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

Four Dy complexes, [Dy(NO)(L)(HO)]·2MeCN (1), [Dy(NO)(L)(HO)]·2(NO)·DMBD·2MeOH (2), [Dy(NO)(L)(TPO)]·2MeCN (3) and [Dy(L')(HO)]·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 ions and two L ligands are almost perpendicular to four nitrate ligands, which provides an opportunity to introduce auxiliary ligands (HO or TPO) at the terminal position along the DyDy orientation of [Dy]. The slightly discrepant coordination environment around the Dy 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 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 bond from 1 to 4, leading to the stronger uniaxial anisotropy of Dy ions and better SMM properties of 3 and 4. In addition, complexes 3 and 4 possess higher energy barriers than reported dinuclear Dy-SMMs also constructed from HL or HL' with β-diketone. It is believed that the ligands coordinating to the Dy ion at both terminals of the DyDy linkage improve the SMM properties of dinuclear Dy complexes. This design may provide a new strategy for obtaining dinuclear Dy-based SMMs.