Differences and\nSimilarities in Two Series of M<sup>II</sup>Ln<sup>III</sup>M<sup>II</sup> Complexes

Two sets of tripodal ligands resulting from the reaction\nof 2-hydroxy-3-methoxybenzaldehyde\n(o-vanillin) with 1,1,1-tris(aminomethyl)ethane, Me–C(CH<sub>2</sub>NH<sub>2</sub>)<sub>3</sub>, or with <i>N</i>,<i>N</i>′,<i>N</i>″-trimethylphosphorothioic\ntrihydrazide, P(S)[NMe–NH<sub>2</sub>]<sub>3</sub>, yield heterotrinuclear\n3d<sup>II</sup>–4f<sup>III</sup>–3d<sup>II</sup> complexes\nin which the 3d ions (Mn<sup>II</sup>, Fe<sup>II</sup>, Co<sup>II</sup>, Ni<sup>II</sup>, and Zn<sup>II</sup>) occupy the inner N<sub>3</sub>O<sub>3</sub> coordination sites while the 4f ions do assemble two\nof these 3d metal–ligand units. As the 3d coordination induces\nhelicity, these achiral ligands can yield homochiral (Λ–Λ\nor Δ–Δ) or heterochiral (Λ–Δ)\ntrinuclear heterometallic complexes, which mainly precipitate as racemates\nin centrosymmetric space groups. These two series of complexes differ\nin their preparation: those involving phosphorus atoms can be isolated\nin an open atmosphere, while the other series requires an inert atmosphere.\nHeterochiral (Λ–Δ) trinuclear complexes are only\ncharacterized with the ligand involving phosphorus atoms, while conglomerates\nare limited to the complexes, implying Ni<sup>II</sup> 3d ions in\nthis series. Conversely, a greater number of complexes that crystallize\nas chiral assemblies are isolated with the other ligand coordinated\nto the Mn<sup>II</sup>, Fe<sup>II</sup>, Co<sup>II</sup>, and Zn<sup>II</sup> ions and 4f ions ranging from Dy<sup>III</sup> to Lu<sup>III</sup>. This difference arises from the propensity of this ligand\nto favor the trigonal pyramidal geometry around the 3d ions. The synthetic\nstrategy consisting in introducing a supplementary metal ion (here,\na 4f ion) to a mixture of conformers (here, Λ and Δmononuclear\n3d complexes) can yield homochiral complexes (here, Λ–Λ\nor Δ–Δtrinuclear molecules) that crystallize as\nracemates in centrosymmetric space groups and sometimes as chiral\nassemblies in noncentrosymmetric space groups. This approach provides\na method for preparing chiral complexes with ligands that lack chiral\natoms. Regarding the magnetic properties of the two series, we have\nfirst shown that they exhibit a similar magnetic behavior. It has\nalso been previously demonstrated that the introduction of Gd ions\nsuppresses quantum tunneling of magnetization in the absence of an\napplied field. Combining strongly anisotropic metal ions having a\nlarge angular momentum with a large isotropic metal ion, along with\na ferromagnetic interaction in between these ions, appears to be an\neffective strategy for designing efficient single-molecule magnets.