Influence of the First Coordination of Uranyl on Its Luminescence Properties: A Study of Uranyl Binitrate with N,N-Dialkyl Amide DEHiBA and Water

Abstract

Uranyl binitrate complexes have a particular interest in the nuclear industry, especially in the reprocessing of spent nuclear fuel. The modified PUREX extraction process is designed to extract U(VI) in the form of UO 2 (NO 3 ) 2 (L) 2 as it has been confirmed by EXAFS, XRD and TRLFS measurements. In this study, the L ligands are two molecules of N,N-di-(ethyl-2-hexyl)isobutyramide (DEHiBA) monoamide used to bind uranyl in its first coordination sphere. DEHiBA ligands can coordinate uranyl in either trans-or cis-positions with respect 1 to the nitrate ligands and these two conformers may co-exist in solution. In order to use luminescence spectroscopy as a speciation technique, it is important to determine whether or not these conformers can be discriminated by their spectroscopic properties. To answer this question, the spectra of trans-and cis-UO 2 (NO 3 ) 2 (DEiBA) 2 conformers were modeled with ab initio methods and compared to the experimental time-resolved luminescence spectra on the UO 2 (NO 3 ) 2 (DEHiBA) 2 systems. Moreover, the hydrated uranyl binitrate UO 2 (NO 3 ) 2 (H 2 O) 2 complexes in the same trans and cis configurations were modeled to quantify the impact of organic DEHiBA on the luminescence properties.

Does the bending of uranyl influence its spectroscopy and luminescence

“…does agree with the fact that the luminescent state corresponds to an excitation to a δ orbital, noting that the excitation involves in almost equal amounts the σ u uranyl orbital and the chloride 3p orbitals. It is also noteworthy the excellent agreement between the computed transition energies and experimental data for UO 2 Cl 4 2as noted previously by Gomes et al 29 for the same system and by Tecmer et al 43 and Oher et al [44][45][46] for other uranyl complexes.…”

“…54 The theoretical vibronic progressions of the UO where. [44][45][46] The first low-lying excited state structures were obtained using TDDFT method as implemented in G16. 30 The temperature for the FCFs calculations was set to repeat the experimental conditions, thus 4 K for UO…”

“…To investigate how the bending of the uranyl moiety influences the energy position and nature of low-lying excited states of UO 2 Cl 2 (phen) 2 , we have chosen a computationally affordable yet reliable approach, that is using time-dependent DFT (TDDFT) combined with the range-separated hybrid CAM-B3LYP functional 41 as it has proven to be more reliable than other hybrid functional for the absorption and emission energies of small to large uranyl(VI) complexes, 19,20,[42][43][44][45][46] including for core-energy levels. 47 The ADF program [48][49][50] was used for all TDDFT calculations with the full (non-ALDA) kernel, and the lowest 16 electronic states were computed.…”

Theoretical Study of the Excited States and Luminescent Properties of (H2O)nUO2Cl2 (n = 1–3)

“…Experimentally, the electronic spectroscopic properties of various uranyl chloride compounds including UO 2 Cl 4 2– in crystals, UO 2 Cl 2 in Ar matrix and UO 2 Cl n 2– n ( n = 2, 4) in nonaqueous solvents have been extensively investigated. − Recently, Huittinen studied the fluorescence spectra of uranyl chloride complexes using the TRLFS technique and obtained the luminescence spectra of UO 2 Cl + and UO 2 Cl 2 in aqueous solution. Theoretically, the excited states of uranyl chloride complexes including UO 2 Cl 4 2– , UO 2 Cl 2 , Ar n UO 2 Cl 2 ( n = 2–3), (acetone) n UO 2 Cl 2 ( n = 3, 4), and (acetone) n UO 2 Cl 3 – ( n = 1, 2) have been carefully computed by employing density functional theory (DFT) and ab initio wave function theory (WFT) methods. − However, theoretical investigations of the luminescent properties of uranyl compounds are still rare, and most of them are based on DFT methods. − Therefore, it is necessary to carry out accurate simulation of luminescence spectra of uranyl complexes using advanced WFT methods.…”

Circularly Polarized Luminescence from Uranyl Improves Resolution of Electronic Transitions

“…Fundamental understanding of the bonding of the uranyl dication to various ligands can have positive implications in nuclear waste management . Due to the characteristic absorption and emission profile of uranyl, photophysical studies of complexes of uranyl have become a powerful tool to help elucidate speciation of the coordination sphere around the uranium center . Circularly polarized luminescence (CPL) is a spectroscopic technique that investigates the preferential emission of one circular polarization handedness of light over the other .…”