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