AlCl3n

AlCl3n is not a single discrete compound but a general notation used in inorganic chemistry to describe aluminum chloride adducts bearing nitrogen-donor ligands. It is typically written as AlCl3·nL or as [AlCl3L], where L represents a donor molecule such as an amine, nitrile, phosphine, or ether. The value of n reflects the number of coordinating ligands and depends on the ligand’s denticity and the synthesis conditions.

In these adducts, aluminum is bonded to three chloride ligands and to one or more L donors, giving four-coordinate or higher geometries that are commonly tetrahedral or distorted. In solution, the classic Al2Cl6 dimer may dissociate to yield monomeric AlCl3L units; adduct formation is typically labile and reversible. Solid adducts vary in structure, with some featuring bridging chloride interactions.

Preparation and use: AlCl3n adducts are usually prepared by combining dry AlCl3 with the donor in an anhydrous solvent under inert atmosphere. They are moisture-sensitive, hydrolyzing to Al(OH)3 and HCl on exposure to water. These adducts act as Lewis acids and serve as catalysts or precursors in organic synthesis, including Friedel–Crafts reactions and polymerization initiation, where controllable activity and stability are advantageous.

Note: The term is informal and rarely denotes a fixed compound; precise species are defined by the exact ligand identity and stoichiometry (for example, AlCl3·THF). See also aluminum trichloride, Lewis acid, and adduct.