Potentiometric, Raman spectroscopy and DFT study of pentaaqua glycine aluminum(III) complex in aqueous solution

Isomerization of Keggin Al13 Ions Followed by Diffusion Rates

“…Control experiments, which only consisted of ϵ‐Al 13 and glycine in D 2 O (Figure SI1‐2 in the Supporting Information), confirmed that the additional signals diffuse at a rate similar to glycine bound to ϵ‐Al 13 ( ϵ‐Al 13 (Gly) x : 2.01±0.02×10 −10 m 2 s −1 ). The fact that the slowest diffusing species’ signals are all singlets indicates that when the glycine molecules bond to the cluster they have rotational freedom, such as would be achieved by binding through only the carboxylic acid moiety …”

“…The fact that the slowest diffusings pecies' signals are all singlets indicates that when the glycine molecules bond to the cluster they have rotational freedom, such as would be achieved by binding through only the carboxylic acid moiety. [16,17] The 1 HNMR data showed that after the first day of heating, most of the glycineb ound to cluster-sized species is no longer e-Al 13 (Gly) x ,e ven thought he 27 Al NMR data indicated am uch sloweri somerization process and that e-Al 13 still exists in solution. These resultss uggest that binding to glycine affects isomerization;t herefore, upon heating, the e-Al 13 (Gly) x quickly becomes d-Al 13 (Gly) x .S urprisingly,t he 1 HDOSY NMR data indicated that although there is al arge amount of Al 30 in solution, it is apparently not an essential intermediate to the glycine-isomerization process.…”