Complexation in Metal Halide Vapors—A Review

A large number of gaseous complexes composed of metal fluorides and metal chlorides have been identified and investigated so far. The data are summarized in various reviews. Our knowledge of the gaseous homo‐ and hetero‐complexes of metal bromides and metal iodides is less than that of the corresponding fluoride and chloride complexes although they are of considerable practical interest for metal halide lamps. A survey of the review articles on gas‐phase complexation and on the various methods used for its investigation is given. By far the most complete information was obtained by the method of Knudsen effusion mass spectrometry. The potential of this method is described with respect to its use for the study of complexation in metal halide lamps. An account of the gaseous homo‐ and hetero‐complexes observed in metal iodide and metal bromide vapors is given. The enthalpy and entropy changes as well as the equilibrium constants determined for the dissociation reactions of the complexes are summarized and discussed. The equations for the partial pressures of the various complexes are tabulated. The data are discussed with respect to their practical significance for metal halide lamps.