Isomerization of Keggin Al13 Ions Followed by Diffusion Rates.

ABSTRACT

The solution chemistry of aluminum has long interested scientists due to its relevance to materials chemistry and geochemistry. The dynamic behavior of large aluminum-oxo-hydroxo clusters, specifically [Al13 O4 (OH)24 (H2 O)12 ]7+ (Al13 ), is the focus of this paper. 27 Al NMR, 1 H NMR, and 1 H DOSY techniques were used to follow the isomerization of the ϵ-Al13 in the presence of glycine and Ca2+ at 90 °C. Although the conversion of ϵ-Al13 to new clusters and/or Baker-Figgis-Keggin isomers has been studied previously, new 1 H NMR and 1 H DOSY analyses provided information about the role of glycine, the ligated intermediates, and the mechanism of isomerization. New 1 H NMR data suggest that glycine plays a critical role in the isomerization. Surprisingly, glycine does not bind to Al30 clusters, which were previously proposed as an intermediate in the isomerization. Additionally, a highly symmetric tetrahedral signal (δ=72 ppm) appeared during the isomerization process, which evidence suggests corresponds to the long-sought α-Al13 isomer in solution.