Orthosilicate
In chemistry, orthosilicate is the anion SiO4−
4, or any of its salts and esters. It is one of the silicate anions. It is occasionally called the silicon tetroxide anion or group.[1]
Orthosilicate salts, like sodium orthosilicate, are stable, and occur widely in nature as silicate minerals, being the defining feature of the nesosilicates.[2] Olivine, a magnesium or iron(II) orthosilicate, is the most abundant mineral in the upper mantle.
The orthosilicate anion is a strong base, the conjugate base of the extremely weak orthosilicic acid H
4SiO
4 (pKa2 = 13.2 at 25 °C). This equilibrium is difficult to study since the acid tends to decompose into a hydrated silica condensate.[3]
Structure
The orthosilicate ion or group has tetrahedral shape, with one silicon atom surrounded by four oxygen atoms.
In the anion, each oxygen carries a unit negative charge.[4] The Si–O bond is 162 pm long.[5]
In organic compounds like tetramethyl orthosilicate, each oxygen is formally neutral and is connected to the rest of the molecule by a single covalent bond.
Uses
Europium doped barium orthosilicate (Ba2SiO4) is a common phosphor used in green light-emitting diodes (LEDs). Phosphor for blue LEDs can be made with strontium doped barium orthosilicate.[6] Barium orthosilicate is a major cause of cathode poisoning in vacuum tubes.[7]
Organic chemistry
Although very important in inorganic chemistry and geochemistry, the orthosilicate ion is rarely seen in organic chemistry. Two silicate compounds, however, are used in organic synthesis: tetraethyl orthosilicate or TEOS is used to link polymers, and is especially important in the manufacture of aerogels. or TMOS is used as an alternative to TEOS, and also has a number of other uses as a reagent. TEOS is preferred over TMOS as TMOS decomposes to produce high concentrations of toxic methanol. Inhaling TMOS can result in toxic build-up of silica in the lungs.
References
- ^ C. A. Kumins, and A. E. Gessler (1953), "Short-Cycle Syntheses of Ultramarine Blue". Indunstrial & Engineering Chemistry, volume 45, issue 3, pages 567–572. doi:10.1021/ie50519a031
- ^ Western Oregon University
- ^ Jurkić, Lela Munjas; Cepanec, Ivica; Pavelić, Sandra Kraljević; Pavelić, Krešimir (2013). "Biological and therapeutic effects of ortho-silicic acid and some ortho-silicic acid-releasing compounds: New perspectives for therapy". Nutrition & Metabolism. 10 (1): 2. doi:10.1186/1743-7075-10-2. ISSN 1743-7075. PMC 3546016.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Balaram Sahoo; Nayak Nimai Charan; Samantaray Asutosh; Pujapanda Prafulla Kumar. Inorganic Chemistry. PHI Learning Pvt. Ltd. p. 306. ISBN 978-81-203-4308-5.
- ^ Horacio E. Bergna; William O. Roberts (19 December 2005). Colloidal Silica: Fundamentals and Applications. CRC Press. p. 10. ISBN 978-1-4200-2870-6.
- ^ Huayna Cerqueira Streit, Jennifer Kramer, Markus Suta, Claudia Wickleder, "Red, green, and blue photoluminescence of Ba₂SiO4:M (M = Eu3+, Eu2+, Sr2+) nanophosphors", Materials (Basel), vol. 6, iss. 8, pp. 3079–3093, 24 July 2013 doi:10.3390/ma6083079.
- ^ Morgan Jones, Valve Amplifiers, p. 301, Elsevier, 2012 ISBN 0080966403.