Metallhalogenides

Metallhalogenides, or metal halides, are binary compounds formed from a metal and a halogen (fluorine, chlorine, bromine, iodine, or astatine). They have the general formula MXn, where M is a metal and X is a halogen, and the exact stoichiometry reflects the metal’s typical oxidation state and coordination. The most common families are alkali metal halides (MX), alkaline earth metal halides (MX2), and a broad range of transition metal halides (such as FeCl2, TiCl4, NiBr2) that exhibit diverse bonding, from ionic to covalent, and variable structures from molecular to extended lattices.

Alkali and alkaline earth halides typically form colorless crystalline solids with high melting points. Many are highly soluble in water (for example, NaCl, KBr), though solubility depends on the specific metal and halogen. Transition metal halides display a wider variety of properties: some are ionic solids, others form covalent networks or discrete molecular species, and several are volatile. Many metal halides act as Lewis acids and are common reagents in synthesis, catalysis, and materials science. They can also form coordination complexes or polymeric structures in the solid state.

Synthesis usually occurs by direct combination of the metal with the halogen at elevated temperature, halogenation of the metal, or metathesis reactions between halide salts. Applications include serving as chemical reagents, catalysts, and precursors for materials synthesis, such as chemical vapor deposition, and for the preparation of functional materials, including metal halide perovskites and related compounds.

Naturally occurring halide minerals, such as sodium chloride and calcium fluoride, illustrate the natural occurrence of metallhalogenides.