IRON-SUBSTITUTED DAWSON-TYPE TUNGSTODIPHOSPHATES - SYNTHESIS, CHARACTERIZATION, AND SINGLE OR MULTIPLE INITIAL ELECTRONATION DUE TO THE SUBSTITUENT NATURE OR POSITION

Isomerically pure alpha 1- and alpha(2)-[Fe(OH2)P2W17O61](7-) and alph a(2)[Fe(OH2)P2Mo2W15O61](7-) were synthesized as aqueous-soluble potas sium salts. The iron-substituted complexes as well as their immediate lacunary precursors have been characterized by IR, UV-visible, and P-3 1 NMR spectroscopies. The acid-base equilibria were studied for the ir on-substituted complexes. The hydroxo compound alpha(2)-[Fe(OH)P2W17O6 1](8-) has also been synthesized, and its elemental analysis is correc t. Its further characterization and study will be published elsewere, For a given pH value, the comparisons of the cyclic voltammograms reve al the influence of the location of the iron-filled site in the framew ork. This influence is strong in the alpha(1) isomer and makes its ele ctrochemistry clearly different from that of the alpha(2) isomer. This observation is ascribed mainly to the large framework distortion indu ced by the vacancy in the alpha(1) site, to subtle variations in the d etailed protonation events which ensue,and to the nature of the iron s ubstituent, which can be considered not to fill ''completely'' the vac ancy. The distortion effect is found to favor the coalescence of waves , as also do lower and lower pH media. The combination of these parame ters appears to be beneficial for the observation of multiple electron ation processes on the first wave of heteropolyanions under very mild conditions.