Aluminium fluoride

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Aluminium fluoride is the inorganic compound with the formula AlF₃. It can be prepared by treating aluminium hydroxide or aluminium metal with HF. As a solid, its structure resembles that of rhenium trioxide, ReO₃, consisting of distorted AlF₆ octahedra.

AlF₃ is refractory, in strong contrast to the other halides of aluminium.^[1] AlCl₃, AlBr₃, and AlI₃ are dimeric in the liquid and evaporate as dimers as well. In the gas phase, at ca. 1000 °C, aluminium fluoride exists as trigonal molecules of D_3h symmetry group. The Al-F bond lengths are 163 pm.

Aluminium fluoride is an important additive during electrolyte aluminium production because it lowers the melting point of the alumina feed and increases the electrolyte‘s conductivity.