Tuning magnetic anisotropy via terminal ligands along the Dy⋯Dy orientation in novel centrosymmetric [Dy2] single molecule magnets

Abstract

Four Dy^III complexes, [Dy₂(NO₃)₄(L)₂(H₂O)₂]·2MeCN (1), [Dy₂(NO₃)₄(L)₂(H₂O)₂]·2(NO₃)·DMBD·2MeOH (2), [Dy₂(NO₃)₄(L)₂(TPO)₂]·2MeCN (3) and [Dy₂(L′)₆(H₂O)₂]·4MeCN (4), were elaborately synthesized, structurally characterized and magnetically investigated (HL = 2,6-dimethoxyphenol, HL′ = 4-hydroxy-3,5-dimethoxybenzaldehyde, DMBD = 1,1′-dimethyl-[4,4′-bipyridine]-1,1′-diium and TPO = phosphine triphenyl oxide). In 1–3, the nearly planar molecular structures consisting of two Dy^III ions and two L ligands are almost perpendicular to four nitrate ligands, which provides an opportunity to introduce auxiliary ligands (H₂O or TPO) at the terminal position along the Dy⋯Dy orientation of [Dy₂]. The slightly discrepant coordination environment around the Dy^III ion with different terminal ligands plays a key role in tuning the magnetic anisotropy, and further strongly affects the magnetic properties of 1–4. The magnetic studies reveal that they all behave as single-molecule magnets (SMMs) at zero dc field with ferromagnetic dipole–dipole interaction between Dy^III ions. The dynamic magnetic investigations give the energy barriers of 107.5 (1), 127.1 (2), 168.7 (3) and 251.9 K (4), respectively. The magnetic axis orientation of the ground state gradually verges on the Dy–O_aux bond from 1 to 4, leading to the stronger uniaxial anisotropy of Dy^III ions and better SMM properties of 3 and 4. In addition, complexes 3 and 4 possess higher energy barriers than reported dinuclear Dy^III-SMMs also constructed from HL or HL’ with β-diketone. It is believed that the ligands coordinating to the Dy^III ion at both terminals of the Dy⋯Dy linkage improve the SMM properties of dinuclear Dy^III complexes. This design may provide a new strategy for obtaining dinuclear Dy^III-based SMMs.