Ferroverdin: Cation variation and recognition of isomeric tris chelate geometries by iron oxidation states

Abstract

Synthetic ferroverdins, NaFe11(RQ)3 afford trinuclear M[Fe(RQ)3]2 upon reaction with bivalent ions (M2+). A probable bonding mode is considered. Ferric ions oxidise ferroverdin to ferriverdin, FeIII(RQ)3. Both fac and mer isomers can be observed for ferro- and ferriverdins but at equilibrium the preferred isomers are fac for ferro- and mer for ferriverdin. Mismatch in geometry with oxidation state gets spontaneously corrected by isomerisation. Equilibrium constants, isomerisation rates, redox potentials and EPR spectra are examined. A study on the pattern of isomer population as a function of oxidation for other 3d analogues of ferro- and ferriverdin is initiated. © 1990 Indian Academy of Sciences.