Selenium trioxide

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Selenium trioxide[1]
Structural formula of the monomer as found in the gas phase Space-filling model of the monomer as found in the gas phase
Identifiers
CAS number 13768-86-0 N
PubChem 115128
ChemSpider 103019 YesY
Jmol-3D images Image 1
Properties
Molecular formula SeO3
Molar mass 126.96 g/mol
Appearance white hygroscopic crystals
Density 3.44 g/cm3
Melting point 118.35 °C
Boiling point sublimes
Solubility in water very soluble
Structure
Crystal structure tetragonal
Hazards
EU classification not listed
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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[edit]

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[edit]

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 + 12 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[edit]

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[edit]

  1. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. pp. 4–81. ISBN 0-8493-0594-2. 
  2. ^ a b c d Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0123526515
  3. ^ a b Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Franceso A. Devillanova, Royal Society of Chemistry, 2007, ISBN 9780854043668
  4. ^ 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[edit]