Self-Assembly of the First Discrete 3d−4f−4f Triple-Stranded Helicate

The connection of an additional bidentate chelating unit at the extremity of a segmental bis-tridentate ligand in L5 provides an unprecedented sequence of binding sites for the self-assembly of heterometallic 3d−4f triple-stranded helicates. Thorough thermodynamic and structural investigations in acetonitrile show the formation of intricate mixtures of complexes when a single type of metal (3d or 4f) is reacted with L5. However, the situation is greatly simplified when Zn(II) (3d-block) and Lu(III) (4f-block) are simultaneously coordinated to L5, thus leading to only two identified species: the target C3-symmetrical trinuclear triple-stranded d−f−f helicate HHH-[ZnLu2(L5)3]8+ and a tetranuclear double-stranded complex [Zn2Lu2(L5)2]10+. Interestingly, the removal of Zn(II) from the former triple-helical complex has only a minor effect on the coordination of Lu(III), and translational autodiffusion coefficients show a simple reduction of the length of the molecular rigid cylinder from L = 2.7 nm in HHH-[ZnLu2(L5)3]8+ to L = 2.3 nm in HHH-[Lu2(L5)3]6+. Finally, the complete thermodynamic picture provides five novel stability macroconstants containing information about short-range (ca. 9 Å) and long-range (ca. 18 Å) intramolecular intermetallic d−f and f−f interactions.