Field-Induced Slow Magnetic Relaxation in a New Family of Tetranuclear Double-Stranded Cu₂^II–Ln₂^III Metallohelicates

A series of tetranuclear Cu₂^IILn₂^III (Ln^III from La^III to Yb^III), double-stranded metallohelicates have been synthesized using a bis-bidentate flexible ligand obtained by condensing o-vanillin with 4,4′-oxydianiline. The complexes exhibit a variety of Ln^III environments and decreasing coordination number along the series and several nitrato coordination modes proved by the structural determination of the La^III (1La), Sm^III (4Sm), Gd^III (5Gd), Er^III (9Er), and Yb^III (10Yb) derivatives. The other members of the family (2Ce, 3Pr, 6Tb, 7Dy, and 8Ho) have been characterized by powder X-ray diffraction to verify their isostructurality. Susceptibility measurements show field-induced slow relaxation of the magnetization for the anisotropic Tb^III and Dy^III complexes and for the isotropic Gd^III system.