Solid-State Hydrogen-Bond Alterations in a [Co₂ Fe₂ ] Complex with Bifunctional Hydrogen-Bonding Donors

Area of Science:

• Coordination Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• External stimuli-responsive spin crossover materials are crucial for advanced functional devices.
• Hydrogen-bonding interactions play a significant role in modulating the properties of coordination complexes.

Purpose of the Study:

• To synthesize and characterize a novel hydrogen-bonding donor-acceptor system based on a tetranuclear cobalt-iron complex.
• To investigate the effect of solvent molecules and hydrogen-bonding interactions on the electron-transfer-coupled spin transition (ETCST) behavior.
• To explore the potential for solid-state modulation of hydrogen-bond strengths via external stimuli.

Main Methods:

• Co-crystallization of a tetranuclear [Co2Fe2] complex with p-aminobenzoic acid.
• X-ray structural analysis to determine crystal structures and hydrogen-bonding arrangements.
• Variable temperature Infrared (IR) spectroscopy to study dynamic hydrogen-bonding interactions and spin transitions.

Main Results:

• The synthesized compound (1solv) displayed a gradual electron-transfer-coupled spin transition (ETCST).
• Removal of solvent molecules (1desolv) induced an abrupt thermal ETCST with a higher transition temperature.
• X-ray analysis revealed significant alterations in hydrogen-bonding modes between the complex and p-aminobenzoic acid upon desolvation, correlating with modified ETCST.

Conclusions:

• The hydrogen-bonding network in the tetranuclear [Co2Fe2] complex is highly sensitive to solvent content.
• External stimuli, such as solvent removal, can effectively modulate hydrogen-bond strengths and consequently alter the spin transition properties.
• This system demonstrates a promising approach for designing solid-state materials with tunable spin-state behaviors.