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Modern molten salt reactor design and the techniques of electrorefining spent nuclear fuels require a better understanding of the chemical and physical behavior of lanthanide/actinide ions with different oxidation states dissolved in various solvent salts. The molecular structures and dynamics that are driven by the short-range interactions between solute cations and anions and long-range solute and solvent cations are still unclear. In order to study the structural change of solute cations caused by different solvent salts, we performed first-principles molecular dynamics simulations in molten salts and extended X-ray absorption fine structure (EXAFS) measurements for the cooled molten salt samples to identify the local coordination environment of Eu 2+ and Eu 3+ ions in CaCl 2 , NaCl, and KCl. The simulations reveal that with the increasing polarizing the outer sphere cations from K + to Na + to Ca 2+ , the coordination number (CN) of Cl - in the first solvation shell increases from 5.6 (Eu 2+ ) and 5.9 (Eu 3+ ) in KCl to 6.9 (Eu 2+ ) and 7.0 (Eu 3+ ) in CaCl 2 . This coordination change is validated by the EXAFS measurements, in which the CN of Cl - around Eu increases from 5 in KCl to 7 in CaCl 2 . Our simulation shows that the fewer Cl - ions coordinated to Eu leads to a more rigid first coordination shell with longer lifetime. Furthermore, the diffusivities of Eu 2+ /Eu 3+ are related to the rigidity of their first coordination shell of Cl - : the more rigid the first coordination shell is, the slower the solute cations diffuse.

Controlling structure and reactivity by manipulating the outer-coordination sphere around a given reagent represents a longstanding challenge in chemistry. Despite advances toward solving this problem, it remains difficult to experimentally interrogate and characterize outer-coordination sphere impact. This work describes an alternative approach that quantifies outer-coordination sphere effects. It shows how molten salt metal chlorides (MCl n ; M = K, Na, n = 1; M = Ca, n = 2) provided excellent platforms for experimentally characterizing the influence of the outer-coordination sphere cations (M n + ) on redox reactions accessible to lanthanide ions; Ln 3+ + e 1- → Ln 2+ (Ln = Eu, Yb, Sm; e 1- = electron). As a representative example, X-ray absorption spectroscopy and cyclic voltammetry results showed that Eu 2+ instantaneously formed when Eu 3+ dissolved in molten chloride salts that had strongly polarizing cations (like Ca 2+ from CaCl 2 ) via the Eu 3+ + Cl 1- → Eu 2+ + ½Cl 2 reaction. Conversely, molten salts with less polarizing outer-sphere M 1+ cations ( e.g. , K 1+ in KCl) stabilized Ln 3+ . For instance, the Eu 3+ /Eu 2+ reduction potential was >0.5 V more positive in CaCl 2 than in KCl. In accordance with first-principle molecular dynamics (FPMD) simulations, we postulated that hard M n + cations (high polarization power) inductively removed electron density from Ln n + across Ln-Cl⋯M n + networks and stabilized electron-rich and low oxidation state Ln 2+ ions. Conversely, less polarizing M n + cations (like K 1+ ) left electron density on Ln n + and stabilized electron-deficient and high-oxidation state Ln 3+ ions.

Increasing access to the short-lived α-emitting radionuclide astatine-211 ( 211 At) has the potential to advance targeted α-therapeutic treatment of disease and to solve challenges facing the medical community. For example, there are numerous technical needs associated with advancing the use of 211 At in targeted α-therapy, e.g., improving 211 At chelates, developing more effective 211 At targeting, and characterizing in vivo 211 At behavior. There is an insufficient understanding of astatine chemistry to support these efforts. The chemistry of astatine is one of the least developed of all elements on the periodic table, owing to its limited supply and short half-life. Increasing access to 211 At could help address these issues and advance understanding of 211 At chemistry in general. We contribute here an extraction chromatographic processing method that simplifies 211 At production in terms of purification. It utilizes the commercially available Pre-Filter resin to rapidly (<1.5 h) isolate 211 At from irradiated bismuth targets (Bi decontamination factors ≥876 000), in reasonable yield (68-55%) and in a form that is compatible for subsequent in vivo study. We are excited about the potential of this procedure to address 211 At supply and processing/purification problems.

Advances in targeted α-therapies have increased the interest in actinium (Ac), whose chemistry is poorly defined due to scarcity and radiological hazards. Challenges associated with characterizing Ac 3+ chemistry are magnified by its 5f 0 6d 0 electronic configuration, which precludes the use of many spectroscopic methods amenable to small amounts of material and low concentrations (like EPR, UV-vis, fluorescence). In terms of nuclear spectroscopy, many actinium isotopes ( 225 Ac and 227 Ac) are equally "unfriendly" because the actinium α-, β-, and γ-emissions are difficult to resolve from the actinium daughters. To address these issues, we developed a method for isolating an actinium isotope ( 228 Ac) whose nuclear properties are well-suited for γ-spectroscopy. This four-step procedure isolates 228 Ra from naturally occurring 232 Th. The relatively long-lived 228 Ra ( t 1/2 = 5.75(3) years) radioisotope subsequently decays to 228 Ac. Because the 228 Ac decay rate [ t 1/2 = 6.15(2) h] is fast, 228 Ac rapidly regenerates after being harvested from the 228 Ra parent. The resulting 228 Ac generator provides frequent and long-term access (of many years) to the spectroscopically "friendly" 228 Ac radionuclide. We have demonstrated that the 228 Ac product can be routinely "milked" from this generator on a daily basis, in chemically pure form, with high specific activity and in excellent yield (∼95%). Hence, in the same way that developing synthesis routes to new starting materials has advanced coordination chemistry for many metals by broadening access, this 228 Ac generator has the potential to broaden actinium access for the inorganic community, facilitating the characterization of actinium chemical behavior.