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Increasing the Symmetry around Lanthanide Ions: The Effect on Single-Ion Magnet Behavior and Electronic Structure
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2023-12-14 , DOI: 10.1021/acs.cgd.3c01380 Jarrod R. Thomas 1 , Marcus J. Giansiracusa 2 , Richard A. Mole 3 , Scott A. Sulway 1
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2023-12-14 , DOI: 10.1021/acs.cgd.3c01380 Jarrod R. Thomas 1 , Marcus J. Giansiracusa 2 , Richard A. Mole 3 , Scott A. Sulway 1
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Bis-capped lanthanide compounds have dominated the single-ion magnet (SIM) field with little variation in design. Herein, we report the new synthesis of the lanthanide compounds [Ln(Tp2-py)2](BPh4) (1-Ln; Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy), which employ the use of the hexadentate hydrotris[3-(2′-pyridyl)-pyrazol-1-yl]borate (Tp2-py) ligand to encapsulate lanthanide ions in pseudo-icosahedral crystal fields. The extension of the latter lanthanide ions yields the hydrated compounds [Ln(κ4-Tp2-py)2(OH2)](BPh4) (2-Ln; Ln = Dy, Y, Ho, Er, Tm, Yb, and Lu) instead due to the decrease in the ionic radii of the lanthanide and steric demand of the ligand. Alternating current magnetometry studies on 1-Ce, 1-Tb, 1-Dy, 2-Dy, and [Dy(Tp2-py)2Cl] (3) revealed slow magnetic relaxation in applied magnetic fields for all compounds, with 1-Tb revealing an extractable Orbach regime with Ueff = 46(2) cm–1, while the remaining compounds are dominated by Raman relaxation mechanisms. The complexity and size of Tp2-py likely afford many low energy vibrational modes which would be responsible for an increase in spin-phonon coupling and the observed dominance of Raman relaxation. CASSCF calculations on the compounds showed that the ground state purity is heavily dependent on the lanthanide; however, all easy axes are aligned with the B···B axis (or pseudo B···B axis for the case of 3) except for 2-Dy, where the easy axis aligns with the Dy–OH2 bond. The resonant nature of the tris-(pyrazolyl)borate ligands results in diffusely spread charge distribution, minimizing the influence of the axially located boron atoms, resulting in the lanthanide ion being encapsulated in a “pseudosphere” of negative charge, impacting the overall crystal field splitting. The magnetic behavior and electronic structure of 1-Ln highlight the importance of low energy vibrational modes to mitigate spin-phonon coupling, charge distribution, and geometry of ligands when designing lanthanide-based SIMs.
中文翻译：
增加稀土离子周围的对称性：对单离子磁体行为和电子结构的影响
双封端镧系元素化合物在单离子磁体（SIM）领域占据主导地位，设计上几乎没有变化。在此，我们报道了镧系化合物 [Ln(Tp 2-py ) 2 ](BPh 4 ) ( 1-Ln ; Ln = La、Ce、Pr、Nd、Sm、Eu、Gd、Tb 和 Dy的新合成），其利用六齿氢三[3-(2'-吡啶基)-吡唑-1-基]硼酸盐（Tp 2-py）配体将镧系元素离子封装在假二十面体晶场中。后面的镧系元素离子的延伸产生水合化合物 [Ln(κ 4 -Tp 2-py ) 2 (OH 2 )](BPh 4 ) ( 2-Ln ; Ln = Dy, Y, Ho, Er, Tm, Yb ，和Lu）相反，由于镧系元素的离子半径和配体的空间需求的减少。对1-Ce、1-Tb、1-Dy、2-Dy和 [Dy(Tp 2-py ) 2 Cl] ( 3 )的交流磁力测定研究表明，所有化合物在外加磁场中都有缓慢的磁弛豫，其中1 -Tb揭示了可提取的 Orbach 体系，U eff = 46(2) cm –1，而其余化合物则以拉曼弛豫机制为主。Tp 2-py的复杂性和尺寸可能提供许多低能振动模式，这将导致自旋声子耦合的增加和观察到的拉曼弛豫的主导地位。CASSCF 对化合物的计算表明，基态纯度很大程度上取决于镧系元素；然而，除了2-Dy之外，所有易轴都与 B…B 轴（或对于3的情况是伪 B…B 轴）对齐，其中 2-Dy 的易轴与 Dy-OH 2键对齐。三（吡唑基）硼酸配体的共振性质导致电荷分布扩散，最大限度地减少轴向硼原子的影响，导致镧系元素离子被封装在负电荷的“赝球层”中，影响整个晶体场分裂。1-Ln的磁性行为和电子结构凸显了低能振动模式在设计基于镧系元素的 SIM 时减轻自旋声子耦合、电荷分布和配体几何形状的重要性。
更新日期：2023-12-14
中文翻译：
增加稀土离子周围的对称性：对单离子磁体行为和电子结构的影响
双封端镧系元素化合物在单离子磁体（SIM）领域占据主导地位，设计上几乎没有变化。在此，我们报道了镧系化合物 [Ln(Tp 2-py ) 2 ](BPh 4 ) ( 1-Ln ; Ln = La、Ce、Pr、Nd、Sm、Eu、Gd、Tb 和 Dy的新合成），其利用六齿氢三[3-(2'-吡啶基)-吡唑-1-基]硼酸盐（Tp 2-py）配体将镧系元素离子封装在假二十面体晶场中。后面的镧系元素离子的延伸产生水合化合物 [Ln(κ 4 -Tp 2-py ) 2 (OH 2 )](BPh 4 ) ( 2-Ln ; Ln = Dy, Y, Ho, Er, Tm, Yb ，和Lu）相反，由于镧系元素的离子半径和配体的空间需求的减少。对1-Ce、1-Tb、1-Dy、2-Dy和 [Dy(Tp 2-py ) 2 Cl] ( 3 )的交流磁力测定研究表明，所有化合物在外加磁场中都有缓慢的磁弛豫，其中1 -Tb揭示了可提取的 Orbach 体系，U eff = 46(2) cm –1，而其余化合物则以拉曼弛豫机制为主。Tp 2-py的复杂性和尺寸可能提供许多低能振动模式，这将导致自旋声子耦合的增加和观察到的拉曼弛豫的主导地位。CASSCF 对化合物的计算表明，基态纯度很大程度上取决于镧系元素；然而，除了2-Dy之外，所有易轴都与 B…B 轴（或对于3的情况是伪 B…B 轴）对齐，其中 2-Dy 的易轴与 Dy-OH 2键对齐。三（吡唑基）硼酸配体的共振性质导致电荷分布扩散，最大限度地减少轴向硼原子的影响，导致镧系元素离子被封装在负电荷的“赝球层”中，影响整个晶体场分裂。1-Ln的磁性行为和电子结构凸显了低能振动模式在设计基于镧系元素的 SIM 时减轻自旋声子耦合、电荷分布和配体几何形状的重要性。
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