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Lanthanum(III) iodide

Names
Other names Lanthanum triiodide
Identifiers
CAS Number	13813-22-4
3D model (JSmol)	Interactive image
ECHA InfoCard	100.034.045
EC Number	237-465-6
PubChem CID	24870325
CompTox Dashboard (EPA)	DTXSID0065640
InChI InChI=1S/3HI.La/h3*1H;/q;;;+3/p-3Key: KYKBXWMMXCGRBA-UHFFFAOYSA-K
SMILES I(I)I
Properties
Chemical formula	LaI 3
Molar mass	519.62
Density	5.63 g/mL at 25 °C
Melting point	772 °C (1,422 °F; 1,045 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references

Lanthanum(III) iodide is an inorganic compound containing lanthanum and iodine with the chemical formula LaI
₃.

Synthesis

Lanthanum(III) iodide can be synthesised by the reaction of lanthanum metal with mercury(II) iodide:

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. 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. This complex is a starting material for amide and cyclopentadienyl complexes of lanthanum.

Related compounds

Lanthanum also forms a diiodide, LaI₂. It is an electride and is best formulated {La,2I,e}, with the electron delocalised in a conduction band. Several other lanthanides form similar compounds, including CeI₂, PrI₂ and GdI₂. Lanthanum diiodide adopts the same tetragonal crystal structure as PrI₂.

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.

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.

References

1. Taylor, Moddie D. (1962). "Preparation of Anhydrous Lanthanon Halides". Chem. Rev. 62 (6): 503–511. doi:10.1021/cr60220a001.
2. ^ Corbett, John D. & Simon, Arndt (1984). "Chapter 6: Lanthanum Triiodide (and Other Rare Earth Metal Triiodides)". In Holt Jr., Smith L. (ed.). Inorg. Synth. Vol. 22. pp. 11–16. doi:10.1002/9780470132531.ch6.
3. ^ Asprey, L. B.; Keenan, T. K.; Kruse, F. H. (1964). "Preparation and Crystal Data for Lanthanide and Actinide Triiodides". Inorg. Chem. 3 (8): 1137–1141. doi:10.1021/ic50018a015.
4. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 949–950. ISBN 978-0-08-037941-8.
5. Wells, A. F. (1984). Structural Inorganic Chemistry (5th ed.). Oxford University Press. p. 420. ISBN 978-0-19-965763-6.
6. ^ Ortu, Fabrizio (2022). "Rare Earth Starting Materials and Methodologies for Synthetic Chemistry". Chem. Rev. 122 (6): 6040–6116. doi:10.1021/acs.chemrev.1c00842. PMC 9007467. PMID 35099940.
7. Li, Yangjuan; Chen, Xiuting; Gong, Yu (2021). "Photoluminescence of LaI₃ switched on and off by association and dissociation of non-luminescent tetrahydrofuran". Dalton Trans. 50 (11): 3797–3800. doi:10.1039/D1DT00162K. PMID 33720234. S2CID 232232544.
8. Windorff, Cory J.; Dumas, Megan T.; Ziller, Joseph W.; Gaunt, Andrew J.; Kozimor, Stosh A.; Evans, William J. (2017). "Small-Scale Metal-Based Syntheses of Lanthanide Iodide, Amide, and Cyclopentadienyl Complexes as Analogues for Transuranic Reactions". Inorg. Chem. 56 (19): 11981–11989. doi:10.1021/acs.inorgchem.7b01968. PMID 28915015.
9. Wells, A. F. (1984). Structural Inorganic Chemistry (5th ed.). Oxford University Press. p. 1250. ISBN 978-0-19-965763-6.
10. Burrow, J. H.; Maule, C. H.; Strange, P.; Tothill, J. N.; Wilson, J. A. (1987). "The electronic conditions in the 5d layer-metal LaI₂ making comparison with the iso-electronic tantalum dichalcogenides, with the other RE di-iodides, and with the RE monochalcogenides". J. Phys. C: Solid State Phys. 20 (26): 4115–4133. Bibcode:1987JPhC...20.4115B. doi:10.1088/0022-3719/20/26/014.
11. Mattausch, Hj.; Oeckler, O.; Simon, A. (2003). "Crystal structure of dilanthanum pentaiodide, La₂I₅". Z. Kristallogr. NCS. 218 (3): 281. doi:10.1524/ncrs.2003.218.3.281. S2CID 94059677.
12. Ryazanov, Mikhail; Kienle, Lorenz; Simon, Arndt; Mattausch, Hansjürgen (2006). "New Synthesis Route to and Physical Properties of Lanthanum Monoiodide". Inorg. Chem. 45 (5): 2068–2074. doi:10.1021/ic051834r. PMID 16499368.

• Lanthanum compounds
• Iodides
• Inorganic compounds
• Lanthanide halides