Tetrachloraluminate

Tetrachloraluminate refers to the chemical species with the formula [AlCl4]-. It is an anion consisting of one aluminum atom bonded to four chlorine atoms. The central aluminum atom is in a +3 oxidation state, and each chlorine atom has a -1 oxidation state, resulting in a net charge of -1 for the anion. This anion is often found in ionic compounds where it is paired with a metal cation, such as sodium tetrachloroaluminate (Na[AlCl4]) or potassium tetrachloroaluminate (K[AlCl4]). It can also exist in solutions where it is formed through reactions involving aluminum chloride.

The tetrachloroaluminate anion is a common component of molten salts, particularly those used as electrolytes in industrial processes. Aluminum chloride (AlCl3) itself can exist as a dimer (Al2Cl6) in the solid and gaseous phases, but in molten salts or in the presence of other chlorides, it readily forms the tetrachloroaluminate anion. This formation is typically a Lewis acid-base reaction, where aluminum chloride acts as a Lewis acid and accepts a chloride ion from another source, acting as a Lewis base. For instance, in the presence of alkali metal chlorides like NaCl, aluminum chloride reacts to form Na[AlCl4]. The geometry of the tetrachloroaluminate anion is tetrahedral, with the aluminum atom at the center and the four chlorine atoms at the vertices.