Lattice Solvent Engineering Improves the Stability of a Cobalt Pyrenylnitronylnitroxide Ferrimagnetic Chain

Area of Science:

• Coordination Chemistry
• Materials Science
• Magnetism

Background:

• Single-chain magnets (SCMs) are molecular materials exhibiting slow magnetic relaxation.
• The stability of SCMs is crucial for their practical applications.
• Lanthanide and transition metal complexes are often investigated for SCM properties.

Purpose of the Study:

• To synthesize and characterize a novel 1D ferrimagnetic complex using a pyrenyl nitroxide radical.
• To investigate the magnetic properties, including relaxation and hysteresis, of the synthesized complex.
• To compare the stability of the synthesized complex with a previously reported analogous compound.

Main Methods:

• Reaction of 2-(1'-pyrenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (PyrNN) with [Co(hfac)2(H2O)2] in n-heptane and bromoform.
• Single-crystal X-ray diffraction for structural determination.
• Magnetic susceptibility and relaxation measurements (DC and AC magnetometry).

Main Results:

• Formation of the 1D ferrimagnetic complex [Co(hfac)2PyrNN]·0.5bf·0.5hep (Co-PyrNN·).
• Observation of slow magnetic relaxation with magnetic blocking below 13.4 K.
• Exhibition of magnetic hysteresis with a high coercive field (51 kOe at 5.0 K), classifying it as a hard magnet.
• Determination of an activation barrier for relaxation of (365 ± 24) K.
• The bromoform-containing compound is an isomorphous and more stable variant of the previously reported chloroform-containing analogue.

Conclusions:

• The synthesized Co-PyrNN· complex demonstrates promising hard magnet characteristics and slow magnetic relaxation.
• The choice of lattice solvent (bromoform vs. chloroform) significantly influences the stability of these single-chain magnets.
• This study highlights the importance of solvent engineering in designing stable molecular magnetic materials.