Oxyhalides oxidation state

No complexes have at present been authenticated in oxidation states greater than +6, whereas oxyhalide complexes exist where the +8 state is known this parallels trends in the halides and oxyhalides. 

As mentioned in the previous section, transition metals in high oxidation states exhibit behavior that is similar to that of some nonmetals. Vanadium(V) does this with the formation of oxyhalides having the formulas VOX3 and V02X. 

Because the highest oxidation state of Cr is + 6, it forms oxyhalides that have the formula Cr02X2 and are known as chromyl halides. However, in the case of the fluorine compound, CrOF4 is also known, as well as some oxyhalides having the formula CrOX3. Some reactions that yield chromyl halides are the following ... 

Thorium forms one series of halides, another one of oxyhalides, and also a series of double or complex halides. In general, stability of these compounds toward heat decreases as die atomic weight of die halogen increases. These compounds are often isostructural with the corresponding compounds of other actinide elements in the (IV) oxidation state. 

Group-5 elements are most stable in their maximum oxidation state +5 and therefore form pentahalides, see Figure 7. Most volatile are the pentafluorides, followed by the pentachlorides and the pentabromides. Besides the pure halides, also the oxyhalides (MOX3) are stable in the gas phase. They should be less volatile compared to the pure halides. This was confirmed experimentally for niobium, see Figure 8. 

Graphite is an example of an extended solid with a band gap equal to 0.0 eV at 0 K. Hence it can readily accept electrons into its vacant conduction band or relinquish electrons from its full valence band. Other hosts used in intercalation reactions, such as transition metal dichalcogendies and transition metal oxyhalides, tend to prefer acting as oxidizing agents only given the high formal oxidation state of the metal ion. 

As might be expected, there is a vast range of compounds containing sulfur halogen bonds (Figure 37), and they play an important role in synthetic sulfur chemistry. For convenience, they are divided by oxidation state. The sulfur oxyhalides are also dealt with in this section. 

A number of unique difficulties pertain to oxidation states of metal ions encountered in molten salt solutions. For example, for first-row transition metals, the highest oxidation state prevailing is often +3, as in the case of Fe and Cr. Frequently, for chlorides in particular, the +3 state compounds are volatile at suitable operating temperatures and, hence, their solutions are thermally unstable.Other problems encountered include rapidly dispropor-tionating states, the formation of oxyhalides, and precipitation of complexes by reaction with the melt. While redox reactions per se involve very fast charge transfer steps, these may occur at the extremes of the range of electrochemical stability, thus leading to concomitant solvent melt decomposition. Nevertheless, suitable processes such as Fe /Fe on vitreous carbon in chloride melts can be employed to determine the effective electrochemical areas of electrodes where diffusion coefficients are accurately known. ... 

The molecular structures of the dehydrated surface chromate species are schematically presented in Figure 1.4. The dehydrated surface Cr04 structures have much in common with their corresponding bulk chromates, Cr04 coordination and different extents of polymerization, but the surface chromates are monoxo, with the possible exception of the Si02 support, and the bulk chromates approach dioxo coordination upon extensive polymerization ( 2> 4 as in bulk Cr03). Thus, monoxo chromates are unique to surface chromate species on oxide supports and some gas phase oxyhalides. Furthermore, the oxide supports stabilize the surface chromate species in the Cr(- -6) oxidation state, and chromia in excess of mono-layer surface coverage becomes reduced to Cr(- -3) 2O3 crystalline particles upon calcination at elevated temperature. 

There are many oxyhalides of actinide oxidation states 34- through 6-t-. In general these are more stable than a mixture of oxide and halide, e.g. 

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