Hexahalometallates

Hexahalometallates are coordination species in inorganic chemistry characterized by an octahedral metal center bound to six halide ligands, giving a general formula [MX6]n−, where M is a metal and X is a halide (F, Cl, Br, or I). They occur as discrete anions in salts and as part of extended solid-state structures. The most extensively studied are the hexafluoro complexes [MF6]2− (MIV), such as K2[TiF6], K2[ZrF6], and K2[HfF6], though chlorometallates [MCl6]2−, and to a lesser extent bromometallates, are known.

In these species the metal is typically in a high coordination environment and the ligands adopt an octahedral arrangement, giving Oh symmetry in idealized geometries. The M–X bonds vary in strength with the halide: fluoride ligands form very strong bonds, stabilizing fluorometallates in a wide range of cations; larger halides yield more covalent character and, in some cases, lower symmetry due to lattice constraints.

Synthesis usually proceeds by salt metathesis or by direct combination of metal halide sources under halide-rich conditions, followed by crystallization from ionic media. Hexahalometallates are important for understanding strong-field halometalates, lattice energies of ionic solids, and the chemistry of high oxidation states in halide-rich environments. They are encountered in solid-state chemistry, inorganic synthesis, and materials science, where they influence properties such as conductivity and optical behavior.

See also: hexachlorometallate, hexafluorometallate.