Spectroscopic studies of aluminum and gallium complexes with oxalate and malonate in aqueous solution

The local structures of Ga(III) in aqueous oxalate and malonate complexes were studied by means of Ga K-edge EXAFS spectroscopy. Irrespective of the number and type of coordinated ligands, the EXAFS results showed very regular first coordination shells consisting of six oxygen atoms. Scattering paths from more distant atoms revealed that both oxalate and malonate form mononuclear chelate structures where one oxygen from each carboxylate group binds to Ga(III). Again, very little variation in bond distances and no changes in coordination modes were detected as the number of ligands coordinated to Ga(III) was varied. Based on the very close resemblance of IR spectra of oxalate and malonate complexes of Al(III), and the corresponding complexes of Ga(III), it is believed that the local structures of the Al(III) complexes are similar to those of the Ga(III) complexes in terms of ligand coordination modes and distortions. This conclusion was corroborated by results from theoretical frequency calculations.