Abstract: Progress in the development of phenomenological models for the microscopic interactions in the halides of polyvalent metals is reviewed, with main attention to neutral and ionized molecular states and to the melts of these materials. The following physical problems are discussed: (1) bond bending in the molecules of the alkaline-earth halides; (2) binding of molecular dimers and halogen transfer reactions relevant to the melts of trivalent metal halides; (3) stability of molecular ions in liquid mixtures of polyvalent metal halides and alkali halides; and (4) stability of molecular ions and reduced-valence states in molten cryolite under addition of sodium metal.

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