Hexachlorometallates

Hexachlorometallates are a class of coordination compounds consisting of an octahedrally coordinated metal center bound to six chloride ligands, forming hexachloro complexes of the type [MCl6]^{n-}. The overall charge n- depends on the oxidation state x of the central metal, following n = x − 6. For example, a metal in the +3 oxidation state yields [MCl6]^{3-}, while a +4 metal yields [MCl6]^{2-}. A well-known member is ferrate(III) hexachlorometallate, [FeCl6]^{3-}.

These hexachlorometallates are typically isolated as salts with alkali metal or quaternary ammonium cations, and can be prepared or accessed through oxidation of metal chlorides in chloride-rich media or via metathesis in concentrated chloride solutions. The solid-state and solution species generally retain an octahedral coordination geometry with Oh symmetry, and the M–Cl bonds are relatively strong due to the high oxidation state of the metal and the chloride ligands.

Physical properties of hexachlorometallates vary with the metal and oxidation state, but many are colored and paramagnetic, reflecting their electronic structure. They are often used as versatile building blocks in inorganic synthesis, serving as precursors to other complexes and as counterions or ligands in coordination polymers and oxometallic materials. In solution, ligand exchange and substitution reactions can occur, enabling the formation of mixed-ligand species or conversion to different oxidation states under appropriate conditions.

Overall, hexachlorometallates represent a broad family of octahedral metal chloride complexes that play a role as synthetic reagents and building blocks in inorganic chemistry.