An all‐uranium‐based electrochemical cell consisting of simple [U IV/V ( t Bu acac) 4 ] 0/+ and [U III/IV (N(SiMe 3 ) 2 ) 4 ] −/0 complexes as anolyte and catholyte species was constructed with a cell voltage of 2.2 V. The [U IV ( t Bu acac) 4 ] ( 1 ) and [U IV (N(SiMe 3 ) 2 ) 4 ] ( 2 ) complexes have favorable properties for redox‐flow‐battery applications, including reversible redox chemistry, relatively high stability toward electrochemical cycling, and high solubility in common organic solvents. The [U III/IV (N(SiMe 3 ) 2 ) 4 ] −/0 complexes were first isolated and characterized by Schelter et al., and performed well in electrochemical studies due to the comparably low reduction potential of −2.05 V vs. Fc/Fc + to the reduced uranium(III) species. Treatment of conveniently accessible 1 with AgSbF 6 allowed the isolation of [U V ( t Bu acac) 4 ][SbF 6 ] ( 3 ), which is the active catholyte species generated during cell charging. Galvanostatic cycling with charging and discharging at currents of 20 and 5 μA, respectively, was performed in a two‐compartment static H‐cell with high‐surface‐area carbon fiber electrodes to achieve a potential of 2.2 V. The success of this 1 || 2 cell‐provides a promising entry point to a potential future class of uranium‐based, nonaqueous redox‐flow‐battery electrolytes, not for use in personal devices but incorporated into underground energy storage systems, where weight and radioactivity levels are not an issue and where this abundant waste material could find new application.

Die in dieser Publikation behandelten Themen sollen viele verschiedene Aspekte der Chemie vermitteln, die einen guten & Uuml;berblick & uuml;ber die grundlegenden Kenntnisse der anorganischen Chemie geben und den gr & ouml;ss ten Teil einer Erstsemestervorlesung abdecken sollen. Dennoch geht das vermittelte Wissen weit & uuml;ber das Verst & auml;ndnis grundlegender Redox- oder S & auml;ure-Base-Reaktionen hinaus. Das Demonstrieren von Versuchen geht immer Hand in Hand mit der Vermittlung des richtigen und sicheren Umgangs mit Chemikalien. In vielen dieser Experimente wurden Chemikalien verwendet, die mit & auml;u ss erster Sorgfalt behandelt werden m & uuml;ssen. Ein Chemiker muss sich immer & uuml;ber die Gefahren im Klaren sein, die mit bestimmten Chemikalien verbunden sind. Stoffe, die stark mit Wasser, Luft oder mit chlorierten L & ouml;sungsmitteln reagieren, m & uuml;ssen immer unter den richtigen Bedingungen gehandhabt werden. Alle gezeigten Experimente sind kontrollierte Explosionen und Verbrennungen. Es w & auml;re schrecklich, sich vorzustellen, welche Sch & auml;den durch Fehlkalkulationen und falsche Anwendung entstehen k & ouml;nnen. Diese Arbeit sollte auch als Mahnung verstanden werden, Chemikalien mit dem n & ouml;tigen Respekt, aber niemals mit Angst zu behandeln. Schlie ss lich sind chemische Reaktionen das t & auml;gliche Gesch & auml;ft fast aller Chemiker. Die Erkenntnisse und Erfahrungen, die man durch die Lekt & uuml;re dieses Artikels oder durch das Anschauen von Videos zu diesen chemischen Experimenten gewinnt, k & ouml;nnen gegebenenfalls den Unterricht im H & ouml;rsaal bereichern, aber sie k & ouml;nnen niemals das Gef & uuml;hl eines Live-Experiments ersetzen. The topics addressed in this publication should have taught many different aspects of chemistry, providing a good overview of the fundamental knowledge of inorganic chemistry and covering the major part of a first-semester lecture. Still, the knowledge transferred goes far beyond the understanding of basic redox or acid-base reactions. Demonstrating experiments always goes hand in hand with teaching the correct and safe handling of chemicals. In many of these experiments, chemicals were used that must be treated with extreme care. A chemist should always be aware of the dangers associated with specific chemicals. Substances that react vigorously with water, in air, or with chlorinated solvents must always be handled under the right conditions. All demonstrated experiments involved controlled explosions and combustions. It would be dreadful to imagine the damage resulting from miscalculations and improper use. This work should also serve as a reminder to treat chemicals with the appropriate respect, but never with fear. In the end, chemical reactions are the everyday business of nearly every chemist. The experience and knowledge gained from reading this text or watching a movie about one of these chemical experiments can enhance classroom teaching, if necessary, but can never replace the feeling of a live performance experiment.

The genuine trivalent uranium complex, K[UIII(mesBAP)4], employing four bidentate bis(2,4,6-trimethylbenzoyl)phosphide (mesBAP) chelating ligands, is reported and obtained by the reduction of the literature-known tetravalent analog [UIV(mesBAP)4]. Hence, the bis(acyl)phosphide mesBAP ligand allowed to establish a fully reversible redox couple with uranium in the oxidation states +III and +IV. In both complexes [U(mesBAP)4]0/-, the uranium ions are coordinated to four mesBAP ligands in a square antiprismatic geometry. All new compounds have been characterized by single-crystal XRD analysis, 1H and 31P NMR, and UV/Vis/NIR electronic absorption spectroscopy, as well as SQUID magnetization and electrochemical measurements, and CW X-band EPR in the case of the trivalent complex. A trivalent uranium complex, K[UIII(mesBAP)4], has been synthesized and spectroscopically, electrochemically, and magnetochemically characterized. An X-ray diffraction analysis on single-crystals of [K(2.2.2-crypt)][UIII(mesBAP)4] reveals the molecular structure, consisting of four bis(acyl)phosphide chelates coordinated to the electron-rich uranium ion in a distorted tetragonal antiprismatic geometry. [UIII(mesBAP)4]- complements the known [UIV(mesBAP)4], thus providing an isostructural U(III/IV) redox pair with axial cavities for small molecule activation.image

Transmetalation of potassium salts of differently substituted acetylacetonate (acac) and β-ketoiminate (acnac) with [U(I)3(dioxane)1.5] and [U(I)4(dioxane)2] resulted in the formation of homoleptic, octahedral complexes [U(tBuacnacPh)3] (with tBuacnacPh = 2,2,6,6-tetramethyl-5-(phenylimino)heptan-3-onate) in the oxidation states +III and +IV and the homoleptic, square prismatic complexes [UIV(MeacnacPh)4] (with MeacnacPh = 4-(phenylimino)pentan-2-onate) and the homoleptic, square antiprismatic complexes [U(tBuacac)4] [with acac = 2,2,6,6-tetramethyl-3,5-heptanedionate (tBuacac), 2,2,6,6-tetramethyl,4-methyl-3,5-heptanedionate (tBuacMeac), and 2,2,6,6-tetramethyl-4-phenyl-3,5-heptanedionate (tBuacPhac)] in oxidation states +III, +IV, and +V. Oxidation of [UIII(tBuacnacPh)3] (1) with AgOTf yielded [UIV(tBuacnacPh)3][OTf] (2), which was fully characterized by single-crystal X-ray diffraction analysis, a combination of ultraviolet/visible/near-infrared, nuclear magnetic resonance, and infrared spectroscopies, and solid-state superconducting quantum interference device magnetization studies. Complexation of the sterically less encumbering ligand derivative MeacnacPh provided access to the tetravalent, square antiprismatic complex [UIV(MeacnacPh)4] (3). Cyclovoltammetric analysis of the square antiprismatic [UIV(tBuacac)4] (4), [UIV(tBuacMeac)4] (5), and [UIV(tBuacPhac)4] (6) revealed reversible anodic and cathodic waves, attributable to the U(III/IV) and U(IV/V) redox couples, both being chemically accessible, as tested in the case of 5. The corresponding U(III) and U(V) compounds, [K(2.2.2-cryptand)][UIII(tBuacMeac)4] (7) and [UV(tBuacMeac)4][SbF6] (8), were synthesized accordingly. Unfortunately, reduced 7 proved to be too reactive for isolation and could only be detected by electron paramagnetic resonance spectroscopy. Notably, electrochemical studies on homoleptic uranium(IV) complexes with differently derivatized (R) acRac ligands (R = H, Me, or Ph) feature large electrochemical windows of up to 2.91 V, measured between the uranium(III) and the uranium(V) species, in addition to high stability toward repeated potential scans.

Abstract With a view to developing multimetallic molecular catalysts that mimic the oxygen‐evolving catalyst (OEC) in Nature's photosystem II, the synthesis of various dicubanoid manganese clusters is described and their catalytic activity investigated for water oxidation in basic, aqueous solution. Pyridinemethanol‐based ligands are known to support polynuclear and cubanoid structures in manganese coordination chemistry. The chelators 2,6‐pyridinedimethanol (H2L1) and 6‐methyl‐2‐pyridinemethanol (HL2) were chosen to yield polynuclear manganese complexes; namely, the tetranuclear defective dicubanes [MnII 2MnIII 2(HL1)4(OAc)4(OMe)2] and [MnII 2MnIII 2(HL1)6(OAc)2] (OAc)2⋅2 H2O, as well as the octanuclear‐dicubanoid [MnII 6MnIII 2(L2)4(O)2(OAc)10(HOMe/OH2)2]⋅3MeOH⋅MeCN. In freshly prepared solutions, polynuclear species were detected by electrospray ionization mass spectrometry, whereas X‐band electron paramagnetic resonance studies in dilute, liquid solution suggested the presence of divalent mononuclear Mn species with g values of 2. However, the magnetochemical investigation of the complexes’ solutions by the Evans technique confirmed a haphazard combination of manganese coordination complexes, from mononuclear to polynuclear species. Subsequently, the newly synthesized and characterized manganese molecular complexes were employed as precursors to prepare electrode‐deposited films in a buffer‐free solution to evaluate and compare their stability and catalytic activity for water oxidation electrocatalysis.

A closed synthetic cycle for the transformation of carbon dioxide to carbonate with a mid-valent tris(aryloxide)-ligated uranium(IV) terminal oxo complex is presented herein. Starting from the previously reported uranium(III) complex, [U-III(OArAd,Ad,Me)(3)], the uranium(V) terminal oxo complex, obtained by oxidation with N2O or NO, can be reduced with KC8 to yield CO2 activating anionic uranium(IV) oxo complexes [((ArO)-Ar-Ad,Ad,Me)(3)U-IV(O)](-). The cycle proceeds with the formation of [((ArO)-Ar-Ad,Ad, Me)(2)(kappa(2)-(ArOCO2)-Ar-Ad,Ad,Me)U-IV(mu-kappa(1):kappa(2)-CO3)](-) upon reaction of the oxo anion with excess CO2 that adds to the terminal oxido ligand and inserts into the uranium-aryloxide bond. Treating this complex with trimethylsilyl halide eliminates both carbonates and generates, for instance, [K(2.2.2-crypt)]-[((ArO)-Ar-Ad,Ad,Me)(3)U-IV(I)(2)], which can ultimately be reduced with KC8 to recover the trivalent starting material, thus closing the cycle. In contrast, reaction of the 18-crown-6 stabilized U(IV) oxo analogue with CO2 yields a rare and isolable example of a uranium complex with a mu-kappa(1):kappa(2)-CO3-bound carbonate weakly interacting with the [K(18-crown-6)(THF)](+) moiety; here, CO2 insertion and formation of an aryl carbonate ligand are not observed.