Cyclic coordination clusters (CCCs) are proving to provide an extra dimension in terms of exotic magnetic behavior as a result of their finite but cyclized chain structures. The Fe 18 Dy 6 CCC is a Single Molecule Magnet with the highest nuclearity among Ln containing clusters. The three isostructural compounds [Fe 18 Ln 6 (μ OH) 6 (ampd) 12 (Hampd) 12 (PhCO 2 ) 24 ](NO 3 ) 6 • 38MeCN for Ln = Dy III (1), Lu III (2), or Y III (3), where H 2 ampd = 2 amino 2 methyl 1,3 propanediol, are reported. These can be described in terms of the cyclization of six {Fe 3 Ln(μOH)(ampd) 2 (Hampd) 2 (PhCO 2 ) 4 } + units with six nitrate counterions to give the neutral cluster. The overall structure consists of two giant Dy 3 triangles sandwiching a strongly antiferromagnetically coupled Fe 18 ring, leading to a toroidal arrangement of the anisotropy axis of the Dy ions, making this the biggest toroidal arrangement on a molecular level known so far.

In this Review we discuss the tuning handles which can be used to steer the magnetic properties of Fe III -4 f "butterfly" compounds. The majority of presented compounds were produced in the context of project A3 "Di-to tetranuclear compounds incorporating highly anisotropic paramagnetic metal ions" within the SFB/TRR88 "3MET". These contain {Fe III 2 Ln 2 } cores encapsulated in ligand shells which are easy to tune in a "test-bed" system. We identify the following advantages and variables in such systems: (i) the complexes are structurally simple usually with one crystallographically independent Fe III and Ln III , respectively. This simplifies theory and anaylsis; (ii) choosing Fe allows 57 Fe Mössbauer spectroscopy to be used as an additional technique which can give information about oxidation levels and spin states, local moments at the iron nuclei and spinrelaxation and, more importantly, about the anisotropy not only of the studied isotope, but also of elements interacting with this isotope; (iii) isostructural analogues with all the available (i. e. not Pm) 4 f ions can be synthesised, enabling a systematic survey of the influence of the 4 f ion on the electronic structure; (iv) this cluster type is obtained by reacting [Fe III 3 O(O 2 CR) 6 (L) 3 ](X) (X = anion, L = solvent such as H 2 O, py) with an ethanolamine-based ligand L' and lanthanide salts. This allows to study analogues of [Fe III 2 Ln 2 (μ 3 -OH) 2 (L') 2 (O 2 CR) 6 ] using the appropriate iron trinuclear starting materials. (v) the organic main ligand can be readily functionalised, facilitating a systematic investigation of the effect of organic substituents on the ligands on the magnetic properties of the complexes. We describe and discuss 34 {M III 2 Ln 2 } (M=Fe or in one case Al) butterfly compounds which have been reported up to 2020. The analysis of these gives perspectives for designing new SMM systems with specific electronic and magnetic signatures [a] Dr.

In an assisted self-assembly approach starting from the [Mn 6 O 2 (piv) 10 (4-Me-py) 2 (pivH) 2 ] cluster a family of MnÀ Ln compounds (Ln = PrÀ Yb) was synthesised. The reaction of [Mn 6 O 2 (piv) 10 (4-Me-py) 2 (pivH) 2 ](1) with N-methyldiethanolamine (mdeaH 2 ) and Ln(NO 3 ) 3 • 6H 2 O in MeCN generally yields two main structure types: for Ln = TbÀ Yb a previously reported Mn 5 Ln 4 motif is obtained, whereas for Ln = PrÀ Eu a series of Mn 7 Ln 3 clusters is obtained. Within this series the Gd III analogue represents a special case because it shows both structural types as well as a third Mn 2 Ln 2 inverse butterfly motif. Variation in reaction conditions allows access to different structure types across the whole series. This prompts further studies into the reaction mechanism of this cluster assisted self-assembly approach. For the Mn 7 Ln 3 analogues reported here variable-temperature magnetic susceptibility measurements suggest that antiferromagnetic interactions between the spin carriers are dominant. Compounds incorporating Ln = Nd III (2), Sm III (3) and Gd III (5) display SMM behaviour. The slow relaxation of the magnetisation for these compounds was confirmed by ac measurements above 1.8 K.

The {Fe2Dy2} butterfly systems can show single molecule magnet (SMM) behaviour, the nature of which depends on details of the electronic structure, as previously demonstrated for the [Fe2Dy2(μ3‐OH)2(Me‐teaH)2(O2CPh)6] compound, where the [N,N‐bis‐(2‐hydroxyethyl)‐amino]‐2‐propanol (Me‐teaH3) ligand is usually used in its racemic form. Here, we describe the consequences for the SMM properties by using enantiopure versions of this ligand and present the first homochiral 3d/4 f SMM, which could only be obtained for the S enantiomer of the ligand for [Fe2Dy2(μ3‐OH)2(Me‐teaH)2(O2CPh)6] since the R enantiomer underwent significant racemisation. To investigate this further, we prepared the [Fe2Dy2(μ3‐OH)2(Me‐teaH)2(O2CPh)4(NO3)2] version, which could be obtained as the RS‐, R‐ and S‐compounds. Remarkably, the enantiopure versions show enhanced slow relaxation of magnetisation. The use of the enantiomerically pure ligand suppresses QTM, leading to the conclusion that use of enantiopure ligands is a “gamechanger” by breaking the cluster symmetry and altering the intimate details of the coordination cluster's molecular structure.

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