Enhancing the single-molecule magnetic performance of β-diketonate Dy(<sc>iii</sc>) complexes by modulating the coordination microenvironment and magnetic interaction: from a mononuclear to a dinuclear structure

Based on a beta-diketonate ligand, a mononuclear Dy(iii) complex, [Dy(dmpd)3(bpy)] (1) (dmpd = 4,4-dimethyl-1-phenylpentane-1,3-dione, bpy = 2,2 '-dipyridyl), of [DyN2O6] type has been synthesized with a capping nitrogen-containing coligand. Then, a dual capping coligand 2,2 '-bipyrimidine (bmp) is introduced to be a bridge to link two beta-diketonate-Dy(iii) motifs, leading to a new dinuclear Dy(iii) complex, [Dy2(dmpd)6(bmp)] (2). Dy(iii) centers in both complexes feature an N2O6 octacoordinated environment with an approximate square-antiprism geometry (D-4d). Without a dc field, the SMM behaviour is absent in complex 1, but can be clearly observed in dinuclear 2 with a U(eff )of 87.29 K. The significantly improved magnetism arising in 2 is mainly due to the modulation of the coordination environment around the Dy(iii) ions and the superexchange magnetic interactions inside the dinuclear units, thus allowing for the effective inhibition of the quantum tunneling of magnetization at low temperatures and promotion of the uniaxial magnetic anisotropy. For 1, a diamagnetic Y(iii) analogue [Y(dmpd)(3)(bpy)] (3) and diluted sample 1@Y were constructed to further perform the dilution experiment, coupled with theoretical calculations further supporting that the synergetic contributions of intermolecular dipole-dipole interactions, intramolecular coupling and uniaxial magnetic anisotropy cause the enhancement of dynamic magnetic relaxation.