| 1. |
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.. |
| 2. |
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.. |
| 3. |
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 ( |
| 4. |
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.. |
| 5. |
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.. |
| 6. |
Shu-Qi Wu, Yuji Miyazaki, Motohiro Nakano, Sheng-Qun Su, Zi-Shuo Yao, Hui-Zhong Kou, Osamu Sato, Slow Magnetic Relaxation in a Mononuclear Ruthenium(III) Complex, CHEMISTRY-A EUROPEAN JOURNAL, 10.1002/chem.201702047, 23, 42, 10028-10033, 2017.07, The development of magnetic molecules with long spin reversal/decoherence times highly depends on the understanding of relaxation behavior under different external conditions. Herein, a magnetic study on a Ru-III complex (1) is presented. Detailed analysis of the relaxation time and the magneto-heat capacity data suggests that the resonant phonon trapping process dominates the magnetic relaxation in the crystalline sample of 1, slowing down the spin relaxation rate, as further confirmed by the measurements on a ground sample and frozen solution. Thus, it provides a rare example showing that 4d metal-centered mononuclear compounds without second-order anisotropy can display slow magnetic relaxation.. |
| 7. |
Zi-Shuo Yao, Shu-Qi Wu, Yasutaka Kitagawa, Sheng-Qun Su, You-Gui Huang, Guo-Ling Li, Zhong-Hai Ni, Hiroyuki Nojiri, Yoshihito Shiota, Kazunari Yoshizawa, Soonchul Kang, Shinji Kanegawa, Osamu Sato, Anisotropic Change in the Magnetic Susceptibility of a Dynamic Single Crystal of a Cobalt(II) Complex, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201606165, 56, 3, 717-721, 2017.01, Atypically anisotropic and large changes in magnetic susceptibility, along with a change in crystalline shape, were observed in a Co-II complex at near room temperature. This was achieved by combining oxalate molecules, acting as rotor, and a Co-II ion with unquenched orbital angular momentum. A thermally controlled 908 rotation of the oxalate counter anion triggered a symmetry-breaking ferroelastic phase transition, accompanied by contraction-expansion behavior (ca. 4.5%) along the long axis of a rod-like single crystal. The molecular rotation induced a minute variation in the coordination geometry around the Co-II ion, resulting in an abrupt decrease and a remarkable increase in magnetic susceptibility along the direction perpendicular and parallel to the long axis of the crystal, respectively. Theoretical calculations suggested that such an unusual anisotropic change in magnetic susceptibility was due to a substantial reorientation of magnetic anisotropy induced by slight disruption in the ideal D-3 coordination environment of the complex cation.. |
