metallihalides

Metallihalides are inorganic compounds composed of a metal atom or ion covalently or ionically bonded to one or more halogen atoms (fluorine, chlorine, bromine or iodine). The term is often used interchangeably with metal halides, although "metallihalide" can emphasize the metallic character of the central atom. These species range from simple dihalides such as iron(III) chloride to complex anionic frameworks such as hexafluorophosphate ions (PF6⁻).

The bonding in metallihalides varies depending on the oxidation state of the metal and the nature of the halogen. Low‑valent metals frequently form covalent M–X bonds, resulting in molecular or polymeric solids. High‑valent metals typically form ionic lattices, producing highly soluble salts that are important reagents in organic synthesis (e.g., AlCl3 in Friedel–Crafts reactions) and catalysts in industrial processes. The halogen ligand can also modify electronic properties, leading to applications in photochemistry and materials science.

Metallihalides are prepared by direct combination of the elements, salt metathesis, or reduction/oxidation of metal salts in the presence of halogen sources. Many are hygroscopic and may hydrolyze to form oxides and halide acids. Because of their Lewis acidity, many metal chlorides act as strong chalcogen or halide abstraction reagents.

Industrial uses of metallihalides include the manufacture of flame retardants, pharmaceuticals, and electronic components. In laboratories, they serve as oxidants, polymerization initiators and as templates for the synthesis of coordination complexes and metal–organic frameworks. Despite their many practical benefits, certain metallihalides such as mercury(II) chloride are toxic and require careful handling.