An Octanuclear Metallosupramolecular Cage Designed To Exhibit Spin‐Crossover Behavior

Abstract By employing the subcomponent self‐assembly approach utilizing 5,10,15,20‐tetrakis(4‐aminophenyl)porphyrin or its zinc(II) complex, 1 H ‐4‐imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O‐symmetric cages having a confined volume of ca. 1300 Å 3 . The use of iron(II) salts yielded coordination cages in the high‐spin state at room temperature, manifesting spin‐crossover in solution at low temperatures, whereas corresponding zinc(II) salts led to the corresponding diamagnetic analogues. The new cages were characterized by synchrotron X‐ray crystallography, high‐resolution mass spectrometry, and NMR, Mössbauer, IR, and UV/Vis spectroscopy. The cage structures and UV/Vis spectra were independently confirmed by state‐of‐the‐art DFT calculations. A remarkably high‐spin‐stabilizing effect through encapsulation of C 70 was observed. The spin‐transition temperature T 1/2 is lowered by 20 K in the host–guest complex.