Effect of Ionothermal Conditions on the Crystallization of Organically Templated Uranyl Sulfate Compounds

Abstract

Seven novel uranyl sulfate compounds were crystallized by ionothermal synthesis methods through systematic changes in experimental conditions. The parameters explored were temperature, soak time, cooling rate, and reactants, including uranium­(VI) salt, a uranium­(VI) concentration in the ionic liquid, and the pH by cosolvent addition. The ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate (EMIm-EtSO4) was used in each experiment. Although the seven uranyl sulfate compounds all contained the EMIm organic cation of the ionic liquid, the different synthetic conditions produced varying uranyl coordination environments that resulted in discrete crystal structures. The impact of the ionothermal synthetic conditions on the resulting crystal structures is discussed.

Targeting Diverse Bridging Motifs within Actinide Borosulfates and Establishing an Unconventional Structural Hierarchy

“…The symmetric stretch of the uranyl ion in the compounds studied here (895–907 cm –1 ) is in accord with uranyl sulfates . The spectrum of TSUBOB-1 contains symmetric and antisymmetric stretching bands of (SO 4 ) at 991, 1002, 1067, 1153, and 1179 cm –1 , as well as in the spectrum of TSUDS at 949, 976, 1053, and 1108 cm –1 …”

“…25 The spectrum of TSUBOB-1 contains symmetric and antisymmetric stretching bands of (SO 4 ) at 991, 1002, 1067, 1153, and 1179 cm −1 , as well as in the spectrum of TSUDS at 949, 976, 1053, and 1108 cm −1 . 26 Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The DRIFTS spectra of TSUBOS-1, TSUBOB-1, and TSUDS are shown in Figures S5−S7.…”

Exploring the Role of Organic Functional Groups in the Ionothermal Synthesis of Uranyl Phosphate Materials

“…This heat treatment with a lower soak temperature and faster cooling rate produces kinetically favored products. [42] Because the uranyl dibutyl phosphate compounds form with both heat treatments while the uranyl diethyl phosphate compound does not, it is possible that the butyl groups provide greater stabilization of the crystal structure (i. e. a more thermodynamically favored product) than the ethyl counterparts. In changing the organic functional group to methyls, the uranyl ion adopts a different coordination, topology, and thus crystal packing in compound 1, which likely allows the even shorter methyl groups to provide enough van der Waals interactions to stabilize the overall crystal structure.…”

“…Overall, 30 reactions incorporated changes in co‐solvents with variable pH, heat treatments, and ionic liquid phosphate anion with variable lengths of the organic functional groups. We previously showed that co‐solvents can affect topologies of uranyl sulfate structural units in conjunction with different heat treatments that promote crystal growth of kinetically or thermodynamically favored products [42] . The main focus here was to apply optimal parameters from the previous study to synthesize uranyl phosphate compounds to investigate the role of the ionic liquid anion in crystal structure stabilization.…”

“…Chain 1 is an isostructural uranyl diethyl phosphate compound that formed under similar co‐solvent systems but only with heat treatments at 80 °C for 72 hours with 2.5 °C/min cooling. This heat treatment with a lower soak temperature and faster cooling rate produces kinetically favored products [42] . Because the uranyl dibutyl phosphate compounds form with both heat treatments while the uranyl diethyl phosphate compound does not, it is possible that the butyl groups provide greater stabilization of the crystal structure (i. e. a more thermodynamically favored product) than the ethyl counterparts.…”