In chemistry tellurate is a compound containing 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 ...

tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

where tellurium has an

oxidation number In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Co ...

of +6. In the naming of inorganic compounds it is a suffix that indicates a

polyatomic anion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero. The term molecule may or may not ...

with a central tellurium atom.Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005
– Full text (PDF)

Tellurium oxyanions

Historically the name tellurate was only applied to oxyanions of tellurium with

+6, formally derived from

telluric acid Telluric acid is a chemical compound with the formula , often written as . It is a white crystalline solid made up of octahedral molecules which persist in aqueous solution. In the solid state, there are two forms, rhombohedral and monoclinic, a ...

, and the name

tellurite The tellurite ion is . A tellurite (compound), for example sodium tellurite, is a compound that contains this ion. They are typically colorless or white salts, which in some ways are comparable to sulfite. A mineral with the formula TeO2 is ...

referred to oxyanions of tellurium with

+4, formally derived from

tellurous acid Tellurous acid is an inorganic compound with the formula H2TeO3. It is the oxoacid of tellurium(IV). This compound is not well characterized. An alternative way of writing its formula is (HO)2TeO. In principle, tellurous acid would form by trea ...

and these names are in common use. However tellurate and

are often referred to as tellurate(VI) and tellurate(IV) respectively in line with IUPAC renaming recommendations. The metatellurate ion is and the orthotellurate

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

is . Other oxyanions include pentaoxotellurate, , ditellurate, Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications and polymeric anions with 6-coordinate tellurium such as ()_''n''.

Metatellurates

The metatellurate ion is analogous to the

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ar ...

ion, and the

selenate The selenate ion is . Selenates are analogous to sulfates and have similar chemistry. They are highly soluble in aqueous solutions at ambient temperatures. Unlike sulfate, selenate is a somewhat good oxidizer; it can be reduced to selenite or ...

ion, . Whereas many sulfates and selenates form isomorphous salts the tetrahedral metatellurate ion is only found in a few compounds such as the tetraethylammonium salt . 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, which contains octahedral tellurium centers sharing edges. : → + O₂ (''E''⁰ = −1.042 V) The ''E''⁰ or

standard reduction potential Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...

value is significant as it gives an indication of the strength of the tellurate ion as an oxidizing agent.

Orthotellurates

Compounds containing the octahedral anion are known, these include , and . There are also hydroxyoxotellurates, containing protonated , such as (sometimes written as ) which contains the octahedral ion.

ion

The compound contains ions which are trigonal bipyramidal. The compound contains both and anions. Other compounds whose stoichiometry suggests the presence of may contain either the dimeric made up of two edge-sharing as in and or corner-sharing octahedra as in .

Polymeric tellurate ions

The dimeric made up of two edge sharing octahedra is found in the compound . A similar hydroxy-oxy anion, is found in sodium potassium ditellurate(VI) hexahydrate, which contains pairs of edge sharing octahedra. Polymeric chain anions consisting of corner-shared octahedra () are found, for example in .

Aqueous chemistry

In aqueous solution tellurate ions are 6 coordinate. In neutral conditions the pentahydrogen orthotellurate ion, , is the most common; in basic conditions, the tetrahydrogen orthotellurate ion, , and in acid conditions,

orthotelluric acid Telluric acid is a chemical compound with the formula , often written as . It is a white crystalline solid made up of octahedral molecules which persist in aqueous solution. In the solid state, there are two forms, rhombohedral and monoclinic, a ...

, or is formed.

Structural comparisons with oxyanions of sulfur and selenium

Sulfur(VI) oxyanions have a coordination number of 4 and in addition to the tetrahedral

ion, , the

pyrosulfate In chemistry, disulfate or pyrosulfate is the anion with the molecular formula . Disulfate is the IUPAC name. It has a dichromate-like structure and can be visualised as two corner-sharing SO4 tetrahedra, with a bridging oxygen atom. In this a ...

, , trisulfate, and pentasulfate ions all contain 4-coordinate sulfur and are built from corner-shared tetrahedra. Selenate compounds include many examples of four coordinate selenium, principally the tetrahedral ion and the pyroselenate ion, which has a similar structure to the

ion. Unlike sulfur there are examples of a 5-coordinate selenium oxyanion, and one example of .

NMR spectroscopy

Tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

has two NMR active nuclei, ¹²³Te and ¹²⁵Te. ¹²³Te has an abundance of 0.9% and a nuclear spin () of . ¹²⁵Te has an abundance of 7% and an equivalent nuclear spin. ¹²⁵Te is more commonly performed because it has a higher sensitivity.Drago, R. S. ''Physical Methods for Chemists 2nd ed''.; Surfside Scientific Publishers: Gainesville, FL 1992. The metatellurate anion has a

chemical shift In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of ...

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.

The tellurate suffix in the naming of inorganic compounds

Following the IUPAC Red Book(2005) some examples are: *metatellurate ion, is tetraoxidotellurate(2–) *orthotellurate ion, is hexaoxidotellurate(6–) * ion is octafluoridotellurate(2–).

References

{{reflist Oxyanions