Hydrogen-bonded cobalt(II)-organic framework: normal and reverse spin-crossover behaviours.

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• Metal-organic frameworks (MOFs) are crystalline materials constructed from metal ions or clusters coordinated to organic ligands.
• Spin-crossover (SCO) materials can switch between low-spin and high-spin states in response to external stimuli like temperature or pressure.
• Hydrogen-bonded MOFs (H-MOFs) offer unique structural properties and potential for functional applications.

Purpose of the Study:

• To synthesize and characterize a novel hydrogen-bonded metal-organic framework (H-MOF).
• To investigate the spin-crossover (SCO) properties of the desolvated H-MOF.
• To explore the thermal hysteresis behavior of the SCO transitions.

Main Methods:

• Synthesis of the H-MOF [Co(HL)2](DMF)1.2(H2O)2.4 (1·solv) using 2,2':6',2''-terpyridine-5,5''-diyl biscarboxylate ligand.
• Single-crystal X-ray diffraction to determine the crystal structure, revealing a 4-fold interpenetrating H-bonded diamond framework.
• Desolvation of the framework to obtain 1·desolv.
• Variable-temperature magnetic susceptibility measurements to study spin-crossover (SCO) behavior.

Main Results:

• The H-MOF 1·solv features an intermolecular single hydrogen bond between carboxy and carboxylate groups.
• The crystal structure of 1·solv displays a 4-fold interpenetrating H-bonded diamond network.
• The desolvated material, 1·desolv, exhibits both normal and reverse spin-crossover (SCO) transitions.
• An asymmetric thermal hysteresis loop was observed for the SCO behavior in 1·desolv.

Conclusions:

• A novel H-MOF with a unique interpenetrating diamond framework and hydrogen bonding has been successfully synthesized.
• The desolvated H-MOF demonstrates intriguing spin-crossover properties with both normal and reverse transitions.
• The observed asymmetric thermal hysteresis loop in the SCO behavior highlights the potential of this material for memory devices or sensors.