Pulse and Continuous Radiolyses of the Europium and Neodymium Decatungstate Anions in Aqueous Solution

We have studied the behavior of aqueous solutions of the [M (3+) (W 5 ‐O 18 (6‐) ) 2 ] 9− complexes (M = Eu or Nd) under pulse and continuous radiolysis conditions. Both complexes react with e − aq at a diffusion controlled rate. For the Nd 3+ complex in solution containing 1% 2‐propanol, the decay of the e − aq absorption was accompanied by the formation of a broad absorption band in the visible (λ max 600–650 nm), with a further increase in absorption up to 2 ms. For the Eu 3+ complex under the same conditions, the decay of the e − aq absorption was accompanied by the formation of an absorption maximum at ∼370 nm, which is characteristic of Eu 2+ species. On a longer time scale, a relatively intense absorption arose in the visible (λ max 600–650 nm) according to a complicated kinetic behavior. The two complexes exhibited a quite similar behavior in continuous radiolysis experiments. Blue products (λ max 600–650 nm) were formed and, for the Eu 3+ complex, the disappearance of the Eu 3+ emission was observed. Even after high irradiation doses, the absorption (and, for Eu 3+ , emission) spectra of the solutions were quantitatively regenerated by air oxidation. The behavior of the Nd 3+ complex is interpreted on the basis of the reduction of a W 5 O 18 6− ligand by e − aq and alcohol radicals, followed by protonation. For the Eu 3+ complex, the reduction by e − aq causes mainly the formation of a Eu 2+ complex. On a longer time scale, protonation and/or reaction with alcohol radicals drive back the electron from Eu 2+ to the W 5 O 18 6− ligands, with formation of stable blue products.