Preparation, Crystal Structures, and Magnetic Features for a Series of Dinuclear [Ni^IILn^III] Schiff-Base Complexes: Evidence for Slow Relaxation of the Magnetization for the Dy^III Derivative

A series of dinuclear [Ni^IILn^III] Schiff-base complexes (using a Schiff-base dicompartmental ligand derived from o-vanillin [H₂valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]) with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and a hydroxo-bridged tetranuclear [Ni^IIYb^III] are reported. The crystal structures have been solved for 10 dinuclear complexes revealing four arrangements for the dinuclear units, which are modulated by the coordinated solvent molecules and the nitrato-anion interactions. The magnetic behaviors have been investigated, and the nature of the Ni^II–Ln^III exchange interaction has been emphasized by comparison with the behavior of the related [Zn^IILn^III] derivatives. This allowed for establishing that the interaction within these compounds is antiferromagnetic with the 4f ions of the beginning of the Ln series and turns ferromagnetic from Gd^III toward the end of the series. AC susceptibility investigations clearly show the occurrence of slow relaxation processes of the magnetization close to 2 K for the dinuclear [Ni^IIDy^III] complex.