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| Identifiers | |||
|---|---|---|---|
3D model (JSmol) |
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| ChemSpider |
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| ECHA InfoCard | 100.033.972 | ||
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| Properties | |||
| SeO3 | |||
| Molar mass | 126.96 g/mol | ||
| Appearance | whitehygroscopic 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:[3] | |||
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| Danger | |||
| H301,H331,H373,H410 | |||
| NFPA 704 (fire diamond) | |||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) | 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)[2] | ||
LC50 (median concentration) | 13 mg/kg (pig, oral) 9.9 mg/kg (cow, oral) 3.3 mg/kg (goat, oral) 3.3 mg/kg (sheep, oral)[2] | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Selenium trioxide is theinorganic compound with the formulaSeO3. It is white, hygroscopic solid. It is also anoxidizing agent and aLewis acid. It is of academic interest as a precursor to Se(VI) compounds.[4]
Selenium trioxide is difficult to prepare because it is unstable with respect tothe dioxide:
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 anhydrousselenic acid withphosphorus pentoxide at 150–160 °C. Another method is the reaction of liquidsulfur trioxide withpotassium selenate.
In its chemistry SeO3 generally resemblessulfur trioxide, SO3, rather thantellurium trioxide, TeO3.[4] The impure substance reactsexplosively withoxidizableorganic compounds.[5]
At 120 °C SeO3 reacts withselenium dioxide to form the Se(VI)-Se(IV) compound diselenium pentaoxide:[6]
It reacts withselenium tetrafluoride to formselenoyl fluoride, the selenium analogue ofsulfuryl fluoride
As with SO3 adducts are formed withLewis bases such aspyridine,dioxane andether.[4]
Withlithium oxide andsodium 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).
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]
