tetrahalide

A tetrahalide is a chemical compound that contains four halogen atoms in its formula, typically attached to a central element. The term is generic and applies to a range of compounds, including neutral molecules such as MX4 (for example SiCl4) and carbon tetrachloride, as well as related ionic species in some contexts. The halogens involved are usually chlorine, bromine, or iodine, with fluorine-containing tetrahalides being less common but known for highly reactive systems.

In many covalent MX4 tetrahalides, the central atom is four-coordinate and the molecule adopts a tetrahedral geometry, as seen with silicon tetrachloride (SiCl4) or carbon tetrachloride (CCl4). Heavier metal tetrachlorides may exist as polymeric solids and can be more prone to hydrolysis. All tetrahalides of this type are typically moisture sensitive and can hydrolyze in water, producing corresponding oxides or hydroxides and hydrogen chloride.

Common examples include carbon tetrachloride (CCl4), a volatile nonpolar solvent historically used in various applications; silicon tetrachloride (SiCl4), a versatile precursor to silicon dioxide and organosilicon compounds; titanium tetrachloride (TiCl4), a volatile liquid used in pigment production and as a precursor to TiO2; and tin tetrachloride (SnCl4), a Lewis acid that can catalyze reactions and hydrolyzes readily in water. Bromine and iodine analogs exist but are less widely encountered due to handling and stability issues.

Preparation generally involves direct chlorination or halogenation of the element or lower halides at elevated temperatures, or chlorination of methane for carbon tetrachloride. Handling requires moisture exclusion and appropriate safety measures due to corrosivity and toxicity.