Contents

Hafnium(III) iodide

Hafnium(III) iodide

Names
IUPAC name Hafnium triiodide
Identifiers
CAS Number	13779-73-2 Y
3D model (JSmol)	Interactive image
PubChem CID	161242838 charge error
InChI InChI=1S/Hf.3HI/h;3*1H/q+3;;;/p-3 Key: VAFXHNPAMHBKMS-UHFFFAOYSA-K
SMILES [I-].[I-].[I-].[Hf+3]
Properties
Chemical formula	HfI3
Molar mass	559.20 g·mol−1
Appearance	black crystals[1]
Melting point	decomposes
Related compounds
Other anions	Hafnium(III) chloride Hafnium(III) bromide
Other cations	Titanium(III) iodide Zirconium(III) iodide
Related compounds	Hafnium(IV) iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Chemical compound

Hafnium(III) iodide is an inorganic compoundofhafnium and iodine with the formula Hf I₃. It is a black solid.^[2]

Like other group 4 trihalides, hafnium(III) iodide can be prepared from hafnium(IV) iodide by high-temperature reduction with hafnium metal, although incomplete reaction and contamination of the product with excess metal often occurs.^[2]

3 Hf I₄ + Hf → 4 Hf I₃

Other metals can be used as the reducing agent, for example aluminium. The product is often nonstoichiometric, with the compositions Hf I_3.2–3.3 and Hf I_3.0–3.5 reported.^[3][4]

Hafnium(III) iodide adopts the same crystal structureaszirconium(III) iodide.^[5] This is very similar to the β-TiCl₃ structure.^[2] The structure is based on hexagonal close packingofiodide ions with one third of the octahedral interstices occupied by Hf³⁺ ions.^[2] It consists of parallel chains of face-sharing {HfI₆} octahedra.^[5]

Hafnium(III) iodide has a lower magnetic moment than is expected for the d¹ metal ion Hf³⁺, indicating non-negligible Hf–Hf bonding.^[2] The Hf–Hf separation was originally reported to be 3.295 Å,^[6] but a subsequent study of nonstoichiometric hafnium(III) iodide indicated a lower symmetry structure.^[3]

Like the chloride and bromide, hafnium(III) iodide is a powerful enough reducing agent to reduce water and therefore does not have any aqueous chemistry.^[2]