Paramagnetic NMR Analysis of Substituted Biscyclooctatetraene Lanthanide Complexes
Paramagnetic NMR Analysis of Substituted Biscyclooctatetraene Lanthanide Complexes
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DOI：
10.1021/acs.organomet.6b00241
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发表时间：
2016-06-13
期刊：
影响因子：
2.8
通讯作者：
Enders, Markus
中科院分区：
文献类型：
--
作者：
Hiller, Markus;Maier, Martin;Enders, Markus
中心环上连接有两个碳环的环辛四烯衍生物（COTR）已被用作双阴离子配体，用于合成[(COTR)(2)M](-)类型的双层配合物。两种配体衍生物与抗磁性 Y3+ 以及与从 Tb3+ 到 Tm3+ 的五种顺磁性镧系元素离子结合。与母体配体 COT 或流行的双三甲基硅基衍生物相比，更复杂的取代模式允许获得足够数量的信号以进行全面的顺磁 NMR 分析。阴离子双层配合物提供了高分辨率的 NMR 谱，几乎所有 H-1 和 C-13 NMR 信号都可以被检测和分配。利用这些数据，可以区分对顺磁位移的两个主要贡献（分别是赝接触位移和费米接触位移），并确定镧系元素离子在其配体场中的磁各向异性。我们可以很容易地获得磁化率各向异性的符号和大小，磁化率本身与单分子磁体中自旋反转的能垒密切相关。我们的结果证实，布莱尼因子不足以描述这些稀土配合物中的磁各向异性。
Cyclooctatetraene derivatives (COTR) with two carbocycles attached to the central ring have been used as dianionic ligands for the synthesis of double-decker complexes of the type [(COTR)(2)M](-). Two ligand derivatives were combined with diamagnetic Y3+ and with the five paramagnetic lanthanide ions from Tb3+ to Tm3+. The more complex substitution pattern in comparison to the parent ligand COT or the popular bistrimethylsilyl derivative allows a sufficient number of signals to be obtained for a comprehensive paramagnetic NMR analysis. The anionic double-decker complexes gave well-resolved NMR spectra where almost all H-1 and C-13 NMR signals could be detected and assigned. With these data, it was possible to separate the two main contributions to the paramagnetic shift (pseudocontact and Fermi contact shifts, respectively) and to determine the magnetic anisotropy of the lanthanide ions in their ligand fields. We can easily obtain the sign and the magnitude of the anisotropy of the magnetic susceptibility, which is itself strongly related to the energy barrier for spin reversal in single-molecule magnets. Our results confirm that Bleaney factors are inadequate descriptors for magnetic anisotropy in these lanthanide complexes.