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<p>The development of high-performance single-molecule magnets (SMMs) benefits significantly from the metal-radical approach, which enables precise control over both magnetic exchange interactions and molecular geometry. We present a series of benzoquinone-bridged dicobalt(II) complexes that demonstrate redox-controlled symmetry transitions between trigonal prismatic and octahedral geometries, accompanied by significant magnetic property modulation. The neutral compounds [{(L-N<sub>4</sub>)Co<sup>II</sup>}<sub>2</sub>(μ-X)](ClO<sub>4</sub>)<sub>2</sub> (X = CA<sup>2−</sup>, <b>1</b>; X = BA<sup>2−</sup>, <b>2</b>; L-N<sub>4</sub> = <i>N</i>,<i>N</i>′-bis[(2-<i>N</i>-methylimidazol-1-yl)methylene]-2,2-dimethyl-propane-1,3-diamine) maintain near-ideal trigonal prismatic coordination with large axial magnetic anisotropy (<i>D</i><sub>Co</sub> = −108 to −114 cm<sup>−1</sup>). Chemical reduction generates radical-bridged analogues [{(L-N<sub>4</sub>)Co<sup>II</sup>}<sub>2</sub>(μ-X)](ClO<sub>4</sub>)·<i>n</i>MeCN (X = CA<sup>3−•</sup>, <i>n</i> = 5, <b>1R</b>; Y = BA<sup>3−•</sup>, <i>n</i> = 2, <b>2R</b>) that undergo a clear transition to octahedral geometry while retaining substantial uniaxial anisotropy (<i>D</i><sub>Co</sub> = −37 to −52 cm<sup>−1</sup>). Especially, these reduced forms exhibit exceptionally strong antiferromagnetic Co<sup>II</sup>-radical coupling (−137 cm<sup>−1</sup> in the 2<i>J</i> formalism)—the largest reported for the metal-benzoquinone system. All complexes display slow relaxation dynamics with effective energy barriers up to 44(3) cm<sup>−1</sup>. Additionally, the neutral forms show metamagnetic ordering due to significant intermolecular π-stacking interactions. This work establishes a new design strategy for redox-switchable molecular magnets through synergistic control of coordination symmetry and radical-mediated exchange coupling.</p>

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Redox-switchable symmetry transition in benzoquinone-bridged Co(II) single-molecule magnets: trigonal prismatic to octahedral

  • 期刊论文

  • 发表日期：

    2026年1月4日

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  • Binling Yao,
  • Akshay Pratap Singh,
  • Jing Xi,
  • Shiyun Liu,
  • Nian Zhao,
  • Yi-Fei Deng,
  • Saurabh Kumar Singh,
  • Yuan-Zhu Zhang

摘要

The development of high-performance single-molecule magnets (SMMs) benefits significantly from the metal-radical approach, which enables precise control over both magnetic exchange interactions and molecular geometry. We present a series of benzoquinone-bridged dicobalt(II) complexes that demonstrate redox-controlled symmetry transitions between trigonal prismatic and octahedral geometries, accompanied by significant magnetic property modulation. The neutral compounds [{(L-N4)CoII}2(μ-X)](ClO4)2 (X = CA2−, 1; X = BA2−, 2; L-N4 = N,N′-bis[(2-N-methylimidazol-1-yl)methylene]-2,2-dimethyl-propane-1,3-diamine) maintain near-ideal trigonal prismatic coordination with large axial magnetic anisotropy (DCo = −108 to −114 cm−1). Chemical reduction generates radical-bridged analogues [{(L-N4)CoII}2(μ-X)](ClO4)·nMeCN (X = CA3−•, n = 5, 1R; Y = BA3−•, n = 2, 2R) that undergo a clear transition to octahedral geometry while retaining substantial uniaxial anisotropy (DCo = −37 to −52 cm−1). Especially, these reduced forms exhibit exceptionally strong antiferromagnetic CoII-radical coupling (−137 cm−1 in the 2J formalism)—the largest reported for the metal-benzoquinone system. All complexes display slow relaxation dynamics with effective energy barriers up to 44(3) cm−1. Additionally, the neutral forms show metamagnetic ordering due to significant intermolecular π-stacking interactions. This work establishes a new design strategy for redox-switchable molecular magnets through synergistic control of coordination symmetry and radical-mediated exchange coupling.