Structural determinations and magnetic properties of a "chiral at metal" complex and its resulting [Cu-Ln] 2 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 II 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 II ion is effective. The distorted square planar environment of the Cu II ion is large enough to induce the presence of a stereogenic Cu II centre. Further reaction with Ln III 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] 2 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 ( S-S ) tetranuclear entity. Such an arrangement implies a conformation change of the diamino chain linked to the Cu II ion in one [LCu-Ln] unit of the ( S-S ) entity, and cancels any chirality contribution of the Cu II ions, as in the meso compound. Ferromagnetic Cu-Ln interactions, resulting from an alternate distribution of the Cu II and Ln III 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] 2 entities are slightly different.