Praseodymium(III) iodide

Praseodymium(III) iodide is an inorganic salt, consisting of the rare-earth metal praseodymium and iodine, with the chemical formula PrI₃. It forms green crystals. It is soluble in water.

Preparation

• Heating praseodymium and iodine in an inert atmosphere produces praseodymium(III) iodide:

• It can also be obtained by heating praseodymium with mercury(II) iodide:

Properties

Praseodymium(III) iodide forms green crystals, which are soluble in water. It forms orthorhombic crystals which are hygroscopic. It crystallizes in the PuBr₃ type with space group Cmcm (No. 63) with a = 4.3281(6) Å, b = 14.003(6) Å and c = 9.988(3) Å. It decomposes through an intermediate phase 2 PrI₃·PrOI to a mixture of praseodymium oxyiodide and praseodymium oxide (5 PrOI·Pr₂O₃).

Reactions

• PrI₃ forms compounds with hydrazine, like I₃Pr·3N₂H₄·4H₂O which has pale yellow crystals and soluble in methanol, slightly soluble in water, and insoluble in benzene, d_{20 °C} = 2.986 g/cm³.

• PrI₃ forms compounds with urea, like I₃Pr·5CO(NH₂)₂ which has pale green crystals.

• PrI₃ forms compounds with thiourea, like I₃Pr·2CS(NH₂)₂·9H₂O which is a green crystal with d = 2.27 g/cm³.

• Praseodymium(III) iodide forms a nonahydrate, PrI₃·9H₂O. It can be obtained by dissolving praseodymium(III) oxide in concentrated aqueous hydroiodic acid:

Pr₂O₃ + 6 HI + 15H₂O → 2 PrI₃·9H₂O

• It adopts the same structure as other light rare earth iodides (La–Ho) and contains a triangular tricapped prismatic nonaaqua ion [Pr(OH₂)₉]³⁺ and iodide counterions.

• Praseodymium(III) iodide reacts with praseodymium metal at elevated temperatures to form praseodymium diiodide:

2 PrI₃ + Pr → 3 PrI₂

See also

• Praseodymium diiodide
• Praseodymium compounds

References