Praseodymium(III) chloride is the inorganic compound with the formula PrCl<sub>3</sub>. Like other lanthanide trichlorides, it exists both in the anhydrous and hydrated forms. It is a blue-green solid that rapidly absorbs water on exposure to moist air to form a light green heptahydrate.

Preparation

Praseodymium(III) chloride is prepared by treating praseodymium metal with hydrogen chloride:

:2 Pr + 6 HCl → 2 PrCl<sub>3</sub> + 3 H<sub>2</sub>

It is usually purified by vacuum sublimation. Alternatively the hydrate can be dehydrated using thionyl chloride.

Reactions

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. PrCl<sub>3</sub> forms a stable Lewis acid-base complex K<sub>2</sub>PrCl<sub>5</sub> by reaction with potassium chloride; this compound shows interesting optical and magnetic properties.

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:

:PrCl<sub>3</sub> + K<sub>3</sub>PO<sub>4</sub> → PrPO<sub>4</sub> + 3 KCl

:PrCl<sub>3</sub> + 3 NaF → PrF<sub>3</sub> + 3 NaCl

:2PrCl<sub>3</sub> + 3 Na<sub>2</sub>CO<sub>3</sub>----> Pr<sub>2</sub>CO<sub>3</sub> + 6NaCl

When heated with alkali metal chlorides, it forms a series of ternary (compounds containing three different elements) materials with the formulae MPr<sub>2</sub>Cl<sub>7</sub>, M<sub>3</sub>PrCl<sub>6</sub>, M<sub>2</sub>PrCl<sub>5</sub>, and M<sub>3</sub>Pr<sub>2</sub>Cl<sub>9</sub> where M = K, Rb, Cs.

thumb|Praseodymium chloride heptahydrate under different light

References

Further reading

  1. <!--old 2--> CRC Handbook of Chemistry and Physics (58th edition), CRC Press, West Palm Beach, Florida, 1977.
  2. <!--old 3--> N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.
  3. <!--old 8--> 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).
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