspired by the development of lanthanide polyoxometalate chemistry. Before plunging into this area it is appropriate to review the main structural features that are often observed for actinide (and lanthanide) POMs. Such features have been termed lacunary... 

Recent years have seen the reports of increasing numbers of very large polyoxometalate anions. These may be divided into two classes (i) composite anions constructed of assemblies of simpler, usually lacunary, polyanions and (ii) mixed-valence polymolybdate anions which comprise common building blocks, e.g., Mo8, Mo6, and Mo2 clusters that have no separate, stable existence. 

K. Kamata, M. Kotani, K. Yamaguchi, S. Hikichi, N. Mizuno, Olefin epoxidation with hydrogen peroxide catalyzed by lacunary polyoxometalate [7-SiWio034(H20)2] U Chem. Eur. J. 13 (2007) 639. 

D. G. Musaev, K. Morokuma, Y. V. Geletii, C. L. Hill, Computational modeling of di-transition-metal-substituted /-Keggin polyoxometalate anions. Structural refinement of the protonated divacant lacunary silicodecatimgstate, Inorg. Chem. 43 (2004) 7702. 

A. Yoshida, S. Hikichi, N. Mizuno, Acid-base catalyses by dimeric disilicoicosatungstates and divacant y-Keggin-type silicodecatungstate parent Reactivity of the polyoxometalate compounds controlled by step-by-step protonation of lacunary W=O sites, J. Organomet. Chem. 692 (2007) 455. 

Lanthanide polyoxometalates can be used in conventional s)mtheses to build up two dimensional materials. Linking up lacunary subunits is accomplished by lanthanide binding to terminal oxygen atoms of an adjacent polyoxometalate, forming dimers. The appropriate cations can link the dimers into a lattice, as found in the case of At. ... 

In the preparation of materials, aqueous lanthanide and polyoxometalate chemistry is fraught with problems owing to multi-equilibria. Occluded water is often hard to remove and may preclude some applications. Additionally, in aqueous syntheses, different counterions complicate the issue as shown from our work and that of others. Therefore, it is very difficult to predict complexes and structures that will be formed in reactions carried out in water. We intend to branch into s)mtheses using organic soluble lacunary polyoxoanions and organic soluble or organometallic lanthanide precursors. We hope to establish reactions that can be depended on to produce complexes that can be reliably used in synthesis of extended materials. 

M. Sadakane, M. H. Dickman, M. T. Pope, Controlled assembly of polyoxometalate chains from lacunary... 

C. Rong, M. T. Pope, lacunary polyoxometalate anions are It-acceptor ligands-Characterization of some tungstoruthenate (II, III, IV, V) heteropolyanions and their atoms-transfer reactivity, J. Am. Chem. Soc. 114 2932 (1992). 

Solid state NMR have not been much used, so far, in the study of metal substituted lacunary polyoxotungstates and only a study of the coordination geometry of boron in polyoxometalates has been reported.However, "B NMR spectra of complexes like BWnCo and BWnZn or Si spectra of SiWuCo " show a single broad signal, that can be used to check the purity of the solids, as it is easily differentiated from those of the possible contaminants XWn and XW12. 

The structural features of large polytungstate clusters can be visualized in terms of subunits based on lacunary fragments of the Keggin ion. In such representations many of the fragments may not actually exist independently from the cluster containing these subunits. This also applies to the building blocks identified as part of the polyoxometallate clusters discussed in Sections 7.1.4 and 7.1.5. 

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