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Oligo(imidazole)s: Novel Building Blocks for Construction of Hydrogen-Bonded
Chiral Supramolecular Assemblies
Yumi Yakiyama
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan,
[email protected]
As typified by double helical structure of DNA and α-helix of proteins, helical chirality plays a
pivotal role for life activity in the living system. Recently, helical chirality attracts a great attention
in material sciences for introducing functionality that depends on its structural and optical
properties. Helicate is supramolecular helical metal complex formed through self-assembling
process and intrinsically possesses a helical chirality originating from the right and left-handed
helicities. We conceived an idea to apply helicates as the component of functional molecular system
in the solid state. These systems will give a new opportunity for realizing fascinating properties
depending on electronic-spins on metal ions and helical chirality. In such functional molecular
assemblies, robustness of the electronic/molecular structures and effective intermolecular
interactions are crucially important. However, most of the known helical metal complexes possess
discrete structures in the crystal and are easily distorted by change of external environment.
Considering these facts, development of new rigid helicates composed of new ligands having
effective interaction sites is quite promising approach for implementation of such helicate-based
functional materials.
We studied on various imidazole derivatives as H-bonded electron-donors which show novel
electronic properties in their charge-transfer complexes.1 Based on these studies and our precedent
works about assembled metal complexes of oligo(imidazole)s,2 we have succeeded in syntheses of
multi-nuclear triple-helicates composed of oligo(imidazole)s, two kinds of tetramer 242- and
424-Qim, and hexamer 42424-Sim, and various metal cations (Figure). Furthermore, we have also
achieved construction of H-bonded 3D network structures in the solid state. These helicates have
robust structures due to rigidly-connected coordination bonds and inter-ligand π-stackings, which
give us a unique chance to separate chiral helicate from racemic mixture by chiral HPLC technique
in a solution state. Here, we present triple-helicates based on oligo(imidazole)s showing intriguing
multi-dimensional network structures based on their H-bonding modes, and their physical
properties both in the solid and solution states. In addition, our recent fundamental study on the
application of helicates for quantum computers3 will also be discussed.
Figure. Triple-helicates composed of oligo(imidazole)s
References
1. a) Y. Morita, T. Murata, K. Nakasuji et al. J. Org. Chem. 2005, 70, 2739. b) T. Murata, Y. Morita, Y. Yakiyama, K.
Nakasuji et al. J. Am. Chem. Soc. 2007, 129, 10837. c) T. Murata, Y. Morita, Y. Yakiyama, Y. Yamamoto, K. Nakasuji et al.
Cryst. Growth Des. 2008, 8, 3058. d) Y. Morita, Y. Yakiyama, T. Murata, K. Nakasuji. Solid State Sci. 2008, 10, 1720.
2. a) Y. Morita, T. Murata, K. Nakasuji et al. J. Chem. Soc., Perkin Trans 1, 2002, 2598-2600. b) Y. Morita, T. Murata, K.
Nakasuji et al. Chem. Lett. 2004, 33, 188. c) T. Murata, Y. Morita, Y. Yakiyama, K. Nakasuji et al. Cryst. Growth Des. 2006,
6, 1043.
3. K. Sato, Y. Yakiyama, Y. Morita, M. Kitagawa, T. Takui et al. J. Mater. Chem. 2009, 22, 3739.