Boron halides as reagents in inorganic syntheses. Part IV. Preparation of tris-µ-chloro-hexabromo-triangulo-trirhenium(III)(3Re–Re) and Re3I9; halogen exchange reactions with Re3Cl9 and the crystal structure of a sublimation product of tris-µ-chloro-hexabromo-triangulo-trirhenium(III)(3Re–Re)

Abstract

The interaction of an excess of boron tribromide and rhenium trichloride in the condensed phase affords the new mixed halide Re₃Br₆Cl₃, identified by u.v. and far-i.r. spectra. Mass spectra confirm this approximate composition but do not provide a suitable method for characterising a mixed halide Re₃(Br,Cl), because of redistribution equilibria; successive high temperature sublimation of Re₃Br₆Cl₃ affords as the most volatile component a compound which progressively approximates to Re₃Cl₉. Repeated sublimation of the mixed halide afforded a crystal suitable for X-ray study. This was identified by a complete single-crystal X-ray study as probably Re₃Br₈Cl (although the study does not distinguish this from mixtures of Re₃Br₉Cl and Re₃BrC₆l₃ or Re₃Br₇Cl₂). The structure of these halides is based on the triangular Re₃ systems in which terminal (preferentially) and bridging (subsequently) chloride ligands are replaced by bromide ligands. Interaction of boron tri-iodide and rhenium trichloride affords rhenium tri-iodide.