Selenium trioxide

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Selenium trioxide [1]
Structural formula of the monomer as found in the gas phase Selenium trioxide.svg
Structural formula of the monomer as found in the gas phase
Space-filling model of the monomer as found in the gas phase Selenium-trioxide-3D-spacefill.png
Space-filling model of the monomer as found in the gas phase
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.033.972 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
  • InChI=1S/O3Se/c1-4(2)3 Yes check.svgY
    Key: VFLXBUJKRRJAKY-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/O3Se/c1-4(2)3
    Key: VFLXBUJKRRJAKY-UHFFFAOYAC
  • monomer:O=[Se](=O)=O
  • cyclic tetramer:O=[Se]0(=O)O[Se](=O)(=O)O[Se](=O)(=O)O[Se](=O)(=O)O0
Properties
SeO3
Molar mass 126.96 g/mol
Appearancewhite 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
Hazards
GHS labelling: [2]
GHS-pictogram-skull.svg GHS-pictogram-pollu.svg
Danger
H301, H331, H373, H410
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
4
0
2
OX
Lethal dose or concentration (LD, LC):
7 mg/kg (rat, oral)
7.08 mg/kg (mouse, oral)
5.06 mg/kg (guinea pig, oral)
2.25 mg/kg (rabbit, oral)
13 mg/kg (horse, oral) [3]
13 mg/kg (pig, oral)
9.9 mg/kg (cow, oral)
3.3 mg/kg (goat, oral)
3.3 mg/kg (sheep, oral) [3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Selenium trioxide is the inorganic compound with the formula Se O3. 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. [4]

Contents

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. [4] One method entails dehydration of anhydrous selenic acid with phosphorus pentoxide at 150–160 °C. Another method is 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. [4] The impure substance reacts explosively with oxidizable organic compounds. [5]

At 120 °C SeO3 reacts with selenium dioxide to form the Se(VI)-Se(IV) compound diselenium pentaoxide: [6]

SeO3 + SeO2 → Se2O5

It reacts with selenium tetrafluoride to form selenoyl fluoride, the selenium analogue of sulfuryl fluoride

2SeO3 + SeF4 → 2SeO2F2 + SeO2

As with SO3 adducts are formed with Lewis bases such as pyridine, dioxane and ether. [4]

With lithium oxide and sodium oxide it reacts to form salts of SeVIO54− and SeVIO66−: [7] 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 172.9 → 181.5 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 181 pm, non-bridging 156 and 154 pm. [7]

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. [8]

References

  1. ↑ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 4–81. ISBN   0-8493-0594-2.
  2. ↑ "C&L Inventory". echa.europa.eu. Retrieved 16 December 2021.
  3. 1 2 "Selenium compounds (as Se)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. 1 2 3 4 Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN   0123526515
  5. ↑ Schmidt, Bornmann & Wilhelm 1963.
  6. ↑ 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
  7. 1 2 Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Francesco A. Devillanova, Royal Society of Chemistry, 2007, ISBN   9780854043668
  8. ↑ 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. Bibcode:1978JRSp....7..158B. doi:10.1002/jrs.1250070310. ISSN   0377-0486.

Further reading

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