Structural determinations and magnetic properties of a "chiral at metal" complex and its resulting [Cu-Ln]2 compounds

Dalton Trans. 2022 Feb 14;51(7):2805-2814. doi: 10.1039/d1dt04249a.

Abstract

A chiral trianionic ligand possessing one amide, one imine, two phenol functions and one asymmetric carbon atom into its diamino chain reacts with CuII 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 CuII ion is effective. The distorted square planar environment of the CuII ion is large enough to induce the presence of a stereogenic CuII centre. Further reaction with LnIII 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 CuII ion in one [LCu-Ln] unit of the (S-S) entity, and cancels any chirality contribution of the CuII ions, as in the meso compound. Ferromagnetic Cu-Ln interactions, resulting from an alternate distribution of the CuII and LnIII 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.