Tellurate

The structure of metatellurate and orthotellurate

The tellurate ion is TeO₄²⁻ or TeO₆⁶⁻.

Unlike sulfate, tellurate is a somewhat good oxidizer; it can be reduced to tellurite or tellurium.

Tellurate exists in two forms, metatellurate ion, TeO₄²⁻, and orthotellurate ion, TeO₆⁶⁻.

Compounds include metatellurates and orthotellurates. Metatellurates are analogous to sulfates, but they are rare. Orthotellurates are much more common and this forms most of the chemistry of tellurates.

In neutral conditions, pentahydrogen orthotellurate ion, H₅TeO₆⁻, is most common; in basic conditions, tetrahydrogen orthotellurate ion, H₄TeO₆²⁻, is found; in acid conditions, the orthotelluric acid, H₆TeO₆ is formed.^[1]

Properties

The metatellurate anion, TeO₄²⁻, has a molecular weight of 191.60 g/mole. It belongs to the T_d molecular point group, thus it has a tetrahedral shape even though two of its oxygen atoms are double bonded.

TeO₄²⁻ → TeO₃²⁻ + 1/2O₂ (E⁰= −1.042 V)

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.^[1]

The orthotellurate anion, TeO₆⁶⁻, has a molecular weight of 223.6 g/mole. It belongs to the O_h molecular point group, thus it has an octahedral shape.

NMR spectroscopy

Tellurium has two NMR active nuclei, ¹²³Te and ¹²⁵Te. ¹²³Te has an abundance of 0.9% and a nuclear spin (I) of 1/2. ¹²⁵Te has an abundance of 7% and an equivalent nuclear spin.^{[2] 125}Te is more commonly performed because it has a higher sensitivity.^[3] 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.^[4]

List of some known salts involving metatellurate anions

Na₂TeO₄*2H₂O

K₂TeO₄*2H₂O

Rb₂TeO₄

Cs₂TeO₄

CaTeO₄

Al₂(TeO₄)₃

(NH₄)₂TeO₄

References

1. ^ ^{a b} Frost, R.L. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2009, 72, 903.
2. ^ Housecroft, C. E.; Sharpe, A. G. (2008). Inorganic Chemistry (3rd ed.). Prentice Hall. ISBN 978-0131755536. 
3. ^ Drago, R. S. Physical Methods for Chemists 2^nd ed.; Surfside Scientific Publishers: Gainesville, FL 1992.
4. ^ Konaka, S.; Ozawa, Y.; Yagasaki, A. Inorg. Chem., 2008, 47, 1244.

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