Molecular structure of the uranyl mineral zippeite - An XRD, SEM and Raman spectroscopic study

Abstract

Raman spectra at 298 and 77 K and infrared spectra of the uranyl sulfate mineral zippeite, K2[(UO2)6 (SO4)3 O(OH)6]. 4H2O, were studied. Observed bands were tentatively attributed to the (UO2)2+ and (SO4)2- stretching and bending vibrations, the OH stretching vibrations of water molecules and hydroxyls, H2O bending vibrations and libration modes, and δ U-OH bending vibrations. Empirical relations were used for calculation of U-O bond lengths in uranyl R = f(v3 or v1 (UO2)2+) Å. This was found in agreement with U-O bond lengths from the single crystal structure analysis. The number of observed bands supports the conclusion from single crystal structure analysis that at least two symmetrically distinct U6+ (in uranyl) and S6+ (in sulfate), and water molecules and hydroxyls may be present in the zippeite crystal structure. Some O-H...O bond lengths were attributed to the hydrogen-bonding network in zippeite crystal structure. © by E. Schweizerbart'sche Verlagsbuchhandlung 2005.