Chiral Zn3Ln3 Hexanuclear Clusters of an Achiral Flexible Ligand

Multifunctional single-molecule magnets (SMMs) have sparked great interest, but chiral SMMs obtained via spontaneous resolution are rarely reported. We synthesized a series of chiral trinuclear hepta-coordinate lanthanide complexes [Zn^II₃Ln^III₃] (1 for Dy, 2 for Tb, 3 for Gd, and 4 for Dy_0.07Y_0.93) using the achiral flexible ligand H₂L (2,2'-[1,2-ethanediylbis[(ethylimino)methylene]]bis[3,5-dimethylphenol]). The complexes crystallize in the chiral P6₃ group space, and two enantiomers of different chirality are spontaneously resolved. Three [Zn(L)Cl]^- anions utilize the two phenoxy oxygen atoms of each L^2- to coordinate with three lanthanide ions, respectively, and the three hepta-coordinate D_5h lanthanide ions are arranged in a triangle. The chirality comes from the propeller arrangement of the peripheral three bidentate chelate L^2- ligands like octahedral [M(AA)₃]^n+/- (M = transition metal ions; AA = bidentate chelate ligands, e.g., 2,2'-bipyridine, 1,10-phenathroline, ethylenediamine, acac^- or oxalate). Complex 1 exhibits an AC susceptibility signal and is frequency-dependent, which is typical of SMMs. Complex 4, doped with a large amount of diamagnetic Y(III) in Dy(III), exhibits U_eff = 48.3 K and τ₀ = 4.4 × 10^-8 s in experiments. Complex 2 shows circularly polarized luminescence and apparent photoluminescence, typical of the f-f transitions of Tb(III).