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© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The concept of oxidation state (OS) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum-chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS=+9 was observed for the isolated [IrO4]+cation in vacuum. The prediction of OS=+10 for isolated [PtO4]2+cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. For high OS species, oxidation of the ligands, for example, of O−2with formation of.O−1and O−O bonds, and partial reduction of the metal center may be favorable, possibly leading to non-Lewis type structures.

© 2018 The Royal Society of Chemistry. Since the discovery of the first all-boron fullerenes B40-/0, metal-doped borospherenes have received extensive attention. So far, in spite of theoretical efforts on metalloborospherenes, the feasibility of actinide analogues remains minimally explored. Here we report a series of actinide borospherenes AnBn(An = U, Th; n = 36, 38, and 40) using DFT-PBE0 calculations. All the AnBncomplexes are found to possess endohedral structures (An@Bn) as the global minima. In particular, U@B36(C2h,3Ag) and Th@B38(D2h,1Ag) exhibit nearly ideal endohedral borospherene structures. The C2hU@B36and D2hTh@B38complexes are predicted to be highly robust both thermodynamically and dynamically. In addition to the actinide size match to the cage, the covalent character of the metal-cage bonding in U@B36and Th@B38affords further stabilization. Bonding analysis indicates that U@B36and Th@B38can be qualified as 32-electron systems, and Th@B38exhibits 3D aromaticity with σ plus π double delocalization bonding. The results demonstrate that doping with appropriate actinide atoms is promising to stabilize diverse borospherenes, and may provide routes for borospherene modification and functionalization.

© 2017 Elsevier B.V. In uranyl coordination complexes, UO2(L)n2+, uranium in the formally dipositive [O=U=O]2+ moiety is coordinated by n neutral organic electron donor ligands, L. The extent of ligand electron donation, which results in partial reduction of uranyl and weakening of the U=O bonds, is revealed by the magnitude of the red-shift of the uranyl asymmetric stretch frequency, ν3. This phenomenon appears in gas-phase complexes in which uranyl is coordinated by electron donor ligands: the ν3 red-shift increases as the number of ligands and their proton affinity (PA) increases. Because PA is a measure of the enthalpy change associated with a proton-ligand interaction, which is much stronger and of a different nature than metal ion-ligand bonding, it is not necessarily expected that ligand PAs should reliably predict uranyl-ligand bonding and the resulting ν3 red-shift. Here, ν3 was measured for uranyl coordinated by ligands with a relatively broad range of PAs, revealing a surprisingly good correlation between PA and ν3 frequency From computed ν3 frequencies for bare UO2 cations and neutrals, it is inferred that the effective charge of uranyl in UO2(L)n2+ complexes can be reduced to near zero upon ligation by sufficiently strong charge-donor ligands. The basis for the correlation between ν3 and ligand PAs, as well as limitations and deviations from it, are considered. It is demonstrated that the correlation evidently extends to a ligand that exhibits polydentate metal ion coordination.

© 2017 American Chemical Society. The reaction of uranyl nitrate with terephthalic acid (H2TP) under hydrothermal conditions in the presence of an organic base, 1,3-(4,4′-bispyridyl)propane (BPP) or 4,4′-bipyridine (BPY), provided four uranyl terephthalate compounds with different entangled structures by a pH-tuning method. [UO2(TP)1.5](H2BPP)0.5·2H2O (1) obtained in a relatively acidic solution (final aqueous pH, 4.28) crystallizes in the form of a noninterpenetrated honeycomb-like two-dimensional network structure. An elevation of the solution pH (final pH, 5.21) promotes the formation of a dimeric uranyl-mediated polycatenated framework, [(UO2)2(μ-OH)2(TP)2]2(H2BPP)2·4.5H2O (2). Another new polycatenated framework with a monomeric uranyl unit, [(UO2)2(TP)3](H2BPP) (3), begins to emerge as a minor accompanying product of 2 when the pH is increased up to 6.61, and turns out to be a significant product at pH 7.00. When more rigid but small-size BPY molecules replace BPP molecules, [UO2(TP)1.5](H2BPP)0.5(4) with a polycatenated framework similar to 3 was obtained in a relatively acidic solution (final pH, 4.81). The successful preparation of 2-4 represents the first report of uranyl-organic polycatenated frameworks derived from a simple H2TP linker. A direct comparison between these polycatenated frameworks and previously reported uranyl terephthalate compounds suggests that the template and cavity-filling effects of organic bases (such as BPP or BPY), in combination with specific hydrothermal conditions, promote the formation of uranyl terephthalate polycatenated frameworks.

© 2017 American Chemical Society. The synthesis, reactivity, structures, and bonding in gas-phase binary and complex oxide anion molecules of protactinium and uranium have been studied by experiment and theory. The oxalate ions, AnVO2(C2O4)−, where An = Pa or U, are essentially actinyl ions, AnVO2+, coordinated by an oxalate dianion. Both react with water to yield the pentavalent hydroxides, AnVO(OH)2(C2O4)−. The chemistry of Pa and U becomes divergent for reactions that result in oxidation: whereas PaVIis inaccessible, UVIis very stable. The UVO2(C2O4)−complex exhibits a remarkable spontaneous exothermic replacement of the oxalate ligand by O2to yield UO4-and two CO2molecules. The structure of the uranium tetroxide anion is computed to correspond to distorted uranyl, UVIO22+, coordinated in the equatorial plane by two equivalent O atoms each having formal charges of −1.5 and U-O bond orders intermediate between single and double. The unreactive nature of PaVO2(C2O4)−toward O2is a manifestation of the resistance toward oxidation of PaV, and clearly reveals the disparate chemistries of Pa and U. The uranium tetroxide anion, UO4-, reacts with water to yield UO5H2-. Infrared spectra obtained for UO5H2-confirm the computed lowest-energy structure, UO3(OH)2

© 2017 the Owner Societies. Actinide disulphide dications, AnS22+, were produced in the gas phase for An = Th and Np by reaction of An2+ cations with the sulfur-atom donor COS, in a sequential abstraction process of two sulfur atoms, as examined by FTICR mass spectrometry. For An = Pu and Am, An2+ ions were unreactive with COS and did not yield any sulphide species. High level multiconfigurational (CASPT2) calculations were performed to assess the structures and bonding of the new AnS22+ species obtained for An = Th, Np, as well as for An = Pu to examine trends along the An series, and for An = U to compare with a previous experimental study and DFT computational scrutiny of US22+. The CASPT2 results showed that, like in the case of uranium, the new AnS22+ ions have ground states with triangular geometries, corresponding to the presence of a persulphide in the case of thorium that formally leads to a stable ThIVS22+ species, while a supersulphide appears to be present in the case of U, Np and Pu, formally leading to a AnIIIS22+ species. The computations also revealed that linear thioactinyl structures are higher in energy, with a difference that increases fourfold upon moving from U to Pu, apparently indicating that it will be even more pronounced for Am.

A non-oxido V(v) complex with glutaroimide-dioxime (H3L), a ligand for recovering uranium from seawater, was synthesized from aqueous solution as Na[V(L)2]·2H2O, and the structure determined by X-ray diffraction. It is the first non-oxido V(v) complex that has been directly synthesized in and crystallized from aqueous solution. The distorted octahedral structure contains two fully deprotonated ligands (L3-) coordinating to V5+, each in a tridentate mode via the imide N (RV-N = 1.96 Å) and oxime O atoms (RV-O = 1.87-1.90 Å). Using 17O-labelled vanadate as the starting material, concurrent 17O/51V/1H/13C NMR, in conjunction with ESI-MS, unprecedentedly demonstrated the stepwise displacement of the oxido V 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 O bonds by glutaroimide-dioxime and verified the existence of the "bare" V5+/glutaroimide-dioxime complex, [V(L)2]-, in aqueous solution. In addition, the crystal structure of an intermediate 1 : 1 V(v)/glutaroimide-dioxime complex, [VO2(HL)]-, in which the oxido bonds of vanadate are only partially displaced, corroborates the observations by NMR and ESI-MS. Results from this work provide important insights into the strong sorption of vanadium on poly(amidoxime) sorbents in the recovery of uranium from seawater. Also, because vanadium plays important roles in biological systems, the syntheses of the oxido and non-oxido V5+ complexes and the unprecedented demonstration of the displacement of the oxido VO bonds help with the on-going efforts to develop new vanadium compounds that could be of importance in biological applications.

© the Owner Societies 2016. Activation of CO2is demonstrated by its spontaneous dissociative reaction with the gas-phase anion complex NUOCl2-, which can be considered as NUO+coordinated by two chloride anion ligands. This reaction was previously predicted by density functional theory to occur exothermically, without barriers above the reactant energy. The present results demonstrate the validity of the prediction of microscopic reversibility, and provide a rare case of spontaneous dissociative addition of CO2to a gas-phase complex. The activation of CO2by NUOCl2-proceeds by conversion of a U≡N bond to a U=O bond and creation of an isocyanate ligand to yield the complex UO2(NCO)Cl2-, in which uranyl, UO22+, is coordinated by one isocyanate and two chloride anion ligands. This activation of CO2by a uranium(VI) nitride complex is distinctive from previous reports of oxidative insertion of CO2into lower oxidation state U(III) or U(IV) solid complexes, during which both C-O bonds remain intact. This unusual observation of spontaneous addition and activation of CO2by NUOCl2-is a result of the high oxophilicity of uranium. If the computed Gibbs free energy of the reaction pathway, rather than the energy, is considered, there are barriers above the reactant asymptotes such that the observed reaction should not proceed under thermal conditions. This result provides a demonstration that energy rather than Gibbs free energy determines reactivity under low-pressure bimolecular conditions.

© 2016 The Royal Society of Chemistry. The divalent oxidation state is increasingly stable relative to the trivalent state for the later actinide elements, with californium the first actinide to exhibit divalent chemistry under moderate conditions. Although there is evidence for divalent Cf in solution and solid compounds, there are no reports of discrete complexes in which CfIIis coordinated by anionic ligands. Described here is the divalent Cf methanesulfinate coordination complex, CfII(CH3SO2)3-, prepared in the gas phase by reductive elimination of CH3SO2from CfIII(CH3SO2)4-. Comparison with synthesis of the corresponding Sm and Cm complexes reveals reduction of CfIIIand SmIII, and no evidence for reduction of CmIII. This reflects the comparative 3+/2+ reduction potentials: Cf3+(-1.60 V) ≈ Sm3+(-1.55 V) ≫ Cm3+(-3.7 V). Association of O2to the divalent complexes is attributed to formation of superoxides, with recovery of the trivalent oxidation state. The new gas-phase chemistry of californium, now the heaviest element to have been studied in this manner, provides evidence for CfIIcoordination complexes and similar chemistry of Cf and Sm.

ATP-sensitive potassium (K+ATP) channel openers such as cromakalim and pinacidil exhibit both potent vasodilatory and anti-ischemic properties. U-89232, a cyanoguanidine analog of cromakalim, has recently been found to exhibit myocardial protection during ischemia without altering in vivo hemodynamics. We examined the effects of U-89232, cromakalim and pinacidil in isolated vascular and cardiac tissue and tested whether glyburide, a KATP channel blocker, could antagonize their effects. All three compounds produced concentration-dependent relaxation in isolated vascular segments, with cromakalim being approximately 100-fold more potent than either pinacidil or U-89232. Glyburide completely antagonized the effects of pinacidil but merely blunted the effects of cromakalim and U-89232. In an isolated rabbit cardiac tissue preparation, U-89232 had little effect on maximum tension in cardiac muscle, whereas cromakalim and pinacidil significantly decreased maximum developed tension in a concentration-dependent manner. Glyburide effectively antagonized the effects of cromakalim and pinacidil in cardiac tissue. These data suggest that U-89232, although chemically related to cromakalim, possesses activity which is not common to known potassium channel openers.