| Research Abstract |
In our preceding research, tetraphenylphosphonium salt of [H_3V_<10>O_<28>]^<3-> formed a large pore that accommodates a water cluster. During this project, we succeeded in synthesizing porous materials that can accommodate organic small molecules, by the use of [H_nV_<10>O_<28>]^<(6-n)-> anion and tetraalkylammonium cations. Analyses of their crystal structures revealed the detailed features of the hydrogen bonds which induces the incorporation of the organic small molecules into these ionic crystals of polyoxometalates. A crystal structure analysis of a smaller polyoxometalate, [V_4O_<12>]^<4->, showed that it forms a crystal with voids that can accommodate water molecules. The hydrogen bond between the tetravanadate and water was clearly observed by the X-ray diffraction experiment, which showed that the water molecules supported on the tetravanadate anion can be a good molecular model for the metal oxide supporting water molecules. We also investigated the interaction between the p
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olyoxometalates and the transition elements in their lower oxidation states. We obtained crystals of Cu_3V_<10>O_<28>・24H_2O and CuNa_4V_<10>O_<28>・23H_2O. In these systems, we were not successful in preparing porous materials, but we revealed that the decavanadate anions were linked into one-dimensional chains through the Cu^<2+> or Na^+ cations. In the crystals of (CH_6N_3)_4Na_2H[PW_<11>O_<39>]・8H_2O, the [PW_<11>O_<39>]^<7-> anions were linked into one-dimensional chains through the Na^+ cations. These exemplify the possibilities of the rational design of polyoxometalate composite material that would exhibit macroscopic physicochemical properties. In parallel with these studies, we introduced a single crystal diffractometer into SPring-8, which enabled the precise structure analyzes of highly x-ray absorbing materials. Thanks to this instrument, the precisions of the structure analyzes of polyoxotungstates were significantly improved. This especially benefited the structure analysis of (CH_6N_3)_4Na_2H[PW_<11>O_<39>]・8H_2O, revealing the structural distortion of the [PW_<11>O_<39>]^<7-> anions due to the interaction with the Na^+ cations. Less
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