The bonding of vanadium in complexes with humic acid: an electron paramagnetic resonance study

Complexes formed by the addition of vanadyl salts to a peat humic acid have been studied by EPR spectroscopy. The spectra show that the vanadium is in an environment with approximately axial symmetry. The g-values and ⁵¹V hyperfine coupling constants indicate that the vanadium remains in the vanadyl state and is complexed possibly either by oxygen donor groups or by mixed oxygennitrogen donor groups in the humic acid. Identical spectra were obtained when the vanadium was added to the humic acid as the metavanadate ion, thus showing that reduction of vanadium from oxidation state (V) to (IV) occurs.