Praseodymium(III) chloride

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Praseodymium(III) chloride
UCl3 without caption.png
Cerium bromide (space filling) 2.png
Praseodymium chloride heptahydrate under fluorescent lamp light and halogen lamp light.png
IUPAC name
Praseodymium(III) chloride
Other names
Praseodymium chloride; praseodymium trichloride
3D model (Jmol)
ECHA InfoCard 100.030.710
Molar mass 247.24 g/mol (anhydrous)
373.77 g/mol (heptahydrate)
Appearance blue-green solid (anhydrous)
light green solid (heptahydrate)
Density 4.02 g/cm3 (anhydrous)
2.250 g/cm3 (heptahydrate)
Melting point 786 °C (1,447 °F; 1,059 K)
Boiling point 1,710 °C (3,110 °F; 1,980 K)
104.0 g/100 ml (13 °C)
+44.5·10−6 cm3/mol
hexagonal (UCl3 type), hP8
P63/m, No. 176
Tricapped trigonal prismatic
Main hazards Irritant
Related compounds
Other anions
Praseodymium(III) oxide, Praseodymium(III) fluoride
Praseodymium bromide
praseodymium iodide
Other cations
Cerium(III) chloride
Neodymium(III) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Praseodymium(III) chloride is the inorganic compound with the formula PrCl3. It is a blue-green solid that rapidly absorbs water on exposure to moist air to form a light green heptahydrate.


Praseodymium(III) chloride is prepared by treating praseodymium metal and hydrogen chloride:[1][2]

2 Pr + 6 HCl → 2 PrCl3 + 3 H2

It is usually purified by vacuum sublimation.[3]

Hydrated salts of praseodymium(III) chloride can be prepared by treatment of either praseodymium metal or praseodymium(III) carbonate with hydrochloric acid:

Pr2(CO3)3 + 6 HCl + 15 H2O → 2 [Pr(H2O)9]Cl3 + 3 CO2

PrCl3∙7H2O is a hygroscopic substance, that will not crystallise from the mother liquor unless it is left to dry in a dessiccator. Anhydrous PrCl3 can be made by thermal dehydration of the hydrate at 400 °C in the presence of ammonium chloride.[3][4] Alternatively the hydrate can be dehydrated using thionyl chloride.[3][5]


Praseodymium(III) chloride is Lewis acidic, classified as "hard" according to the HSAB concept. Rapid heating of the hydrate may cause small amounts of hydrolysis.[3] PrCl3 forms a stable Lewis acid-base complex K2PrCl5 by reaction with potassium chloride; this compound shows interesting optical and magnetic properties.[1]

Aqueous solutions of praseodymium(III) chloride can be used to prepare insoluble praseodymium(III) compounds. For example, praseodymium(III) phosphate and praseodymium(III) fluoride can be prepared by reaction with potassium phosphate and sodium fluoride, respectively:

PrCl3 + K3PO4 → PrPO4 + 3 KCl
PrCl3 + 3 NaF → PrF3 + 3 NaCl

When heated with alkali metal chlorides, it forms a series of ternary (compounds containing three different elements) materials with the formulae MPr2Cl7, M3PrCl6, M2PrCl5, and M3Pr2Cl9 where M = K, Rb, Cs.[6]


  1. ^ a b J. Cybinska, J. Sokolnicki, J. Legendziewicz, G. Meyer, Journal of Alloys and Compounds, 341, 115–123 (2002).
  2. ^ L. F. Druding, J. D. Corbett, "Lower Oxidation States of the Lanthanides. Neodymium(II) Chloride and Iodide", J. Am. Chem. Soc. 83, 2462 (1961); J. D. Corbett, Rev. Chim. Minerale 10, 239 (1973),
  3. ^ a b c d F. T. Edelmann, P. Poremba, in: Synthetic Methods of Organometallic and Inorganic Chemistry, (W. A. Herrmann, ed.), Vol. 6, Georg Thieme Verlag, Stuttgart, 1997.
  4. ^ M. D. Taylor, P. C. Carter, "Preparation of anhydrous lanthanide halides, especially iodides", J. Inorg. Nucl. Chem., 24, 387 (1962); J. Kutscher, A. Schneider, Inorg. Nucl. Chem. Lett., 7, 815 (1971).
  5. ^ J. H. Freeman, M. L. Smith, "The preparation of anhydrous inorganic chlorides by dehydration with thionyl chlorid", J. Inorg. Nucl. Chem., 7, 224 (1958).
  6. ^ Gerd Meyer, "Ternary Chlorides and Bromides of the Rare-Earth Elements", Inorganic Syntheses, 1990, Volume 30, pp. 72–81. doi:10.1002/9780470132616.ch15

Further reading[edit]

  1. CRC Handbook of Chemistry and Physics (58th edition), CRC Press, West Palm Beach, Florida, 1977.
  2. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.
  3. S. Sugiyama, T. Miyamoto, H. Hayashi, M. Tanaka, J. B. Moffatt, "Effects of chlorine additives in the gas- and solid-phases on the oxidative dehydrogenation of ethane over praseodymium oxide", Journal of Molecular Catalysis A, 118, 129-136 (1997).
  4. Druding L. F.; Corbett J. D.; Ramsey B. N. (1963). "Rare Earth Metal-Metal Halide Systems. VI. Praseodymium Chloride". Inorganic Chemistry. 2 (4): 869–871. doi:10.1021/ic50008a055.