Determination by multi-NMR studies of new stable aluminum complexes with pyrophosphate and fluoride in aqueous solution

Multi-NMR studies (Al-27, F-19, P-31) show that, in the presence of pyropho sphate at pH 7, fluoride and aluminum (Al3+) ions combine in aqueous soluti on, to generate a wide variety of ternary complexes. Among the latter, a ne w class of stable complexes, showing J(FF) and J(FP) coupling constants, ha s been identified in which two octahedral aluminum cations are bound by two pyrophosphate moieties, with a common fluorine atom bridging the two alumi num ions. Both the pyrophosphate groups and the fluoride ion contribute to the stability of these molecules. The existence of J(FF) couplings provides evidence for the octahedral coordination of aluminum in these complexes.