Strukturuntersuchungen an β-RuCl3, RuBr3 und RuJ3

Honeycomb-Structure RuI3 , A New Quantum Material Related to α-RuCl3

The layered honeycomb lattice material α-RuCl₃ has emerged as a prime candidate for displaying the Kitaev quantum spin liquid state, and as such has attracted much research interest. Here a new layered honeycomb lattice polymorph of RuI₃ , a material that is strongly chemically and structurally related to α-RuCl₃ is described_. The material is synthesized at moderately elevated pressures and is stable under ambient conditions. Preliminary characterization reveals that it is a metallic conductor, with the absence of long-range magnetic order down to 0.35 K and an unusually large T-linear contribution to the heat capacity. It is proposed that this phase, with a layered honeycomb lattice and strong spin-orbit coupling, provides a new route for the characterization of quantum materials.

Consistent gaussian basis sets of double- and triple-zeta valence with polarization quality of the fifth period for solid-state calculations

Consistent basis sets of double- and triple-zeta valence with polarization quality for the fifth period have been derived for periodic quantum-chemical solid-state calculations with the crystalline-orbital program CRYSTAL. They are an extension of the pob-TZVP basis sets, and are based on the full-relativistic effective core potentials (ECPs) of the Stuttgart/Cologne group and on the def2-SVP and def2-TZVP valence basis of the Ahlrichs group. We optimized orbital exponents and contraction coefficients to supply robust and stable self-consistent field (SCF) convergence for a wide range of different compounds. The computed crystal structures are compared to those obtained with standard basis sets available from the CRYSTAL basis set database. For the applied hybrid density functional PW1PW, the average deviations of calculated lattice constants from experimental references are smaller with pob-DZVP and pob-TZVP than with standard basis sets. © 2018 Wiley Periodicals, Inc.

Recent advances in technetium halide chemistry

Transition metal binary halides are fundamental compounds, and the study of their structure, bonding, and other properties gives chemists a better understanding of physicochemical trends across the periodic table. One transition metal whose halide chemistry is underdeveloped is technetium, the lightest radioelement. For half a century, the halide chemistry of technetium has been defined by three compounds: TcF6, TcF5, and TcCl4. The absence of Tc binary bromides and iodides in the literature was surprising considering the existence of such compounds for all of the elements surrounding technetium. The common synthetic routes that scientists use to obtain binary halides of the neighboring elements, such as sealed tube reactions between elements and flowing gas reactions between a molecular complex and HX gas (X = Cl, Br, or I), had not been reported for technetium. In this Account, we discuss how we used these routes to revisit the halide chemistry of technetium. We report seven new phases: TcBr4, TcBr3, α/β-TcCl3, α/β-TcCl2, and TcI3. Technetium tetrachloride and tetrabromide are isostructural to PtX4 (X = Cl or Br) and consist of infinite chains of edge-sharing TcX6 octahedra. Trivalent technetium halides are isostructural to ruthenium and molybdenum (β-TcCl3, TcBr3, and TcI3) and to rhenium (α-TcCl3). Technetium tribromide and triiodide exhibit the TiI3 structure-type and consist of infinite chains of face-sharing TcX6 (X = Br or I) octahedra. Concerning the trichlorides, β-TcCl3 crystallizes with the AlCl3 structure-type and consists of infinite layers of edge-sharing TcCl6 octahedra, while α-TcCl3 consists of infinite layers of Tc3Cl9 units. Both phases of technetium dichloride exhibit new structure-types that consist of infinite chains of [Tc2Cl8] units. For the technetium binary halides, we studied the metal-metal interaction by theoretical methods and magnetic measurements. The change of the electronic configuration of the metal atom from d(3) (Tc(IV)) to d(5) (Tc(II)) is accompanied by the formation of metal-metal bonds in the coordination polyhedra. There is no metal-metal interaction in TcX4, a Tc═Tc double bond is present in α/β-TcCl3, and a Tc≡Tc triple bond is present in α/β-TcCl2. We investigated the thermal behavior of these binary halides in sealed tubes under vacuum at elevated temperature. Technetium tetrachloride decomposes stepwise to α-TcCl3 and β-TcCl2 at 450 °C, while β-TcCl3 converts to α-TcCl3 at 280 °C. The technetium dichlorides disproportionate to Tc metal and TcCl4 above ∼600 °C. At 450 °C in a sealed Pyrex tube, TcBr3 decomposes to Na{[Tc6Br12]2Br}, while TcI3 decomposes to Tc metal. We have used technetium tribromide in the preparation of new divalent complexes; we expect that the other halides will also serve as starting materials for the synthesis of new compounds (e.g., complexes with a Tc3(9+) core, divalent iodide complexes, binary carbides, nitrides, and phosphides, etc.). Technetium halides may also find applications in the nuclear fuel cycle; their thermal properties could be utilized in separation processes using halide volatility. In summary, we hope that these new insights on technetium binary halides will contribute to a better understanding of the chemistry of this fascinating element.

Synthetic and coordination chemistry of the heavier trivalent technetium binary halides: uncovering technetium triiodide

Technetium tribromide and triiodide were obtained from the reaction of the quadruply Tc-Tc-bonded dimer Tc2(O2CCH3)4Cl2 with flowing HX(g) (X = Br, I) at elevated temperatures. At 150 and 300 °C, the reaction with HBr(g) yields TcBr3 crystallizing with the TiI3 structure type. The analogous reactions with flowing HI(g) yield TcI3, the first technetium binary iodide to be reported. Powder X-ray diffraction (PXRD) measurements show the compound to be amorphous at 150 °C and semicrystalline at 300 °C. X-ray absorption fine structure spectroscopy indicates TcI3 to consist of face-sharing TcI6 octahedra. Reactions of technetium metal with elemental iodine in a sealed Pyrex ampules in the temperature range 250-400 °C were performed. At 250 °C, no reaction occurred, while the reaction at 400 °C yielded a product whose PXRD pattern matches the one of TcI3 obtained from the reaction of Tc2(O2CCH3)4Cl2 and flowing HI(g). The thermal stability of TcBr3 and TcI3 was investigated in Pyrex and/or quartz ampules at 450 °C under vacuum. Technetium tribromide decomposes to Na{[Tc6Br12]2Br} in a Pyrex ampule and to technetium metal in a quartz ampule; technetium triiodide decomposes to technetium metal in a Pyrex ampule.

Structural frustration in a rod packing – An analogy to the disordered triangular Ising net

Single crystals of Na22Ba14(Ca, Sr)N6 show diffuse scattering which arranges in Kagomé nets in layers hkl with l = integer ≠ 0. The hexagons of the nets are centered by sharp Bragg spots. The structure represents a hexagonal rod packing, and in the averaged structure a superposition of the rods in two different orientations, type A and B, at equal weight is found. Due to a periodic alternation of bond character in the rod frustration effects occur which closely correspond to those in a triangular two-dimensional antiferromagnetic Ising spin system and give rise to diffuse scattering. The computer simulated diffuse scattering is in very good agreement with experiment, particularly, when the ideally frustrated system is slightly modified towards some randomness in the rod packing.

EELS data acquisition, processing and display for the Zeiss CEM 902 based on LOTUS 1-2-3: application examples from a biological system and inorganic transition metal compounds

A personal computer combined with LOTUS 1-2-3 software, including the RS232 module of LOTUS MEASURE and a 12-bit ADC, has been used for data acquisition of electron energy-loss spectroscopy (EELS) spectra with the Zeiss CEM 902. The internal macro language of LOTUS 1-2-3 allows a menu-driven procedure. Macro-programs partly combined with external FORTRAN programs can be chosen from the menu for background subtraction, removal of multiple scattering effects by deconvolution, elemental quantification and several utilities. For special applications or conditions the macro programs can easily be modified. Spectra from crystals of two inorganic transition metal compounds, ruthenium trichloride and vanadium disulphide, and from a biological sample are presented as examples of the application of this software.