Breaking Symmetry Relaxes Structural and Magnetic Restraints, Suppressing QTM in Enantiopure Butterfly Fe$_{2}$Dy$_{2}$ SMMs**

These 2 coordination clusters are similar but different both in the fine details of their structures as well as their magnetic behaviour. [Fe$_{2}$Dy$_{2}$(μ$_{3}$-OH)$_{2}$(Me-teaH)$_{2}$(O$_{2}$CPh)$_{6}$], which normally forms with the racemic version of Me-teaH3 by using enantiopure ligand, allows access to the S-version, but for the R-version there is significant racemisation. Surprisingly, by using the synthesis of [Fe$_{2}$Dy$_{2}$(μ$_{3}$-OH)$_{2}$(Me-teaH)$_{2}$(O$_{2}$CPh)$_{4}$(NO$_{3}$)$_{2}$] both enantiopure R- and S-compounds were obtained. In both cases breaking the symmetry of the parent compounds leads to enhanced SMM behaviour.

The {Fe$_{2}$Dy$_{2}$} 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 [Fe$_{2}$Dy$_{2}$(μ$_{3}$-OH)$_{2}$(Me-teaH)$_{2}$(O$_{2}$CPh)$_{6}$] compound, where the [N,N-bis-(2-hydroxyethyl)-amino]-2-propanol (Me-teaH$_{3}$) 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 [Fe$_{2}$Dy$_{2}$(μ$_{3}$-OH)$_{2}$(Me-teaH)$_{2}$(O$_{2}$CPh)$_{6}$] since the R enantiomer underwent significant racemisation. ... mehrTo investigate this further, we prepared the [Fe$_{2}$Dy$_{2}$(μ$_{3}$-OH)$_{2}$(Me-teaH)$_{2}$(O$_{2}$CPh)$_{4}$(NO$_{3}$)$_{2}$] 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.