Hofmann Clathrates: A “Blue Box” Approach to Modulate Spin‐Crossover Properties

Hofmann coordination polymers (CPs) with cationic ligands provide an innovative strategy for recognizing π‐electron‐rich aromatic molecules – similar to the “little blue box”. In this study, we demonstrate that hydroquinone molecules can be incorporated into these coordination polymers when redox‐active bipyridinium derivatives are used as axial ligands. The insertion leads to a significant structural modification, resulting in a shift of the spin transition by 150 K and an approximate 23 % increase in volume, caused by the strong donor‐acceptor π‐π stacking interaction formed between the ligands and the guest molecule. These findings have been confirmed through temperature‐dependent single crystal X‐ray diffraction, magnetic measurements and optical reflectivity measurements.