Beijing National Laboratory of Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China.
Inorg Chem. 2012 Mar 5;51(5):3079-87. doi: 10.1021/ic202511n. Epub 2012 Feb 22.
The synthesis, structures, and magnetic properties of a series of lanthanide organometallic mixed sandwich molecules, (Cp*)Ln(COT), are investigated, where Cp* is the pentamethylcyclopentadiene anion and COT is the cyclooctatetraene dianion and Ln represents Tb(III), Dy(III), Ho(III), Er(III), and Tm(III). Among the five complexes, Dy and Ho complexes are determined to be single-ion magnets in addition to the previously reported Er complex. Both Dy and Ho complexes show obvious quantum tunneling magnetization relaxation in the absence of a static field. The diluted Ho complex behaves two sets of thermally activated relaxation as we reported previously in Er due to the COT ring static disorder. A stair-shaped hysteresis for the Er compound can be observed at 1.6 K with Hc = 1 kOe at a sweeping rate over 700 Oe/s. The quantum tunneling decoherence relaxation rate increases from Er to Ho to Dy, which may be caused by the relative increase of transverse anisotropy coming from the larger tilting of the two aromatic rings within the molecule. The fine electronic structure is analyzed with ligand-field theory employing the effective Hamiltonian method. The zero-field splitting is determined to be Ising type, and the energy gap between the ground state and the first excited one is consistent with the barrier obtained by Arrhenius analysis.
研究了一系列镧系金属有机夹心分子（Cp*）Ln（COT）的合成、结构和磁性质，其中 Cp*为五甲基环戊二烯阴离子，COT 为环辛四烯二阴离子，Ln 代表 Tb（III）、Dy（III）、Ho（III）、Er（III）和 Tm（III）。在这五个配合物中，除了先前报道的 Er 配合物外，Dy 和 Ho 配合物也被确定为单离子磁体。在没有静磁场的情况下，Dy 和 Ho 配合物都表现出明显的量子隧穿磁弛豫。由于 COT 环的静态无序，我们之前在 Er 中报道过，稀释的 Ho 配合物表现出两组热激活弛豫。在 1.6 K 下，可以观察到 Er 化合物的阶梯形滞后，在 700 Oe/s 以上的扫速下，Hc = 1 kOe。量子隧穿退相干弛豫速率从 Er 增加到 Ho 再到 Dy，这可能是由于分子内两个芳环的倾斜较大导致横向各向异性的相对增加所致。采用有效哈密顿方法的配体场理论分析了精细电子结构。确定零场分裂为 Ising 型，基态和第一激发态之间的能隙与 Arrhenius 分析得到的势垒一致。
