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