| 1. |
Xiaopeng Zhang, Wen-Huang Xu, Wenwei Zheng, Sheng-Qun Su, Yu-Bo Huang, Qirui Shui, Tianchi Ji, Mikoto Uematsu, Qian Chen, Masashi Tokunaga, Kaige Gao, Atsushi Okazawa, Shinji Kanegawa, Shu-Qi Wu, Osamu Sato, Magnetoelectricity Enhanced by Electron Redistribution in a Spin Crossover [FeCo] Complex, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/jacs.3c02977, 145, 29, 15647-15651, 2023.07, Molecular-basedmagnetoelectric materials are among themost promisingmaterials for next-generation magnetoelectric memory devices. However,practical application of existing molecular systems has proven difficultlargely because the polarization change is far lower than the practicalthreshold of the ME memory devices. Herein, we successfully obtainedan [FeCo] dinuclear complex that exhibits a magnetic field-inducedspin crossover process, resulting in a significant polarization changeof 0.45 & mu;C cm(-2). Mo''ssbauer spectroscopyand theoretical calculations suggest that the asymmetric structuralchange, coupled with electron redistribution, leads to the observedpolarization change. Our approach provides a new strategy toward rationallyenhancing the polarization change.. |
| 2. |
Pritam Sadhukhan, Shu-Qi Wu, Shinji Kanegawa, Sheng-Qun Su, Xiaopeng Zhang, Takumi Nakanishi, Jeremy Ian Long, Kaige Gao, Rintaro Shimada, Hajime Okajima, Akira Sakamoto, Joy G. Chiappella, Myron S. Huzan, Thomas Kroll, Dimosthenis Sokaras, Michael L. Baker, Osamu Sato, Energy conversion and storage via photoinduced polarization change in non-ferroelectric molecular [CoGa] crystals, Nature Communications, 10.1038/s41467-023-39127-8, 14, 1, 3394, 2023.06, Abstract
To alleviate the energy and environmental crisis, in the last decades, energy harvesting by utilizing optical control has emerged as a promising solution. Here we report a polar crystal that exhibits photoenergy conversion and energy storage upon light irradiation. The polar crystal consists of dinuclear [CoGa] molecules, which are oriented in a uniform direction inside the crystal lattice. Irradiation with green light induces a directional intramolecular electron transfer from the ligand to a low-spin CoIII centre, and the resultant light-induced high-spin CoII excited state is trapped at low temperature, realizing energy storage. Additionally, electric current release is observed during relaxation from the trapped light-induced metastable state to the ground state, because the intramolecular electron transfer in the relaxation process is accompanied with macroscopic polarization switching at the single-crystal level. It demonstrates that energy storage and conversion to electrical energy is realized in the [CoGa] crystals, which is different from typical polar pyroelectric compounds that exhibit the conversion of thermal energy into electricity.. |
| 3. |
Yao Li, Mohammad Khurram Javed, Shu-Qi Wu, Arshia Sulaiman, Ying-Ying Wu, Zhao-Yang Li, Osamu Sato, Xian-He Bu, Aggregation-induced emission meets magnetic bistability: Synergy between spin crossover and fluorescence in iron(II) complexes, Chinese Chemical Letters, 10.1016/j.cclet.2022.05.006, 34, 4, 107492-107492, 2023.04. |
| 4. |
Feng Cheng, Shuqi Wu, Wenwei Zheng, Shengqun Su, Takumi Nakanishi, Wenhuang Xu, Pritam Sadhukhan, Hibiki Sejima, Shimon Ikenaga, Kaoru Yamamoto, Kaige Gao, Shinji Kanegawa, Osamu Sato, Macroscopic Polarization Change of Mononuclear Valence Tautomeric Cobalt Complexes Through the Use of Enantiopure Ligand, Chemistry – A European Journal, 10.1002/chem.202202161, 28, 59, 2022.08. |
| 5. |
Xue-Ru Wu, Zhi-Kun Liu, Min Zeng, Ming-Xing Chen, Jun Tao, Shu-Qi Wu, Hui-Zhong Kou, Fluorescence emission modulation in cyanido-bridged Fe(II) spin crossover coordination polymers, Science China Chemistry, 10.1007/s11426-022-1294-8, 65, 8, 1569-1576, 2022.07. |
| 6. |
Sheng-Qun Su, Shu-Qi Wu, Yu-Bo Huang, Wen-Huang Xu, Kai-Ge Gao, Atsushi Okazawa, Hajime Okajima, Akira Sakamoto, Shinji Kanegawa, Osamu Sato, Photoinduced Persistent Polarization Change in a Spin Transition Crystal., Angewandte Chemie (International ed. in English), 10.1002/anie.202208771, e202208771, 2022.07, Using light as a local heat source to induce a temporary pyroelectric current is widely recognized as an effective way to control the polarization of crystalline materials. In contrast, harnessing light directly to modulate the polarization of a crystal via excitation of the electronic bands remains less explored. In this study, we report an FeII spin crossover crystal that exhibits photoinduced macroscopic polarization change upon excitation by green light. When the excited crystal relaxes to the ground state, the corresponding pyroelectric current can be detected. An analysis of the structures, magnetic properties and the Mössbauer and infrared spectra of the complex, supported by calculations, revealed that the polarization change is dictated by the directional relative movement of ions during the spin transition process. The spin transition and polarization change occur simultaneously in response to light stimulus, which demonstrates the enormous potential of polar spin crossover systems in the field of optoelectronic materials.. |
| 7. |
Arshia Sulaiman, Yi-Zhan Jiang, Mohammad Khurram Javed, Shu-Qi Wu, Zhao-Yang Li, Xian-He Bu, Tuning of spin-crossover behavior in two cyano-bridged mixed-valence (Fe2FeII)-Fe-III trinuctear complexes based on a Tp(R) tigand, INORGANIC CHEMISTRY FRONTIERS, 10.1039/d1qi01086g, 9, 2, 241-248, 2022.01, Spin-crossover (SCO) complexes have been extensively studied in the past few decades owing to their bistable nature which find application in a myriad of areas. In order to enhance and optimize the SCO behavior, considerable attention is being paid towards the synthesis of discrete multinuclear spin-crossover complex systems. Here, two mixed-valence (Fe2FeII)-Fe-III trinuclear complexes of the formula {[Fe-II(TPMA)][Fe-III(Tp(R))(CN)(3)](2)}center dot MeOH center dot 2H(2)O (1) and {[Fe-II(TPMA)][Fe-III(Tp(R))(CN)(3)](2)}center dot H2O (2) [where TPMA = tris(2-pyridylmethyl)amine, Tp = tris(pyrazol-1-yl)borate, R = 3,5-dimethyl for 1 and H for 2] were synthesized and characterized. Magnetic measurements confirmed that complex 1 undergoes SCO at a high temperature (T-1/2 = 410 K for the fresh sample and T-1/2 = 406 K for the dried sample), while complex 2 displays near room temperature SCO (T-1/2 = 283 K for the fresh sample and T-1/2(up arrow) = 283 K and T-1/2(down arrow) = 257 K for the dried sample). To the best of our knowledge, complex 1 has the highest transition temperature reported among trinuclear SCO complexes so far, which is a remarkable feature of multinuclear materials. Slight structural modifications tend to upend the SCO behavior which paves the way for fine tuning SCO.. |
| 8. |
Yun Li, Shu-Qi Wu, Jin-Peng Xue, Xiao-Lei Wang, Osamu Sato, Zi-Shuo Yao, Jun Tao, A Molecular Crystal Shows Multiple Correlated Magnetic and Ferroelectric Switchings, CCS Chemistry, 10.31635/ccschem.020.202000489, 3, 9, 2464-2472, 2021.09. |
| 9. |
Pritam Sadhukhan, Shu-Qi Wu, Jeremy Ian Long, Takumi Nakanishi, Shinji Kanegawa, Kaige Gao, Kaoru Yamamoto, Hajime Okajima, Akira Sakamoto, Michael L Baker, Thomas Kroll, Dimosthenis Sokaras, Atsushi Okazawa, Norimichi Kojima, Yoshihito Shiota, Kazunari Yoshizawa, Osamu Sato, Manipulating electron redistribution to achieve electronic pyroelectricity in molecular [FeCo] crystals., Nature communications, 10.1038/s41467-021-25041-4, 12, 1, 4836-4836, 2021.08, Pyroelectricity plays a crucial role in modern sensors and energy conversion devices. However, obtaining materials with large and nearly constant pyroelectric coefficients over a wide temperature range for practical uses remains a formidable challenge. Attempting to discover a solution to this obstacle, we combined molecular design of labile electronic structure with the crystal engineering of the molecular orientation in lattice. This combination results in electronic pyroelectricity of purely molecular origin. Here, we report a polar crystal of an [FeCo] dinuclear complex exhibiting a peculiar pyroelectric behavior (a substantial sharp pyroelectric current peak and an unusual continuous pyroelectric current at higher temperatures) which is caused by a combination of Fe spin crossover (SCO) and electron transfer between the high-spin Fe ion and redox-active ligand, namely valence tautomerism (VT). As a result, temperature dependence of the pyroelectric behavior reported here is opposite from conventional ferroelectrics and originates from a transition between three distinct electronic structures. The obtained pyroelectric coefficient is comparable to that of polyvinylidene difluoride at room temperature.. |
| 10. |
Hui-Miao Li, Gui-Ming Zhong, Shu-Qi Wu, Osamu Sato, Xiao-Yan Zheng, Zi-Shuo Yao, Jun Tao, Adjusting Rotational Behavior of Molecular Rotors by a Rational Tuning of Molecular Structure, INORGANIC CHEMISTRY, 10.1021/acs.inorgchem.1c00558, 60, 11, 8042-8048, 2021.06, Many crystalline molecular rotors have been developed in the past decades. However, manipulating the rotational gesture that intrinsically controls the physical performance of materials remains a challenge. Herein, we report a series of crystalline rotors whose rotational gestures can be modulated by modifying the structures of molecular stators. In these dynamic crystals, the ox(2-) (ox(2-) = oxalate anion) behave as molecular rotators performing axial-free rotation in cavities composed of five complex cations, [M-II(en)(3)](2+) (en = ethylenediamine). The structure of [M-II(en)(3)](2+) that serves as a molecular stator can be tuned by varying the metal center with different ionic radii, consequently altering the chemical environment around the molecular rotator. Owing to the quasi-transverse isotropy of ox(2-) and multiple hydrogen-bond interactions around it, the molecular rotator exhibits unusual motional malleability, i.e., it can rotate either longitudinally in the compound of Zn-II, or with a tilt angle of 42 degrees in the compound of Fe-II, or even laterally in the compound of Cd-II. The atypical dynamic behavior demonstrated here provides a new chance for the development of exquisite crystalline molecular rotors with advanced tunable functionalities.. |
| 11. |
Sheng-Qun Su, Shu-Qi Wu, Masato Hagihala, Ping Miao, Zhijian Tan, Shuki Torii, Takashi Kamiyama, Tongtong Xiao, Zhenxing Wang, Zhongwen Ouyang, Yuji Miyazaki, Motohiro Nakano, Takumi Nakanishi, Jun-Qiu Li, Shinji Kanegawa, Osamu Sato,, Water-oriented magnetic anisotropy transition, Nat. Commun., https://doi.org/10.1038/s41467-021-23057-4, 2021.05. |
| 12. |
Sheng-Qun Su, Shu-Qi Wu, Masato Hagihala, Ping Miao, Zhijian Tan, Shuki Torii, Takashi Kamiyama, Tongtong Xiao, Zhenxing Wang, Zhongwen Ouyang, Yuji Miyazaki, Motohiro Nakano, Takumi Nakanishi, Jun-Qiu Li, Shinji Kanegawa, Osamu Sato, Water-oriented magnetic anisotropy transition., Nature communications, 10.1038/s41467-021-23057-4, 12, 1, 2738-2738, 2021.05, Water reorientation is essential in a wide range of chemical and biological processes. However, the effects of such reorientation through rotation around the metal-oxygen bond on the chemical and physical properties of the resulting complex are usually ignored. Most studies focus on the donor property of water as a recognized σ donor-type ligand rather than a participant in the π interaction. Although a theoretical approach to study water-rotation effects on the functionality of a complex has recently been conducted, it has not been experimentally demonstrated. In this study, we determine that the magnetic anisotropy of a Co(II) complex can be effectively controlled by the slight rotation of coordinating water ligands, which is achieved by a two-step structural phase transition. When the water molecule is rotated by 21.2 ± 0.2° around the Co-O bond, the directional magnetic susceptibility of the single crystal changes by approximately 30% along the a-axis due to the rotation of the magnetic anisotropy axis through the modification of the π interaction between cobalt(II) and the water ligand. The theoretical calculations further support the hypothesis that the reorientation of water molecules is a key factor contributing to the magnetic anisotropy transition of this complex.. |
| 13. |
Takumi Nakanishi, Yuta Hori, Shuqi Wu, Hiroyasu Sato, Atsushi Okazawa, Norimichi Kojima, Yusuke Horie, Hajime Okajima, Akira Sakamoto, Yoshihito Shiota, Kazunari Yoshizawa, Osamu Sato, Three-Step Spin State Transition and Hysteretic Proton Transfer in the Crystal of an Iron(II) Hydrazone Complex, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.202006763, 59, 35, 14781-14787, 2020.08, A proton-electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi-step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and yr electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric-like arrangement.. |
| 14. |
Sheng-Qun Su, Shu-Qi Wu, Michael L. Baker, Peter Bencok, Nobuaki Azuma, Yuji Miyazaki, Motohiro Nakano, Soonchul Kang, Yoshihito Shiota, Kazunari Yoshizawa, Shinji Kanegawa, Osamu Sato, Quenching and Restoration of Orbital Angular Momentum through a Dynamic Bond in a Cobalt(II) Complex, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/jacs.0c02257, 142, 26, 11434-11441, 2020.07, Orbital angular momentum plays a vital role in various applications, especially magnetic and spintronic properties. Therefore, controlling orbital angular momentum is of paramount importance to both fundamental science and new technological applications. Many attempts have been made to modulate the ligand-field-induced quenching effects of orbital angular momentum to manipulate magnetic properties. However, to date, reported changes in the magnitude of orbital angular momentum are small in both molecular and solid-state magnetic materials. Moreover, no effective methods currently exist to modulate orbital angular momentum. Here we report a dynamic bond approach to realize a large change in orbital angular momentum. We have developed a Co(II) complex that exhibits coordination number switching between six and seven. This cooperative dynamic bond switching induces considerable modulation of the ligand field, thereby leading to substantial quenching and restoration of the orbital angular momentum. This switching mechanism is entirely different from those of spin-crossover and valence tautomeric compounds, which exhibit switching in spin multiplicity.. |
| 15. |
Xiao-Lei Wang, Jin-Peng Xue, Xiao-Peng Sun, Yan-Xin Zhao, Shu-Qi Wu, Zi-Shuo Yao, Jun Tao, Giant Single-Crystal Shape Transformation with Wide Thermal Hysteresis Actuated by Synergistic Motions of Molecular Cations and Anions, CHEMISTRY-A EUROPEAN JOURNAL, 10.1002/chem.202000845, 26, 30, 6778-6783, 2020.05, Manipulating the collective molecular movements to implement macroscopic mechanical response of bulk material is attractive and challenging. Here, an organic-inorganic hybrid single crystal is synthesized, which exhibits a giant macroscopic shape transformation with a remarkable thermal hysteretic feature. The colossal anisotropic shape change, which manifests as an abrupt elongation of ca. 9 % along the crystallographic c-axis and a concomitant contraction of ca. 9 % in a perpendicular direction, is induced by a significant reorientation of imidazolium, accompanied with a substantial configurational variation in CuBr42- complex anions. The synergistic motions of both the molecular cations and anions engender a remarkable large thermal hysteresis (>30 K) in the shape transformation of the single crystal, implying that this material may play a role in alternating memory media. Furthermore, due to the stable crystal lattice, a single crystal that demonstrates naked-eye detectable large shape transformation was used as a thermal actuator to spontaneously control an electric circuit by temperature variation.. |
| 16. |
Shu-Qi Wu, Meijiao Liu, Kaige Gao, Shinji Kanegawa, Yusuke Horie, Genki Aoyama, Hajime Okajima, Akira Sakamoto, Michael L. Baker, Myron S. Huzan, Peter Bencok, Tsukasa Abe, Yoshihito Shiota, Kazunari Yoshizawa, Wenhuang Xu, Hui-Zhong Kou, Osamu Sato, Macroscopic Polarization Change via Electron Transfer in a Valence Tautomeric Cobalt Complex, Nature Communications, https://doi.org/10.1038/s41467-020-15988-1, 2020.04, Polarization change induced by directional electron transfer attracts wide attention for its fast switching rate and potential light control. Here, electronic pyroelectricity was investigated in the crystal of a mononuclear complex, [Co(phendiox)(rac-cth)](ClO4)·0.5EtOH (1·0.5EtOH, H2phendiox = 9, 10-dihydroxyphenanthrene, rac-cth = racemic 5, 5, 7, 12, 12, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradecane), which undergoes a two-step valence tautomerism (VT). Correspondingly, pyroelectric current exhibited double peaks in the same temperature domain with the polarization change consistent with the change in dipole moments during the VT process. The time-resolved IR spectroscopy showed that the photo-induced metastable state can be generated within 150 ps at 190 K. Such state can be trapped for tens of minutes at 7 K, revealing that photo-induced polarization change could be realized in this system. These results directly demonstrate that the change in the molecular dipole moments induced by intramolecular electron transfer can introduce a macroscopic polarization change in VT compounds.. |
| 17. |
Arpan Mondal, Shu-Qi Wu, Osamu Sato, Sanjit Konar, Effect of Axial Ligands on Easy-Axis Anisotropy and Field-Induced Slow Magnetic Relaxation in Heptacoordinated Fe-II Complexes, CHEMISTRY-A EUROPEAN JOURNAL, 10.1002/chem.201905166, 26, 21, 4780-4789, 2020.04, A rational approach to modulating easy-axis magnetic anisotropy by varying the axial donor ligand in heptacoordinated Fe-II complexes has been explored. In this series of complexes with formulae of [Fe(H4L)(NCS)(2)].3 DMF.0.5 H2O (1), [Fe(H4L)(NCSe)(2)].3 DMF.0.5 H2O (2), and [Fe(H4L)(NCNCN)(2)].DMF.H2O (3) [H4L=2,2 '-{pyridine-2,6-diylbis(ethan-1-yl-1-ylidene)}bis(N-phenylhydrazinecarboxamide)], the axial positions are successively occupied by different nitrogen-based pi-donor ligands. Detailed dc and ac magnetic susceptibility measurements reveal the existence of easy-axis magnetic anisotropy for all of the complexes, with 1 [U-eff=21 K, tau(0)=1.72x10(-6) s] and 2 [U-eff=25 K, tau(0)=2.25x10(-6) s] showing field-induced slow magnetic relaxation behavior. However, both experimental studies and theoretical calculations indicate the magnitude of the D value of complex 3 to be larger than those of complexes 1 and 2 due to the axial bond angle being smaller than that for an ideal geometry. Detailed analysis of the field and temperature dependences of relaxation time for 1 and 2 has revealed that multiple relaxation processes (quantum tunneling of magnetization, direct, and Raman) are involved in slow magnetic relaxation for both of these complexes. Magnetic dilution experiments support the role of intermolecular short contacts.. |
| 18. |
Shu-Qi Wu, Meijiao Liu, Kaige Gao, Shinji Kanegawa, Yusuke Horie, Genki Aoyama, Hajime Okajima, Akira Sakamoto, Michael L. Baker, Myron S. Huzan, Peter Bencok, Tsukasa Abe, Yoshihito Shiota, Kazunari Yoshizawa, Wenhuang Xu, Hui-Zhong Kou, Osamu Sato, Macroscopic Polarization Change via Electron Transfer in a Valence Tautomeric Cobalt Complex, NATURE COMMUNICATIONS, 10.1038/s41467-020-15988-1, 11, 1, 2020.04, Polarization change induced by directional electron transfer attracts considerable attention owing to its fast switching rate and potential light control. Here, we investigate electronic pyroelectricity in the crystal of a mononuclear complex, [Co(phendiox)(rac-cth)](ClO4).0.5EtOH (1.0.5EtOH, H(2)phendiox=9, 10-dihydroxyphenanthrene, rac-cth = racemic 5, 5, 7, 12, 12, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradecane), which undergoes a two-step valence tautomerism (VT). Correspondingly, pyroelectric current exhibits double peaks in the same temperature domain with the polarization change consistent with the change in dipole moments during the VT process. Time-resolved Infrared (IR) spectroscopy shows that the photo-induced metastable state can be generated within 150ps at 190K. Such state can be trapped for tens of minutes at 7K, showing that photo-induced polarization change can be realized in this system. These results directly demonstrate that a change in the molecular dipole moments induced by intramolecular electron transfer can introduce a macroscopic polarization change in VT compounds. Polarization change from directional electron transfer attracts considerable attention owing to its fast switching rate and potential light control. Here, the authors provide a proof-of-concept of electronic pyroelectricity induced by intramolecular electron transfer in the single crystal of a valence tautomeric compound.. |
| 19. |
Junqiu Li, Shuqi Wu, Shengqun Su, ShinjShinji Kanegawa, Osamu Sato, Manipulating Slow Magnetic Relaxation by Light in a Charge Transfer {Fe2Co} Complex, CHEMISTRY-A EUROPEAN JOURNAL, 10.1002/chem.202000154, 26, 15, 3259-3263, 2020.03, Some cyanide-bridged complexes are known for exhibiting slow magnetic relaxation behavior in a light-induced metastable state. Herein, an unexpected reverse effect is observed for the first time in the S=1/2 {Fe-LS(II)-Co-LS(III)-Fe-LS(III)} (HS=high spin, LS=low spin) ground state of a novel V-shaped trinuclear cyanide-bridged {Fe2Co} complex. In this complex, light-switchable iron-cobalt charge transfer with repeatable off/on switching of slow magnetic relaxation is discovered upon alternating laser irradiation at 785 and 560 nm. An important characteristic of the present compound is that the S=1/2 ground state exhibits slow magnetic relaxation before irradiation, whereas this is accelerated after irradiation. This is different from the typical behavior, where the light-induced metastable state exhibits slow magnetic relaxation.. |
| 20. |
Mei-Jiao Liu, Shu-Qi Wu, Jia-Xin Li, Yi-Quan Zhang, Osamu Sato, Hui-Zhong Kou, Structural Modulation of Fluorescent Rhodamine-Based Dysprosium(III) Single-Molecule Magnets, INORGANIC CHEMISTRY, 10.1021/acs.inorgchem.9b03105, 59, 4, 2308-2315, 2020.02, Two rhodamine 6G-based mononuclear dysprosium complexes, [DY(L-R)(L-A)(2)](ClO4)(3)center dot Et2O center dot 1.5MeOH center dot 0.5H(2)O (1) and [Dy(L-R)-(H2O)(4)(MeCN)](ClO4)(3)center dot 2H(2)O center dot MeCN (2) (L-R = salicylaldehyde rhodamine 6G hydrazone, L-A = 2-pyridylcarboxaldehyde benzoyl hydrazone), are synthesized, aiming at improving the magnetic behavior by modulating their coordination environment. Both complexes own one exclusive short Dy-O-phenoxy coordination bond as the predominant bond and exhibit singlemolecule magnet behavior under zero dc field with the energy barrier (U-eff/k(B)) of 90 K (1) and 320 K (2) and apparent hysteresis at 1.9 K. The ab initio calculations indicate that the short Dy-O-phenoxy bond determines the direction of magnetic anisotropic axis for 1 and 2. The quantum tunneling of magnetization (QTM) between the ground Kramers doublets (KDs) in 1 cannot be neglected, leading to an experimental U-eff/k(B) much lower than the calculated energy of the first excited state (318.2 K). For 2, the stronger magnetic anisotropy and negligible QTM between the ground KDs guarantees that the energy barrier is close to the calculated energy of first KDs (320.8 K). On the other hand, the presence of ring-opened xanthene moiety makes complexes 1 and 2 in the solid state emit red light with emission bands of 645 and 658 nm, respectively.. |
| 21. |
Wei Huang, Shuqi Wu, Xiangwei Gu, Yao Li, Atsushi Okazawa, Norimichi Kojima, Shinya Hayami, Michael L. Baker, Peter Bencok, Mariko Noguchi, Yuji Miyazaki, Motohiro Nakano, Takumi Nakanishi, Shinji Kanegawa, Yuji Inagaki, Tatsuya Kawae, Gui-Lin Zhuang, Yoshihito Shiota, Kazunari Yoshizawa, Dayu Wu, Osamu Sato, Temperature dependence of spherical electron transfer in a nanosized [Fe-14] complex, NATURE COMMUNICATIONS, 10.1038/s41467-019-13279-y, 10, 2019.12, The study of transition metal clusters exhibiting fast electron hopping or delocalization remains challenging, because intermetallic communications mediated through bridging ligands are normally weak. Herein, we report the synthesis of a nanosized complex, [Fe(Tp) (CN)(3)](8)[Fe(H2O)(DMSO)](6) (abbreviated as [Fe-14], Tp(-)hydrotris(pyrazolyl)borate; DMSO, dimethyl sulfoxide), which has a fluctuating valence due to two mobile d-electrons in its atomic layer shell. The rate of electron transfer of [Fe-14] complex demonstrates the Arrhenius-type temperature dependence in the nanosized spheric surface, wherein high-spin centers are ferromagnetically coupled, producing an S=14 ground state. The electronhopping rate at room temperature is faster than the time scale of Mossbauer measurements ( |
| 22. |
Zi-Shuo Yao, Hanxi Guan, Yoshihito Shiota, Chun-Ting He, Xiao-Lei Wang, Shu-Qi Wu, Xiaoyan Zheng, Sheng-Qun Su, Kazunari Yoshizawa, Xueqian Kong, Osamu Sato, Jun Tao, Giant anisotropic thermal expansion actuated by thermodynamically assisted reorientation of imidazoliums in a single crystal, NATURE COMMUNICATIONS, 10.1038/s41467-019-12833-y, 10, 2019.10, Materials demonstrating unusual large positive and negative thermal expansion are fascinating for their potential applications as high-precision microscale actuators and thermal expansion compensators for normal solids. However, manipulating molecular motion to execute huge thermal expansion of materials remains a formidable challenge. Here, we report a single-crystal Cu(II) complex exhibiting giant thermal expansion actuated by collective reorientation of imidazoliums. The circular molecular cations, which are rotationally disordered at a high temperature and statically ordered at a low temperature, demonstrate significant reorientation in the molecular planes. Such atypical molecular motion, revealed by variable-temperature single crystal X-ray diffraction and solid-state NMR analyses, drives an exceptionally large positive thermal expansion and a negative thermal expansion in a perpendicular direction of the crystal. The consequent large shape change (similar to 10%) of bulk material, with remarkable durability, suggests that this complex is a strong candidate as a microscale thermal actuating material.. |
| 23. |
Takumi Nakanishi, Yuta Hori, Hirorsu Sato, Shu-Qi Wu, Atsushi Okazawa, Norimichi Kojima, Takashi Yamamoto, Yasuaki Einaga, Shinya Hayami, Yusuke Horie, Hajime Okajima, Akira Sakamoto, Yoshihito Shiota, Kazunari Yoshizawa, Osamu Sato, Observation of Proton Transfer Coupled Spin Transition and Trapping of Photoinduced Metastable Proton Transfer State in an Fe(II) Complex, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/jacs.9b07204, 141, 36, 14384-14393, 2019.09, An important technique to realize novel electron- and/or proton-based functionalities is to use a proton-electron coupling mechanism. When either a proton or electron is excited, the other one is modulated, producing synergistic functions. However, although compounds with proton-coupled electron transfer have been synthesized, crystalline molecular compounds that exhibit proton-transfer-coupled spin-transition (PCST) behavior have not been reported. Here, we report the first example of a PCST Fe(II) complex, wherein the proton lies on the N of hydrazone and pyridine moieties in the ligand at high-spin and low-spin Fe(II), respectively. When the Fe(II) complex is irradiated with light, intramolecular proton transfer occurs from pyridine to hydrazone in conjunction with the photoinduced spin transition via the PCST mechanism. Because the light-induced excited high-spin state is trapped at low temperatures in the Fe(II) complex-a phenomenon known as the light-induced excited-spin-state trapping effect-the light-induced proton-transfer state, wherein the proton lies on the N of hydrazone, is also trapped as a metastable state. The proton transfer was accomplished within 50 ps at 190 K. The bistable nature of the proton position, where the position can be switched by light irradiation, is useful for modulating proton-based functionalities in molecular devices.. |
| 24. |
Michael L. Baker, Shu-Qi Wu, Soonchul Kang, Satoshi Matsuzawa, Marie-Anne Arrio, Yasuo Narumi, Takumi Kihara, Tetsuya Nakamura, Yoshinori Kotani, Osamu Sato, Hiroyuki Nojiri, Electron-Transfer Activity in a Cyanide-Bridged Fe-42 Nanomagnet, INORGANIC CHEMISTRY, 10.1021/acs.inorgchem.9b01216, 58, 15, 10160-10166, 2019.08, The ability to switch a molecule between different magnetic states is of considerable importance for the development of new molecular electronic devices. Desirable properties for such applications include a large-spin ground state with an electronic structure that can be controlled via external stimuli. Fe-42 is a cyanide-bridged stellated cuboctahedron of mixed-valence Fe ions that exhibits an extraordinarily large S = 45 spin ground state. We have found that the spin ground state of Fe(42 )can be altered by controlling the humidity and temperature. Dehydration results in a 15 mu B reduction of the saturation magnetization that can be partially recovered upon rehydration. The complementary use of UV-vis, IR, L-2,L-3-edge X-ray absorption spectroscopy and X-ray magnetic circular dichroism is applied to uncover the mechanism for the observed dynamic behavior. It is identified that dehydration is concurrent with metal-to-metal electron transfer between Fe pairs via a cyanide pi hybridization. Upon dehydration, electron transfer occurs from low-spin {Fe-II(Tp)(CN)(3)} sites to high-spin Fe-III centers. The observed reduction in magnetization upon dehydration of Fe-42 is inconsistent with a ferrimagnetic ground state and is proposed to originate from a change in zero-field splitting at electron-reduced high-spin sites.. |
| 25. |
Juan Yuan, Mei-Jiao Liu, Shu-Qi Wu, Xin Zhu, Nan Zhang, Osamu Sato, Hui-Zhong Kou, Substituent effects on the fluorescent spin-crossover Fe(ii) complexes of rhodamine 6G hydrazones, INORGANIC CHEMISTRY FRONTIERS, 10.1039/c9qi00111e, 6, 5, 1170-1176, 2019.05, Two new complexes were constructed via the coordination of fluorophores with Fe(II) ions to study the effects of ligand substituents on fluorescent-spin crossover (SCO) materials. Single-crystal structural determination suggests that the central iron(II) of complexes 1-2 adopted an N4O2 coordination configuration, chelated by two ligands L-1 or L-2. The pi center dot center dot center dot pi stacking interaction between the pi-conjugated xanthene groups of the adjacent ligands for complex 1 is apparently stronger than that for complex 2. Magnetic susceptibility measurements show that complex 1 is high spin, while complex 2 is diamagnetic at room temperature. Interestingly, the desolvated form 1-d of complex 1 exhibits SCO behavior (T-c = 175 K) without hysteresis. Significantly, complex 1-d displays the correlation between the spin crossover and the fluorescence.. |
| 26. |
Juan Yuan, Shu-Qi Wu, Mei-Jiao Liu, Osamu Sato, Hui-Zhong Kou, Rhodamine 6G-Labeled Pyridyl Aroylhydrazone Fe(II) Complex Exhibiting Synergetic Spin Crossover and Fluorescence, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/jacs.8b00103, 140, 30, 9426-9433, 2018.08, Here, we use a pyridinecarbaldehyde rhodamine 6G hydrazone ligand (L) to synthesize an Fe(II) complex 1 for the search of new fluorescent-spin crossover (SCO) materials. Single-crystal structural determinations suggest that the Fe(II) ion is chelated by two ring-opened ligands (L-o) to form a FeN4O2 coordination environment, and intermolecular pi---pi contacts of the xanthene groups connect the adjacent molecules to form a supramolecular one-dimensional chain. Magnetic susceptibility measurements on complex 1 show that three-step SCO takes place in the temperature range of 120-350 K, and its desolvated form 1-d exhibits SCO around room temperature (T-c up arrow = 343 K and T-c down arrow = 303 K) with a wide hysteresis loop of 40 K. Moreover, complex 1-d displays light-induced excited spin-state trapping phenomenon. Intriguingly, the fluorescence intensity of the maximum emission at 560 nm for complex 1-d displays discontinuous variation in the range of 250-400 K, indicative of the occurrence of synergetic fluorescence and SCO.. |
