Modulated spin dynamics of [Co₂] coordination helicates via differential strand composition

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Nanomaterials Science

Background:

• Supramolecular chemistry offers routes to nanoscale materials with technological applications.
• Bis-pyrazolylpyridine ligands are key components in constructing complex molecular architectures.

Purpose of the Study:

• To synthesize and characterize dinuclear triple-stranded helicates using Co(II) ions and two distinct bis-pyrazolylpyridine ligands.
• To investigate the magnetic properties and relaxation dynamics of these supramolecular constructs when encapsulating different anionic guests.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• Extensive magnetic measurements (e.g., SQUID magnetometry) and calorimetric measurements (e.g., specific heat).
• Numerical treatments and theoretical calculations to analyze magnetic behavior.

Main Results:

• Three distinct dinuclear triple-stranded helicate complexes were synthesized and structurally characterized: (Cl@[Co2(L1)3])3+, (SiF6@[Co2(L1)(L2)3])2+, and (ClO4@[Co2(L2)3])3+.
• All Co(II) centers within these supramolecular entities exhibited field-induced slow relaxation of magnetization, primarily governed by direct and Raman relaxation mechanisms.
• Specific heat measurements indicated the presence of two vibronic pathways for magnetic relaxation, one related to the host lattice and the other to the encapsulated guest.

Conclusions:

• Dinuclear cobalt helicates can encapsulate various anionic guests, forming stable supramolecular structures.
• The magnetic relaxation in these systems is influenced by both the intrinsic properties of the cobalt centers and the surrounding environment, including the guest molecule.
• Understanding these relaxation mechanisms is crucial for developing nanoscale magnetic materials.