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 ...
of
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 I
3. 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 I
4 + Hf → 4 Hf I
3
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 Hf
3+ ions.
It consists of parallel chains of
face-sharing octahedra.
Hafnium(III) iodide has a
lower magnetic moment than
is expected for the d
1 metal ion Hf
3+, 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