Influence of heterocyclic N-donors on the structural topologies and vibrational spectra of uranyl selenate phases

Abstract

Uranyl (U(VI)O22+) selenate compounds represent a well-studied family of structures with diverse structural arrays. Differences in the overall topology and bonding with the uranyl cation combined with additional intermolecular interactions can lead to variation in the resulting spectroscopic signals. In the current study, we evaluated the structural chemistry and vibrational spectroscopy for uranyl selenates crystallized with heterocyclic N-donors. Five compounds ((C4H12N2)[(UO2)(SeO4)2(H2O)]·H2O (USe_pip), (C4H5N2)2[(UO2)(SeO4)2(H2O)] (USe_pyrdz), (C5H5N)2[(UO2)2(SeO4)3(H2O)] ∙ 3H2O (USe_pyrmd), (H3O)2(C4H5N2)2[(UO2)3(SeO4)5(H2O)]·H2O (USe_pyrz), and (C5H6N)2[(UO2)2(SeO4)3(H2O)] ∙ 3H2O (USe_pyr)) were characterized using X-ray diffraction (single-crystal and powder) and vibrational (Raman and IR) spectroscopy. Two one-dimensional (1-D) chain and three two-dimensional sheet (2-D) topologies were identified and classified based upon previous graphical representations. Overall, the arrangement of the heteroatoms could be linked to the hydrogen bonding network associated with the heterocycles and selenate anions. Vibrational spectra of the solid-state compounds were complex, with multiple bands associated with the uranyl cation, selenate anion, and heteroatoms. The ν1 symmetric stretching band of the uranyl was relatively consistent across all compounds, whereas differences were observed for the ν3 asymmetric band between the 1-D and 2-D structural topologies.