Publications
Speciation in the AlCl3/SO2Cl2 catholyte system
The fundamental chemical behavior of the AlCl{sub 3}/SO{sub 2}Cl{sub 2} catholyte system was investigated using {sup 27}Al NMR spectroscopy, Raman spectroscopy, and single-crystal X-ray diffraction. Three major Al-containing species were found to be present in this catholyte system, where the ratio of each was dependent upon aging time, concentration, and/or storage temperature. The first species was identified as [Cl{sub 2}Al({mu}-Cl)]{sub 2} in equilibrium with AlCl{sub 3}. The second species results from the decomposition of SO{sub 2}Cl{sub 2} which forms Cl{sub 2}(g) and SO{sub 2}(g). The SO{sub 2}(g) is readily consumed in the presence of AlCl{sub 3} to form the crystallographically characterized species [Cl{sub 2}Al({mu}-O{sub 2}SCl)]{sub 2} (1). For 1, each Al is tetrahedrally (T{sub d}) bound by two terminal Cl and two {mu}-O ligands whereas, the S is three-coordinated by two {mu}-O ligands and one terminal Cl. The third molecular species also has T{sub d}-coordinated Al metal centers but with increased oxygen coordination. Over time it was noted that a precipitate formed from the catholyte solutions. Raman spectroscopic studies show that this gel or precipitate has a component that was consistent with thionyl chloride. We have proposed a polymerization scheme that accounts for the precipitate formation. Further NMR studies indicate that the precipitate is in equilibrium with the solution.