Pyrosilicate
Chemical compound
From Wikipedia, the free encyclopedia
A pyrosilicate is a type of chemical compound; either an ionic compound that contains the pyrosilicate anion Si
2O6−
7, or an organic compound with the hexavalent ≡O
3Si-O-SiO
3≡ group. The anion is also called disilicate[1] or diorthosilicate.
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| Names | |
|---|---|
| IUPAC name
Pyrosilicate | |
| Other names
disilicate, diorthosilicate | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChemSpider | |
| 326578 | |
PubChem CID |
|
CompTox Dashboard (EPA) |
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| |
| |
| Properties | |
| O7Si2−6 | |
| Molar mass | 168.166 g·mol−1 |
| Conjugate acid | Pyrosilicic acid |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Ionic pyrosilicates can be considered salts of the unstable pyrosilicic acid, H
6Si
2O
7. Unlike the acid, the salts can be stable. Indeed, pyrosilicates occur widely in nature as a class of silicate minerals, specifically the sorosilicates - though some sorosilicate minerals, such as gehlenite, replace one of the silicon atoms with tetracoordinated aluminium or boron, giving the isostructural anions AlSiO7−7 and BSiO7−7.
Some notable synthetic pyrosilicates include
- sodium pyrosilicate Na
6Si
2O
7, a possible component of water glass. - sodium iron(II) pyrosilicate Na
2Fe
2Si
2O
7, a potential cathode material for batteries.[2] - sodium manganese(II) pyrosilicate Na
2Mn
2Si
2O
7, another potential cathode material.[3][4]
Structure
The pyrosilicate anion can be described as two SiO
4 tetrahedra that share a vertex (an oxygen atom). The vertices that are not shared carry a negative charge each.
The structure of solid sodium pyrosilicate was described by Volker Kahlenberg and others in 2010.[5]
Yuri Smolin and Yuri Shepelev determined in 1970 the crystal structures of pyrosilicates of rare earth elements with generic formula Ln
2Si
2O
7, where "Ln" stands for either one of lanthanum, cerium, neodymium, samarium, europium, gadolinium, dysprosium, holmium, yttrium, erbium, thulium, or ytterbium. They were found to belong to four distinct crystallographic classes, determined by the size of the cation.[6] Other researchers also studied yttrium pyrosilicate Y
2Si
2O
7.,[7][8] gadolinium pyrosilicate Gd
2Si
2O
7.,[8] and scandium pyrosilicate Sc
2Si
2O
7.[7]
Preparation
Rare earth pyrosilicates Ln
2Si
2O
7 can be obtained by fusing the corresponding oxide Ln
2O
3 with silica in 1:2 molar ratio,[6] Single crystals can be grown by the Verneuil process[6] or the Czochralski method.[7]
Industrial pyrosilicate can be produced by the depolymerisation of metasilicate by alkali, which releases water on breaking the Si−O−Si bond.[9] This proceeds according to the idealised equation
- 2 SiO2−3 + 2 OH− → Si2O6−7 + H2O
Additional alkali will degrade the bonds further, instead yielding orthosilicate.[10]