Mössbauer, vibrational spectroscopic and solution X-ray diffraction studies of the structure of iron(III) complexes formed with indole-3-alkanoic acids in acidic aqueous solutions

The chemical reactions between iron(III) and indole-3-acetic (IAA), -propionic (IPA), and -butyric (IBA) acids were studied in acidic aqueous solutions. The motivation of this work was that IAA is one of the most powerful natural plant-growth-regulating substances (phytohormones of the auxin series). Mössbauer spectra of the frozen aqueous solutions of iron(III) with indole-3-alkanoic acids as ligands (L), showed parallel reactions between Fe3+ and the K. Kovács · E. Kuzmann · A. Vértes Research Group for Nuclear Techniques in Structural Chemistry, Hungarian Academy of Sciences; Department of Nuclear Chemistry, Eötvös Loránd University, 1518, Budapest 112, Hungary email: [email protected] A. A. Kamnev ( ) Laboratory of Biochemistry of Plant-Bacterial Symbioses, Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, 410049 Saratov, Russia e-mail: [email protected] J. Mink · C. Németh · T. Megyes · T. Grósz Chemical Research Center of the Hungarian Academy of Sciences, 1525, Budapest, P.O. Box 77, Hungary J. Mink Analytical Chemistry Research Group, Hungarian Academy of Sciences and Faculty of International Technology, Research Institute of Chemical and Process Engineering, University of Veszprém, Veszprém, 8200, Hungary H. Medzihradszky-Schweiger Research Group of Peptide Chemistry, Department of Organic Chemistry, Eötvös Loránd University, 1518, Budapest 112, Hungary ligands. Partly, it resulted in a complex formation which precipitated in aqueous solution and partly, in a redox process with iron(II) and the oxidised indole-3-alkanoic acids as products. The Mössbauer parameters of the Fe2+ species suggested a hexaaquo coordination environment. The chemical composition and coordination structure of the precipitated complexes were investigated using elemental analysis, Mössbauer spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopic techniques. The complexes were soluble in some organic solvents. So, Mössbauer, FTIR and solution X-ray diffraction measurements were carried out on the solution of complexes in acetone, hexadeutero acetone and methanol, respectively. The data obtained supported the existence of the μ-dihydroxo-bridging structure of the dimer: [L2Fe<(OH)2>FeL2] (where L is indole-3propionate, -acetate or -butyrate).