holmium(III) Chloride
Properties
| State | Solid (hygroscopic; commonly hydrated) |
| Color | pale yellow |
| Solubility | Very soluble in water; soluble in alcohols |
| Melting Point | 853 °C (anhydrous) |
About holmium(III) Chloride
Holmium(III) chloride is the soluble entry point into holmium chemistry — a pale-yellow hygroscopic salt (anhydrous formula HoCl3, 271.29 g/mol) that almost nobody actually has in the anhydrous form because it doesn't survive contact with moist air. Try to dehydrate the heptahydrate by simply heating it and you get HoOCl (the oxychloride) plus HCl gas, not anhydrous HoCl3. The clean route is heating the hydrate with a 6-fold excess of NH4Cl under nitrogen at 350 °C; the ammonium chloride sublimes off and takes the equilibrium with it, leaving anhydrous HoCl3 behind. In the solid state, Ho(III) sits in a 9-coordinate tricapped trigonal prism — typical for the larger Ln(III) ions where coordination number tracks ionic radius. The biggest commercial use is as the holmium source for growing Ho:YAG laser crystals (holmium-doped yttrium aluminum garnet), the workhorse 2.1-micron solid-state laser. That wavelength sits right on a strong water absorption band, which makes Ho:YAG nearly perfect for cutting through wet tissue with shallow penetration depth (~400 micrometers). Urologists use it for laser lithotripsy — over 500,000 kidney-stone procedures per year in the US alone — and it's the standard tool for transurethral prostate resection.
Where you'll encounter it
If you've had a kidney stone broken up with a laser, watched a urology resident demo a Ho:YAG fiber, or worked with rare-earth catalysts in organic synthesis, the holmium probably entered the supply chain as HoCl3. Over half a million laser lithotripsy procedures per year in the US alone fragment kidney stones with pulsed 2.1-micron Ho:YAG output threaded through a flexible ureteroscope — the holmium dopant in those YAG crystals starts as HoCl3 hydrate dissolved into the Czochralski melt. Urologists also use the same wavelength for HoLEP transurethral prostate enucleation, which has displaced traditional TURP in many academic centers because of its lower bleeding risk. ENT surgeons and dermatologists keep Ho:YAG handpieces for selective soft-tissue ablation in moist environments where the strong water absorption gives them micrometer-scale precision.
Common Uses
- Holmium dopant source for Ho:YAG laser crystal growth (2.1 micron output)
- Starting material for Ho-doped fiber amplifiers and upconversion phosphors
- Mild Lewis-acid catalyst for Mukaiyama aldol and Diels-Alder reactions
- Precursor for organoholmium reagents via metathesis with alkali alkyls
- Source of Ho(III) for ICP-MS and ICP-OES calibration standards
- Reagent in lanthanide ion-exchange separation research
- Intermediate in producing Ho metal by Ca reduction
Safety Information
GHS: H315 (skin irritation Cat 2), H319 (eye irritation Cat 2A), H335 (respiratory irritation). Hygroscopic — will deliquesce on the bench and release small amounts of HCl mist as it absorbs water and partially hydrolyzes. No OSHA PEL specifically for HoCl3, but treat as a soluble lanthanide salt: nuisance dust limit 5 mg/m3 (respirable). Modest acute toxicity (rat oral LD50 around 3.7 g/kg), but chronic lanthanide exposure can cause pulmonary granulomas. Standard PPE: safety glasses, nitrile gloves, fume hood for any heating or grinding. Store in a desiccator.
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.