Tungstate
In chemistry a tungstate is a compound that contains an oxoanion of tungsten or is a mixed oxide containing tungsten. The simplest tungstate ion is WO42−, "orthotungstate".[1] There are many other tungstate ions that contain more than one tungsten atom and belong to a large group of polyatomic ions that are termed polyoxometalates, ("POMs"), and specifically termed isopolyoxometalates as they contain, along with oxygen and maybe hydrogen, only one other element. Comparing tungsten to the other group 6 elements, the large tungstate ions generally contain 6 coordinate metal atoms similar to molybdenum (molybdates) and contrast to chromium (chromates) where 4 coordination predominates.[1]
Some examples of tungstate ions that have been detected in solution in the solid state include[2]:
- [W7O24]6− (paratungstate A)[2]
- [W10O32]4− (tungstate Y)[4]
- [H2W12O42]10− (paratungstate B) [2]
- α-[H2W12O40]6− (metatungstate)[4])
- β-[H2W12O40]6− (tungstate X)[4])
See the tungstates category for a list of tungstates.
[edit] Occurrence
Tungstates occur naturally with molybdates. Powellite is a mineral form of calcium molybdate containing a small amount of tungstate, and scheelite is a mineral form of calcium tungstate containing a small amount of molybdate. Wolframite is manganese and iron tungstate, and all these are valuable sources of tungsten.
[edit] Chemical and physical properties
Solutions of tungstates, like those of molybdates, give intensely blue solutions of complex tungstate(V,VI) analoguous to the molybdenum blues when reduced by most organic materials.[1]
Tungstate can also be used as an oxidizing agent in the oxidation of cyclohexene. The tungstate can be constantly regenerated through the presence of hydrogen peroxide.
Unlike chromate, tungstate is not a good oxidizer, but like chromate, it polymerizes in acid and depolymerizes back to tungstates in alkaline solutions.
[edit] References
- ^ a b c Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0123526515
- ^ a b c d Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419.
- ^ Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
- ^ a b c Jon A. McCleverty, N. G. Connelly,Nomenclature of inorganic chemistry II: recommendations 2000, International Union of Pure and Applied Chemistry Commission on the Nomenclature of Inorganic Chemistry, Published by Royal Society of Chemistry, 2001, ISBN 0854044876
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