# New Materials and Effects in Molecular Nanomagnets
## 4 Single-Molecule Magnets
investigated the molecules containing heterometallic (FeDy) complexes with the formulas C50H100 Dy2 Fe4N10O32 and C40H76 Dy2 Fe8N12O42. The structures of the complexes showed different bonds when the molecules formed a crystal, thus resulting in different stacking patterns and, correspondingly, different temperature-dependent susceptibilities in different DC fields [69]. [PERSON] et al. also investigated Dy compounds, more specifically [Dy(TTA)\({}_{2}\)L]\({}_{2}\) and [Dy(dbm)\({}_{2}\)L]\({}_{2}\) with the \(\beta\)-diketones TTA (2-thenoyltrifluoroacetone) and dbm (dibenzoyl-methane), as well as the Schiff base ligand 2:[(4-chlorophenylenyl)imino]methyl]-8-hydroxyquinoline. While the structures, as depicted in Figure 3, are similar for both compounds, strongly different susceptibilities were also measured [70]. Figure 3: Molecular structures of **(a)** [Dy(TTA)\({}_{2}\)L]\({}_{2}\); **(b)** [Dy(dbm)\({}_{2}\)L]\({}_{2}\). Hydrogen atoms are omitted for clarity; abbreviations are given in the main text. Reprinted from [70], copyright 2020, with permission from Elsevier. Generally, many researchers have concentrated on the aforementioned 3d-4f metal complexes. [PERSON] et al. recently gave an overview of the structural variety of 3d-4f heterometallic polyoxometalates, including dimers, trimers, and tetramers, and the different polyanions, such as pure 3d-4f polyanions, 3d substituted anions with 4f linkers, 4f substituted anions with 3d linkers, and polyoxometalates with 3d and 4 d linkers. They concentrated not only on the possibilities of using such 3d-4f polyoxometalates as single-molecule or single-ion magnets, but also for applications in catalysis [71]. [PERSON] et al. prepared 3d-4f clusters with CoIII\({}_{2}\)DyIII\({}_{4}\) and CoIII\({}_{2}\)GdIII\({}_{4}\), respectively, using chemical reactions and structural X-ray characterization. Their investigations revealed centrosymmetric hexanuclear metallic cores. Interestingly, they found ferromagnetic coupling for the DyIII ions and antiferromagnetic coupling for the GdIII ions, in spite of the otherwise identical composition, with the lanthanide ions being coplanar, thus underlining the importance of the choice of the lanthanide [72]. On the other hand, Dy4 was also reported in similar structures, working as a single-molecule magnet, but with different energy barriers and other physical properties, indicating the importance of the whole molecular structure, even in the case of structures that seemed very similar at first glance [73; 74; 75]. In these works, the structural single-crystal X-ray diffraction investigations were additionally supported by dc and ac magnetic susceptibility studies [73]. In tetranuclear 3d-4f systems containing DyFe(CN)\({}_{6}\), TbFe(CN)\({}_{6}\), HoFe(CN)\({}_{6}\), DyCo(CN)\({}_{6}\), TbCo(CN)\({}_{6}\), or HoCo(CN)\({}_{6}\), respectively, [PERSON] et al. also found differences between the isomorphic compounds. Especially, the complex containing DyFe(CN)\({}_{6}\) showed a weak antiferromagnetic interaction between Dy and Fe, and no slow magnetic relaxation above 2 K, which would be typical for an SMM, while this effect was found in the complex containing DyCo(CN)\({}_{6}\). [PERSON] et al. attributed this finding to a larger intermolecular Dy-Dy distance for the second complex, based on the diamagnetic properties of the CoIII ion, as opposed to the paramagnetic FeIII ion [76]. The authors concluded these results from magnetic susceptibility experiments, including real and imaginary parts, as a function of the temperature within the range of 2-20 K. Many other authors investigated these and other lanthanide-hexacyanidometallate SMMs [77; 78; 79; 80]. [PERSON] et al. also investigated CoIII\({}_{2}\) combined with Dy, using structural characterization, in this case in the complex {[CoIII\({}_{2}\)Dy\({}_{3}\)Na(CH\({}_{3}\)CH\({}_{2}\)COO)\({}_{6}\)(OH)\({}_{6}\)(NO\({}_{3}\))\({}_{4}\)(H\({}_{2}\)O)\({}_{2}\)]\(\cdot\)H\({}_{2}\)O]\({}_{n}\).