An Octanuclear Metallosupramolecular Cage Designed To Exhibit Spin-Crossover Behavior

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Subcomponent self-assembly is a powerful strategy for constructing complex supramolecular architectures.
• Coordination cages offer confined environments for hosting guest molecules and studying their properties.
• Spin-crossover (SCO) materials exhibit a change in spin state in response to external stimuli, with potential applications in sensing and data storage.

Purpose of the Study:

• To synthesize novel O-symmetric coordination cages with a defined internal volume.
• To investigate the spin-crossover properties of iron(II)-containing cages.
• To explore the effect of guest encapsulation on the spin-crossover behavior.

Main Methods:

• Subcomponent self-assembly using 5,10,15,20-tetrakis(4-aminophenyl)porphyrin, 1H-4-imidazolecarbaldehyde, and metal salts (Zn(II) or Fe(II)).
• Characterization by synchrotron X-ray crystallography, high-resolution mass spectrometry, NMR, Mössbauer, IR, and UV/Vis spectroscopy.
• Density Functional Theory (DFT) calculations to confirm cage structures and electronic properties.

Main Results:

• Successfully prepared O-symmetric cages with a volume of approximately 1300 ų.
• Iron(II) cages displayed high-spin states at room temperature and exhibited spin-crossover in solution at low temperatures.
• Zinc(II) analogues were diamagnetic.
• Encapsulation of C70 fullerenes within the iron(II) cages significantly stabilized the high-spin state, lowering the spin-transition temperature (T1/2) by 20 K.

Conclusions:

• The study demonstrates the successful synthesis and characterization of novel coordination cages.
• The iron(II) cages exhibit tunable spin-crossover behavior, influenced by guest encapsulation.
• The observed high-spin stabilization by C70 highlights the potential of these cages for host-guest chemistry and spin-state manipulation.