Plutonium is a metal of both technological relevance and fundamental scientific interest. Nevertheless, the electronic structure of plutonium, which directly influences its metallurgical properties, is poorly understood. For example, plutonium's 5f electrons are poised on the border between localized and itinerant, and their theoretical treatment pushes the limits of current electronic structure calculations. Here we extend the range of complexity exhibited by plutonium with the discovery of superconductivity in PuCoGa5. We argue that the observed superconductivity results directly from plutonium's anomalous electronic properties and as such serves as a bridge between two classes of spin-fluctuation-mediated superconductors: the known heavy-fermion superconductors and the high-T(c) copper oxides. We suggest that the mechanism of superconductivity is unconventional; seen in that context, the fact that the transition temperature, T(c) approximately 18.5 K, is an order of magnitude greater than the maximum seen in the U- and Ce-based heavy-fermion systems may be natural. The large critical current displayed by PuCoGa5, which comes from radiation-induced self damage that creates pinning centres, would be of technological importance for applied superconductivity if the hazardous material plutonium were not a constituent.

Covalency in Ln-Cl bonds of Oh-LnCl6(x-) (x = 3 for Ln = Ce(III), Nd(III), Sm(III), Eu(III), Gd(III); x = 2 for Ln = Ce(IV)) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L3,2-edge and M5,4-edge XAS were also used to characterize CeCl6(x-) (x = 2, 3). The M5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce(III) and Ce(IV)). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (t2g* and eg*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce(III) to Ce(IV) had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl6(3-) (formally Ln(III)), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce(IV) 4f-orbital mixing (t1u* + t2u*) in CeCl6(2-). This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl6(2-) (M = Ti, Zr, Hf, U).

The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation (BEC) and superfluidity, which have been tested experimentally in a variety of different systems. When bosons are interacting, disorder can destroy condensation leading to a so-called Bose glass. This phase has been very elusive to experiments due to the absence of any broken symmetry and of a finite energy gap in the spectrum.Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (Br-doped dichloro-tetrakis-thiourea-Nickel, DTN).The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand-canonical ensemble; Br-doping introduces disorder in the hoppings and interaction strengths, leading to localization of the bosons into a Bose glass down to zero field, where it acquires the nature of an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the BEC (corresponding to a magnetically ordered phase) is marked by a novel, universal exponent governing the scaling on the critical temperature with the applied field, in excellent agreement arXiv:1109.4403v2 [cond-mat.str-el] 21 Sep 2011 2 with theoretical predictions. Our study represents the first, quantitative account of the universal features of disordered bosons in the grand-canonical ensemble.PACS numbers: 03.75. Lm, 71.23.Ft, 68.65.Cd, 72.15.Rn Introduction. Disorder can have a very strong impact on quantum fluids. Due to their wave-like nature, quantum particles are subject to destructive interference when scattering against disordered potentials. This leads to their quantum localization (or Anderson localization), which prevents e.g.electrons from conducting electrical currents in strongly disordered metals [1], and non-interacting bosons from condensing into a zero-momentum state [2]. Yet interacting bosons represent a matter wave with arbitrarily strong non-linearity, whose localization properties in a random environment cannot be deduced from the standard theory of Anderson localization. For strongly interacting bosons it is known that Anderson localization manifests itself in the Bose glass: in this phase the collective modes of the system -and not the individual particles -are Anderson-localized over arbitrarily large regions, leading to a gapless energy spectrum, and a finite compressibility of the fluid [3, 4]. Moreover nonlinear bosonic matter waves can undergo a localization-delocalization quantum phase transition in any spatial dimension when the interaction strength is varied [3, 4]; the transition brings the system from a non-interacting Anderson insulator to an interacting superfluid condensate, or from a superfluid to a Bose glass. Such a transition is relevant for a large variety of physical systems, including superfluid helium in porous media [6], Cooper pairs in disordered superconductors [7], and cold atoms in random optical potenti...

A series of ionic liquids containing different paramagnetic anions have been prepared and all show paramagnetic behavior with potential applications for magnetic and electrochromic switching as well as novel magnetic transport; also, the tetraalkylphosphonium-based ionic liquids reveal anomalous magnetic behavior.

The replacement of precious-metal catalysts with cheap and abundant metals is a major goal of sustainable chemistry. [1] Hydrogenation catalysts have diverse and widespread applications, including the production of biorenewable chemicals and fuels, commodity chemicals, and the synthesis of fine chemicals and pharmaceuticals. [2][3][4] Homogeneous rhodium, ruthenium, and iridium catalysts are also of critical importance in asymmetric hydrogenation. [5] Despite significant recent advances, the design of earth-abundant-metal hydrogenation catalysts has lagged behind, perhaps because of the tendency of 3d metals to engage in one-electron or radical chemistry. Several iron catalysts have been developed for the hydrogenation of ketones or alkenes, but they are typically chemoselective, reducing only one class of substrate. [6][7][8][9] Furthermore, iron catalysts are often quite sensitive to additional oxygen-and nitrogen-containing functional groups and water. [10] There is growing evidence that cobalt complexes can be effective catalysts for homogeneous hydrogenation. Cobalt(I) complexes, such as [Co(H)(CO) 4 ] and [Co(H)(CO)(PnBu 3 ) 3 ], are known to catalyze the hydrogenation of alkenes and arenes under hydroformylation conditions (> 120 8C, > 30 atm H 2 /CO). [11][12][13] Diiminopyridine cobalt complexes and the dinitrogen complex [Co(H)(N 2 )(PPh 3 ) 3 ] catalyze olefin hydrogenation at room temperature, [14,15] and an asymmetric hydrogenation of substituted styrenes was recently developed. [16] However, prior examples of cobalt hydrogenation catalysts have been quite limited in substrate scope, and nearly all have involved cobalt(I). [17,18] Herein, we report a cobalt-based catalytic system for the homogeneous hydrogenation of alkenes, aldehydes, ketones, and imines. The hydrogenation reactions take place under very mild conditions and require no base additives. The ability to hydrogenate multiple classes of substrates and broad functional-group tolerance make this cobalt system a significant advance over previously reported earth-abundant-metal hydrogenation catalysts.We synthesized cobalt(II) complexes of the tridentate ligand bis[2-(dicyclohexylphosphino)ethyl]amine (PNHP Cy ) (Scheme 1). Previous work by Fryzuk et al. had shown that a related pincer amidodiphosphine ligand stabilized a squareplanar 15-electron d 7 -cobalt(II)-alkyl complex, [19] and we were interested in exploring the reactivity of this type of unusual odd-electron cobalt-alkyl species. Reaction of PNHP Cy with [(pyr) 2 Co(CH 2 SiMe 3 ) 2 ] [20] (pyr = pyridine) afforded the new cobalt(II)-alkyl complex [(PNP Cy )Co-(CH 2 SiMe 3 )] (1) as dark-yellow crystals. In the solid state, paramagnetic complex 1 has a square-planar geometry, and solution-state magnetic-moment measurements are also consistent with a square-planar low-spin d 7 configuration (m eff = 2.2 m B ). [21,22] The solution-state magnetic moment of complex 1 is quite similar to that of the related square-planar complex [(N(SiMe 2 CH 2 PPh 2 ) 2 )Co(CH 2 SiMe 3 )] (2.