Sodium pyrosilicate

Sodium pyrosilicate is the chemical compound Na
₆Si
₂O
₇. It is one of the sodium silicates, specifically a pyrosilicate, formally a salt of the unstable pyrosilicic acid H
₆Si
₂O
₇.[1][2]

Sodium pyrosilicate

Names
Other names hexasodium diorthosilicate
Identifiers
CAS Number	15593-82-5
3D model (JSmol)	Interactive image
EC Number	239-671-1
PubChem CID	61803
UNII	VNJ6H8MB6Z
InChI InChI=1S/6Na.O7Si2/c;;;;;;1-8(2,3)7-9(4,5)6/q6*+1;-6 Key: PMYUVOOOQDGQNW-UHFFFAOYSA-N
SMILES [Si](O[Si]([O-])([O-])[O-])([O-])([O-])[O-].[Na+].[Na+].[Na+].[Na+].[Na+].[Na+]
Properties
Chemical formula	Na6O7Si2
Molar mass	306.102 g·mol^−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure

The anhydrous solid has the triclinic crystal structure, with space group P⁻
₁ (a = 5.8007(8) Å, b = 11.5811(15) Å, c = 23.157(3) Å, α = 89.709(10)°, β = 88.915(11)°, γ = 89.004(11)°, V = 1555.1(4) ų, Z = 8, Dx = 2.615 g·cm⁻³, μ(Mo‐Kα) = 7.94 cm⁻¹). The Si
₂O⁶⁺
₇ anions are arranged in layers parallel to the (100) plane, with the sodium cations distributed in 24 distinct crystallographic positions, coordinated by 4 to 6 near oxygen atoms. Some of the 4-coordinated sodium atoms can be interpreted as parallel columns of edge-sharing NaO
₄ tetrahedra. The columnar arrangement forms tunnels that house the remaining sodium cations. Twinning at a microscopic scale simulates a much larger monoclinic C centered lattice (V′ = 6220 ų, Z = 32).[3]

See also

• Sodium metasilicate, Na
  ₂SiO
  ₃
• Sodium orthosilicate, Na
  ₄SiO
  ₄

References

1. Myron C Waddell (1932): "Process of purifying technical sodium pyrosilicate hydrates". US patent US1931364A.
2. J. F. Schairer and N. L. Bowen (1956): "The system Na
   ₂O—Al
   ₂O
   ₃—SiO
   ₂". American Journal of Science, volume 254, issue 3, pages 129-195 doi:10.2475/ajs.254.3.129
3. Volker Kahlenberg, Thomas Langreiter, and Erik Arroyabe (2010): "Na6Si2O7 – 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