Tetranuclear [Cu–Ln]2 single molecule magnets: synthesis, structural and magnetic studies

Abstract

A trianionic ligand H₃L (2-hydroxy-N-(2-{[(2-hydroxyphenyl)methylene]amino}-2-methylpropyl)benzamide) with an inner N₂O₂ coordination site and an oxygen atom coming from an amide function not involved in this site yields monoanionic LCu⁻ complexes that react with Ln(hfa)₃·2H₂O (hfa = hexafluoroacetylacetonato ligand) to give dinuclear Cu–Ln complexes that self-assemble into tetranuclear species, as demonstrated by the structural determination of the [LCuDy(hfa)₂(dmf)₂]₂ complex. High-spin species are then isolated for two ferromagnetic interactions are active in the [Cu–Gd]₂ entities, through the double phenoxo bridge (J = 3.2 cm⁻¹) and through the single amide bridge (j = 0.54 cm⁻¹). These interactions are still present in the [Cu–Tb]₂ and [Cu–Dy]₂ complexes which behave as single molecule magnets (SMMs), due to the introduction of anisotropic Ln ions in place of Gd ions.