Lanthanide Triple-Stranded Helicates:  Controlling the Yield of the Heterobimetallic Species Thomas B. Jensen Rosario Scopelliti Jean-Claude G. Bünzli 10.1021/ic0608501.s002 https://acs.figshare.com/articles/journal_contribution/Lanthanide_Triple_Stranded_Helicates_Controlling_the_Yield_of_the_Heterobimetallic_Species/3058849 Two unsymmetrical ditopic hexadentate ligands designed for the simultaneous recognition of two different trivalent lanthanide ions have been synthesized, L<sup>AB2</sup> and L<sup>AB3</sup>, where A represents a tridentate benzimidazole-pyridine-benzimidazole coordination unit, B2 a diethylamine-substituted benzimidazole-pyridine-carboxamide one, and B3 a chlorine-substituted benzimidazole-pyridine-carboxamide moiety. Under stoichiometric 2:3 (Ln/L) conditions, these ligands self-assemble with lanthanide ions to yield triple-stranded bimetallic helicates. The crystal structures of four helicates with L<sup>AB3</sup> of composition [LnLn‘(L<sup>AB3</sup>)<sub>3</sub>](ClO<sub>4</sub>)<sub>6</sub>·solv (CeCe, PrPr, PrLu, NdLu) show the metal ions embedded into a helical structure with a pitch of about 13.2−13.4 Å. The metal ions lie at a distance of 9.1−9.2 Å and are nine-coordinated by the three ligand strands, which are oriented in a HHH (head−head−head) fashion, where all ligand strands are oriented in the same direction. In the presence of a pair of different lanthanide ions in acetonitrile solution, the ligand L<sup>AB3</sup> shows selectivity and gives high yields of heterobimetallic complexes. L<sup>AB2</sup> displays less selectivity, and this is shown to be directly related to the tendency of this ligand to form high yields of HHT (head−head−tail) isomer. A fine-tuning of the HHH ⇆ HHT equilibrium and of the selectivity for heteropairs of Ln<sup>III</sup> ions is therefore at hand. 2006-09-18 00:00:00 LAB 2 displays ligand strands metal ions selectivity lanthanide ions trivalent lanthanide ions Å. Heterobimetallic SpeciesTwo unsymmetrical ditopic hexadentate ligands ligand LAB 3 HHT HHH