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

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 Ni-II-Ln(III) 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 Ln(III) 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 Tb-III or Dy-III ions. It is noteworthy that the quantum tunneling effect at low temperatures can be effectively suppressed by employing a 2 kOe direct current field. (C) 2015 Elsevier B.V. All rights reserved.