europium(III) Chloride
Properties
| State | Solid (hygroscopic; commonly hydrated) |
| Color | pale yellow |
| Solubility | Very soluble in water; soluble in alcohols |
| Melting Point | 767 °C (anhydrous) |
About europium(III) Chloride
Europium(III) chloride is the trivalent partner to EuCl2 and the workhorse soluble form of europium for almost all phosphor and coordination-chemistry work. The anhydrous salt is pale yellow, hygroscopic, and surprisingly hard to obtain in pure form — heating any of the common hydrates (the heptahydrate and hexahydrate are both well-characterized) in air gives EuOCl with loss of HCl rather than clean EuCl3, because the Eu(III)–O bond strength wins out as soon as water has anywhere to leave the lattice. Clean anhydrous EuCl3 requires either vacuum sublimation of the hydrate above 700°C, dehydration in flowing HCl gas, or the NH4Cl-flux method (heating EuCl3·6H2O with excess NH4Cl under inert atmosphere, which generates HCl in situ to suppress oxychloride formation). In the crystal Eu(III) sits in a 9-coordinate tricapped trigonal prismatic site, the typical geometry for the early-to-mid trivalent rare earths whose ionic radii are still large enough to support high coordination numbers. Dissolved EuCl3 is the standard precursor for Y2O2S:Eu³⁺ red phosphor synthesis (the dominant red emitter in CRT TVs and tricolor fluorescent lamps for decades), for Eu³⁺-doped molecular complexes used as luminescent probes in fluoroimmunoassay (DELFIA technology), and for chiral-shift NMR reagents like Eu(fod)3 made by ligand exchange. Its other claim to fame is photoreduction: shining UV on aqueous EuCl3 in the presence of a sacrificial reductant generates EuCl2 — a unique reactivity among the lanthanides shared only by Sm and Yb.
Where you'll encounter it
If you've ever opened a bottle of EuCl3·6H2O sitting on a shelf for a few years, you can usually see the problem — partial conversion to EuOCl shows up as a slight color shift toward white-yellow and a chunk of insoluble residue at the bottom of the glassware after you try to dissolve it for a synthesis. For real anhydrous EuCl3 you either pay for ampouled material or you make it fresh. In Eu³⁺ luminescent probe work for time-resolved immunoassay, EuCl3 plus a chelator (DTPA, DOTA, or a cryptand) makes a kinetically inert complex with the very long ~ms emission lifetime that lets you gate out short-lived autofluorescence from biological samples — DELFIA assays exploit exactly this and have been a clinical immunoassay platform since the 1980s.
Common Uses
- Precursor for red Eu³⁺-doped phosphors (Y2O2S:Eu³⁺, YVO4:Eu³⁺, Y2O3:Eu³⁺)
- Eu³⁺ source for luminescent lanthanide chelates in time-resolved fluoroimmunoassay (DELFIA)
- Starting material for chiral lanthanide-shift NMR reagents (Eu(fod)3, Eu(hfc)3)
- Photoreducible Eu(III) source for generating Eu(II) in solution under UV
- Lewis acid catalyst in selected aldol and Diels–Alder reactions
- Analytical reagent for lanthanide ion-exchange separation studies
Safety Information
GHS: H315 skin irritation, H319 eye irritation, H335 may cause respiratory irritation. Hygroscopic — moisture contact releases HCl mist. Low acute toxicity by oral route (rat LD50 >5000 mg/kg). Standard lab PPE: nitrile gloves, eye protection, lab coat. For dehydration work in HCl gas atmosphere, use a fume hood with an acid-resistant exhaust and HCl scrubber on the vent line.
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.