Hafnium(III) iodide is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

hafnium Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri M ...

and

iodine Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

Hf I₃. It is a black solid.

Preparation

Like other group 4 trihalides, hafnium(III) iodide can be prepared from

hafnium(IV) iodide Hafnium(IV) iodide is the inorganic compound with the formula HfI4. It is a red-orange, moisture sensitive, sublimable solid that is produced by heating a mixture of hafnium with excess iodine. It is an intermediate in the crystal bar process for ...

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 In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...

, with the compositions Hf I_3.2–3.3 and Hf I_3.0–3.5 reported.

Structure and bonding

Hafnium(III) iodide adopts the same

crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...

as zirconium(III) iodide. 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, but a subsequent study of nonstoichiometric hafnium(III) iodide indicated a lower symmetry structure.

Reactivity

Like the chloride and bromide, hafnium(III) iodide is a powerful enough

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

to reduce water and therefore does not have any aqueous chemistry.

References

{{DEFAULTSORT:Hafnium(Iii) Iodide Hafnium compounds Iodides Metal halides