A peculiar bonding feature of a-rhombohedral boron is found in the electron density distribution of the icosahedral B 12 cluster. The electron density distribution is obtained by using the maximum entropy method with synchrotron radiation powder data. It clearly shows the characteristic two-and three-center covalent bond network which threads through atoms on the cluster surface. Besides, two kinds of covalent bonds in intercluster space are also shown in detail: a three-center trilaterally formed bond among the three clusters and a two-center bond with a remarkable feature of a bent bond between the clusters. The obtained covalent bonding features indicate the cluster-based nature of this material.

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Observation of metal-insulator transition in Al-Pd-Re quasicrystals by x-ray absorption and photoemission spectroscopy Appl.We present the composition dependence of the Seebeck coefficient and the electrical conductivity of AlPdRe icosahedral alloys. As the concentration of transition metal ͑either Pd or Re͒ increases, the Seebeck coefficient rapidly increases. The strong composition dependence is related to the pseudogap structure in the electron density of states at the Fermi energy, and to the variation in bonding nature between Al and transition metal. Glass-like transport behavior in thermal conduction is also observed. The dimensionless thermoelectric figure of merit has a maximum value of approximately 0.1 in the temperature range from 600 to 700 K and reveals strong composition dependence.

Observation of metal-insulator transition in Al-Pd-Re quasicrystals by x-ray absorption and photoemission spectroscopy Appl.The thermoelectric properties of the quaternary AlPdReRu icosahedral quasicrystals (i-AlPdReRu) obtained by replacing Re with Ru in AlPdRe icosahedral quasicrystals have been studied. In the middle of the substitution of Ru for Re, the electrical conductivity increases and the peak of Seebeck coefficient shifts to a higher temperature side. By Ru substitution for the AlPdRe quasicrystal, the dimensionless figure of merit ͑ZT͒ increases 1.5 times from 0.1 to 0.15. According to the result of two-band analysis, the effective mass has peaks at both the compositions of i-AlPdRe and i-AlPdReRu which reveal the peak ZT values. We ascribe the behavior of effective mass to the change in the bond strength of intra-and inter-Mackay icosahedral clusters.

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A series of copper(I) complexes bearing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (dmpp) and a diphosphine ligand have been prepared. The diphosphine ligands used have two, three or four methylene carbons between the two phosphorus atoms. The crystallographic study has revealed that two of the three complexes have the mononuclear structure bearing dmpp and a bidentate diphosphine ligand, and one is a diphosphine-bridged binuclear complex. The photoluminescence of the complexes in solution was studied and compared with the previously reported complexes bearing 2,9-dimethyl-1,10-phenanthroline (dmp). It was found that the two phenyl groups on the phenanthroline ligand have a marked effect on the photophysical properties of the complexes; the intensity of the emission of the complexes is greatly enhanced by the phenyl groups. The photophysics of the complexes is discussed with the results of DFT and TDDFT calculations.

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We have characterized the thermoelectric properties of FeGeγ, which is one of the promising Nowotny chimney-ladder compounds. A glass-like low lattice thermal conductivity below 1.0 W m–1 K–1 is observed around 373 K because of its complex structural nature, i.e., incommensurate structure. A first-principles band structure calculation implies that a narrow band gap of ∼0.2 eV is formed near the Fermi level for a hypothetical composition of Fe2Ge3 with a Ru2Sn3-type structure, leading to a large power factor of 1.90 mW m–1 K–2 near 600 K. The maximum dimensionless figure-of-merit of 0.57 is attractive as a starting point; calculation using the Boltzmann transport equation under a constant relaxation time approximation predicts that a further enhancement of ZT exceeding unity at 600–700 K can be achieved by optimizing the valence electron count per transition metal and further reduction of the lattice thermal conductivity.