Self-assembly of fish-bone and grid-like CoII-based single-molecule magnets using dihydrazone ligands with NNN and NNO pockets

Abstract

Three Co^II complexes, [Co₂(H₂L¹)₂](ClO₄)₄·4CH₃OH (1), [Co₂(H₄L²)₂](ClO₄)₄ (2) and [Co₄(H₄L²)₄](ClO₄)₈ (3), were constructed by the self-assembly of the symmetrical dihydrazone ligands H₂L¹ and H₄L² with Co^II ions under different synthetic conditions. The fish-bone-like complex 1 was obtained using the ligand H₂L¹ in methanol via the solvothermal method, while the self-assembly of H₄L² with Co^II ions is solvent-dependent, producing the fish-bone-like complex 2 and [2 × 2] grid-like complex 3. Magnetic susceptibility measurements and theoretical calculations reveal that the large negative D values for the three complexes stem from their easy-axis magnetic anisotropy. Ac magnetic susceptibility measurements disclosed field-induced slow magnetic relaxation behaviors and the presence of Raman and/or direct processes of the three complexes at various applied dc fields.