Tuning the Magnetization Dynamic Properties of Nd⋅⋅⋅Fe and Nd⋅⋅⋅Co Single‐Molecular Magnets by Introducing 3 d–4 f Magnetic Interactions

By using paramagnetic [Fe(CN)6 ]3- anions in place of diamagnetic [Co(CN)6 ]3- anions, two field-induced mononuclear single-molecular magnets, [Nd(18-crown-6)(H2 O)4 ][Co(CN)6 ]⋅2 H2 O (1) and [Nd(18-crown-6)(H2 O)4 ][Fe(CN)6 ]⋅2 H2 O (2), have been synthesized and characterized. Single-crystal X-ray diffraction analysis revealed that compounds 1 and 2 were ionic complexes. The NdIII ions were located inside the cavities of the 18-crown-6 ligands and were each bound by four water molecules on either side of the crown ether. Magnetic investigations showed that these compounds were both field-induced single-molecular magnets. By comparing the slow relaxation behaviors of compounds 1 and 2, we found significant differences between the direct and Raman processes for these two complexes, with a stronger direct process in compound 2 at low temperatures. Complete active space self-consistent field (CASSCF) calculations were also performed on two [Nd(18-crown-6)(H2 O)4 ]3+ fragments of compounds 1 and 2. Ab initio calculations showed that the magnetic anisotropies of the NdIII centers in complexes 1 and 2 were similar to each other, which indicated that the difference in relaxation behavior was not owing to the magnetic anisotropy of NdIII . Our analysis showed that the magnetic interaction between the NdIII ion and the low-spin FeIII ion in complex 2 played an important role in enhancing the direct process and suppressing the Raman process of the single-molecular magnet.