Raman spectroscopic study of the molecular structure of the uranyl mineral zippeite from Jáchymov (Joachimsthal), Czech Republic

Raman spectra at 298 and 77 K and infrared spectra of the uranyl sulfate mineral zippeite from Jáchymov (Joachimsthal), Czech Republic, K0.6(H3O)0.4[(UO2)6(SO4)3(OH)7]·8H2O, 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, hydroxyls and oxonium ions, and H2O, oxonium, and δ U-OH bending vibrations. Empirical relations were used for the calculation of U-O bond lengths in uranyl R (Å) = f(ν3 or ν1(UO2)2+). Calculated U-O bond lengths are in agreement with U-O bond lengths from the single crystal structure analysis and those inferred for uranyl anion sheet topology of uranyl pentagonal dipyramidal coordination polyhedra. The number of observed bands supports the conclusion from single crystal structure analysis that at least two symmetrically distinct U6+ (in uranyls) and S6+ (in sulfates), water molecules and hydroxyls may be present in the crystal structure of the zippeite studied. Strong to very weak hydrogen bonds present in the crystal structure of zippeite studied were inferred from the IR spectra.