Abstract
In aqueous, mineral-acid electrolytes, the cyclic voltammetry of the europium-exchanged Preyssler heteropolyanion, [Eu111P5W30O110]12- , is unique among all the other trivalent-lanthanide-exchanged anions. [Ln111P5W30Oll012-] for Ln≡Ce-Lu. To obtain insights about this issue, we conductedin situ Eu L3-edge XANES IX-ray absorption near edge structure) spectroelectrochemical experiments on an aqueous solution of[EuP5W30O110]12- (5.5 mM) in a sup-porting electrolyte of I M H2SO4 at two extreme potentials. The results demonstrate that the Eu111 ion in the colorless Preyssler anion solution at open circuit potential (+0.21 V vs. Ag/AgCI) is electroactive and is reduced to Eu11 in the resulting heteropoly blue solution through constant-potential bulk elec-trolysis at -0.55 V vs. Ag/AgCI. The reduction is reversible upon complete reoxidation of the reduced anion, the Eu XANES is indistinguishable from that observed at the open circuit potential before electrolysis. This unusual redox behavior of[EuP5W30Oll0]12- may be of technological importance in the area of oxidation catalysis.
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