Institute of Inorganic Chemistry, University of Heidelberg , Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany.
J Am Chem Soc. 2013 Sep 25;135(38):14349-58. doi: 10.1021/ja4069485. Epub 2013 Sep 17.
Several small paramagnetic complexes combine large hyperfine NMR shifts with large magnetic anisotropies. The latter are a prerequisite for single molecule magnet (SMM) behavior. We choose the SMM tris(octabutoxyphthalocyaninato) diterbium (1) for a high resolution NMR study where we combined for the first time a comprehensive (1)H and (13)C chemical shift analysis of a SMM with the evaluation of large residual dipolar couplings (RDCs). The latter are a consequence of partial alignment of SMM 1 in the strong magnetic field of the NMR spectrometer. To the best of our knowledge RDCs in SMMs have never been reported before. We measured RDCs between -78 and +99 Hz for the (13)C-(1)H vectors of CH bonds and up to -109 Hz for (1)H-(1)H vectors of geminal hydrogen atoms (magnetic field of 14.09 T, temperature 295 K). Considerable negative Fermi contact shifts (up to -60 ppm) were determined for (13)C atoms at the phthalocyaninato core. Paramagnetic (13)C NMR shifts of the butoxy chains as well as all (1)H NMR chemical shifts are a result of pseudocontact shifts (pcs), and therefore it is easily possible to determine the positions of the respective nuclei in solution. Measurements of CH and HH vectors by RDC analysis are in accordance with the geometry as determined by the pseudocontact shifts, but in addition to that, RDCs give information about internal mobility. The axial component of the magnetic susceptibility tensor has been determined independently by pcs and by RDC.
一些小的顺磁配合物将大的超精细 NMR 位移与大的磁各向异性结合在一起。后者是单分子磁体（SMM）行为的前提。我们选择 SMM 三（辛氧基酞菁）二铽（1）进行高分辨率 NMR 研究，在该研究中，我们首次将 SMM 的全面（1）H 和（13）C 化学位移分析与大的残余偶极耦合（RDC）的评估结合起来。后者是 SMM 1 在 NMR 光谱仪强磁场中部分取向的结果。据我们所知，以前从未报道过 SMM 中的 RDC。我们测量了-CH 键的（13）C-（1）H 矢量之间的 RDC 范围为-78 至+99 Hz，偕二氢原子的（1）H-（1）H 矢量的 RDC 高达-109 Hz（磁场为 14.09 T，温度为 295 K）。在酞菁核的（13）C 原子上确定了相当大的负费米接触位移（高达-60 ppm）。烷氧基链的顺磁（13）C NMR 位移以及所有（1）H NMR 化学位移均为赝接触位移（pcs）的结果，因此很容易确定各核在溶液中的位置。通过 RDC 分析测量 CH 和 HH 矢量与由赝接触位移确定的几何形状一致，但除此之外，RDC 还提供了关于内部流动性的信息。磁各向异性张量的轴向分量通过 pcs 和 RDC 独立确定。
