Akira Sato

Structural refinement and thermal expansion of hexaborides

Abstract In the boron-framework of hexaborides, CaB 6 , SrB 6 , BaB 6 , YB 6 and LaB 6 , the boron position was found to be adjusted so as to compensate the interaction between the cations. It was estimated from the boron position that a boron–boron bond between the boron octahedra has a 1.5 times higher force constant than that in the octahedron, which is consistent with the results of the neutron and Raman scattering experiments. In addition, the adjustment of the boron position well corresponded with the thermal expansion.

Fermi Surface and Mass Enhancement in KFe2As2 from de Haas-van Alphen Effect Measurements

We report on a band structure calculation and de Haas–van Alphen measurements of KFe 2 As 2 . Three cylindrical Fermi surfaces are found. Effective masses of electrons range from 6 to 18 m e , m e being the free electron mass. Remarkable discrepancies between the calculated and observed Fermi surface areas and the large mass enhancement (({gtrsim}3)) highlight the importance of electronic correlations in determining the electronic structures of iron pnicitide superconductors.

Reversible photoredox switching of porphyrin-bridged bis-2,6-di- tert -butylphenols

Porphyrin derivatives bearing 2,6-di-tert-butylphenol substituents at their 5,15-positions undergo reversible photoredox switching between porphyrin and porphodimethene states as revealed by UV-vis spectroscopy, fluorescence spectroscopy, and X-ray single-crystal analyses. Photoredox interconversion is accompanied by substantial variations in electronic absorption and fluorescence emission spectra and a change of conformation of the tetrapyrrole macrocycle from planar to roof-shaped. Oxidation proceeds only under photoillumination of a dianionic state prepared through deprotonation using fluoride anions. Conversely, photoreduction occurs in the presence of a sacrificial electron donor. Transient absorption spectroscopy and electron spin resonance spectroscopy were applied to investigate the processes in photochemical reaction, and radical intermediates were characterized. That is, photooxidation initially results in a phenol-substituent-centered radical, while the reduction process occurs via a delocalized radical state involving both the macrocycle and 5,15-substituents. Forward and reverse photochemical processes are governed by different chemical mechanisms, giving the important benefit that conversion reactions are completely isolated, leading to better separation of the end states. Furthermore, energy diagrams based on electrochemical analyses (cyclic voltammetry) were used to account for the processes occurring during the photochemical reactions. Our molecular design indicates a simple and versatile method for producing photoredox macrocyclic compounds, which should lead to a new class of advanced functional materials suitable for application in molecular devices and machines.

Synthesis of Self-Threading Bithiophenes and their Structure–Property Relationships Regarding Cyclic Side-Chains with Atomic Precision

We have recently reported a self-threading polythiophene as a new family of insulated molecular wires. Herein, we focused on the structure-property relationships of the unique three-dimensional architecture of the monomer. We have synthesized nine self-threading bithiophene monomers that have cyclic side-chains of different size and flexibility: i.e., 21-, 22-, 23-, 24-, 26-, and 30-membered rings composed of paraffinic, olefinic, or alkynic chains. To investigate their structure-property relationships, (1) Hu2005NMR spectroscopy, UV absorption, and fluorescence spectroscopy measurements were conducted. We found that cyclic side-chains define the movable range of the dihedral angle of the bithiophene backbone, thereby affecting its photophysical properties. Therefore, the ability to design a structure with atomic precision as described herein would lead to the fine-tuning of the electronic properties of insulated molecular wires.

Preparation, crystal structure and silver ionic conductivity of the new compound Ag8TiS6

Abstract The new compound Ag 8 TiS 6 has been prepared by solid state reaction. The crystal structure, phase transition and transport properties have been studied using X-ray diffraction, Raman spectra, ionic conductivity measurement and the e.m.f method. The dc conductivities of silver ion of Ag 8 TiS 8 reach values around 10 −3 Ω −1 cm −1 at ambient temperatures. The transference numbers of silver ion are found to be close to unity.

Incorporation of carbon atoms in rare earth boron-rich solids and formation of superstructures

Abstract The boron-rich solid of YB 25 can incorporate certain amounts of carbon atoms. With increase of carbon content, two kinds of superstructures of YB 25 , which modulate the basic structure in the (001) plane, appeared. The framework of boron icosahedra in the superstructures remains the same as that of YB 25 and the structural modulation is just caused by the variation of carbon distribution in the voids of the framework. In addition, one superstructure with a large unit cell is quenchable and transformed into another superstructure by thermal annealing at 1400°C for 80 h.

Crystal structure of new rare-earth boron-rich solids: REB28.5C4

Abstract New rare-earth boron-rich solids of the composition REB 28.5 C 4 (Re=Y, Ho, Er, Tm and Lu) were synthesized by solid state reaction and single crystals were grown using a high temperature metal solution method. The structure was solved by a direct method from single crystal X-ray diffraction data with Y–B–C as a representative. It shows a layered structure with trigonal symmetry (space group: R 3 m (No. 166)) and the unit cell parameters are: a = b =5.6457(9) A, c =56.8873(13) A.

Incommensurate crystallographic shear structure of BaxBi2-2xTi4-xO11-4x (x = 0.275)

The title compound generates diffraction patterns which are indexable within the framework of the higher-dimensional description of incommensurate structures. However, it is difficult to discriminate the main reflections from the satellite ones. This paper has clarified that the structure can be treated as a strongly modulated structure with sawtooth-like modulation functions and is classified as an incommensurate crystallographic shear (CS) structure. The structure consists of domains isostructural to beta-Bi(2)Ti(4)O(11) and domain boundaries composed of TiO(6) octahedra. Ba and Bi ions are accommodated in the cavities between TiO(6) octahedra in the domain. Domain boundaries are aperiodically inserted, in contrast to the usual CS structures, forming an incommensurate structure.

Phase transition and crystal structure of silver-ion conductor Ag12−nM+nS6 (M=Ti, Nb, Ta)

Abstract Phase transition of Ag-ion conductor of argyrodite sulfides, Ag 12− n M + n S 6 (M=Ti, Nb or Ta), has been investigated through thermal analyses and the low-temperature X-ray diffraction methods. It was found that all the room-temperature phase with the cubic F 43 m structure transforms into the several less symmetric forms at lower temperatures than 293 K. In Ag 8 TiS 6 , the low temperature modification of type β crystallizes in the orthorhombic symmetry with a =15.095 A, b =7.462 A, c =10.641 A, space group Pna 2 1 (No. 33), Z =4. The structure was determined from the Rietveld refinement of powder X-ray diffraction data and the final R factors were R wp =0.13 and R F =0.048. The structure of Ag 8 TiS 6 contains four tetrahedral TiS 4 units and Ag and S atoms. The coordination of the Ag atoms by sulfur is distorted tetrahedral (Ag–S, 2.28–2.79 A), trigonal planar (Ag–S, 2.36–2.89 A), or linear (Ag–S, 2.46–2.64 A).

A New Hexagonal κ Phase of Al–Cr–Ni

A new hexagonal aluminium-chromium-nickel phase, Al 14.4 Cr 3.4 Ni 1.1 , is described. The structure includes 12 icosahedral clusters in the unit cell, each of which consists of a transition metal (TM) atom at the center and 11 aluminium and one TM atom on the fivefold vertices of the icosahedron. Pairs of the clusters are linked along the c axis by sharing a triangular face. Two pairs of the clusters are joined by two trigonal antiprisms, constructing a column along the c axis. Six such columns are included in the unit cell and form the crystal structure. The second neighboring atoms connecting the columns are on the threefold axes of the icosahedral cluster.