Breaking Symmetry Relaxes Structural and Magnetic Restraints, Suppressing QTM in Enantiopure Butterfly Fe2Dy2 SMMs**

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(mu(3)-OH)(2)(Me-teaH)(2)(O2CPh)(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 [Fe2Dy2(mu(3)-OH)(2)(Me-teaH)(2)(O2CPh)(6)] since the R enantiomer underwent significant racemisation. To investigate this further, we prepared the [Fe2Dy2(mu(3)-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.