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 photoluminescence properties of three new bifunctional Schiff-base complexes [Dy(L1)2(py)2][B(Ph)4]·py (1), [Dy(L1)2Cl(DME)]·0.5DME (2) and [Dy(L2)2Cl]·2.5(C7H8) (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 anisotropic 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.