Understanding the excited state dynamics and redox behavior of highly luminescent and electrochemically active Eu(III)-DES complex

Deep eutectic solvents (DES) are considered a novel class of environmentally benign molecular solvents that are considered as potential solvents for nuclear fuel reprocessing, material recycling, and many other technological applications in both research and industry. However, there is a complete dearth of understanding pertaining to the behavior of metal ions in DES. Herein, we have investigated the speciation, complexation behavior, photochemistry, and redox properties and tried to obtain insight into the chemical aspects of the europium ion in DES (synthesized from heptyltriphenylphosphonium bromide and decanoic acid). The same has been probed using time-resolved photoluminescence (TRPL), cyclic voltammetry (CV), synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) calculations. TRPL indicated the stabilization of europium in the +3 oxidation state, favoring the potential of the Eu(III)-DES complex to emit red light under near UV excitation and the existence of inefficient energy transfer between DES and Eu3+. EXAFS analysis revealed the presence of Eu-O and Eu-Br, which represent the local surroundings of Eu3+ in the Eu(III)-DES complex. TRPL measurement has also suggested two distinct local environments of europium ions in the complex. DFT calculations supported the EXAFS findings, confirming that the Eu(III)-DES structure involves not only the oxygen atom of decanoic acid but also the oxygen atoms from the nitrate ions, contributing to the local coordination of Eu(III). Electrochemical studies demonstrated that the redox reaction of Eu(III)/Eu(II) in DES displays quasi-reversible behavior. The reaction rate was observed to increase with higher temperatures. The findings of this study can contribute to the understanding of the fundamental properties and potential applications of this luminescent and electrochemically active complex and pave the way for further studies and the development of novel materials with enhanced luminescent and electrochemical properties.

The Rise of Trichlorides Enabling an Improved Chlorine Technology

Chlorine plays a central role for the industrial production of numerous materials with global relevance. More recently, polychlorides have been evolved from an area of academic interest to a research topic with enormous industrial potential. In this minireview, the value of trichlorides for chlorine storage and chlorination reactions are outlined. Particularly, the inexpensive ionic liquid [NEt₃ Me][Cl₃ ] shows a similar and sometimes even advantageous reactivity compared to chlorine gas, while offering a superior safety profile. Used as a chlorine storage, [NEt₃ Me][Cl₃ ] could help to overcome the current limitations of storing and transporting chlorine in larger quantities. Thus, trichlorides could become a key technique for the flexibilization of the chlorine production enabling an exploitation of renewable, yet fluctuating, electrical energy. As the loaded storage, [NEt₃ Me][Cl₃ ], is a proven chlorination reagent, it could directly be employed for downstream processes, paving the path to a more practical and safer chlorine industry.

Synthesis, Crystallization, and Electrochemical Characterization of Room Temperature Ionic Liquid Bromidostannates(II/IV)

Ionic liquids (IL) are valuable in a variety of applications due to their high electrochemical stability and physical properties. Using the cation 1-methyl-3-octylimidazolium, [OMIM]⁺, the bromidostannate RTIL [OMIM][Sn^+IIBr₃], "undercooled melt" [OMIM][Sn^+IVBr₅], and IL [OMIM]₂[Sn^+IVBr₆] were synthesized. The uncommon solid state structure of [SnBr₅]^- was elucidated in the form of its RTIL salt. Additionally, the IL based on tribromine-monoanion [OMIM][Br₃] was used to dissolve metallic Sn, selectively resulting in the formation of [SnBr₃]^- as confirmed by Raman spectroscopy. Subsequent cyclic voltammograms (CV) of [SnBr₃]^- confirmed the deposition potential of metallic Sn and renewal of the polybromide [Br₃]^-. The RTIL bromidostannates were stable compounds, making a selective electrochemical investigation of the deposition of metallic Sn(0) to Sn(+II)/Sn(+IV) redox process possible, via conductance and CV measurements. The CVs of the RTILs and of solutions in propylene carbonate had the redox couples of Sn(0)/[Sn^+IIBr₃]^-/[Sn^+IVBr₅]^-.

Conductivity and Redox Potentials of Ionic Liquid Trihalogen Monoanions [X3 ]- , [XY2 ]- , and [BrF4 ]- (X=Cl, Br, I and Y=Cl, Br)

The ionic liquid (IL) trihalogen monoanions [N2221 ][X3 ]- and [N2221 ][XY2 ]- ([N2221 ]+ =triethylmethylammonium, X=Cl, Br, I, Y=Cl, Br) were investigated electrochemically via temperature dependent conductance and cyclic voltammetry (CV) measurements. The polyhalogen monoanions were measured both as neat salts and as double salts in 1-butyl-1-methyl-pyrrolidinium trifluoromethane-sulfonate ([BMP][OTf], [X3 ]- /[XY2 ]- 0.5 M). Lighter IL trihalogen monoanions displayed higher conductivities than their heavier homologues, with [Cl3 ]- being 1.1 and 3.7 times greater than [Br3 ]- and [I3 ]- , respectively. The addition of [BMP][OTf] reduced the conductivity significantly. Within the group of polyhalogen monoanions, the oxidation potential develops in the series [Cl3 ]- >[BrCl2 ]- >[Br3 ]- >[IBr2 ]- >[ICl2 ]- >[I3 ]- . The redox potential of the interhalogen monoanions was found to be primarily determined by the central halogen, I in [ICl2 ]- and [IBr2 ]- , and Br in [BrCl2 ]- . Additionally, tetrafluorobromate(III) ([N2221 ]+ [BrF4 ]- ) was analyzed via CV in MeCN at 0 °C, yielding a single reversible redox process ([BrF2 ]- /[BrF4 ]- ).

Direct dissolution of UO2 in carboxyl-functionalized ionic liquids in the presence or absence of Fe-containing ionic liquids

Dissolution of UO₂ is a prerequisite for the reprocessing of spent nuclear fuel. This study showed that UO₂ could be directly dissolved in a single carboxyl-functionalized ionic liquid (IL), [HOOCMmim][Tf₂N] 1-carboxymethyl-3-methylimidazolium bistriflimide, or [HOOCEtmim][Tf₂N] 1-carboxyethyl-3-methylimidazolium bistriflimide. The addition of an extra Fe-containing IL, [Emim][FeCl₄] (Emim, 1-ethyl-3-methylimidazolium) or [Bmim][FeCl₄] (Bmim, 1-butyl-3-methylimidazolium) could significantly improve the dissolution kinetics. Results demonstrated that the dissolution process in the early stage could be described by using the pseudo first-order rate law. The apparent activation energy for UO₂ dissolution in the mixture of the Fe-containing IL and carboxyl-functionalized IL was calculated to be ∼67 kJ mol^-1, implying that the reaction was mainly controlled by a chemical process. Nevertheless, the influence of the diffusion process is non-negligible since the IL has a relatively high viscosity that can retard the diffusion of the formed uranyl species from the UO₂ surface. Spectroscopic studies and density functional theory calculations indicated that the uranyl ion coordinated with carboxylate groups is the predominant product for UO₂ dissolution in the single carboxyl-functionalized IL, while uranyl chloride complexes would also form in the mixed ILs. The dissolved uranyl species can be successfully recovered from the ILs by extraction. The success of UO₂ dissolution in the carboxyl-functionalized IL with or without the Fe-containing IL indicates that the Fe-containing IL and oxygen can serve as an effective catalyst and oxidant for the dissolution of UO₂, respectively.