Etude, par RMN large bande du proton, d'hydrogénophosphates et -arséniates d'un métal trivalent (Al, Ga) et de sodium

Eleven aluminum-sodium or gallium-sodium hydrogenphosphates or -arsenates and an aluminum hydrogenarsenate have been studied. The preparation and characteristic properties of the new compounds are described. The wide-band proton-NMR powder spectra have been interpreted by shape function calculation. The models used imply two types of magnetic configuration: one with two spins, the other with three spins located at the apexes of an isosceles triangle. The hydrogen distribution between water molecules and OH groups has been determined and the constitution of the salts has thus been deduced. The constitution of the hydroxyhydrogen salts Na ₃Al(OH)(H XO ₄)( XO ₄) ( X = P, As) is confirmed, but two compounds previously considered as orthoarsenates probably contain condensed anions as expressed by the formula Na M^IIIH ₃As ₃O ₁₁ · 2H ₂O. The method for interpreting NMR spectra is discussed.