Crystal structure of the uranyl arsenate mineral h ü gelite, Pb2(UO2)3O2(AsO4)2(H2O)5, revisited: a correct unit cell, twinning and hydrogen bonding

Revisiting the structure of uranyl arsenate mineral h ü gelite provided some corrections to the available structural data. The previous twinning model (by reticular merohedry) in h ü gelite has been corrected. Twinning of the monoclinic unit cell [a   = 7.0189   (7)   Å , b   = 17.1374   (10)   Å , c   = 8.1310   (10)   Å and β   = 108.904   (10) ° ], which can be expressed as a mirror in [100], leads to a pseudo-orthorhombic unit cell (a   = 7.019   Å , b   = 17.137   Å , c   = 61.539   Å and β   = 90.02 ° ), which is eight times larger, with respect to the unit-cell volume, than a real cell. Moreover, the unit cell of chosen here and the unit cell given by the previous structure description both lead to the same supercell. A new structure refinement undertaken on an untwinned crystal of h ü gelite resulted in R   = 4.82% for 12   864 reflections with Iobs> 3 σ (I) and GOF   = 1.12. The hydrogen-bonding scheme has been proposed for h ü gelite for the first time.

Source: Acta Crystallographica Section B - May 14, 2021 Category: Chemistry Authors: Pl á š il, J. Pet ř í č ek, V. Š k á cha, P. Tags: h ü gelite uranyl arsenate crystal structure twinning JANA2006 reticular merohedry research papers Source Type: research