Indium(III) selenate is an inorganic compound of indium and the selenate ion, with the chemical formula In2(SeO4)3. It forms highly water-soluble, hygroscopic crystalline hydrates.
Preparation Indium(III) selenate can be prepared by dissolving indium(III) hydroxide in aqueous selenic acid and crystallizing the resulting solution.
2 In(OH)3 + 3 H2SeO4 → In2(SeO4)3 + 6 H2O
The original preparation gave white, readily water-soluble, hygroscopic crystals whose analysis corresponded approximately to a decahydrate, In2(SeO4)3·10H2O.
Hydrates and solubility Several hydrated forms of indium(III) selenate have been reported. Older literature describes the pentahydrate, octahydrate, nonahydrate and decahydrate.
At 293 K, the equilibrium solid phase in contact with saturated aqueous solution has been identified as the nonahydrate, In2(SeO4)3·9H2O. The OECD/NEA review accepts a solubility of approximately 1.87 mol of In2(SeO4)3 per kilogram of water at 293.15 K.
The pentahydrate, In2(SeO4)3·5H2O, has also been structurally characterized. Its framework is closely related to those of Al2(SO4)3·5H2O and Fe2(SO4)3·5H2O.
Structure Anhydrous In2(SeO4)3 crystallizes in the monoclinic crystal system, in space group P21/n (No. 14). Reported lattice parameters are approximately a = 8.73 Å, b = 9.21 Å, c = 12.26 Å and β = 91.63°, with four formula units per unit cell.
The structure belongs to the same general family as several trivalent-metal sulfates and selenates, with InO6 octahedra linked to SeO4 tetrahedra.
Double salts and complexes Indium(III) selenate forms double salts with alkali-metal selenates. The caesium compound CsIn(SeO4)2·12H2O was already reported in the early literature and crystallizes as colorless, water-soluble crystals.
Phase-equilibrium studies have also been reported for indium selenate with lithium, sodium, potassium, rubidium, caesium and ammonium selenates.
Indium(III) selenate also forms coordination compounds with organic ligands; for example, a bipyridine-containing selenate complex, In2(2,2′-bipy)2(SeO4)3(H2O)2·2H2O, contains two InO4N2 octahedra bridged by selenate tetrahedra.
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