Selenium trioxide
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3D model (JSmol)
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| ECHA InfoCard | 100.033.972 | ||
PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |||
| SeO3 | |||
| Molar mass | 126.96 g/mol | ||
| Appearance | white hygroscopic crystals | ||
| Density | 3.44 g/cm3 | ||
| Melting point | 118.35 °C | ||
| Boiling point | sublimes | ||
| very soluble | |||
| Structure | |||
| tetragonal | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Selenium trioxide (SeO3) is a chemical compound used in the manufacture of photoelectric cells and solar energy devices. It is hygroscopic, a strong oxidizing agent and a Lewis acid.[2]
Preparation
Selenium trioxide can be prepared in a number of ways:[2]
The reaction of anhydrous selenic acid and phosphorus pentoxide at 150-160 °C
Selenium metal with oxygen in a high frequency glow discharge
- 2Se + 3O2 → 2SeO3
The reaction of liquid sulfur trioxide with potassium selenate
- SO3 + K2SeO4 → K2SO4 + SeO3
Reactions
In its chemistry SeO3 generally resembles sulfur trioxide, SO3, rather than tellurium trioxide, TeO3.[2] It is thermodynamically unstable with respect to selenium dioxide and above 185 °C it begins to decompose:
- SeO3 → SeO2 + 1⁄2 O2;
At 120 °C SeO3 reacts with selenium dioxide to form diselenium pentoxide, Se2O5
- SeO3 + SeO2 → Se2O5
It reacts with selenium tetrafluoride to form selenoyl fluoride, the selenium analogue of sulfuryl fluoride
- SeO3 + SeF4 → SeO2F2
As with SO3 adducts are formed with Lewis bases such as pyridine, dioxane and ether.[2]
With lithium oxide and sodium oxide reaction in a sealed tube forms selenate(VI) compounds containing SeVIO54– and SeVIO66–:[3]
- 1 mole of SeO3 and 2 moles of Li2O gives Li4SeO5 ;trigonal pyramidal ion SeVIO54– with equatorial bonds , 170.6-171.9 pm; and axial bonds longer 179.5 pm
- 1 mole SeO3 and 2 moles Na2O gives Na4SeO5 square pyramidal containing the SeVIO54– , with bond lengths ranging from range 1.729 → 1.815 pm
- 4 moles SeO3 and 6 moles Na2O gives Na12(SeO4)3(SeO6) containing octahedral SeVIO66–
Structure
In the solid phase SeO3 consists of cyclic tetramers, with an 8 membered (Se-O)4 ring. Selenium atoms are 4 coordinate, bond lengths are Se-O bridging are 175 pm and 181pm, non-bridging 156 and 154 pm.[3]
SeO3 in the gas phase consists of tetramers and monomeric SeO3 which is trigonal planar with an Se-O bond length of 168.78 pm.[4]
References
- ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. pp. 4–81. ISBN 0-8493-0594-2.
- ^ a b c d Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0123526515
- ^ a b Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Franceso A. Devillanova, Royal Society of Chemistry, 2007, ISBN 9780854043668
- ^ Brassington, N. J.; Edwards, H. G. M.; Long, D. A.; Skinner, M. (1978). "The pure rotational Raman spectrum of SeO3". Journal of Raman Spectroscopy. 7 (3): 158–160. doi:10.1002/jrs.1250070310. ISSN 0377-0486.
External links
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- Schmidt, Prof. Dr. Max (1963-10-02). "The Chemistry of Selenium Trioxide". Angewandte Chemie International Edition in English. 2 (11): 691–692. doi:10.1002/anie.196306913.
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