TetrachloroferrateIII

Tetrachloroferrate(III) refers to the tetrachloroferrate anion, [FeCl4]−, a tetrahedral complex of iron in the +3 oxidation state. The four chloride ligands coordinate to iron in a single tetrahedral array, giving a negatively charged anion that forms salts with various countercations such as alkali metals or ammonium. In solution, stability is strongly dependent on chloride concentration and the solvent.

Formation and occurrence: [FeCl4]− is typically generated in strongly chloride-rich environments. In aqueous solution, ferric iron tends to hydrolyze, so stable [FeCl4]− species are mainly observed under high Cl− activity or in nonaqueous media. Salts of the form M[FeCl4], where M is a monovalent cation, are the common solid-state manifestations of tetrachloroferrate(III).

Structure and properties: The iron center in [FeCl4]− is tetracoordinate and adopts a tetrahedral geometry. The complex is high-spin (d5 for Fe3+ in a weak field) and paramagnetic, with five unpaired electrons. Physically, salts containing [FeCl4]− are typically pale yellow to brown and are more stable in concentrated chloride solutions or certain nonaqueous solvents than in water.

Chemistry and reactivity: Ligand exchange can occur, with chloride ligands replaced by other ligands under appropriate conditions. The redox chemistry involves Fe3+/Fe2+ processes under suitable reducing conditions, but the chloride environment can influence redox potentials. Hydrolysis and formation of iron oxyhydroxide species are common when water is involved.

Applications: Tetrachloroferrate(III) is encountered mainly in inorganic chemistry as a chlorometalate reference or synthetic intermediate and in studies of ferric chloride complexes. It is not widely used as a bulk reagent outside specialized chloride chemistry.

Safety: Handling ferric salts and chloride solutions should follow standard lab safety practices to avoid irritation and exposure.