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Ryo Ohtani Last modified date：2023.11.27

Associate Professor / Department of Chemistry / Faculty of Sciences


Papers
1. Morphology and magnetic properties of synthesized lipid packaged iron(II) complex.
2. Haruka Yoshino, Narumi Tomokage, Akio Mishima, Benjamin Le Ouay, Ryo Ohtani, Wataru Kosaka, Hitoshi Miyasaka, Masaaki Ohba, Guest-selective and reversible magnetic phase switching in a pseudo-pillared-layer porous magnet, CHEMICAL COMMUNICATIONS, 10.1039/d1cc01526e, 2021.04, A novel porous magnet consisting of cationic two-dimensional (2-D) layers extended by Fe-III-CN-Ni-II linkages and pseudo-pillar dianions was synthesized. The size-selective guest adsorption behaviour of water and methanol molecules originates from the narrow bottle-neck-type pores in the flexible pseudo-pillared-layer structure, which results in the switching of the magnetic phases from antiferromagnetic to ferromagnetic, involving significant changes in the interlayer distance..
3. Ryohei Akiyoshi, Keita Kuroiwa, Mina Sakuragi, Soichiro Yoshimoto, Ryo Ohtani, Masaaki Nakamura, Leonard F Lindoy, Shinya Hayami, Double-layered honeycomb architectures constructed via hierarchical self-assembly of hexagonal spin crossover cobalt(ii) metallacycles., Chemical communications (Cambridge, England), 10.1039/d0cc02628j, 56, 43, 5835-5838, 2020.05, A hexagonal cobalt(ii) metallacycle and its "lipid packaged" derivatives, [Co6(R-bisterpy)6]X12 (R = H, OC16H33, OC27H55; X = BF4, C12-Glu), have been synthesized and characterized. The compounds incorporating BF4- anions formed sphere-like aggregates while the compounds with C12-Glu lipid anions gave double-layered honeycomb architectures composed of hexagonal stacked tubular structures, which exhibit spin crossover behaviour..
4. Yuta Ohtsubo, Akio Mishima, Akihiro Hori, Ryotaro Matsuda, Ryo Ohtani, Masaaki Ohba, Swift and efficient nuclear spin conversion of molecular hydrogen confined in Prussian blue analogs, Chemistry Letters, 10.1246/cl.190829, 49, 2, 149-152, 2020.01, The ortho-isomer of molecular hydrogen (o-H2) was converted to the para-isomer (p-H2) within 600 s by using Prussian blue analogs, {MII 3[CrIII(CN)6]2} (MCr; M = Mn and Ni), as nuclear-spin conversion catalysts. The swift conversion was confirmed by in-situ Raman micro-spectroscopy under an H2 gas atmosphere (100 kPa) in a low temperature range (2090 K). The o-p ratio observed in MCr deviated from the theoretical value based on the Boltzmann distribution of H2 in a free rotational state to the para-rich proportion, which suggested the promotion of the o-p conversion at higher temperature..
5. Ryo Ohtani, Junichi Yanagisawa, Hiromu Matsunari, Masaaki Ohba, Leonard F. Lindoy, Shinya Hayami, Homo- and Heterosolvent Modifications of Hofmann-Type Flexible Two-Dimensional Layers for Colossal Interlayer Thermal Expansions, Inorganic chemistry, 10.1021/acs.inorgchem.9b01660, 58, 19, 12739-12747, 2019.10, Two-dimensional Hofmann-type coordination polymers of type Mn(H2O)2[Pd(CN)4]·xH2O (1·xH2O; x = 0, 1, and 4), Mn(H2O)(MeOH)[Pd(CN)4]·2MeOH (2·2MeOH), and Mn(MeOH)2[Pd(CN)4]·MeOH (3·MeOH) have been synthesized. The homosolvent-bound 1·4H2O, 1·H2O, and 3·MeOH polymers consist of undulating layer structures, whereas the structure of heterosolvent-bound 2·2MeOH consists of "Janus-like" flat layers in which water-bound and MeOH-bound-sides are present. 1·4H2O and 1·H2O exhibited anisotropic two-dimensional thermal expansions involving structural transformations of the undulating layers; one layer axis expands while the other contracts. 2·2MeOH exhibits anisotropic thermal expansion in which the flat layers shift sideways as the temperature is increased, with colossal interlayer expansion occurring (αc = +200 MK-1 over 140-180 K, αc = +165 MK-1 over 200-280 K). 3·MeOH also showed colossal interlayer expansion (αc = +216 MK-1) together with expansion of the undulating layers..
6. Structure and magnetic property of mu-oxo bridged dinuclear iron(III) complex with trialkylated tridentated ligands.
7. Triply methoxo-bridged tetranuclear nickel cubane complexes with salicylate esters.
8. Fumiya Kobayashi, Ryo Ohtani, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Slow Magnetic Relaxation Triggered by a Structural Phase Transition in Long-Chain-Alkylated Cobalt(II) Single-Ion Magnets, Inorganic chemistry, 10.1021/acs.inorgchem.9b00543, 58, 11, 7409-7415, 2019.06, The behavior of single-ion magnets (SIMs) that reflects large distortions of their coordination environments caused by the packing of long alkyl chains for two Co(II) complexes of the type [Co(Cn-terpy)2](BF4)2 (Cn-terpy = 4′-alkoxy-2,2':6′,2″-terpyridine; n = 10 (1), 16 (2)) is reported. 1·2MeOH, which features a highly distorted octahedral high-spin Co(II) center, exhibits field-induced slow magnetic relaxation under an applied dc field of 1000 Oe. Further detailed analysis of the relaxation process indicated the prevalence of the Raman process at low temperature. Surprisingly, 2 shows a reverse spin transition (rST) and also exhibits remarkable field-induced SIM behavior, revealing the presence of magnetic anisotropy for this high-spin Co(II) species that is triggered by a structural phase transition. We present here the first examples of the coexistence of field-induced slow magnetic relaxation and rST associated with structural phase transitions involving long-alkyl-chain conformational changes from gauche to anti. These results indicate the prospect of inducing SIM properties in other distorted high-spin Co(II) species bearing long alkyl chains..
9. Fumiya Kobayashi, Ryo Otani, Saki Teraoka, Masaki Yoshida, Masako Kato, Yingjie Zhang, Leonard F. Lindoy, Shinya Hayami, Masaaki Nakamura, Phosphorescence at Low Temperature by External Heavy-Atom Effect in Zinc(II) Clusters, Chemistry - A European Journal, 10.1002/chem.201900343, 25, 23, 5875-5879, 2019.04, Luminescent Zn
II
clusters [Zn
4
L
4
(μ
3
-OMe)
2
X
2
] (X=SCN (1), Cl (2), Br (3)) and [Zn
7
L
6
(μ
3
-OMe)
2
(μ
3
-OH)
4
]Y
2
(Y=I
−
(4), ClO
4

−
(5)), HL=methyl-3-methoxysalicylate, exhibiting blue fluorescence at room temperature (λ
max
=416≈429 nm, Φ
em
=0.09–0.36) have been synthesised and investigated in detail. In one case the external heavy-atom effect (EHE) arising the presence of iodide counter anions yielded phosphorescence with a long emission lifetime (λ
max
=520 nm, τ=95.3 ms) at 77 K. Single-crystal X-ray structural analysis and time-dependent density-functional theory (TD-DFT) calculations revealed that their emission origin was attributed to the fluorescence from the singlet ligand-centred (
1
LC) excited state, and the phosphorescence observed in 4 was caused by the EHE of counter anions having strong CH−I interactions..
10. Tomoaki Hiraoka, Ryo Otani, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Water-Induced Breaking of the Coulombic Ordering in a Room-Temperature Ionic Liquid Metal Complex, Chemistry - A European Journal, 10.1002/chem.201900069, 2019.01, Control of ion arrangements in ionic liquids represents a major challenge owing to the presence of the predominant coulombic interactions between cationic and anionic ion species that forms the coulombic ordering. Here, water-induced ion rearrangement in a room-temperature ionic liquid (RT-IL) metal complex, (1-ethyl-3-methylimidazolium)
2
[MnN(CN)
4
], is demonstrated through coordinative interactions between anions. Solidification occurred, which was associated with the formation of a “separated” structure consisting of cation columns and anionic cyanide-bridged one-dimensional coordination polymers. The energy diagram is in accord with the resultant RT-IL incorporating mononuclear [MnN(CN)
4
]
2−
molecules being a kinetic phase stabilized by inter-ion repulsions of the anionic divalent metal complex moieties. Water acts to decrease the coulombic interactions, including repulsion, giving rise to breaking of the coulombic ordering arising from coordination bond formation in the IL phase..
11. Ryo Ohtani, Riho Yamamoto, Hiroyoshi Ohtsu, Masaki Kawano, Jenny Pirillo, Yuh Hijikata, Masaaki Sadakiyo, Leonard F. Lindoy, Shinya Hayami, Consecutive oxidative additions of iodine on undulating 2D coordination polymers
Formation of I-Pt-I chains and inhomogeneous layers, Dalton Transactions, 10.1039/c8dt04624g, 48, 21, 7198-7202, 2019.01, The 2D coordination polymers, [Mn(salen)]2[PtII(CN)4]1-x[PtIV(CN)4(I2)]x (salen = N,N'-ethylenebis(salicylideneaminato), x = 0.18 (1), 0.45 (2), 0.85 (3)), have been synthesized via consecutive oxidative additions of iodine to the 2D undulating layers in [Mn(salen)]2[PtII(CN)4]. The presence of I-Pt-I chains perpendicular to the layers and the inhomogeneity of individual I-Pt-I sites were demonstrated. The I-Pt-I chains in 3 give rise to an absorption band involving the excitation that arises from an antibonding nature orbital to the corresponding bonding nature orbital between iodides in the I-Pt-I bridging units. Moreover, variable-temperature X-ray powder diffraction patterns and Raman spectra for 1 and 2 indicate that some I-Pt-I sites display different vibrational energies that are associated with the contraction of the zigzag 2D layers..
12. Sotaro Kusumoto, Atsushi Koga, Fumiya Kobayashi, Ryo Ohtani, Yang Kim, Leonard F. Lindoy, Shinya Hayami, Masaaki Nakamura, Weak ferromagnetism derived from spin canting in an amido-bridged homochiral Mn(iii) 1-D coordination polymer, Dalton Transactions, 10.1039/c9dt00593e, 48, 24, 8617-8622, 2019.01, A homochiral one-dimensional (1D) Mn(iii) coordination polymer [MnL]n (1) was synthesised employing the N3O-donor tetradentate ligand (L = 2-hydroxy-N-[2-[[(2-aminophenyl)methylene]amino]-2-methylpropyl]-benzamide). The X-ray structure of 1 and its magnetic properties were investigated in detail. The crystal structure of 1 shows a homochiral helical arrangement in which spontaneous resolution has occurred, despite the ligand being achiral. Magnetic characterization revealed an antiferromagnetic interaction between manganese(iii) ions (J = -2.48 cm-1, g = 1.96) that leads to an antiferromagnetic spin-ordering phase transition at TN ≈ 7 K. Noteworthily, 1 exhibits weak ferromagnetism with a relatively large coercive field of 3.0 kOe based on the spin canting, indicating the formation of a homochiral weak ferromagnet..
13. Ryo Otani, Riho Yamamoto, Takuya Aoyama, Arnaud Grosjean, Masaaki Nakamura, Jack K. Clegg, Shinya Hayami, Positive and Negative Two-Dimensional Thermal Expansion via Relaxation of Node Distortions, Inorganic Chemistry, 10.1021/acs.inorgchem.8b01617, 57, 18, 11588-11596, 2018.09, The ability to tune physical properties is attractive for the development of new materials for myriad applications. Understanding and controlling the structural dynamics in complicated network structures like coordination polymers (CPs) is particularly challenging. We report a series of two-dimensional CPs [Mn(salen)]2[M(CN)4]·xH2O (M = Pt (1), PtI2 (2), and MnN (3)) incorporating zigzag cyano-network layers that display composition-dependent anisotropic thermal expansion properties. Variable-temperature single-crystal X-ray structural analyses demonstrated that the thermal expansion behavior is caused by double structural distortions involving [Mn(salen)]+ units incorporated into the zigzag layers. Thermal relaxations produce structural transformations resulting in positive thermal expansion for 2·H2O and negative thermal expansion for 3. In the case of 1·H2O, the relaxation does not occur and zero thermal expansion results in the plane between 200 to 380 K. The present study proposes a new strategy based on structural distortions in coordination networks to control thermal responsivities of frameworks..
14. Yuki Komatsumaru, Manabu Nakaya, Fumiya Kobayashi, Ryo Otani, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Post-synthetic Modification of a Dinuclear Spin Crossover Iron(III) Complex, Zeitschrift fur Anorganische und Allgemeine Chemie, 10.1002/zaac.201800087, 644, 14, 729-734, 2018.08, The dinuclear iron(III) complex [Fe(salten)2(bipytz)](BPh4)2·EtOH (1) was synthesized and its post-synthesis modification yielded [Fe(salten)2(bipydz)](BPh4)2·EtOH (2). The crystal structures and magnetic behaviors of 1 and 2 were investigated by variable temperature XRD, magnetic susceptibility, and Mössbauer spectra measurements, with each of these dinuclear iron(III) complexes exhibiting gradual spin crossover behavior..
15. Asami Tsukiashi, Manabu Nakaya, Fumiya Kobayashi, Ryo Otani, Masaaki Nakamura, Jack M. Harrowfield, Yang Kim, Shinya Hayami, Intermolecular Interaction Tuning of Spin-Crossover Iron(III) Complexes with Aromatic Counteranions, Inorganic Chemistry, 10.1021/acs.inorgchem.7b03126, 57, 5, 2834-2842, 2018.03, Iron(III) spin-crossover (SCO) complexes [Fe(qsal)
2
]BS·MeOH·H
2
O (1), [Fe(qsal)
2
](NS)·MeOH (2), [Fe(qnal)
2
](NS) (3), and [Fe(qnal)
2
]PS·MeOH·CH
2
Cl
2
(4) (Hqsal, N-(8-quinolinyl)salicylaldimine; Hqnal, N-(8-quinolinyl)-2-hydroxy-1-naphthaldimine; BS, benzenesulfonate; NS, 1-naphthalenesulfonate; PS, 1-pyrenesulfonate) have been synthesized and characterized by X-ray structure determinations and temperature-dependent magnetic susceptibility measurements. The aromatic counteranions BS, NS, and PS can be used for the tuning of intermolecular coupling through a variety of weak interactions. All of the complexes show temperature-dependent SCO behavior. but the light-induced excited spin-state trapping (LIESST) effect was observed only for 1, 3, and 4 when the samples were illuminated (λ 808 nm) for 1 h at 5 K. In particular, 59% of the LS form of 1 was converted to the metastable HS state by illumination, equal to the highest degree of conversion yet known for LIESST in [Fe(qsal)
2
]
+
derivatives. The lack of a LIESST effect for 2 may be due to the relatively limited degree of interaction between the cations and anions in the lattice, reflected in a much longer minimum Fe···Fe separation in this complex in comparison to the others..
16. Nurun Nahar Rabin, Shintaro Ida, Mohammad Razaul Karim, Md Saidul Islam, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Leonard F. Lindoy, Shinya Hayami, Super Dielectric Materials of Two-Dimensional TiO2 or Ca2Nb3O10 Nanosheet Hybrids with Reduced Graphene Oxide, ACS Omega, 10.1021/acsomega.7b01764, 3, 2, 2074-2083, 2018.02, High dielectric constants (er) were observed in two-dimensional composites obtained from stacking of reduced graphene oxide (RGO) with Ca2Nb3O10 and with TiO2 nanosheets. The relative dielectric permittivity values of the composites were found to be higher than 105, an amazingly high value compared to that of similar GO composites and other common dielectric materials. As a consequence, we considered application of the hybrids as super dielectric materials in high capacitance supercapacitors. The route to high capacitance involves the variation of oxygen vacancies within the surface and in the closest bulk interior of the hybrids. The effective charges generated throughout the metal oxide and carbon-oxygen polar bonding systems within the graphene skeleton appear to highly influence dielectric polarization. Moreover, the replenishment of oxygen vacancies at the RGO and metal oxide interface also contributes to polarizability..
17. Manabu Nakaya, Ryo Otani, Jong Won Shin, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Abrupt spin transition in a modified-terpyridine cobalt(ii) complex with a highly-distorted [CoN6] core, Dalton Transactions, 10.1039/c8dt02367k, 47, 39, 13809-13814, 2018.01, The cobalt(ii) complex incorporating π-conjugated substituent, [Co(Naph-C2-terpy)2](BF4)2 (1; Naph-C2-terpy = 4′-(2-naphthoxy(ethoxy))-2,2′:6′,2′′-terpyridine), exhibits an abrupt spin transition (ST) behavior (cooperative factor C = 0.91) while its solvated product, 1·2MeOH, shows gradual spin crossover (SCO) behavior (C = 0.49). Single crystal X-ray structural analyses demonstrated that the octahedral coordination core [CoN6] in 1 shows larger distortion in both high-spin and low-spin states than solvated 1·2MeOH or another two derivatives, [Co(R-terpy)2](BF4)2 (R = 2-naphthyl (2), 9-anthracenyl (3)). The respective distortion parameters (Σ) are compared with those for previously reported SCO cobalt(ii) compounds. The highly-distorted [CoN6] core in 1 (Σ = 126 in the HS state and 101.6 in the LS state) was stabilized by strong intermolecular interactions and observed an abrupt ST behaviour..
18. Hitomi Ohmagari, Mohammad Razaul Karim, Yuta Shudo, Shintaro Ida, Ryo Otani, Shinya Hayami, Ca2-αLaαNb3-βXβO10 Nanosheet Photocatalyst for Hydrogen Generation from Water Splitting, MRS Advances, 10.1557/adv.2018.461, 3, 47-48, 2847-2854, 2018.01, Ca2-αLaαNb3-βXβO10 nanosheets ((α, β=0-0.14), X= Rh(LaRh), Mn(LaMn), Fe(LaFe), Ni(LaNi)) were synthesized by exfoliation using the surfactant aided sonication method. These nanosheets demonstrated superior photocatalytic activities for water splitting into hydrogen at room temperature. SEM-EDX images and spectra confirmed the morphology and composition of the materials where doped metal precursors inserted into the heterogeneous structure aided the photocatalytic activity..
19. Sotaro Kusumoto, Fumiya Kobayashi, Ryo Otani, Yingjie Zhang, Jack Harrowfield, Yang Kim, Shinya Hayami, Masaaki Nakamura, Creating capsules with cubanes, Dalton Transactions, 10.1039/c8dt01911h, 47, 29, 9575-9578, 2018.01, A sextuply linked capsule incorporating two Ni(ii) cubane units is formed when Ni(ii) salts are reacted with N-aminoalkyl salicylamidato ligands in a 4:3 ratio in methanol. With a short (propyl) alkyl substituent, additional chloride counter ions are included in the cavity by occupation of one apex of each of the linked cubanes, while with a longer (pentyl) substituent, perchlorate and tetrafluoroborate anions are included, probably by H-bonding involving hydroxyl groups on the inner apices of the cubanes, indicating that the cavity can be regarded as suited to binding of hydrophilic units despite the lipophilic character of its links. The dicubane capsules show ferromagnetic behaviour typical of Ni(ii) cubanes in general, with coupling constants dependent upon the nature of the salt-derived counter anions..
20. Ryohei Akiyoshi, Yuma Hirota, Daisuke Kosumi, Ryo Otani, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Ferroelectric and luminescence properties of zinc(ii) and platinum(ii) soft complexes, Dalton Transactions, 10.1039/c8dt01100a, 47, 40, 14288-14292, 2018.01, Zinc(ii) and platinum(ii) complexes [M(X-4-C18-salmmen)] (M = Zn (1) and Pt (2), X = R, S (optical isomer) and rac (racemate), salmmen = N,N′-monomethylenebis-salicylideneimine) were synthesized and investigated. The series of compounds represented by 1 (R, S and rac forms) display liquid crystalline state behaviour at 413 K, and exhibit both ferroelectric and fluorescence properties, while the compounds represented by 2 (R and S, and rac forms) do not display liquid crystal behaviour but do exhibit ferroelectric and fluorescence properties. The ferroelectric behaviour was confirmed by second harmonic generation (SHG) experiments. It is considered that the motion and fluctuation of the long alkyl chains in these complexes results in the observed ferroelectric properties..
21. Yuta Shudo, Mohammad Razaul Karim, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Hybrids from the π−π Stacking of Graphene Oxide and Aromatic Sulfonic Compounds for Improved Proton Conductivity, ChemElectroChem, 10.1002/celc.201701026, 5, 2, 238-241, 2018.01, π-π stacking between GO and benzene sulfonic acid (BS), naphthalene sulfonic acid (NS), pyrene sulfonic acid (PS), and naphthalene disulfonic acid (ND) results in the formation of respective GO-BS, GO-NS, GO-PS and GO-ND hybrid materials. The proton conductivities of these materials follow the trend as GO-NS>GO-BS>GO-PS>GO>GO-ND. GO-NS, possessing the highest interlayer distance, exhibits the optimum proton conductivity. Evidently, GO-sulfonic acid hybrids reveal excellent superionic conductivity..
22. Asami Tsukiashi, Kil Sik Min, Hiroaki Terasawa, Sosuke Yoshinaga, Mitsuhiro Takeda, Ryo Otani, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Proton relaxation time in water-soluble metal complex nanoparticles, Chemistry Letters, 10.1246/cl.180038, 47, 4, 598-600, 2018.01, Water dispersible metal complex nanoparticles were synthesized using the polyethylene glycol (PEG) coating method. The χmT values at room temperature for the NPs 1-3 were calculated using the Evans method, and the proton relaxation times, T1 and T2, were measured employing MRI. Both relaxation times were observed to decrease with increasing χmT value..
23. Fumiya Kobayashi, Ryo Otani, Sotaro Kusumoto, Leonard F. Lindoy, Shinya Hayami, Masaaki Nakamura, Wheel-type heterometallic ferromagnetic clusters
[Ni7−xMx(HL)6(μ3-OMe)4(μ3-OH)2]Cl2 (M = Zn, Co, Mn; x = 1, 3), Dalton Transactions, 10.1039/c8dt03275k, 47, 46, 16422-16428, 2018.01, Wheel-type heptanuclear heterometallic clusters of stoichiometry [Ni7−xMx(HL)6(μ3-OMe)4(μ3-OH)2]Cl2 (L = 1-(2-hydroxy-3-methoxybenzamido)-2-(benzylideneamino)ethane; M = Zn2+, Co2+, Mn2+; x = 1, 3) were synthesized, and their metal ion dependent ferromagnetic properties were investigated. It was demonstrated that the central position of each cluster was occupied by a Ni2+ ion while other metal ions (Zn2+, Co2+ or Mn2+) were accommodated in peripheral positions. The magnetic interactions, anisotropy and magnetization of the resultant clusters were all influenced by the combinations of metal ions present..
24. Yusuke Sekimoto, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Leonard F. Lindoy, Shinya Hayami, Tuneable pressure effects in graphene oxide layers, Scientific reports, 10.1038/s41598-017-12444-x, 7, 1, 2017.12, Tuneable pressure effects associated with changing interlayer distances in two-dimensional graphene oxide (GO)/reduced GO (rGO) layers are demonstrated through monitoring the changes in the spin-crossover (SCO) temperature (T
1/2
) of [Fe(Htrz)
2
(trz)](BF
4
) nanoparticles (NPs) incorporated in the interlayer spaces of the GO/rGO layers. The interlayer separation along the GO to GO/rGO-NP composites to rGO series decreases smoothly from 9.00 Å (for GO) to 3.50 Å (for rGO) as the temperature employed for the thermal reduction treatments of the GO-NP composites is increased. At the same time, T
1/2
increases from 351 K to 362 K along the series. This T
1/2
increment of 11 K corresponds to that observed for pristine [Fe(Htrz)
2
(trz)](BF
4
) NPs under a hydrostatic pressure of 38 MPa. The influence of the stacked layer structures on the pseudo-pressure effects has been further probed by investigating the differences in T
1/2
for [Fe(Htrz)
2
(trz)](BF
4
) that is present in the composite as larger bulk particles rather than as NPs..
25. Yuta Shudo, Md Saidul Islam, Mohammad Razaul Karim, Nurun Nahar Rabin, Kosuke Wakata, Ryo Ohtani, Masaaki Nakamura, Leonard F Lindoy, Shinya Hayami, Development of an All Solid State Battery Incorporating Graphene Oxide as Proton Conductor., Global challenges (Hoboken, NJ), 10.1002/gch2.201700054, 1, 6, 1700054-1700054, 2017.09, Graphene oxide (GO) shows high proton conductivity (≈10-4 Scm-1), excellent mechanical stability, and electrical insulation property, which makes it an ideal candidate for use as a proton conducting solid state electrolyte. The prospects of using GO as single phase solid electrolyte in an all solid battery is presented herein. A battery with the cell configuration: Zn + ZnSO4•7H2O + graphite (anode) || GO (electrolyte) || MnO2 + graphite (cathode) is fabricated. Cyclic voltammetry confirms its rechargeable nature. The respective discharge capacity and power density of the cell are 360 μAh and 19.5 mW kg-1 at a constant current drain of 3 μA under the experimental conditions employed. GO based proton conductors are cleaner and cheaper than other solid electrolytes. The current study strongly suggests that GO can be used as a practical and beneficial component in solid state battery applications with low energy feedback..
26. Ryo Otani, Arnaud Grosjean, Ryuta Ishikawa, Riho Yamamoto, Masaaki Nakamura, Jack K. Clegg, Shinya Hayami, Zero in-Plane Thermal Expansion in Guest-Tunable 2D Coordination Polymers, Inorganic Chemistry, 10.1021/acs.inorgchem.7b00282, 56, 11, 6225-6233, 2017.06, Zero in-plane thermal expansion (TE) in a two-dimensional (2D) coordination polymer is demonstrated. The combination of components that expand and those that shrink into zigzag layers results in no net area change in the 2D materials with temperature. Single crystals of [Mn(salen)]
2
[Mn(N)(CN)
4
(guest)] (salen = N,N′-ethylenebis(salicylideneaminato), guest = MeOH and MeCN) were prepared, and variable-temperature single-crystal X-ray structural analyses demonstrated that these compounds exhibited both anisotropic positive and negative thermal expansion depending on the guest species. The TE behavior results from distortions of the octahedral coordination geometry of [Mn(salen)]
+
units in the zigzag layers. When both guests MeOH and MeCN were incorporated into one material, [Mn(salen)]
2
[Mn(N)(CN)
4
(MeOH)
0.25
(MeCN)
0.75
], zero in-plane TE resulted in a range of temperature between 380 and 440 K..
27. Manabu Nakaya, Ryo Otani, Kunihisa Sugimoto, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Molecular Assemblies of Metal Complexes via Base-Pairing of Nucleic Acids in the Crystalline State, Chemistry - A European Journal, 10.1002/chem.201700593, 23, 30, 7232-7237, 2017.05, The nature of the molecular assemblies formed in the crystalline state by cobalt(II) terpyridine (terpy) complexes incorporating appended adenine (A) or thymine (T) bases was found to be controlled by which bases are present. Single-crystals of the cobalt(II) complexes [Co(A-C6-terpy)2](BF4)2 (1) and [Co(T-C6-terpy)2](BF4)2 (2) have needle and block habits, respectively. Subsequent mixing of 1 and 2 in MeOH resulted in isolation of [Co(A-C6-terpy)1.5(T-C6-terpy)0.5](BF4)2 (3) as plate-like crystals. A 3D network structure is present in 1 that incorporates 1D chains, whereas 2 adopts a 2D stacked structure constructed from ladder-type assemblies. For 3, “dimer-rings” consisting of [Co(A-C6-terpy)2]2+ and [Co(A-C6-terpy)(T-C6-terpy)]2+ units are generated by means of base-pairing between A and T. Notably, 3 displays the first crystal structure of a heteroleptic cobalt(II) complex of [Co(A-C6-terpy)(T-C6-terpy)](BF4)2. These assembly differences involving the terpyridine cobalt(II) complex units in 1–3 affect the cooperativities influencing their spin crossover (SCO) behavior. The influence of the terminal nucleobases on the resulting assembly has been probed by investigating the co-crystallization of [Co(terpy)2](BF4)2 (4) with [Co(C6-terpy)2](BF4)2 (5) and 1 with 5..
28. Yusuke Sekimoto, Mohammad Razaul Karim, Naoto Saigo, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Crystal Structures and Spin-Crossover Behavior of Iron(II) Complexes with Chiral and Racemic Ligands, European Journal of Inorganic Chemistry, 10.1002/ejic.201700131, 2017, 7, 2017.02, Invited for the cover of this issue is the group of Shinya Hayami at Kumamoto University, Japan. The cover image shows a Japanese New Year’s card symbolizing the dawn of a new era for chiral magnetism. Mt. Aso, which is the symbol of Kumamoto, was chosen for the background..
29. Ryo Otani, Shinya Hayami, Guest-Dependent Spin-Transition Behavior of Porous Coordination Polymers, Chemistry - A European Journal, 10.1002/chem.201601880, 23, 10, 2236-2248, 2017.02, The host–guest composites of Hofmann-type iron(II) spin-transition (ST) porous coordination polymers incorporating guest molecules show guest-dependent ST behavior in accordance with the respective guest species, which may be a gas, solvent, halogen, or organic molecule. The guest also works as a chemical stimulant to switch the spin state of the host between high and low spin at room temperature. In this review, we discuss guest properties including size, shape, flexibility, chemical properties, and pore loading content, which impact the spin states of the host framework and the ST behavior exhibited by the host–guest composites..
30. Yusuke Sekimoto, Mohammad Razaul Karim, Naoto Saigo, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Crystal Structures and Spin-Crossover Behavior of Iron(II) Complexes with Chiral and Racemic Ligands, European Journal of Inorganic Chemistry, 10.1002/ejic.201601232, 2017, 7, 1049-1053, 2017.01, Chiral iron(II) complexes, [Fe{(R)-L}2(NCS)2] (1) and [Fe{(S)-L}2(NCS)2] (2), and racemic complex [Fe(rac)-L)2(NCS)2] (3) {L = α-methyl-N-(2-pyridinylmethylene)cyclohexanemethanamine} were synthesized. Their structures and magnetic properties were investigated by X-ray crystallography, magnetic susceptibility measurements, and Mössbauer spectroscopy. Complexes 1 and 2 crystallize in the trigonal system with space group P3121 and P3221, respectively. All complexes exhibit spin-crossover (SCO) behavior and light induced excited spin state trapping (LIESST) effects at 532 nm. Complexes 1 and 2 show similar gradual SCO behavior, and complex 3 shows more gradual SCO, which seems to be a result of the different crystal packing, as complex 3 is the symmetric isomer but 1 and 2 are asymmetric..
31. Fumiya Kobayashi, Atsushi Koga, Ryo Otani, Shinya Hayami, Masaaki Nakamura, Crystal structure of [2-({2-[(2-azanidylbenzylidene)amino]benzylidene}amino)-4-chlorophenolato]nickel(II), Acta Crystallographica Section E: Crystallographic Communications, 10.1107/S2056989017004613, 73, 637-639, 2017.01, The title complex, [Ni(C20H14ClN3O)], with an asymmetrically chloride-appended Schiff base ligand has been synthesized and structurally characterized at 100K. In the compound, the central nickel(II) ion has a square-planar coordination geometry with N3O donors of the π-conjugated tetradentate Schiff base ligand. In the crystal, the complexes are connected into an inversion dimer via an Ni⋯Ni interaction [3.1753(5)Å] and a pair of π-π interactions [centroid-centroid distance = 3.8416(16)Å]. The dimers are linked via a C-H⋯Cl hydrogen bond, forming a chain along the c-axis direction. The dimer chains interact with each other through π-π interactions [centroid-centroid distance = 3.8736(16)Å], forming a layer expanding parallel to the ac plane..
32. Mohammad Razaul Karim, Md Saidul Islam, Nurun Nahar Rabin, Hiroshi Takehira, Kosuke Wakata, Masaaki Nakamura, Ryo Otani, Kei Toda, Shinya Hayami, Interlayer Void Space as the Key Semipermeable Site for Sieving Molecules and Leaking Ions in Graphene Oxide Filter, ChemistrySelect, 10.1002/slct.201700503, 2, 15, 4248-4254, 2017.01, Within the nanopores, junctions and interlayer void space (IVS) in graphene oxide film (GOf), we report that IVS function as the key semipermeable site during sieving. The GOf could filter only dye molecules having nanometer-ranged dimensions. Tinier hydrated ions with angstrom-ranged dimensions couldn't be sieved by GOf. Nature and extent of this molecular sieving property have been justified by observing sieving efficacy and flow times for aqueous solutions of dyes, inorganic salts and their mixtures. GOf also could separate the dyes from mixtures with salts. The flow time followed the trend as: mixtures > salt solutions > dye solutions. PXRD data reveal entering of dye molecules at IVS during sieving. Obviously, a part of dye molecules leaking through the nanopores and junctions of GOf, finally become trapped at the IVS. IVS, therefore has been recognized as the key semipermeable site for molecular sieving in GO. With exploring the insight features of molecular sieving in GOf, this report clearly indicates that IVS needs to be tuned to adopt GOf for various analytical aspects including water purification, desalination and organic inorganic separation..
33. Ryo Otani, Yuu Kitamura, Yuh Hijikata, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Modulation of redox potentials utilizing the flexible coordination sphere of a penta-coordinate complex in the solid state, Dalton Transactions, 10.1039/c7dt00233e, 46, 11, 3749-3754, 2017.01, Slight changes in the coordination structure of the manganese(v)-nitrido anionic complex, [MnV(N)(CN)4]2−, induced by using a “lipid package” approach markedly made an impact on the corresponding redox potentials. The single crystals of four lipid assemblies, [dabco-(CH2)n−1-CH3]2[Mn(N)(CN)4(H2O)]·xH2O (n = 15, 16, 17 and 18; dabco = 1,4-diazabicyclo[2,2,2]octane), were synthesized and solid-state cyclic voltammetric studies demonstrated that the [MnV(N)(CN)4]2− anions with smaller “cross” NC-Mn-CN bond angles exhibit higher redox potentials. The observed trend reflects the energy change associated with the structural transformation from [MnV(N)(CN)4]2− to [MnVI(N)(CN)4]2− and is supported by the results of DFT calculations. The NC-Mn-CN bond angles in the flexible [Mn(N)(CN)4]2− structure exhibit excellent correlation with the redox potentials of the complexes in the solid state..
34. Risa Nakahara, Manabu Nakaya, Jong Won Shin, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Molecular Assemblies and Spin-Crossover Behaviour of Cobalt(II) Complexes with Terpyridine Incorporating Different Nitrogen Positions in Pyridine Rings, Australian Journal of Chemistry, 10.1071/CH16556, 70, 5, 494-498, 2017.01, Cobalt(ii) complexes with terpyridine-type ligands, [Co(n-pyterpy)2](ClO4)2 (n=3 (1), 4 (2)), were prepared and characterised. Different positions of the nitrogen atom in the terpyridine ligands influenced their assembly properties in the crystal structures. Complex 1 showed a 2D network structure consisting of 1D chains connected by intermolecular NHC interactions. On the other hand, complex 2 consisted of two different cobalt ion sites (Co1 and Co2) with slightly different coordination environments. Complex 2 showed 1D chains with no interchain interactions. Such differences are discussed with the cooperativities estimated by their spin crossover behaviours..
35. Nurun Nahar Rabin, Mohammad Razaul Karim, Md Saidul Islam, Hitomi Omagari, Narumi Kameda, Yuta Shudo, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Oxidation route dependent proton conductivities of oxidized fullerenes, New Journal of Chemistry, 10.1039/c7nj02964k, 41, 23, 14708-14712, 2017.01, We reported the proton conductivities of a series of oxidized fullerenes (fullerenols) having varied polarity and hydrophilicity. The samples were generated from the oxidation of fullerenes by using different oxidation techniques and oxidizing agents. XPS, IR and TGA data confirmed the successful oxidation of fullerenes. Electrochemical impedance showed that fullerenols can support proton conductivity. At room temperature and 90% RH, a maximum proton conductivity of 1.4 × 10-2 S cm-1 was observed in fullerenols obtained from the oxidation of fullerene (C60) by caustic soda. We expect the use of fullerenols as solid electrolytes in fuel cells, sensors, chemical filters and so on..
36. Saidul Islam, Mohammad Razaul Karim, Nurun Nahar Rabin, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Oxygen-functionalized porous carbon as single-phase mixed electron/proton conductor with capacitance properties, Chemistry Letters, 10.1246/cl.170677, 46, 12, 1828-1831, 2017.01, A stable single-phase mixed electron/proton conductor with excellent capacitance from oxygen-functionalized porous carbon (OPC) has been presented herein. Electrochemical study suggested that at room temperature and 90% RH the values of electronic and protonic conductivity of OPC are 1.68.
37. Hiroshi Takehira, Md Saidul Islam, Mohammad Razaul Karim, Yuta Shudo, Ryo Otani, Leonard F. Lindoy, Takaaki Taniguchi, Minoru Osada, Shinya Hayami, Photoreduction Dependent p- and n-Type Semiconducting Field-Effect Transistor Properties in Undoped Reduced Graphene Oxide, ChemistrySelect, 10.1002/slct.201701509, 2, 24, 6941-6944, 2017.01, Both p- and n-type field effect transistors (FET) properties have been observed in undoped reduced graphene oxide (rGO). Short and long time exposure of GO during photo reduction results in the formation of respective p- and n-type rGO semiconductor. Achieving duel behavior of this type in an undoped material is exceedingly unusual. Herein we report the presence of such behavior in the reduced from of graphene oxide (rGO) for the first time..
38. Mohammad Razaul Karim, Md Saidul Islam, Nurun Nahar Rabin, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Shinya Hayami, Proton Conductivity of Graphene Oxide on Aging, Australian Journal of Chemistry, 10.1071/CH16557, 70, 5, 642-645, 2017.01, The aging effect on the proton conductivity of graphene oxide (GO) is investigated. Characterizations of oxygenated functional groups and measurement of the proton conductivity have been performed using freshly prepared GO and the same sample after preserving for three years under ambient conditions. Although GO retains its layered structure, a slight deviation in its powder X-ray diffraction (PXRD) pattern and Raman spectra upon aging implies some changes in the interlayer distance and functional groups. Decomposition of epoxy groups on aging has been recognised by X-ray photoelectron spectroscopy (XPS) analysis. The proton conductivity was found to be reduced by 25% after three years of aging..
39. Kosuke Wakata, Md Saidul Islam, Mohammad Razaul Karim, Kazuto Hatakeyama, Nurun Nahar Rabin, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Shinya Hayami, Role of hydrophilic groups in acid intercalated graphene oxide as a superionic conductor, RSC Advances, 10.1039/c7ra01634d, 7, 35, 21901-21905, 2017.01, Hybrid materials that are obtained from intercalation of different polar and hydrophilic acid guest molecules within graphene oxide (GO) have been found to exhibit high proton conductivity. The accommodation of these guest precursors within the GO interlayer takes place through weak physical forces. PXRD patterns with enhanced interlayer distance confirmed successful intercalation processes. Raman and IR spectral data reveal the absence of any covalent bond between the functional groups of the guest and the GO host. TGA data confirms improved water adsorbing capacity of the hybrids. At ambient conditions and 90% relative humidity (RH), a RH dependent impedance study shows that intercalation of formic acid (FA) and phosphoric acid (PA) within GO results in ∼7 times higher proton conductivity compared with that for the pristine GO sample. The low activation energy values suggest that proton conduction in the samples is aided by the Grotthuss mechanism. Improvement in the water adsorbing capacity is primarily responsible for such high proton conductivity. The current study suggests that cheap and environmentally friendly GO-based intercalated hybrid materials, such as GO/PA and GO/FA with enhanced proton conductivity, can be appropriate replacements for the expensive Nafion-based solid electrolytes..
40. Kosuke Wakata, Mohammad Razaul Karim, Md Saidul Islam, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Shinya Hayami, Superionic Conductivity in Hybrid of 3-Hydroxypropanesulfonic Acid and Graphene Oxide, Chemistry - An Asian Journal, 10.1002/asia.201601488, 12, 2, 194-197, 2017.01, Insertion of 3-hydroxypropanesulfonicacid (HPS) in the graphene oxide (GO) interlayer results in high proton conductivity (10−2–10−1 S cm−1), owing to an improvement in oxygen content, interlayer distance and water absorbing capacity. This result indicates that hydroxyalkylsulfonicacids can be perfect guest molecules for improving the proton conductivity of carbon materials..
41. Ryohei Akiyoshi, Keita Kuroiwa, Saliu Alao Amolegbe, Manabu Nakaya, Ryo Otani, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Supramolecular architectures self-assembled using long chain alkylated spin crossover cobalt(II) compounds, Chemical Communications, 10.1039/c7cc01501a, 53, 34, 4685-4687, 2017.01, Self-assembled hybrid supramolecular architectures formed between amphiphilic anions and long alkylated cationic cobalt(ii) complexes of type [Co(Cn-terpy)2](C12-Glu)2 (n = 15-20) have been synthesized and characterized by TEM, PXRD and magnetic susceptibility measurements. The hybrids display wire or rolled sheet supramolecular arrangements with odd and even alkyl chain dependence, with the cobalt(ii) centres exhibiting gradual spin-crossover behaviours..
42. Fumiya Kobayashi, Ryo Otani, Saki Teraoka, Wataru Kosaka, Hitoshi Miyasaka, Yingjie Zhang, Leonard F. Lindoy, Shinya Hayami, Masaaki Nakamura, Syntheses, structures and magnetic properties of tetranuclear cubane-type and heptanuclear wheel-type nickel(II) complexes with 3-methoxysalicylic acid derivatives, Dalton Transactions, 10.1039/c7dt01757j, 46, 26, 8555-8561, 2017.01, Two ferromagnetic multinuclear Ni(ii) clusters, [Ni
4
L
1
4
(μ
3
-OMe)
4
(CH
3
OH)
4
] (1) and [Ni
7
(HL
2
)
6
(μ
3
-OMe)
6
]Cl
2
(2), and a mononuclear complex [NiL
3
]·2H
2
O (3) (HL
1
= benzyl 2-hydroxy-3-methoxybenzoate; H
2
L
2
= 1-(2-hydroxy-3-methoxybenzamido)-2-(benzylideneamino)ethane; H
2
L
3
= 1-(2-hydroxy-3-methoxybenzamido)-2-(pyridylmethyleneamino)ethane) were synthesised, and their structures and magnetic behaviours were investigated in detail. 1 has a [Ni
4
O
4
] cubane structure while 2 has a wheel-like [Ni@Ni
6
] arrangement. The temperature-dependent magnetic susceptibilities for 1 and 2 are in accord with the presence of dominating intra-cluster ferromagnetic interactions between Ni(ii) ions. The best fits for their behaviours gave the following parameters: J
1
= 11.06 cm
-1
, J
2
= 1.43 cm
-1
, g = 2.29 for 1, and J
1
= 6.87 cm
-1
, J
2
= -3.41 cm
-1
, g = 2.24 for 2..
43. Ryo Otani, Tsukasa Tokita, Tomohisa Takaya, Koichi Iwata, Masanao Kinoshita, Nobuaki Matsumori, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, The impact of metal complex lipids on viscosity and curvature of hybrid liposomes, Chemical Communications, 10.1039/c7cc07944c, 53, 99, 13249-13252, 2017.01, A morphology transformation of hybrid liposomes was shown to occur from spherical vesicles to tubular micelles when increasing the ratio of the metal complex lipid present. Phase transition temperatures increased while viscosities decreased, indicating that the hybrids exhibit stronger interaction between heads but weaker interaction between alkyl chains than occurs in pristine liposomes..
44. Mayu Tsutsumi, Md Saidul Islam, Mohammad Razaul Karim, Nurun Nahar Rabin, Ryo Otani, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Tri-functional OER, HER and ORR electrocatalyst electrodes from in situ metal-nitrogen co-doped oxidized graphite rods, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20170102, 90, 8, 950-954, 2017.01, Trifunctional catalysts for simultaneously generating H2, O2 and H2O provide a crucial means for improving the overall efficiency of H2O electrolysis. A series of nonnoble metal [M = Fe(III), Co(II), Ni(II)]-nitrogen co-doped oxidized graphite rods (M-N/OGR) that function as in situ working electrodes for tri-functional oxygen evolution reaction, hydrogen evolution reaction, and oxygen reduction reaction electrocatalysis was prepared. The enhanced performance of the hybrid catalysts appear mostly associated with dual active site mechanisms originating from the synergic effects of M-N/Co-doped on the surface of the OGR. The development of multifunctional electrocatalysts with optimal catalytic activity using transition metals and nitrogen doped OGR opens new fields for in situ synthesized electrocatalysts for use in clean electrochemical energy storage and conversion technologies..
45. Mohammad Razaul Karim, Md Saidul Islam, Kazuto Hatakeyama, Masaaki Nakamura, Ryo Otani, Michio Koinuma, Shinya Hayami, Effect of interlayer distance and oxygen content on proton conductivity of graphite oxide, Journal of Physical Chemistry C, 10.1021/acs.jpcc.6b06301, 120, 38, 21976-21982, 2016.09, The effect of interlayer distance and oxygen content on proton conductivity of graphite oxide is presented. Bulk-state proton conductivities were measured using coin-shaped pellets of three different graphite oxide samples, namely, H-GO, S-GO, and B-GO, generated respectively from the techniques of Hummers, Staudenmaier, and Brodie. The extent of oxidation, nature of functional groups, interlayer distances, and morphologies are studied through Raman spectroscopy, XPS, powder XRD pattern, and SEM images. The proton conductivities follow the trend H-GO > S-GO > B-GO. In the XPS study, the total oxygen contents were found to follow the trend H-GO > B-GO > S-GO, whereas the interlayer distances obtained from the powder XRD patterns show the trend H-GO > S-GO > B-GO. Beside the nature of the functional groups and extent of oxidation, the interlayer distance displays a significant effect on the proton conductivity values. The temperature-dependent Arrhenius plots reveal the activation energy (Ea) of the samples as 0.274, 0.291, and 0.296 eV. These low Ea values imply the Grotthuss mechanism for proton conduction. The high conductivity value and low activation energy of H-GO with a maximum interlayer distance indicate that hydronium ion's rotational movement and re-formation of hydrogen bonds by the Grotthuss mechanism are supported by a more flexible interlayer. We propose that this physical insight might be considered to improve the proton conductivity through modulating layer distances not only in carbon allotropes but also in other materials..
46. Md Saidul Islam, Mohammad Razaul Karim, Kazuto Hatakeyama, Hiroshi Takehira, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Shinya Hayami, Thermally Stable Super Ionic Conductor from Carbon Sphere Oxide, Chemistry - An Asian Journal, 10.1002/asia.201600835, 11, 16, 2322-2327, 2016.08, A highly stable proton conductor has been developed from carbon sphere oxide (CSO). Carbon sphere (CS) generated from sucrose was oxidized successfully to CSO using Hummers’ graphite oxidation technique. At room temperature and 90 % relative humidity, the proton conductivity of thin layer CSO on microsized comb electrode was found to be 8.7×10−3 S cm−1, which is higher than that for a similar graphene oxide (GO) sample (3.4×10−3 S cm−1). The activation energy (Ea) of 0.258 eV suggests that the proton is conducted through the Grotthuss mechanism. The carboxyl functional groups on the CSO surface are primarily responsible for transporting protons. In contrast to conventional carbon-based proton conductors, in which the functional groups decompose around 80 °C, CSO has a stable morphology and functional groups with reproducible proton conductivity up to 400 °C. Even once annealed at different temperatures at high relative humidity, the proton conductivity of CSO remains almost unchanged, whereas significant change is seen with a similar GO sample. After annealing at 100 and 200 °C, the respective proton conductivity of CSO was almost the same, and was about ∼50 % of the proton conductivity at room temperature. Carbon-based solid electrolyte with such high thermal stability and reproducible proton conductivity is desired for practical applications. We expect that a CSO-based proton conductor would be applicable for fuel cells and sensing devices operating under high temperatures..
47. Yusuke Murashima, Mohammad Razaul Karim, Ryo Furue, Takeshi Matsui, Hiroshi Takehira, Kosuke Wakata, Kei Toda, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Reduced graphene oxide-transition metal hybrids as p-type semiconductors for acetaldehyde sensing, Inorganic Chemistry Frontiers, 10.1039/c6qi00058d, 3, 6, 842-848, 2016.06, Acetaldehyde gas sensing using hybrids of reduced graphene oxide (rGO) and transition metal elements, rGO-M (M = oxide/hydroxide of Mn, Fe, Co and Ni) has been investigated. Thin films of GO, rGO and rGO-M on conductive glass were deposited through simple and affordable techniques and characterized using Raman spectroscopy, powder X-ray diffraction patterns, field emission scanning electron microscopy and electrical conductivity measurements. Concentration dependent resistances during the oxidation of acetaldehyde gas in air (10 to 50%) were investigated by using a sensing probe devised from rGO, GO-M and the rGO-M hybrids, of which rGO-Ni exhibited the maximum sensitivity. In rGO-Ni, in combination with rGO the NiOOH precursor can capture electrons (generated from acetaldehyde oxidation) through the holes, while indicating rGO-Ni to be a p-type semiconductor. This report implies the possibility of developing inexpensive graphene based p-type semiconductors for sensing other gases as well..
48. Mohammad Razaul Karim, Hiroshi Takehira, Mohammed M. Rahman, Abdullah M. Asiri, M. K. Amin, Ryo Otani, Shinya Hayami, Magnetic and liquid crystalline property of long-alkyl chain appended iron (II) imidazole complexes, Journal of Organometallic Chemistry, 10.1016/j.jorganchem.2016.02.014, 808, 42-47, 2016.04, Fe[((py)im-C16)
3
](BF
4
)
2
(1) and Fe[((py)imH)
3
](BF
4
)
2
(2), the Iron(II) compounds with C16 long alkyl chain appended (py)imH and unmodified (py)imH [(py)imH = 2-(2-pyridyl)imidazole] have been synthesized and characterized by NMR, IR spectra and elemental analysis. For containing C16 long alkyl chain, complex 1 exhibits the liquid crystalline property around room temperature. The magnetic study suggests that 1 exists only in low spin state but 2 exhibits gradual spin crossover behavior. These observation suggests the possibility for synchronizing liquid crystallinity and spin crossover behavior of (py)imH complex in near future..
49. Ryo Otani, Saki Egawa, Manabu Nakaya, Hitomi Ohmagari, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Metal Dilution Effects on the Reverse Spin Transition in Mixed Crystals of Type [Co1-xZnx(C16-terpy)2](BF4)2 (x = 0.1-0.7), Inorganic Chemistry, 10.1021/acs.inorgchem.5b02582, 55, 7, 3332-3337, 2016.04, Metal dilution effects on reverse spin transition (rST) in mixed crystals of type [Co1-xZnx(C16-terpy)2](BF4)2 (x = 0.1-0.7) were investigated by comparison with behavior of [Co1-xFex(C16-terpy)2](BF4)2 (x = 0.1-0.4). In the mixed crystals, the Zn complexes increased rST temperatures linearly with increasing values of x, without changing the hysteresis width, while the Fe complexes decreased rST temperatures. Moreover, the strength of the metal dilution effects in the CoZn mixed crystals is weaker than what occurs in the CoFe mixed crystals..
50. Takeshi Matsui, Mohammad Razaul Karim, Hiroshi Takehira, Masaaki Nakamura, Ryo Ohtani, Michio Koinuma, Shinya Hayami, Photocurrent Generation of Graphene Oxide Hybrid with Ru(II) Complex, CHEMISTRY LETTERS, 10.1246/cl.151123, 45, 3, 365-367, 2016.03, A graphene oxide (GO) and ruthenium(II) complex with bromine-substituted terpyridine ligand, [Ru(Br-terpy)(2)]Cl-2 (Br-terpy: 4'-bromo-2,2':6',2 ''-terpyridine), reacts to form a GO-[Ru(Br-terpy)(2)](2+) hybrid, which after photoreduction turns to the reduced graphene oxide (rGO)-based hybrid rGO-[Ru(Br-terpy)(2)](2+). The hybrids were characterized by UV, IR, and XPS spectra. rGO-[Ru(Br-terpy)(2)](2+) exhibits excellent photocurrent generation through the cathodic photoreduction process. This observation indicates the possibility of designing an rGO-based energy generating material..
51. Md Saidul Islam, Mohammad Razaul Karim, Saiful Islam, Jaekook Kim, Nurun Nahar Rabin, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Shinya Hayami, In Situ Generation of Silicon Oxycarbide Phases on Reduced Graphene Oxide for Li–Ion Battery Anode, ChemistrySelect, 10.1002/slct.201601363, 1, 20, 6429-6433, 2016.01, A highly stable composite from in situ growth of silicon oxycarbide phases (SiOC) within reduced graphene oxide (rGO) has been synthesized. The resulted SiOC/rGO anode exhibits high porosity, reversible Li intercalation capacity and a cycling stability of 507 mAhg
−1
at 100 mAg
−1
(50 cycles)..
52. Saliu Alao Amolegbe, Hitomi Ohmagari, Kosuke Wakata, Hiroshi Takehira, Ryo Otani, Masaaki Nakamura, Chengzhong Yu, Shinya Hayami, Synthesis of mesoporous materials as nano-carriers for an antimalarial drug, Journal of Materials Chemistry B, 10.1039/c5tb02200b, 4, 6, 1040-1043, 2016.01, An antimalarial drug artesunate (ATS) was encapsulated in both functionalized MCM-41 and ordinary MCM-41 with an excellent loading capacity and sustained release behavior for possible biomedical applications..
53. Hitomi Ohmagari, Ryo Otani, Manabu Nakaya, Masaaki Ohba, Masaaki Nakamura, Leonard F. Lindoy, Osamu Sato, Shinya Hayami, Water-dependent charge-transfer-induced spin transition of Prussian blue analogues, Dalton Transactions, 10.1039/c6dt03474h, 45, 42, 16784-16788, 2016.01, Cobalt-iron Prussian blue analogues are magnetic functional compounds that exhibit charge-transfer-induced spin transition (CTIST), however, the role of guest species such as water in influencing the magnetic behaviour has remained unclear. Here, we report the water-dependent CTIST behaviour of Na0.46Co[Fe(CN)6]0.78(H2O)1.31 together with its single crystal X-ray structural analysis, for the first time..
54. Ryo Otani, Manabu Nakaya, Hitomi Ohmagari, Masaaki Nakamura, Kazuchika Ohta, Leonard F. Lindoy, Shinya Hayami, Molecular Designs for Enhancement of Polarity in Ferroelectric Soft Materials, Scientific reports, 10.1038/srep16606, 5, 2015.11, The racemic oxovanadium(IV) salmmen complexes, [VO((rac)-(4-X-salmmen))] (X=C12C10C5 (1), C16 (2), and C18 (3); salmmen=N,N′-monomethylenebis-salicylideneimine) with "banana shaped" molecular structures were synthesized, and their ferroelectric properties were investigated. These complexes exhibit well-defined hysteresis loops in their viscous phases, moreover, 1 also displays liquid crystal behaviour. We observed a synergetic effect influenced by three structural aspects; the methyl substituents on the ethylene backbone, the banana shaped structure and the square pyramidal metal cores all play an important role in generating the observed ferroelectricity, pointing the way to a useful strategy for the creation of advanced ferroelectric soft materials..
55. Yusuke Murashima, Mohammad Razaul Karim, Naoto Saigo, Hiroshi Takehira, Ryo Otani, Masaaki Nakamura, Michio Koinuma, Leonard F. Lindoy, Keita Kuroiwa, Shinya Hayami, Graphene oxide and reduced graphene oxide hybrids with spin crossover iron(iii) complexes, Inorganic Chemistry Frontiers, 10.1039/c5qi00097a, 2, 10, 886-892, 2015.10, Graphene (rGO) based hybrid materials exhibiting electrical conductivity and spin crossover (SCO) behavior are reported. The non-conductive [Fe(qnal)2]nGO (1·GO) and [Fe(qsal)2]nGO (2·GO) hybrids have been prepared by employing the electrostatic interaction between the negatively charged graphene oxide (GO) nanosheet and the respective iron(iii) complex cations in [Fe(qnal)2]+Cl- and [Fe(qsal)2]+Cl-. The conductive [Fe(qnal)2]nrGO (1·rGO) and [Fe(qsal)2]nrGO (2·rGO) hybrids were obtained by thermal reduction of 1·GO and 2·GO. 1·GO and 1·rGO exhibit SCO behavior, and 1·rGO also shows a light-induced excited spin state trapping (LIESST) effect. Thus, in 1·rGO the electrical conductivity of rGO and the SCO behavior of [Fe(qnal)2]+ coexist in a single structure. We propose that the observed cooperativity for the rGO nanosheet-bound iron(iii) [Fe(qnal)2]+ SCO material occurs through formation of large domains via π-π stacking between the graphene skeleton and the [Fe(qnal)2]+ cations..
56. Ryo Otani, Kodai Shimayama, Akio Mishima, Masaaki Ohba, Ryuta Ishikawa, Satoshi Kawata, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, The impact of halogen ions on the guest dependent spin crossover behaviour and porosity of Co(II) one-dimensional coordination polymers [CoX2(4′-(4-pyridyl)-2,2′
6′,2′′-terpyridine)] (X = Cl and Br), Journal of Materials Chemistry C, 10.1039/c5tc00864f, 3, 30, 7865-7869, 2015.08, Discrete Co(II) spin crossover (SCO) compounds have attracted much attention for constructing highly sensitive molecular devices; however, the use of Co(II) SCO-coordination polymers (CPs) in such applications is extremely limited. The syntheses of the one-dimensional Co(II) SCO-CPs, [CoX2(pyterpy)] (pyterpy = 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine; X = Cl (1), Br (2)), are presented. The structure of 1 shows a 'closed' packing arrangement that exhibits gate-type water adsorption at room temperature while 2 has an 'open' packing arrangement that shows type I water adsorption behaviour at room temperature. In addition, both 1 and 2 adsorb CO2 at 201 K. Following water adsorption, 1·H2O and 2·H2O showed cooperative SCO at 226 K and 299 K, respectively..
57. Hitomi Ohmagari, Aya Fukahori, Manabu Nakaya, Ryo Otani, Shinya Hayami, Masaaki Nakamura, Crystal structures and magnetic properties of manganese(III) complexes with tridentate Schiff base ligands, Journal of Inclusion Phenomena and Macrocyclic Chemistry, 10.1007/s10847-015-0492-0, 82, 1-2, 213-218, 2015.06, Manganese(III) complexes [MnL 2 1 ]BPh4 (1) and [MnL 2 2 (MeOH)2]BPh4 (2) were synthesized (HL1 = 2-{N-[2-(2-pyridyl)ethyl]iminomethyl}-6-methoxyphenol and HL2 = 2-{N-[2-(2-pyridyl)ethyl]iminomethyl}-4-methylphenol) and characterized. The crystal structures were determined by single crystal X-ray crystallography for 1 and 2 and magnetic properties were characterized by magnetic susceptibility. Compounds 1 and 2 crystallized in the triclinic system with space groups P-1. The crystal structure of 1 showed that the central manganese(III) ions were coordinated by four nitrogen and two oxygen atoms of two ligands in trans positions, exhibiting a pseudo-octahedral geometry. On the other hand, the crystal structure of 2 showed that the manganese(III) ions were coordinated by the two nitrogen and two oxygen atoms of two ligands and two methanol solvent molecules. The variable temperature-dependence magnetic susceptibilities have shown that the compounds 1 and 2 manganese(III) oxidation state; there is no magnetic interaction between complexes..
58. Naoto Saigo, Yusuke Sekimoto, Manabu Nakaya, Ryo Otani, Msaaki Nakamura, Shinya Hayami, Direct observation of low-temperature bistability in an iron(III) LIESST compound, Journal of Inclusion Phenomena and Macrocyclic Chemistry, 10.1007/s10847-015-0521-z, 82, 1-2, 225-228, 2015.06, Iron(III) Schiff base compound [Fe(pap)2]ClO4·H2O (1, and Hpap = (2-(2-pyridylmethyleneamino)phenol)) shows abrupt spin crossover (SCO) with a hysteresis (T1/2↓ = 165 K, T1/2↑ = 180 K) and anomalous light induced excited spin state trapping. In the complex 1, the existence of the interaction between molecules by π electrons is suggested from single crystal structure. An anomalous LS → HS conversion, aberrant increase of HS molar fraction, was observed at low-temperature (50 K) in 1 after rapid cooling, and interpreted in terms of bistability resulted from strong cooperative interactions..
59. Kodai Shimayama, Mohammad Razaul Karim, Saliu Alao Amolegbe, Manabu Nakaya, Masaaki Nakamura, Ryo Otani, Leonard F. Lndoy, Shinya Hayami, Photoswitching of the dielectric property of salicylideneaniline, Journal of Inclusion Phenomena and Macrocyclic Chemistry, 10.1007/s10847-015-0524-9, 82, 1-2, 219-223, 2015.06, Temperature dependent dielectric constant changes for salicylideneaniline (SA) were observed before and after light irradiation. The dielectric constant for a non-illuminated sample is higher than that for an illuminated one. It was considered that this fascinating observation might reflect dynamic chromophoric structural changes within the tautomers of SA..
60. Shinya Hayami, Manabu Nakaya, Hitomi Ohmagari, Amolegbe Saliu Alao, Masaaki Nakamura, Ryo Otani, Ryotaro Yamaguchi, Takayoshi Kuroda-Sowa, Jack K. Clegg, Spin-crossover behaviors in solvated cobalt(ii) compounds, Dalton Transactions, 10.1039/c4dt03743j, 44, 20, 9345-9348, 2015.05, Two solvated cobalt(ii) terpyridine complexes, [Co(MeO-terpy)2](BF4)2·H2O (1·H2O) and [Co(MeO-terpy)2](BF4)2·acetone (1·acetone) were prepared. Annealing each of these complexes resulted in the formation of two desolvated species, 1 and 1′, respectively. 1·H2O and 1 exhibited two-step and gradual SCO. The compound 1·acetone has high-spin at all temperatures and 1′ undergoes a reverse spin transition due to a phase change..
61. Yusuke Murashima, Ryo Otani, Takeshi Matsui, Hiroshi Takehira, Ryotaro Yokota, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami, Coexistence of electrical conductivity and ferromagnetism in a hybrid material formed from reduced graphene oxide and manganese oxide, Dalton Transactions, 10.1039/c5dt00299k, 44, 11, 5049-5052, 2015.03, The coexistence of electrical conductivity and ferromagnetism has been achieved in a reduced graphene oxide/manganese oxide hybrid (rGO-Mn) synthesized by chemical reduction of a graphene oxide and Mn2+ (as its GO-Mn2+ complex) using hydrazine. The rGO-Mn and GO-Mn2+ complexes were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). In rGO-Mn the Mn was present as manganese oxide nanoparticles located on the rGO nanosheets. This rGO-Mn exhibits both electrical conductivity and ferromagnetism. The synthesis of hybrids incorporating rGO and metal oxides is proposed as a useful strategy for generation of new multifunctional nano-composite materials..
62. Hitomi Ohmagari, Manabu Nakaya, Ryo Otani, Masaaki Nakamura, Shinya Hayami, Crystal structure of bis[4'-(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)-2,2':6',2″-terpyridine]-cobalt(III) tris(perchlorate) methanol monosolvate monohydrate, Acta Crystallographica Section E: Crystallographic Communications, 10.1107/S2056989015014164, 71, 997-999, 2015.01, In the title compound, [Co(C25H30N4O4)2](ClO4)3·CH3OH·H2O, the metal atom is coordinated by two tridentate crown ether terpyridine ligands, forming a distorted CoN6 octahedron. The three pyridine rings in each crown-terpyridine ligand are approximately coplanar [maximum deviations = 0.088 (12) and 0.102 (15) Å] and the mean planes through the three pyridine rings are perpendicular to each other, making a dihedral angle of 89.95 (17)°. An intramolecular C-H···π interaction is observed between the two terpyridine ligands. In the crystal, O-H···O and C-H···O hydrogen bonds, a π-π stacking interaction [centroid-centroid distance = 3.923 (7) Å] and a C-H···π interaction connect the complex cation, the perchlorate anions and the two types of solvent molecules, forming a three-dimensional network..
63. Kohei Takami, Ryo Otani, Masaaki Nakamura, Takayuki Kurogi, Manabu Sugimoto, Leonard F. Lindoy, Shinya Hayami, Redox induced colour changes between red-violet and blue in hetero-metal complexes of the type [CoII(4′-ferrocenyl-2,2′;6′2′′-terpyridine)2]X2 (X = counter anion), Dalton Transactions, 10.1039/c5dt02592c, 44, 42, 18354-18359, 2015.01, The hetero-metal complexes [CoII(Fctpy)2]X2 (Fctpy = 4′-ferrocenyl-2,2′;6′2′′-terpyridine, X = PF6 (1), BF4 (2), ClO4 (3), BPh4 (4)) were prepared and their structures and properties were investigated by single crystal X-ray structural analysis, cyclic voltammetry, Mössbauer spectroscopy, UV-vis spectroscopy measurements and DFT calculations. These compounds show reversible redox behaviour in the solid state and switching of the colour between red-violet and blue in response to the change of the oxidation state of the cobalt ion centres. [CoII(Fctpy)2](PF6)2 (1) and [CoIII(Fctpy)2](PF6)3 (5) were isolated as the red and blue crystalline products, and the crystal structures were determined. From the results of UV-vis spectroscopy and the DFT calculations, we assigned the respective colours as resulting from MLCT involving the ferrocenyl substituents, with the shift in the wavelength of the MLCT reflecting the respective HOMO/LUMO stabilizations induced by the change in the oxidation state of the cobalt centres. Furthermore, these compounds 1-4 also showed counter anion-dependent spin crossover behaviours..
64. Ryo Otani, Munehiro Inukai, Yuh Hijikata, Tetsuya Ogawa, Mikihito Takenaka, Masaaki Ohba, Susumu Kitagawa, Sequential synthesis of coordination polymersomes, Angewandte Chemie - International Edition, 10.1002/anie.201408101, 54, 4, 1139-1143, 2015.01, Novel organic-inorganic hybrid liposomes, socalled coordination polymersomes (CPsomes), with artificial domains that exhibit strong lateral cohesion were prepared by a three-step procedure that formed a coordinative interaction leading to a lipid bilayer. First, the lipophilic complex (dabco-C18)[Mn(N)(CN)4(dabco-C18)] (1; dabco-C18 + = 1,4-diazabicyclo[2,2,2]octane-(CH2)17-CH3 cation), was synthesized. 1 has a lipophilic alkyl tail part and a tetracyanometallate head group, which can be used for an expansion to two-dimensional coordination networks. Second, 1 and 1,2-dipal-mitoyl-sn-glycero-3-phosphocholine were mixed to prepare the liposomes. Finally, CPsomes were obtained by the addition of transition-metal ions (M) to form unilamellar faceted liposomes with plain CP raft domains with Mn-CN-M linkages. The concentration of 1 influences the size of the CP raft domains and the shape of the CPsomes. The synthesis of coordination polymers in lipid bilayers is a novel approach for the construction of artificial architectures as raft domains, for example, in cell membranes..
65. Daniel Aravena, Zulema Arcís Castillo, M. Carmen Muñoz, Ana B. Gaspar, Ko Yoneda, Ryo Otani, Akio Mishima, Susumu Kitagawa, Masaaki Ohba, José Antonio Real, Eliseo Ruiz, Guest modulation of spin-crossover transition temperature in a porous Iron(II) metal-organic framework
Experimental and periodic DFT studies, Chemistry - A European Journal, 10.1002/chem.201402292, 20, 40, 12864-12873, 2014.09, The synthesis, structure, and magnetic properties of three clathrate derivatives of the spin-crossover porous coordination polymer {Fe(pyrazine)[Pt(CN)4]} (1) with five-membered aromatic molecules furan, pyrrole, and thiophene is reported. The three derivatives have a cooperative spin-crossover transition with hysteresis loops 14-29?K wide and average critical temperatures Tc=201?K (1fur), 167?K (1pyr), and 114.6?K (1thio) well below that of the parent compound 1 (Tc=295?K), confirming stabilization of the HS state. The transition is complete and takes place in two steps for 1fur, while 1pyr and 1thio show 50?% spin transition. For 1fur the transformation between the HS and IS (middle of the plateau) phases occurs concomitantly with a crystallographic phase transition between the tetragonal space groups P4/mmm and I4/mmm, respectively. The latter space group is retained in the subsequent transformation involving the IS and the LS phases. 1pyr and 1thio display the tetragonal P4/mmm and orthorhombic Fmmm space groups, respectively, in both HS and IM phases. Periodic calculations using density functional methods for 1fur, 1pyr, 1thio, and previously reported derivatives 1CS2, 1I, 1bz(benzene), and 1pz(pyrazine) have been carried out to investigate the electronic structure and nature of the host-guest interactions as well as their relationship with the changes in the LS-HS transition temperatures of 1Guest. Geometry-optimized lattice parameters and bond distances in the empty host 1 and 1Guest clathrates are in general agreement with the X-ray diffraction data. The concordance between the theoretical results and the experimental data also comprises the guest molecule orientation inside the host and intermolecular distances. Furthermore, a general correlation between experimental Tc and calculated LS-HS electronic energy gap was observed. Finally, specific host-guest interactions were studied through interaction energy calculations and crystal orbital displacement (COD) curve analysis..
66. Kazuki Kajitani, Tomomi Koshiyama, Akihiro Hori, Ryo Otani, Akio Mishima, Kohei Torikai, Makoto Ebine, Tohru Oishi, Masaki Takata, Susumu Kitagawa, Masaaki Ohba, Guest responsivity of a two-dimensional coordination polymer incorporating a cholesterol-based co-ligand, Dalton Transactions, 10.1039/c3dt51465j, 42, 45, 15893-15897, 2013.12, To implement specific guest responsivity, a hydrophobic cholesterol-based co-ligand, cholest-5-en-3-yl-4-isonicotinate (Cholpy), was incorporated into a two-dimensional Hofmann-type Co(ii)Ni(ii) coordination polymer. The chemically programmed structure successfully demonstrated the unique guest response with remarkable chromatic changes..
67. Ryo Otani, Susumu Kitagawa, Masaaki Ohba, Coordination pillared layers using a dinuclear Mn(V) complex as a secondary building unit, Polyhedron, 10.1016/j.poly.2012.08.006, 52, 591-597, 2013.03, Coordination pillared layers (CPLs) are among the most attractive framework compounds displaying unique porous properties depending on their components. Three-dimensional Hofmann-type porous coordination polymers consisting of pillared cyanide-bridged layers with a tetracyanometallate anion [M II(CN)4]2- (M = Ni, Pd, Pt) as a secondary building unit (SBU) are the representative functional CPLs. In this paper, we report a new synthetic strategy for constructing CPLs using a new SBU linking two tetracyanometallate complexes, [{MnV(N)(CN)4} 2(bpy)]4- (bpy = 4,4′-bipyridyl). The [Mn V(N)(CN)4]2- part in the SBU permits expansion of the 2-D cyanide-bridged layers and the pillar part bpy simultaneously links the layers. Two CPLs, [MII(bpy){MnV(N)(CN) 4(bpy)1/2}]·MeCN·H2O (M = Zn, Cd), were synthesized by applying the SBU and characterized by X-ray single-crystal structural analysis and gas adsorption measurements..
68. Ryo Otani, Masashi Arai, Hisayoshi Ohba, Akihiro Hori, Masaki Takata, Susumu Kitagawa, Masaaki Ohba, Modulation of the interlayer structures and magnetic behavior of 2D spin-crossover coordination polymers [FeII(L)2Pt II(CN)4], European Journal of Inorganic Chemistry, 10.1002/ejic.201201204, 5-6, 738-744, 2013.02, Two 2D Hofmann-type spin-crossover coordination polymers, [Fe(stpy) 2Pt(CN) 4]·0.5MeOH (stpy = 4-styrylpyridine; 1) and [Fe(pep) 2Pt(CN) 4] {pep = 4-(2-phenylethyl)pyridine; 2}, have been prepared by using long co-ligands with different flexibilities. These compounds form 3D interdigitate structures based on 2D layers extended by Pt-CN-Fe linkages with different interlayer structures depending on the nature of the axial co-ligand. The stpy co-ligand forms one-directional π-π networks between the layers, whereas pep forms twodirectional π-π networks as a result of its perpendicularly twisted structure. Coordination polymer 1 exhibits a half-spin transition with Tc ↓ = 106 K and Tc ↑ = 110 K. In contrast, coordination polymer 2 shows a sharp, two-step spin transition in the temperature range 184-236 K. The difference in spintransition behavior is discussed in terms of the interlayer packing structure..
69. Ryo Otani, Masashi Arai, Akihiro Hori, Masaki Takata, Shinji Kitao, Makoto Seto, Susumu Kitagawa, Masaaki Ohba, Modulation of Spin-Crossover Behavior in an Elongated and Flexible Hofmann-Type Porous Coordination Polymer, Journal of Inorganic and Organometallic Polymers and Materials, 10.1007/s10904-012-9747-z, 23, 1, 104-110, 2013.01, Three porous coordination polymers {Fe(dpa)[Pt(CN)4]·G·nH2O} (1-G; dpa = 1,2-di(4-pyridyl)ethane, G = dpa, bibenzyl (bbz) and stilbene (stb)) have been prepared by using a long and flexible ligand dpa. These compounds formed analogous 3-D elongated Hofmann-type frameworks based on 2-D planar layers extended by Pt-CN-Fe linkages with dpa as flexible pillar ligands. 1-dpa showed a characteristic three-step spin transition (ST) in the temperature range 180-240 K. The ST behavior was reversibly modulated by dehydration and hydration processes in keeping with the three steps. 1-bbz and 1-stb exhibited a gradual three-step ST over the range 80-200 K and an abrupt ST with Tc = 163 K. The guest-dependent cooperativity of the ST behavior is discussed by considering the flexibility of the framework and guest molecules..
70. Francisco J. Muñoz Lara, Ana B. Gaspar, Daniel Aravena, Eliseo Ruiz, M. Carmen Muñoz, Masaaki Ohba, Ryo Otani, Susumu Kitagawa, José A. Real, Enhanced bistability by guest inclusion in Fe(ii) spin crossover porous coordination polymers, Chemical Communications, 10.1039/c2cc31048a, 48, 39, 4686-4688, 2012.05, Inclusion of thiourea guest molecules in the tridimensional spin crossover porous coordination polymers {[Fe(pyrazine)[M(CN) 4]} (M = Pd, Pt) leads to novel clathrates exhibiting unprecedented large thermal hysteresis loops of ca. 60 K wide centered near room temperature..
71. J. Alberto Rodríguez-Velamazán, Miguel A. González, José A. Real, Miguel Castro, M. Carmen Muñoz, Ana B. Gaspar, Ryo Otani, Masaaki Ohba, Ko Yoneda, Yuh Hijikata, Nobuhiro Yanai, Motohiro Mizuno, Hideo Ando, Susumu Kitagawa, A switchable molecular rotator
Neutron spectroscopy study on a polymeric spin-crossover compound, Journal of the American Chemical Society, 10.1021/ja206228n, 134, 11, 5083-5089, 2012.03, A quasielastic neutron scattering and solid-state 2H NMR spectroscopy study of the polymeric spin-crossover compound {Fe(pyrazine)[Pt(CN) 4]} shows that the switching of the rotation of a molecular fragment-the pyrazine ligand-occurs in association with the change of spin state. The rotation switching was examined on a wide time scale (10 -13-10 -3 s) by both techniques, which clearly demonstrated the combination between molecular rotation and spin-crossover transition under external stimuli (temperature and chemical). The pyrazine rings are seen to perform a 4-fold jump motion about the coordinating nitrogen axis in the high-spin state. In the low-spin state, however, the motion is suppressed, while when the system incorporates benzene guest molecules, the movements of the system are even more restricted..
72. Ming Hu, Shuhei Furukawa, Ryo Otani, Hiroaki Sukegawa, Yoshihiro Nemoto, Julien Reboul, Susumu Kitagawa, Yusuke Yamauchi, Synthesis of Prussian blue nanoparticles with a hollow interior by controlled chemical etching, Angewandte Chemie - International Edition, 10.1002/anie.201105190, 51, 4, 984-988, 2012.01, A facile route has been found to prepare Prussian blue (PB) hollow particles with a cubic shape (see picture). With PB mesocrystals used as a starting material, hollow interiors were created through controlled chemical etching in the presence of poly(vinylpyrrolidone). The hollow cavities and particle sizes could be tuned by changing the synthetic conditions, and the original PB crystallinity was preserved even after formation of interior hollows..
73. Ryo Otani, Ko Yoneda, Shuhei Furukawa, Nao Horike, Susumu Kitagawa, Ana B. Gaspar, M. Carmen Muñoz, José A. Real, Masaaki Ohba, Precise control and consecutive modulation of spin transition temperature using chemical migration in porous coordination polymers, Journal of the American Chemical Society, 10.1021/ja111674c, 133, 22, 8600-8605, 2011.06, Precise control of spin transition temperature (Tc) is one of the most important challenges in molecular magnetism. A Hofmann-type porous coordination polymer {Fe(pz)[PtII(CN)4]} (1; pz = pyrazine) exhibited cooperative spin transition near room temperature (T cup = 304 K and Tcdown = 284 K) and its iodine adduct {Fe(pz)[PtII/IV(CN)4(I)]} (1-I), prepared by oxidative addition of iodine to the open metal sites of Pt II, raised the Tc by 100 K. DSC and microscopic Raman spectra of a solid mixture of 1-I and 1 revealed that iodine migrated from 1-I to 1 through the grain boundary after heating above 398 K. We have succeeded in precisely controlling the iodine content of {Fe(pz)[Pt(CN)4(I) n]} (1-In; n = 0.0-1.0), which resulted in consecutive modulation of Tc in the range 300-400 K while maintaining the hysteresis width. Furthermore, it was demonstrated that iodine migration in the solid mixture was triggered by the spin transition of 1-I. The magnetically bistable porous framework decorating guest interactive open-metal-site in the pore surface makes it possible to modulate Tc ad arbitrium through unique postsynthetic method using iodine migration..
74. Gloria Agusti, Ryo Otani, Ko Yoneda, Ana B. Gaspar, Masaaki Ohba, Juan F. Sánchez-Royo, M. Carmen Muñoz, Susumu Kitagawa, José A. Real, Oxidative addition of halogens on open metal sites in a microporous spin-crossover coordination polymer, Angewandte Chemie - International Edition, 10.1002/anie.200904379, 48, 47, 8944-8947, 2009.11, Mixing with the guests: Exposure of the porous spin-crossover framework {Fe(pz)[Ptll(CN)4]}to X2(pz=pyrazine; X2=Cl2, Br2, and 12) leads to incorporation of the halides in the coordi natively unsaturated [Ptll(CN)4]2- moieties through oxidative addition, thus affording the mixed-valence series {Fe(pz)[Ptll/IV(CN)4(X)]], which features quite distinct cooperative spin-transition properties..


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