31P NMR and raman spectroscopic studies on binding isomerism and isomerization equilibrium of aluminium complexes of monomeric phosphorus oxoanions in solution

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The binding isomerism of Al 3+-phosphinate, -phosphite and -phosphate complexes was investigated by using 31P NMR and Raman spectroscopies in solution. It was found that there are two types of binding mode in the complexes: a non-chelate binding mode in which the monomeric phosphorus oxoanions coordinate to the aluminium ion as monodentate ligands, and a chelate binding mode in which the monomeric phosphorus oxoanions coordinate to the aluminium ion as bidentate ligands. Furthermore, an isomerization equilibrium analysis was made on the chelate and the non-chelate isomers. The isomerization constants, K non-chel chel, for formation of the chelate isomer from the non-chelate one, were evaluated to be 2.8 for the AlPH 2O 2 2+ complex, 3.7 for the AlPHO 3 + complex and 3.9 for the AlPO 4 complex.