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

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)center dot 2H(2)O ( 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.