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) ] anions in place of diamagnetic [Co(CN) ] anions, two field-induced mononuclear single-molecular magnets, [Nd(18-crown-6)(H O) ][Co(CN) ]⋅2 H O (1) and [Nd(18-crown-6)(H O) ][Fe(CN) ]⋅2 H O (2), have been synthesized and characterized. Single-crystal X-ray diffraction analysis revealed that compounds 1 and 2 were ionic complexes. The Nd 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)(H O) ] fragments of compounds 1 and 2. Ab initio calculations showed that the magnetic anisotropies of the Nd 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 Nd . Our analysis showed that the magnetic interaction between the Nd ion and the low-spin Fe ion in complex 2 played an important role in enhancing the direct process and suppressing the Raman process of the single-molecular magnet.