Single-Molecule Magnetism in a Family of {CoIII2DyIII2} Butterfly Complexes: Effects of Ligand Replacement on the Dynamics of Magnetic Relaxation
Single-Molecule Magnetism in a Family of {CoIII2DyIII2} Butterfly Complexes: Effects of Ligand Replacement on the Dynamics of Magnetic Relaxation
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DOI：
10.1021/ic4029645
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发表时间：
2014-05-05
影响因子：
4.6
通讯作者：
Murray, Keith S.
中科院分区：
文献类型：
--
作者：
Langley, Stuart K.;Ungur, Liviu;Murray, Keith S.
四种相关的式[1]的异金属配合物的合成和结构表征（Dy 2Co 2 III）-Co-III（OMe）（2）（teaH）（2）（O（2）Cph）（4）（MeOH）（4）]（NO3）（2）中心点MeOH中心点H2O（1a）和[（Dy 2Co 2 III）-Co-III（OMe）（2）-（teaH）（2）（O2 CPh）（4）（MeOH）（2）（NO3）（2）]中心点MeOH中心点H2O（1b），[（Dy2Co2III）-Co-III（OMe）（2）（dea）（2）（O2CPh）（4）（MeOH）（4）]（NO3）（2）（2），[（Dy2CO2III）-C-III（OMe）（2）（mdea）（2）（O2CPh）（4）（NO3）（2）]（3），及[（Dy 2Co 2 III）-Co-III（OMe）（2）（bdea）（2）（O2 CPh）（4）（MeOH）（4）]（NO3）（2）中心点0.5MeOH中心点H2O（4a）[报道了（Dy 2Co 2 III）-Co-III（OMe）（2）（bdea）（2）-（O2 CPh）（4）（MeOH）（2）（NO3）（2）]中心点MeOH中心点1.5H（2）O（4 b）（teaH（3）=三乙醇胺，deaH（2）=二乙醇胺，mdeaH（2）= N-甲基二乙醇胺，和bdeaH（2）= N-正丁基二乙醇胺）。化合物1（相当于Ia和Ib）和4（相当于4a和4 h）都在同一晶体内显示出两个独特的分子，并且所有化合物都显示出蝴蝶型核，其中Dy-III离子占据中心体位置，而抗磁性Co-离子占据外部翼尖位置。化合物1-4通过直流和交流磁化率测量进行了研究，发现每个配合物都显示出单分子磁体（SMM）行为。所有四种化合物显示独特的协调和周围的Dy-III离子的几何环境，它被发现，每个显示不同的各向异性障碍。对1-4进行了从头计算，这些计算确定了每个Dy-III离子的低位电子结构和每个簇的磁相互作用。结果发现，有一个强的相关性之间的计算的单离子配体场分裂Dy-III级的基态和第一激发态的能隙和实验观察到的各向异性势垒。此外，横向g因子发现的Dy-III离子，定义的隧道速率内的地面Kramers双峰，是最大的1，这与实验观察到的最短的弛豫时间在高温域中的复杂。Dym离子之间的磁交换揭示了每个化合物的整体反铁磁相互作用，来自占主导地位的偶极交换导致1-4的基态。与小的隧穿间隙耦合的抗磁性基态导致在0. 1和> 1. 5 s之间的零场处的量子隧穿时间尺度。
The synthesis and structural characterization of four related heterometallic complexes of formulas [(Dy2Co2III)-Co-III(OMe)(2)(teaH)(2)(O(2)Cph)(4)(MeOH)(4)](NO3)(2)center dot MeOH center dot H2O (1a) and [(Dy2Co2III)-Co-III(OMe)(2)-(teaH)(2)(O2CPh)(4)(MeOH)(2)(NO3)(2)]center dot MeOH center dot H2O (1b), [(Dy2Co2III)-Co-III(OMe)(2)(dea)(2)(O2CPh)(4)(MeOH)(4)](NO3)(2) (2), [(Dy2CO2III)-C-III(OMe)(2)(mdea)(2)(O2CPh)(4)(NO3)(2)] (3), and [(Dy2Co2III)-Co-III(OMe)(2)(bdea)(2)(O2CPh)(4)(MeOH)(4)](NO3)(2)center dot 0.5MeOH center dot H2O (4a) [(Dy2Co2III)-Co-III(OMe)(2)(bdea)(2)-(O2CPh)(4)(MeOH)(2)(NO3)(2)]center dot MeOH center dot 1.5H(2)O (4b) are reported (teaH(3) = triethanolamine, deaH(2) = diethanolamine, mdeaH(2) = N-methyldiethanolamine, and bdeaH(2) = N-n-butyldiethanolamine). Compounds 1 (equivalent to la and lb) and 4 (equivalent to 4a and 4h) both display two unique molecules within the same crystal and all compounds display a butterfly type core, with the Dy-III ions occupying the central body positions and the diamagnetic Co" ions the outer wing-tip sites. Compounds 1-4 were investigated via direct current and alternating current magnetic susceptibility measurements, and it was found that each complex displayed single-molecule magnet (SMM) behavior. All four compounds display unique coordination and geometric environments around the Dy-III ions and it was found that each displays a different anisotropy barrier. Ab initio calculations were performed on 1-4 and these determined the low lying electronic structure of each Dy-III ion and the magnetic interactions for each cluster. It was found that there was a strong correlation between the calculated energy gap between the ground and first excited states of the single-ion ligand-field split Dy-III levels and the experimentally observed anisotropy barrier. Furthermore, the transverse g factors found for the Dy-III ions, defining the tunnelling rates within the ground Kramers doublets, are largest for 1, which agrees with the experimental observation of the shortest relaxation time in the high-temperature domain for this complex. The magnetic exchange between the Dym ions revealed overall antiferromagnetic interactions for each compound, derived from the dominant dipolar exchange resulting in nonmagnetic ground states for 1-4. The diamagnetic ground states coupled with small tunneling gaps resulted in quantum tunneling time scales at zero field of between 0.1 and >1.5 s.