Ammonium hexachloroiridate(IV) is the

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

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

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

of the iridium(IV)

complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

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, which has been used interchangeably.

Structure and synthesis

The compound has been characterized by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

. The salt crystallizes in a cubic motif like that of

ammonium hexachloroplatinate Ammonium hexachloroplatinate, also known as ammonium chloroplatinate, is the inorganic compound with the formula (NH4)2 tCl6 It is a rare example of a soluble platinum(IV) salt that is not hygroscopic. It forms intensely yellow solutions in water. ...

. 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 o ...

. The compound is prepared in the laboratory by the addition of ammonium chloride to an aqueous solution of sodium hexachloroiridate. The salt is poorly soluble like most other diammonium hexachlorometallates.

Uses

It is an 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 toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

, but rCl₆sup>2− resists ligand substitution. Upon heating under hydrogen, the solid salt converts to the metal: :

Bonding

The electronic structure of ammonium hexachloroiridate(IV) has attracted much attention. Its magnetic moment is less than that calculated for one electron. This result is attributed to antiferromagnetic coupling between Ir centers mediated by Cl---Cl interactions.

Electron spin resonance Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a method for studying materials that have unpaired electrons. The basic concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but the spin ...

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