Tellurium dioxide

Tellurium dioxide (TeO₂) is a solid oxide of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite, β-TeO₂, and the synthetic, colourless tetragonal (paratellurite), α-TeO₂.^[2] Most of the information regarding reaction chemistry has been obtained in studies involving paratellurite, α-TeO₂.^[3]

Tellurium dioxide

α-TeO2, paratellurite
Names
Other names Tellurium(IV) oxide
Identifiers
CAS Number	7446-07-3 Y
3D model (JSmol)	Interactive image
ChemSpider	56390 Y
ECHA InfoCard	100.028.357
PubChem CID	62638
UNII	397E9RKE83 Y
CompTox Dashboard (EPA)	DTXSID8052487
InChI InChI=1S/O2Te/c1-3-2 Y Key: LAJZODKXOMJMPK-UHFFFAOYSA-N Y InChI=1/O2Te/c1-3-2 Key: LAJZODKXOMJMPK-UHFFFAOYAO
SMILES O=[Te]=O
Properties
Chemical formula	TeO2
Molar mass	159.60 g/mol
Appearance	white solid
Density	5.670 g/cm3(orthorhombic) 6.04 g/cm3 (tetragonal) [1]
Melting point	732 °C (1,350 °F; 1,005 K)
Boiling point	1,245 °C (2,273 °F; 1,518 K)
Solubility in water	negligible
Solubility	soluble in acid and alkali
Refractive index (nD)	2.24
Hazards
Flash point	Non-flammable
Related compounds
Other cations	Sulfur dioxide Selenium dioxide
Related tellurium oxides	Tellurium trioxide Tellurium monoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Preparation

Paratellurite, α-TeO₂, is produced by reacting tellurium with O₂:^[2]

Te + O₂ → TeO₂

An alternative preparation is to dehydrate tellurous acid, H₂TeO₃, or to thermally decompose basic tellurium nitrate, Te₂O₄·HNO₃, above 400 °C.^[2]

Physical properties

The longitudinal speed of sound in Tellurium dioxide is 4,260 metres per second (14,000 ft/s) at around room temperature.^[4]

Chemical properties

TeO₂ is barely soluble in water and soluble in strong acids and alkali metal hydroxides.^[5] It is an amphoteric substance and therefore can act both as an acid or as a base depending on the solution it is in.^[6] It reacts with acids to make tellurium salts and bases to make tellurites. It can be oxidized to telluric acid or tellurates.

The tellurite ion is kinetically inert, but TeO₂ equivalents will oxidize thioates in acid to the diacyl disulfide.^[7]

Structure

Paratellurite, α-TeO₂, converts at high pressure into the β-, tellurite form.^[8] Both the α-, (paratellurite) and β- (tellurite forms) contain four coordinate Te with the oxygen atoms at four of the corners of a trigonal bipyramid. In paratellurite all vertices are shared to give a rutile-like structure, where the O-Te-O bond angle are 140°. α-TeO₂ In tellurite pairs of trigonal pyramidal, TeO₄ units, sharing an edge, share vertices to then form a layer.^[8] The shortest Te-Te distance in tellurite is 317 pm, compared to 374 pm in paratellurite.^[8] Similar Te₂O₆ units are found in the mineral denningite.^[8]

TeO
₂ melts at 732.6 °C, forming a red liquid.^[9] The structure of the liquid, as well as the glass which can be formed from it with sufficiently rapid cooling, are also based on approximately four coordinate Te. However, compared to the crystalline forms, the liquid and glass appear to incorporate short-range disorder (a variety of coordination geometries) which marks TeO₂ glass as distinct from the canonical single-oxide glass-formers such as SiO₂, which share the same short-range order with their parent liquids.^[10]

Uses

It is used as an acousto-optic material.^[4]

Tellurium dioxide is also a reluctant glass former, it will form a glass under suitable cooling conditions,^[11] or with additions of a small molar fraction of a second compound such as an oxide or halide. TeO₂ glasses have high refractive indices and transmit into the mid-infrared part of the electromagnetic spectrum, therefore they are of technological interest for optical waveguides. Tellurite glasses have also been shown to exhibit Raman gain up to 30 times that of silica, useful in optical fibre amplification.^[12]

Safety

TeO₂ is a possible teratogen.^[13]

Exposure to tellurium compounds produces a garlic-like odour on the breath, caused by the formation of diethyl telluride.^[14]

References

1. Pradyot Patnaik (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8.
2. Greenwood NN, Earnshaw A (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 911. ISBN 978-0-08-022057-4.
3. W.R.McWhinnie (1995) Tellurium - Inorganic chemistry Encyclopedia of Inorganic Chemistry Ed. R. Bruce King (1994) John Wiley & Sons ISBN 978-0-471-93620-6
4. "MODEL ATM SERIES ACOUSTO-OPTIC MODULATOR" (PDF). Intraaction.com. Retrieved 14 March 2022.
5. Mary Eagleson (1994). Concise Encyclopedia Chemistry. Berlin: Walter de Gruyter. p. 1081. ISBN 3-11-011451-8.
6. K. W. Bagnall (1966). The Chemistry of Selenium, Tellurium and Polonium. London: Elsevier. pp. 59–60. ISBN 0-08-018855-9.
7. Subrahmanyan T, Aravamudan G, Rout GC, Seshasayee M (1984) [18 March 1983]. "Synthesis, properties, and molecular structure of bis(thiobenzoato-S)tellurium(II), C₁₄H₁₀O₂S₂Te(II)". Journal of Crystallographic and Spectroscopic Research. 14 (3). Plenum: 242–243. Bibcode:1984JCCry..14..239S. doi:10.1007/BF01161161.
8. Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6
9. Egon Wiberg, Nils Wiberg, Arnold Frederick Holleman (2001). Inorganic chemistry. Academic Press. pp. 592–593. ISBN 0-12-352651-5.
10. Alderman O, Benmore C, Feller S, Kamitsos E, Simandiras E, Liakos D, Jesuit M, Boyd M, Packard M, Weber R (2020). "Short-Range Disorder in TeO2 Melt and Glass". J. Phys. Chem. Lett. 11 (2): 427–431. doi:10.1021/acs.jpclett.9b03231. OSTI 1591765. PMID 31867975. S2CID 209446093.
11. Tagiara NS, Palles D, Simandiras E, Psycharis V, Kyritsis A, Kamitsos EI (2017). "Synthesis, thermal and structural properties of pure TeO2 glass and zinc-tellurite glasses". Journal of Non-Crystalline Solids. 457: 116–125. doi:10.1016/j.jnoncrysol.2016.11.033.
12. Stegeman R, Jankovic L, Kim H, Rivero C, Stegeman G, Richardson K, Delfyett P, Guo Y, Schulte A, Cardinal T (2003). "Tellurite glasses with peak absolute Raman gain coefficients up to 30 times that of fused silica". Optics Letters. 28 (13): 1126–8. Bibcode:2003OptL...28.1126S. doi:10.1364/OL.28.001126. PMID 12879929.
13. Perez-D'Gregorio RE, Miller RK, Baggs RB (1988). "Maternal toxicity and teratogenicity of tellurium dioxide in the Wistar rat: relationship to pair-feeding". Reprod. Toxicol. 2 (1): 55–61. Bibcode:1988RepTx...2...55P. doi:10.1016/S0890-6238(88)80009-1. PMID 2980402.
14. Atta-ur-Rahman (2008). Studies in Natural Products Chemistry, Volume 35. Elsevier. p. 905. ISBN 978-0-444-53181-0.

External links

• TeO₂ properties at Moltech Berlin
• Safety data for TeO₂ Archived 2007-01-09 at the Wayback Machine