Antimony pentoxide (molecular formula: Sb<sub>2</sub>O<sub>5</sub>) is a chemical compound of antimony and oxygen. It contains antimony in the +5 oxidation state.
Antimony pentoxide has the same structure as the B form of niobium pentoxide and can be derived from the rutile structure, with antimony coordinated by six oxygen atoms in a distorted octahedral arrangement. The SbO<sub>6</sub> octahedra are corner- and edge-sharing.
The hydrated oxide is prepared by hydrolysis of antimony pentachloride; or by acidification of potassium hexahydroxoantimonate(V). It may also be prepared by oxidation of antimony trioxide with nitric acid.
Antimony pentoxide finds use as a flame retardant in ABS and other plastics and as a flocculant in the production of titanium dioxide, and is sometimes used in the production of glass, paint and adhesives.
It is also used as an ion exchange resin for a number of cations in acidic solution including Na<sup>+</sup> (especially for their selective retentions), and as a polymerization and oxidation catalyst.
The hydrated oxide is insoluble in nitric acid, but dissolves in a concentrated potassium hydroxide solution to give potassium hexahydroxoantimonate(V), or KSb(OH)<sub>6</sub>.
When heated to , the yellow hydrated pentoxide converts to an anhydrous white solid with the formula Sb<sub>6</sub>O<sub>13</sub>, containing both antimony(III) and antimony(V). Heating to produces a white, insoluble powder of Sb<sub>2</sub>O<sub>4</sub> in both ñ and ò forms. The ò form consists of antimony(V) in octahedral interstices and pyramidal Sb<sup>III</sup>O<sub>4</sub> units. In these compounds, the antimony(V) atom is octahedrally coordinated to six hydroxy groups.
The pentoxide can be reduced to antimony metal by heating with hydrogen or potassium cyanide.