Perxenate

In chemistry, perxenates are salts of the yellow This anion has octahedral molecular geometry, as determined by Raman spectroscopy, having O–Xe–O bond angles varying between 87° and 93°. The Xe–O bond length was determined by X-ray crystallography to be 1.875 Å.

Synthesis

Perxenates are synthesized by the disproportionation of xenon trioxide when dissolved in strong alkali:

:2 XeO₃ () + 4 OH⁻ () → Xe () + () + O₂ () + 2 H₂O ()

When Ba(OH)₂ is used as the alkali, barium perxenate can be crystallized from the resulting solution.

:

Its extrapolated formula, H₄XeO₆, is inferred from the octahedral geometry of the perxenate ion () in its alkali metal salts. Due to its rapid decomposition under acidic conditions as described above, however, it is most commonly known as perxenate salts, bearing the anion . capable of oxidising silver(I), copper (II) and manganese(II) to (respectively) silver(III), copper(III), The perxenate anion is unstable in acidic solutions,

The sodium, potassium, and barium salts are soluble. Barium perxenate solution is used as the starting material for the synthesis of xenon tetroxide (XeO₄) by mixing it with concentrated sulfuric acid:

: Ba₂XeO₆ (s) + 2 H₂SO₄ (l) → XeO₄ (g) + 2 BaSO₄ (s) + 2 H₂O (l)

Most metal perxenates are stable, except silver perxenate, which decomposes violently.

Applications

Sodium perxenate, Na₄XeO₆, can be used for the analytic separation of trace amounts of americium from curium. The separation involves the oxidation of Am³⁺ to Am⁴⁺ by sodium perxenate in acidic solution in the presence of La³⁺, followed by treatment with calcium fluoride, which forms insoluble fluorides with Cm³⁺ and La³⁺, but retains Am⁴⁺ and Pu⁴⁺ in solution as soluble fluorides.