Substitution reactions and luminescence spectra of the mixed complexes [ReClxBr6–x]2–

Abstract

Reaction of [ReBr₆]^2– with aqueous HCl followed by rapid precipitation of Cs₂[SnCl₆] from the reaction medium produces homogeneous crystalline solids which luminesce strongly under blue or ultraviolet excitation. Analysis of the spectra obtained at low temperatures with selective excitation shows the presence of [ReCl₅Br]^2–, cis-[ReCl₄Br₂]^2–, and fac-[ReCl₃Br₃]^2–. The corresponding reaction starting from [ReCl₆]^2– with aqueous HBr produces predominantly [ReBr₆]^2– together with the intermediates trans-[ReCl₄Br₂]^2– and trans-[ReCl₂Br₄]^2– even under conditions when much of the [ReCl₆]^2– remains unchanged. In contrast to our earlier study of the corresponding technetium(IV) complexes, a trans effect dominates the substitution processes in the rhenium(IV) compounds.