Single-molecule magnets of ferrous cubes: structurally controlled magnetic anisotropy.
Single-molecule magnets of ferrous cubes: structurally controlled magnetic anisotropy.
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DOI：
10.1021/ja0487933
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发表时间：
2004-06
影响因子：
15
通讯作者：
H. Oshio;Norihisa Hoshino;Tasuku Ito;M. Nakano
中科院分区：
文献类型：
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作者：
H. Oshio;Norihisa Hoshino;Tasuku Ito;M. Nakano
合成了以席夫碱为配体桥联Fe（II）中心的四核Fe（II）立方配合物。六个铁立方体[Fe_4（sap）_4（MeOH）_4]·2 H_2 O（1）、[Fe_4（sap）_4（MeOH）_4]·2 H_2 O（1）、[Fe_4（sap）_4（MeOH）_4]·2 H_2 O（2）的X射线结构分析（5-Br-sap）4（MeOH）4]（2）、[Fe4（3-MeO-sap）4（MeOH）4].2MeOH（3）、[Fe4（sae）4（MeOH）4]（4）、[Fe4（sae）4（MeOH）4]（4）（5-Br-sae）4（MeOH）4]、MeOH（5）和[Fe 4（3，5-Cl2-sae）4（MeOH）4]（6）（R-sap和R-sae分别通过水杨醛衍生物与氨基丙醇和氨基乙醇的缩合制备），并对其磁性能进行了研究。在1-6中，席夫碱配体的烷氧基以μ 3-模式桥接四个Fe（II）离子，形成[Fe 4 O 4]立方核。立方体中的Fe（II）离子具有四方拉长的八面体配位几何构型，4-6中的赤道配位键长比1-3中的短。1-6的直流磁化率测量表明，分子内铁磁相互作用是有效的，导致S = 8自旋基态。对1.8 K下的磁化数据进行分析，得到1-6的轴向零场分裂参数（D）分别为+0.81、+0.80、+1.15、-0.64、-0.66和-0.67 cm（-1）。4-6的交流磁化率测量显示了频率依赖的同相和异相信号，而1-3在低至1.8 K时没有显示出异相信号，这意味着4-6是单分子磁体（SMM）。对于4-6，使自旋在上自旋和下自旋之间翻转的能垒估计分别为28.4、30.5和26.2 K。桥连配体R-sap 2- in 1-3和R-sae 2- in 4-6分别形成六元和五元螯合环，在Fe（II）中心引起不同的空间应变和Jahn-Teller畸变。利用角重叠模型（AOM）计算了不同配位构型的铁，讨论了D值的符号。
Tetranuclear Fe(II) cubic complexes were synthesized with Schiff base ligands bridging the Fe(II) centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4].2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4].2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4].MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1-6, the alkoxo groups of the Schiff base ligands bridge four Fe(II) ions in a mu3-mode forming [Fe4O4] cubic cores. The Fe(II) ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4-6 are shorter than those in 1-3. Dc magnetic susceptibility measurements for 1-6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, -0.64, -0.66, and -0.67 cm(-1) for 1-6, respectively. Ac magnetic susceptibility measurements for 4-6 showed both frequency dependent in- and out-of-phase signals, while 1-3 did not show out-of-phase signals down to 1.8 K, meaning 4-6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4-6. The bridging ligands R-sap2- in 1-3 and R-sae2- in 4-6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn-Teller distortions at Fe(II) centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry.