Synthesis, redox, and magnetic properties of a neutral, mixed-valent heptanuclear manganese wheel with S = 27/2 high-spin ground state.
Synthesis, redox, and magnetic properties of a neutral, mixed-valent heptanuclear manganese wheel with S = 27/2 high-spin ground state.
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DOI：
10.1021/ic0614059
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发表时间：
2007-02
影响因子：
4.6
通讯作者：
R. Saalfrank;A. Scheurer;R. Prakash;F. Heinemann;Takayuki Nakajima;F. Hampel;R. Leppin;B. Pilawa;Holger Rupp;P. Müller
中科院分区：
文献类型：
--
作者：
R. Saalfrank;A. Scheurer;R. Prakash;F. Heinemann;Takayuki Nakajima;F. Hampel;R. Leppin;B. Pilawa;Holger Rupp;P. Müller
在 LiH 存在下，四氯锰酸锂 (II) 与 N-正丁基二乙醇胺 H2L3 (3) 反应，形成轮状混合价七核中性络合物 {MnII 子集[MnII2MnIII4Cl6(L3)6]} (4)。当乙醚或正戊烷扩散到4的氯仿或四氢呋喃溶液中时，锰轮在三斜空间群P中结晶为4.2CHCl3或4.3THF。 4.2CHCl3 或 4.3THF 中每种锰离子的氧化态是根据详细的对称性、键长和电荷考虑因素以及根据锰 (III) 离子观察到的 Jahn-Teller 轴向伸长来指定的，并得到循环伏安法的进一步支持。对配合物4.2CHCl3的SQUID磁化率数据的分析表明，锰(II,III)离子的分子内磁耦合以铁磁交换相互作用为主。这导致低磁场下 S = 27/2 基态多重态。在高于 0.68 T 的场中，由于塞曼效应，能量最低状态由 S = 31/2 多重态的 mS = 31/2 分量给出。配体场分裂参数通过沿晶体学 x、y 和 z 轴（D = -0.055 K，E = 6.6 mK）对单晶样品进行各向异性 SQUID 测量以及对 4.2CHCl3 多晶粉末（D = -0.068 K，E = 9.7 mK）进行高频电子自旋共振测量来确定。由此产生的磁化反转势垒高度约为 10 K。最后，2DEG 霍尔磁化测量表明，4.2CHCl3 在高达约 0.6 K 的阻挡温度时表现出单分子磁体行为，并且由于磁化的量子隧道效应，磁滞中的间隔步长很近。
Reaction of lithium tetrachloromanganate(II) with N-n-butyldiethanolamine H2L3 (3) in the presence of LiH leads to the formation of wheel-shaped, mixed-valent heptanuclear, neutral complex {MnII subset[MnII2MnIII4Cl6(L3)6]} (4). The manganese wheel crystallizes in the triclinic space group P as 4.2CHCl3 or 4.3THF when either diethyl ether or n-pentane was allowed to diffuse into solutions of 4 in chloroform or tetrahydrofuran. The oxidation states of each manganese ion in 4.2CHCl3 or 4.3THF were assigned on the basis of detailed symmetry, bond length, and charge considerations, as well as by the Jahn-Teller axial elongation observed for the manganese(III) ions, and were further supported by cyclic voltammetry. The analysis of the SQUID magnetic susceptibility data for complex 4.2CHCl3 showed that the intramolecular magnetic coupling of the manganese(II,III) ions is dominated by ferromagnetic exchange interactions. This results in an S = 27/2 ground-state multiplet at low magnetic field. At fields higher than 0.68 T, the energetically lowest state is given by the mS = 31/2 component of the S = 31/2 multiplet due to the Zeeman effect. The ligand-field-splitting parameters were determined by anisotropy SQUID measurements on single crystalline samples along the crystallographic x, y, and z axes (D = -0.055 K, E = 6.6 mK) and by high-frequency electron spin resonance measurements on a polycrystalline powder of 4.2CHCl3 (D = -0.068 K, E = 9.7 mK). The resulting barrier height for magnetization reversal amounts to U approximately 10 K. Finally, 2DEG Hall magnetization measurements revealed that 4.2CHCl3 shows single-molecule magnet behavior up to the blocking temperature of about 0.6 K with closely spaced steps in the hysteresis because of the quantum tunneling of the magnetization.