Tetrairon(II) extended metal atom chains as single-molecule magnets.
Tetrairon(II) extended metal atom chains as single-molecule magnets.
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DOI：
10.1039/d1dt01007g
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发表时间：
2021-06-08
期刊：
影响因子：
--
通讯作者：
Cornia A
中科院分区：
文献类型：
--
作者：
Nicolini A;Affronte M;SantaLucia DJ;Borsari M;Cahier B;Caleffi M;Ranieri A;Berry JF;Cornia A
铁基扩展金属原子链（EMAC）是具有轴向磁各向异性的高自旋分子，因此是候选的单分子磁体（SMM）。本文中，我们比较了四铁（II），卤化物封端的配合物[Fe 4（tpda）3Cl 2]（1Cl）和[Fe 4（tpda）3Br 2]（1Br），通过在甲苯中，在严格无水和厌氧条件下（HMes =均三甲苯），使二卤化铁（II）与[Fe 2（Mes）4]和N2，N6-二（吡啶-2-基）吡啶-2，6-二胺（H2 tpda）反应得到。详细的结构，电化学和穆斯堡尔谱数据沿着与直流（DC）和交流（AC）的磁特性。直流测量显示两种衍生物的静态磁性相似，室温下的χMT高于独立自旋载流子的χMT，但在低温下低得多。通过从头计算（CASSCF-NEVPT 2-SO）探索了每个衍生物中的铁（II）离子的电子结构，这表明所有金属的主磁轴都指向靠近链的轴。外层金属Fe 1和Fe 4具有易轴磁各向异性（D =-11至19 cm-1，|E/D| = 0.05-0.18），而内部金属Fe 2和Fe 3具有较弱的难磁化轴各向异性（D = 8-10 cm-1，|E/D| = 0.06-0.21）。这些单离子参数在直流磁场数据的拟合中保持不变，这揭示了铁磁Fe 1-Fe 2和Fe 3-Fe 4相互作用和反铁磁Fe 2-Fe 3耦合。超交换相互作用和金属位置处的大的非共线各向异性之间的竞争导致弱磁性非Kramers双重基态。这解释了SMM行为所显示的两个衍生物在AC磁化率数据中，与缓慢的磁弛豫在1Br可观察到，即使在零静态场。当X = Br时，Fe（II）基EMAC [Fe 4（tpda）3X 2]（X = Cl，Br）显示出SMM性质，即使在零直流电场下也可检测到。一个弱磁性的非Kramers双重基态被证明是由交替的J符号沿着链和大的单离子各向异性。
Iron-based extended metal atom chains (EMACs) are potentially high-spin molecules with axial magnetic anisotropy and thus candidate single-molecule magnets (SMMs). We herein compare the tetrairon(II), halide-capped complexes [Fe4(tpda)3Cl2] (1Cl) and [Fe4(tpda)3Br2] (1Br), obtained by reacting iron(II) dihalides with [Fe2(Mes)4] and N2,N6-di(pyridin-2-yl)pyridine-2,6-diamine (H2tpda) in toluene, under strictly anhydrous and anaerobic conditions (HMes = mesitylene). Detailed structural, electrochemical and Mössbauer data are presented along with direct-current (DC) and alternating-current (AC) magnetic characterizations. DC measurements revealed similar static magnetic properties for the two derivatives, with χMT at room temperature above that for independent spin carriers, but much lower at low temperature. The electronic structure of the iron(II) ions in each derivative was explored by ab-initio (CASSCF-NEVPT2-SO) calculations, which showed that the main magnetic axis of all metals is directed close to the axis of the chain. The outer metals, Fe1 and Fe4, have an easy-axis magnetic anisotropy (D = −11 to −19 cm−1, |E/D| = 0.05–0.18), while the internal metals, Fe2 and Fe3, possess weaker hard-axis anisotropy (D = 8–10 cm−1, |E/D| = 0.06–0.21). These single-ion parameters were held constant in the fitting of DC magnetic data, which revealed ferromagnetic Fe1-Fe2 and Fe3-Fe4 interactions and antiferromagnetic Fe2-Fe3 coupling. The competition between super-exchange interactions and the large, noncollinear anisotropies at metal sites results in a weakly magnetic non-Kramers doublet ground state. This explains the SMM behavior displayed by both derivatives in the AC susceptibility data, with slow magnetic relaxation in 1Br being observable even in zero static field. The iron(II)-based EMACs [Fe4(tpda)3X2] (X = Cl, Br) display SMM properties, detectable even in zero DC field when X = Br. A weakly magnetic non-Kramers doublet ground state is shown to arise from the alternating J signs along the chain and the large single-ion anisotropies.
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