Structural determinations and magnetic properties of a "chiral at metal" complex and its resulting [Cu-Ln] compounds.

A chiral trianionic ligand possessing one amide, one imine, two phenol functions and one asymmetric carbon atom into its diamino chain reacts with Cu ions to yield anionic [LCu] units that crystallize in a non-centrosymmetric space group as infinite 1D zig-zag chains in which a transmission of chirality to the Cu ion is effective. The distorted square planar environment of the Cu ion is large enough to induce the presence of a stereogenic Cu centre. Further reaction with Ln ions in presence of ancillary ligands does not preserve such an arrangement but yields a tetranuclear complex made of two [LCu-Ln] units in a head-to-tail position. The tetranuclear [LCu-Ln] complexes made with the racemic and chiral LCu units crystallize in different space groups, so that racemization does not occur. The structural determinations confirm that a symmetry centre is present in the two structures, except for the methyl groups linked to the chiral carbon atoms, which appear as disordered in the () tetranuclear entity. Such an arrangement implies a conformation change of the diamino chain linked to the Cu ion in one [LCu-Ln] unit of the () entity, and cancels any chirality contribution of the Cu ions, as in the meso compound. Ferromagnetic Cu-Ln interactions, resulting from an alternate distribution of the Cu and Ln ions, are the only ones to be active. Eventually the micro-Squid studies confirm that the hysteresis loops of the corresponding racemate and chiral tetranuclear [LCu-Dy] entities are slightly different.