Papers - Einaga, Yasuaki

Photomagnetic Co-Fe Prussian blue thin films fabricated by the modified Langmuir-Blodgett technique

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Chemistry Letters 33 ( 5 ) 500 - 501 2004.05

ISSN  0366-7022

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<p>Co-Fe Prussian blue thin films have been prepared by means of a modified Langmuir-Blodgett technique, in which the hybrid monolayer composed of amphiphiles and clay platelets plays a template role for the formation Co-Fe Prussian blue thin films. Photoinduced magnetization was observed in the thin films as observed in the bulk Co-Fe Prussian blue. To the best of our knowledge, this is the first example of successful formation of Co-Fe Prussian blue thin films, which possess the ordered structure and, in addition, exhibit photoinduced magnetization.</p>

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Trans-Bis(5,5-diphenylhydantoinato)bis-(2-phenylethylamine)copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 5 )  2004.05

ISSN  1600-5368

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<p>The title compound, [Cu(C₁₅H₁₁N₂O ₂)₂(C₈H₁₁N)₂], has its metal atom in a square-planar trans-CuN₄ coordination environment; the Cu^II atom lies on a center of symmetry. The 5,5- diphenylhydantoinate and 2-phenylethylamine ligands behave as monodentate ligands and bind through their N atoms. The crystal structure is stabilized by N-H⋯O=C intermolecular hydrogen bonds [N⋯O = 2.864 (3) Å]. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.</p>

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Photoswitchable Magnetic Films

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Chemistry of Materials 16 ( 7 ) 1195 - 1201 2004.04

ISSN  0897-4756

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<p>A novel photocontrollable magnetic thin film consisting of amphiphilic azobenzene cations, a smectite clay, and Prussian Blue has been designed and prepared by using the Langmuir-Blodgett method and an ion-exchange reaction. This magnetic thin film possesses a well-organized nanoscale layered structure. Reversible photoisomerization of the azobenzene chromophore realized photoswitching of the magnetization. The changes in the magnetization values were estimated to be ca. 11%. This figure was much larger than our previous system, which contained azobenzene multi-bilayered vesicles in a poly(vinyl alcohol) matrix (J. Am. Chem. Soc. 1999, 121, 3745). These larger changes in the magnetization values are due to the highly ordered structure of the hybrid multilayered films.</p>

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Bis(5-chloro-N-isopropylsalicyldenaminato-κ²/V,O) -copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 4 )  2004.04

ISSN  1600-5368

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<p>The title compound, [Cu(C₁₀H₁₁ClNO)₂], has been structurally characterized in the low-temperature phase (brown form). It adopts a stepped conformation and affords a square-planar frans-[CuN ₂O₂] coordination geometry, in which the Cu^II ion lies on a center of symmetry. The Cu - N and Cu - O bond distances are 2.032 (3) and 1.891 (2) Å, respectively. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.</p>

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Bis(acetone-κO)bis(N,N′-dimethyl ethylenediamine- κ²N,N′)copper(II) diperchlorate

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section C: Crystal Structure Communications 60 ( 4 )  2004.04

ISSN  0108-2701

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<p>The crystal structure of the bis(acetone-κO)bis(N,N′- dimethylethylenediamine-κ²N,N′)copper(II) diperchorate was investigated. It was found that an elongated octahedral trans-[CuN ₄O₂] coordination geometry was adopted by the complex compound. Two ligands, at the axial sites having O-M-O axial acetone bonds, were also observed in the crystal structure of the metal complex. The results show that the bond length for inplane Cu-N is 2.041(3) Å and that for axial Cu-O is 2.507 (5) Å.</p>

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First observation of photoinduced magnetization for the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅.H₂O (DMF = N,N-dimethylformamide)

Li Guangming, Akitsu Takashiro, Sato Osamu, Einaga Yasuaki

Hyperfine Interactions 156-157 ( 1-4 ) 143 - 149 2004.03

ISSN  0304-3843

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<p>Photoinduced magnetization of the cyano-bridged 3d-4f hetero-bimetallic assembly Nd (DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅.H₂O (1) (DMF = N,N-dimethylformamide) is described in this paper. The χM_T values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing molecule-based magnetic materials. © 2004 Kluwer Academic Publishers.</p>

Synthesis, crystal structures and magnetic properties of two new hetero-bimetallic assemblies

Li Guangming, Akitsu Takashiro, Sato Osamu, Einaga Yasuaki

Journal of Coordination Chemistry 57 ( 3 ) 189 - 198 2004.02

ISSN  0095-8972

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<p>Two new cyanide-bridged 3d-4f hetero-dinuclear complexes, namely Ln(DMF)₄(H₂O)₃(μ-CN)Co(CN)₅ · H₂O (Ln=Nd (1) and Gd (2), DMF=N,N-dimethylformamide), were synthesized by the facile reaction of LnCl₃.6H₂O and K₃Co(CN)₆. Characterization includes microanalysis, IR spectrometric identifications, X-ray crystallographic analysis and magnetic properties. Both 1 and 2 crystallize in the centrosymmetric monoclinic space group P2₁/n (No. 14) with Z=4. The lanthanide(III) ions are eight-coordinate in a square-antiprism arrangement, while cobalt(III) ions are six-coordinate in an octahedral environment in each complex. A cyanide bridge links an LN(III) ion to a Co(III) ion. Molecules in the crystal cell of each compound are held together by van der Waals forces and a network of hydrogen bonding. Magnetic analysis shows that antiferromagnetic interactions are observed below 7 K for both 1 and 2, which are attributed to intermolecular interactions between the Ln(III) ions in the network through hydrogen bonds. This series of compounds may be of importance in photo-induced magnetism because of the cyanide bridge between 3d and 4f metals.</p>

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Bis(N,N-dimethylethylenediamine-k²N,N′)-bis(perchlorato- kO)copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 2 )  2004.02

ISSN  1600-5368

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<p>In the title compound, [Cu(ClO₄)₂(C₄H ₁₂N₂)₂], the Cu atom is located at a center of symmetry. It adopts an elongated octahedral trans-[CuN₄O₂] coordination geometry, which is a typical feature of the pseudo-Jahn-Teller effect. The axial Cu-O bond length is 2.605 (4) Å, while the in-plane Cu-N bond lengths are 1.987 (2) and 2.098 (2) Å. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.</p>

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[N,N′-Bis(2-methoxycarbonyl-3-oxobutylidene)-ethylenediaminato- κ⁴O,N,N′O′]cobalt(II)

Akitsu Takashiro, Iwakura Izumi, Tanaka Hirotaka, Ikeno Taketo, Einaga Yasuaki, Yamada Tohru

Acta Crystallographica Section E: Structure Reports Online 60 ( 2 )  2004.02

ISSN  1600-5368

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<p>The title compound, [Co(C₁₄H₁₈N₂O ₆)], is the first structurally characterized example of a β-ketoiminato Co^II complex without axial ligands. It adopts a square-planar cis-[CoN₂O₂] coordination geometry, and lies on a mirror plane. The planar complexes are stacked along 2₁ screw axes parallel to b to form columns, the Co⋯Co distance in the column being 3.5213 (2) Å. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.</p>

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Electrochemical oxidation of Mn²⁺ on boron-doped diamond electrodes with Bi³⁺ used as an electron transfer mediator

Lee Joowook, Einaga Yasuaki, Fujishima Akira, Park Su Moon

Journal of the Electrochemical Society 151 ( 8 )  2004

ISSN  0013-4651

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<p>Electrochemical oxidation of Mn²⁺ with and without the presence of Bi³⁺ was studied using voltammetric and in situ spectro-electrochemical techniques at boron-doped diamond (BDD) electrodes in 1.0 M HClO₄. Electrochemical oxidation of only Mn²⁺ resulted in the formation of mostly MnO₂ with MnO₄ ^- produced as a minor product. The MnO₂ film formed on the electrode surface, which is an inevitable part of Mn²⁺ oxidation, shows a blocking effect on the formation of MnO₄^-, and reduces the overall current efficiency of MnO₄^- production. Higher Mn²⁺ concentrations result in less MnO ₄^- production due to the formation of more MnO ₂. The addition of Bi³⁺ increased the current efficiency of MnO₄^- production. The Bi³⁺ is oxidized to Bi(V), which acts as an electrocatalyst in MnO₄^- production. The Bi(V) oxidizes MnO₂, formed on the electrode surface, to MnO₄^-. This increases the production of MnO ₄^- by removing the blocking film to provide an active electrode (bare BDD) surface, which is available for further Mn²⁺ oxidation. © 2004 The Electrochemical Society. All rights reserved.</p>

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Thermal and Photo-Responsibility of Axial Semi-Coordination Bonds in a Copper(II) Complex

Akitsu Takashiro, Einaga Yasuaki

Bulletin of the Chemical Society of Japan 77 ( 4 ) 763 - 764 2004

ISSN  0009-2673

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<p>The thermal and photo-responsibility of the axial semicoordination Cu-O bonds in [Cu(en)₂](ClO₄)₂ (1) (en = ethylenediamine) have been investigated. We discovered a new photoresponsive behavior that was attributed to photoinduced ClO₄^- cleavage accompanied by compression of the Cu-O bonds using the structural degree of freedom of the semi-coordination bonds.</p>

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Magnetic Vesicles of Amphiphilic Spiropyran Containing Iron Oxide Particles on a Solid State Substrate

Taguchi Minori, Li Guangming, Gu Zhongze, Sato Osamu, Einaga Yasuaki

Chemistry of Materials 15 ( 25 ) 4756 - 4760 2003.12

ISSN  0897-4756

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<p>Incorporation of photochromic compounds into magnetic systems is one of the new strategies being implemented to realize the control of magnetic properties by photoillumination. We have designed composite materials comprising iron oxide particles and photochromic spiropyran vesicles as cast films on substrates. Photofunctional magnetic vesicles of amphiphilic spiropyran (SP1822) containing iron oxide particles exhibit superparamagnetic properties at room temperature. Both photoisomerization and photoinduced aggregation of the photoresponsive magnetic vesicles were observed, even without any supporting media such as solvents or polymer matrixes. As a result of the assembly of the vesicles, magnetic dipolar interactions among adjacent iron oxide particles were induced by photoillumination at room temperature, even in the solid state.</p>

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A redetermination of bis(N-methylethyl-enediamine-κ²/N, N′)bis(perchlorato-κO)-copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 59 ( 11 )  2003.11

ISSN  1600-5368

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<p>In the title compound, [Cu(ClO₄)2(C₃H ₁₀N₂)₂], the Cu atom is located at a center of symmetry. Despite asymmetric introduction of TV-methyl groups into the ethylenediamine moieties, a second-order Jahn-Teller effect produces a typical semi-coordination trans-[CuN₄(O₂)] environment with long axial Cu - O bonds of 2.569 (2) Å. The Cu - N bond distances are 2.004 (2) and 2.057 (2) Å. © 2003 International Union of Crystallography Printed in Great Britain - all rights reserved.</p>

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Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)₄(H₂O)₃(μ-CN)Fe(CN) ₅·H₂O (DMF = N,N-dimethylformamide)

Li Guangming, Akitsu Takashiro, Sato Osamu, Einaga Yasuaki

Journal of the American Chemical Society 125 ( 41 ) 12396 - 12397 2003.10

ISSN  0002-7863

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<p>Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅·H₂O (1) (DMF = N,N-dimethylformamide) is described in this paper. The χ_MT values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing the molecule-based magnetic materials. Copyright © 2003 American Chemical Society.</p>

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Electrochemical Properties of Ar⁺ Sputtered Polycrystalline Diamond Electrodes with Smoothed Surfaces

Sato Rika, Kondo Takeshi, Shimizu Kenichi, Honda Kensuke, Shibayama Yoshiyuki, Shirahama Keiya, Fujishima Akira, Einaga Yasuaki

Chemistry Letters 32 ( 10 ) 972 - 973 2003.10

ISSN  0366-7022

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<p>The initial rough, faceted surfaces of boron-doped conductive polycrystalline diamond electrodes were smoothed by Ar⁺ ion sputtering at very low energy (50 eV). A lower background current was measured at the modified electrodes with a mirror-like appearance than at the initial polycrystalline electrodes. The electrochemical responses to several redox systems also showed a morphological-dependence in some cases. Here, we discuss the electrochemical properties of the diamond electrodes with the smoothed surfaces from the point of view of a novel electrode material.</p>

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An abrupt spin transition based on short S⋯S contacts in a novel Fe(II) complex whose ligand contains a 1,3-dithiole ring

Takahashi Kazuyuki, Kawakami Tomoko, Gu Zhong Ze, Einaga Yasuaki, Fujishima Akira, Sato Osamu

Chemical Communications 9 ( 18 ) 2374 - 2375 2003.09

ISSN  1359-7345

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<p>The first preparation of an Fe(II) spin-crossover complex including a 1,3-dithiole ligand is reported. Crystal analyses of both the low- and the high-temperature phases reveal that short S⋯S contacts play a key role in an abrupt spin transition.</p>

⁵⁷Fe Mössbauer Study on Photoinduced Spin Transition of Ferrocene in Polymer Matrices

Einaga Yasuaki, Kotake Masahiro, Yamada Yasuhiro, Sato Osamu

Chemistry Letters 32 ( 9 ) 846 - 847 2003.09

ISSN  0366-7022

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<p>A polymer matrix isolation technique was examined as a potentially novel strategy for realizing optically switchable materials. Not only was a ferricinium ion ([Cp₂Fe^III]⁺) produced, but also was produced an isomer of ferrocene (Cp₂Fe) with high spin Fe^II in a poly(methyl methacrylate) (PMMA) matrix film containing CCl₄ by the photoillumination of ferrocene at low temperature. The high spin state could be maintained for an extended period when the sample was kept below ≈ 130 K. This is the first observation of a photoinduced spin transition for ferrocene. The strategy that we used to achieve the spin transition using optical stimuli may open up many possibilities for the development of new magneto-optical devices.</p>

Magnetization increase of iron oxide by photoinduced aggregation of spiropyran

Einaga Yasuaki, Taguchi Minori, Li Guangming, Akitsu Takashiro, Gu Zhongze, Sugai Takeshi, Sato Osamu

Chemistry of Materials 15 ( 1 ) 8 - 10 2003.01

ISSN  0897-4756

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<p>Photofunctional magnetic vesicles of spiropyran (SP1822) that contain iron oxide particles, which exhibit super-paramagnetic properties at room temperature, were prepared. Photoinduced aggregation of the vesicles was observed by UV illumination. As a result, we were able to increase the magnetization value by photoillumination at room temperature.</p>

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Control of the magnetic and optical properties in molecular compounds by electrochemical, photochemical and chemical methods

Sato Osamu, Hayami Shinya, Einaga Yasuaki, Gu Zhong Ze

Bulletin of the Chemical Society of Japan 76 ( 3 ) 443 - 470 2003

ISSN  0009-2673

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<p>The electrochemical, photochemical and chemical control of the magnetic properties in molecular compounds is described. The preparation of various thin films of CrCr and FeFe Prussian blue on a conducting electrode allowed us to control the magnetic properties by varying the oxidation state of the component metals. The magnetic properties of CrCr Prussian blue show that the critical temperature and coercive field can be drastically modified by electrochemical treatment. That is, the compound, Cr^II
_1.29Cr^III
_0.14 [Cr^III(CN)₆] has ferrimagnetic properties with T_c (critical temperature) = 240 K and H_c (coercive field) = 25 G, while the reduced form, KCr^II
_1.29Cr^III
_0.14 [Cr^II(CN)₆], has T_c = 100 K and H_c = 220 G. Similarly, it was found that the critical temperature of FeFe Prussian blue shifts continuously from paramagnetic to magnetic with T_c = 12 K. These changes can be expressed as K₄Fe^II
₄[Fe^II (CN)₆]₃ (paramagnetic) ⇆ Fe^III
₄[Fe^II(CN)₆]₃ (ferromagnetic, T_c = 4.5 K) + 4 K⁺ + 4e^- and Fe^III
₄[Fe^II(CN)₆]₃ (ferromagnetic, T_c = 4.2 K) + 3Cl^- - 3e^- ⇆ Fe^III
₄[Fe^III(CN)₆] ₃(Cl)₃ (T_c = 12 K). Furthermore, we have discovered that the FeCo Prussian blue and Co valence tautomeric compounds exhibit photo-reversible magnetization effects. The photoinduced magnetization in FeCo Prussian blue is expressed as Na_0.4Co^II-HS
_0.3Co^III-LS [Fe^II(CN)₆] (paramagnetic) ⇆ Na_0.4Co^II-HS
_1.3[Fe^III (CN)₆] (ferrimagnetic, T_c = 26 K and H_c = 6000 G), where HS and LS denote high-spin and low-spin. An example of the photoinduced valence tautomeric behavior is expressed as [Co^III-LS(3,5-dbsq)(3,5-dbcat)(tmeda)] ⇆ [Co^II-HS(3,5-dbsq)₂(tmeda)], where tmeda, 3,5-dbsq and 3,5-dbcat represent N,N,N′,N′-tetramethylethylenediamine, 3,5-di-tert-butyl-1,2-semiquinonate and 3,5-di-tert-butyl-1,2-catecholate, respectively. Additionally, we succeeded in tuning the phase transition temperature by varying the ligand field of the Co ions in the FeCo Prussian blue. Brief comments are also included regarding the first examples of light-induced excited spin state trapping observed in an Fe^III complex, i.e. [Fe^III-LS(pap)₂]ClO₄·H₂O ⇆ [Fe^III-HS(pap)₂]- ClO₄·H₂O (pap = N-2-pyridylmethylidene-2-hydroxy-phenylaminato) and a photoinduced structural change observed in a Cu^II complex, [Cu^II(dieten)₂](BF₄)₂ [dieten = bis(N,N-diethylethylenediamine)].</p>

Reversible photocontrollable magnetic vesicles consisting of azobenzene

Einaga Yasuaki, Yamamoto Takashi, Sugai Takeshi, Sato Osamu

Chemistry of Materials 14 ( 11 ) 4846 - 4850 2002.11

ISSN  0897-4756

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<p>Photochromic magnetic vesicles have been designed by intercalation of Prussian blue into a lipid bilayer membrane which consists of azobenzene. Reversible photoisomerization of the solid system realized reversible photocontrol of the magnetic properties. Here, we have synthesized an amphiphile azo moiety containing a long alkyl chain, and we have prepared photochromic magnetic vesicles consisting of only this azo moiety. As a result, the magnetic property change brought about by visible light illumination was estimated to be ca. 13%, which is much larger than the figure achieved for the similar system that we reported previously (∼1%), which contained the double-chain ammonium amphiphile (J. Am. Chem. Soc. 1999, 121, 3745.).</p>

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