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High-quality single crystals of NaYbSe2, which resembles a perfect triangular-lattice antiferromagnet without intrinsic disorder, are investigated by magnetization and specific heat, as well as the local probe techniques nuclear magnetic resonance (NMR) and electron spin resonance. The low-field measurements confirm the absence of any spin freezing or long-range magnetic order down to 50 mK, which suggests a quantum spin liquid ground (QSL) state with gapless excitations. Instability of the QSL state is observed upon applying magnetic fields. For the H⊥c direction, a field-induced magnetic phase transition is observed above 2 T from the CP(T ) data, agreeing with a clear Ms/3 plateau of M(H), which is associated with an up-up-down spin arrangement. For the H ǀǀ c direction, a field-induced transition could be evidenced at a much higher field range (9–21 T). The 23Na NMR measurements provide microscopic evidence of field-induced ordering for both directions. A reentrant behavior of TN, originating from the thermal and quantum spin fluctuations, is observed for both directions. The anisotropic exchange interactions J⊥ ≃ 4.7 K and Jz ≃ 2.33 K are extracted from the modified bond-dependent XXZ model for the spin- 1/2 triangular-lattice antiferromagnet. The absence of magnetic long-range order at zero fields is assigned to the effect of strong bond frustration, arising from the complex spin-orbit entangled 4 f ground state. Finally, we derive the highly anisotropic magnetic phase diagram, which is discussed in comparison with the existing theoretical models for spin- 1/2 triangular-lattice antiferromagnets.

The crystal structure of the important industrial orangepigment PO82, major part of the BASF Colors amp; Effects productSicopal Orange K L 2430, was solved from combined X ray singlecrystal, X ray and neutron powder diffraction,119Sn Mössbauer spec troscopy, transmission electron microscopy, electron diffraction, andchemical analyses. The structure contains Keggin type clusters com posed of four [M3O13] trimers consisting each of three MO6 octahedra that share edges and one common oxygen atom connecting the trimersto the central ZnO4tetrahedron. The octahedrally coordinated metalatom position is mixed occupied by Ti4 ,Sn4 , and Zn2 . AdjacentKeggin clusters share vertices and are further interconnected to fourZnO4tetrahedra. This framework of interconnectedMO6octahedra andZnO4tetrahedra contains channels along [110], in which the Sn2 cat ions are located

Magnetization and high-resolution x-ray diffraction measurements of the Kitaev-Heisenberg material α− RuCl3 reveal a pressure-induced crystallographic and magnetic phase transition at a hydrostatic pressure of p∼0.2 GPa. This structural transition into a triclinic phase is characterized by a very strong dimerization of the Ru-Ru bonds, accompanied by a collapse of the magnetic susceptibility. Ab initio quantum-chemistry calculations disclose a pressure-induced enhancement of the direct 4d−4d bonding on particular Ru-Ru links, causing a sharp increase of the antiferromagnetic exchange interactions. These combined experimental and computational data show that the Kitaev spin-liquid phase in α−RuCl3 strongly competes with the crystallization of spin singlets into a valence bond solid., This research has been supported by the DFG via SFB 1143 and WO 1532/3-2 and by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 796048. M. Mezouar is acknowledged for providing beamtime at ID27 at the ESRF and for fruitful discussions. S.P.L. is grateful to CONICET for financial support during her stay at the ESRF. R.Y. and L.H. acknowledge Ulrike Nitzsche for technical support as concerns the ab initio calculations. P.L.K and D.G.M. were supported by the Gordon and Betty Moore Foundation EPiQS Initiative Grant No. GBMF4416. S.N. was supported by the U.S. Department of Energy, Basic Energy Sciences, Scientific User Facilities Division under contract DE-AC0500OR22725 with the Oak Ridge National Laboratory.

A quantum spin liquid might be realized in α-RuCl3, a honeycomb-lattice magnetic material with substantial spin-orbit coupling. Moreover, α-RuCl3 is a Mott insulator, which implies the possibility that novel exotic phases occur upon doping. Here, we study the electronic structure of this material when intercalated with potassium by photoemission spectroscopy, electron energy loss spectroscopy, and density functional theory calculations. We obtain a stable stoichiometry at K0.5RuCl3. This gives rise to a peculiar charge is proportionation into formally Ru2+ (4d6) and Ru3+ (4d5). Every Ru 4d5 site with one hole in the t2g shell is surrounded by nearest neighbors of 4d6 character, where the t2g level is full and magnetically inert. Thus, each type of Ru site forms a triangular lattice, and nearest-neighbor interactions of the original honeycomb are blocked.

We optimized the syntheses of α- and β-Bi4I4 and transferred the method to the very bismuth-rich iodides Bi14I4, Bi16I4, and Bi18I. Phase-pure, microcrystalline powders of BimI4 (m = 4, 14, 18) can now by synthesized on a multigram scale. Conditions for the growth of single crystals of Bi16I4 and Bi18I4 were determined. The redetermination of the crystal structure of Bi16I4 hints at a stacking disorder or the presence of 1͚[BimI4] ribbons with m = 14 and 18 among the dominant type along with m = 16. The electronic band structures for m = 14, 16, and 18 were calculated including spin-orbit coupling. They vary markedly with m and show numerous bands crossing the Fermi level, predicting a 3D-metallic behavior. Measurements of the electrical resistivity of a polycrystalline sample of Bi14I4 as well as polycrystalline and single-crystalline samples of Bi18I4 confirmed their metallic nature over the temperature range 300 K to 2 K. For BiI4, a positive and strictly linear magnetoresistance at 2 K in static magnetic fields up to 14 T was observed, which could indicate a topologically nontrivial electronic state.

PdBi2S2 and Pd3Bi2Se2 have been successfully prepared in the form of nanoparticles with diameters of ∼50 nm by microwave-assisted modified polyol synthesis at low temperatures. The composition and morphology of the samples have been studied by means of powder X-ray diffraction as well as electron microscopy methods, including X-ray intensity mapping on the nanoscale. Superconducting properties of the as-prepared samples have been characterized by electrical resistivity measurements down to low temperatures (∼0.2 K). Deviations from the bulk metallic behavior originating from the submicrometer nature of the samples were registered for both phases. A significant critical-field enhancement up to 1.4 T, i.e., 4 times higher than the value of the bulk material, has been revealed for Pd3Bi2Se2. At the same time, the critical temperature is suppressed to 0.7 K from the bulk value of ∼1 K. A superconducting transition at 0.4 K has been observed in nanocrystalline Pd3Bi2S2. Here, a zero-temperature upper critical field of ∼0.5 T has been estimated. Further, spark plasma-sintered Pd3Bi2S2 and Pd3Bi2Se2 samples have been investigated. Their superconducting properties are found to lie between those of the bulk and nanosized samples.

Two novel 46-membered Co(II) metallomacrocycles, [Co2Cl4(L1)2]∙CH2Cl2 and [Co2(NO3)2(L1)2(H2O)2](NO3)2∙4H2O, with 1,4-bis[4-(2-pyridylmethylideneamino)phenyloxy]benzene (L1) have been synthesized and characterized. Both Co(II) centers in these dinuclear complexes possess an octahedral coordination environment formed by a N4 donor set of two L1 ligands and two chloride anions or one monodentate nitrate and one water molecule, respectively. Whereas in the first case disordered solvent molecules are present in the macrocycle’s cavity in the second one a nitrate anion is embedded in the macrocycle. Furthermore, the molecular structures of L1, L3 and L4 were determined and solution studies of the complex formation of these ligands with Co(II), Ni(II) and Cu(II) in dichloromethane/methanol (v/v = 1:1) using UV/Vis and ESI-MS spectroscopic measurements were performed. In contrast to the self-assembling behavior of the bis(2-pyridylimine) ligand L1 the bis(3-pyridylimine) ligand L4 was also demonstrated to form metallogels when reacted with NiCl2∙6H2O in tetrahydrofuran under defined conditions.

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Die Koordinationschemie von Uran(VI) hat in den letzten Jahren vielfältiges Interesse gefunden. Ursachen dafür sind sowohl dessen Bedeutung im Rahmen der Kernenergiegewinnung als auch Probleme bei der Aufarbeitung sowie Lagerung von verbrauchten Kernbrennstoffen. Weitere Fragestellungen beziehen sich auf die Umweltrelevanz von U(VI) als Folge seiner natürlichen Verbreitung sowie bergbaulicher Altlasten. Schließlich werden auch potentielle Anwendungsoptionen von spezifischen Komplexverbindungen des Urans diskutiert. Wir haben einige Imin-Liganden synthetisiert und drei neue Komplexverbindungen mit UO2(NO3)2 strukturell charakterisiert. Zum Vergleich wurden auch die strukturanalogen Aminderivate in die Untersuchungen einbezogen. Extraktionsexperimente mit den genannten Liganden zeigen differenzierte Extraktionseigenschaften gegenüber U(VI) mit einer ausgeprägten Selektivität gegenüber Eu(III).

wird nachgereicht

The coordination chemistry of uranium in different oxidation states has recently generated much attention due to several reasons. The most important reason is the separation of U(VI) present in radioactive waste, but also the effects of U(VI) on our environment are of great interest.[1] The extraction and separation of U(VI) and other actinides, especially the separation from lanthanides, is most difficult due to their similar chemical behavior.[2] However, the introduction of soft heteroatoms, as imine nitrogen, in the ligand systems could be used as a tool for more selective and effective binding and extraction. We have synthesized and characterized some novel U(VI) complexes using multidentate Schiff base ligands. Structures of these complexes were characterized by X-ray crystallography and DFT calculations. It is the intention of this work to determine not only the structure of these complexes but also the extraction ability of the ligands towards U(VI) and Eu(III).