praseodymium(III) Chloride
Properties
| State | Solid (hygroscopic; commonly hydrated) |
| Color | pale green |
| Solubility | Very soluble in water; soluble in alcohols |
| Melting Point | 803 °C (anhydrous) |
About praseodymium(III) Chloride
PrCl3 is the workhorse soluble Pr(III) salt — pale green, hygroscopic, and almost always shipped as the heptahydrate because anyone who has tried to dehydrate it in air knows what happens: instead of clean PrCl3, you get the oxychloride PrOCl and a face full of HCl. The clean route to anhydrous PrCl3 is either vacuum sublimation or the NH4Cl trick — co-melting the hydrate with ammonium chloride under flowing argon, then driving off the ammonium chloride at higher temperature. In the crystal the Pr(III) center sits in a 9-coordinate tricapped trigonal prism, the standard geometry for the larger trivalent lanthanides. The pale green color is diagnostic: weak Laporte-forbidden 4f-4f transitions in the blue (around 450-490 nm) and yellow (570-600 nm) regions of a 4f² ion, with extinction coefficients of only 1-10 M⁻¹ cm⁻¹, leave green light to transmit.
Where you'll encounter it
If you've worked on Pr-doped fiber amplifiers for the 1.3-µm telecom window, the precursor solution that goes into the fluoride-glass fiber preform almost certainly started as PrCl3·7H2O dissolved in dilute HCl. The same salt is the standard feedstock for upconversion phosphors that take infrared excitation and emit visible light — the kind sintered into anti-counterfeiting inks and security taggants. In a synthetic lanthanide-organometallic lab, anhydrous PrCl3 is what you weigh out in the glovebox to make Pr(III) cyclopentadienyl and Pr(III) silylamide complexes. And in any rare-earth pilot plant doing solvent-extraction separations, the chloride is the dissolved form that gets loaded onto the D2EHPA or HEH/EHP organic phase before stripping back into a cleaner aqueous fraction.
Common Uses
- Precursor for Pr-doped fluoride fiber amplifiers operating in the 1.3-µm telecom window
- Feedstock for upconversion phosphors used in anti-counterfeiting inks and security taggants
- Glovebox starting material for Pr cyclopentadienyl and silylamide organometallic complexes
- Lewis-acid catalyst for Mukaiyama aldol and selected hetero-Diels-Alder reactions
- Aqueous feed for D2EHPA solvent-extraction separations in rare-earth refining
- Reduction precursor for Pr metal production via calciothermic or molten-salt electrolysis
Safety Information
GHS classification: Skin irritation Category 2 (H315), Eye irritation Category 2A (H319). Hygroscopic — releases HCl vapor on contact with atmospheric moisture, so weighing in a fume hood with nitrile gloves and splash goggles is standard. No OSHA-specific PEL for praseodymium compounds; the ACGIH lacks a TLV for soluble lanthanide salts but practitioners apply the general particulate-not-otherwise-classified limit of 10 mg/m³ inhalable. Acute oral toxicity is moderate (LD50 in rats around 4500 mg/kg for the trichloride), but the real concern is chronic accumulation in liver and bone if respired as dust over years. Decontaminate spills with damp paper towels rather than dry sweeping to keep dust airborne load down.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.