Tellurate
In chemistry, tellurate is a compound containing an oxyanion of tellurium where tellurium has an oxidation number of +6. In the naming of inorganic compounds it is a suffix that indicates a polyatomic anion with a central tellurium atom.[1]
Tellurium oxyanions
Historically the name tellurate was only applied to oxyanions of tellurium with oxidation number +6, formally derived from telluric acid Template:Chem2, and the name tellurite referred to oxyanions of tellurium with oxidation number +4, formally derived from tellurous acid Template:Chem2 and these names are in common use. However tellurate and tellurite are often referred to as tellurate(VI) and tellurate(IV) respectively in line with IUPAC renaming recommendations.[1] The metatellurate ion is Template:Chem and the orthotellurate ion is Template:Chem. Other oxyanions include pentaoxotellurate, Template:Chem,[2] ditellurate, Template:Chem[3] and polymeric anions with 6-coordinate tellurium such as (Template:Chem)n.[4]
Metatellurates
The metatellurate ion Template:Chem is analogous to the sulfate ion, Template:Chem and the selenate ion, Template:Chem. Whereas many sulfates and selenates form isomorphous salts[5] the tetrahedral metatellurate ion is only found in a few compounds such as the tetraethylammonium salt Template:Chem2.[6] Many compounds with a stoichiometry that suggests the presence of a metatellurate ion actually contain polymeric anions containing 6-coordinate tellurium(VI), for example sodium tellurate, Template:Chem2 which contains octahedral tellurium centers sharing edges.[7]
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The E0 or standard reduction potential value is significant as it gives an indication of the strength of the tellurate ion as an oxidizing agent.[8]
Orthotellurates
Compounds containing the octahedral Template:Chem anion are known, these include Template:Chem2, Template:Chem2 and Template:Chem2.[9] There are also hydroxyoxotellurates, containing protonated Template:Chem, such as Template:Chem2 (sometimes written as Template:Chem2) which contains the octahedral Template:Chem ion.[10]
Template:Chem ion
The compound Template:Chem2 contains Template:Chem ions which are trigonal bipyramidal.[2] The compound Template:Chem2 contains both Template:Chem and Template:Chem anions.[11] Other compounds whose stoichiometry suggests the presence of Template:Chem may contain either the dimeric Template:Chem made up of two edge-sharing {TeO6} as in Template:Chem2[3] and Template:Chem2[12] or corner-sharing {TeO6} octahedra as in Template:Chem2.[4]
Polymeric tellurate ions
The dimeric Template:Chem made up of two edge sharing {TeO6} octahedra is found in the compound Template:Chem2.[3] A similar hydroxy-oxy anion, Template:Chem2 is found in sodium potassium ditellurate(VI) hexahydrate, Template:Chem2 which contains pairs of edge sharing octahedra.[13] Polymeric chain anions consisting of corner-shared {TeO6} octahedra (Template:Chem2)Template:Su are found, for example in Template:Chem2.[3]
Aqueous chemistry
In aqueous solution tellurate ions are 6 coordinate. In neutral conditions the pentahydrogen orthotellurate ion, Template:Chem, is the most common; in basic conditions, the tetrahydrogen orthotellurate ion, Template:Chem, and in acid conditions, orthotelluric acid, Template:Chem2 or Template:Chem2 is formed.[8]
Structural comparisons with oxyanions of sulfur and selenium
Sulfur(VI) oxyanions have a coordination number of 4 and in addition to the tetrahedral sulfate ion, Template:Chem, the pyrosulfate, Template:Chem, trisulfate, Template:Chem and pentasulfate Template:Chem ions all contain 4-coordinate sulfur and are built from corner-shared Template:Chem2 tetrahedra.[14] Selenate compounds include many examples of four coordinate selenium, principally the tetrahedral Template:Chem ion and the pyroselenate ion, Template:Chem which has a similar structure to the pyrosulfate ion.[15] Unlike sulfur there are examples of a 5-coordinate selenium oxyanion, Template:Chem and one example of Template:Chem.[16][17][18]
NMR spectroscopy
Tellurium has two NMR active nuclei, 123Te and 125Te. 123Te has an abundance of 0.9% and a nuclear spin (Template:Mvar) of Template:Sfrac. 125Te has an abundance of 7% and an equivalent nuclear spin.[19] 125Te is more commonly performed because it has a higher sensitivity.[20] The metatellurate anion has a chemical shift around 610 ppm when analyzed using 125Te NMR at 25 °C at a frequency of 94.735 MHz and referenced externally against aqueous 1.0 M telluric acid.[6]
The tellurate suffix in the naming of inorganic compounds
Following the IUPAC Red Book(2005)[1] some examples are:
- metatellurate ion, or tetraoxotellurate(VI) Template:Chem is tetraoxidotellurate(2−)
- orthotellurate ion, or hexaoxotellurate(VI) Template:Chem is hexaoxidotellurate(6−)
- octafluorotellurate(VI) ion Template:Chem is octafluoridotellurate(2−).
References
- ↑ a b c Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 – Full text (PDF)
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- ↑ a b c d Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications Template:ISBN
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- ↑ Template:Holleman&Wiberg
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- ↑ Template:Greenwood&Earnshaw
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- ↑ Template:Greenwood&Earnshaw
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- ↑ Template:Housecroft3rd
- ↑ Drago, R. S. Physical Methods for Chemists 2nd ed.; Surfside Scientific Publishers: Gainesville, FL 1992.