The formation and stability of [EuP5W30O110](12-) and [AmP5W30O110](12-)

A comparison of the standard reduction potentials of Eu3+ and Am3+, as well as their similar ionic radii, suggest that Am in the Preyssler anion, [AmP 5W30O110](12-), may be reduced under an applied potential. However, cyclic voltammetric studies performed in a noncomplexing electrolyte, together wit h XANES and EXAFS data, consistently demonstrate that Am is trivalent when encrypted in [AmP5W30O110](12-) There is no evidence of Am3+ reduction, eve n at the lowest potentials probed. A comparison of bond distances of the tr ivalent Am analog, determined from EXAFS spectroscopy, with those of other tetravalent f ions shows a correlation with ionic radii that appears indepe ndent of the charge on the ion. (C) 2000 Elsevier Science S.A. All rights r eserved.