Hofmann Clathrates: A "Blue Box" Approach to Modulate Spin-Crossover Properties

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Coordination Chemistry

Background:

• Hofmann coordination polymers (CPs) with cationic ligands are effective for recognizing π-electron-rich aromatic molecules.
• The "little blue box" highlights the potential of CPs in molecular recognition.

Purpose of the Study:

• To investigate the incorporation of hydroquinone molecules into Hofmann CPs using redox-active bipyridinium axial ligands.
• To understand the structural and electronic consequences of guest molecule inclusion in CPs.

Main Methods:

• Synthesis of Hofmann coordination polymers with specific bipyridinium ligands.
• Temperature-dependent single crystal X-ray diffraction to analyze structural changes.
• Magnetic and optical reflectivity measurements to probe spin transition behavior.

Main Results:

• Hydroquinone molecules were successfully incorporated into the Hofmann CPs.
• Guest inclusion induced significant structural modification, including a ~23% volume increase.
• A substantial shift in the spin transition temperature by 150 K was observed.

Conclusions:

• The strong donor-acceptor π-π stacking interaction between ligands and hydroquinone drives structural changes.
• This study demonstrates a novel method for tuning CP properties through guest inclusion.
• The findings offer new avenues for designing responsive coordination materials.