Co-reporter:Koji Nakabayashi, Szymon Chorazy, Masaya Komine, Yasuto Miyamoto, Daisuke Takahashi, Barbara Sieklucka, and Shin-ichi Ohkoshi
Crystal Growth & Design September 6, 2017 Volume 17(Issue 9) pp:4511-4511
Publication Date(Web):July 31, 2017
DOI:10.1021/acs.cgd.7b00794
An octacyanidometalate-based nanochannel magnet, Co7[W(CN)8]4Cl2·29H2O, is reported. Single-crystal synchrotron X-ray diffraction measurements reveal that this compound has a three-dimensional cyanido-bridged network based on {Co5W4}n columns situated along the c-axis. The channels resemble a lotus root and have a remarkably large diameter of 1.4 nm, which corresponds to a 44% vacancy. Although the channel size is very large, the compound exhibits ferromagnetic ordering with a Curie temperature of 29 K and coercive field of 5500 Oe. Such a ferromagnetic lotus root can adsorb large molecules and may realize host–guest chemistry in ferromagnets.
Co-reporter:Shin-ichi Ohkoshi, Kenta Imoto, Asuka Namai, Shizuka Anan, Marie Yoshikiyo, and Hiroko Tokoro
Journal of the American Chemical Society September 27, 2017 Volume 139(Issue 38) pp:13268-13268
Publication Date(Web):September 13, 2017
DOI:10.1021/jacs.7b07087
Magnetic ferrites are stable, sustainable, and economical. Consequently, they have been used in various fields. The development of large coercive field (large Hc) magnetic ferrites is a very important but challenging issue to accelerate the spread of use and to expand practical applications. In this study, we prepared a rhodium-substituted ε-iron oxide film and observed a remarkably large Hc value of 35 kOe at room temperature. This is the largest value among magnetic ferrites to date. Such a large-Hc ferrite is expected to greatly expand the application of magnetic ferrites. Furthermore, when the temperature dependence of the magnetic properties was measured, an even larger Hc value of 45 kOe was recorded at 200 K. Such large Hc values are much larger than those of conventional hard magnetic ferrites.
Co-reporter:Szymon Chorazy, Kunal Kumar, Koji Nakabayashi, Barbara Sieklucka, and Shin-ichi Ohkoshi
Inorganic Chemistry May 1, 2017 Volume 56(Issue 9) pp:5239-5239
Publication Date(Web):April 18, 2017
DOI:10.1021/acs.inorgchem.7b00369
Coordination compounds built of trivalent lanthanide ions have been demonstrated as promising solid-state materials for diverse photoluminescent applications and as attractive magnetic objects with the prospective application in information storage and spintronics. We present a synthetic methodology in which both luminescent and magnetic functionalities are induced within lanthanide-based coordination polymers by the application of hexacyanocobaltate(III) anions and 3-hydroxypyridine (3-OHpy), both coordinated to 4f-metal ions modulating the lanthanide-centered properties. We report a series of trimetallic cyanido-bridged chains {[EuIIIxTbIII1–x(3-OHpy)2(H2O)4][CoIII(CN)6]}·H2O (x = 1, 0.8, 0.5, 0.4, 0.3, 0.2, 0.1, 0; compounds 1, 2, ..., 7, 8). They reveal tunable visible photoluminescence ranging from green, through yellow and orange, to red color depending on the composition of material and the wavelength of UV excitation light. Such multicolored emission is realized by the adjusted ratio between red emissive Eu3+ and green emissive Tb3+ and by the selection of wavelengths of UV light controlling the intensities of Eu- and Tb-based components of visible luminescence. The photoluminescence is enhanced by the energy-transfer (ET) process from [CoIII(CN)6]3– and 3-OHpy to lanthanides, and the efficiencies of ET to Eu and Tb play an important role in the switchable emission. The whole family, 1–8, exhibits temperature-dependent paramagnetism due to the intrinsic property of lanthanide(3+) ions. Tb-containing 2–8 reveal the field-induced slow relaxation of magnetization due to the magnetic anisotropy of Tb3+. Moreover, the compounds built of large amounts of Tb reveal the double relaxation, the faster of a typical TbIII single-ion origin, and the slower originating from the magnetic dipole–magnetic dipole interactions between neighboring TbIII centers. Compound 2, which can be considered as a magnetically diluted sample, exhibits almost single relaxation process with the thermal energy barrier ΔE/kB of 35.8(6) K and τ0 = 1.1(2) × 10–8 s at Hdc = 1500 Oe, indicating a single-molecule magnet behavior.
Co-reporter:Shin-ichi Ohkoshi, Marie Yoshikiyo, Yoshikazu Umeta, Masaya Komine, Rei Fujiwara, Hiroko Tokoro, Kouji Chiba, Takeo Soejima, Asuka Namai, Yasuto Miyamoto, and Tomomichi Nasu
The Journal of Physical Chemistry C March 16, 2017 Volume 121(Issue 10) pp:5812-5812
Publication Date(Web):February 27, 2017
DOI:10.1021/acs.jpcc.6b12694
Gallium-substituted epsilon iron oxide (ε-Ga0.5Fe1.5O3) has drawn attention because its millimeter wave absorption frequency meets the millimeter wave radar frequency for automobiles. We report the phonon modes of ε-Ga0.5Fe1.5O3, which has an orthorhombic structure in the Pna21 space group. First-principles phonon-mode calculations show that ε-Ga0.5Fe1.5O3 has 117 optical phonon modes (fundamental vibrations) with symmetries of A1, A2, B1, and B2 as well as three acoustic phonon modes. The phonon density of states demonstrates that the movements of Fe and Ga contribute to the phonon modes in the lower energy region of 20–370 cm–1, while the movements of O contribute to the phonon modes in the higher energy region of 370–720 cm–1. We directly measure the optical phonon modes of ε-Ga0.48Fe1.52O3 nanoparticles using far- and mid-infrared (IR) and Raman spectroscopies, which agree well with those obtained by first-principles phonon-mode calculations. Additionally, the thermodynamic parameters of the internal energy (U), the vibrational entropy (Svib), and the Helmholtz energy (A) are calculated and understood through the investigation of the phonon modes. Heat capacity measurements confirm that the observed thermodynamic parameters are consistent with the predicted values.
Co-reporter:Ryo Takano, Ryo Shintani, Aiko Fukazawa, Shigehiro Yamaguchi, Koji Nakabayashi, Shin-ichi Ohkoshi, and Kyoko Nozaki
Organometallics July 24, 2017 Volume 36(Issue 14) pp:2646-2646
Publication Date(Web):May 18, 2017
DOI:10.1021/acs.organomet.7b00260
Diindenosilole Si1, a silicon-bridged fulvalene derivative, was successfully reduced to its dianions using various alkali metals, and the structures were characterized by X-ray crystallographic analysis. Radical anions of Si1 as well as dianions of π-extended Si3 could also be synthesized, and the structural and physical properties were systematically compared. It was also found that the NMR spectra of dianions Si12– and Si32– show countercation and temperature dependency for their signal broadness, indicating the possible existence of thermal interconversion between closed-shell singlet states and open-shell triplet states.
Co-reporter:Shin-ichi Ohkoshi;Shintaro Saito;Tomohiro Nuida;Hiroko Tokoro;Tomoyuki Matsuda
The Journal of Physical Chemistry C August 28, 2008 Volume 112(Issue 34) pp:13095-13098
Publication Date(Web):Publication Date (Web): August 1, 2008
DOI:10.1021/jp8021216
In this work, we continuously control the second-order nonlinear optical activity by tuning the piezoelectric property in a series of rubidium manganese hexacyanoferrates, RbIxMnII[FeIII(CN)6](x+2)/3·zH2O. Above x = 0.7, second harmonic generation (SHG) is observed, and the SH light intensity (ISH) gradually increases with increasing x. The crystal structures of this series are analyzed using Rietveld analysis and the maximum entropy method. The crystal structural data shows that the difference between the existing probability of the Rb ion in interstitial site-1 (PRb1) and site-2 (PRb2), PRb1 − PRb2, gradually increases with increasing x. Because the difference between PRb1 and PRb2 produces a 4̅ rotoinversion, the PRb1 − PRb2 value is considered to be related to the magnitude of piezoelectricity or SH susceptibility (χSH). From the analysis of the χSH tensors elements, the observed x dependence of ISH can be explained by the PRb1 − PRb2 value. Such a tunable system of second-order nonlinear optical activity is very rare in condensed matters.
Co-reporter:Mateusz Reczyński, Szymon Chorazy, Beata Nowicka, Barbara Sieklucka, and Shin-ichi Ohkoshi
Inorganic Chemistry 2017 Volume 56(Issue 1) pp:179-185
Publication Date(Web):December 19, 2016
DOI:10.1021/acs.inorgchem.6b01883
An inorganic three-dimensional [NiII(H2O)2]2[WIV(CN)8]·4H2O (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase NiII2[WIV(CN)8] (1d). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While 1 reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, 1d is the first ever reported octacyanido-based solid revealing negative thermal expansion, also exhibiting a deep red color and diamagnetism. Such drastic shift in the physical properties is explained by the removal of water molecules, leaving the exclusively cyanido-bridged bimetallic network, which is accompanied by the transformation of the octahedral paramagnetic [NiII(H2O)2(NC)4]2– to the square-planar diamagnetic [NiII(NC)4]2– moieties.
Co-reporter:Fumiyoshi Hakoe, Hiroko Tokoro, Shin-ichi Ohkoshi
Materials Letters 2017 Volume 188() pp:8-12
Publication Date(Web):1 February 2017
DOI:10.1016/j.matlet.2016.09.084
•A blue transparent lambda-trititanium-pentoxide (λ-Ti3O5) film was prepared.•The λ-Ti3O5 film is oriented; the (110) plane parallel to the plane of the substrate.•Dielectric constants for λ-Ti3O5 were determined by spectroscopic ellipsometry.•Refraction index and extinction coefficient for λ-Ti3O5 were also determined.A thin film of lambda-trititanium pentoxide (λ-Ti3O5) was prepared by sintering titanium dioxide nanoparticles on a quartz substrate. The dielectric constants of the real (ε′) and the imaginary (ε″) parts, the optical constants of the refraction index (n), and the extinction coefficient (k) for λ-Ti3O5 were determined by spectroscopic ellipsometry. The optical transitions of λ-Ti3O5 are attributed to the electronic transitions due to the free electron carrier and the oxygen-to-metal charge transfer band.
Co-reporter:Masaya Komine;Szymon Chorazy;Kenta Imoto;Koji Nakabayashi
CrystEngComm (1999-Present) 2017 vol. 19(Issue 1) pp:18-22
Publication Date(Web):2016/12/21
DOI:10.1039/C6CE02214F
The rare heteroligand pentacyanidonitrosylmolybdate(I) anion was employed in the construction of d–f bimetallic cyanido-bridged {[LnIII(dmf)6][MoI(CN)5(NO)]} (Ln = Gd, 1; Eu, 2) chains crystallizing in the non-centrosymmetric Pna21 space group. 1 exhibits Gd–Mo antiferromagnetic coupling giving rise to the ferrimagnetic spin chain behaviour with the onset of magnetic ordering below 2 K, and shows high second harmonic generation (SHG) activity with SH susceptibility of 1.2 × 10−10 esu, opening a novel family of non-centrosymmetric molecule-based magnets.
Co-reporter:Szymon Chorazy;Michał Rams;Junhao Wang;Barbara Sieklucka
Dalton Transactions 2017 vol. 46(Issue 40) pp:13668-13672
Publication Date(Web):2017/10/17
DOI:10.1039/C7DT02239E
Ytterbium (3+) ions combined with 3-pyridone and hexacyanido-cobaltate(III) anions in a concentrated aqueous solution produce cyanido-bridged {[YbIII(3-pyridone)2(H2O)2][CoIII(CN)6]} (1) chains. The resulting YbIII complexes of an elongated octahedral geometry reveal two coexisting functionalities: a field-induced slow magnetic relaxation with an energy barrier of ΔE/kB = 45(1) K at Hdc = 1 kOe, and an YbIII-centered near-infrared fluorescence in the 950–1100 nm range sensitized by 3-pyridone and [CoIII(CN)6]3−.
Co-reporter:Szymon Chorazy;Michał Rams;Junhao Wang;Barbara Sieklucka
Dalton Transactions 2017 vol. 46(Issue 40) pp:13668-13672
Publication Date(Web):2017/10/17
DOI:10.1039/C7DT02239E
Ytterbium (3+) ions combined with 3-pyridone and hexacyanido-cobaltate(III) anions in a concentrated aqueous solution produce cyanido-bridged {[YbIII(3-pyridone)2(H2O)2][CoIII(CN)6]} (1) chains. The resulting YbIII complexes of an elongated octahedral geometry reveal two coexisting functionalities: a field-induced slow magnetic relaxation with an energy barrier of ΔE/kB = 45(1) K at Hdc = 1 kOe, and an YbIII-centered near-infrared fluorescence in the 950–1100 nm range sensitized by 3-pyridone and [CoIII(CN)6]3−.
Co-reporter:Szymon Chorazy; Jan J. Stanek; Wojciech Nogaś; Anna M. Majcher; Michał Rams; Marcin Kozieł; Ewa Juszyńska-Gałązka; Koji Nakabayashi; Shin-ichi Ohkoshi; Barbara Sieklucka;Robert Podgajny
Journal of the American Chemical Society 2016 Volume 138(Issue 5) pp:1635-1646
Publication Date(Web):January 13, 2016
DOI:10.1021/jacs.5b11924
Precisely controlled stoichiometric mixtures of Co2+ and Fe2+ metal ions were combined with the [WV(CN)8]3– metalloligand in a methanolic solution to produce a series of trimetallic cyanido-bridged {Fe9–xCox[W(CN)8]6(MeOH)24}·12MeOH (x = 0, 1, ..., 8, 9; compounds 0, 1, ..., 8, 9) clusters. All the compounds, 0–9, are isostructural, and consist of pentadecanuclear clusters of a six-capped body-centered cube topology, capped by methanol molecules which are coordinated to 3d metal centers. Thus, they can be considered as a unique type of a cluster-based molecular solid solution in which different Co/Fe metal ratios can be introduced while preserving the coordination skeleton and the overall molecular architecture. Depending on the Co/Fe ratio, 0–9 exhibit an unprecedented tuning of magnetic functionalities which relate to charge transfer assisted phase transition effects and slow magnetic relaxation effects. The iron rich 0–5 phases exhibit thermally induced reversible structural phase transitions in the 180–220 K range with the critical temperatures being linearly dependent on the value of x. The phase transition in 0 is accompanied by HSFeII WV ↔ HSFeIII WIV charge transfer (CT) and the additional minor contribution of a Fe-based spin crossover (SCO) effect. The Co-containing 1–5 phases reveal two simultaneous electron transfer processes which explore HSFeII WV ↔ HSFeIII WIV CT and the more complex HSCoII WV ↔ LSCoIII WIV charge transfer induced spin transition (CTIST). Detailed structural, spectroscopic, and magnetic studies help explain the specific role of both types of CN–-bridged moieties: the Fe-NC-W linkages activate the molecular network toward a phase transition, while the subsequent Co–W CTIST enhances structural changes and enlarges thermal hysteresis of the magnetic susceptibility. On the second side of the 0–9 series, the vanishing phase transition in the cobalt rich 6–9 phases results in the high-spin ground state, and in the occurrence of a slow magnetic relaxation process at low temperatures. The energy barrier of the magnetic relaxation gradually increases with the increasing value of x, reaching up to ΔE/kB = 22.3(3) K for compound 9.
Co-reporter:Szymon Chorazy, Michał Rams, Anna Hoczek, Bernard Czarnecki, Barbara Sieklucka, Shin-ichi Ohkoshi and Robert Podgajny
Chemical Communications 2016 vol. 52(Issue 26) pp:4772-4775
Publication Date(Web):22 Feb 2016
DOI:10.1039/C5CC10371A
Pentadecanuclear {CoII9[WV(CN)8]6} clusters were combined with bidentate 2,2′-bipyridine N,N′-dioxide (2,2′-bpdo) ligands resulting in two distinct molecules, {Co9W6(2,2′-bpdo)7} (cluster A) and {Co9W6(2,2′-bpdo)6} (cluster B), capped by seven and six 2,2′-bpdo ligands, respectively. They crystallize within a single {Co9W6(2,2′-bpdo)7}·{Co9W6(2,2′-bpdo)6}·solvent (1) supramolecular network, and reveal single-molecule magnet behaviour with an enhanced energy barrier, a ΔE/kB of 30.0(8) K, which was tentatively ascribed to seven-capped axially deformed cluster A.
Co-reporter:Szymon Chorazy, Barbara Sieklucka, and Shin-ichi Ohkoshi
Crystal Growth & Design 2016 Volume 16(Issue 9) pp:4918
Publication Date(Web):August 1, 2016
DOI:10.1021/acs.cgd.6b00476
Hexacyanidochromate(III) anion is here explored as the building block for the construction of bimetallic 3d-4f coordination polymers that combine spin ordering and luminescence. We report the two-dimensional cyanido-bridged {[NdIII(pmmo)2(H2O)3][CrIII(CN)6]} (1) layered framework obtained by the spontaneous crystallization from the aqueous solution of Nd3+, pyrimidine N-oxide (pmmo), and [CrIII(CN)6]3–. 1 crystallizes as light green plates in the orthorhombic Pbca space group and reveals a topology of a square grid built of nine-coordinated [NdIII(μ-NC)4(H2O)3(pmmo)2]− complexes of a nearly capped square antiprism geometry, and six-coordinated octahedral [CrIII(CN)6]3– moieties. Because of the presence of cyanide-mediated ferromagnetic coupling between paramagnetic NdIII (J = 9/2) and CrIII (S = 3/2) centers, 1 exhibits a long-range ferromagnetic ordering below Curie temperature of 2.8 K, with a tiny magnetization-field hysteresis loop detected at 1.8 K. Under the UV light irradiation, 1 shows the near-infrared fluorescence originated from the 4F3/2 → 4I9/2 (λmax = 895 nm) and 4F3/2 → 4I11/2 (λmax = 1060 nm) electronic transitions of NdIII. The near-infrared emission is realized through the energy transfer from [CrIII(CN)6]3– anions and pmmo ligands to NdIII centers which was possible due to the spectral overlap between the visible-light and near-infrared emission bands of CrIII and pmmo, and the absorption bands of NdIII. Thus, 1 can be considered as a novel type of bifunctional magneto-luminescent layered material taking advantage of the fruitful electronic and magnetic interplay between NdIII(pmmo) and [CrIII(CN)6]3– complexes.
Co-reporter:Takuro Ohno, Szymon Chorazy, Kenta Imoto, and Shin-ichi Ohkoshi
Crystal Growth & Design 2016 Volume 16(Issue 7) pp:4119-4128
Publication Date(Web):June 14, 2016
DOI:10.1021/acs.cgd.6b00626
The introduction of 4-bromopyridine (4-Brpy) to a self-assembled MII-[NbIV(CN)8] (M = 3d metal ion) coordination system results in the formation of three-dimensional cyanido-bridged networks, {[MII(4-Brpy)4]2[NbIV(CN)8]}·nH2O (M = Zn, n = 1, 1; M = Mn, n = 0.5, 2; M = Ni, n = 2, 3). All these compounds are coordination frameworks composed of octahedral [MII(4-Brpy)4(μ-NC)2] complexes bonded to square antiprismatic [NbIV(CN)8]4– ions bearing four bridging and four terminal cyanides. 1 and 2 crystallize in the chiral I4122 space group as the mixture of two enantiomorphic forms, named 1(+)/1(−) and 2(+)/2(−), respectively. The chirality is here induced by the spatial arrangement of nonchiral but sterically expanded 4-Brpy ligands positioned around MII centers in the distorted square geometry, which gives two distinguishable types of coordination helices, A and B, along a 4-fold screw axis. The (+) forms contain left handed helices A, and right handed helices B, while the opposite helicity is presented in the (−) enantiomers. On the contrary, 3 crystallizes in the nonchiral Fddd space group and creates only one type of helix. Half of them are right handed, and the second half are left handed, which originates from the ideally symmetrical arrangement of 4-Brpy around NiII and results in the overall nonchiral character of the network. 1 is a paramagnet due to paramagnetic NbIV centers separated by diamagnetic ZnII. 2 is a ferrimagnet below a critical temperature, Tc of 28 K, which is due to the CN–-mediated antiferromagnetic coupling within Mn–NC–Nb linkages. 3 reveals a ferromagnetic type of NiII–NbIV interaction leading to a ferromagnetic ordering below Tc of 16 K, and a hysteresis loop with a coercive field of 1400 Oe at 2 K. Thus, 1 is a chiral paramagnet, 3 is a nonchiral ferromagnet, and 2 combines both of these functionalities, being a rare example of a chiral molecule-based magnet whose chirality is induced by the noninnocent 4-Brpy ligands.
Co-reporter:Yoshikazu Umeta;Szymon Chorazy;Koji Nakabayashi
European Journal of Inorganic Chemistry 2016 Volume 2016( Issue 13-14) pp:1980-1988
Publication Date(Web):
DOI:10.1002/ejic.201500823
Abstract
A gel crystallization technique was successfully applied in the pioneering preparation of a single-crystalline form of the three-dimensional copper(II) octacyanidomolybdate(IV) network, which is a photomagnetic material. This assembly crystallizes with the formula {[CuII(H2O)]2[MoIV(CN)8]}·2H2O in the tetragonal crystal system and reveals a three-dimensional cyanido-bridged framework constructed of five-coordinate square-pyramidal [CuII(H2O)(NC)4]2– complexes and [MoIV(CN)8]4– ions of square-antiprismatic geometry. First-principles calculations by the GGA + U method indicate that the visible-light absorption band, crucial for the observation of a photomagnetic effect, is interpreted in terms of MoIV to CuII charge transfer, which is enabled owing to the accompanying pz spx transition of the nitrogen atoms of the bridging cyanido ligands. The optical transitions in the visible range are anisotropic, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges.
Co-reporter:Hiroki Eimura;Yoshikazu Umeta;Dr. Hiroko Tokoro;Dr. Masafumi Yoshio;Dr. Shin-ichi Ohkoshi;Dr. Takashi Kato
Chemistry - A European Journal 2016 Volume 22( Issue 26) pp:8872-8878
Publication Date(Web):
DOI:10.1002/chem.201505213
Abstract
Macroscopically oriented stable organic radicals have been obtained by using a liquid–crystalline (LC) gel composed of an l-isoleucine-based low molecular weight gelator containing a 2,2,6,6-tetramethylpiperidine 1-oxyl moiety. The LC gel has allowed magnetic measurements of the oriented organic radical. The gelator has formed fibrous aggregates in liquid crystals via intermolecular hydrogen bonds. The fibrous aggregates of the radical gelator are formed and oriented on cooling by applying a magnetic field to the mixture of liquid crystals and the gelator. Superconducting quantum interference device (SQUID) measurements have revealed that both oriented and nonoriented fibrous aggregates exhibited antiferromagnetic interactions, in which super-exchange interaction constant J is estimated as −0.89 cm−1.
Co-reporter:Szymon Chorazy, Mirosław Arczynski, Koji Nakabayashi, Barbara Sieklucka, and Shin-ichi Ohkoshi
Inorganic Chemistry 2015 Volume 54(Issue 10) pp:4724-4736
Publication Date(Web):May 6, 2015
DOI:10.1021/acs.inorgchem.5b00040
Complexes of lanthanides(III) (Ce–Yb) with 2,2′-bis(2-oxazoline) (Box) combined with octacyanidomolybdate(V) gave a series of magneto-luminescent coordination polymers, {[LnIII(Box)n(DMF)m][MoV(CN)8]}·x(solvent) (1–12). They are built of cyanido-bridged layers of a mixed 4- and 8-metal rings topology and show unique sliding of layers dependent on a 4f metal ion. For light lanthanides, dominant phase A, {[LnIII(Box)2(DMF)2][MoV(CN)8]}·1.5MeCN (Ln = Ce, 1; Pr, 2; Nd, 3), consists of ideally aligned, not shifted layers, giving large channels (13.7 × 14.0 Å). Intermediate lanthanides reveal phase B, {[LnIII(Box)2(DMF)2] [MoV(CN)8]}·H2O (Ln = Sm, 4; Eu, 5; Gd, 6; Tb, 7; Dy, 8), of smaller pores (8.4 × 10.6 Å) due to layer-H2O hydrogen bonding, which induces sliding of CN–-bridged layers. Heavy lanthanides show phase C, {[LnIII(Box)(DMF)3][MoV(CN)8]}·MeCN (Ln = Ho, 9; Er, 10; Tm, 11; Yb, 12), with large channels (13.7 × 13.7 Å) of a similar size to light lanthanides. This effect comes from the changes in LnIII coordination sphere affecting solvent–layer interactions. Compounds 1–12 reveal diverse emission depending on the interaction between LnIII and Box luminophors. For 2–5, 9, and 12, the ligand-to-metal energy-transfer-induced visible f-centered emission ranging from green for HoIII-based 9, orange from SmIII-based 4, to red for PrIII- and EuIII-containing 2 and 5, respectively. Near-infrared emission was found for 2–4, 9, and 12. Red phosphorescence of Box was detected for GdIII-based 6, whereas the selective excitation of ligand or LnIII excited states resulting in the switchable red to green emission was found for TbIII-based 7. The materials revealed LnIII–MoV magnetic coupling leading to ferromagnetism below 2.0 and 2.2 K for 4 and 7, respectively. The onset of magnetic ordering at low temperatures was found for 6 and 8. Compounds 1–12 form a unique family of cyanido-bridged materials of a bifunctional magneto-luminescence character combined with dynamic structural features.
Co-reporter:Kenji Tanaka, Tomomichi Nasu, Yasuto Miyamoto, Noriaki Ozaki, Shu Tanaka, Toshiaki Nagata, Fumiyoshi Hakoe, Marie Yoshikiyo, Kosuke Nakagawa, Yoshikazu Umeta, Kenta Imoto, Hiroko Tokoro, Asuka Namai, and Shin-ichi Ohkoshi
Crystal Growth & Design 2015 Volume 15(Issue 2) pp:653
Publication Date(Web):December 15, 2014
DOI:10.1021/cg5013439
The phase transition between gamma-trititanium-pentoxide (γ-Ti3O5) and delta-trititanium-pentoxide (δ-Ti3O5) was clarified from both experimental and theoretical viewpoints. With decreasing temperature, the monoclinic I2/c crystal structure of γ-Ti3O5 was found to switch to a monoclinic P2/a crystal structure of δ-Ti3O5 due to lowering of symmetry. Electrical conductivity (σ) measurement shows that γ-Ti3O5 behaves like a metallic conductor with a σ value of 4.7 S cm–1 at 320 K, while δ-Ti3O5 shows a semiconductive property with a σ value of 2.5 × 10–5 S cm–1 at 70 K. Optical measurement also supports that γ-Ti3O5 is a metallic conductor, while δ-Ti3O5 is a semiconductor with a band gap of 0.07 eV. First-principles calculations show that γ-Ti3O5 is a metallic conductor, and the energy state on the Fermi energy is composed of the 3d orbital of Ti and 2p orbital of O with one-dimensional linkage along the crystallographic c-axis. On the contrary, δ-Ti3O5 has a band gap, and the energy state around the Fermi energy is split into the valence band and the conduction band, which are assigned to the lower and upper Hubbard bands, respectively. Thus, the phase transition between γ-Ti3O5 and δ-Ti3O5 is caused by breaking of a one-dimensionally conducting pathway due to a Mott–Hubbard metal–insulator phase transition.
Co-reporter:Kenta Imoto, Miho Takemura, Koji Nakabayashi, Yasuto Miyamoto, Keiko Komori-Orisaku, Shin-ichi Ohkoshi
Inorganica Chimica Acta 2015 Volume 425() pp:92-99
Publication Date(Web):30 January 2015
DOI:10.1016/j.ica.2014.10.001
•MnII–[NbIV(CN)8] (1, 2) and CoII–[NbIV(CN)8] (3) assemblies are synthesized.•Coordination geometries of Nb are square antiprism (1, 2) and dodecahedron (3).•3 exhibits large coercive field of 15 000 Oe.•Magnetic interaction is affected by the population of 2p orbital on N atoms.•A large coercivity of 3 is suggested to be due to single-ion anisotropy of CoII.We report three-dimensional (3D) cyanido-bridged Mn–Nb and Co–Nb bimetal assemblies, MnII2[NbIV(CN)8]·(L)2·nH2O (1: L = 5-aminopyrimidine, n = 5; 2: L = 5-methylpyrimidine, n = 4), and CoII2[NbIV(CN)8] (4-pyridinealdoxime)8·2H2O (3). The single-crystal X-ray structural analyses show that 1 and 2 consist of isomorphic 3D cyanido-bridged network (monoclinic, P21/n) composed of square antiprism Nb sites and distorted octahedral Mn sites. Both 1 and 2 show ferrimagnetism with Curie temperatures (TC) of 32 and 34 K, respectively, which is caused by the antiferromagnetic superexchange interaction between MnII (S = 5/2) and NbIV (S = 1/2) through the CN groups. 3 has a 3D cyanido-bridged network (tetragonal, I41/a) composed of a dodecahedral Nb site and axially distorted pseudo-octahedral Co site. This compound shows ferromagnetic ordering with a TC of 18 K. Magnetization versus rotation angle of single crystal reveals that 3 has a large coercive field of 15 000 Oe as crystal is oriented to a-axis, which is due to the strong magnetic anisotropy on distorted CoII.Cyanido-bridged Mn–Nb and Co–Nb bimetal assemblies, MnII2[NbIV(CN)8]·(L)2·nH2O (1: L = 5-aminopyrimidine, n = 5; 2: L = 5-methylpyrimidine, n = 4), and CoII2[NbIV(CN)8]·(4-pyridinealdoxime)8·2H2O (3) are synthesized. 1 and 2 have isomorphic three-dimensional (3D) cyanido-bridged network composed of a square antiprism Nb sites, showing ferrimagnetism with Curie temperatures (TC) of 32 and 34 K, respectively, due to the antiferromagnetic coupling between MnII (S = 5/2) and NbIV (S = 1/2) through the CN groups. 3 has a 3D cyanido-bridged network composed of a dodecahedral Nb site and axially distorted Co site, exhibiting ferromagnetism with a TC of 18 K. Magnetization versus rotation angle of single crystal reveals that 3 has a large coercive field of 15 000 Oe as crystal is oriented to a-axis, which is due to the strong magnetic anisotropy on distorted CoII.
Co-reporter:Koji Nakabayashi, Szymon Chorazy, Daisuke Takahashi, Takaaki Kinoshita, Barbara Sieklucka, and Shin-ichi Ohkoshi
Crystal Growth & Design 2014 Volume 14(Issue 11) pp:6093-6100
Publication Date(Web):September 23, 2014
DOI:10.1021/cg501250p
Two-dimensional cesium bimetal cyano-bridged assemblies CsI4CoII[MoV(CN)8]Cl3 (CsCoMo) and CsI4CoII[WV(CN)8]Cl3 (CsCoW) were synthesized. The negatively charged and solvent-free {CoII[MV(CN)8]Cl3}4– (M = Mo, W) coordination layers are separated by Cs+ ions. Themogravimetric measurements show that these compounds reveal high thermal durability up to 523 K (250 °C), which is due to the absence of solvent molecules in their crystal structures. The magnetic measurements show that CsCoMo and CsCoW are metamagnets showing the field-induced transition from an antiferromagnetic phase with Néel temperature of 25 K to a ferromagnetic phase, which is observed at high critical magnetic field of 24 kOe at 1.8 K. These originate from antiferromagnetic interactions between ferromagnetically coupled cyano-bridged CoII–MV layers, and the contribution from single-ion anisotropy of CoII.
Co-reporter:Szymon Chorazy;Dr. Koji Nakabayashi;Miros&x142;aw Arczynski;Dr. Robert Pe&x142;ka; Shin-ichi Ohkoshi; Barbara Sieklucka
Chemistry - A European Journal 2014 Volume 20( Issue 23) pp:7144-7159
Publication Date(Web):
DOI:10.1002/chem.201304772
Abstract
Two chiral luminescent derivatives of pyridine bis(oxazoline) (Pybox), (SS/RR)-iPr-Pybox (2,6-bis[4-isopropyl-2-oxazolin-2-yl]pyridine) and (SRSR/RSRS)-Ind-Pybox (2,6-bis[8H-indeno[1,2-d]oxazolin-2-yl]pyridine), have been combined with lanthanide ions (Gd3+, Nd3+) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN−-bridged coordination chains: {[LnIII(SS/RR-iPr-Pybox)(dmf)4]3[WV(CN)8]3}n⋅dmf⋅4 H2O (Ln=Gd, 1-SS and 1-RR; Ln=Nd, 2-SS and 2-RR) and {[LnIII(SRSR/RSRS-Ind-Pybox)(dmf)4][WV(CN)8]}n⋅5 MeCN⋅4 MeOH (Ln=Gd, 3-SRSR and 3-RSRS; Ln=Nd, 4-SRSR and 4-RSRS). These materials display enantiopure structural helicity, which results in strong optical activity in the range 200–450 nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/Vis absorption spectra. Under irradiation with UV light, the GdIII-WV chains show dominant ligand-based red phosphorescence, with λmax≈660 nm for 1-(SS/RR) and 680 nm for 3-(SRSR/RSRS). The NdIII-WV chains, 2-(SS/RR) and 4-(SRSR/RSRS), exhibit near-infrared luminescence with sharp lines at 986, 1066, and 1340 nm derived from intra-f 4F3/24I9/2,11/2,13/2 transitions of the NdIII centers. This emission is realized through efficient ligand-to-metal energy transfer from the Pybox derivative to the lanthanide ion. Due to the presence of paramagnetic lanthanide(III) and [WV(CN)8]3− moieties connected by cyanide bridges, 1-(SS/RR) and 3-(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between GdIII (SGd=7/2) and WV (SW=1/2) centers with J1-(SS)=−0.96(1) cm−1, J1-(RR)=−0.95(1) cm−1, J3-(SRSR)=−0.91(1) cm−1, and J3-(RSRS)=−0.94(1) cm−1. 2-(SS/RR) and 4-(SRSR/RSRS) display ferromagnetic coupling within their NdIII-NC-WV linkages.
Co-reporter:Asuka Namai, Marie Yoshikiyo, Sayaka Umeda, Takayuki Yoshida, Tatsuro Miyazaki, Makoto Nakajima, Keita Yamaguchi, Tohru Suemoto and Shin-ichi Ohkoshi
Journal of Materials Chemistry A 2013 vol. 1(Issue 34) pp:5200-5206
Publication Date(Web):17 Jul 2013
DOI:10.1039/C3TC30805G
In this study, we demonstrate a synthesis of rhodium substituted ε-iron oxide, ε-RhxFe2−xO3 (0 ≤ x ≤ 0.19), nanoparticles in silica. The synthesis features a sol–gel method to coat the metal hydroxide sol containing Fe3+ and Rh3+ ions with a silica sol via hydrolysis of alkoxysilane to form a composite gel. The obtained samples are barrel-shaped nanoparticles with average long- and short-axial lengths of approximately 30 nm and 20 nm, respectively. The crystallographic structure study using X-ray diffraction shows that ε-RhxFe2−xO3 has an orthorhombic crystal structure in the Pna21 space group. Among the four non-equivalent substitution sites (A–D sites), Rh3+ ions mainly substitute into the C sites. The formation mechanism of ε-RhxFe2−xO3 nanoparticles is considered to be that the large surface area of the nanoparticles increases the contribution from the surface energy to Gibbs free energy, resulting in a different phase, ε-phase, becoming the most stable phase compared to that of bulk or single crystal. The measured electromagnetic wave absorption characteristics due to natural resonance (zero-field ferromagnetic resonance) using terahertz time domain spectroscopy reveal that the natural resonance frequency shifts from 182 GHz (ε-Fe2O3) to 222 GHz (ε-Rh0.19Fe1.81O3) upon rhodium substitution. This is the highest natural resonance frequency of a magnetic material, and is attributed to the large magnetic anisotropy due to rhodium substitution. The estimated coercive field for ε-Rh0.19Fe1.81O3 is as large as 28 kOe.
Co-reporter:Keiko Komori-Orisaku, Kenta Imoto, Yoshihiro Koide, and Shin-ichi Ohkoshi
Crystal Growth & Design 2013 Volume 13(Issue 12) pp:5267-5271
Publication Date(Web):October 18, 2013
DOI:10.1021/cg401011d
We report a mixed-valence cobalt(II/III)–octacyanidotungstate(IV/V) magnet, [CoII(H2O)]2[CoIII{μ-(R)-1-(4-pyridyl)ethanol}2][WIV(CN)8][WV(CN)8]·5H2O. Synchrotron-radiation X-ray single crystal structural analysis, infrared spectrum, and density-functional theory (DFT) calculation indicate that this compound has a chiral structure with the P21 space group and both CoII(S = 3/2)–NC–WV(S = 1/2) and CoIII(S = 0)–NC–WIV(S = 0) moieties, which are structurally distinguishable in the crystal structure. Magnetic measurements reveal that this compound exhibits ferromagnetism with a Curie temperature of 11 K and a coercive field of 1500 Oe, which is caused by the coexistence of the superexchange interaction in the CoII–WV chain and double exchange interaction between the chains.
Co-reporter:Kenta Imoto, Kosuke Nakagawa, Hiroyuki Miyahara, and Shin-ichi Ohkoshi
Crystal Growth & Design 2013 Volume 13(Issue 11) pp:4673-4677
Publication Date(Web):September 12, 2013
DOI:10.1021/cg400390b
A two-dimensional manganese-octacyanoniobate based magnet, MnII3[NbIV(CN)8]2(4-aminopyridine)10(4-aminopyridinium)2·12H2O, was prepared. This compound shows a spin-flip transition with a critical magnetic field value of ca. 200 Oe, which originates from metamagnetism. In addition, an impedance measurement indicates that this compound is a super-ionic conductor with 4.6 × 10–4 S cm–1. The observed super-ionic conductivity is explained by the proton conduction (so-called the Grotthuss mechanism) through the hydrogen-bonding network, i.e., Lewis acidity of the Mn ion accelerates the deprotonation of the ligand water molecules, and then the released proton propagates via ligand water molecules, noncoordinated water molecules, and 4-aminopyridinium cations.
Co-reporter:Szymon Chorazy, Koji Nakabayashi, Noriaki Ozaki, Robert Pełka, Tomasz Fic, Jacek Mlynarski, Barbara Sieklucka and Shin-ichi Ohkoshi
RSC Advances 2013 vol. 3(Issue 4) pp:1065-1068
Publication Date(Web):26 Nov 2012
DOI:10.1039/C2RA23033J
Unique one-dimensional cyanido-bridged {[EuIII(RR-Pri-Pybox)(dmf)4]3[WV(CN)8]3}n·dmf·8H2O (1-RR) and {[EuIII(SS-Pri-Pybox)(dmf)4]3[WV(CN)8]3}n·dmf·8H2O (1-SS) (Pri-Pybox = 2,2′-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline)) chains were synthesized and characterized. They combine chiral helicity with paramagnetism and thermally switchable luminescence, and have a great potential in the aspect of magneto-optical phenomena.
Co-reporter:Daisuke Takahashi, Koji Nakabayashi, Shu Tanaka, Shin-ichi Ohkoshi
Inorganic Chemistry Communications 2013 Volume 27() pp:47-50
Publication Date(Web):January 2013
DOI:10.1016/j.inoche.2012.09.021
We report the crystal structure and magnetic properties of a two-dimensional cyano-bridged MnII(S = 5/2)–NbIV(S = 1/2) bimetal assembly (1), and the magnetic properties of an isostructural cyano-bridged MnII–MoIV(S = 0) bimetal assembly (2). 1 contains 3-hydroxypyridine ligands with four types of coordination arrangements, includes μ-oxo-bridged Mn–Mn sites, and shows ferrimagnetism with a Curie temperature of 16 K due to the antiferromagnetic MnII–NbIV superexchange interaction through the cyano groups. 2 exhibits paramagnetism with the antiferromagnetic interaction between Mn and Mn through the μ-oxo-bridges.2-D cyano-bridged MnII-NbIV bimetal assembly includes four different coordination arrangements of 3-hydroxypyridines and μ-oxo-bridged Mn-Mn sites, exhibiting ferrimagnetism with TC of 16 K due to the antiferromagnetic interaction of Nb―C≡N―Mn. The isostructural MnII-NoIV assembly shows paramagnetism.Highlights► 2-D cyano-bridged MnII(S = 5/2) –NbIV(S = 1/2) bimetal assembly 1 and isostructural MnII–MoIV(S = 0) compound 2 are prepared. ► Compound 1 includes four different coordination arrangements of 3-hydroxypyridines. ► Compound 1 contains μ-oxo-bridged Mn–Mn sites in the cyano-bridged network. ► Compound 1 exhibits ferrimagnetism with TC of 16 K due to the antiferromagnetic superexchange interaction of Nb―C ≡ N―Mn. ► Compound 2 shows paramagnetism due to the antiferromagnetic superexchange interaction of Mn–Mn through μ-oxo-bridges.
Co-reporter:Jean-Daniel Compain, Koji Nakabayashi, Shin-ichi Ohkoshi
Polyhedron 2013 Volume 66() pp:116-122
Publication Date(Web):13 December 2013
DOI:10.1016/j.poly.2013.03.004
We report the syntheses of ε-Keggin polyoxomolybdates capped by neodymium, samarium, europium and terbium and the corresponding multidimensional materials connected with hexacyanoferrate, [PMo12O37(OH)3{Ln(H2O)5(Fe(CN)6)0.25}4] (Ln = Nd, Sm, Eu, and Tb). The single crystal X-ray diffraction measurement of the Ln = Nd system reveals a multilayered structure (orthorhombic, Pmmn). The magnetic measurement showed that these four compounds exhibit paramagnetism due to each LnIII centre. In addition, the electrochemistry shows the reversible Mo(V)/Mo(VI) redox behaviour.We have been studying the structural, magnetic and electrochemical properties of the [PMo12O37(OH)3{Ln(H2O)5(Fe(CN)6)0.25}4] systems (Ln = Nd, Sm, Eu, Tb), a new class of multilayered networks combining cyanometalates with polyoxometalates (POM) units. All the compounds (Ln = Nd, Sm, Eu, Tb) exhibit paramagnetism due to each LnIII centre, while the electrochemistry shows the reversible Mo(V)/Mo(VI) redox behaviour.
Co-reporter:Kosuke Nakagawa, Kenta Imoto, Hiroyuki Miyahara, Shin-ichi Ohkoshi
Polyhedron 2013 Volume 52() pp:424-428
Publication Date(Web):22 March 2013
DOI:10.1016/j.poly.2012.08.058
In this paper, we report the syntheses, crystal structures, and magnetic properties of two manganese(II)–octacyanoniobate(IV)-based magnets: MnII2[NbIV(CN)8](3-pyridinemethanol)8·2H2O (1) and MnII2[NbIV(CN)8](3-aminopyridine)8·2H2O (2). 1 and 2 possess 3D network structures where a [Nb(CN)8]4− ion is connected to four Mn ions, and a Mn ion is connected to two [Nb(CN)8]4− ions via bridged cyanides. The coordination geometry of [Nb(CN)8] in 1 is square antiprism, while that in 2 is dodecahedron. Magnetic measurements show that 1 and 2 are ferrimagnets with Curie temperatures (TC) of 24 and 43 K, respectively, although the coordination numbers of the bridged CN groups around Nb and Mn ions are the same. The difference in TC can be understood by considering the difference in the coordination geometries of [Nb(CN)8]. Molecular orbital calculations of [NbIV(CN)8] using the discrete variational (DV)-Xα method indicate that the population of the 2p orbital on the bridged N with a dodecahedron geometry is larger than that with a square antiprism geometry. The calculation results suggest that the charge population of the 2p orbital on the cyano-nitrogen affects the superexchange interaction for the magnetic orbital of NbCNMn, which determines the TC value.Graphical abstractIn this paper, we report the syntheses, crystal structures, and magnetic properties of two manganese(II)–octacyanoniobate(IV)-based magnets: MnII2[NbIV(CN)8](3-pyridinemethanol)8·2H2O (1) and MnII2[NbIV(CN)8](3-aminopyridine)8·2H2O (2) with 3D network structures. The coordination geometry of [Nb(CN)8] in 1 is square antiprism, while that in 2 is dodecahedron. Magnetic measurements show that 1 and 2 are ferrimagnets with Curie temperatures (TC) of 24 and 43 K, respectively, although the bridged CN groups around Nb and Mn ions have the same coordination numbers. Molecular orbital calculations indicate that the population of the 2p orbital on the bridged N with a dodecahedron geometry is larger than that with a square antiprism geometry. The results suggest that the charge population of the 2p orbital on the cyano-nitrogen affects the superexchange interaction for the magnetic orbital of NbCNMn, which determines the TC value.Highlights► We synthesized two novel Mn–[Nb(CN)8]-based compounds (1 and 2). ► Nb coordination geometries are square antiprism (1) and dodecahedron (2). ► The Curie temperature (TC) of 1 is 24 K, while that of 2 is 43 K. ► Molecular orbital calculations were conducted using the DV-Xα method. ► The charge population of the 2p orbital on the N atoms affects the TC value.
Co-reporter:Shin-ichi Ohkoshi and Hiroko Tokoro
Accounts of Chemical Research 2012 Volume 45(Issue 10) pp:1749
Publication Date(Web):August 6, 2012
DOI:10.1021/ar300068k
The study of photoinduced phase-transition materials has implications for the fields of inorganic chemistry, solid-state chemistry, and materials science. Cyano-bridged bimetal assemblies are promising photomagnetic materials. Because cyano-bridged bimetal assemblies possess various absorption bands in the visible light region, their electronic and spin states can be controlled by visible light irradiation. Moreover, the selection of magnetic metal ions and organic ligands provide a way of controlling spin–spin interactions through a cyano bridge.In this Account, we describe cyano-bridged bimetal assemblies developed in our laboratory. CuII2[MoIV(CN)8]·8H2O (CuMo), RbIMnII[FeIII(CN)6] (RbMnFe), and CoII3[WV(CN)8]2·(pyrimidine)4·6H2O (CoW) induce photomagnetism via photoinduced metal-to-metal charge transfers (MM′CT), while FeII2[NbIV(CN)8]·(4-pyridinealdoxime)8·2H2O (FeNb) exhibits a photoinduced magnetization via a photoinduced spin crossover. Irradiation with 473 nm light causes the CuMo system to exhibit a spontaneous magnetization with a Curie temperature (TC) of 25 K, but irradiation with 532, 785, and 840 nm light reduces the magnetization. In this reversible photomagnetic process, excitation of the MM′CT from MoIV to CuII produces a ferromagnetic mixed-valence isomer of CuICuII[MoV(CN)8]·8H2O (CuMo′). CuMo′ returns to CuMo upon irradiation in the reverse-M′MCT band. RbMnFe shows a charge transfer (CT)-induced phase transition from the MnII–FeIII phase to the MnIII–FeII phase. Irradiation with 532 nm light converts the MnIII–FeII phase into the MnII–FeIII phase, and we observe photodemagnetization. In contrast, irradiation of the MnII–FeIII phase with 410 nm light causes the reverse phase transition. A CT-induced Jahn–Teller distortion is responsible for this visible light-induced reversible photomagnetic effect. In the CoW system, a CT-induced spin transition causes the thermal phase transition from the CoII–WV phase to the CoIII–WIV phase. Irradiation of the CoIII–WIV phase with 840 nm light causes ferromagnetism with a TC of 40 K and magnetic coercive field (Hc) of 12 000 Oe, but excitation of the back M′MCT (CoII → WV) with 532 nm light leads to the reverse phase transition.These examples of the photomagnetic effect have occurred by exciting MM′CT bands. In the fields of inorganic chemistry and materials science, researchers have studied extensively the photoinduced phase transitions between low-spin (LS) and high-spin (HS) transition metal ions. Recently, we have observed the first example of photoinduced spin crossover ferromagnetism with a FeNb system (TC = 20 K and Hc = 240 Oe), in which a strong superexchange interaction between photoproduced FeII(HS) and neighboring paramagnetic NbIV operates through a CN bridge. The optical switching magnets described in this Account may lead to novel optical recording technologies such as optomagnetic memories and optical computers.
Co-reporter:Szymon Chorazy ; Koji Nakabayashi ; Kenta Imoto ; Jacek Mlynarski ; Barbara Sieklucka
Journal of the American Chemical Society 2012 Volume 134(Issue 39) pp:16151-16154
Publication Date(Web):September 18, 2012
DOI:10.1021/ja307520k
The addition of chiral 2,2′-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline) (iPr-Pybox) to a self-assembled CoII–[WV(CN)8] magnetic system gives two enantiomorphic cyano-bridged chains, {[CoII((S,S)-iPr-Pybox)(MeOH)]3[WV(CN)8]2·5.5MeOH·0.5H2O}n (1-SS) and {[CoII((R,R)-iPr-Pybox) (MeOH)]3[WV(CN)8]2·5.5MeOH·0.5H2O}n (1-RR). Both compounds crystallize with a structure containing a unique crossed arrangement of one-dimensional chains that form a microporous supramolecular network with large channels (14.9 Å × 15.1 Å × 15.3 Å) filled with methanol. The investigated materials exhibited optical chirality, as confirmed by natural circular dichroism and UV–vis absorption spectra. 1-(SS) and 1-(RR) are paramagnets with cyano-mediated CoII–WV magnetic couplings that lead to a specific spin arrangement with half of the WV ions coupled ferromagnetically with their CoII neighbors and the other half coupled antiferromagnetically. Significant magnetic anisotropy with the easy axis along the [101] direction was confirmed by single-crystal magnetic studies and can be explained by the single-ion anisotropy of elongated octahedral CoII sites. Below 3 K, the frequency-dependent χM″(T) signal indicated slow magnetic relaxation characteristic of single-chain magnets.
Co-reporter:Yoshitaka Aramaki ; Hideki Omiya ; Makoto Yamashita ; Koji Nakabayashi ; Shin-ichi Ohkoshi ;Kyoko Nozaki
Journal of the American Chemical Society 2012 Volume 134(Issue 49) pp:19989-19992
Publication Date(Web):December 3, 2012
DOI:10.1021/ja3094372
The first isolation and full characterization of the stable, persistent diazaboracyclic neutral radical 3 is reported. Reduction of base-stabilized difluororoborane 2 provided radical 3 as a neutral molecule having a planar sp2 boron atom attached to one fluorine and two nitrogen atoms. ESR spectroscopy and DFT calculations indicated that the unpaired electron is delocalized over the six-membered ring. Because of an electronic transition related to the singly occupied molecular orbital, 3 has a characteristic red color, as UV–vis spectroscopy showed an absorption maximum at 498 nm. Although DFT calculations suggested that radical 3 has relatively low spin density on the boron atom in comparison with the nitrogen and carbon atoms in the six-membered ring, 3 reacted as a base-stabilized boryl radical when treated with benzoquinone or benzoyl peroxide.
Co-reporter:Noriaki Ozaki;Hiroko Tokoro;Yoshiho Hamada;Asuka Namai;Tomoyuki Matsuda;Souhei Kaneko
Advanced Functional Materials 2012 Volume 22( Issue 10) pp:2089-2093
Publication Date(Web):
DOI:10.1002/adfm.201102727
Abstract
The crystal structure, magnetic properties, and temperature- and photoinduced phase transition of [{CoII(4-methylpyridine)(pyrimidine)}2{CoII(H2O)2}{WV(CN)8}2]·4H2O are described. In this compound, a temperature-induced phase transition from the CoII (S = 3/2)-NC-WV(S = 1/2) [high-temperature (HT)] phase to the CoIII(S = 0)-NC-WIV(S = 0) [low temperature (LT)] phase is observed due to a charge-transfer-induced spin transition. When the LT phase is irradiated with 785 nm light, ferromagnetism with a high Curie temperature (TC) of 48 K and a gigantic magnetic coercive field (Hc) of 27 000 Oe are observed. These TC and Hc values are the highest in photoinduced magnetization systems. The LT phase is optically converted to the photoinduced phase, which has a similar valence state as the HT phase due to the optically induced charge-transfer-induced spin transition.
Co-reporter:Noriaki Ozaki;Hiroko Tokoro;Yoshiho Hamada;Asuka Namai;Tomoyuki Matsuda;Souhei Kaneko
Advanced Functional Materials 2012 Volume 22( Issue 10) pp:
Publication Date(Web):
DOI:10.1002/adfm.201290061
Co-reporter:Hiroko Tokoro, Kosuke Nakagawa, Kenta Imoto, Fumiyoshi Hakoe, and Shin-ichi Ohkoshi
Chemistry of Materials 2012 Volume 24(Issue 7) pp:1324
Publication Date(Web):March 9, 2012
DOI:10.1021/cm203762k
A zero thermal expansion (ZTE) material based on plate-shaped rubidium manganese hexacyanoferrate, Rb0.97Mn[Fe(CN)6]0.99·0.3H2O, is prepared using a polyethylene glycol monolaurate (PEGM) surfactant matrix. The prepared microcrystals show a charge transfer induced phase transition between the cubic MnII–NC–FeIII and tetragonal MnIII–NC–FeII phases. The MnIII–NC–FeII phase exhibits a small negative thermal expansion (NTE) along the aLT and cLT axes with a thermal expansion coefficient of α(aLT) = −1.40 ± 0.12 × 10–6 K–1 and α(cLT) = −0.17 ± 0.13 × 10–6 K–1 over a wide temperature range of 15 K – 300 K. Such small |α| materials are classified as ZTE materials. The far-infrared spectra show that NTE originates from the transverse modes δ(Fe–C≡N–Mn)of the transverse translational mode around 304 cm–1, and transverse librational modes at 253 and 503 cm–1, which are assigned according to first principle calculations. Molecular orbital calculations indicate that ZTE and the charge transfer phase transition both originate from the transverse mode. Additionally, an oriented film on SiO2 glass is prepared using a microcrystal dispersive methanol solution and a spin-coating technique. This is the first example of a ZTE film that maintains a constant film thickness over a wide temperature range of 300 K.Keywords: charge transfer induced phase transition; oriented film; transverse mode; zero thermal expansion;
Co-reporter:Yong Wu, Yuki Hirai, Yoshihide Tsunobuchi, Hiroko Tokoro, Hiroki Eimura, Masafumi Yoshio, Shin-ichi Ohkoshi and Takashi Kato
Chemical Science 2012 vol. 3(Issue 10) pp:3007-3010
Publication Date(Web):29 Jun 2012
DOI:10.1039/C2SC00714B
Magnetic fibers were obtained through self-assembly of a nitroxide radical gelator derived from an L-isoleucine-based scaffold. Spins in the fibers are aligned one-dimensionally due to the parallel β-sheet conformation of the intermolecular hydrogen bonds. The spin nanowires exhibit magnetic behavior reproducible by the Bonner–Fisher model.
Co-reporter:Jean-Daniel Compain ; Koji Nakabayashi
Inorganic Chemistry 2012 Volume 51(Issue 9) pp:4897-4899
Publication Date(Web):April 16, 2012
DOI:10.1021/ic300263f
The reaction of the ε-Keggin polyoxometalate (POM) [PMo12O36(OH)4{La(H2O)4}4]5+ with FeII(CN)64– under typical bench conditions at room temperature and ambient pressure has afforded the novel [ε-PMo12O37(OH)3{La(H2O)5(Fe(CN)6)0.25}4] network, which exhibits a three-dimensional multilayered structure. The compound has been fully characterized by synchrotron-radiation X-ray crystallography, IR spectroscopy, elemental analysis, and thermogravimetric analysis. This coordination network constitutes the first example of a cyanometalate bonded to a POM unit.
Co-reporter:Ryo Yamada, Hiroko Tokoro, Noriaki Ozaki, and Shin-ichi Ohkoshi
Crystal Growth & Design 2012 Volume 12(Issue 4) pp:2013-2017
Publication Date(Web):February 29, 2012
DOI:10.1021/cg201710s
In this work, we synthesized a cyano-bridged Cu–W bimetal assembly, [CuII(pyrimidine)2]4[CuII(H2O)2]2[WV(CN)8]4·4H2O (1), which has a monoclinic crystal structure (P21/n space group, a = 15.7365(3) Å, b = 21.1555(4) Å, c = 27.1871(5) Å, β = 91.8630(7)°, and Z = 4). In this compound, Cu and W sites form two-dimensional (2-D) layers along the ab plane, while the other Cu sites are bridged between the 2-D layers, constructing a three-dimensional (3-D) structure. The magnetic susceptibility measurement showed that ferromagnetic interaction operates in the magnetic spins of the present compound. The field-cooled-magnetization (FCM) curve indicates that the magnetization gradually increases in the temperature range of ca. 40–8 K, and the spontaneous magnetization appears at a Curie temperature of 8 K. To understand the anomalous magnetization increase in the temperature range of ca. 40–8 K, we measured the magnetic heat capacity (Cmag). The Cmag vs T plots have a broad peak around 18 K and a sharp peak at 8 K. Such a type of Cmag vs T plots indicates a dimensional crossover from a 2-D to a 3-D Heisenberg magnetic model. This is because 1 has a pseudo 2-D network structure; that is, the magnitude of the intralayer superexchange interaction is much larger than that of the interlayer superexchange interaction. Such a magnetic dimensional crossover is a rare and intriguing issue in the field of magnetic substances.
Co-reporter:Kenta Imoto;Miho Takemura;Hiroko Tokoro
European Journal of Inorganic Chemistry 2012 Volume 2012( Issue 16) pp:
Publication Date(Web):
DOI:10.1002/ejic.201290047
Co-reporter:Kenta Imoto;Miho Takemura;Hiroko Tokoro
European Journal of Inorganic Chemistry 2012 Volume 2012( Issue 16) pp:2649-2652
Publication Date(Web):
DOI:10.1002/ejic.201101219
Abstract
We report a cyano-bridged V–Nb bimetal assembly, K0.59VII1.59VIII0.41[NbIV(CN)8]·(SO4)0.50·6.9H2O, exhibiting ferrimagnetism with a high Curie temperature (TC) of 210 K, which is the highest TC value among those of octacyano-bridged bimetal assemblies. Such a high TC value originates from the high coordination number of octacyanoniobate and the strong superexchange interaction between VII (S = 3/2) and NbIV (S = 1/2) through the CN groups.
Co-reporter:Marie Yoshikiyo, Kana Yamada, Asuka Namai, and Shin-ichi Ohkoshi
The Journal of Physical Chemistry C 2012 Volume 116(Issue 15) pp:8688-8691
Publication Date(Web):March 23, 2012
DOI:10.1021/jp300769z
ε-Fe2O3 is known to exhibit a large coercive field of 20 kOe at room temperature. In this work, we examine the electronic structure and magnetic properties of ε-Fe2O3 using first-principles calculation and discrete variational (DV)-Xα molecular orbital calculation. The first-principles calculation shows that ε-Fe2O3 is a charge-transfer type insulator with a valence band of O2p and a conduction band of Fe3d. The optical transition is an indirect transition from Γ to S point. The density of states (DOS) of the four nonequivalent Fe sites (FeA, FeB, FeC, and FeD) indicates that ε-Fe2O3 has ferrimagnetic ordering due to α spins on FeB and FeC and β spins on FeA and FeD. The charge density map of the occupied Fe3d band displays a strong hybridization between Fe3d and O2p. Molecular orbital calculation for each Fe site also supports the existence of a strong Fe3d–O2p hybridization. Such a strong hybridization induces nonzero orbital angular momentum L on Fe3d through the partial charge transfer from O2p to Fe3d. The appearance of L causes a large magnetic anisotropy through spin–orbit interaction, which induces the large coercive field.
Co-reporter:Dawid Pinkowicz, Robert Podgajny, Wojciech Nitek, Michał Rams, Anna Małgorzata Majcher, Tomohiro Nuida, Shin-ichi Ohkoshi, and Barbara Sieklucka
Chemistry of Materials 2011 Volume 23(Issue 1) pp:21
Publication Date(Web):December 9, 2010
DOI:10.1021/cm102388q
Incorporation of urea molecules into the magnetic system MnII-[NbIV(CN)8] results in formation of two magnetic polymorphs {[MnII(H2O)(urea)2]2[NbIV(CN)8]}n chiral α and centric β crystallizing in space groups P41 and P1̅, respectively. Both polymorphs exhibit extremely similar structures and are soft ferrimagnets with critical temperatures of 43 and 42 K, respectively. The presence of coordinated urea in the noncentrosymmetric α produces NLO functionality, second harmonic generation (SHG), whereas centric β is just another molecular magnet. As a result of interaction of both functionalities below magnetic ordering temperature, the magnetization-induced SHG (MSHG) is observed for polymorph α. The observed MSHG/SHG signal ratio was the largest among molecule-based noncentrosymmetric magnets. The presence of urea molecules in both polymorphs gives also rise to their interesting topotactic reactivity. Both polymorphs can be easily transformed into a new entity {[MnII(H2O)]2[NbIV(CN)8]·2.5MeOH}n 2b with significant shift of critical temperature Tc to 70 K. Subsequent hydration of 2b leads to {[MnII(H2O)2]2[NbIV(CN)8]·4H2O}n 3 with Tc of 47 K.
Co-reporter:Hiroko Tokoro and Shin-ichi Ohkoshi
Dalton Transactions 2011 vol. 40(Issue 26) pp:6825-6833
Publication Date(Web):29 Mar 2011
DOI:10.1039/C0DT01829E
Cyano-bridged bimetal assemblies demonstrate novel magnetic functionalities, particularly Prussian blue analogs, which have unique properties. In this perspective, we describe a charge-transfer phase transition, reversible photomagnetism, second harmonic generation and magnetization-induced second harmonic generation, ferroelectric ferromagnetism, humidity-sensitive magnetism, high ionic conductivity, and a coupling effect (which we named spin-ionics) between ionic conduction and magnetic ordering with Prussian blue analogs.
Co-reporter:Yoshihide Tsunobuchi, Souhei Kaneko, Koji Nakabayashi, and Shin-ichi Ohkoshi
Crystal Growth & Design 2011 Volume 11(Issue 12) pp:5561-5566
Publication Date(Web):October 18, 2011
DOI:10.1021/cg2011265
Two-dimensional (2-D) cyano-bridged Cu–W bimetallic assemblies that include halogen-substituted pyridine molecules, [CuII(3-iodopyridine)4][CuII(3-iodopyridine)2]2[WV(CN)8]2 (1) (triclinic crystal structure, P1̅ space group), [CuII(3-bromopyridine)4][CuII(3-bromopyridine)2]2[WV(CN)8]2 (2) (triclinic, P1̅), and [CuII(3-chloropyridine)2(H2O)2][CuII(3-chloropyridine)2]2[WV(CN)8]2·4H2O (3) (monoclinic, P21/c), were synthesized. Thermogravimetric measurements demonstrate that 1 and 2 have high thermal durability up to ca. 150 °C (423 K) due to the lack of water molecules in the crystal and the stacked Cu–W 2-D layers with halogen bonding between halogen-substituted pyridine and the cyano nitrogen of octacyanotungstate. In contrast, 3 exhibits weight loss above ca. 50 °C (323 K) as the water molecules between the 2-D layers are removed upon heating. Magnetic measurements show that 1–3 are ferromagnets due to parallel ordering of the magnetic spins on CuII (S = 1/2) and WV (S = 1/2) with Curie temperatures (TC) of 4.7 K (1), 5.2 K (2), and 7.2 K (3).
Co-reporter:Shin-ichi Ohkoshi ; Kosuke Nakagawa ; Keisuke Tomono ; Kenta Imoto ; Yoshihide Tsunobuchi ;Hiroko Tokoro
Journal of the American Chemical Society 2010 Volume 132(Issue 19) pp:6620-6621
Publication Date(Web):April 26, 2010
DOI:10.1021/ja100385f
We observed high proton conductivities of 1.2 × 10−3 and 1.6 × 10−3 S cm−1 on Co[Cr(CN)6]2/3·zH2O and V[Cr(CN)6]2/3·zH2O, respectively, and an interference effect between magnetic ordering and ionic conduction below the magnetic phase transition temperature.
Co-reporter:Jiří Tuček, Radek Zbořil, Asuka Namai, and Shin-ichi Ohkoshi
Chemistry of Materials 2010 Volume 22(Issue 24) pp:6483
Publication Date(Web):October 27, 2010
DOI:10.1021/cm101967h
Nanosized iron oxides still attract significant attention within the scientific community, because of their application-promising properties. Among them, ε-Fe2O3 constitutes a remarkable phase, taking pride in a giant coercive field at room temperature, significant ferromagnetic resonance, and coupled magnetoelectric features that are not observed in any other simple metal oxide phase. In this work, we review basic structural and magnetic characteristics of this extraordinary nanomaterial with an emphasis on questionable and unresolved issues raised during its intense research in the past years. We show how a combination of various experimental techniques brings essential and valuable information, with regard to understanding the physicochemical properties of the ε-polymorph of Fe2O3, which remained unexplored for a long period of time. In addition, we recapitulate a series of synthetic routes that lead to the formation of ε-Fe2O3, highlighting their advantages and drawbacks. We also demonstrate how magnetic properties of ε-Fe2O3 can be tuned through the exploitation of various morphologies of ε-Fe2O3 nanosystems, the alignment of ε-Fe2O3 nanoobjects in a supporting matrix, and various degrees of cation substitution. Based on the current knowledge of the scientific community working in the field of ε-Fe2O3, we finally arrive at two main future challenges: (i) the search for optimal synthetic conditions to prepare single-phase ε-Fe2O3 with a high yield, desired size, morphology, and stability; and (ii) the search for a correct description of the magnetic behavior of ε-Fe2O3 at temperatures below the characteristic magnetic ordering temperature.
Co-reporter:Keisuke Tomono ; Yoshihide Tsunobuchi ; Koji Nakabayashi
Inorganic Chemistry 2010 Volume 49(Issue 4) pp:1298-1300
Publication Date(Web):January 15, 2010
DOI:10.1021/ic9022079
We prepared a vanadium heptacyanomolybdate-based magnet, VII2[MoIII(CN)7]·(pyrimidine)2·4.5H2O (VMo), with a Curie temperature (TC) of 110 K, which is the highest TC value in [MoIII(CN)7]-based magnets. Additionally, MnII2[MoIII(CN)7]·(pyrimidine)2·2H2O (MnMo) of a monoclinic structure (P21/n) with TC = 47 K was prepared to confirm the crystal structure of VMo.
Co-reporter:Kenta Imoto;Daisuke Takahashi;Yoshihide Tsunobuchi;Wataru Kosaka;Michio Arai;Hiroko Tokoro
European Journal of Inorganic Chemistry 2010 Volume 2010( Issue 26) pp:4079-4082
Publication Date(Web):
DOI:10.1002/ejic.201000720
Abstract
Nanoporous magnetic materials composed of metal-assembled complexes are expected to exhibit chemical sensitivity. In this work, we observed a humidity-induced reversible change between ferromagnetism and antiferromagnetism in a new type of a cobalt octacyanoniobate based magnet in the high-humidity region. This humidity response is caused by the adsorption and desorption of non-coordinated water (so-called zeolitic water) molecules in the interstitial site. Such a phenomenon is achieved by the structural flexibility of an octacyanometalate-based magnet.
Co-reporter:Cyrille Train ; Tomohiro Nuida ; Ruxandra Gheorghe ; Michel Gruselle
Journal of the American Chemical Society 2009 Volume 131(Issue 46) pp:16838-16843
Publication Date(Web):November 2, 2009
DOI:10.1021/ja9061568
The absence of centrosymmetry in the enantiopure chiral magnet [N(CH3)(n-C3H7)2(C*H(CH3)C2H5)][MnIICrIII(ox)3] allows the observation of bulk second harmonic generation (SHG) in this material. At low temperature, the onset of magnetization gives birth to a magnetization-induced SHG (MSHG) contribution. With an angular shift of 13.1° upon magnetization reversal, the MSHG effects appear to be much larger than the corresponding linear magneto-optical effects. Thanks to the single-crystalline state of the sample, the variation of the signal with the orientation of the magnetic field and/or the angle between the polarization of the incident radiation and the outgoing SHG signal in the paramagnetic and ferromagnetic phases is reproduced and well-understood through the use of a symmetry-based analysis of the nonlinear susceptibility tensor.
Co-reporter:Shunsuke Sakurai ; Asuka Namai ; Kazuhito Hashimoto
Journal of the American Chemical Society 2009 Volume 131(Issue 51) pp:18299-18303
Publication Date(Web):November 25, 2009
DOI:10.1021/ja9046069
Iron oxide (Fe2O3) has four crystal structures: γ-, ε-, β-, and α-Fe2O3. Until now, routes of the phase transformations among the four Fe2O3 phases have not been clarified because a systematic synthesis that yields all four Fe2O3 phases has yet to be reported. Herein we report the synthesis of a series of Fe2O3 nanoparticles using mesoporous SiO2. The crystal structures of the Fe2O3 nanoparticles change in the order of γ-Fe2O3 → ε-Fe2O3 → β-Fe2O3 → α-Fe2O3 as the particle size increases. Threshold sizes were estimated as γ → ε at 8 nm, ε → β at 30 nm, and β → α at 50 nm in the synthesis using FeSO4 as a precursor. The phase transformations among the four Fe2O3 phases have been observed for the first time.
Co-reporter:Wataru Kosaka, Kenta Imoto, Yoshihide Tsunobuchi and Shin-ichi Ohkoshi
Inorganic Chemistry 2009 Volume 48(Issue 11) pp:4604-4606
Publication Date(Web):April 20, 2009
DOI:10.1021/ic9001576
In this work, we prepared a three-dimensional vanadium octacyanoniobate-based magnet, K0.10VII0.54VIII1.24[NbIV(CN)8]·(SO4)0.45·6.8H2O. This compound exhibits ferrimagnetism with a Curie temperature of 138 K, in which the sublattice magnetizations of VII (S = 3/2) and VIII (S = 1) are antiparallelly ordered to that of NbIV (S = 1/2). The estimated superexchange interaction constants of VII−NbIV and VIII−NbIV are −51 and −25 cm−1, respectively.
Co-reporter:Koji Nakabayashi and Shin-ichi Ohkoshi
Inorganic Chemistry 2009 Volume 48(Issue 18) pp:8647-8649
Publication Date(Web):August 17, 2009
DOI:10.1021/ic900625a
We prepared a three-dimensional monometallic lanthanoid assembly, Na5[Ho(THB4−)2]·7H2O (THB = 1,2,4,5-tetrahydroxybenzene), that exhibits ferromagnetism with a Curie temperature of 11 K. Such a ferromagnetic ordering is due to the effective mediation of the magnetic interaction between Ho3+ ions by the THB4− ligand.
Co-reporter:Yoshihide Tsunobuchi, Wataru Kosaka, Tomohiro Nuida and Shin-ichi Ohkoshi
CrystEngComm 2009 vol. 11(Issue 10) pp:2051-2053
Publication Date(Web):01 Jul 2009
DOI:10.1039/B906778G
The magnetization-induced second harmonic generation (MSHG) is observed using a three-dimensional MnII–NbIV pyroelectric ferrimagnet, [{MnII(H2O)2}{MnII(pyrazine)(H2O)2}{NbIV(CN)8}]·4H2O, in which electric polarization is along the b-axis and the magnetic easy axis is along the a-axis. The SH intensity gradually increases due to superparamagnetism below 90 K, and then rapidly increases near the Curie temperature (TC = 48 K) due to spontaneous magnetization.
Co-reporter:Keiji Takeda, Hiroko Tokoro, Fumiyoshi Hakoe, Akira Yamaguchi, Hatsumi Mori, Hidehiko Ishimoto, Takayoshi Nakamura, Shinya Kuriki, Shin-ichi Ohkoshi
Polyhedron 2009 28(9–10) pp: 1746-1749
Publication Date(Web):
DOI:10.1016/j.poly.2008.11.016
Co-reporter:Souhei Kaneko, Yoshihide Tsunobuchi, Koji Nakabayashi, Shin-ichi Ohkoshi
Polyhedron 2009 28(9–10) pp: 1893-1897
Publication Date(Web):
DOI:10.1016/j.poly.2008.10.065
Co-reporter:Wataru Kosaka, Hiroko Tokoro, Tomoyuki Matsuda, Kazuhito Hashimoto and Shin-ichi Ohkoshi
The Journal of Physical Chemistry C 2009 Volume 113(Issue 35) pp:15751-15755
Publication Date(Web):August 11, 2009
DOI:10.1021/jp902735v
We report a unique type of spin-crossover phenomenon in a three-dimensional (3-D) Fe−Mo network with a cubic structure, Fe2[Mo(CN)8]·(3-pyCH2OH)8·3H2O (3-py = 3-pyridyl). This compound exhibits an extremely gradual FeII spin-crossover over a wide temperature range, which is more gradual than the crossover according to the Boltzmann distribution. The electronic states at 320 and 50 K are represented as (FeIIhs)2[MoIV(CN)8]·(3-pyCH2OH)8·3H2O and (FeIIhs)0.48(FeIIls)1.52[MoIV(CN)8]·(3-pyCH2OH)8·3H2O, respectively, where hs and ls denote high spin (S = 2) and low spin (S = 0), respectively. The model calculation based on Slichter−Drickamer’s model suggests this extremely gradual spin-crossover can be explained by the contribution of 3-D alternating alignment of hs and ls sites, i.e., −hs−ls−hs−ls−. This system is a strongly correlated system of spin-crossover sites because the spin-crossover FeII sites are directly linked by −NC−Mo−CN− with a high symmetry (FeII sites have one type of symmetry). The elastic interaction due to the volume change in a spin-crossover site isotropically propagates in the whole crystal. Since the CN bridges cannot be disconnected during spin-crossover, a 3-D alternating order of hs and ls sites is considered to be preferable.
Co-reporter:Shin-ichi Ohkoshi, Asuka Namai and Shunsuke Sakurai
The Journal of Physical Chemistry C 2009 Volume 113(Issue 26) pp:11235-11238
Publication Date(Web):June 2, 2009
DOI:10.1021/jp901637y
Up to date, the origin of ferromagnetism in ε-Fe2O3 and ε-GaxFe2−xO3 has been ambiguous. In this work, the origin can be well explained by using a molecular-field (MF) model with four nonequivalent Fe sites (A−D sites). The MF calculation demonstrates that ε-Fe2O3 is a Néel P-type ferrimagnet, which consists of positive sublattice magnetizations of MB and MC and negative ones of MA and MD. This magnetic ordering mechanism can be understood by the product of the number of exchange pathways (Zij) and the superexchange interaction constants (Jij). The calculated saturation magnetization vs. x plots in ε-GaxFe2−xO3 at 300 K have a maximum around x = 0.47, and the TC value monotonously decreases with increasing x. These magnetic properties are explained by the position of Ga replacement and weakness of the ZijJij values.
Co-reporter:Hiroko Tokoro, Tomoyuki Matsuda, Tomohiro Nuida, Yutaka Moritomo, Kenji Ohoyama, Edgard Davy Loutete Dangui, Kamel Boukheddaden and Shin-ichi Ohkoshi
Chemistry of Materials 2008 Volume 20(Issue 2) pp:423
Publication Date(Web):December 19, 2007
DOI:10.1021/cm701873s
The photoreversibility of a photoinduced phase transition was investigated in a rubidium manganese hexacyanoferrate, Rb0.88Mn[Fe(CN)6]0.96·0.5H2O. The present material shows a charge-transfer phase transition from the MnII−FeIII [high-temperature (HT)] phase to the MnIII−FeII [low-temperature (LT)] phase, and the LT phase shows ferromagnetism. Spectroscopic ellipsometry measurements of the dielectric constant suggest that the optical transitions in the LT and HT phases are a metal-to-metal charge transfer (FeII → MnIII) band at 420–540 nm and a ligand-to-metal charge transfer (CN– → FeIII) band of [FeIII(CN)6] at 410 nm, respectively. By irradiation with 532 nm light, the LT phase is transmitted to the photoinduced (PI) phase, which has a valence state similar to that of the HT phase, and photodemagnetization is observed. In contrast, irradiating the PI phase with 410 ± 30 nm light causes the reverse phase transition. Neutron powder diffraction measurement of an analogue compound, Rb0.58Mn[Fe(CN)6]0.86·2.3H2O, which does not show a charge-transfer phase transition and maintains the MnII−FeIII phase at a very low temperature, confirms that the PI phase is an antiferromagnet. Hence, the present visible-light-induced reversible photomagnetic effect is due to optical switching between the ferromagnetic LT phase and the antiferromagnetic PI phase.
Co-reporter:Shin-ichi Ohkoshi, Yoshiho Hamada, Tomoyuki Matsuda, Yoshihide Tsunobuchi and Hiroko Tokoro
Chemistry of Materials 2008 Volume 20(Issue 9) pp:3048
Publication Date(Web):February 5, 2008
DOI:10.1021/cm703258n
This paper describes the crystal structure, magnetic properties, and photoreversible magnetic properties of CoII3[WV(CN)8]2(pyrimidine)4·6H2O. We found that complexes of this formula had two types of crystal structures ([{CoII(pyrimidine)2}2{CoII(H2O)2}{WV(CN)8}2]·4H2O (1) and [{CoII(pyrimidine)(H2O)}2{CoII(H2O)2}{WV(CN)8}2](pyrimidine)2·2H2O (2)). These two structures had similar metal−organic frameworks but differed in the coordination environment around Co1, i.e., Co1(NC)4(pyrimidine)2 in 1 and Co1(NC)4(pyrimidine)(H2O) in 2. In 1, a temperature-induced phase transition from the CoII (S = 3/2)−NC−WV (S = 1/2) [high-temperature (HT)] phase to the CoIII (S = 0)−NC−WIV (S = 0) [low-temperature (LT)] phase was observed due to a charge-transfer-induced spin transition. However, 2 did not exhibit such a phase transition. When the LT phase of 1 was irradiated by 840 nm light, ferromagnetism with a Curie temperature of 40 K and magnetic coercive field of 12 kOe were observed. UV–vis reflectance and infrared measurements suggested that the LT phase optically transited to the photoinduced (PI) phase, which had a similar valence state as the HT phase, through the metal-to-metal charge-transfer (WIV → CoIII) band. In contrast, when the back metal-to-metal charge transfer (CoII → WV) band of the PI phase was excited by 532 nm light, the reverse phase transition from the PI phase to the LT phase occurred, and the spontaneous magnetization decreased.
Co-reporter:Kosuke Nakagawa ; Hiroko Tokoro
Inorganic Chemistry 2008 Volume 47(Issue 23) pp:10810-10812
Publication Date(Web):October 28, 2008
DOI:10.1021/ic8016563
We report the observation of ferroelectricity in a copper octacyanomolybdate-based paramagnet, Cu2[Mo(CN)8]·8H2O (CuII, S = 1/2; MoIV, S = 0). This compound has a freezing point for the fixation of hydrogen bonding at 150 K. Around this temperature, an enhancement in the ferroelectricity and an increase in the dielectric constant are observed. The ferroelectricity of this system is classified into amorphous ferroelectrics; i.e., the electric poling effect induces an electric polarization. The electric polarization is maintained by the structural local disorder of hydrogen bonding and the three-dimensional CN network. In this ferroelectricity, the crystal structure is a polar group of C∞v after application of an electric field.
Co-reporter:Shunsuke Sakurai, Jun-ichi Shimoyama, Kazuhito Hashimoto, Shin-ichi Ohkoshi
Chemical Physics Letters 2008 Volume 458(4–6) pp:333-336
Publication Date(Web):17 June 2008
DOI:10.1016/j.cplett.2008.04.121
We report the fabrication and magnetic coercive field of oriented ε-Fe2O3 nanorods. Oriented ε-Fe2O3 nanorods embedded in SiO2 matrix were obtained by a sol–gel method under an applied external magnetic field. The longitudinal axis, which corresponds to a-axis of the crystal structure of ε-Fe2O3 nanorods, was oriented parallel to the direction of external magnetic field. The sample achieved a magnetic coercive field along the longitudinal axis of 23.4 kOe, which is the largest value among metal oxide-based magnetic materials. The shape of the magnetic hysteresis loop is well understood by considering the magnetization rotation process and the uniaxial magnetic anisotropy.Oriented ε-Fe2O3 nanorods achieved a magnetic coercive field of 23.4 kOe, the largest value among metal oxide-based magnets.
Co-reporter:Michio Arai;Wataru Kosaka;Tomoyuki Matsuda Dr. Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 36) pp:6885-6887
Publication Date(Web):
DOI:10.1002/anie.200802266
Co-reporter:Michio Arai;Wataru Kosaka;Tomoyuki Matsuda Dr. Dr.
Angewandte Chemie 2008 Volume 120( Issue 36) pp:6991-6993
Publication Date(Web):
DOI:10.1002/ange.200802266
Co-reporter:Shunsuke Sakurai, Kotaro Tomita, Kazuhito Hashimoto, Hisashi Yashiro and Shin-ichi Ohkoshi
The Journal of Physical Chemistry C 2008 Volume 112(Issue 51) pp:20212-20216
Publication Date(Web):2017-2-22
DOI:10.1021/jp806336f
The nanowire form of ε-Fe2O3 single crystal was prepared by combining the reverse-micelle and sol−gel methods. To elucidate the detailed formation process of ε-Fe2O3 nanowires, the morphology of a sample at each process was measured using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and X-ray diffraction (XRD). SAXS measurements showed that the diameter of the water phase in a reverse-micelle containing Fe(NO3)3 and Ba(NO3)2 was 7.5 ± 2.1 nm, whereas that in another reverse-micelle containing NH3 was 6.5 ± 2.0 nm. Mixing these two solutions caused the hydroxylation reaction in the water phase, which yielded Fe(OH)3 nanoparticles. By injecting Si(C2H5O)4, Fe(OH)3 was covered by SiO2 through the hydrolysis reaction. TEM observations showed that the size of Fe(OH)3 nanoparticles in the SiO2 matrix was 5 ± 1 nm. By heating to 900 °C, Fe(OH)3 transformed into spherical-shaped γ-Fe2O3 (Fd3̅m, a = 8.35 Å) without changing size. Moreover, upon heating the sample to 1025 °C, nanorod-type ε-Fe2O3 (Pna21, a = 5.10 Å, b = 8.78 Å, c = 9.47 Å) was obtained. Barium adsorption to the crystal induced anisotropic growth along the crystallographic a-axis of the ε-Fe2O3 nanorod, and the long axis length of ε-Fe2O3 nanowire reached 1.5 μm. This is the first example of a nanowire form of ε-Fe2O3 single crystal.
Co-reporter:S. Sakurai;S. Kuroki;H. Tokoro;K. Hashimoto;S. Ohkoshi
Advanced Functional Materials 2007 Volume 17(Issue 14) pp:
Publication Date(Web):9 AUG 2007
DOI:10.1002/adfm.200600581
A series of ϵ-InxFe2–xO3 nanorods are prepared by combining the reverse-micelle and the sol–gel methods. Metal replacement was achieved in the region of 0 ≤ x ≤ 0.24. The crystal structures are orthorhombic structures (space group: Pna21), which are pyroelectric with an electric polarization along the c axis. The transmission electron microscopy images show that the particle sizes are (80 ± 40) × (23 ± 5) nm (x = 0), (65 ± 30) × (30 ± 10) nm (x = 0.12), and (80 ± 40) × (35 ± 15) nm (x = 0.24). The magnetization versus temperature curves of the samples with x = 0, x = 0.12, and x = 0.24 show spontaneous magnetization with Curie temperatures of 495 K, 456 K, and 414 K, respectively. Their coercive fields at 300 K are 20 kOe (x = 0), 14 kOe (x = 0.12), and 9 kOe (x = 0.24). These samples show a spin reorientation with reorientation temperatures (Tp) of 102 K (x = 0), 149 K (x = 0.12), and 180 K (x = 0.24). In particular, the samples with x = 0.12 and x = 0.24 show antiferromagnetic behavior below Tp. This series of ϵ-InxFe2–xO3 is the first example of a pyroelectric material that exhibits a phase transition between ferrimagnetism and antiferromagnetism.
Co-reporter:Shin-ichi Ohkoshi Dr.;Hiroko Tokoro Dr.;Tomoyuki Matsuda;Hitomi Takahashi;Hiroshi Irie Dr.;Kazuhito Hashimoto Dr.
Angewandte Chemie 2007 Volume 119(Issue 18) pp:
Publication Date(Web):7 MAR 2007
DOI:10.1002/ange.200604452
Ein multiferroisches Material: Rb0.82Mn[Fe(CN)6]0.94⋅H2O (siehe Bild; MnII rote Oktaeder, FeIII rote Kugeln, MnIII blaue Oktaeder, FeII blaue Kugeln, CN weiße Linien, Fe-Leerstellen Lücken; H2O weggelassen) ist sowohl ferroelektrisch, vermutlich durch ein Mischen von Fe-Leerstellen und FeII-, FeIII-, MnII- sowie Jahn-Teller-verzerrten MnIII-Zentren, als auch ferromagnetisch, durch ein paralleles Ausrichten der magnetischen Spins von MnIII.
Co-reporter:Shin-ichi Ohkoshi ;Shiro Kuroki;Shunsuke Sakurai;Kazuyuki Matsumoto;Kimitaka Sato;Shinya Sasaki
Angewandte Chemie International Edition 2007 Volume 46(Issue 44) pp:
Publication Date(Web):2 NOV 2007
DOI:10.1002/anie.200790223
Millimeter waves , with a range of 30–300 GHz, are beginning to be used in electronic devices for high-speed wireless communications. In their Communication on page 8392 ff., S. Ohkoshi et al. report a new millimeter-wave absorber composed of ε-GaxFe2−xO3 (0.10≤x≤0.67) nanomagnets, which shows a ferromagnetic resonance in the 35–190-GHz region. The picture shows a Japanese landscape garden, Zuiho-in in Kyoto, in which the center rock, the ripples of sand, and the near rock evoke a millimeter-wave generator, millimeter waves, and the millimeter-wave absorber, respectively.
Co-reporter:Shin-ichi Ohkoshi Dr.;Hiroko Tokoro Dr.;Tomoyuki Matsuda;Hitomi Takahashi;Hiroshi Irie Dr.;Kazuhito Hashimoto Dr.
Angewandte Chemie International Edition 2007 Volume 46(Issue 18) pp:
Publication Date(Web):7 MAR 2007
DOI:10.1002/anie.200604452
Multiferroic material: RbI0.82MnII0.20MnIII0.80[FeII(CN)6]0.80[FeIII(CN)6]0.14⋅H2O (see picture; MnII red octahedra, FeIII red spheres, MnIII blue octahedra, FeII blue spheres, CN white lines, gaps are Fe vacancies; H2O omitted) displays both ferroelectricity, explained by a mixing of FeII, FeIII, Fe vacancies, MnII, and Jahn–Teller-distorted MnIII centers, and ferromagnetism, caused by a parallel ordering of the magnetic spins of MnIII.
Co-reporter:Tomohiro Nuida;Toshiya Hozumi;Hiroko Tokoro
Journal of Solid State Electrochemistry 2007 Volume 11( Issue 6) pp:763-772
Publication Date(Web):2007 June
DOI:10.1007/s10008-006-0219-7
This article describes novel optical functionalities such as photomagnetic effects and magnetization-induced second harmonic generation (MSHG) in several cyano-bridged metal assemblies. Single crystal- and film-types of a cyano-bridged Cu–Mo bimetallic assembly, \( {\text{Cs}}^{{\text{I}}}_{{\text{2}}} {\text{Cu}}^{{{\text{II}}}}_{{\text{7}}} {\left[ {{\text{Mo}}^{{{\text{IV}}}} {\left( {{\text{CN}}} \right)}_{{\text{8}}} } \right]}_{{\text{4}}} \cdot {\text{6H}}_{{\text{2}}} {\text{O}} \), were electrochemically prepared. When this compound was irradiated with light, spontaneous magnetization with a Curie temperature (TC) of 23 K was observed. Electrochemically prepared FeII[CrIII(CN)6]2/3·5H2O thin film, which was a ferromagnet with TC=21 K, showed photoreduced magnetization. This photomagnetism is due to the change of ferromagnetic coupling between FeII and CrIII. MSHG was observed in CsICoII[CrIII(CN)6]·0.5H2O. This \( F{\text{\ifmmode\expandafter\bar\else\expandafter\=\fi{4}3}}m \)-type Prussian blue analog-based magnet is proven to be a piezoelectric ferromagnet, i.e., condensed matter with both piezoelectric and ferromagnetism. This MSHG is due to the coupling between a piezoelectric structure of \( F{\text{\ifmmode\expandafter\bar\else\expandafter\=\fi{4}3}}m \) and ferromagnetism with a TC of 46 K.
Co-reporter:Shin-ichi Ohkoshi ;Shiro Kuroki;Shunsuke Sakurai;Kazuyuki Matsumoto;Kimitaka Sato;Shinya Sasaki
Angewandte Chemie International Edition 2007 Volume 46(Issue 44) pp:
Publication Date(Web):17 OCT 2007
DOI:10.1002/anie.200703010
Restraining electromagnetic interference in the millimeter-wave region has been accomplished with a new electromagnetic absorber composed of ε-GaxFe2−xO3 (0.10≤x≤0.67) nanomagnets, which shows a ferromagnetic resonance in the range 35–147 GHz. The possibility that the ferromagnetic resonance can achieve a frequency of 190 GHz at x0 is also suggested. See picture: Hc=coercive field; fr=ferromagnetic resonance frequency.
Co-reporter:Shin-ichi Ohkoshi ;Shiro Kuroki;Shunsuke Sakurai;Kazuyuki Matsumoto;Kimitaka Sato;Shinya Sasaki
Angewandte Chemie 2007 Volume 119(Issue 44) pp:
Publication Date(Web):17 OCT 2007
DOI:10.1002/ange.200703010
Gegen elektromagnetische Einflüsse im Bereich von Millimeterwellen wirkt ein neuer Strahlungsabsorber aus ε-GaxFe2−xO3-Nanomagneten (0.10≤x≤ 0.67) mit einer ferromagnetischen Resonanz bei 35–147 GHz, die für x0 vielleicht sogar 190 GHz erreichen könnte. Siehe Bild: Hc=Koerzitivfeldstärke; fr=ferromagnetische Resonanzfrequenz.
Co-reporter:Shin-ichi Ohkoshi ;Shiro Kuroki;Shunsuke Sakurai;Kazuyuki Matsumoto;Kimitaka Sato;Shinya Sasaki
Angewandte Chemie 2007 Volume 119(Issue 44) pp:
Publication Date(Web):2 NOV 2007
DOI:10.1002/ange.200790223
Millimeterwellen bei 30–300 GHz werden verstärkt in elektronischen Bauteilen für die drahtlose Hochgeschwindigkeitskommunikation eingesetzt. S. Ohkoshi et al. beschreiben in der Zuschrift auf S. 8544 ff. einen Millimeterwellenabsorber aus ε-GaxFe2−xO3-Nanomagneten (0.10≤x≤0.67) mit einer ferromagnetischen Resonanz bei 35–190 GHz. Der zentrale Fels, die Wellen im Sand und der Fels im Vordergrund des im Bild gezeigten japanischen Landschaftsgartens (Zuiho-in in Kyoto) lassen an einen Millimeterwellengenerator, Millimeterwellen bzw. einen Millimeterwellenabsorber denken.
Co-reporter:Tomoyuki Matsuda, Hiroko Tokoro, Kazuhito Hashimoto and Shin-ichi Ohkoshi
Dalton Transactions 2006 (Issue 42) pp:5046-5050
Publication Date(Web):07 Sep 2006
DOI:10.1039/B605269J
A series of caesium manganese hexacyanoferrates is prepared; CsI1.78MnII[FeII(CN)6]0.78[FeIII(CN)6]0.22 (1), CsI1.57MnII[FeII(CN)6]0.57[FeIII(CN)6]0.43 (2), CsI1.51MnII[FeII(CN)6]0.51[FeIII(CN)6]0.49 (3), and CsI0.94MnII[FeII(CN)6]0.21[FeIII(CN)6]0.70·0.8H2O (4). 1–3 show charge-transfer phase transitions between the high-temperature (HT) and low-temperature (LT) phases with transition temperatures (T1/2↓, T1/2↑) of (207 K, 225 K) (1), (190 K, 231 K) (2), and (175 K, 233 K) (3) at a cooling and warming rates of 0.5 K min−1. Variable temperature IR spectra indicate that the valence states of the LT phases of 1–3 are CsI1.78MnII0.78MnIII0.22[FeII(CN)6], CsI1.57MnII0.57MnIII0.43[FeII(CN)6], and CsI1.51MnII0.51MnIII0.49 [FeII(CN)6], respectively. The XRD measurements for 1–3 show that crystal structures of the HT and LT phases are cubic structures (Fmm), but the lattice constants decrease from the HT phase to the LT phase; a = 10.5446(17) → 10.4280(7) Å (1), 10.5589(17) → 10.3421(24) Å (2), and 10.5627(11) → 10.3268(23) Å (3). The magnetization vs. temperature curves and the magnetization vs. external magnetic field curves show that the LT phases are ferromagnetic with Curie temperatures of 4.3 (1), 5.0 (2), and 5.6 K (3). At a cooling rate of −0.5 K min−1, 4 does not show the charge-transfer phase transition, but does show a behavior of zero thermal expansion with a thermal expansivity of +0.2 × 10−6 K−1 throughout the temperature range 300 and 20 K.
Co-reporter:Yong Wu, Yuki Hirai, Yoshihide Tsunobuchi, Hiroko Tokoro, Hiroki Eimura, Masafumi Yoshio, Shin-ichi Ohkoshi and Takashi Kato
Chemical Science (2010-Present) 2012 - vol. 3(Issue 10) pp:NaN3010-3010
Publication Date(Web):2012/06/29
DOI:10.1039/C2SC00714B
Magnetic fibers were obtained through self-assembly of a nitroxide radical gelator derived from an L-isoleucine-based scaffold. Spins in the fibers are aligned one-dimensionally due to the parallel β-sheet conformation of the intermolecular hydrogen bonds. The spin nanowires exhibit magnetic behavior reproducible by the Bonner–Fisher model.
Co-reporter:Y. Miyamoto, T. Nasu, N. Ozaki, Y. Umeta, H. Tokoro, K. Nakabayashi and S. Ohkoshi
Dalton Transactions 2016 - vol. 45(Issue 48) pp:NaN19256-19256
Publication Date(Web):2016/11/14
DOI:10.1039/C6DT03793C
A two-dimensional cyanide-bridged Co–W bimetal assembly, (H5O2+)[Co(4-bromopyridine)2{W(CN)8}], was prepared. A synchrotron radiation (SR) X-ray single-crystal measurement shows that the crystal structure is monoclinic in the P21/c space group. Magnetic and spectroscopic measurements show that this assembly takes CoIIIlow-spin(S = 0)–WIV(S = 0) in the temperature range of 2–390 K. Such a wide temperature range CoIIIlow-spin–WIV phase has not been reported so far. First-principles calculations show that the band gap is composed of a WIV valence band and a CoIII conduction band. 785 nm light irradiation causes photo-induced magnetization with a Curie temperature of 27 K and a coercive field of 2000 Oe. The crystal structure of the photo-induced phase was determined to have larger lattice constants in the two-dimensional layer (bc-plane) by 3% compared to the original phase, which is due to the expansion of the distance of Co–N. The photo-induced phase returns to the original phase upon thermal treatment. First-principles calculations, and magnetic, and optical measurements prove that this photomagnetism is caused by the optical charge-transfer-induced spin transition from CoIIIlow-spin(S = 0)–WIV(S = 0) to CoIIhigh-spin(S = 3/2)–WV(S = 1/2).
Co-reporter:Szymon Chorazy, Junhao Wang and Shin-ichi Ohkoshi
Chemical Communications 2016 - vol. 52(Issue 71) pp:NaN10798-10798
Publication Date(Web):2016/08/08
DOI:10.1039/C6CC05337H
A cyanido-bridged layered {[DyIII(4-OHpy)2(H2O)3][CoIII(CN)6]}·0.5H2O (1) (4-OHpy = 4-hydroxypyridine) framework with dual photo-luminescence and magnetic properties was prepared. 1 exhibits visible emission whose color, yellow to greenish-blue, is switchable by selected wavelengths of UV excitation light. Magnetic data revealed that 1 shows not only the slow magnetic relaxation of a typical DyIII single-ion origin but also the relaxation process caused by the magnetic dipole–magnetic dipole interactions between the neighbouring DyIII centers.
Co-reporter:Szymon Chorazy, Michał Rams, Anna Hoczek, Bernard Czarnecki, Barbara Sieklucka, Shin-ichi Ohkoshi and Robert Podgajny
Chemical Communications 2016 - vol. 52(Issue 26) pp:NaN4775-4775
Publication Date(Web):2016/02/22
DOI:10.1039/C5CC10371A
Pentadecanuclear {CoII9[WV(CN)8]6} clusters were combined with bidentate 2,2′-bipyridine N,N′-dioxide (2,2′-bpdo) ligands resulting in two distinct molecules, {Co9W6(2,2′-bpdo)7} (cluster A) and {Co9W6(2,2′-bpdo)6} (cluster B), capped by seven and six 2,2′-bpdo ligands, respectively. They crystallize within a single {Co9W6(2,2′-bpdo)7}·{Co9W6(2,2′-bpdo)6}·solvent (1) supramolecular network, and reveal single-molecule magnet behaviour with an enhanced energy barrier, a ΔE/kB of 30.0(8) K, which was tentatively ascribed to seven-capped axially deformed cluster A.
Co-reporter:Asuka Namai, Marie Yoshikiyo, Sayaka Umeda, Takayuki Yoshida, Tatsuro Miyazaki, Makoto Nakajima, Keita Yamaguchi, Tohru Suemoto and Shin-ichi Ohkoshi
Journal of Materials Chemistry A 2013 - vol. 1(Issue 34) pp:NaN5206-5206
Publication Date(Web):2013/07/17
DOI:10.1039/C3TC30805G
In this study, we demonstrate a synthesis of rhodium substituted ε-iron oxide, ε-RhxFe2−xO3 (0 ≤ x ≤ 0.19), nanoparticles in silica. The synthesis features a sol–gel method to coat the metal hydroxide sol containing Fe3+ and Rh3+ ions with a silica sol via hydrolysis of alkoxysilane to form a composite gel. The obtained samples are barrel-shaped nanoparticles with average long- and short-axial lengths of approximately 30 nm and 20 nm, respectively. The crystallographic structure study using X-ray diffraction shows that ε-RhxFe2−xO3 has an orthorhombic crystal structure in the Pna21 space group. Among the four non-equivalent substitution sites (A–D sites), Rh3+ ions mainly substitute into the C sites. The formation mechanism of ε-RhxFe2−xO3 nanoparticles is considered to be that the large surface area of the nanoparticles increases the contribution from the surface energy to Gibbs free energy, resulting in a different phase, ε-phase, becoming the most stable phase compared to that of bulk or single crystal. The measured electromagnetic wave absorption characteristics due to natural resonance (zero-field ferromagnetic resonance) using terahertz time domain spectroscopy reveal that the natural resonance frequency shifts from 182 GHz (ε-Fe2O3) to 222 GHz (ε-Rh0.19Fe1.81O3) upon rhodium substitution. This is the highest natural resonance frequency of a magnetic material, and is attributed to the large magnetic anisotropy due to rhodium substitution. The estimated coercive field for ε-Rh0.19Fe1.81O3 is as large as 28 kOe.
Co-reporter:Hiroko Tokoro and Shin-ichi Ohkoshi
Dalton Transactions 2011 - vol. 40(Issue 26) pp:NaN6833-6833
Publication Date(Web):2011/03/29
DOI:10.1039/C0DT01829E
Cyano-bridged bimetal assemblies demonstrate novel magnetic functionalities, particularly Prussian blue analogs, which have unique properties. In this perspective, we describe a charge-transfer phase transition, reversible photomagnetism, second harmonic generation and magnetization-induced second harmonic generation, ferroelectric ferromagnetism, humidity-sensitive magnetism, high ionic conductivity, and a coupling effect (which we named spin-ionics) between ionic conduction and magnetic ordering with Prussian blue analogs.
![Poly[oxycarbonyloxy(methyl-1,2-ethanediyl)]](http://img.cochemist.com/ccimg/37300/37248-85-4.png)
![Poly[oxycarbonyloxy(methyl-1,2-ethanediyl)]](http://img.cochemist.com/ccimg/37300/37248-85-4_b.png)
