Polyoxometallate anions

Some fimctionalized materials have also been prepared by coprecipitation at low supersaturation. A perylene chromophore, for example, has been intercalated into LDH in an attempt to prepare stabihzed pigments [40]. Catalyt-ically active species have also been introduced into the interlayers of LDHs by direct synthesis, e.g. the intercalation of (PWi204o) or (SiWi204o) gives catalysts or catalyst precursors containing interlayer polyoxometalate anions [41]. Vein et al. reported the synthesis of Zr-containing LDH-Hke... 

Complexes of Phosphate Esters and Nucleotides with Polyoxometalate Anions... 

Polyoxometalate anions, especially those of hexavalent molybdenum and tungsten interact with rare-earth cations to generate a seemingly endless variety of complexes in which the rare earths function as encrypted cations, as core heteroatoms, or as linkers of polyoxometalate fragments to yield discrete anionic assemblies currently incorporating as few as 8 and as many as 164 metal centers,... 

Polyoxometalate anions have also been incorporated by the direct coprecipitation of a ZnAl-LDH with a-(SiWn039)8 under mildly acidic conditions [83], and a ZnCr-LDH with V10O 8 at pH 4.5 [84]. The reconstruction method has also been used to incorporate such anions into MgAl- and NiAl-LDHs [5, 29, 85, 86]. 

Evans, J., Pillinger, M. and Zhang, J. (1996). Structural studies of polyoxometalate-anion-pillared layered double hydroxides. J. Chem. Soc., Dalton Trans., 2963. 

In recent years, the design and synthesis of functional molecular materials is a focus of active research in the fields of chemistry and materials science. Polyoxometalate anions constitute a distinctive class of compounds which are receiving increasing interest in catalysis, medicine and materials science. Their chemical, structural and electronic versatility make them act as electron acceptors and accommodate magnetic transition metal centers in their structures. 

The present review focuses first on actinide complexes of polymolybdates (section 2) and pol5durrgstates (section 3) that have beetr isolated and structurally characterized. There are currently no reported actinide polyvanadates, -niobates, or -tantalates. A final section (4) summarises solution studies of equilibria between actinide cations and polyoxometalate anions. 

Solution equilibria btween actinide cations and polyoxometalate anions... 

A recent communication reported an interesting ferrocene-anion solid state interaction between Compound 121 and polyoxometalate anions (Fig. 15) (235). An electrostatic interaction between the trimethylammonio group and the an-... 

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. 

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. 

FIGURE 16.1 Structure of the [WZn3(ZnW9034)2] sandwich polyoxometalate anion. 

Coordinatively saturated metal complexes that are kinetically inert with respect to ligand substitution may undergo outer-sphere electron transfer reactions with dioxygen. Typical examples include oxidations of six-coordinate chromium(II) complexes29 (Equation 4.6) and oxidations of polyoxometallate anions.30... 

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). 

Having studied speciation in polyoxometalate systems for three decades, we found it worthwhile to make a quantitative study of a system to try to determine the extent of medium cation complexation to polyoxometalate anions. We thereby chose the H - V(V) system since V is an ideal NMR nucleus, making this system extremely suitable for the powerful EMF-NMR technique. Moreover, the analysis of the experimental data can be performed with the least squares computer program LAKE, capable of simultaneously... 

We have also synthesized several other polyoxometalates, which contain cluster cations. For example, [MS4Cu4(y-MePy)g][M60i9] (M= Mo, W)" contains M-Cu-S cluster cation and polyoxometalate anion. The compound [Ag(PPh3)4]2[M060i9] 3CH2Cl2 is a hexamolybdate with two tetrakis(triphenylphosphine)silver cations acting as counter ions." ... 

Polyoxometalate anions, due to the large number of oxygen atoms, have also been used to control the hydrolysis of the oxophilic lanthanide ions (Pope, 2008). Hydrolysis of Y(III) or Yb(III) by carbonate in the presence of the trivacant Wells-Dawson polyoxoanion, a-[P2Wi505g] produced... 

The layered double hydroxides have been of interest as anion exchangers, basic catalysts, and catalyst precursors. Pillared derivatives of the type discussed earlier for the clays have been synthesized by ion exchange with polyoxometallate anions but have lower thermal stability. Several authors have reported synthesis of layered double hydroxides pillared with the Vio028 ion by direct ion exchange or by techniques that involve preswelling the layer structure with an organic anion. For example, the terephthalate anion was used in the synthesis ofVio028 and Mo7 024 intercalated phases. 

---