Coordinated Heteropoly Compounds

Heteropolyanions and isopolyanions are polymeric oxoanions (polyoxometalates) (2, 3, 5, 6). The structure of a heteropolyanion or polyoxoanion molecule itself is called a primary structure (5, 6, 77). There are various kinds of polyoxoanion structure (Section II.A. 1). In solution, heteropoly anions are present in the unit of the primary structure, being coordinated with solvent molecules and/ or protonated. Most heteropolyanions tend to hydrolyze readily at high pH (Section 1I.C). Protonation and hydrolysis of the primary structure may be major structural concerns in solution catalysis. Heteropoly compounds in the solid state are ionic crystals (sometimes amorphous) consisting of large polyanions, cations, water of crystallization, and other molecules. This three-dimensional arrangement is called the secondary structure. For understanding catalysis by solid heteropoly compounds, it is important to distinguish between the primary structure and the secondary structure (5, 6, 17). Recently, it has been realized that, in addition... 

Miolati-Rosenheim formulas. The elaborate Miolati-Rosenheim theory, now outmoded, dominated the field of heteropoly compounds for several decades, and much of the literature is expressed with these formulas. In Miolati-Rosenheim formulas [Mo04] 2 ions or the now discarded [M02O7]-2 ions are represented as coordinated to the central atoms. The Miolati-Rosenheim formulas are still frequently used deliberately to indicate that modern structural information is lacking. 

Terminal alkenes can be hydrogenated selectively in the presence of PdCI2 [63] or RhCl(PPhj)3 [64] and heteropoly compounds. The catalytic system is also highly active for the production of urethane or isocyanate compounds by the reductive carbonylation of nitrobenzene. It is considered that polyoxometalate coordinating with Pd2+ in the reduced form is the active species, since easily reducible heteropolyanions are more active [63]. 

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