Substituent Effects on Exchange Coupling and Magnetic Relaxation in 2,2′-Bipyrimidine Radical-Bridged Dilanthanide Complexes
Substituent Effects on Exchange Coupling and Magnetic Relaxation in 2,2′-Bipyrimidine Radical-Bridged Dilanthanide Complexes
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DOI：
10.1021/jacs.0c10612
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发表时间：
2020-12-16
影响因子：
15
通讯作者：
Long, Jeffrey R.
中科院分区：
文献类型：
--
作者：
Gould, Colin A.;Mu, Edward;Long, Jeffrey R.
相关化合物的系统分析对于设计具有改进性能的单分子磁体至关重要，但对具有强磁耦合的多核镧系配合物的此类研究仍然很少。本文报道了一系列自由基桥联的稀土配合物[（Cp-2*Ln）（2）（mu-5，5 '-R（2）bpym）]（BPh 4）（Ln = Gd，Dy; R = NMe 2（1），OEt（2），Me（3），F（4）; bpym = 2，2'-联嘧啶）的合成和磁性表征。桥连5，5 '-R（2）bpym自由基阴离子上的取代基的修饰使得该系列中的钆化合物的磁交换耦合常数J（Gd-rad）在-2.7 cm（-1）（1）至-11.1 cm（-1）（4）的范围内调整，吸电子或供电子取代基分别增加或降低交换耦合的强度。交换耦合相互作用的调制对单分子磁体1-Dy至4-Dy的磁弛豫动力学具有显著影响，其中对应Gd'化合物的较强J（Gd-rad）与磁弛豫的较大热势垒（U-eff）、在较高温度下的开放磁滞以及通过势垒过程的较慢磁弛豫速率相关联。此外，我们推导出经验的1-Dy通过4-Dy的U-eff值和J（Gd-rad）的大小为相应的钆衍生物，提供洞察这些配合物的电子结构之间的线性相关性。这个简单的模型适用于文献中的其他有机自由基桥连的镝配合物，它建立了明确的设计标准，提高自由基桥连分子的磁工作温度。
Systematic analysis of related compounds is crucial to the design of single-molecule magnets with improved properties, yet such studies on multinuclear lanthanide complexes with strong magnetic coupling remain rare. Herein, we present the synthesis and magnetic characterization of the series of radical-bridged dilanthanide complex salts [(Cp-2*Ln)(2)(mu-5,5'-R(2)bpym)](BPh4) (Ln = Gd, Dy; R = NMe2 (1), OEt (2), Me (3), F (4); bpym = 2,2'-bipyrimidine). Modification of the substituent on the bridging 5,5'-R(2)bpym radical anion allows the magnetic exchange coupling constant, J(Gd-rad), for the gadolinium compounds in this series to be tuned over a range from -2.7 cm(-1) (1) to -11.1 cm(-1) (4), with electron-withdrawing or -donating substituents increasing or decreasing the strength of exchange coupling, respectively. Modulation of the exchange coupling interaction has a significant impact on the magnetic relaxation dynamics of the single-molecule magnets 1-Dy through 4-Dy, where stronger J(Gd-rad) for the corresponding Gd' compounds is associated with larger thermal barriers to magnetic relaxation (U-eff), open magnetic hysteresis at higher temperatures, and slower magnetic relaxation rates for through-barrier processes. Further, we derive an empirical linear correlation between the experimental U-eff values for 1-Dy through 4-Dy and the magnitude of J(Gd-rad) for the corresponding gadolinium derivatives that provides insight into the electronic structure of these complexes. This simple model applies to other organic radical-bridged dysprosium complexes in the literature, and it establishes clear design criteria for increasing magnetic operating temperatures in radical-bridged molecules.