Lanthanum(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 ...

containing

lanthanum Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...

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 chemical formula .

Synthesis

Lanthanum(III) iodide can be synthesised by the reaction of lanthanum metal with

mercury(II) iodide Mercury(II) iodide is a chemical compound with the molecular formula Hg I2. It is typically produced synthetically but can also be found in nature as the extremely rare mineral coccinite. Unlike the related mercury(II) chloride it is hardly solu ...

: :2 La + 3 HgI₂ → 2 LaI₃ + 3 Hg It can also be prepared from the elements, that is by the reaction of metallic lanthanum with iodine: :2 La + 3 I₂ → 2 LaI₃ While lanthanum(III) iodide solutions can be generated by dissolving

lanthanum oxide Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock ...

hydroiodic acid Hydroiodic acid (or hydriodic acid) is an aqueous solution of hydrogen iodide (HI). It is a strong acid, one that is ionized completely in an aqueous solution. It is colorless. Concentrated solutions are usually 48% to 57% HI. Reactions Hyd ...

, the product will hydrolyse and form polymeric hydroxy species: :La₂O₃ + 6 HI → 2 LaI₃ + 3 H₂O ''→ further reactions''

Structure

Lanthanum(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 ...

plutonium(III) bromide Plutonium(III) bromide is an inorganic salt of bromine and plutonium with the formula PuBr3. This radioactive green solid has few uses, however its crystal structure is often used as a structural archetype in crystallography. Crystal structure ...

, with 8-coordinate metal centres arranged in layers. This

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

structure is typical of the triiodides of the lighter lanthanides (La–Nd), whereas heavier lanthanides tend to adopt the

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

bismuth(III) iodide Bismuth(III) iodide is the inorganic compound with the formula Bi I3. This gray-black salt is the product of the reaction of bismuth and iodine, which once was of interest in qualitative inorganic analysis. Bismuth(III) iodide adopts a distinc ...

structure.

Reactivity and applications

Lanthanum(III) iodide is very soluble in water and is

deliquescent Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...

. Anhydrous lanthanum(III) iodide reacts with

tetrahydrofuran Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...

to form a photoluminescent complex, LaI₃(THF)₄, with an average La–I bond length of 3.16 Å. This complex is a starting material for

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...

and

cyclopentadienyl Cyclopentadienyl can refer to *Cyclopentadienyl anion, or cyclopentadienide, **Cyclopentadienyl ligand *Cyclopentadienyl radical, • *Cyclopentadienyl cation, See also *Pentadienyl In organic chemistry, pentadienyl refers to the organic radic ...

complexes of lanthanum.

Related compounds

Lanthanum also forms a diiodide, LaI₂. It is an

electride An electride is an ionic compound in which an electron is the anion. Solutions of alkali metals in ammonia are electride salts. In the case of sodium, these blue solutions consist of a(NH3)6sup>+ and solvated electrons: :Na + 6 NH3 → a(N ...

and is best formulated , with the electron delocalised in a conduction band. Several other lanthanides form similar compounds, including CeI₂, PrI₂ and GdI₂. Lanthanum diiodide adopts the same

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square ...

crystal structure as PrI₂. Lanthanum(III) iodide reacts with lanthanum metal under an argon atmosphere in a tantalum capsule at 1225 K to form the mixed-valence compound La₂I₅. Reduction of LaI₂ or LaI₃ with metallic sodium in an argon atmosphere at 550 °C gives lanthanum monoiodide, LaI, which has a hexagonal crystal structure.

References

{{Lanthanide halides Lanthanum compounds Iodides Inorganic compounds Lanthanide halides