The chemistry of iron in biosystems-V Study of complex formation between iron(III) and tartaric acid in alkaline aqueous solutions.

Complex formation between Fe(III) and tartaric acid (H(2)L) has been studied in O.5M NaNO(3) medium at 25 degrees by potentiometry at pH 4.5-11. The following complex species and corresponding values of the stability constants (charges omitted) are proposed: 2Fe + 2L + 5H(2)O --> Fe(2)(OH)(5)L(2) + 5H(+); log* beta(-522) = 4.95 Fe + L + 3H(2)O --> Fe(OH)(3)L + 3H(+); log* beta(-311) = -1.55 Fe + L + 5H(2)O --> Fe(OH)(5)L + 5H(+); log* beta(-511) = -21.2 These results are in good agreement with those reported for this system in acid. The results may be presented as the degeneration of the "core + link" mechanism observed in the acidic zone. Structures are suggested for the complex species formed.