# New Materials and Effects in Molecular Nanomagnets
## 4 Single-Molecule Magnets
They found a trigonal bipyramidal geometry in the Co\({}_{2}\)Dy\({}_{3}\) core and a single-molecule magnetic behavior for the whole complex with an energy barrier of 60.3 K under a zero dc field [81]. CoII was investigated by [PERSON] et al. They prepared 3d-4f heterometallic complexes with CoII\({}_{2}\)-LnIII\({}_{2}\) units, applying Nd, Sm, Eu, Gd, Tb, Dy, and Er as the lanthanides. The structures of the complexes containing Er and all of the other lanthanides are depicted in Figure 4. Interestingly, they found, on the one hand, that the molecular structures of all complexes besides the one containing Er were identical, which was attributed to ErIII being smaller than DyIII. On the other hand, a weak ferromagnetic interaction between the metal ions was found for Gd and Er, while the complex containing Dy again showed field-induced slow magnetic relaxation, typical for SMMs [82]. [PERSON] et al. also worked with Co\({}^{\Pi}\), in the form of Co\({}^{\Pi}\)-Ln\({}^{\Pi\Pi}\) with the lanthanides Y, Gd, Tb, Dy, and Ho, and found SMM behavior for the combination with Dy [83]. In these studies, the magnetic susceptibility method was complemented with fluorescence spectroscopy, revealing the characteristic energy levels of the Tb ions. Again, another metal, Cr, was used by [PERSON] et al. in different coordination polymers with the basic units of Gd\({}_{4}\)Cr\({}_{4}\), Tb\({}_{4}\)Cr\({}_{4}\), or Er\({}_{4}\)Cr\({}_{4}\). They found a butterfly-like structure of the basic unit and each basic unit was connected with four Ln\({}_{4}\)Cr\({}_{4}\) clusters in a 3D structure resembling a 1D honeycomb [84]. Apart from standard single-crystal X-ray diffractometry and magnetic susceptibility studies, they employed isothermal thermogravimetry/differential thermal analysis (TG/DTA) experiments to detect the magnetic entropy changes. With Zn as the metal and Dy, Tb, or Er as the lanthanide, [PERSON] et al. prepared heterometallic complexes with a windmill-like structure and a (Ln\({}_{3}\)Zn\({}_{3}\)) core. They found field-induced frequency-dependent signals, measured by field-induced frequency-dependent signals, as a sign of SMM behavior for Dy and Tb, while the Er-based complex showed a slow magnetic relaxation [85]. Cu was combined with Dy, Tb, and Gd to prepare the tetranuclear Cu\({}^{\Pi}\)\({}_{2}\)Ln\({}^{\Pi\Pi}\) complexes. These complexes were isostructural and isomorphic, and showed ferromagnetic interactions between Cu\({}^{\Pi}\) and Ln\({}^{\Pi\Pi}\) in all cases, as well as SMM behavior, with Cu\({}^{\Pi}\)Gd\({}^{\Pi\Pi}\) exhibiting a magneto-caloric effect [86]. Quite a different approach was recently chosen by [PERSON] et al., who combined Mn\({}_{6}\) clusters with Dy\({}^{\Pi\Pi}\) and a triazine-like ligand to create a large bean-shaped cluster [Mn\({}_{26}\)Dy\({}_{6}\)O\({}_{16}\) (OH)\({}_{12}\)(O\({}_{2}\)CCHMe\({}_{2}\))\({}_{42}\) with Mn\({}^{\Pi}\), Mn\({}^{\Pi\Pi}\), and Dy\({}^{\Pi\Pi}\) ions, in this way enabling diverse magnetic interactions and leading to a high-nuclearity Mn-Dy cluster that still exhibits an SMM behavior [87]. Multi-decker systems of lanthanides with phthalocyanine molecules have been described by different groups. [PERSON] et al. prepared sandwich-like complexes based on phthalocyanine molecules and a closed-macrocyclic Schiff base of the form [(Pc)\({}_{2}\)Ln\({}_{3}\)(L)(OAc)(OCH\({}_{3}\))\({}_{2}\)] (with Ln\({}^{3+}\) = Dy\({}^{3+}\) or Er\({}^{3+}\), H\({}_{2}\)Pc = phthalocyanine and H\({}_{2}\)L = closed-macrocyclic Schiff base molecules), and found a single-molecule magnetic behavior in the complex containing dysprosim [88]. In these sandwich structures, the strong coupling between the lanthanide ions resulted in an important role for the rare earth atom in the SMM properties [89], making these multi-decker structures highly interesting for diverse applications [90; 91; 92]. Going one step further, [PERSON] et al.