Langbahn Team – Weltmeisterschaft

Pyrosilicate

Pyrosilicate anion
Names
IUPAC name
Pyrosilicate
Other names
disilicate, diorthosilicate
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
326578
  • InChI=1S/O7Si2/c1-8(2,3)7-9(4,5)6/q-6 checkY
    Key: KUDCBYUNCUYIDU-UHFFFAOYSA-N checkY
  • [O-][Si]([O-])([O-])O[Si]([O-])([O-])[O-]
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).
☒N (what is checkY☒N ?)

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.

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

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]

References

  1. ^ "Disilicate". Chemspider website, CSID:5257009, Accessed 2018-05-26
  2. ^ Abhishek Panigrahi, Shin-ichi Nishimura, Tatau Shimada, Eriko Watanabe, Wenwen Zhao, Gosuke Oyama, and Atsuo Yamada (2017): "Sodium Iron(II) Pyrosilicate Na
    2    Fe
    2    Si
    2    O
    7    : A Potential Cathode Material in the Na
    2    O    -FeO-SiO
    2     System". Chemistry of Materials, volume 29, issue 10, pages 4361–4366. doi:10.1021/acs.chemmater.7b00764
  3. ^ Viktor Renman, Mario Valvo, Cheuk-Wai Tai, and Cesar Pay Gómez (2017): "Manganese Pyrosilicates as Novel Positive Electrode Materials for Na-Ion Batteries". Uppsala University Publications, DIVA urn:nbn:se:uu:diva-334063
  4. ^ Viktor Renman (2017): "Structural and Electrochemical Relations in Electrode Materials for Rechargeable Batteries", Doctoral Thesis, Uppsala University, Department of Chemistry. ORCID: 0000-0001-8739-4054
  5. ^ Volker Kahlenberg, Thomas Langreiter, and Erik Arroyabe (2010): "Na
    6    Si
    2    O
    7     – The Missing Structural Link among Alkali Pyrosilicates". Zeitschrift für anorganishe und allgemeine Chemie (Journal for Inorganic and General Chemistry), volume 636, issue 11, pages 1974-1979. doi:10.1002/zaac.201000120
  6. ^ a b c Yu. I. Smolin and Yu. F. Shepelev (1970): "The crystal structures of the rare earth pyrosilicates". Acta Crystallographica Section B, volume B26, pages 484-492. doi:10.1107/S0567740870002698
  7. ^ a b c Anan'eva, G.V.; Karapetyan, V.E.; Korovkin, A.M.; Merkulyaeva, T.I.; Peschanskaya, I.A.; Savinova, I.P.; and Feofilov, P.P. (1982): "Strukturnye kharakteristiki i fizicheskie svojstva kristallov diorto(piro)silikatov lantanoidov, ittriya i skandiya, vyrashchennykh metodom Chokhral'skogo" ("Structural characteristics and physical properties of diortho(pyro)silicate crystals of lanthanides yttrium and scandium grown by the Czochralski technique"). Izv. Akad. Nauk SSSR, Neorg. Mater (translated in Inorganic Materials, USA) volume 18, issue 3, pages 442-445. ISSN 0002-337X.
  8. ^ a b Dias, H.W.; Glasser, F.P.; Gunwardane, R.P.; and Howie, R.A. (1990): "The crystal structure of δ-yttrium pyrosilicate, δ-Y
    2    Si
    2    O
    7    ". Zeitschrift für Kristallographie, volume 191, issues 1/2, pages 117-123; ISSN 0044-2968
  9. ^ US patent 1953840, Myron C. Waddell, "Process for making sodium pyrosilicate hydrate", issued 1934-04-03, assigned to Grasselli Chemical Company 
  10. ^ US patent 2351385A, Eduard Zintl, "Process of preparing anhydrous sodium-orthosilicate", issued 1944-06-13 
Quelle: http://en.wikipedia.org/wiki/Pyrosilicate