論文 - 山本　崇史

Preparation of Dihydroquinazoline Carbohydrazone Fe(II) Complexes for Spin Crossover

Shen Fu-Xing, Huang Wei, Takashi Yamamoto, Einaga Yasuaki, Wu Dayu

New Journal of Chemistry （ROYAL SOC CHEMISTRY）  40 （ 5 ） 4534 - 4542 2016年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1144-0546

　概要を見る

Dihydroquinazoline FeII complexes, namely [Fe(pq-R)(2)](X)(2)center dot CH3OH center dot yCH(3)CN center dot zH(2)O (R = 2-py: X = ClO4-, x = 1, y = 0, z = 2 (1), BF4-, x = 0, y = 2, z = 1.75 (2), CF3SO3-, x = 1, y = 1, z = 0 (3); and X = ClO4-: R = 2-OCH3, x = 0, y = 0, z = 1 (4), R = 3-OCH3, x = 0, y = 0, z = 1 (5)), were prepared and the effects of the solvent, counteranion and ligand substituent on spin crossover properties were discussed. Comparison of X-ray diffraction data for these complexes revealed the sole presence of high-spin FeII at 298 K and the bond distances around the FeII center at low temperature fall much closer to those at high temperature, which is consistent with variable-temperature dc magnetic susceptibility data. However, the loss of solvent induced a significant change in the spin state of complexes 1 and 2. Moreover, fits to magnetic data of the desolvated samples provide crossover temperatures of T-1/2 = 182.9(6), 157.0(8) and 138.3(5) K for 1-des (ClO4-), 2-des (BF4-) and 3-des (CF3SO3-), respectively, indicative of the anion-dependent transition temperature. The cooperativity operating in the complexes is thought to be mainly from the intermolecular pi center dot center dot center dot pi interactions between dihydroquinazoline rings on the neighboring molecules. The ligand substituent effect was also investigated on Fe-II SCO properties. This work revealed the spin crossover properties of new types of dihydroquinazoline Fe(II) complexes, including the transition temperature, the degree of completion and the cooperative nature of the transition, which can be optimally designed when developing new spin-crossover materials.

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Co-Fe Prussian Blue Analogue Intercalated into Diamagnetic Mg‒Al Layered Double Hydroxides

Zhang Cuijuan, YAMAMOTO Takashi, Einaga Yasuaki

Nanomaterials and Nanotechnology （InTech Europe）  6 （ 1 ） 26-7pp 2016年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1847-9804

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A heterostructure of diamagnetic magnesium-aluminium layered double hydroxides (Mg-Al LDHs) and photomagnetic cobalt-iron Prussian Blue analogue (Co-Fe PBA) was designed, synthesized and then designated as LDH-PB. The cyanide-bridged Co-Fe PBA was two-dimensionally intercalated into the Mg-Al LDH template by the stepwise anion exchange method. LDH-PB showed ferrimagnetic properties with in-plane antiferromagnetic exchange interactions, as well as small photo-induced magnetization by visible light illumination due to the low dimensional structures and the characteristic photo-induced electronic states of the mixed valence of FeIII(low spin, S = 1/2)-CN-CoII(high spin, S = 3/2)-NC-FeII (low spin, S = 0).

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New Family of Anionic Fe^III Spin Crossover Complexes Featuring a Weak-Field N₂O₄ Coordination Octahedron

Takahashi Kazuyuki, Kawamukai Kiko, Okai Mitsunobu, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Shiota Yoshihito, Yoshizawa Kazunari

Chemistry A European Journal 22 （ 4 ） 1253 - 1257 2015年12月

研究論文（学術雑誌）, 共著, 査読有り

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Novel Fe(II) Spin Crossover Complexes Involving Chalcogen-Bond and π-Stacking Interactions with a Paramagnetic and Nonmagnetic M(dmit)2 Anion (M = Ni, Au; dmit = 4,5-dithiolato-1,3-dithiole-2-thione)

Okai Mitsunobu, Takahashi Kazuyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki

Journal of Materials Chemistry C （Royal Society of Chemistry）  3 （ 30 ） 7858 - 7864 2015年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2050-7526

　概要を見る

To introduce both an inter-sulphur atom and p-stacking interaction between a spin crossover (SCO) cation and paramagnetic anion, we designed and synthesised two novel Fe(II) SCO compounds involving a terpyridine-type thiazole containing ligand with the paramagnetic Ni(dmit)(2) and nonmagnetic Au(dmit)(2) anion (dmit = 4,5-dithiolato-1,3-dithiole-2-thione). The temperature variations of magnetic susceptibility and Mossbauer spectroscopy revealed that both complexes exhibited an almost complete SCO conversion, and moreover, the Ni(dmit)(2) anion was in a paramagnetic state down to 2 K. The crystal structures for the Ni(dmit)(2) complex at 213 and 400 K indicated that the chalcogen-bond and p-stacking interaction would be enhanced by the electrostatic interaction between the cation and anion, preventing the p-radicals from dimerising. The light-induced excited spin state trapping effect was observed at 5 K.

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Antiferromagnetic Transition in a Novel Star-Shaped High-Spin Fe(III) Tetranuclear Cluster from a Mononuclear Coordination Anion Featuring π-Extended Schiff Base Ligands

Takahashi Kazuyuki, Kawamukai Kiko, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Mori Hatsumi, Shimura Yasuyuki, Sakakibara Toshiro, Fujisawa Takumi, Yamaguchi Akira, Sumiyama Akihiko

Chemistry Letters （The Chemical Society of Japan）  44 （ 6 ） 840 - 842 2015年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0366-7022

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A novel star-shaped high-spin Fe(III) tetranuclear cluster was unexpectedly obtained by the reaction of an [Fe-III(phsal)(2)](-) anion with an Fe(III) coordination cation (H(2)phsal: N-(2-hydroxyphenyl)salicylaldimine). Despite a star-shaped Fe(III) tetranuclear structure similar to reported Fe(III) single molecule magnets, the present compound exhibited a bulk antiferromagnetic transition at 0.6 K due to a magnetic exchange coupling through intercluster pi-stacking interactions.

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Photochromism-Induced Amplification of Critical Current Density in Superconducting Boron-Doped Diamond with an Azobenzene Molecular Layer

NATSUI Keisuke, YAMAMOTO Takashi, AKAHORI Miku, EINAGA, Yasuaki

ACS Applied Materials & Interfaces （American Chemical Society）  7 （ 1 ） 887 - 894 2014年12月

共著, 査読有り,  ISSN  1944-8244

　概要を見る

A key issue in molecular electronics is the control of electronic states by optical stimuli, which enables fast and high-density data storage and temporal-spatial control over molecular processes. In this article, we report preparation of a photoswitchable superconductor using a heavily boron-doped diamond (BDD) with a photochromic azobenzene (AZ) molecular layer. BDDs electrode properties allow for electrochemical immobilization, followed by copper(I)-catalyzed alkyne-azide cycloaddition (a click reaction). Superconducting properties were examined with magnetic and electrical transport measurements, such as field-dependent isothermal magnetization, temperature-dependent resistance, and the low-temperature voltage-current response. These measurements revealed reversible amplification of the critical current density by 55% upon photoisomerization. This effect is explained as the reversible photoisomerization of AZ inducing an inhomogeneous electron distribution along the BDD surface that renormalizes the surface pinning contribution to the critical current.

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Synergistic Spin Transition between Spin-Crossover and Spin-Peierls-Like Singlet Formation in the Halogen-bonded Molecular Hybrid System: [Fe(Iqsal)₂][Ni(dmit)₂]•CH₃CN•H₂O

Kappei Fukuroi, Kazuyuki Takahashi, Tomoyuki Mochida, Takahiro Sakurai, Hitoshi Ohta, Takashi Yamamoto, Yasuaki Einaga, Hatsumi Mori

Angewandte Chemie International Edition （WILEY-V C H VERLAG GMBH）  53 （ 7 ） 1983 - 1986 2014年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1433-7851

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To introduce halogen-bond interactions between a cation and an anion, a novel Fe-III complex from iodine-substituted ligands involving a paramagnetic nickel dithiolene anion was prepared and characterized. The compound exhibited the synergy between a spin-crossover transition and a spin-Peierls-like singlet formation. The halogen-bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of -spins and played a crucial role in the synergistic magnetic transition between d- and -spins. In addition, the compound showed the light-induced excited spin state trapping effect.

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Structure-Distortion-Induced Photomagnetic Effect in Azobenzene/Polyoxometalate Langmuir–Blodgett Films

Takashi Yamamoto, Yasushi Umemura, Yasuaki Einaga

Dalton Transactions （ROYAL SOC CHEMISTRY）  42 （ 45 ） 16014 - 16020 2013年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1477-9226

　概要を見る

We have prepared photomagnetic Langmuir-Blodgett films composed of an amphiphilic azobenzene and a magnetic polyoxometalate. The obtained film possesses a well-organized layered structure where polyoxometalate anions are sandwiched by azobenzene cations in a single-layered manner. Reversible photoisomerization of azobenzene was achieved even at low temperature, accompanying intensity changes in the d-d transition of polyoxometalate anions. The photomagnetic effect was observed reversibly upon alternate UV and visible light irradiation. Based on polarized spectroscopy, the observed photomagnetic effect is ascribed to the structure-distortion of polyoxometalate layers.

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A Neutral Fe(III) Compound Exhibiting A Two-Step Spin Transition and Dielectric Anomalies

Zhao-Yang Li, Jing-Wei Dai, Kevin J. Gagnon, Hong-Ling Cai, Takashi Yamamoto, Yasuaki Einaga, Han-Hua Zhao, Shinji Kanegawa, Osamu Sato, Kim R. Dunbar, Ren-Gen Xiong

Dalton Transactions 42 （ 41 ） 14685 - 14688 2013年10月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1477-9226

　概要を見る

The mononuclear ferric compound Fe(H-5-Cl-thsa-Me)(5-Cl-thsa-Me) ·H2O (1) was synthesized and characterized using powder/single-crystal X-ray diffraction, Mössbauer spectroscopy, differential scanning calorimetry (DSC), and magnetic susceptibility measurements. This photo-responsive compound shows reversible, two-step spin-crossover behaviour. Moreover, dielectric anomalies were observed during the spin transitions, demonstrating the multifunctional properties of compound 1. © 2013 The Royal Society of Chemistry.

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Modulation of Critical Current Density in Polycrystalline Boron-Doped Diamond by Surface Modification

Keisuke Natsui, Takashi Yamamoto, Takeshi Watanabe, Yoichi Kamihara, Yasuaki Einaga

Physica Status Solidi B 250 （ 8 ） 1943 - 1949 2013年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0370-1972

　概要を見る

The maximum current flowed with zero resistance, referred to the critical current density, is desired to be sufficiently large in order to apply superconducting wire rods and electromagnets to various devices. Although the critical current density can be enhanced by introduction of non-superconducting impurities, the transition temperature would become diminished in such a case. Here, we report modulation of a critical current density in heavily boron-doped diamonds (BDDs) by changing the surface-termination without introducing any impurity. The surface of a BDD was changed between hydrogen- and oxygen-termination. As a result, the critical current density could be modulated in a reversible manner between the hydrogen- and oxygen-terminated diamonds with maintenance of the superconducting transition temperature. This is because the volume fractions of the superconducting phases were modulated by surface modification. © 2013 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

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Synthesis and Size Control of Iron(II) Hexacyanochromate(III) Nanoparticles and the Effect of Particle Size on Linkage Isomerism

Matthieu F. Dumont, Olivia N. Risset, Elisabeth S. Knowles, Takashi Yamamoto, Daniel M. Pajerowski, Mark. W. Meisel, Daniel R. Talham

Inorganic Chemistry （AMER CHEMICAL SOC）  52 （ 8 ） 4494 - 4501 2013年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0020-1669

　概要を見る

The controlled synthesis of monodisperse nano-particles of the cubic Prussian blue analogue iron(II) hexacyanochromate(III) is reported along with a kinetic study, using cyanide stretching frequencies, showing the variations of the activation energy (E-a) of the linkage isomerism as a function of the particle size. Highly reproducible, cubic-shaped iron(11) hexacyanochromate(110 nanocrystals, with sizes ranging from 2 to 50 nm, are synthesized using a microemulsion technique, whereas a bulk synthesis yields nonuniform less monodisperse particles with sizes greater than 100 nm. Monitoring the cyanide stretching frequency with FTIR spectroscopy shows that the rate of isomerization is faster for smaller particles. Moreover, a kinetic analysis at different temperatures (255 K <= T <= 321 K) gives insight into the evolution of E-a with the particle size. Finally, time-dependent powder X-ray diffraction and net magnetization confirm the FTIR observations. The data are interpreted within the concept of a simple two-component model with different activation energies for structures near the surface of the solid and within the bulk.

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Paramagnetic Phase of a heavy-Fermion Compound, CeFePO, Probed by ⁵⁷Fe Mössbauer Spectroscopy

Tetsuro Nakamura, Takashi Yamamoto, Masanori Matoba, Yasuaki Einaga, Yoichi Kamihara

Journal of the Physical Society of Japan （PHYSICAL SOC JAPAN）  81 （ 6 ） 064714-4pp 2012年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0031-9015

　概要を見る

Fe-57 Mossbauer spectroscopy was applied to an iron-based layered compound CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed in the Mossbauer spectra of CeFePO indicating a paramagnetic phase of the Fe magnetic sublattice. All the spectra were fitted with a small quadrupole splitting, and the Debye temperature of CeFePO was found to be similar to 448 K. The isomer shift at room temperature, 0.32 mm/s, was almost equal to those of LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts and unit cell volumes, it was found that the Fe of CeFePO has a similar valence state to other layered iron-based quaternary oxypnictides except LaFePO.

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Anodic Oxidation on a Boron-Doped Diamond Electrode Mediated by Methoxy Radicals

Takenori Sumi, Tsuyoshi Saitoh, Keisuke Natsui, Takashi Yamamoto, Mahito Atobe, Yasuaki Einaga, Shigeru Nishiyama

Angewandte Chemie International Edition （WILEY-V C H VERLAG GMBH）  51 （ 22 ） 5443 - 5446 2012年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1433-7851

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Photomagnetic K_0.25Ni_1-xCo_x[Fe(CN)₆]•nH₂O and K_0.25Co[Fe(CN)₆]_0.75y[Cr(CN)₆]_0.75(1-y)•nH₂O Prussian Blue Analogue Solid Solutions

Daniel. M. Pajerowski, Takashi Yamamoto, Yasuaki Einaga

Inorganic Chemistry （AMER CHEMICAL SOC）  51 （ 6 ） 3648 - 3655 2012年03月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0020-1669

　概要を見る

Magnetically bistable solid solutions of Prussian blue analogues with chemical formulas of KaNi1-xCox[Fe(CN)(6)](beta)center dot nH(2)O (Ni1-xCoxFe) and K alpha Co gamma[Fe(CN)(6)](y)[Cr(CN)(6)](1-y)center dot nH(2)O (CoFeyCr1-y) have been synthesized and studied using mass spectrometry, Mossbauer spectroscopy, X-ray diffraction, temperature-dependent infrared spectroscopy, and dc magnetometry. These compounds provide insight into interfaces between the photomagnetic Co-Fe Prussian blue analogue and the high-T-C Ni-Cr Prussian blue analogue that exist in high-T-C photomagnetic heterostructures. This investigation shows that the bistability of Co-Fe is strongly modified by metal substitution, with Ni1-xCoxFe stabilizing high-spin cobalt-iron pairs and CoFeyCr1-y stabilizing low-spin cobalt iron pairs, while both types of substitution cause a dramatic decrease in the bistability of the material.

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Electronic Conductivity in Berlin Green and Prussian Blue

Daniel. M. Pajerowski, Takeshi Watanabe, Takashi Yamamoto, Yasuaki Einaga

Physical Review B （AMER PHYSICAL SOC）  83 （ 15 ） 153202-4pp 2011年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1098-0121

　概要を見る

We report the temperature dependent (100-300 K) conductivity of Berlin green and Prussian blue powders. The method of electronic conduction in vacuum dried Berlin green is identified as hopping of localized electrons and vacuum dried Prussian blue is reaffirmed as an insulator. The assignment of the conduction mechanism is based upon fits to the experimental data, and the different conductivities of the two samples can be understood in terms of both molecular and simple crystalline energy levels of the solids.

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Block Copolymer Permeable Membrane with Visualized High-Density Straight Channels of Poly(ethylene oxide)

Takashi Yamamoto, Taro Kimura, Motonori Komura, Yukimitsu Suzuki, Tomokazu Iyoda, Sadayuki Asaoka, Haruyuki Nakanishi

Advanced Functional Materials （WILEY-BLACKWELL）  21 （ 5 ） 918 - 926 2011年03月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1616-301X

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A simple fabrication, scalable to centimeter scale, of a permeable membrane made of block copolymer containing molecular transport channels is demonstrated by coating photo-crosslinkable liquid-crystalline block copolymer, consisting of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) bearing stilbene (Stb) mesogens in the side chains (PEO(114)-b-PMA(Stb)(52)), onto a sacrificial cellulose acetate film substrate. After thermal annealing, perpendicularly aligned and hexagonally arranged PEO cylindrical domains with a surface density of 10(11) cm(-2) were formed and then fixed efficiently by photo-crosslinking the stilbene moieties in the PMA(Stb) domains by [2 + 2] dimerization. The fully penetrating straight PEO cylindrical domains across the 480-nm-thick membrane were well-defined and visualized as molecule-transport channels. After exfoliated by removal of the cellulose acetate layer, the membrane could be transferred onto another substrate by either scooping or a horizontal lifting method. Throughout the processes, the fully penetrating PEO channels across the membrane are preserved to open at both ends. A simple permeation experiment demonstrates that rhodamine dyes permeate efficiently through the PEO cylindrical channels of the annealed membrane but not across a non-annealed one.

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Photoreduction of Prussian Blue Intercalated into Titania Nanosheet Ultrathin Films

Takashi Yamamoto, Naoki Saso, Yasushi Umemura, Yasuaki Einaga

Journal of the American Chemical Society （AMER CHEMICAL SOC）  131 （ 37 ） 13196 - 13197 2009年08月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0002-7863

　概要を見る

Ultrathin fims composed of titania nanosheets and Prussian Blue were prepared by using the modified Langmuir-Blodgett technique. The ultrathin films could be deposited in a layer-by-layer manner with lamellar structure. Upon band gap excitation of titania nanosheets, the generated electrons were injected into ferromagnetic Prussian Blue, resulting in reduction to paramagnetic Prussian White. It was revealed that the reaction could proceed only in the presence of hole-scavenging interlayer water molecules.

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Langmuir–Blodgett Films of Molecular Organic Materials

Daniel R. Talham, Takashi Yamamoto, Mark W. Meisel

Journal of Physics: Condensed Matter （IOP PUBLISHING LTD）  20 （ 18 ） 184006-13pp 2008年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0953-8984

　概要を見る

Langmuir-Blodgett methods are perhaps the original approach for achieving controlled deposition of organic thin films. Molecules are first organized into a monolayer array on the surface of water before transfer as a monolayer onto solid supports. Molecular monolayers, multilayers, and multilayered heterostructures can be achieved. The capability of exercising such control over thin film assemblies has attracted materials chemists and physicists to develop Langmuir-Blodgett films for studies on organic conductors, magnets, non-linear optics, rectifiers, and intermolecular electron transfer. This article reviews objectives in each of these areas and selects some specific examples from the literature to highlight the state of the art, mostly from the point of view of the chemical systems that are studied. Mixed organic/inorganic hybrid films represent a new direction for Langmuir-Blodgett films in materials science, combining conventional inorganic solid-state phenomena with the properties of the organic networks, and recent examples, taken principally from the authors' work, are highlighted.

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Normal Photochromism of Spiropyran in Montmorillonite Interlayer

Naoki Saso, Takashi Yamamoto, Yasushi Umemura, Yasuaki Einaga

Colloids and Surfaces A: Physicochemical and Engineering Aspects （ELSEVIER SCIENCE BV）  317 （ 1-3 ） 309 - 315 2008年03月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0927-7757

　概要を見る

Spiropyran-montmorillonitehybrid materials have been fabricated by the Langmuir-Blodgett(LB) and an intercalation method. The LB method using clay minerals could be applied to fabricate hybrid ultrathin films consisting of a non-amphiphilic spiropyran. It is confirmed that hybrid LB films possess the layered structure and exhibit "normal photochromism" without any changes in the layered structure. In case of the intercalation method, hybrid compounds also possess the layered structure. Interestingly, intercalation hybrid compounds exhibit "reverse photochromism". It is suggested that a different process in formation of the layered structure influences the observed photochromism. (C) 2007 Elsevier B.V. All rights reserved.

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Photomagnetic Hybrid Ultrathin Films

Takashi Yamamoto, Yasuaki Einaga

Journal of Solid State Electrochemistry （SPRINGER）  11 （ 6 ） 781 - 790 2007年06月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1432-8488

　概要を見る

Two novel types of photomagnetic hybrid ultrathin film (film A and B) of metal cyanides have been fabricated by means of the modified Langmuir-Blodgett method using a smectite clay mineral. Film A is composed of an amphiphilic azobenzene cation, a montmorillonite, and Prussian Blue in which photocontrol in the magnetization was realized by the photoisomerization of azobenzene chromophore. The observed photomagnetic efficiency was large (ca. 11%) due to the well-organized structure of the ultrathin film. Film B is composed of a quaternary ammonium salt, a montmorillonite, and Co-Fe Prussian Blue in which the photoinduced magnetization caused by the electron transfer exhibited an anisotropic response with regards to the direction of the applied magnetic field. This phenomenon is ascribed to the unique structure of Co-Fe Prussian Blue formed onto the clay layer.

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