CHARGE-DISTRIBUTION IN PARTICLES OF TRANSITION-METAL CHELATE COMPLEXES AS THE FACTOR DETERMINING THEIR REDUCTION KINETICS AND THE OUTER-SPHERE ASSOCIATION MECHANISM

The polarographic behavior of the Co(3+), Fe(3+), Cr(3+), and vanadyl complexes with ethylenediaminetetraacetate (edta) and its analogs cont aining aliphatic substituents is studied. It is shown that the slopes of polarographic waves measured on a dropping mercury electrode for ch elate complexes of cobalt and iron that reduce on the positively charg ed mercury surface are practically independent of the ligand nature, w hile, for chromium and vanadyl complexes, which reduce at negative cha rges of the electrode surface, the charge-transfer rate substantially decreases with introduction of substituents. The ratio between the red uction rate constants of [Medta] and [Mcydta] (where cydta is diaminoc yclohexanetetraacetate) at a zero overpotential are similar to 1 and s imilar to 10 for M = Co and Cr, respectively. These results, as well a s the data of spectrophotometric studies of the formation of chelate-c omplex/iodide(thiosulfate) anion-anion pairs are discussed with due al lowance made for a nonuniform charge distribution in complex anions, w hich are dipoles with the positive pole near the nitrogen atoms.