An EXAFS and HR-XANES Study of the Uranyl Peroxides [UO2(η2-O2)(H2O)2].nH2O (n = 0,2) and Uranyl (Oxy)hydroxide [(UO2)4O(OH)6].6H2O

Abstract

The solid-sate structures of the two uranyl peroxides studtite, [UO 2 ( ? 2 -O 2 )(H 2 O) 2 ]?2H 2 O, and metastudtite [UO 2 ( ? 2 -O 2 )(H 2 O) 2 ] have been determined by U ? L 3 edge extended X-ray absorption fi ne structure (EXAFS) spectroscopy and show that upon removal of the interstitial water in studtite there are structural changes with a small shortening of the U ? O peroxo and small lengthening of the U ? O yl bonds. High- energy resolution X-Ray absorption near edge structure (HR-XANES) spectroscopy has been used to probe the di ff erences in the local electronic structure and, supported by ab initio FEFF9.5.1 calculations, dehydration causes a shift to higher energies of the occupied O p-DOS and U d- and f-DOS of meta- studtite. The HR-XANES spectrum of schoepite, [(UO 2 ) 4 O(OH) 6 ]?6H 2 O,hasbeenmeasuredastheWhiteLine intensity can give information on the mixing of metal and ligand atomic orbitals. There is an indication for higher degree of ionicity for the U ? OH bond in schoepite compared to the U ? O 2 bond in studtite