Chemistry Letters
Online ISSN : 1348-0715
Print ISSN : 0366-7022
ISSN-L : 0366-7022
Volume 42 , Issue 9
Showing 1-50 articles out of 54 articles from the selected issue
Highlight Review
  • Takafumi Yamamoto, Hiroshi Kageyama
    2013 Volume 42 Issue 9 Pages 946-953
    Published: September 05, 2013
    Released: September 05, 2013
    [Advance publication] Released: July 18, 2013
    Low-temperature reactions are a powerful approach to generate new transition metal oxides that are inaccessible by conventional high-temperature reactions. In this review, we describe the recent progress of the topochemical reduction method using metal hydrides for transition metal oxides, in particular, focusing on structural modifications (relations), chemical and physical properties, and the factors that direct selective and rational preparations. The hydride reduction has been so far extensively applied to 3d transition metal perovskite oxides, yielding highly reduced products with unusual coordination environment (e.g., FeO4 square-planar coordination), and extremely low-valent metal centers (e.g., Mn(I) and Co(I)). Non-perovskite oxides like pyrochlore and hexagonal perovskite can be also reduced. Moreover, this method allows access to oxyhydride materials (LaSrCoO3H0.7 and BaTiO3−xHx) that are promising for use as hydride ion conductors. Morphology-controlled oxides (thin film- and nano-oxides) are useful targets for hydride reduction, opening new possibilities for extending functions.
    Hydride reduction of transition metal oxides has been extensively studied over the last decade, yielding highly reduced oxides (or oxyhydrides) with various extended networks. The use of low temperature allows access to unusual low-valence state and coordination geometry and gives rise to novel chemical and physical properties. Fullsize Image
  • Takashi Takeda, Yasuto Uchimura, Hidetoshi Kawai, Ryo Katoono, Kenshu ...
    2013 Volume 42 Issue 9 Pages 954-962
    Published: September 05, 2013
    Released: September 05, 2013
    [Advance publication] Released: July 10, 2013
    Over the past few decades, many studies have been conducted on ultralong C–C bonds (bond length greater than 1.7 Å). This highlight review discusses the molecular design of ultralong C–C bonds and their bonding properties, especially their “expandability.” In particular, the ultralong C–C bonds in tetraarylpyracene derivatives can change in length by adopting a slightly different conformation in the crystalline state. This expandability of ultralong C–C bonds could be due to the smaller decrease in bond energy at a longer interatomic distance (>1.7 Å). This interesting property can be applied to stimulus-responsive materials, as illustrated in the thermochromism of a bis(methylacridan)-substituted pyracene crystal, since the thermally induced change in bond-length modifies the HOMO–LUMO gap.
    In this highlight review, we discuss the molecular design of ultralong C–C bonds based on previous studies on hexaphenylethane derivatives and describe our recent studies on ultralong C–C bonds and their bonding properties especially their expandability. Fullsize Image
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