Pyrosilicate
# Pyrosilicate

A pyrosilicate is a type of chemical compound; either an ionic compound that contains the pyrosilicate anion Si $_2O^{6−}$ $_7,$ or an organic compound with the hexavalent ≡O $_3Si-O-SiO$ $_3≡$ group. The anion is also called disilicate 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.

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.
* sodium manganese(II) pyrosilicate Na $_2Mn$ $_2Si$ $_2O$ $_7,$ another potential cathode material.

## 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.

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. Other researchers also studied yttrium pyrosilicate Y $_2Si$ $_2O$ $_7.,$ gadolinium pyrosilicate Gd $_2Si$ $_2O$ $_7.,$ and scandium pyrosilicate Sc $_2Si$ $_2O$ $_7.$

## 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, Single crystals can be grown by the Verneuil process or the Czochralski method.

