Robust and High Temperature Spin Crossover Controlled via the Self-Assembly of Chiral and Racemic Polymorphs in Triazolylimine [Fe2L3](BF4)4 Helicates

Three new chiral spin crossover (SCO) dinuclear triple helicates of type [Fe2L3]­(BF4)4 are reported exhibiting a robust magnetic behavior that is resistant to rapid changes in temperature, moisture and light. The selective formation of racemic aggregates upon crystallization of a solution of the respective racemic complexes was found to be associated with the helical torsion, intermetallic distance as well as the spatial arrangement of the enantiomers and anions. Torsional stress and particular hydrogen bonding interactions were related to the potential coiling and uncoiling mechanisms inherent to some helically chiral systems as well as to the efficacy of cooperativity transmission within the crystal lattice. These unique structural dynamics were correlated with the display of a chirality-dependent semiabrupt SCO profile observed for each enantiopure aggregate. This study highlights how the molecular shape as well as the crystal packing of helically chiral compounds can be altered to modulate the magnetic behavior toward a robust and high temperature SCO system.