Keggin polyanions

The presence of transition metal ions as cations for the Keggin polyanion is necessary in order to develop an active and selective catalyst. 

The IR spectra of the reaction solutions showed that the structures of the Keggin polyanions remained unchanged during the reaction. When the concentration of H2O2 was increased, however, new bands appeared in the 500 - 600 cm-i region possibly due to peroxo species. It seems that active peroxo species are formed by the reaction of vanadium-substituted polyanions and H2O2 or that other active oxygen species are derived from the peroxo species. Either or both species are probably active for the hydroxylation of benzene. 

The complex P04[W(0)(02)2]4 / can be isolated from a reaction of H3PW12O40 and H2O2 after going through several higher nuclearity species derived from sequential breakdown of the parent Keggin polyanion. 

Several research groups have studied the interaction between vacant, TMSP or their parent Keggin polyanions and hydrogen peroxide. In some cases, alkyhydroperoxides have also been used. °... 

Wang X, Wang Y, Liu G, Tian A, Zhang J, Lin H (2011) Novel inorganic-organic hybrids constructed from multinuclear copper cluster and Keggin polyanions fr om ID wave-Uke chain to 2D network. Dalton Trans 40 9299-9305... 

SAXSAVAXS AI-MIL-53-NH2, AI-MOF-235-NH2 and AI-MIL-IOI-NH2 Live encapsulation of Keggin polyanions, evaluation 105... 

Most phosphatotungstates belong to three structural types. The first type is that of the Keggin polyanion o-[PWi204o] [39] (Figure 5.10). Its structure is analogous to... 

Figure 1. Ball and stick (A) and polyhedral (B) representation of the monosubstituted Keggin-type polyanion [XWl lM(L)039]n-. Reprinted from J. Mol. Catal. A Chem. 262, Kholdeeva, O. A. Maksimovskaya, R. L, 7-24, Copyright (2007), with permission from Elsevier.

Depending on the solvent, the acidity of the solution, and the charge of the polyanion, the reductions involve either single-electron or multi-electron steps, often accompanied by protonation. In protic solvents, the Keggin anions exhibit... 

Figure 44 Examples of heteropolyanions (A) Keggin-type polyanion, for example 0 -PW,2O403-, (B) Dawson-type polyanion, for example P2Wn80626 (C) disubstituted polyanion, for example >-SiW,oFe204o,0. Taken from Ref. [216]. Reproduced by permission of The Royal Society of Chemistry.

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