Mossbauer, 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

摘要

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). Mossbauer spectra of the frozen aqueous solutions of iron(III) with indole-3-alkanoic acids as ligands (L), showed parallel reactions between Fe3+ and the 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 Mossbauer 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, Mossbauer spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopic techniques. The complexes were soluble in some organic solvents. So, Mossbauer, 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 mu-dihydroxo-bridging structure of the dimer: [L2Fe <(OH)(2)> FeL2] (where L is indole-3-propionate, -acetate or -butyrate).