Keisuke Fukaya
Thailand National Science and Technology Development Agency
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Featured researches published by Keisuke Fukaya.
Inorganic Chemistry | 2012
Toshihiro Yamase; Hirofumi Ishikawa; Hiroko Abe; Keisuke Fukaya; Hiroyuki Nojiri; Hideo Takeuchi
Ferromagnetic [n-BuNH(3)](12)[(CuCl)(6)(SbW(9)O(33))(2)]·6H(2)O (1) and antiferromagnetic [n-BuNH(3)](12)[(MnCl)(6)(AsW(9)O(33))(2)]·6H(2)O (4) have been synthesized and structurally and magnetically characterized. Two complexes are structural analogues of [n-BuNH(3)](12)[(CuCl)(6)(AsW(9)O(33))(2)]·6H(2)O (2) and [n-BuNH(3)](12)[(MnCl)(6)(SbW(9)O(33))(2)]·6H(2)O (3) with their ferromagnetic interactions, first reported by us in 2006. (1) When variable temperature (T) direct current (dc) magnetic susceptibility (χ(M)) data are analyzed with the isotropic exchange Hamiltonian for the magnetic exchange interactions, χ(M)T vs T curves fitted by a full matrix diagonalization (for 1) and by the Kambe vector coupling method/Van Vlecks approximation (for 4) yield J = +29.5 and -0.09 cm(-1) and g = 2.3 and 1.9, respectively. These J values were significantly distinguished from +61.0 and +0.14 cm(-1) for 2 and 3, respectively. The magnetization under the pulsed field (up to 10(3) T/s) at 0.5 K exhibits hysteresis loops in the adiabatic process, and the differential magnetization (dM/dB) plots against the pulsed field display peaks characteristic of resonant quantum tunneling of magnetization (QTM) at Zeeman crossed fields, indicating single-molecule magnets for 1-3. High-frequency ESR (HFESR) spectroscopy on polycrystalline samples provides g(∥) = 2.30, g(⊥) = 2.19, and D = -0.147 cm(-1) for 1 (S = 3 ground state), g(∥) = 2.29, g(⊥) = 2.20, and D = -0.145 cm(-1) for 2 (S = 3), and g(∥) = 2.03 and D = -0.007 cm(-1) for 3 (S = 15). An attempt to rationalize the magnetostructural correlation among 1-4, the structurally and magnetically modified D(3d)-symmetric M (=Cu(II) and Mn(II))(6) hexagons sandwiched by two diamagnetic α-B-[XW(9)O(33)](9-) (X = Sb(III) and As(III)) ligands through M-(μ(3)-O)-W linkages, is made. The strongest ferromagnetic coupling for the Cu(6) hexagon of 2, the structure of which approximately provides the Cu(6)(μ(3)-O)(12) cylindrical geometry, is demonstrated by the polarization mechanism based on the point-dipole approximation, which provides a decrease of the ferromagnetic interaction due to the out-of-cylinder deviation of the Cu atoms for 1. The different nature of the magnetic exchange interaction in 3 and 4 is understood by the combined effect of the out-of plane deviation (the largest for 4) of the Mn atoms from the Mn(μ(3)-O)(2)Mn least-squares plane and the antiferromagnetic contribution arising from the large Mn-O-Mn bond angle. The primary contribution to D is discussed in terms of the magnetic dipole-dipole interaction between the electrons located on the magnetic sites in the M(6) hexagon.
Advanced Materials Research | 2010
Keisuke Fukaya; Atthapon Srifa; Apinan Soottitantawatb
The photocatalytic reaction of polyoxotungstate, [BW12O40]5- and [SiW12O40]4-, led to the generation of hydrogen gas from biomass such as a sugarcane juice and tapioca starch under irradiation of UV light. These photoreactions were investigated in the pH dependence. The results showed that hydrogen was obtained at 2<pH<4. The photolysis of [BW12O40]5- and [SiW12O40]4- in presence of 60 ml of sugarcane juice at pH 2 level were obtained 0.15 ml and 0.51 ml of hydrogen, respectively. Especially, it was observed that the photolysis of the starch evolved oxygen without any catalysts. The oxygen contents affected to the reduced species of polyoxotungstates. Each photoreaction exhibited a different behaviour for the dependence of the amounts of catalyst. Lowering amounts of [SiW12O40]4- produced much hydrogen at pH 2 level. In contrast, lowering amounts of [BW12O40]5- could not evolve much hydrogen due to the domination of reoxidation of the reduced species by oxygen.
Inorganic Chemistry | 2006
Toshihiro Yamase; Keisuke Fukaya; Hiroyuki Nojiri; Yuhgo Ohshima
Chemistry Letters | 2001
Toshihiro Yamase; Bogdan Botar; Eri Ishikawa; Keisuke Fukaya
Bulletin of the Chemical Society of Japan | 2007
Keisuke Fukaya; Toshihiro Yamase
Journal of The Taiwan Institute of Chemical Engineers | 2010
Kitirote Wantala; Laksana Laokiat; Pongtanawat Khemthong; Keisuke Fukaya
Chemistry Letters | 1999
Toshihiro Yamase; Miyao Inoue; Haruo Naruke; Keisuke Fukaya
Journal of Alloys and Compounds | 2012
Yusuke Fujita; Noritaka Ishihara; Keisuke Fukaya; Atthapon Srifa; Haruo Naruke
Journal of Alloys and Compounds | 2006
Keisuke Fukaya; Toshihiro Yamase
Journal of Molecular Structure | 2010
Keisuke Fukaya; Atthapon Srifa; Eri Isikawa; Haruo Naruke
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Thailand National Science and Technology Development Agency
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