Single-chain magnet (NEt4)[Mn2(5-MeOsalen)2Fe(CN)6] made of MnIII-FeIII-MnIII trinuclear single-molecule magnet with an ST = 9/2 spin ground state
Single-chain magnet (NEt4)[Mn2(5-MeOsalen)2Fe(CN)6] made of MnIII-FeIII-MnIII trinuclear single-molecule magnet with an ST = 9/2 spin ground state
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DOI：
10.1021/ja0468123
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发表时间：
2005-03-09
影响因子：
15
通讯作者：
Clérac, R
中科院分区：
文献类型：
--
作者：
Ferbinteanu, M;Miyasaka, H;Clérac, R
Miyasaka等人（参考文献19 d）先前报道的氰基桥接三核化合物（NEt 4）[Mn-2（salmen）（2）（MeOH）（2）Fe（CN）（6）]（1）（salmen（2-）rac-N，N '-（1-methylethylene）bis（salicylideneiminate））已使用交流和直流磁化率测量的组合进行了重新研究。交流磁化率的强频率依赖性和磁化强度的缓慢弛豫表明1表现为具有S-T = 9/2自旋基态的单分子磁体。它的弛豫时间（T）遵循阿克里尼乌斯定律，τ（0）= 2.5 × 10（-7）s，Delta（eff）/k（B）14 K。此外，低于0.3 K时，τ在470 s左右饱和，表明磁化的量子隧穿成为弛豫的主要过程。（NEt 4）[Mn 2（5-MeOsalen）（2）Fe（CN）（6））（2）（5-MeOsalen（2-）= N，N '-亚乙基双（5-甲氧基水杨叉基亚胺））是由类似于1的三核[Mn-III（SB）-NC-Fe-III-CN-Mn-III（SB）]（SB是salen型席夫碱配体）基序制成的异金属一维组装体。化合物2具有两种类型的桥，氰基桥（-NC-）和联苯酚桥（-（O）（2）-），分别连接Mn-III和Fe-III离子以及两个Mn-III离子。两个桥介导铁磁相互作用，如通过对10 K以上的磁化率进行建模所示，g（av）= 2.03，J（Mn）-（Fe）/k（B）= +6.5 K，并且zeta/k（B）= +0.07 K，其中zeta是三聚体单元之间的交换耦合。用微型SQUID和霍尔探针磁强计对单晶进行了直流磁测量，结果表明单晶具有单轴各向异性（D-T/k（B）= -0.94 K），易磁化轴沿着链方向。交流磁化率的频率依赖性和直流磁化的时间依赖性已经被执行来研究磁化的缓慢弛豫。一个平均弛豫时间已被发现，并已研究其温度依赖性。在1.4K以上，磁化率和弛豫时间与R. J. Glauber对具有铁磁耦合伊辛自旋的一维系统（τ（0）= 3.7 × 10（-10）s和Delta（1）/k（B）= 31 K）的计算。正如预期的那样，在低于1.4 K的较低温度下，弛豫过程由有限尺寸链效应τ '（0）= 3 × 10（-8）s和Delta（2）/k（B）= 25 K）主导。该单链磁体行为及其两种制度的详细分析与独立估计的磁性参数（zeta和D-T）一致，并且允许测定60 nm（或44个三聚体单元）的平均链长。这项工作很好地说明了一种新的策略，设计单链磁铁耦合铁磁单分子磁铁在一维。
The cyano-bridged trinuclear compound, (NEt4)[Mn-2(salmen)(2)(MeOH)(2)Fe(CN)(6)] (1) (salmen(2-) rac-N,N'-(1-methylethylene)bis(salicylideneiminate)), reported previously by Miyasaka et al. (ref 19d) has been reinvestigated using combined ac and dc susceptibility measurements. The strong frequency dependence of the ac susceptibility and the slow relaxation of the magnetization show that 1 behaves as a single-molecule magnet with an S-T = 9/2 spin ground state. Its relaxation time (T) follows an Arrhenius law with tau(0) = 2.5 x 10(-7) s and Delta(eff)/k(B) 14 K. Moreover, below 0.3 K, tau saturates around 470 s, indicating that quantum tunneling of the magnetization becomes the dominant process of relaxation. (NEt4)[Mn2 (5-MeOsalen)(2)Fe(CN)(6)) (2) (5-MeOsalen(2-) = N,N'-ethylenebis(5-methoxysalicylideneiminate)) is a heterometallic one-dimensional assembly made of the trinuclear [Mn-III(SB)-NC-Fe-III-CN-Mn-III(SB)] (SB is a salen-type Schiff-base ligand) motif similar to 1. Compound 2 has two types of bridges, a cyano bridge (-NC-) and a biphenolate bridge (-(O)(2)-), connecting Mn-III and Fe-III ions and the two Mn-III ions, respectively. Both bridges mediate ferromagnetic interactions, as shown by modeling the magnetic susceptibility above 10 K with g(av) = 2.03, J(Mn)-(Fe)/k(B) = +6.5 K, and zeta/k(B) = +0.07 K, where zeta is the exchange coupling between the trimer units. The dc magnetic measurements of a single crystal using micro-SQUID and Hall-probe magnetometers revealed a uniaxial anisotropy (D-T/k(B) = -0.94 K) with an easy axis lying along the chain direction. Frequency dependence of the ac susceptibility and time dependence of the dc magnetization have been performed to study the slow relaxation of the magnetization. A mean relaxation time has been found, and its temperature dependence has been studied. Above 1.4 K, both magnetic susceptibility and relaxation time are in agreement with the dynamics described in the 1960s by R. J. Glauber for one-dimensional systems with ferromagnetically coupled Ising spins (tau(0) = 3.7 x 10(-10) s and Delta(1)/k(B) = 31 K). As expected, at lower temperatures below 1.4 K, the relaxation process is dominated by the finite-size chain effects tau'(0) = 3 x 10(-8) s and Delta(2)/k(B) = 25 K). The detailed analysis of this single-chain magnet behavior and its two regimes is consistent with magnetic parameters independently estimated (zeta and D-T) and allows the determination of the average chain length of 60 nm (or 44 trimer units). This work illustrates nicely a new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension.