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.
The pyrosilicate anion can be described as two SiO 4tetrahedra 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]
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]
^Abhishek Panigrahi, Shin-ichi Nishimura, Tatau Shimada, Eriko Watanabe, Wenwen Zhao, Gosuke Oyama, and Atsuo Yamada (2017): "Sodium Iron(II) Pyrosilicate Na 2Fe 2Si 2O 7: A Potential Cathode Material in the Na 2O-FeO-SiO 2 System". Chemistry of Materials, volume 29, issue 10, pages 4361–4366. doi:10.1021/acs.chemmater.7b00764
^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
^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
^Volker Kahlenberg, Thomas Langreiter, and Erik Arroyabe (2010): "Na 6Si 2O 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
^ abcYu. 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
^ abcAnan'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.
^ abDias, H.W.; Glasser, F.P.; Gunwardane, R.P.; and Howie, R.A. (1990): "The crystal structure of δ-yttrium pyrosilicate, δ-Y 2Si 2O 7". Zeitschrift für Kristallographie, volume 191, issues 1/2, pages 117-123; ISSN 0044-2968
^US patent 1953840, Myron C. Waddell, "Process for making sodium pyrosilicate hydrate", issued 1934-04-03, assigned to Grasselli Chemical Company
^US patent 2351385A, Eduard Zintl, "Process of preparing anhydrous sodium-orthosilicate", issued 1944-06-13
