Selenium trioxide
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Identifiers | |||
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13768-86-0 | |||
ChemSpider | 103019 | ||
Jmol 3D model | Interactive image | ||
PubChem | 115128 | ||
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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 (245.03 °F; 391.50 K) | ||
Boiling point | sublimes | ||
very soluble | |||
Structure | |||
tetragonal | |||
Vapor pressure | {{{value}}} | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references | |||
Selenium trioxide is the inorganic compound with the formula SeO3. It is white, hygroscopic solid. It is also an oxidizing agent and a Lewis acid. It is of academic interest as a precursor to Se(VI) compounds.[2]
Preparation
Selenium trioxide is difficult to prepare because it is unstable with respect to the dioxide:
- 2 SeO3 → 2 SeO2 + O2
It has been generated in a number of ways despite the fact that the dioxide does not combust under normal conditions.[2] One method entails dehydration of anhydrous selenic acid with phosphorus pentoxide at 150-160 °C. 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]
At 120 °C SeO3 reacts with selenium dioxide to form the Se(VI)-Se(IV) compound diselenium pentoxide:[3]
- 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 it reacts to form salts of SeVIO54− and SeVIO66−:[4] With Li2O, it gives Li4SeO5, containing the trigonal pyramidal anion SeVIO54− with equatorial bonds, 170.6-171.9 pm; and longer axial Se-O bonds of 179.5 pm. With Na2O it gives Na4SeO5, containing the square pyramidal SeVIO54−, with Se-O bond lengths ranging from range 1.729 → 1.815 pm, and Na12(SeO4)3(SeO6), containing octahedral SeVIO66−. SeVIO66− is the conjugate base of the unknown orthoselenic acid (Se(OH)6).
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 being Se-O bridging are 175 pm and 181pm, non-bridging 156 and 154 pm.[4]
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.[5]
References
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 2.0 2.1 2.2 2.3 Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0123526515
- ↑ Z. Žák "Crystal structure of diselenium pentoxide Se2O5" Zeitschrift für anorganische und allgemeine Chemie 1980, volume 460, pp. 81–85. doi:10.1002/zaac.19804600108
- ↑ 4.0 4.1 Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Franceso A. Devillanova, Royal Society of Chemistry, 2007, ISBN 9780854043668
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
Further reading
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