Lanthanum(III) iodide explained

Lanthanum(III) iodide is an inorganic compound containing lanthanum and iodine with the chemical formula .^[1]

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 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:

La₂O₃ + 6 HI → 2 LaI₃ + 3 H₂O → further reactions

Structure

Lanthanum(III) iodide adopts the same crystal structure as plutonium(III) bromide, with 8-coordinate metal centres arranged in layers.^[4] 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.

Reactivity and applications

Lanthanum(III) iodide is very soluble in water and is deliquescent. 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.^{[5] [6]} This complex is a starting material for amide and cyclopentadienyl complexes of lanthanum.^[7]

Related compounds

Lanthanum also forms a diiodide, LaI₂. It is an electride and is best formulated, with the electron delocalised in a conduction band. Several other lanthanides form similar compounds, including CeI₂, PrI₂ and GdI₂.^[8] Lanthanum diiodide adopts the same tetragonal crystal structure as PrI₂.^[9]

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.^[10]

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.^[11]

Notes and References

1. Preparation of Anhydrous Lanthanon Halides . Moddie D. . Taylor . . 1962 . 62 . 6 . 503–511 . 10.1021/cr60220a001 .
2. Book: John D. . Corbett . Arndt . Simon . 1984 . 10.1002/9780470132531.ch6 . Holt Jr. . Smith L. . . 22 . 11–16 . Chapter 6: Lanthanum Triiodide (and Other Rare Earth Metal Triiodides) . amp .
3. L. B. . Asprey . T. K. . Keenan . F. H. . Kruse . Preparation and Crystal Data for Lanthanide and Actinide Triiodides . . 1964 . 3 . 8 . 1137–1141 . 10.1021/ic50018a015 .
4. Book: A. F. . Wells . Structural Inorganic Chemistry . 5th . 1984 . Oxford University Press . 978-0-19-965763-6 . 420 .
5. Rare Earth Starting Materials and Methodologies for Synthetic Chemistry . Fabrizio . Ortu . . 2022 . 122 . 6 . 6040–6116 . 10.1021/acs.chemrev.1c00842 . 35099940 . 9007467 .
6. Photoluminescence of LaI₃ switched on and off by association and dissociation of non-luminescent tetrahydrofuran . Yangjuan . Li . Xiuting . Chen . Yu . Gong . . 2021 . 50 . 11 . 3797–3800 . 10.1039/D1DT00162K . 33720234 . 232232544 .
7. Small-Scale Metal-Based Syntheses of Lanthanide Iodide, Amide, and Cyclopentadienyl Complexes as Analogues for Transuranic Reactions . Cory J. . Windorff . Megan T. . Dumas . Joseph W. . Ziller . Andrew J. . Gaunt . Stosh A. . Kozimor . William J. . Evans . . 2017 . 56 . 19 . 11981–11989 . 10.1021/acs.inorgchem.7b01968 . 28915015 .
8. Book: A. F. . Wells . Structural Inorganic Chemistry . 5th . 1984 . Oxford University Press . 978-0-19-965763-6 . 1250 .
9. The electronic conditions in the 5d¹ layer-metal LaI₂ making comparison with the iso-electronic tantalum dichalcogenides, with the other RE di-iodides, and with the RE monochalcogenides . J. H. . Burrow . C. H. . Maule . P. . Strange . J. N. . Tothill . J. A. . Wilson . 1987 . . 20 . 26 . 4115–4133. 10.1088/0022-3719/20/26/014 . 1987JPhC...20.4115B .
10. Crystal structure of dilanthanum pentaiodide, La₂I₅ . Hj. . Mattausch . O. . Oeckler . A. . Simon . . 218 . 3 . 2003 . 281 . 10.1524/ncrs.2003.218.3.281 . 94059677 . free .
11. New Synthesis Route to and Physical Properties of Lanthanum Monoiodide . Mikhail . Ryazanov . Lorenz . Kienle . Arndt . Simon . Hansjürgen . Mattausch . . 2006 . 45 . 5 . 2068–2074 . 10.1021/ic051834r . 16499368 .