Monatshefte ffir Chemie 123, 1071 - 1079 (1992) Monatshefte fiir Chemie Chemical Monthly © Springer-Verlag 1992 Printed in Austria Voltammetric and Titrimetric Study of Acid-Base Properties of Some p-oxo Dimeric Iron(III) Complexes in DMF Ljiljana S. Jovanovi~*, Nikola J. Evil, Luka J. Bjelica, Biljana F. Abramovi~, Ferenc F. Gafil and Nfindor L. Rehfik Institute of Chemistry, Faculty of Sciences, University of Novi Sad, YU-21000 Novi Sad, Yugoslavia Summary. The acid-base properties of the g-oxo bridged dimeric iron complexes [FeL]20 with the ligands based on S-alkyl-l,4-bis(substituted salicylidene)isothiosemicarbazide and a tetramer with S- methyl-1,4-bis(salicylidene)isothiosemicarbazide, {[FeL]20}213.I2, were investigated by cyclic voltam- metry at glassy carbon electrode in DMF. Studies were carried out in the presence of either a weak (phenol) or a strong (HC104 aq.) acid. The stoichiometry of the reaction, changes in the general voltammetric pattern and the electrode reaction mechanism were discussed. These studies served as the basis for three-electrode amperometric titrations to determine the content of several of these complexes. Keywords. Iron complexes; Acid-base properties; Cyclic voltammetry; Titrimetric determination; Three-electrode amperometry. Voltammetrischeund titrimetrischeUntersuchung der S~iure-Base-Eigenschaften einiger g-oxo dimerer Eisen(III)-Komplexe in DMF-L/isungen Zusammenfassung. Die Sfiure-Base-Eigenschaften einiger dimerer ~-oxo-Eisen(III)-Komplexe [FeL]20 mit Liganden auf Basis yon 1,4-bis(substituierten Salicyliden)S-(alkyl)isothiosemicarbaziden sowie eines tetrameren Komplexes mit 1,4-Bis(salicyliden)S-methylisothiosemicarbazid, {[FeL]20}213.I2, wurden mittels zyklischer Voltammetrie an der Glaskohlenstoffelektrode in DMF- L6sungen untersucht. Die Messungen wurden in Gegenwart entweder einer schwachen (Phenol) oder einer starken (HC104 aq.) Sfiure ausgeffihrt. Die St6chiometrie der Reaktion, die ~nderungen der voltammetrischen Kurven und der Elektroden-Reaktionsmechanismus wurden diskutiert. Diese Un- tersuehungen stellten eine Basis ffir Drei-Elektroden amperometrische Titrationen dar, die ffir die Bestimmung des Gehalts einiger dieser Komplexe angewendet wurden. Introduction The oxo-bridged dimeric iron complexes constitute a group of compounds which are of considerable interest, primarily for their apparent similarity to some bio- logically important systems [1]. Besides, many of these dimers show unusual mag- netic and spectroscopic properties, so that their physicochemical [1] and structural [2] studies can be of particular interest. Because the monomer-dimer equilibria