Holmium(III) iodide

Holmium(III) iodide is an iodide of holmium, with the chemical formula of HoI₃. It is used as a component of metal halide lamps.^[5]

Holmium(III) iodide

Names
Other names Holmium iodide Holmium triiodide
Identifiers
CAS Number	13813-41-7 Y
3D model (JSmol)	Interactive image
ChemSpider	75570
ECHA InfoCard	100.034.050
EC Number	237-470-3
PubChem CID	83748
CompTox Dashboard (EPA)	DTXSID5065645
InChI InChI=1S/Ho.3HI/h;3*1H/q+3;;;/p-3 Key: KXCRAPCRWWGWIW-UHFFFAOYSA-K
SMILES [Ho+3].[I-].[I-].[I-]
Properties
Chemical formula	HoI3
Molar mass	545.6437 g/mol
Appearance	Pale-yellow solid[1][2]
Density	5.4 g/cm3[3]
Melting point	994 °C[2]
Boiling point	1300 °C[4]
Solubility in water	soluble in water[2]
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H315, H319, H335, H360
Precautionary statements	P203, P233, P260, P261, P264, P264+P265, P271, P272, P280, P284, P302+P352, P304+P340, P305+P351+P338, P318, P319, P321, P332+P317, P333+P317, P337+P317, P342+P316, P362+P364, P403, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

Holmium(III) iodide can be obtained by directly reacting holmium and iodine:^[4]

2 Ho + 3 I₂ → 2 HoI₃

Holmium(III) iodide can also be obtained via the direct reaction between holmium and mercury(II) iodide:

2 Ho + 3 HgI₂ → 2 HoI₃ + 3 Hg

The mercury produced in the reaction can be removed by distillation.^[6]

Holmium(III) iodide hydrate can be converted to the anhydrous form by dehydration with a large excess of ammonium iodide (since the compound is prone to hydrolysis).^[4]

Properties

Holmium(III) iodide is a highly hygroscopic substance that dissolves in water.^[7][3][2] It forms yellow hexagonal crystals with a crystal structure similar to bismuth(III) iodide.^[4] In air, it quickly absorbs moisture and forms hydrates. The corresponding oxide iodide is also readily formed at elevated temperature.^[4]