VIBRATION SPECTRUM OF PHOSPHORIC-ACID .6. VIBRATION SPECTROSCOPY AND NUCLEAR-MAGNETIC-RESONANCE OF ALUMINUM PHOSPHATE COMPLEX-FORMATION IN THE SYSTEM ALCL3-H3PO4-H2O

By Raman-, IR-, Al-27 and P-31-NMR spectroscopy we investigated the formation of complexes between Al3+ and phosphoric acid in the system AlCl3-H3PO4-H2O at 22-degrees-C. In equilibrium to the Hexaquo-AI(III)-ions phosphato-complexes of aluminium were found. In the course of this study we investigated in dependence of the molar ratio Al:P the amount of ''free'' and complexed aluminium, and of ''free'' and complexed phosphoric acid. The phosphoric acid is bonded to the aluminium via oxygen of the phosphorylgroup and is of C3upsilon symmetry, like in the ''free'' state. The main ligand in these acidic solutions is the phosphoric acid, and to a smaller part the H2PO4-ion. We could exclude HPO42- and PO43- as ligands, and also the polymeric phosphoric acids (e.g. H6P2O8) postulated by earlier investigators. From Raman- and IR-spectroscopic measurements followed, that such H-bonded polymeric acids do not occur. Six P-31 NMR lines were observed at -15-degrees-C, they were interpreted as representing ''free'' phosphoric acid and a series of five different aluminium-phosphato-complex species of up to now unknown composition.