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Lanthanum(III) iodide
Chemical compound From Wikipedia, the free encyclopedia
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Lanthanum(III) iodide is an inorganic compound containing lanthanum and iodine with the chemical formula LaI
3.[1]
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Synthesis
Lanthanum(III) iodide can be synthesised by the reaction of lanthanum metal with mercury(II) iodide:[2][3]
- 2 La + 3 HgI2 → 2 LaI3 + 3 Hg
It can also be prepared from the elements, that is by the reaction of metallic lanthanum with iodine:[2]
- 2 La + 3 I2 → 2 LaI3
While lanthanum(III) iodide solutions can be generated by dissolving lanthanum oxide in hydroiodic acid, the product will hydrolyse and form polymeric hydroxy species:[4]
- La2O3 + 6 HI → 2 LaI3 + 3 H2O → further reactions
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Structure
Lanthanum(III) iodide adopts the same crystal structure as plutonium(III) bromide, with 8-coordinate metal centres arranged in layers.[4][5] This orthorhombic structure is typical of the triiodides of the lighter lanthanides (La–Nd), whereas heavier lanthanides tend to adopt the hexagonal bismuth(III) iodide structure.[3]
Reactivity and applications
Lanthanum(III) iodide is very soluble in water and is deliquescent.[4] Anhydrous lanthanum(III) iodide reacts with tetrahydrofuran to form a photoluminescent complex, LaI3(THF)4, with an average La–I bond length of 3.16 Å.[6][7] This complex is a starting material for amide and cyclopentadienyl complexes of lanthanum.[6][8]
Related compounds
Lanthanum also forms a diiodide, LaI2. It is an electride and is best formulated {LaIII,2I−,e−}, with the electron delocalised in a conduction band.[4] Several other lanthanides form similar compounds, including CeI2, PrI2 and GdI2.[9] Lanthanum diiodide adopts the same tetragonal crystal structure as PrI2.[10]
Lanthanum(III) iodide reacts with lanthanum metal under an argon atmosphere in a tantalum capsule at 1225 K to form the mixed-valence compound La2I5.[11]
Reduction of LaI2 or LaI3 with metallic sodium in an argon atmosphere at 550 °C gives lanthanum monoiodide, LaI, which has a hexagonal crystal structure.[12]
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References
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