HexachloroferrateIII

Hexachloroferrate(III) refers to the hexachloroferrate(III) anion, [FeCl6]3−, in which iron is in the +3 oxidation state and is octahedrally coordinated by six chloride ligands. The complex carries an overall −3 charge and forms salts with various counter-cations, such as potassium, ammonium, or organic bases, for example K3[FeCl6] or (NH4)3[FeCl6].

The [FeCl6]3− ion is typically formed in chloride-rich environments. In solution, high chloride concentration stabilizes the hexacoordinate iron(III) center; in much lower chloride media, iron(III) tends to hydrolyze to form aquated species. The complex is paramagnetic due to the high-spin d5 configuration of Fe3+ in an octahedral field, which yields five unpaired electrons.

Common salts containing the hexachloroferrate(III) anion include K3[FeCl6], (NH4)3[FeCl6], and related species with different cations. These salts can often be prepared by reacting iron(III) chloride with a large excess of chloride and adding the desired counter-cation to crystallize the hexachloroferrate(III) salt. The crystals are typically colored yellow to pale brown, reflecting the electronic transitions within the chloride-coordinated iron(III) center.

Hexachloroferrate(III) salts are used as inorganic reagents and precursors in synthesis, particularly in chloride-rich media where the [FeCl6]3− anion is stable. They serve as sources of ferric chloride in certain processes and as educational examples of octahedral coordination chemistry for iron(III). Safety precautions apply as with most iron(III) compounds and chlorides, including avoidance of ingestion and precautions against inhalation and contact.