Density-functional theory (DFT) methods were used for investigations on the
aluminum-hexaaquo complex and on aqueous aluminum-acetate complexes. Solve
nt effects were computed by means of the polarized continuum model (PCM). E
xtensive basis set studies and comparison of several functionals lead to ef
ficient and accurate procedures which were applied to the computation of al
uminum-acetate complexes. A variety of structural arrangements such as mono
dentate or bidentate with respect to the bonding of the carboxylate group o
r cis/trans with respect to the relative position of two acetate molecules
were considered, Delta H and Delta G values were calculated for the substit
ution reaction of water molecules in the aluminum-hexaaquo complex by aceta
te anions, Characteristic differences in Delta S were found depending on th
e number of water molecules released per acetate, Overall, we find that mon
odentate structures are only slightly preferred over bidentate ones and tha
t we expect a relatively complicated system of chemical equilibria without
any dominant complex.