Synthesis, structure, and spectroscopic and magnetic characterization of [Mn12O12(O2CCH2But)16(MeOH)4]·MeOH, a Mn12 single-molecule magnet with true axial symmetry.
Synthesis, structure, and spectroscopic and magnetic characterization of [Mn12O12(O2CCH2But)16(MeOH)4]·MeOH, a Mn12 single-molecule magnet with true axial symmetry.
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真正轴对称的Mn12单分子磁体[Mn12O12(O2CCH2But)16(MeOH)4]·MeOH的合成、结构以及光谱和磁性表征。
DOI：
10.1021/ic301764t
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发表时间：
2013
影响因子：
4.6
通讯作者：
G. Christou
中科院分区：
文献类型：
--
作者：
C. Lampropoulos;M. Murugesu;A. Harter;Wolfgang Wernsdofer;S. Hill;N. Dalal;A. Reyes;P. Kuhns;K. Abboud;G. Christou
报道了一种罕见的具有真正轴对称性的Mn（12）单分子磁体（SMM）的合成和性质。以[Mn（12）O（12）（O（2）CMe）（16）（H（2）O）（4）]·2 MeCO（2）H·4 H（2）O（1）为原料，通过羧酸酯取代反应合成了[Mn（12）O（12）（O（2）CCH（2）Bu（t））（16）（MeOH）（4）]·MeOH（3·MeOH）。发现该复合物具有S = 10的基态，如Mn（12）族的典型，并且在单晶磁化与直流场扫描中显示频率依赖的异相AC磁化率信号和磁滞回线。循环也表现出量子隧穿的磁化步骤在周期性的字段值。使用高达360 GHz的频率对3·MeOH的单晶高频电子顺磁共振谱显示出比1明显更尖锐的信号。此外，作为磁场取向的函数的仔细研究没有发现任何卫星峰，如对于1所观察到的，这表明3的晶体是均匀的并且不包含多个Mn（12）环境。在单晶（55）Mn NMR谱中，在零外加磁场下，观察到三个分辨良好的峰，在三个不同的位置产生超精细和四极分裂。然而，在Mn（4+）峰中观察到轻微的不对称性，这表明Mn（4+）位点的局部对称性可能降低。在低至400 mK的3·MeOH单晶上进行自旋-晶格（T（1））弛豫研究，以接近量子隧穿机制，并采用多函数拟合数据。目前的工作和其他最近的研究继续强调，新一代的真正高对称性Mn（12）配合物是更好的模型，彻底调查的物理性质的SMM比他们的前辈，如1。
The synthesis and properties are reported of a rare example of a Mn(12) single-molecule magnet (SMM) in truly axial symmetry (tetragonal, I4). [Mn(12)O(12)(O(2)CCH(2)Bu(t))(16)(MeOH)(4)]·MeOH (3·MeOH) was synthesized by carboxylate substitution on [Mn(12)O(12)(O(2)CMe)(16)(H(2)O)(4)]·2MeCO(2)H·4H(2)O (1). The complex was found to possess an S = 10 ground state, as is typical for the Mn(12) family, and displayed both frequency-dependent out-of-phase AC susceptibility signals and hysteresis loops in single-crystal magnetization vs DC field sweeps. The loops also exhibited quantum tunneling of magnetization steps at periodic field values. Single-crystal, high-frequency electron paramagnetic resonance spectra on 3·MeOH using frequencies up to 360 GHz revealed perceptibly sharper signals than for 1. Moreover, careful studies as a function of the magnetic field orientation did not reveal any satellite peaks, as observed for 1, suggesting that the crystals of 3 are homogeneous and do not contain multiple Mn(12) environments. In the single-crystal (55)Mn NMR spectrum in zero applied field, three well-resolved peaks were observed, which yielded hyperfine and quadrupole splitting at three distinct sites. However, observation of a slight asymmetry in the Mn(4+) peak was detectable, suggesting a possible decrease in the local symmetry of the Mn(4+) site. Spin-lattice (T(1)) relaxation studies were performed on single crystals of 3·MeOH down to 400 mK in an effort to approach the quantum tunneling regime, and fitting of the data using multiple functions was employed. The present work and other recent studies continue to emphasize that the new generation of truly high-symmetry Mn(12) complexes are better models for thorough investigation of the physical properties of SMMs than their predecessors such as 1.