# New Materials and Effects in Molecular Nanomagnets
## (1) Ferromagnetic-chain strategy  
### (2) Ferrimagnetic-chain strategy  
Figure 5: Possible strategies for single-chain magnets. Reprinted from [22], copyright 2010, with permission from [PERSON]. Nowadays, research on SCMs is, on the one hand, still focused on fully understanding the theoretical basics, and, on the other hand, practical, application-related interests such as high blocking temperatures and very slow relaxation are also being investigated. Two magnetic phase transitions were found by [PERSON] et al. in a Ni\({}_{4}\)O\({}_{4}\)-cubane-based network of 1D linear chains of NiII ions, crosslinked via Ni\({}_{4}\)O\({}_{4}\) cubanes. While magnetic ordering occurred below 23.9 K, a structural phase transition was recognized at 2.8 K through the use of susceptibility measurements [115]. Another interesting feature was reported by [PERSON] et al. for CoII chains. In the single-chain magnets of Co(hfac)\({}_{2}\)(R-NapNIT) with R-NapNIT = 2-(2'-(R-naphthyl)]-4,4,5,5-tetram ethylimidazololine-1-oxyl-3-oxide and R = MeO or EtO, very large coercive fields were found at low temperatures, i.e., 62 kOe and 65 kOe for both compounds, respectively [116]. The research group used static and pulsed high-intensity magnetic fields to obtain these results. [PERSON] et al. prepared azide-bridged homogenin coordination polymers based on FeII and CoII, more specifically [Fe\({}_{2}\)(Brp)\({}_{2}\)(N\({}_{3}\))\({}_{4}\)]\({}_{n}\) and [Co\({}_{4}\)(Brzp)\({}_{4}\)(N\({}_{3}\))\({}_{8}\)-(MeOH)\({}_{2}\)]\({}_{n}\), respectively, with bzp = 2-benzoylpyridine, forming neutral chains with azido-bridges. They found ferromagnetic intrachain interactions in both SCMs and broad hysteresis loops [117]. Cyanbridges were used to prepare a [Mo(CN)\({}_{7}\)]\({}^{4-}\) based SCM in which the magnetic anisotropy stemmed from the anisotropic magnetic exchange of the cyanide ligands of the MoIII units and the MnII spins, resulting in relatively high blocking temperature and large coercive fields of up to 15 kOe [118]. [PERSON] et al. also used cyanide bridges in an Fe\({}_{2}\)Co 4,2-ribbon single-chain magnet [119]. Several other studies on cyanide-bridged SCMs have been performed by [PERSON] and [PERSON] with their groups [120; 121; 122], as well as by other research groups [123; 124; 125]. Other lanthanides may also offer interesting SCM properties. [PERSON] et al. prepared [LnCu(hfac)\({}_{5}\)NIT-Ph-\(p\)-OCH\({}_{2}\)trz.\(0.5\)C\({}_{6}\)H\({}_{14}\)]\({}_{n}\) with Ln = Er, Ho, Yb, resulting in ladder-like chain structures, as depicted in Figure 6 for the case of Er. Here, inserting Ho into the complex resulted in single-chain magnet behavior, as indicated by the frequency-dependent out-of-phase AC magnetic susceptibility [126]. In the so-called \"butterfly molecule\" [Fe\({}_{3}\)Y(\(\upmu\)3-O)\({}_{2}\)(CCl\({}_{3}\)COO)\({}_{8}\)(H\({}_{2}\)O)(THF)\({}_{3}\)], the Fe\({}^{3+}\) ions form an Fe\({}_{3}\) cluster with a strong intracluster exchange and a \(S\) = 5/2 total spin without long-range magnetic ordering down to 20 mK. At low temperatures, a quantum tunneling process was revealed, as is usual in SMMs, and this single-chain magnet was described as combining single-molecule magnetic anisotropy with a spin-spin correlation along the chains [127]. Single-chain magnet behavior was also observed, using powder X-ray diffraction, for the Cu-Tb chain complexes [TbCu(hfac)\({}_{5}\)NIT-Ph-\(p\)-OCH\({}_{2}\)trz.\(0.5\)C\({}_{6}\)H\({}_{14}\)]\({}_{n}\) and [LnCu(hfac)\({}_{5}\)NIT  
Figure 6: Crystal packing of [ErCu(hfac)\({}_{5}\)NIT-Ph-\(p\)-OCH\({}_{2}\)trz.\(0.5\)C\({}_{6}\)H\({}_{14}\)]\({}_{n}\) chains. Reprinted from [126], copyright 2020, with permission from Elsevier. Ph-\(p\)-OCH\({}_{2}\)trz]\({}_{n}\) with NIT-Ph-\(p\)-OCH\({}_{2}\)trz = 2-(4-((1H-1,2,4-triazolezol-1-yl)methoxy)phenyl)-4,4,5,-tetramethylimidazololine-1-oxyl-3-oxide and hfac = hexafluoroacetylacetonate. While the first complex shows a ladder-chain structure, the second one forms a linear chain.