Tetrachloroferrate

Tetrachloroferrate is the name given to the anion [FeCl4]−, a tetra-coordinate iron(III) complex of chloride. The anion forms salts with various countercations, such as potassium tetrachloroferrate(III) KFeCl4 or ammonium tetrachloroferrate(III) (NH4)FeCl4, and is most commonly encountered in strongly chloride-rich solutions or solids.

Structure and properties: In [FeCl4]− iron is in the +3 oxidation state and the four chloride ligands arrange around the metal in a tetrahedral geometry. The complex is typically paramagnetic due to the high-spin d5 configuration of Fe3+ in a weak-field chloride environment. The bond framework and electronic structure reflect characteristic behavior of tetra-coordinate iron(III) chloride complexes, including sensitivity to hydrolysis and changes in coordination when the ligand environment is altered.

Synthesis and occurrence: [FeCl4]− forms in strongly acidic, chloride-rich media where Fe3+ is surrounded by chloride ligands. It can be isolated as salts with suitable cations (for example K+, NH4+). In aqueous solution, the species is favored under high chloride concentration, while hydrolysis can occur upon dilution or neutralization, leading to other iron-oxide or hydroxide species.

Applications and context: Tetrachloroferrate serves mainly as a representative species in coordination chemistry and inorganic spectroscopy, illustrating tetra-coordinate Fe3+ chemistry and ligand-field effects. It is used in studies of ligand binding, electronic structure, and magnetic properties of iron(III) chloride complexes. Safety and handling follow standard procedures for iron(III) salts and concentrated chloride solutions.