chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, a tungstate is a compound that contains an

oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determine ...

tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...

or is a mixed oxide containing tungsten. The simplest tungstate ion is , "orthotungstate". Many other tungstates belong to a large group of polyatomic ions that are termed

polyoxometalate In chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are ...

s, ("POMs"), and specifically termed isopolyoxometalates as they contain, along with oxygen and maybe hydrogen, only one other element. Almost all useful tungsten ores are tungstates.

Structures

Orthotungstates feature tetrahedral W(VI) centres with short W–O distances of 1.79 Å. Structurally, they resemble sulfates. Six-coordinate, octahedral tungsten dominates in the polyoxotungstates. In these compounds, the W–O distances are elongated. Some examples of tungstate ions: * (hydrogentungstate) * polymeric ions of various structures in , and Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications * (paratungstate A) * (tungstate Y)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, * (paratungstate B) * (metatungstate) * (tungstate X) See the tungstates category for a list of tungstates.

Occurrence

Tungstates occur naturally with

molybdate In chemistry, a molybdate is a compound containing an oxyanion with molybdenum in its highest oxidation state of +6: . Molybdenum can form a very large range of such oxyanions, which can be discrete structures or polymeric extended structures, ...

Scheelite Scheelite is a calcium tungstate mineral with the chemical formula Ca W O4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist Carl Wilhelm Scheele (1742–1786). Well-formed crystals are sought ...

, the mineral calcium tungstate, often contains a small amount of molybdate. Wolframite is manganese and iron tungstate, and all these are valuable sources of tungsten. Powellite is a mineral form of calcium molybdate containing a small amount of tungstate.

Reactions

Solutions of tungstates, like those of molybdates, give intensely blue solutions of complex tungstate(V,VI) analogous to the molybdenum blues when reduced by most organic materials. Unlike chromate, tungstate is not a good

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...

, but like chromate, solutions of tungstate condense to give the isopolytungstates upon acidification.

References

{{reflist Transition metal oxyanions