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<p>Herein, we present novel heterotrispin compounds [Cp*<sub>2</sub>Ln<sup>III</sup>(<i>m</i>-bpym<sup>·</sup>)Co<sup>II</sup>(nacnac)][BPh<sub>4</sub>] (<b>2-Ln</b>, Ln = Gd, Dy; Cp* = pentamethylcyclopentadienyl; bpym = 2,2′-bipyrimidine; nacnac = CH[C(Me)N(2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)]<sub>2</sub>) which feature the simplest 3d-radical-4f model. These compounds were isolated by mixing [Cp*<sub>2</sub>Ln<sup>III</sup>(<i>m</i>-bpym)][BPh<sub>4</sub>] (<b>1-Ln</b>) with [(nacnac)Co<sup>I</sup>(toluene)] in tetrahydrofuran (THF). The monovalent cobalt compound in the reaction acts as both a reducing agent and a transition metal source. Single-crystal X-ray crystallography and UV/vis-NIR spectroscopy confirm the existence of bpym<sup>·−</sup> radical. Magnetic investigations and computational studies reveal that the overall ferromagnetic behaviors in <b>2-Ln</b> are attributed to the strong antiferromagnetic coupling of the metal centers with the bpym<sup>·−</sup> radical. Compounds <b>1-Dy</b> and <b>2-Dy</b> share similar coordination environments, and both exhibit single-molecule magnet (SMM) behaviour. In the case of <b>2-Dy</b>, strong exchange interactions result in significantly reduced quantum tunneling of magnetization (QTM), allowing a considerable enhancement of relaxation times by around 30000-fold increase, compared to compound <b>1-Dy</b>. Importantly, the 100-s magnetic blocking temperature (<i>T</i><sub>B(100s)</sub>) for compound <b>2-Dy</b> is up to 4.1 K, which, as far as we know, is the highest temperature reported to date for any 3d-radical-4f SMMs. The hysteresis loops for compound <b>1-Dy</b> are butterfly-shaped, and the loops are closed at zero field, due to fast relaxation. In contrast, compound <b>2-Dy</b> exhibits open hysteresis loops up to 7 K. <i>Ab initio</i> calculations were performed to investigate the relaxation mechanism, revealing that the extracted energy barrier of <b>2-Dy</b> is a multilevel exchange type rather than originating from excited Kramers doublets on individual metal ions. These results provide a facile route to access 3d-radical-4f compounds, and further reveal the opportunities for the design and synthesis of high-performing 3d-radical-4f SMMs.</p>

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Strong exchange interactions and single-molecule magnetism of heterotrispin compounds with the simplest 3d-radical-4f model

  • 期刊论文

  • 发表日期：

    2026年3月6日

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  • Tao Shang,
  • Yan-Cong Chen,
  • Yun-Xiang Jing,
  • Xiao-Han Peng,
  • Ming-Liang Tong,
  • Yi-Quan Zhang,
  • Fu-Sheng Guo

摘要

Herein, we present novel heterotrispin compounds [Cp*2LnIII(m-bpym·)CoII(nacnac)][BPh4] (2-Ln, Ln = Gd, Dy; Cp* = pentamethylcyclopentadienyl; bpym = 2,2′-bipyrimidine; nacnac = CH[C(Me)N(2,6-iPr2C6H3)]2) which feature the simplest 3d-radical-4f model. These compounds were isolated by mixing [Cp*2LnIII(m-bpym)][BPh4] (1-Ln) with [(nacnac)CoI(toluene)] in tetrahydrofuran (THF). The monovalent cobalt compound in the reaction acts as both a reducing agent and a transition metal source. Single-crystal X-ray crystallography and UV/vis-NIR spectroscopy confirm the existence of bpym·− radical. Magnetic investigations and computational studies reveal that the overall ferromagnetic behaviors in 2-Ln are attributed to the strong antiferromagnetic coupling of the metal centers with the bpym·− radical. Compounds 1-Dy and 2-Dy share similar coordination environments, and both exhibit single-molecule magnet (SMM) behaviour. In the case of 2-Dy, strong exchange interactions result in significantly reduced quantum tunneling of magnetization (QTM), allowing a considerable enhancement of relaxation times by around 30000-fold increase, compared to compound 1-Dy. Importantly, the 100-s magnetic blocking temperature (TB(100s)) for compound 2-Dy is up to 4.1 K, which, as far as we know, is the highest temperature reported to date for any 3d-radical-4f SMMs. The hysteresis loops for compound 1-Dy are butterfly-shaped, and the loops are closed at zero field, due to fast relaxation. In contrast, compound 2-Dy exhibits open hysteresis loops up to 7 K. Ab initio calculations were performed to investigate the relaxation mechanism, revealing that the extracted energy barrier of 2-Dy is a multilevel exchange type rather than originating from excited Kramers doublets on individual metal ions. These results provide a facile route to access 3d-radical-4f compounds, and further reveal the opportunities for the design and synthesis of high-performing 3d-radical-4f SMMs.