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A new, air-stable, permanently porous uranium(iv) metal-organic framework U(bdc)2 (1, bdc2- = 1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example of cooperative framework contraction (ΔV = -7.8%), triggered by D2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen (Q st = -8.6 kJ mol-1) per pore, in agreement with H2 adsorption data. Analogous experiments with CD4 (Q st = -24.8 kJ mol-1) and N,N-dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal-organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity.

A new, air-stable, permanently porous uranium(iv) metal-organic framework U(bdc)2 (1, bdc2- = 1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example of cooperative framework contraction (ΔV = -7.8%), triggered by D2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen (Q st = -8.6 kJ mol-1) per pore, in agreement with H2 adsorption data. Analogous experiments with CD4 (Q st = -24.8 kJ mol-1) and N,N-dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal-organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity.

A new series of Ln3+ and Ln2+ complexes has been synthesized using the tris(aryloxide)arene ligand system, ((Ad,MeArO)3mes)3-, recently used to isolate a complex of U2+. The triphenol precursor, (Ad,MeArOH)3mes, reacts with the Ln3+ amides, Ln(NR2)3 (R = SiMe3), to form a series of [((Ad,MeArO)3mes)Ln] complexes, 1-Ln. Crystallographic characterization was achieved for Ln = Nd, Gd, Dy, and Er. The complexes 1-Ln can be reduced with potassium graphite in the presence of 2.2.2-cryptand (crypt) to form highly absorbing solutions with properties consistent with Ln2+ complexes, [K(crypt)][((Ad,MeArO)3mes)Ln], 2-Ln. The synthesis of the Nd2+ complex [K(crypt)][((Ad,MeArO)3mes)Nd], 2-Nd, was unambiguously confirmed by X-ray crystallography. In the case of the other lanthanides, crystals were found to contain mixtures of 2-Ln co-crystallized with either a Ln3+ hydride complex, [K(crypt)][((Ad,MeArO)3mes)LnH], 3-Ln, for Ln = Gd, Dy, and Er, or a hydroxide complex, [K(crypt)][((Ad,MeArO)3mes)Ln(OH)], 4-Ln, for Ln = Dy. A Dy2+ complex with 18-crown-6 as the potassium chelator, [K(18-crown-6)(THF)2][((Ad,MeArO)3mes)Dy], 5-Dy, was isolated as a co-crystallized mixture with the Dy3+ hydride complex, [K(18-crown-6)(THF)2][((Ad,MeArO)3mes)DyH], 6-Dy. Structural comparisons of 1-Ln and 2-Ln are presented with respect to their uranium analogs and correlated with density functional theory calculations on their electronic structures.

Electrocatalytic hydrogenation of 1‐octene as non‐activated model substrate with neutral water as H‐donor is reported, using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96 % and a kobs of 87 s−1. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl− and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]− (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(tBuPCP)Ir(H)2] (3) in 88 % FE from the reaction of 2 with H2O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro‐hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H2 formation. Even in strongly alkaline conditions (Bu4NOH added), the electro‐hydrogenation of 1‐octene with 1 also proceeds cleanly (89 % FE), suggesting a highly robust process that may rely on H2O activation, reminiscent to transfer hydrogenation pathways, instead of classical H+ reduction. DFT calculations confirmed oxidative addition of H2O as a key step in this context. [ABSTRACT FROM AUTHOR]

Stable reference electrodes (REs) are crucial for reliable voltammetry, controlled potential electrosynthesis, or spectro‐electrochemistry. Yet, inferior pseudo‐REs, such as plain Ag wire are often used, because commercial REs are expensive, may degrade or contaminate under required conditions, or don't fit geometric restrictions of custom setups. Addressing such cases, we report construction, benchmarking and utilization of easy to make, cheap (<1 €), and robust miniature REs from pasteur pipettes, molecular sieve beads and Ag wire. Excellent potential precision and accuracy with at least 1 week device stability was obtained for aqueous Ag/AgCl REs with 3 M NaCl in H2O and anhydrous 0.1 M TBACl in MeCN inner‐electrolytes. Even in alkaline 1 M NaOH electrolyte, where initial Ag/AgCl REs quickly convert to Ag/Ag2O (1 M NaOH) REs, perfect potential precision, accuracy, and at least 1 week stability are demonstrated. According to experimental needs, miniature REs can be built with many organic and aqueous electrolytes. For these custom use‐cases, we report guidelines to calibrate absolute RE potential, and to assess device precision, accuracy and stability. Finally, electro‐hydrogenation of styrene on nickel electrodes exemplifies superiority of Ag/AgCl REs over Ag wire pseudo‐REs, affording more reliable electrolysis current, cell potential and potential dependent Faraday efficiency. [ABSTRACT FROM AUTHOR]

Uranium complexes can be stabilized in a wide range of oxidation states, ranging from UII to UVI and a very recent example of a UI complex. This review provides a comprehensive summary of electrochemistry data reported on uranium complexes in nonaqueous electrolyte, to serve as a clear point of reference for newly synthesized compounds, and to evaluate how different ligand environments influence experimentally observed electrochemical redox potentials. Data for over 200 uranium compounds are reported, together with a detailed discussion of trends observed across larger series of complexes in response to ligand field variations. In analogy to the traditional Lever parameter, we utilized the data to derive a new uranium-specific set of ligand field parameters UEL(L) that more accurately represent metal–ligand bonding situations than previously existing transition metal derived parameters. Exemplarily, we demonstrate UEL(L) parameters to be useful for the prediction of structure–reactivity correlations in order to activate specific substrate targets. [ABSTRACT FROM AUTHOR]

Depleted uranium is a mildly radioactive waste product that is stockpiled worldwide. The chemical reactivity of uranium complexes is well documented, including the stoichiometric activation of small molecules of biological [...]

Electrocatalytic energy conversion with molecular f-element catalysts is still in an early phase of its development. We here report detailed electrochemical investigations on the recently reported trivalent lanthanide coordination complexes [((Ad,MeArO)3mes)Ln] (1-Ln), with Ln = La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and Yb, which were now found to perform as active electrocatalysts for the reduction of water to dihydrogen. Reactivity studies involving complexes 1-Ln and the Ln(II) analogues [K(2.2.2-crypt)]-[((Ad,MeArO)3mes)Ln] (2-Ln) suggest a reaction mechanism that differs significantly from the reaction pathway found for the corresponding uranium catalyst [((Ad,MeArO)3mes)U] (1-U). While complexes 1-Ln activate water via a radical pathway, only upon a 1 e- reduction to yield the reduced species 2-Ln, the 5f analogue 1-U directly reduces H2O via a 2 e- pathway. The electrocatalytic H2O reduction by complexes 1-Ln is initiated by the respective Ln(III)/Ln(II) redox couples, which gradually turn to more positive values across the Ln series. This correlation has been exploited to tune the catalytic overpotential of water reduction by choice of the lanthanide ion. Kinetic studies of the 1-Ln series were performed to elucidate correlations between overpotential and turnover frequencies of the 4f-based electrocatalysts. [ABSTRACT FROM AUTHOR]

Triarylphosphine oxides (Ar3P=O) are being intensely studied as electron-accepting (n-type) materials. Despite the widespread application of these compounds as electron conductors, experimental data regarding the structural and electronic properties of their negatively charged states remain scarce owing to their propensity for follow-up chemistry. Herein, a carefully designed triarylphosphine oxide scaffold is disclosed that comprises sterically demanding spirofluorenyl moieties to shield the central phosphoryl (P=O) moiety. This compound undergoes chemical one-electron reduction to afford an exceptionally stable radical anion, which was isolated and characterized by X-ray crystallography for the very first time. The experimental data, corroborated by computational studies, shall allow for the construction of phosphine oxide materials with enhanced stability. [ABSTRACT FROM AUTHOR]

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The syntheses of four nearly isostructural uranium(IV) monoarene complexes, supported by the arene anchored tris(aryloxide) chelate, [(Ad,MeArO)3mes]3-, are reported. Oxidation of the uranium(III) precursor [((Ad,MeArO)3mes)U], 1, in the presence of tetrahydrofuran (THF) results in THF coordination and distortion of the equatorial coordination sphere to afford the uranium(IV) η6-arene complexes, [((Ad,MeArO)3mes)U(X)(THF)], 2-X-THF, (where X = F, Cl, Br, or I) as their THF adducts. The solvate-free trigonally ligated [((Ad,MeArO)3mes)U(F)], 2-F, was prepared and isolated in the absence of coordinating solvents for comparison. [ABSTRACT FROM AUTHOR]

Synthetic studies on the redox chemistry of trivalent uranium monoarene complexes were undertaken with a complex derived from the chelating tris(aryloxide)arene ligand (Ad,MeArO)3mes3−. Cyclic voltammetry of [{(Ad,MeArO)3mes}UIII] ( 1) revealed a nearly reversible and chemically accessible reduction at −2.495 V vs. Fc/Fc+-the first electrochemical evidence for a formally divalent uranium complex. Chemical reduction of 1 indicates that reduction induces coordination and redox isomerization to form a uranium(IV) hydride, and addition of a crown ether results in hydride insertion into the coordinated arene to afford uranium(IV) complexes. This stoichiometric reaction sequence provides structural insight into the mechanism of arene functionalization at diuranium inverted sandwich complexes. [ABSTRACT FROM AUTHOR]

Electrocatalytic hydrogenation of 1-octene as non-activated model substrate with neutral water as H-donor is reported, using [( tBu PCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96 % and a k obs of 87 s -1 . Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl - and afford the highly reactive anionic Ir(I) hydride complex [( tBu PCP)Ir(H)] - (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [( tBu PCP)Ir(H) 2 ] (3) in 88 % FE from the reaction of 2 with H 2 O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro-hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H 2 formation. Even in strongly alkaline conditions (Bu 4 NOH added), the electro-hydrogenation of 1-octene with 1 also proceeds cleanly (89 % FE), suggesting a highly robust process that may rely on H 2 O activation, reminiscent to transfer hydrogenation pathways, instead of classical H + reduction. DFT calculations confirmed oxidative addition of H 2 O as a key step in this context., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Three new coordination polymers (CPs) constructed from the linker 1,4-di(dithiocarboxylate) (BDDTC 2- )─the sulfur-analog of 1,4-benzenedicarboxylate (BDC 2- )─together with Mn-, Zn-, and Fe-based inorganic SBUs are reported with description of their structural and electronic properties. Single-crystal X-ray diffraction revealed structural diversity ranging from one-dimensional chains in [Mn(BDDTC)(DMF) 2 ] ( 1 ) to two-dimensional (2D) honeycomb sheets observed for [Zn 2 (BDDTC) 3 ][Zn(DMF) 5 (H 2 O)] ( 2 ). Gas adsorption experiments confirmed a 3D porous structure for the mixed-valent material [Fe 2 (BDDTC) 2 (OH)] ( 3 ). 3 contains a 1:1 ratio of Fe 2+/3+ ions, as evidenced by 57 Fe Mössbauer, X-band EPR, and X-ray absorption spectroscopy. Its empirical formula was established by elemental analysis, thermal gravimetric analysis, infrared vibrational spectroscopy, and X-ray absorption spectroscopy in lieu of elusive single-crystal X-ray diffraction data. In contrast to the Mn- and Zn-based compounds 1 and 2 , the Fe 2+/3+ CP 3 showed remarkably high electrical conductivity of 5 × 10 -3 S cm -1 (according to van der Pauw measurements), which is within the range of semiconducting materials. Overall, our study confirms that sulfur derivatives of typical carboxylate linkers (e.g., BDC) are suitable for the construction of electrically conducting CPs, due to acceptedly higher covalency in metal-ligand bonding compared to the electrically insulating carboxylate CPs or metal-organic frameworks. At the same time, the direct comparison between insulating CPs 1 and 2 with CP 3 emphasizes that the electronic structure of the metal is likewise a crucial aspect to construct electrically conductive materials.

Transmetalation of the β-diketiminate salt [M][ Me nacnac Ph ] (M + = Na or K; Me nacnac Ph- = {PhNC(CH 3 )} 2 CH - ) with UI 3 (THF) 4 resulted in the formation of the homoleptic, octahedral complex [U( Me nacnac Ph ) 3 ] ( 1 ). Green colored 1 was fully characterized by a solid-state X-ray diffraction analysis and a combination of UV/vis/NIR, NMR, and EPR spectroscopic studies as well as solid-state SQUID magnetization studies and density functional theory calculations. Electrochemical studies of 1 revealed this species to possess two anodic waves for the U(III/IV) and U(IV/V) redox couples, with the former being chemically accessible. Using mild oxidants, such as [CoCp 2 ][PF 6 ] or [FeCp 2 ][Al{OC(CF 3 ) 3 } 4 ], yields the discrete salts [1][A] (A = PF 6 - , Al{OC(CF 3 ) 3 } 4 - ), whereas the anion exchange of [1][PF 6 ] with NaBPh 4 yields [1][BPh 4 ] .

The synthesis of 4f n Ln 3+ complexes of the tris(aryloxide) mesitylene ligand, (( Ad,Me ArO) 3 mes) 3- , with Ln = La, Ce, Pr, Sm, and Yb, and their reduction with potassium have revealed that this ligand system can be redox active with some metals. Protonolysis of [Ln(N(SiMe 3 ) 2 ) 3 ] (Ln = La, Ce, Pr, Sm, Yb) with the tris(phenol) ( Ad,Me ArOH) 3 mes yielded the Ln 3+ complexes [(( Ad,Me ArO) 3 mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 1-Ln. Single electron reduction of each 4f n complex, 1-Ln, using potassium yielded the reduced products, [K(2.2.2-cryptand)][(( Ad,Me ArO) 3 mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 2-Ln. The Sm and Yb complexes have properties consistent with the presence of Ln 2+ ions with traditional 4f n+1 electron configurations. However, the La, Ce, and Pr complexes appear to formally contain Ln 3+ ions and (( Ad,Me ArO) 3 mes) 4- ligands. Structural comparisons of the [(( Ad,Me ArO) 3 mes)Ln] and [(( Ad,Me OAr) 3 mes)Ln] 1- complexes along with UV-vis absorption and EPR spectroscopy as well as density functional theory calculations support these ground state assignments.

The reactivity of uranium compounds towards small molecules typically occurs through stoichiometric rather than catalytic processes. Examples of uranium catalysts reacting with water are particularly scarce, because stable uranyl groups form that preclude the recovery of the uranium compound. Recently, however, an arene-anchored, electron-rich uranium complex has been shown to facilitate the electrocatalytic formation of H 2 from H 2 O. Here, we present the precise role of uranium-arene δ bonding in intermediates of the catalytic cycle, as well as details of the atypical two-electron oxidative addition of H 2 O to the trivalent uranium catalyst. Both aspects were explored by synthesizing mid- and high-valent uranium-oxo intermediates and by performing comparative studies with a structurally related complex that cannot engage in δ bonding. The redox activity of the arene anchor and a covalent δ-bonding interaction with the uranium ion during H 2 formation were supported by density functional theory analysis. Detailed insight into this catalytic system may inspire the design of ligands for new uranium catalysts.

Electrocatalytic energy conversion with molecular f-element catalysts is still in an early phase of its development. We here report detailed electrochemical investigations on the recently reported trivalent lanthanide coordination complexes [(( Ad,Me ArO) 3 mes)Ln] (1-Ln), with Ln = La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and Yb, which were now found to perform as active electrocatalysts for the reduction of water to dihydrogen. Reactivity studies involving complexes 1-Ln and the Ln(II) analogues [K(2.2.2-crypt)][(( Ad,Me ArO) 3 mes)Ln] (2-Ln) suggest a reaction mechanism that differs significantly from the reaction pathway found for the corresponding uranium catalyst [(( Ad,Me ArO) 3 mes)U] (1-U). While complexes 1-Ln activate water via a radical pathway, only upon a 1 e - reduction to yield the reduced species 2-Ln, the 5f analogue 1-U directly reduces H 2 O via a 2 e - pathway. The electrocatalytic H 2 O reduction by complexes 1-Ln is initiated by the respective Ln(III)/Ln(II) redox couples, which gradually turn to more positive values across the Ln series. This correlation has been exploited to tune the catalytic overpotential of water reduction by choice of the lanthanide ion. Kinetic studies of the 1-Ln series were performed to elucidate correlations between overpotential and turnover frequencies of the 4f-based electrocatalysts.

Triarylphosphine oxides (Ar 3 P=O) are being intensely studied as electron-accepting (n-type) materials. Despite the widespread application of these compounds as electron conductors, experimental data regarding the structural and electronic properties of their negatively charged states remain scarce owing to their propensity for follow-up chemistry. Herein, a carefully designed triarylphosphine oxide scaffold is disclosed that comprises sterically demanding spirofluorenyl moieties to shield the central phosphoryl (P=O) moiety. This compound undergoes chemical one-electron reduction to afford an exceptionally stable radical anion, which was isolated and characterized by X-ray crystallography for the very first time. The experimental data, corroborated by computational studies, shall allow for the construction of phosphine oxide materials with enhanced stability., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The syntheses of four nearly isostructural uranium(IV) monoarene complexes, supported by the arene anchored tris(aryloxide) chelate, [((Ad,Me)ArO)3mes](3-), are reported. Oxidation of the uranium(III) precursor [(((Ad,Me)ArO)3mes)U], 1, in the presence of tetrahydrofuran (THF) results in THF coordination and distortion of the equatorial coordination sphere to afford the uranium(IV) η(6)-arene complexes, [(((Ad,Me)ArO)3mes)U(X)(THF)], 2-X-THF, (where X = F, Cl, Br, or I) as their THF adducts. The solvate-free trigonally ligated [(((Ad,Me)ArO)3mes)U(F)], 2-F, was prepared and isolated in the absence of coordinating solvents for comparison.

Synthetic studies on the redox chemistry of trivalent uranium monoarene complexes were undertaken with a complex derived from the chelating tris(aryloxide)arene ligand ((Ad,Me) ArO)3 mes(3-) . Cyclic voltammetry of [{((Ad,Me) ArO)3 mes}U(III) ] (1) revealed a nearly reversible and chemically accessible reduction at -2.495 V vs. Fc/Fc(+) -the first electrochemical evidence for a formally divalent uranium complex. Chemical reduction of 1 indicates that reduction induces coordination and redox isomerization to form a uranium(IV) hydride, and addition of a crown ether results in hydride insertion into the coordinated arene to afford uranium(IV) complexes. This stoichiometric reaction sequence provides structural insight into the mechanism of arene functionalization at diuranium inverted sandwich complexes., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)