IMPLICATIONS OF THE UNUSUAL REDOX BEHAVIOR EXHIBITED BY THE HETEROPOLYANION [EUP5W30O110](12-)

We report on the novel electrochemical behavior of the heteropolyanion [EuP5W30O110](12-), with specific emphasis on the valence of Eu in bo th the oxidized and reduced forms of the anion. In aqueous electrolyte s, the P-W-O framework is electroactive, and can reversibly accept up to 10 electrons before the potential becomes reducing enough for H-2 e volution. Europium L-3-edge X-ray absorption near edge structure (XANE S) results demonstrate that Eu is also electroactive under the same co nditions. The implications of this work will be discussed in terms of their contribution to long-standing questions about intermediate-valen t materials.