Lanthanum(III) iodide

Lanthanum(III) iodide is an inorganic compound containing lanthanum and iodine with the chemical formula LaI
3.[1]

Lanthanum(III) iodide
Names
Other names
Lanthanum triiodide
Identifiers
3D model (JSmol)
ECHA InfoCard 100.034.045
EC Number
  • 237-465-6
  • InChI=1S/3HI.La/h3*1H;/q;;;+3/p-3
    Key: KYKBXWMMXCGRBA-UHFFFAOYSA-K
  • I[La](I)I
Properties
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 [77 °F], 100 kPa).
Infobox references

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

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]

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]

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 5d1 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.
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