View source for Tellurate

{{short description|Compound containing an oxyanion of tellurium}}
[[Image:Tellurate.png|thumb|300px|The structure of metatellurate and orthotellurate]]

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 ion|polyatomic anion]] with a  central tellurium atom.<ref name="IUPAC2005">[http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005] – Full text (PDF)</ref>

==Tellurium oxyanions==
Historically the name tellurate was only applied to oxyanions of tellurium with [[oxidation number]] +6, formally derived from [[telluric acid]] {{chem2|Te(OH)6}}, and the name [[Tellurite (ion)|tellurite]] referred to oxyanions of tellurium with [[oxidation number]] +4, formally derived from [[tellurous acid]] {{chem2|(HO)2TeO}} and these names are in common use. However tellurate and [[Tellurite (ion)|tellurite]] are often referred to as tellurate(VI) and tellurate(IV) respectively in line with IUPAC renaming recommendations.<ref name="IUPAC2005"/> 
The '''metatellurate''' ion is {{chem|TeO|4|2−}} and the '''orthotellurate''' [[ion]] is {{chem|TeO|6|6−}}. Other oxyanions include pentaoxotellurate, {{chem|TeO|5|4−}},<ref name="UnteneckerHoppe1986">{{cite journal|last1=Untenecker|first1=H.|last2=Hoppe|first2=R.|title=Die koordinationszahl 5 bei telluraten: Cs2K<sub>2</sub>[TeO<sub>5</sub>]|journal=Journal of the Less Common Metals|volume=124|issue=1–2|year=1986|pages=29–40|issn=0022-5088|doi=10.1016/0022-5088(86)90474-1}}</ref>  ditellurate, {{chem|Te|2|O|10|8−}}<ref name = "Wells">Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications {{ISBN|0-19-855370-6}}</ref> and polymeric anions with 6-coordinate tellurium such as ({{chem|TeO|5|4−}})<sub>''n''</sub>.<ref name="Weil2003">{{cite journal|last1=Weil|first1=Matthias|title=Preparation, Thermal Behaviour and Crystal Structure of the Basic Mercury(II) Tetraoxotellurate(VI), Hg<sub>2</sub>TeO<sub>5</sub>, and Redetermination of the Crystal Structure of Mercury(II) Orthotellurate(VI), Hg<sub>3</sub>TeO<sub>6</sub>|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=629|issue=4|year=2003|pages=653–657|issn=0044-2313|doi=10.1002/zaac.200390111}}</ref>

===Metatellurates===
The metatellurate ion {{chem|TeO|4|2−}} is analogous to the [[sulfate]] ion, {{chem|SO|4|2−}} and the [[selenate]] ion, {{chem|SeO|4|2−}}. Whereas many sulfates and selenates form isomorphous salts<ref>{{Cotton&Wilkinson6th|pages = 531}}</ref> the tetrahedral metatellurate ion is only found in a few compounds such as the tetraethylammonium salt {{chem2|(N[[Ethyl group|Et]]4)2TeO4}}.<ref name="KonakaOzawa2008">{{cite journal|last1=Konaka|first1=Saki|last2=Ozawa|first2=Yoshiki|last3=Yagasaki|first3=Atsushi|title=Tetrahedral Tellurate|journal=Inorganic Chemistry|volume=47|issue=4|year=2008|pages=1244–1245|issn=0020-1669|doi=10.1021/ic701578p|pmid=18220344}}</ref> 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, {{chem2|Na2TeO4}} which contains octahedral tellurium centers sharing edges.<ref name="KratochvílJenšovský1977">{{cite journal|last1=Kratochvíl|first1=B.|last2=Jenšovský|first2=L.|title=The crystal structure of sodium metatellurate|journal=Acta Crystallographica Section B|volume=33|issue=8|year=1977|pages=2596–2598|issn=0567-7408|doi=10.1107/S0567740877008978|doi-access=}}</ref>

:{{chem|TeO|4|2−}} → {{chem|TeO|3|2−}} + {{1/2}}&nbsp;O<sub>2</sub>{{spaces|5}} (''E''<sup>0</sup>&nbsp;=&nbsp;−1.042&nbsp;V)

The ''E''<sup>0</sup> or [[standard reduction potential]] value is significant as it gives an indication of the strength of the tellurate ion as an oxidizing agent.<ref name="Frost2009"/>

===Orthotellurates===
Compounds containing the octahedral {{chem|TeO|6|6−}} anion are known, these include {{chem2|Ag6TeO6}}, {{chem2|Na6TeO6}} and {{chem2|Hg3TeO6}}.<ref name = "Holleman&Wiberg">{{Holleman&Wiberg|pages = 593}}</ref> There are also hydroxyoxotellurates, containing protonated {{chem|TeO|6|6−}}, such as {{chem2|(NH4)2TeO2(OH)4}} (sometimes written as {{chem2|NH4TeO4*2H2O}}) which contains the octahedral {{chem|TeO|2|(OH)|4|2−}} ion.<ref name="JohanssonLindqvist1979">{{cite journal|last1=Johansson|first1=G. B.|last2=Lindqvist|first2=O.|last3=Moret|first3=J.|title=Diammonium tellurium(VI) dioxide tetrahydroxide|journal=Acta Crystallographica Section B|volume=35|issue=7|year=1979|pages=1684–1686|issn=0567-7408|doi=10.1107/S056774087900741X|url=http://journals.iucr.org/b/issues/1979/07/00/a17652/a17652.pdf}}</ref>

==={{chem|TeO|5|4−}} ion ===
The compound {{chem2|Cs2K2TeO5}} contains {{chem|TeO|5|4−}} ions which are trigonal bipyramidal.<ref name="UnteneckerHoppe1986"/> The compound {{chem2|Rb6Te2O9}} contains both {{chem|TeO|5|4−}} and {{chem|TeO|4|2−}} anions.<ref name = "Greenwood">{{Greenwood&Earnshaw|page = 782}}</ref> Other compounds whose stoichiometry suggests the presence of {{chem|TeO|5|4−}} may contain either the dimeric {{chem|Te|2|O|10|8−}} made up of two edge-sharing {TeO<sub>6</sub>} as in {{chem2|Li4TeO5}}<ref name="Wells"/> and {{chem2|Ag4TeO5}}<ref name="Weil2007">{{cite journal|last1=Weil|first1=Matthias|title=New Silver Tellurates – The Crystal Structures of a Third Modification of Ag<sub>2</sub>Te<sub>2</sub>O<sub>6</sub> and of Ag<sub>4</sub>TeO<sub>5</sub>|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=633|issue=8|year=2007|pages=1217–1222|issn=0044-2313|doi=10.1002/zaac.200700106}}</ref> or corner-sharing {TeO<sub>6</sub>} octahedra as in {{chem2|Hg2TeO5}}.<ref name="Weil2003"/>

===Polymeric tellurate ions===
The dimeric {{chem|Te|2|O|10|8−}} made up of two edge sharing {TeO<sub>6</sub>} octahedra is found in the compound {{chem2|Li4TeO5}}.<ref name = "Wells"/> A similar hydroxy-oxy anion, {{chem2|Te2O6(OH)4}} is found in sodium potassium ditellurate(VI) hexahydrate, {{chem2|Na0.5K3.5Te2O6(OH)4*6H2O}} which contains pairs of edge sharing octahedra.<ref name="KratochvílPodlahová1978">{{cite journal|last1=Kratochvíl|first1=B.|last2=Podlahová|first2=J.|last3=Jenšovský|first3=L.|title=Sodium potassium ditellurate(VI) hexahydrate|journal=Acta Crystallographica Section B|volume=34|issue=1|year=1978|pages=256–258|issn=0567-7408|doi=10.1107/S056774087800271X|doi-access=}}</ref>
Polymeric chain anions consisting of corner-shared {TeO<sub>6</sub>} octahedra ({{chem2|TeO5}}){{su|b=''n''|p=4''n''−}} are found, for example in {{chem2|Li4TeO5}}.<ref name = "Wells"/>

===Aqueous chemistry===
In aqueous solution tellurate ions are 6 coordinate. In neutral conditions the '''pentahydrogen orthotellurate''' ion, {{chem|H|5|TeO|6|−}}, is the most common; in basic conditions, the '''tetrahydrogen orthotellurate''' ion, {{chem|H|4|TeO|6|2−}}, and in acid conditions, [[Telluric acid|orthotelluric acid]], {{chem2|Te(OH)6}} or {{chem2|H6TeO6}} is formed.<ref name="Frost2009">{{cite journal|last1=Frost|first1=Ray L.|title=Tlapallite H<sub>6</sub>(Ca,Pb)<sub>2</sub>(Cu,Zn)<sub>3</sub>SO<sub>4</sub>(TeO<sub>3</sub>)<sub>4</sub>TeO<sub>6</sub>, a multi-anion mineral: A Raman spectroscopic study|journal=Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy|volume=72|issue=4|year=2009|pages=903–906|issn=1386-1425|doi=10.1016/j.saa.2008.12.008|pmid=19167264|bibcode=2009AcSpA..72..903F|url=https://eprints.qut.edu.au/17594/1/17594.pdf}}</ref>

===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, {{chem|SO|4|2−}}, the [[pyrosulfate]], {{chem|S|2|O|7|2−}}, trisulfate, {{chem|S|3|O|10|2−}} and pentasulfate {{chem|S|5|O|16|2−}} ions all contain 4-coordinate sulfur and are built from corner-shared {{chem2|{SO4}|}} tetrahedra.<ref name = "Greenwood2">{{Greenwood&Earnshaw|page = 712}}</ref> Selenate compounds include many examples of four coordinate selenium, principally the tetrahedral {{chem|SeO|4|2−}} ion and the pyroselenate ion, {{chem|Se|2|O|7|2−}} which has a similar structure to the [[pyrosulfate]] ion.<ref name="PaetzoldAmoulong1965">{{cite journal|last1=Paetzold|first1=R.|last2=Amoulong|first2=H.|last3=Růžička|first3=A.|title=Untersuchungen an Selen-Sauerstoff-Verbindungen. XXVI. Schwingungsspektrum und Kraftkonstanten des Diselenations|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=336|issue=5–6|year=1965|pages=278–285|issn=0044-2313|doi=10.1002/zaac.19653360508}}</ref> Unlike sulfur there are examples of a 5-coordinate selenium oxyanion, {{chem|SeO|5|4−}} and one example of {{chem|SeO|6|6−}}.<ref name="HaasJansen2000">{{cite journal|last1=Haas|first1=Helmut|last2=Jansen|first2=Martin|title=Octahedral SeO<sub>6</sub><sup>6−</sup> and Square-Pyramidal SeO<sub>5</sub><sup>4−</sup>, Two New Oxoselenate Anions|journal=Angewandte Chemie|volume=39|issue=23|year=2000|pages=4362–4364|issn=1433-7851|doi=10.1002/1521-3773(20001201)39:23<4362::AID-ANIE4362>3.0.CO;2-S}}</ref><ref name="OroselDinnebier2006">{{cite journal|last1=Orosel|first1=Denis|last2=Dinnebier|first2=Robert|last3=Jansen|first3=Martin|title=High-Pressure Synthesis and Structure Determination of K<sub>6</sub>(SeO<sub>4</sub>)(SeO<sub>5</sub>), the First Potassium Orthoselenate(VI)|journal=Inorganic Chemistry|volume=45|issue=26|year=2006|pages=10947–10950|issn=0020-1669|doi=10.1021/ic061548v|pmid=17173453}}</ref><ref name="HaasJansen2001">{{cite journal|last1=Haas|first1=H.|last2=Jansen|first2=M.|title=Na<sub>4</sub>SeO<sub>5</sub>, ein neues Pentaoxoselenat(VI) – Synthese, Charakterisierung und Vergleich mit isotypem Na<sub>4</sub>MoO<sub>5</sub>|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=627|issue=4|year=2001|pages=755–760|issn=0044-2313|doi=10.1002/1521-3749(200104)627:4<755::AID-ZAAC755>3.0.CO;2-L}}</ref>

==NMR spectroscopy==

[[Tellurium]] has two NMR active nuclei, <sup>123</sup>Te and <sup>125</sup>Te. <sup>123</sup>Te has an abundance of 0.9% and a nuclear spin ({{mvar|I}}) of {{sfrac|1|2}}. <sup>125</sup>Te has an abundance of 7% and an equivalent nuclear spin.<ref>{{Housecroft3rd}}</ref> <sup>125</sup>Te is more commonly performed because it has a higher sensitivity.<ref>Drago, R. S. ''Physical Methods for Chemists 2nd ed''.; Surfside Scientific Publishers: Gainesville, FL '''1992'''.</ref> The '''metatellurate''' anion has a [[chemical shift]] around 610&nbsp;ppm when analyzed using <sup>125</sup>Te NMR at 25&nbsp;°C at a frequency of 94.735&nbsp;[[MHz]] and referenced externally against aqueous 1.0&nbsp;[[Molar concentration|M]] telluric acid.<ref name="KonakaOzawa2008"/>

==The tellurate suffix in the naming of inorganic compounds==
Following the IUPAC Red Book(2005)<ref name="IUPAC2005"/> some examples are:
*metatellurate ion, or tetraoxotellurate(VI) {{chem|TeO|4|2−}} is tetraoxidotellurate(2−)
*orthotellurate ion, or hexaoxotellurate(VI) {{chem|TeO|6|6−}} is hexaoxidotellurate(6−) 
*octafluorotellurate(VI) ion {{chem|TeF|8|2−}} is octafluoridotellurate(2−).

==References==
{{reflist}}

[[Category:Chalcogen oxyanions]]
[[Category:Tellurates| ]]