Gaseous Chloride Complexes with Halogen Bridges—Homo‐Complexes and Hetero‐Complexes

Abstract

The chemistry of the gaseous halide complexes which have been observed in large numbers in recent years is discussed for the example of chlorides.Homo‐complexes—dimeric or polymeric chloride molecules containing chlorine‐bridge linkages [e.g.(NaCl)_n,n= 2—4; (CuCl)_n,n= 2—5; (BeCl₂)_n,n= 2—4; Pd₆Cl₁₂]—occur through broad areas of the Periodic Table. Comparison of the dissociation enthalpy of such molecules with the vaporization enthalpy of the liquid chlorides is particularly informative.Hetero‐complexesare formed from different chloride molecules by linkage through Cl bridges. Not only 1:1 complexes (e.g.NaAlCl₄, TIPbCl₃, KThCl₅, CdPbCl₄, AlUCl₈) but also larger molecules (e.g.CoAl₂Cl₈, CrAl₃Cl₁₂, Cu₂UCl₆, In₂UCl₁₀) are known. Types of formulas, structures, and above all the formation enthalpies of such complexes are discussed critically. Hetero‐complexes are useful in chemical transport reactions, as aids in syntheses, and in gas‐chromatographic separations (lanthanoids, actinoids). They also play a part in many industrial processes (chlorination of ores) and in recently developed types of high‐pressure discharge tubes.