A pyrosilicate is a type of

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

; either an

ionic compound In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions (Cation, cations) and negatively charged ions (Anion, anions), which results in a compound with no net electric charge (electrica ...

that contains the pyrosilicate anion , or an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the hexavalent ≡-O-≡

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

. The anion is also called disilicate"Disilicate"
''Chemspider'' website, CSID:5257009, Accessed 2018-05-26 or diorthosilicate. Ionic pyrosilicates can be considered

salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

of the unstable pyrosilicic acid, . Unlike the acid, the salts can be stable. Indeed, pyrosilicates occur widely in nature as a class of

silicate minerals Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

, specifically the sorosilicates - though some sorosilicate minerals, such as gehlenite, replace one of the silicon atoms with tetracoordinated

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

, giving the isostructural anions and . Some notable synthetic pyrosilicates include * sodium pyrosilicate , a possible component of water glass. * sodium iron(II) pyrosilicate , a potential

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

material for batteries.Abhishek Panigrahi, Shin-ichi Nishimura, Tatau Shimada, Eriko Watanabe, Wenwen Zhao, Gosuke Oyama, and Atsuo Yamada (2017): "Sodium Iron(II) Pyrosilicate : A Potential Cathode Material in the -- System". ''Chemistry of Materials'', volume 29, issue 10, pages 4361–4366. * sodium manganese(II) pyrosilicate , another potential

material.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, DIV
urn:nbn:se:uu:diva-334063
/ref>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

Structure

The pyrosilicate anion can be described as two

tetrahedra In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

that share a vertex (an

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

atom). The vertices that are not shared carry a negative charge each. The structure of solid sodium pyrosilicate was described by

Volker Kahlenberg Volker may refer to: * Volker (name), including a list of people with the given name or surname * Volker, Kansas City, a historic neighborhood in Kansas City * Volker Boulevard, Kansas City * ''Alien Nations'' (German: ''Die Völker''), a real-time ...

and others in 2010.Volker Kahlenberg, Thomas Langreiter, and Erik Arroyabe (2010): " – 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. Yuri Smolin and Yuri Shepelev determined in 1970 the crystal structures of pyrosilicates of

rare earth element The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set o ...

s with generic formula , where "Ln" stands for either one of

lanthanum Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements bet ...

cerium Cerium is a chemical element; it has Chemical symbol, symbol Ce and atomic number 58. It is a hardness, soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it ...

neodymium Neodymium is a chemical element; it has Symbol (chemistry), symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth element, rare-earth metals. It is a hard (physics), hard, sli ...

, samarium,

europium Europium is a chemical element; it has symbol Eu and atomic number 63. It is a silvery-white metal of the lanthanide series that reacts readily with air to form a dark oxide coating. Europium is the most chemically reactive, least dense, and soft ...

gadolinium Gadolinium is a chemical element; it has Symbol (chemistry), symbol Gd and atomic number 64. It is a silvery-white metal when oxidation is removed. Gadolinium is a malleable and ductile rare-earth element. It reacts with atmospheric oxygen or moi ...

dysprosium Dysprosium is a chemical element; it has symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it ...

holmium Holmium is a chemical element; it has symbol Ho and atomic number 67. It is a rare-earth element and the eleventh member of the lanthanide series. It is a relatively soft, silvery, fairly corrosion-resistant and malleable metal. Like many other ...

yttrium Yttrium is a chemical element; it has Symbol (chemistry), symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost a ...

erbium Erbium is a chemical element; it has Symbol (chemistry), symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare- ...

thulium Thulium is a chemical element; it has symbol Tm and atomic number 69. It is the thirteenth element in the lanthanide series of metals. It is the second-least abundant lanthanide in the Earth's crust, after radioactively unstable promethium. It i ...

, or

ytterbium Ytterbium is a chemical element; it has symbol Yb and atomic number 70. It is a metal, the fourteenth and penultimate element in the lanthanide series, which is the basis of the relative stability of its +2 oxidation state. Like the other lanthani ...

. They were found to belong to four distinct crystallographic classes, determined by the size of the

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

.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. Other researchers also studied yttrium pyrosilicate .,Dias, H.W.; Glasser, F.P.; Gunwardane, R.P.; and Howie, R.A. (1990): "The crystal structure of δ-yttrium pyrosilicate, δ-". ''Zeitschrift für Kristallographie'', volume 191, issues 1/2, pages 117-123; ISSN 0044-2968 gadolinium pyrosilicate ., and scandium pyrosilicate .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.

Preparation

Rare earth pyrosilicates can be obtained by fusing the corresponding oxide with silica in 1:2 molar ratio, Single crystals can be grown by the Verneuil process or the

Czochralski method The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals (monocrystals) of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, platin ...

. Industrial pyrosilicate can be produced by the depolymerisation of metasilicate by alkali, which releases

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

on breaking the bond. This proceeds according to the idealised equation : Additional alkali will degrade the bonds further, instead yielding

orthosilicate In chemistry, orthosilicate is the anion , or any of its salts and esters. It is one of the silicate anions. It is occasionally called the silicon tetroxide anion or group.C. A. Kumins, and A. E. Gessler (1953), "Short-Cycle Syntheses of Ultr ...

References

{{reflist Silicon oxyanions Sorosilicates