Pyridinderivate als Komplexbildner II. Komplexbildung des dreiwertigen Eisen‐Ions mit Pyridincarbonsäuren

Abstract

Abstract The formation of bivalent iron complexes with the anions of picolinic acid and dipicolinic acid has been described in a preceding publication. The behavior of iron has now been investigated with the aid of oxidation‐reduction potentials Fe III /Fe II measured in presence of a large excess of the organic ligand on solutions each with constant pH and total [Fe III ] t , and over a wide range of variation of these two factors. Dipicolinic acid forms simply the complexes Fe(Dipic) + and Fe(Dipic) 2 − , already at very low pH‐values. The situation with monopicolinic acid is different. In spite of the bidentate nature of this ligand, only 1:1 and 1:2 complexes are formed with Fe 3+ , the latter forming Fe(Pic) 2 OH already below pH = 3, and its dimer Fe 2 (Pic) 4 (OH) 2 if [Fe III ] t is above 10 −4 . The optical behavior of this dimer is very similar to the absorption of Fe 2 (OH) 2 4+ , suggesting an analogous structure: magnified image .