Aja. Aquino et al., A density functional theoretical study on solvated Al3+-oxalate complexes:structures and thermodynamic properties, PHYS CHEM P, 2(13), 2000, pp. 2845-2850
Density functional theory calculations using split-valence polarized basis
sets augmented by diffuse s and p functions on the carbon and oxygen atoms
were carried out for the complexes of hydrated Al3+ with oxalic acid, and t
he oxalate mono- and dianions. Monodentate and bidentate structures with up
to three ligands have been computed. The polarized continuum model was use
d to study the solvent effect on the structures and stabilities of the comp
lexes. Reaction energies for the replacement of water molecules in the alum
inum-hexaaquo complex by oxalate ligands have been computed. Based on a det
ailed thermodynamical analysis, characteristic differences in the formation
of mono- and bidentate structures were found. In the former case the entro
py contributions to Delta G are rather small, whereas in the latter case th
ey are substantial. Thus, the formation reactions for the monodentate compl
exes are energy-driven whereas those for the bidentate complexes are entrop
y-driven. In agreement with experiment, the most dominant complex in soluti
on is [AlOx(3)](3-). From the complexes with oxalic acid and the partially
deprotonated form HOx(-), only the latter should give stable bidentate comp
lexes in solution.