Lanthanide chlorides

Structure of [La2(μ-X)2(H2O)14]4+ (X = Cl), a representative lanthanide chloride complex.

Lanthanide chlorides are inorganic compounds that contain a lanthanide (Ln) and chloride. The simplest members, the Lanthanide trichlorides, have the formula LnCl3. Important derivatives are the hydrates with the formula LnCl3(H2O)n. Various ether complexes are also well known. Myriad mixed ligand complexes are known.

The anhydrous solids have melting points range from ca. 582 (Tb) - 925 °C (Lu). They are generally pale colored, often white. As coordination polymers, they only dissolve in donor solvents, including water.

Lanthanide(III) trichlorides and related compounds
MCl3colorstructure typef-configurationhydrateTHF complexes comments
ScCl3colorlessAlCl3-typef0[Sc(H2O)7]Cl3ScCl3(THF)3 not classified as a lanthanide usually
YCl3colorlessAlCl3-typef0[Y(H2O)6]Cl3 not classified as a lanthanide usually
LaCl3colorlessUCl3-typef0[LaCl(H2O)7]2Cl4[LaCl3(thf)2] = [La(μ-Cl)3(thf)2]n diamagnetic
CeCl3colorlessUCl3-typef1, doublet[CeCl(H2O)7]2Cl4[CeCl3(thf)2] = [Ce(μ-Cl)2Cl(thf)2]n; [CeCl3(thf)4]-
PrCl3greenUCl3-typef2, triplet[PrCl2(H2O)6]Cl[PrCl3(thf)2] = [Pr(μ-Cl)2Cl(thf)2]n-
NdCl3pinkUCl3-typef3, quartet[NdCl2(H2O)6]Cl[NdCl3(thf)4], [NdCl(μ-Cl)2(thf)2]n,
PmCl3greenUCl3-typef4, quintet[PmCl3(thf)2]n radioactive
SmCl3yellowUCl3-typef5, sextet[SmCl2(H2O)6]Cl[SmCl3(thf)4]
EuCl3yellowUCl3-typef6, septet[EuCl2(H2O)6]ClEuCl3(thf)4
GdCl3colorlessUCl3-typef7, octet[GdCl2(H2O)6]Cl[GdCl3(thf)3.5] = [GdCl2(thf)5]+[GdCl4(thf)2]-, [GdCl3(thf)4, [GdCl3(thf)2]n symmetrical electronic shell
TbCl3whitePuBr3-typef8, septet[TbCl2(H2O)6]Cl[TbCl3(thf)3·5] = [TbCl2(thf)5]+[TbCl4(thf)2]-
DyCl3whiteAlCl3-typef9, sextet[DyCl2(H2O)6]Cl[DyCl3(thf)3·5] = [DyCl2(thf)5]+[DyCl4(thf)2]-
HoCl3yellowAlCl3-typef10, quintet[HoCl2(H2O)6]Cl[HoCl3(thf)3·5] = [HoCl2(thf)5]+[HoCl4(thf)2]-
ErCl3violetAlCl3-typef11, quartet[ErCl2(H2O)6]Cl[ErCl3(thf)3·5] = [ErCl2(thf)5]+[ErCl4(thf)2]-
TmCl3yellowAlCl3-typef12, triplet[TmCl2(H2O)6]Cl
YbCl3colorlessYCl3-typef13, doublet[YbCl2(H2O)6]Cl[YbCl3(thf)3·5] = [YbCl2(thf)5]+[YbCl4(thf)2]-, YbCl3(THF)3, Yb2(μ-Cl)2Cl4(THF)4
LuCl3colorlessAlCl3-typef14[LuCl2(H2O)6]ClLuCl3(thf)3 diamagnetic
Subunit of PrCl3(tetrahydrofuran)2 polymer as determined by X-ray crystallography. Color code: red = O, white = C, green = Cl
Structure of GdCl3.6H2O, which consists of [GdCl2(H2O)6]+ centers. The coordination spheres are interconnected by hydrogen bonds between the protons and both the coordinated and the ionic chlorides.

In terms of their structures, anhydrous trichlorides follow two main motifs, UCl3 and YCl3. The UCl3 structure features 9-coordinate metal centers. The PuBr3 structure, adopted uniquely by TbCl3, features 8-coordinated metals. The remaining later metals are 6-coordinate as is aluminium trichloride.

In the gas phase the trihalides are planar or approximately planar, the lighter lanthanides have a lower % of dimers, the heavier lanthanides a higher proportion. The dimers have a similar structure to Al2Cl6.

Reactions

Lanthanide trichlorides are commercial precursors to the metals by reduction, e.g. with aluminium:

LnCl3 + Al → Ln + AlCl3

In some cases, the trifluoride is preferred.

They react with humid air to give oxychlorides:

LnCl3 + H2O → LnOCl + 2 HCl

For synthetic chemists, this reaction is a problematic since the oxychlorides are less reactive.

Preparation

The lanthanide oxides and carbonates dissolve in hydrochloric acid to give chloride salt of the hydrated cations:

M2O3 + 6 HCl + n H2O → 2 [Ln(H2O)n]Cl3

Industrial routes

Anhydrous trichlorides are produced commercially by carbothermic reaction of the oxide:

M2O3 + 3 Cl2 + 3 C → 2 MCl3 + 3 CO

Ammonium chloride route

The ammonium chloride route refers to a general procedure to produce anhydrous lanthanide chlorides. The method has the advantages of being general for the 14 lanthanides and it produces air-stable intermediates that resist hydrolysis. The use of ammonium chloride as a reagent is convenient because the salt is anhydrous, even when handled in air. Ammonium chloride is also attractive because it thermally decomposes to volatile products at temperatures compatible with the stability of the trichloride targets.

Step 1
preparation of ammonium lanthanide chlorides

The reaction of an intimate mixture of lanthanide oxides with excess ammonium chloride produces anhydrous ammonium salts of the penta- and hexachlorides. Typical reaction conditions are hours at 230-250 °C. Some lanthanides (as well as scandium and yttrium) form pentachlorides:

M2O3 + 10 NH4Cl → 2 (NH4)2MCl5 + 3 H2O + 6 NH3

(M = Dy, Ho, Er, Tm, Lu, Yb, Y, Sc)

Tb4O7 + 22 NH4Cl → 4 (NH4)2TbCl5 + 7 H2O + 14 NH3[dubious – discuss]

Other lanthanides for hexachlorides:

M2O3 + 12 NH4Cl → 2 (NH4)3MCl6 + 3 H2O + 6 NH3

(M = La, Ce, Nd, Pm, Sm, Eu, Gd)

These reactions can also start with the metals, e.g.:

Y + 5 NH4Cl → (NH4)2YCl5 + 1.5 H2 + 3 NH3
Step 2
thermolysis of ammonium lanthanide chlorides

The ammonium lanthanum chlorides are converted to the trichlorides by heating in a vacuum. Typical reaction temperatures are 350–400 °C:

(NH4)2MCl5 → MCl3 + 2 HCl + 2 NH3
(NH4)3MCl6 → MCl3 + 3 HCl + 3 NH3
One-pot route

In the preparation of PrCl3 from its oxide, intermediates need not be isolated. The proposed stoichiometry follows:

Pr6O11 + 22 NH4Cl → 6 PrCl3 + 22 NH3 + 11 H2O + 2 Cl2

Other methods

Hydrated lanthanide trichlorides dehydrate under a hot stream of hydrogen chloride.

Lanthanide dichlorides

Examples include neodymium dichloride, samarium dichloride, europium(II) chloride, dysprosium dichloride, thulium dichloride, and ytterbium dichloride. They can be prepared by reducing the trivalent chloride with lithium metal/naphthalene in tetrahydrofuran:

LnCl3 + Li → LnCl2 + LiCl

Reducing the chloride with the metal or hydrogen is also possible:

2 LnCl3 + Ln → 3 LnCl2 (Ln=Nd,Sm,Eu?,Dy,Tm,Yb)
2 LnCl3 + H2 → 2 LnCl2 + 2 HCl (Ln=Nd,Sm,Eu,Dy,Tm,Yb)


See also

References

  1. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
  2. ↑ Kandabadage, Thimira; Legnon, Beau; Baranets, Sviatoslav (2024). "Comprehensive structural study of lanthanide(III) chloride hydrates: [ RECl3·xH2O (RE = La–Nd, Sm–Lu; x = 6, 7)]". Acta Crystallographica Section E. 80 (12): 1342–1349. doi:10.1107/S2056989024011319. PMC 11789172. PMID 39906789.
  3. ↑ Lim, Kevin C.; Skelton, Brian W.; White, Allan H. (2001). "Crystal Structures of the ('Maximally') Hydrated Scandium Halides, ScX3.nH2O (X = Cl, Br, I)". Australian Journal of Chemistry. 53 (10): 875–878. doi:10.1071/CH00120.
  4. ↑ Manzer, L. E. (1982). "Tetrahydrofuran Complexes of Selected Early Transition Metals". Inorganic Syntheses. 21: 135–40. doi:10.1002/9780470132524.ch31.
  5. 1 2 3 4 5 6 7 Deacon, Glen B.; Feng, Tiecheng; Junk, Peter C.; Skelton, Brian W.; Sobolev, Alexander N.; White, Allan H. (1998). "Preparation and X-Ray Crystal Structures of Tetrahydrofuran-Complexed Rare Earth Chlorides — a Structurally Rich Series". Australian Journal of Chemistry. 51: 75–89. doi:10.1071/C97174.
  6. ↑ Hirneise, Lars; Buschmann, Dennis A.; Maichle-Mössmer, Cäcilia; Anwander, Reiner (2022). "Cerium Fluorenyl Complexes Including CC Coupling Reactions". Organometallics. 41 (8): 962–976. doi:10.1021/acs.organomet.2c00029.
  7. ↑ Wenqi, Chen; Zhongsheng, Jin; Yan, Xing; Yuguo, Fan; Guangdi, Yang (1987). "Crystal structure of NdCl3·4THF and its catalytic activity in polymerization of diene". Inorganica Chimica Acta. 130: 125–129. doi:10.1016/S0020-1693(00)85941-1.
  8. 1 2 Evans, William J.; Shreeve, Julie L.; Ziller, Joseph W.; Doedens, Robert J. (1995). "Structural Diversity in Solvated Lanthanide Halide Complexes". Inorganic Chemistry. 34 (3): 576–585. doi:10.1021/ic00107a009.
  9. ↑ Deacon, Glen B.; Feng, Tiecheng; Junk, Peter C.; Skelton, Brian W.; Sobolev, Alexander N.; White, Allan H. (1998). "Preparation and X-Ray Crystal Structures of Tetrahydrofuran-Complexed Rare Earth Chlorides — a Structurally Rich Series". Australian Journal of Chemistry. 51: 75–89. doi:10.1071/C97174.
  10. ↑ Anfang, S.; Karl, M.; Faza, N.; Massa, W.; Dehnicke, K.; Magull, J. (1997). "Synthese und Kristallstrukturen der Seltenerd-Komplexe [LaI2(THF)5]+I3−, [SmCl3(THF)4], [ErCl2(THF)5]+ [ErCl4(THF)2]−, [ErCl3(DME)2] und [Na(18-Krone-6)(THF)2]+ [YbBr4(THF)2]−". Zeitschrift für Anorganische und Allgemeine Chemie. 623 (9): 1425–1432. doi:10.1002/zaac.19976230918.
  11. ↑ Lin, S. H.; Dong, Z. C.; Huang, J. S.; Zhang, Q. E.; Lu, J. X. (1991). "Structure of trichlorotetrakis(tetrahydrofuran)europium(III)". Acta Crystallographica Section C. 47 (2): 426–427. doi:10.1107/S0108270190007788.
  12. 1 2 Willey, Gerald R.; Woodman, Timothy J.; Drew, Michael G. B. (1997). "Lanthanide(III)chloride-tetrahydrofuran solvates: Structural patterns within the series LnCl3(THF)n, where n = 2, 3, 3.5 and 4: Crystal and molecular structures of [PrCl(μ-Cl)2(THF)2]n, [Nd(μ-Cl)3(H2O)(THF)]n and GdCl3(THF)4". Polyhedron. 16 (19): 3385–3393. doi:10.1016/S0277-5387(97)00078-8.
  13. 1 2 Barbosa, Guilherme A.; Carneiro Neto, José Severiano; Stoeberl, Bruno J.; Wisbeck, Sarita; Giese, Siddhartha O. K.; Yokaichiya, Fabiano; Costa, Daniel da S.; Barison, Andersson; Ribeiro, Ronny R.; Piovan, Leandro; Hughes, David L.; Briganti, Matteo; Poneti, Giordano; Nunes, Giovana G.; Santana, Francielli S.; Soares, Jaísa F. (2025). "High-yield synthesis of heavy rare earth(III) anhydrous solvates: Known, new, and unexpected products". Dalton Transactions. 54 (20): 8251–8269. doi:10.1039/D5DT00254K. PMID 40191991.
  14. ↑ Saša Petriček (2009). "Synthesis and Structural Similarities of Yttrium and Lanthanide Chloride Complexes with Diglyme and Tetrahydrofuran". Acta Chimica Slovenica. 56: 426–433.
  15. ↑ Deacon, Glen B.; Evans, David J.; Junk, Peter C. (2002). "New Variations on the LnCl3(L)n (L = tetrahydrofuran or 1, 2-dimethoxyethane) Structural Theme — NdCl3(dme)2 and YbCl3(THF)3.5". Zeitschrift für Anorganische und Allgemeine Chemie. 628 (9–10): 2033–2036. doi:10.1002/1521-3749(200209)628:9/10<2033::AID-ZAAC2033>3.0.CO;2-G.
  16. ↑ Deacon, Glen B.; Feng, Tiecheng; Nickel, Siegbert; Skelton, Brian W.; White, Allan H. (1993). "A simple synthesis of tetrahydrofuran complexes of lanthanoid trichlorides: Convenient substitutes for anhydrous lanthanoid chlorides". Journal of the Chemical Society, Chemical Communications (17): 1328. doi:10.1039/c39930001328.
  17. ↑ G. K.-I. Magomedov, A. Z. Voskoboinikov, N. I. Kirillova, A. I. Gusev, I. N. Parshina, I. P. Beletskaya (1992). "Tris(cyclopentadienyl)lanthanides in reactions with chlorosilanes and chlorostannanes". Metalloorg.Khim. 5: 679.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ↑ Habenschuss, A.; Spedding, F. H. (1980). "Dichlorohexaaquagadolinium(III) Chloride (GdCl2(H2O)6)C". Crystal Structure Communications. 9: 213–218.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. ↑ Cotton, Simon A. (2011). "Scandium, Yttrium & the Lanthanides: Inorganic & Coordination Chemistry". Encyclopedia of Inorganic and Bioinorganic Chemistry. doi:10.1002/9781119951438.eibc0195. ISBN 9781119951438.
  20. ↑ Kovács, Attila (2004). "Structure and Vibrations of Lanthanide Trihalides: An Assessment of Experimental and Theoretical Data". Journal of Physical and Chemical Reference Data. 33 (1): 377. Bibcode:2004JPCRD..33..377K. doi:10.1063/1.1595651.
  21. 1 2 I. McGill (2005). "Rare Earth Elements". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_607. ISBN 978-3-527-30673-2.
  22. 1 2 3 K. Wetzel (1963). "Rare Earth Trichlorides". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2. NY, NY: Academic Press. p. 1146.
  23. 1 2 3 4 Meyer, G. (1989). "The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides—The Example of Ycl 3". The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides-The Example of YCl3. Inorganic Syntheses. Vol. 25. pp. 146–150. doi:10.1002/9780470132562.ch35. ISBN 978-0-470-13256-2.
  24. ↑ Edelmann, F. T.; Poremba, P. (1997). Herrmann, W. A. (ed.). Synthetic Methods of Organometallic and Inorganic Chemistry. Vol. VI. Stuttgart: Georg Thieme Verlag. ISBN 978-3-13-103021-4.
  25. ↑ Mendil, Fatsiha; Berkani, Madjid; Zamouche, Abdelmalek; Rycerz, Leszek (2013). "Determination of the optimum conditions for the synthesis of praseodymium(III) chloride". Comptes Rendus. Chimie. 16 (9): 795–798. doi:10.1016/j.crci.2013.02.017.
  26. ↑ Rossmainth, Kurt (1979-01-01). "Herstellung der klassischen Seltenerd(II)-chloride in Lösung" [Preparation of the classical rare earth(II) chlorides in solution]. Anorganische, Struktur- und Physikalische Chemie. 110 (4): 109–114. doi:10.1007/BF00903752. S2CID 91731356.
  27. ↑ Gerd Meyer, Lester R. Morss (1991). Synthesis of lanthanide and actinide compounds. Springer. p. 161. ISBN 0-7923-1018-7.