We report the use of redox-switchable carboranes for the tunable and reversible capture of CO2. Two substituted 1-PR2-2-BR'2-ortho-carboranes (denoted R/R'Cb) with Lewis acid (LA) and Lewis base (LB) groups were synthesized. These were Ph/CyCb containing weaker LB/LA groups, and tBu/C6F5Cb with stronger LB/LA groups. While closo forms of these were unreactive to CO2, reduction using KC8 yielded reactive nido species. The reduced compound, [K(18-c-6)]2[Ph/CyCb] (18-c-6 = 18-crown-6), captured and reduced CO2 to generate the cage-appended formate species, [K(18-c-6)]2[Ph/CyCb-HCO2]. In contrast, the nido compound, [K(18-c-6)]2[tBu/C6F5Cb], weakly captured CO2 to generate the species [K(18-c-6)]2[tBu/C6F5Cb-CO2], wherein CO2 capture was thought to occur between the P and K+ centers. This was structurally confirmed by performing the reaction with added Li+ to generate the strongly activated P-C(O)O-Li species, [Li]1.5[K]0.5[tBu/C6F5Cb-CO2]. This also provided an avenue to tune CO2 binding constants by controlling the addition of added alkali cations to the solution. Using the encapsulated nido species, [K(kryp)]2[tBu/C6F5Cb] (kryp = kryptofix 2,2,2), binding constants (K) were calculated upon the addition of 1 equiv of [M][TFSI] (M = Li, Na, K; TFSI = bis(trifluoromethanesulfonyl)imide) and resulted in log K values of: 5.5 (Li+), 4.5 (Na+), and 3.4 (K+). Binding constants with >1.0 equiv. M+ were qualitatively similar, whereas lower values were observed with <1.0 equiv of M+. Chemical oxidation of the CO2-captured products also led to CO2 release. Together, these results open avenues to redox-controlled CO2 capture/release coupled with tunable CO2 capture binding constants, significant areas of interest in carbon capture technologies.

We report the synthesis of a new 1,2-(1,2-bis-sulfoxide-12-crown-4)-ortho-carborane (12C4SOCb) and its selective chemical and electrochemical capture of Li+ from mixed metal (Li+/Na+/K+) solutions upon 2e- reduction to its nido state. The synthesis and characterization of closo-12C4SOCb, nido-, and the Li+-captured nido salt, , are reported. Bulk electrolysis of 12C4SOCb in the presence of various mixed metal alkali salt solutions in organic media, coupled with ICP-OES measurements, reveal highly selective Li+ capture and release against competing ions, enabling its selective separation.

Lithium is a critical element with a projected exponential rise in demand due to its widespread use in battery energy storage. New methods to extract Li + , such as through membrane adsorption‐based direct Li + extraction (DLE) technologies, are at various stages of development and aim to separate Li + from brine and even seawater. In this report, we present a fundamentally new class of highly selective Li + ‐capture agent, the carborane‐crown compound, 1,2‐((6,6,7,7‐Me 4 )14‐crown‐4)‐ ortho ‐carborane ( 14C4 Cb ), which is electrochemically activated for strong, selective Li + binding over Na + and K + . This newly synthesized extractant features a redox‐tunable cavity size, giving rise to tunable binding constants for Li + capture, favorable coulombic interactions between the reduced anionic capture agent and the Li + cations, and boasts the benefit of rapid, electrochemically driven capture kinetics. Weak, negligible binding to Li + was observed in the neutral “ closo ” carborane state ( 14C4 Cb ), whereas strong binding was observed in the cage‐opened reduced nido state ( 14C4 Cb 2− ). Equilibrium ( K ) binding constants were measured through experimental and simulated voltammetry, yielding the following log K metal (experimental; simulation ) values: log K Li (6.8 ± 0.6; 8.0 ), log K Na (3.7 ± 0.2; 4.9 ), log K K (1.7 ± 0.2; 2.2 ). Rapid mass transport of Li + to the electrode surface resulted in the simulated value (log K Li = 8.0) representing a lower‐limit value for log K Li as described herein. The observed strong binding to Li + over Na + and K + is attributed to both the favorable redox‐tunable crown cavity size of the 14C4 Cb/ 14C4 Cb 2− couple, combined with strong coulombic interactions in the reduced nido state. This platform offers a potential new, rapid, and highly selective technique for Li + capture in next‐generation electrochemical DLE technologies.

Li and U are the only trace metals dissolved in seawater that are proposed to be economical to extract. Both are at very low concentrations (Li (0.17 ppm), U (3.3 ppb)); however, their total content are approximately 10,000 and 1,000 times higher than in land-based reserves, respectively, representing huge untapped resources which could be collected in an environmentally friendly manner. With surging demand for Li-ion batteries for energy storage, it is estimated that current production methods will soon not meet market demands. In addition, low-carbon nuclear energy production is also expected to increase dramatically in many major countries. Previous studies have shown that reduction of the substituted closo -carborane polyhedral cluster, 1,2-L 2 -C 2 B 10 H 10 , to the nido -carborane, [1,2-L 2 -C 2 B 10 H 10 ] 2- , resulted in the rupture of the C–C bond, cage opening, and an increased bite angle, Θ (Scheme). This talk will start by describing how we used this redox-controlled chelation for the selective electrochemical capture and release of UO 2 2+ from mixed-metal mixtures mimicking spent nuclear fuel in monophasic and biphasic media (Scheme; M = UO 2 2+ ; L = Ph 2 PO). 1-2 We will then discuss our current efforts to target other metals of energy importance, in particular M = Li + , for seawater extraction by incorporating Li-selective donating groups, L (Scheme). This talk will then focus heavily on our current work on anchoring these carboranes onto electrode surfaces using anchoring groups – e.g., allyl, pyrene, or thiols – for heterogeneous capture and release using galvanostatic charge/discharge cycles. Recent, soon-to-be published results demonstrate the successful application of this redox-controlled chelation for heterogeneous, selective capture of UO 2 2+ from mixed-metal mixtures. Keener, M.; Hunt, C.; Carroll, T. G.; Kampel, V.; Dobrovetsky, R.; Hayton, T. W.; Ménard, G. Redox-switchable carboranes for uranium capture and release. Nature 2020, 577 , 652-655. Keener, M.; Mattejat, M.; Zheng, S.-L.; Wu, G.; Hayton, T. W.; Ménard, G. Selective electrochemical capture and release of uranyl from aqueous alkali, lanthanide, and actinide mixtures using redox-switchable carboranes. Chem. Sci. 2022, 13 , 3369-3374. Figure 1

We report the heterogenization of molecular, electrochemically switchable ortho-substituted carboranes (POCb, POCb-Pyr) for selective metal capture. Films of POCb and POCb-Pyr on glassy carbon and carbon fiber (CF) electrodes demonstrated heterogeneous electrochemical behaviour that was enhanced by the inclusion of single-walled carbon nanotubes (CNTs). Galvanostatically charged CF|CNT|POCb and CF|CNT|POCb-Pyr electrodes selectively captured and released actinides (Th4+, UO22+) from mixed solutions containing alkali (Cs+), lanthanide (Nd3+, Sm3+) and actinide (Th4+, UO22+) metal ions.

The storage of renewable energy in ammonia (NH3) isa promising alternative to hydrogen (H-2) for our transitionfrom fossil fuels. Solid oxide fuel cells (SOFCs) are the leadingtechnology for direct ammonia fuel cells (DAFCs); however, their hightemperature of operation makes them unsuitable for light-duty vehicles.As such, there has been growing interest in aqueous-fed DAFCs. Suchtechnologies face challenges with respect to reaction selectivity,precious metal catalyst loading, and stability; however, there isa dearth of reported molecular catalysts to address such issues. Rutheniumbipyridinedicarboxylate complexes are known for catalyzing water oxidationat rapid rates and were recently reported to catalyze the oxidationof ammonia, i.e., nitrogen evolution reaction (NER) in acetonitrile,albeit at sluggish rates. Herein, we present our use of the knowncomplex [Ru(bipyridinedicarboxylate)(4-methylpyridine)(2)] (RuBda, 1) to electrocatalyze ammonia oxidation ofaqueous NH3 to N-2 at high faradaic efficiencies(>80%), unprecedented rates (turnover frequency & AP; 3757 s(-1)), and high turnover. Our kinetic analyses suggestthat the catalyst operates via a unimolecular mechanism, which ishighly applicable for commercially viable fuel cells.

We report the synthesis and characterization of a series of new, tunable 1,2-bis(diarylphosphine oxide)-ortho-carboranes, derivatives of our previously reported uranyl (UO22+) capture agent 1,2-(Ph2PO)2-1,2-C2B10H10 (POCb). The series features new cage-substituted variants of POCb, namely, 9-I-POCb (POCbI), 9,12-I2-POCb (POCbI2), 9,12-Me2-POCb (POCbMe2), 9,12-Et2-POCb (POCbEt2), and 4,5,7,8,9,10,11,12-Me8-POCb (POCbMe8). Aryl-substituted variants include 1,2-((4-MeO-Ph)2PO)2-Cb ((OMe)POCb) and 1,2-((4-F-Ph)2PO)2-Cb ((F)POCb). The effects of electron-withdrawing (EWG) and electron-donating (EDG) groups on resulting carborane redox potentials were assessed using electrochemical means, and the resulting Lewis basicities were quantified using empirical and competition-based NMR experiments. In organic solution, carboranes substituted with EWGs exhibited weaker coordination to UO22+, whereas those with EDGs exhibited stronger coordination. Similar to the previously reported unsubstituted POCb, the tunable new series of carboranes were electrochemically reduced and used for the biphasic capture of UO22+ from an aqueous to an organic phase and back again (release) through electrochemical oxidation. Extraction and back-extraction efficiencies were determined by analyses of the aqueous phases by ICP-OES. While all reduced nido-carboranes efficiently extracted UO22+ in high yields (78-88%)─with seemingly no correlation to the aforementioned measured Lewis basicities─we found the back-extraction of UO22+ to be significantly improved from POCb and, surprisingly, more closely related to their hydrophobic rather than their Lewis basic properties.

The development of inexpensive charge carriers with long-term stability is critical to increase the economic viability of redox flow batteries (RFBs). Herein, we compare the performance metrics of a series of synthesized or commercially available inexpensive phthalocyanine metal (PcM) charge carriers with varying metal-or ligand-based substitution patterns. All systems were charged-discharged as slurries in conjunction with a conductive heterogeneous carbon source, Ketjenblack (KB). The synthesized, peripherally substituted 1,4,8,11,15,18,22,25-octaethoxyphthalocyanine (EtOPc) metal complexes, OEtPcVO and OEtPcNi, were cycled with KB, and their performance metrics were compared to their commercially unsubstituted analogues, PcVO and PcNi. No significant advantages were found in using the synthesized versus commercial variants despite the increased solubility of the former. Expanding these electrochemical analyses to several commercial first-row variants (PcTiCl2, PcVO, PcMnCl, PcFe, PcCo, PcNi, and PcCu) as well as one heavy-metal analogue (PcPb) revealed that most of these were effective charge carriers for slurry-based PcM/ KB RFB applications. Of these, PcCu proved to have the highest efficiencies, energy density (1.23 Wh/L), and stability (>99% capacity retention) of the series while also having the lowest cost by mass.

This cover picture shows the facile and efficient synthesis of common electrophilic haloboranes via a protonolysis reaction between Piers’ borane, HB(C6F5)2, and the corresponding hydrogen halides, H–X (X = Cl, Br), generating H2 gas as the sole byproduct. The vacuum distillation setup shown here illustrates the in situ-generated hydrogen halide crossing a glass bridge to react with the hydridic B–H bond in Piers’ borane. Preparing the tri-coordinate boranes and their etherates using this route may provide a gateway into more Lewis acid-mediated transformations. (DOI: 10.1002/zaac.202300007).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Ion-selective membranes are an essential, yet expensive fixture in redox flow batteries, preventing charge carrier crossover between the two half-cells. This work demonstrates the viability of replacing these membranes with an electrolyte solution that is mutually immiscible with the two half-cell solutions, eliminating the direct anolyte-catholyte interface that leads to self-discharge in existing biphasic cells. We developed a simple dichloromethane (DCM)/water model system consisting of charge carriers in the organic phase connected by an immiscible aqueous electrolyte sharing a common anion (PF6-) with the DCM phase. This "split biphasic" model cell maintained high Coulombic efficiencies (> 99%) and capacity retention (similar to 95%) over a period of 24 h for fully charged cells. Lastly, we demonstrated the performance of this model system at scale in high-surface-area cells while retaining rapid charge-discharge at a rate of 1C.

We report the facile and efficient synthesis of common electrophilic haloboranes via a protonolysis reaction between Piers' borane, HB(C6F5)(2), and H-X (X=Cl, Br). This route benefits from fast reaction times, easy setup, and minimal workup to yield the analytically pure etherates, (C6F5)(2)BCl(OEt2) (1) and (C6F5)(2)BBr(OEt2) (2), as well as the ether-free tri-coordinate species, (C6F5)(2)BBr (3).

We report the facile and efficient synthesis of common electrophilic haloboranes via a protonolysis reaction between Piers’ borane, HB(C 6 F 5 ) 2 , and H−X (X=Cl, Br). This route benefits from fast reaction times, easy setup, and minimal workup to yield the analytically pure etherates, (C 6 F 5 ) 2 BCl(OEt 2 ) ( 1 ) and (C 6 F 5 ) 2 BBr(OEt 2 ) ( 2 ), as well as the ether‐free tri‐coordinate species, (C 6 F 5 ) 2 BBr ( 3 ).

Redox flow batteries (RFBs) are leading contenders for grid-scale energy storage devices. 1. RFBs can be rapidly deployed and demonstrate high durability (>10,000 cycles2), making them appealing for long-term energy storage. Despite these advantages, commercial RFBs are hampered by high capital costs. Ion-selective membranes in RFB cell stacks make up a significant fraction (up to ~37% 3) of the RFB cost – for both new RFBs and expanding existing RFBs. The need for a large membrane area in the cell stacks stems from the cell power capacity (maximum charge-discharge current) being directly dependent on the membrane size. In this talk, we report our progress on a new RFB layout coined the “split biphasic architecture.” This is a development on membrane-less biphasic RFBs which use mutually immiscible phases for the anolyte and catholyte4. Self-discharge at the anolyte-catholyte interface is a rampant issue in these biphasic RFBs, and we discuss our approach to resolving this issue and increasing Coulombic efficiencies from ~70% to >99%. Further, we will discuss trends in interfacial ion transfer resistance vis-a-vis dependence on the solvents and electrolytes (Hoffmeister series). Building on this fundamental proof-of-concept, we hope to extend the scope of battery chemistry compatible with the split biphasic layout in the future. (1) Skyllas-Kazacos et al., J. Electrochem. Soc. 2011, 158 (8), R55 (2) Janoschka et. al., Nature 2015, 527 (7576), 78–81 (3) Minke, C.; Kunz, U.; Turek, T., J. Power Sources 2017, 361, 105–114 (4) Molina-Osorio, et. al., Curr. Opin. Electrochem. 2020, 21, 100–108 Figure 1

We report the selective electrochemical biphasic capture of the uranyl cation (UO22+) from mixed-metal alkali (Cs+), lanthanide (Nd3+, Sm3+), and actinide (Th4+, UO22+) aqueous solutions to an organic, 1,2-dichloroethane (DCE), phase using the ortho-substituted nido-carborane anion, [1,2-(Ph2PO)2-1,2-C2B10H10]2- (POCb2-). The reduced POCb2- is generated by electrochemical reduction of the closo-carborane, POCb, prior to mixing with the aqueous mixed-metal solution. Subsequent UO22+ release from the captured product, [UO2(POCb)2]2-, was performed by galvanostatic bulk electrolysis of the DCE phase and back-extraction of UO22+ to a fresh aqueous phase. The selective capture and release of UO22+ was confirmed by combined ICP-OES and NMR spectral analyses of the aqueous and organic phases, respectively, against the newly synthesized nido-carborane complexes, [[CoCp*2][Cs(POCb)]]2, [CoCp*2]3[Nd(POCb)3], [CoCp*2]3[Sm(POCb)3], and [CoCp*2]2[Th(POCb)3].