Sodium stannate, formally sodium hexahydroxostannate(IV), is the inorganic compound with the formula Na2[Sn(OH)<sub>6</sub>]. This colourless salt forms upon dissolving metallic tin or tin(IV) oxide in sodium hydroxide and is used as a stabiliser for hydrogen peroxide.[1] In older literature, stannates are sometimes represented as having the simple oxyanion SnO32−,[2] in which case this compound is sometimes named as sodium stannate - 3 - water and represented as Na2SnO3·3H2O, a hydrate with three waters of crystallisation. The anhydrous form of sodium stannate, Na2SnO3, is recognised as a distinct compound with its own CAS Registry Number,[3] and a distinct material safety data sheet.[4]
Alkali metal stannate compounds are prepared by dissolving elemental tin in a suitable metal hydroxide, in the case of sodium stannate by the reaction:[5]
Sn + 2 NaOH + 4 H2O → Na2[Sn(OH)<sub>6</sub>] + 2 H2A similar reaction occurs when tin dioxide is dissolved in base:
SnO2 + 2 NaOH + 2 H2O → Na2[Sn(OH)<sub>6</sub>]The anhydrous form can also be prepared from tin dioxide by roasting with sodium carbonate in a mixed carbon monoxide / carbon dioxide environment:[6]
SnO2 + Na2CO3 → Na2SnO3 + CO2
The anion is a coordination complex that is octahedral in shape, similar to most stannates, such as the hexachlorostannate anion . The Sn - O bond distances average 2.071 Å.[7]