Praseodymium(III) chloride

Praseodymium(III) chloride is the inorganic compound with the formula PrCl₃. 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.

Praseodymium(III) chloride

Names
IUPAC name Praseodymium(III) chloride
Other names Praseodymium chloride; praseodymium trichloride
Identifiers
CAS Number	10361-79-2 Y heptahydrate: 10025-90-8
3D model (JSmol)	Interactive image heptahydrate: Interactive image
ChemSpider	59695
ECHA InfoCard	100.030.710
EC Number	233-794-4 heptahydrate: 812-561-6
PubChem CID	66317 heptahydrate: 21546488
UNII	1JB99PM4G8 N
CompTox Dashboard (EPA)	DTXSID7044766 heptahydrate: DTXSID60615795
InChI Key: LHBNLZDGIPPZLL-UHFFFAOYSA-K InChI=1S/3ClH.Pr/h3*1H;/q;;;+3/p-3 heptahydrate: InChI=1S/3ClH.7H2O.Pr/h3*1H;7*1H2;/q;;;;;;;;;;+3/p-3 Key: RQHUQJCIAFYPAI-UHFFFAOYSA-K
SMILES Cl[Pr](Cl)Cl heptahydrate: O.O.O.O.O.O.O.[Cl-].[Cl-].[Cl-].[Pr+3]
Properties
Chemical formula	PrCl3
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)
Solubility in water	104.0 g/100 ml (13 °C)
Magnetic susceptibility (χ)	+44.5·10−6 cm3/mol
Structure
Crystal structure	hexagonal (UCl3 type), hP8
Space group	P63/m, No. 176
Coordination geometry	Tricapped trigonal prismatic (nine-coordinate)
Hazards
Occupational safety and health (OHS/OSH):
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). N verify (what is YN ?) Infobox references

Preparation

Praseodymium(III) chloride is prepared by treating praseodymium metal with 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 crystallize from the mother liquor unless it is left to dry in a desiccator. Anhydrous PrCl₃ can be made by thermal dehydration of the hydrate at 400 °C in the presence of ammonium chloride, the so-called ammonium chloride route.^[3][4][5] Alternatively the hydrate can be dehydrated using thionyl chloride.^[3][6]

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.^[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

2PrCl₃ + 3 Na₂CO₃----> Pr₂CO₃ + 6NaCl

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.^[7]

Praseodymium chloride heptahydrate under different light