On the acid-base chemistry of the Keggin polymers: GaAl12 and GeAl12.
The acid-base properties of GaAl12 and GeAl12 molecules have been investigated and compared to those of the Al13 molecule using alkalimetric titration at two concentrations of the Keggin complex. As in the case of Al13, the positive charge of both GaAl13 and GeAl12 is entirely lost within half a pH unit if the concentration of the Keggin molecules is low (1.25 microM). We find that GeAl12 is significantly more acidic than either the GaAl12 or the Al13 molecules. As positive charge is removed from the Keggin complexes by deprotonation, they tend to aggregate, resulting in titration curves that flatten out at higher Z values. Molecule-molecule interactions appear to be more distinct at elevated concentrations of the Keggin complexes (12.5 microM).