Iron(III)–phosphonate complexes

B.C. BARJA; J. HERSZAGE; M. DOS SANTOS AFONSO

POLYHEDRON

Año: 2001 vol. 20 p. 1821 - 1830

0277-5387

The Fe(III) complexes of methylphosphonic acid (MPA), Fe2(CH3PO3)3·3H2O, and aminomethylphosphonic acid (AMPA), FeOH(NH3CH2PO3)2·H2O, were prepared in solid state and obtained as fine powders. In aqueous solution, both ligands form a complex with a 1:1 Fe(III) to ligand ratio and the proposed structures for these complexes are the monodentate protonated [FeO–PO(OH)CH3]2+ and the deprotonated chelate [FeO2–POCH2NH3]2+, respectively. These results permit the evaluation of the chemical bonds involved in the complex of Fe(III) and glyphosate, (N-phosphonomethylglycine, PMG) in solid state and the formula FeOH(−OOC–CH2–NH2 +–CH2–PO3 2−)·2.25H2O is proposed. While the phosphonate moiety of these ligands always bonds to the metal ion, the amino group remains protonated and not coordinated. The carboxylic acid of PMG only coordinates the Fe(III) in solid state, not in aqueous solution. Infrared spectra of the PMG complexes of Al(III) and Co(III) in the solid state are also presented and compared with the Fe(III) complex. Elemental microanalysis, UV–Vis, atenuated total reflection–Fourier transformed infrared (ATR–FTIR) spectroscopy, inductively coupled plasma (ICP) emission spectrometry, AAS and X-ray powder diffraction were used for the characterization of the complexes. © 2001 Elsevier Science Ltd. All rights reserved.