Synthesis, Structure, Magnetic and Photoluminescent Properties of Dysprosium(III) Schiff Base Single-Molecule Magnets: Investigation of the Relaxation of the Magnetization

We report here the synthesis, structure, magnetic and photoluminescent properties of three new bifunctional Schiff-base complexes [Dy(L₁ )₂ (py)₂ ][B(Ph)₄ ]⋅py (1), [Dy(L₁ )₂ Cl(DME)] ⋅ 0.5DME (2) and [Dy(L₂ )₂ Cl] ⋅ 2.5(C₇ H₈ ) (3) (HL₁ =Phenol, 2,4-bis(1,1-dimethylethyl)-6-[[(2-methoxy-5-methylphenyl)imino]methyl]; HL₂ =Phenol, 2,4-bis(1,1-dimethylethyl)-6-[[(2-methoxyphenyl)imino]methyl]). The coordination environment of the Dy³⁺ ion and the direction of the anisotropic axis may be controlled by the combination of the substituent groups of the Schiff bases, the nature of the counter-ions (Cl^- vs. BPh₄ ^- ) and the coordinative solvent molecules. A zero-field slow relaxation of the magnetization is evidenced for all complexes but strong differences in the relaxation dynamics are observed depending on the Dy³⁺ site geometry. In this sense, complex 1 exhibits an anisotropy barrier of 472 cm^-1 _, which may be favourably compared to other related examples due to the shortening of the Dy-O bond in the axial direction. Besides, the three complexes exhibit a ligand-based luminescence making them as bifunctional magneto-luminescent systems.