【公開日：2025.06.10】【最終更新日：2025.05.26】

課題データ / Project Data

課題番号 / Project Issue Number

24MS1047

利用課題名 / Title

Investigation of photoinduced metastable phases in molecular crystal exhibiting photoinduced polarization switching

利用した実施機関 / Support Institute

自然科学研究機構 分子科学研究所 / IMS

機関外・機関内の利用 / External or Internal Use

外部利用/External Use

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）物質・材料合成プロセス/Molecule & Material Synthesis（副 / Sub）計測・分析/Advanced Characterization

【重要技術領域 / Important Technology Area】（主 / Main）量子・電子制御により革新的な機能を発現するマテリアル/Materials using quantum and electronic control to perform innovative functions（副 / Sub）革新的なエネルギー変換を可能とするマテリアル/Materials enabling innovative energy conversion

キーワード / Keywords

Pyroelectricity, Photoelectricity, Valence Tautomerism, Spin Crossover,熱電材料/ Thermoelectric material,X線回折/ X-ray diffraction,スピン制御/ Spin control

利用者と利用形態 / User and Support Type

利用者名（課題申請者）/ User Name (Project Applicant)

呉 樹旗

所属名 / Affiliation

Institute for Materials Chemistry and Engineering, Kyushu University Division of Fundamental Organic Chemistry

共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes

鄭 文偉,水 棋鋭

ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes

岡野 芳則

利用形態 / Support Type

（主 / Main）機器利用/Equipment Utilization（副 / Sub）-

利用した主な設備 / Equipment Used in This Project

MS-207：単結晶X線回折（微小結晶用）

報告書データ / Report

概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)

Electric polarization is one of the key properties of crystalline materials, with state switching induced by external stimuli like temperature and light leading to various interesting functionalities. Recently, novel heterometallic dinuclear complexes coordinated with a chiral tetraazacyclic ligand (5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) have been developed, exhibiting thermally-, light- and magnetic field-induced polarization switching. In this research, we firstly focus on a dinuclear [CoCr](AsF₆)₃ complex showing a remarkable light-induced valence tautomerism, with metastable HS molecules persisting up to 60 K. Pyroelectric measurements after light irradiation at 20 K revealed a polarization change different from the thermally-induced values. This motivated us to study the change in the single-crystal structure at the same condition using the Rigaku HyPix-AFC at IMS. Experimental results indeed revealed the formation of superstructures, which might be correlated to the observed enhancement in polarization. Similar measurements were also performed on a spin-crossover Fe(II) complex (Fe(HL)₂(BBS)·3H₂O, HL = (E)-2-[(6-methoxypyridin-2-yl)methylidene]hydrazine-1-thioamide, BBS = (2S,3S)-2,3-bis(benzoyl)succinate) exhibiting photomagnetic effect and reversal of polarization change upon irradiation. Another molecular system, [FeGa](AsF₆)₃, demonstrated low-temperature spin transitions and magnetic field-induced polarization switching. We characterized its temperature-dependent single-crystal structures at 25, 50 and 100 K using Rigaku HyPix-AFC.

実験 / Experimental

The ultralow temperature (ca. 30 K) single-crystal data for [CoCr](AsF₆)₃ before and after 1340 nm irradiation (660 nm laser for Fe(HL)₂(BBS)·3H₂O) for 20 minutes until clear changes in the cell parameters were found. The laser directly focused on the single crystals in the cryogenic conditions. The single-crystal data of [FeGa](AsF₆)₃ were collected without light irradiation were collected with helium gas stream at Institute for Molecular Science with Rigaku Hypix-AFC diffractometer equipped with a Hypix-6000 area detector and multi-layer mirror monochromated Mo-Kα radiation of λ= 0.71073 Å. The structures were solved by a direct method and refined via full-matrix least-squares on F² using the SHELX program implemented in the OLEX2 program with anisotropic thermal parameters for all non-hydrogen atoms. The hydrogen atoms were geometrically added and refined by the riding model.

結果と考察 / Results and Discussion

The X-ray structural analyses of [CoCr](AsF6)3 before and after 1340 nm laser irradiation showed that the space group remained the P21, which is identical to the thermally induced high-temperature and how-temperature phases. However, doubling in the unit cell was observed, suggestive of formation of a superstructure. This resulted in two isolated [CrCo] molecules in the asymmetric unit due to the change of translational symmetry, both showing [Co2+-dhbq2−-Cr3+] configuration with average Co-O bond lengths of 2.11 Å and Co-N bond lengths of 2.14 Å, respectively, confirming the light-induced VT behavior. In the photoinduced phase, two separated layers with varying degrees of ion displacement of AsF6− ion along the b- and c-axes formed, as compared to the high-temperature phase. The AsF6− intermediate [CoCr] motif moved toward Co site along the b-axis, accompanied by a slight rotation in the first layer (blue), while no significant change was found in the second layer (yellow). The direction of such anion movement is the same with that caused by electron transfer. As the temperature increase to 80 K, crystal structure recovered to the conventional low-temperature phase, consistent with the photoinduced magnetization and polarization measurements (Fig. 1).
Fe(HL)₂(BBS)·3H₂O also exhibited a superstructure after light irradiation with four independent asymmetric units in a unit cell. Bond length analysis reveals that half of the Fe centers remain in the LS state. Only the values of d(Fe-N)_Avg and d(Fe-S)_Avg in one Fe(II) ion increase by 0.18 Å and 0.16 Å, respectively. These changes indicate that a quarter of Fe centers undergoes a partial ST during irradiation but does not fully convert to the HS state. The resulting structure after irradiation resembles the configuration observed at 140 K.  [FeGa](AsF₆)₃ complex also crystallized in the polar P2₁ space group. The bond lengths around the Fe ion were 1.89-1.90 Å (Fe-O) and 2.01-2.06 Å (Fe-N) at 25 K and 2.02-2.03 Å (Fe-O) and 2.15-2.19 Å (Fe-N) at 100 K. These value were characteristic of the Fe³⁺ LS and Fe³⁺ HS states, respectively, thus confirming the observed spin transition behavior from magnetometry.

図・表・数式 / Figures, Tables and Equations

Fig. 1 Single-crystal structures of [CoCr](AsF₆)₃ before and after 1340nm irradiation at 30 K.

その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)

本実験を行うに辺り、単結晶X線回折装置 微小結晶Rigaku HyPix-AFC装置担当者の岡野芳則 技術職員に大変お世話になりました。ありがとうございました。

成果発表・成果利用 / Publication and Patents

論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)

1. Wenwei Zheng, Giant Near-Infrared Induced Polarization Change via a Long-Lived Hidden Phase of a Valence Tautomeric Complex, Journal of the American Chemical Society, 147, 13953-13961(2025).
   DOI: doi.org/10.1021/jacs.5c02909
   

口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.

1. Shu-Qi Wu, Magnetic Field-Induced Polarization Switching in Fe Complexes with Spin Transition Behavior (Invited), China-Japan Rigaku International Workshop on Functional Materials, Tianjin, China, January 10-13, 2025.

特許 / Patents

特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件