Ammonium hexachloroiridate(IV) is the

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 ...

with the formula (NH₄)₂ rCl₆ This dark brown solid is the

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

salt of the iridium(IV) complex rCl₆sup>2−. It is a commercially important iridium compound one of the most common complexes of iridium(IV). A related but ill-defined compound is

iridium tetrachloride Iridium tetrachloride is an inorganic compound with the approximate formula IrCl4(H2O)n. It is a water-soluble dark brown amorphous solid. A well defined derivative is ammonium hexachloroiridate ((NH4)2IrCl6). It is used to prepare catalysts, s ...

, which is often used interchangeably.

Structure

The compound has been characterized by X-ray crystallography. The salt crystallizes in a cubic motif like that of ammonium hexachloroplatinate. The rCl₆sup>2− centers adopt

octahedral molecular geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc ...

Uses

It is a key intermediate in the isolation of iridium from ores. Most other metals form insoluble sulfides when aqueous solutions of their chlorides are treated with

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...

, but rCl₆sup>2− resists ligand substitution. Upon heating under hydrogen, the solid salt converts to the metal: : (NH₄)₂ rCl₆ + 2 H₂ → Ir + 6 HCl + 2 NH₃

Bonding

The electronic structure of ammonium hexachloroiridate(IV) has attracted much attention. Its magnetic moment is less that than calculated for one electron. This result is interpreted as the result of antiferromagnetic coupling between Ir centers mediated by Cl---Cl interactions. Electron spin resonance, studies reveal that more than half of the spin density resides on chloride, thus the description of the complex as Ir(IV) is an oversimplification.

References

{{Ammonium salts Iridium compounds Ammonium compounds Chloro complexes Chlorometallates