Transition metal oxide halides

Table 5-9 Bond Distances in Transition-Metal Oxides, Halides and Oxyhalides... 

Preparation and properties of high valent first row transition metal oxides and halides. C. Rosen-blum and S. L. Holt, Transition Met. Chem. (N.Y.), 1972, 7,87-182 (303). 

Based on the concept of mixed-framework lattices, we have reported a novel class of hybrid solids that were discovered via salt-inclusion synthesis [4—7]. These new compounds exhibit composite frameworks of covalent and ionic lattices made of transition-metal oxides and alkali and alkaline-earth metal halides, respectively [4]. It has been demonstrated that the covalent frameworks can be tailored by changing the size and concentration of the incorporated salt. The interaction at the interface of these two chemically dissimilar lattices varies depending upon the relative strength of covalent vs. ionic interaction of the corresponding components. In some cases, the weak interaction facilitates an easy... 

This structure is commonly adopted by oxides, nitrides halides, and sulfides MX, including the nonstoichiometric 3d transition-metal oxides TiO, VO, MnO, FeO, CoO, and NiO. 

Relatively strong satellites, 5—10 eV from the main peaks, have been observed in the metal 2p spectra of 3d transition metal oxides and halides. These satellites... 

Alkali metal halides can be volatile at incineration temperatures. Rapid quenching of volatile salts results in the formation of a submicrometer aerosol which must be removed or else exhaust stack opacity is likely to exceed allowed limits. Sulfates have low volatility and should end up in the ash. Alkaline earths also form basic oxides. Calcium is the most common and sulfates are formed ahead of halides. Calcium carbonate is not stable at incineration temperatures (see Calcium compounds). Transition metals are more likely to form an oxide ash. Iron (qv), for example, forms ferric oxide in preference to halides, sulfates, or carbonates. Silica and alumina form complexes with the basic oxides, eg, alkali metals, alkaline earths, and some transition-metal oxidation states, in the ash. 

There are also catalysts that lack any apparent source of metal-carbon bonds. These catalysts include the aforementioned alumina- and silica-sup-ported transition metal oxides (which, in principle, do not demand any activation by organometallic compounds), and also several group 6-8 transition metal chlorides (soluble in hydrocarbons or chlorohydrocarbons), most typically RuC13. Some of these transition metal halides require activation by a cocatalyst of the Lewis acid type (e.g. A1C13, GaBr3, TiCU) [66,67], Noble metal chlorides may be used in alcoholic solvents or in water containing emulsifiers [68]. 

As we have shown, there is a clear correlation between the frequency shift of the stretching frequency of CO adsorbed at positively charged centers at the surfaces of non-transition metal oxides and halides and the electric held sensed by the molecule (Stark effect). This is the reason why CO is considered a specific and sensitive probe of the surface fields of ionic sohds. 

The synthetic method for the preparation of thiocyanate complexes of air- and water-unstable transition-metal oxidation states has been found suitable for the synthesis of K[Ta(NCS)6] and K2[M(NCS)6] (where M = Ti4+,2 (Zr4+, Nb4+, Mo4+, or W4+), as well as the compound described above. By use of different solvents (e.g., diethyl ether or nitromethane), it can be expanded to include metal halides which undergo reduction... 

Only a few chalcogen halide adducts with oxide halides are known. In the course of a systematic study on exchange reactions of transition metal oxides with SCI2/CI2, paramagnetic [SCla JtMoOCU ] was obtained and characterized (157,241). 

The first row transition metal oxides are also surprisingly volatile (Figure 6). Iron (primarily relying on estimates based on the relatively limited data for halides), appears to possess the most stable oxide with acceptable volatility to temperatures as high as 1000°C. Ruthenium and copper oxides are extremely volatile and caimot be tecoimnended as active components in combustion catalysts. The least volatile transition metal oxide is iron (based primarily on estimated enthalpies of formation). A trend is observed for the more active transition metal oxides of increasing volatil-... 

E3.43 AgjS and CuBr (low-oxidation-number metal chalcogenide and halide) would be a p-type, and VO2 (high-oxidation-number transition metal oxide) would be an n-type. 

The complex composition of the systems using O2/H2 oxidant gives evidence that pure metal catalysts do not operate effectively without promoter, which can be halide ions and/or transition metal oxides. Our idea was to bring into contact platinum metal ions with probable promoter by means of synthesis of metal ion containing heteropolytungstates. 

All the above-said concerns alkali-metal carbonates dissolved in melts based on alkaline- and alkaline-earth metal halides. It should be mentioned that there is a lack of data on the behaviour of alkaline-earth carbonates, in high-temperature alkaline halide melts. Nevertheless, these data are necessary, in particular, for the purification of halide melts. For example, it is known that alkaline-earth oxides possess appreciable solubilities in molten alkaline halides, and that they can be used for precipitation of less soluble transition metal-oxides. After such a precipitation, the excess of alkaline-earth oxide remains in the dissolved state. The question arises, therefore, whether it can be removed from the halide melt by passing C02 according to the conventional reaction... 

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