Anions heteropoly

It is a simple process to form a phosphate glass. Phosphates are called glass formers. Phosphate melts are complex mixtures of reorganizing molecules. Glasses can be formed from many of these melts when they are chilled quickly. The amorphous solids are mixtures of molecules that happened to exist as they were frozen in time. No two mixtures of phosphate glasses are ever exactly the same, but their average properties are very similar. 

Studies of crystalline systems are definitive, because a thermodynamically defined condition may be specified and analyses by X-ray and similar techniques leave little reason to doubt the results. In other amorphous systems some properties of the systems are so dramatically different from the unreacted materials that there is no room for doubt. Such a system is the amorphous system composed of phosphates and silicates. 

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The reaction between organic cation (OC) of the alkaloids of Papaver Somnifeiaim and heteropoly anion (HPA) was studied by the... 

Recently, Corma et al. have patented a process of oxidizing cycloalkane with molecular oxygen to produce cycloalkanol and/or cycloalkanone in the presence of hydrotalcite-intercalated heteropoly anion [Co MnCo (H20)039] (M = W or Mo), which comprised one cobalt as a central atom and another as a substitute of a W=0 fragment in the Keggin structure [98]. At 130 °C and 0.5 MPa, 64 and 24% selectivity to cyclohexanone and cyclohexanol, respectively, was achieved at cyclohexane conversion about 5%. This catalytic system could be of practical importance provided a true heterogeneous nature of catalysis and good catalyst recyclability had been proved. Unfortunately, this information was lacking in [98]. 

At present count, some 68 elements (other than Mo and W) have been observed as heteroatoms in polyanions (see Table 5). Since each element may form more than one heteropoly anion (e.g. at least 18 tungstophosphates) and there are polyanions with combinations of several heteroatoms, the total number of known heteropolyanions is extremely large. It is therefore out of the question to attempt a complete accounting of every type of heteropolyanion on the following pages. We shall restrict discussion to the main structural types. More complete reviews are available.1-3... 

According to the patent literature, Ru02 can be used as a stoichiometric oxidant in aldehyde formation.648 RuC13649 and a ruthenium-substituted heteropoly anion [SiRu(H20)Wn0395-]650 651 have been found to serve as a selective catalyst in this oxidation. H202649 and NaI04650 651 as oxidants, or electrochemical oxidation651 have been used. 

Alkali slowly decomposes the yellow heteropoly anions, but the reduced blue forms are more stable. Presumably alkaline conditions are... 

Fig. 16.13 (a) The structures of two heteropoly anions, 12-molybdcphosphate or 12-tunastophosphule. (b) and (c) Details of coordination of three MOs octahedra with one corner of the heteroatom tetrahedron. 

Between 35 and 40 heteroatoms are known to form heteropoly anions and their corresponding acids. Large heteroaloms such as Ceoctahedra share faces to form MojGg groups which are corner connected to each other.39... 

Heteropoly anions. 760-764 Hexagonal crystal system, 75. 78 Hexanuclear dusters. 816 VtexgonsA closest packed (hep)... 

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... 

Solid HjPMo o reduced by H2 at a lower temperature shows a very weak ESR signal intensity of Mo5 +, probably because most of the Mo5+ ions are not detectable due to the rapid hopping of electrons. Heat treatment, which eliminates oxide ions from the heteropoly anion, leads to development of the Mo5 + signal, indicating the localization of electrons (101, 102). Early reports of ESR spectra of reduced PMo C o are likely due to these species. Several different species are observed in highly reduced samples. 

B. Metal Ion- or Metal Salt-Heteropoly anion Complexes 1. Simple Combinations... 

Condensed heteropoly anions and their complexes with lanthanide (III) ions. Spectroscopic studies Lis (1998)... 

Principle possibility of measuring hydrodynamic radii of colloidal nanoparticles rT from the reorientation correlation times tr was demonstrated in [132] for three quasi-spherical heteropoly anions in buffered aqueous solutions at several temperatures. The analysis of EPR line widths of V4+ ions by Kivelson equations allowed to determine Tr, from which rt were estimated by the ratio ... 

Tables 2 and 3 illustrate the principal series of heteropolymolybdates and heteropolytungstates, respectively, which have been reported. Table 4 represents central atoms that form heteropoly anions, the composition and structure of which have not yet been elucidated.

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