Mondal Arpan, Konar Sanjit
Department of Chemistry, Indian Institute of Science Education and Research, Bhopal, Bhopal By-pass Road, Bhauri, Bhopal, 462066, Madhya Pradesh, India.
Chemistry. 2021 Feb 15;27(10):3449-3456. doi: 10.1002/chem.202004379. Epub 2021 Jan 27.
The importance of equatorial crystal fields on magnetic anisotropy of ytterbium single molecule magnets (SMMs) is observed for the first time. Herein, we report three similar dinuclear ytterbium complexes with the formula [Yb (3-OMe-L) (DMF) (NO ) ]⋅DMF (1), [Yb (3-H-L) (DMF) (NO ) ]⋅DMF⋅H O (2), and [Yb (3-NO -L) (DMF) (NO ) ] (3), [where 3-X-H L=N'-(2-hydroxy-3-X-benzylidene)picolinohydrazide, X=OMe (1), H (2) NO (3)]. Detailed magnetic measurements reveal the presence of weak antiferromagnetic interactions between the Yb centers and a field-induced slow relaxation of magnetization in all complexes. A higher energy barrier for spin reversal was observed for complex 1 (U =50 K) and it decreases in the order of 2 (47 K) to 3 (40 K). Notably, complex 1 shows a remarkable energy barrier within the frequency range of 1-850 Hz reported for Yb-based SMMs. Further, ab initio calculations show a higher axial anisotropy and lower quantum tunneling of magnetization (QTM) in the ground state for 1 compared to 2 and 3. It was also observed that the presence of a strong crystal field in the equatorial plane (when the ∡ O1-Yb-O3 bond angle is close to 90°) enhances the axial anisotropy and improves the SMM behavior in the studied complexes. Both the experimental and theoretical analysis of relaxation dynamics discloses that Raman and QTM play major role on slow relaxation process for all complexes. To provide more insight into the exchange interactions, broken-symmetry DFT calculations were performed.
首次观察到赤道晶场对镱单分子磁体（SMMs）磁各向异性的重要性。在此，我们报道了三种化学式为[Yb(3-OMe-L)(DMF)(NO)]⋅DMF (1)、[Yb(3-H-L)(DMF)(NO)]⋅DMF⋅H₂O (2) 和 [Yb(3-NO₂-L)(DMF)(NO)] (3) 的类似双核镱配合物，[其中 3-X-H₂L = N'-(2-羟基-3-X-苄叉基)吡啶甲酰肼，X = OMe (1)、H (2)、NO₂ (3)]。详细的磁性测量揭示了所有配合物中 Yb 中心之间存在弱反铁磁相互作用以及场诱导的磁化缓慢弛豫。配合物 1 观察到更高的自旋反转能垒（Ueff = 50 K），其按 2（47 K）到 3（40 K）的顺序降低。值得注意的是，配合物 1 在报道的基于 Yb 的 SMMs 的 1 - 850 Hz 频率范围内显示出显著的能垒。此外，从头算计算表明，与 2 和 3 相比，1 在基态具有更高的轴向各向异性和更低的磁化量子隧穿（QTM）。还观察到赤道平面中强晶场的存在（当∠O1 - Yb - O3 键角接近 90°时）增强了轴向各向异性并改善了所研究配合物的 SMM 行为。弛豫动力学的实验和理论分析均表明，拉曼和 QTM 在所有配合物的缓慢弛豫过程中起主要作用。为了更深入了解交换相互作用，进行了破缺对称性 DFT 计算。
