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

Takuya Kanetomo1, Zhen Ni1, Masaya Enomoto1

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A novel hydrogen-bonded metal-organic framework exhibits spin-crossover behavior. This material shows both normal and reverse spin transitions with an asymmetric thermal hysteresis loop after solvent removal.

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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.