Hafnium(III) iodide is an inorganic compound of hafnium and iodine with the formula Hf I3. It is a black solid.
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.
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 I3.2–3.3 and Hf I3.0–3.5 reported.[1] [2]
Hafnium(III) iodide adopts the same crystal structure as zirconium(III) iodide.[3] This is very similar to the β-TiCl3 structure. The structure is based on hexagonal close packing of iodide ions with one third of the octahedral interstices occupied by Hf3+ ions. It consists of parallel chains of face-sharing octahedra.
Hafnium(III) iodide has a lower magnetic moment than is expected for the d1 metal ion Hf3+, indicating non-negligible Hf–Hf bonding. The Hf–Hf separation was originally reported to be 3.295 Å,[4] but a subsequent study of nonstoichiometric hafnium(III) iodide indicated a lower symmetry structure.
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.