A family of nickel–lanthanide heterometallic dinuclear complexes derived from a chiral Schiff-base ligand exhibiting single-molecule magnet behaviors

Abstract

A new family of nickel–lanthanide heterometallic dinuclear complexes derived from a chiral Schiff-base ligand, (R,R)-N,N′-bis(3-methoxysalicylidene)cyclohexane-1,2-diamine (H2L), namely [Ni(L)Ln(NO3)3(H2O)] (Ln=Ce (1), Nd (2)) and [Ni(L)Ln(NO3)3] (Ln=Sm (3), Eu (4), Gd (5), Tb (6), Dy (7) and Yb (8)) have been synthesized and structurally characterized. X-ray single-crystal structure determination revealed that these complexes are diphenoxo-bridged NiII–LnIII dinuclear clusters, which crystallize in the chiral space group P1. The solid circular dichroism (CD) spectra confirmed the optical activity and enantiomorphous properties of all these complexes. Magnetic investigations suggested that crystal-field effects and/or the possible antiferromagnetic dipole–dipole interaction between the molecules exist in the complexes and single-ion properties of LnIII ions lead to their magnetic behaviors. The alternating current (ac) magnetic susceptibilities showed that complexes 6 and 7 exhibit field-induced single-molecule magnet behaviors due to the strong anisotropy and important crystal-field effect of the TbIII or DyIII ions. It is noteworthy that the quantum tunneling effect at low temperatures can be effectively suppressed by employing a 2kOe direct current field.