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

Four DyIII 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 DyIII 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 DyDy orientation of [Dy2]. The slightly discrepant coordination environment around the DyIII 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 DyIII 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-Oaux bond from 1 to 4, leading to the stronger uniaxial anisotropy of DyIII ions and better SMM properties of 3 and 4. In addition, complexes 3 and 4 possess higher energy barriers than reported dinuclear DyIII-SMMs also constructed from HL or HL' with β-diketone. It is believed that the ligands coordinating to the DyIII ion at both terminals of the DyDy linkage improve the SMM properties of dinuclear DyIII complexes. This design may provide a new strategy for obtaining dinuclear DyIII-based SMMs.