Fachbereich Physik and Institut für Physik und Chemie neuer Materialien, Universität Osnabrück, Barbarastr. 7, Osnabrück D-49069, Germany.
Phys Chem Chem Phys. 2018 Aug 22;20(33):21286-21293. doi: 10.1039/c7cp08689j.
We apply X-ray magnetic circular dichroism to study the internal magnetic structure of two very promising star shaped macrocyclic complexes with a CuII3TbIII core. These complexes are rare examples prepared with a macrocyclic ligand that show indications of SMM (Single Molecule Magnet) behavior, and they differ only in ring size: one has a propylene linked macrocycle, CuII3TbIII(LPr)(NO3)2(MeOH)(H2O)2·3H2O (nickname: Cu3Tb(LPr)), and the other has the butylene linked analogue, CuII3TbIII(LBu)(NO3)2(MeOH)(H2O)·3H2O (nickname: Cu3Tb(LBu)). We analyze the orbital and spin contributions to the Cu and Tb ions quantitatively by applying the spin and orbital sum rules concerning the L2 (M4)/L3 (M5) edges. In combination with appropriate ligand field simulations, we demonstrate that the Tb(iii) ions contribute with high orbital magnetic moments to the magnetic anisotropy, whereas the ligand field determines the easy axis of magnetization. Furthermore, we confirm that the Cu(ii) ions in both molecules are in a divalent valence state, the magnetic moments of the three Cu ions appear to be canted due to 3d-3d intramolecular magnetic interactions. For Cu3Tb(LPr), the corresponding element specific magnetization loops reflect that the Cu(ii) contribution to the overall magnetic picture becomes more important as the temperature is lowered. This implies a low value for the 3d-4f coupling.
我们应用 X 射线磁圆二色性来研究具有 CuII3TbIII 核的两个非常有前途的星形大环配合物的内部磁结构。这些配合物是仅在环大小上有所不同的用大环配体制备的 SMM（单分子磁体）行为的罕见实例：一个具有丙烯连接的大环，CuII3TbIII(LPr)(NO3)2(MeOH)(H2O)2·3H2O（昵称：Cu3Tb(LPr)），另一个具有丁烯连接的类似物，CuII3TbIII(LBu)(NO3)2(MeOH)(H2O)·3H2O（昵称：Cu3Tb(LBu)）。我们通过应用有关 L2（M4）/L3（M5）边缘的自旋和轨道总和规则，对 Cu 和 Tb 离子的轨道和自旋贡献进行定量分析。结合适当的配体场模拟，我们证明 Tb(iii)离子对磁各向异性贡献高轨道磁矩，而配体场决定了磁化的易轴。此外，我们证实了两种分子中的 Cu(ii)离子均处于二价价态，三个 Cu 离子的磁矩由于 3d-3d 分子内磁相互作用而出现倾斜。对于 Cu3Tb(LPr)，相应的元素特异性磁化回线表明，随着温度降低，Cu(ii)对整体磁图的贡献变得更加重要。这意味着 3d-4f 耦合值较低。
