Synthesis, stereocontrol and structural studies of highly luminescent chiral tris-amidepyridyl-triazacyclononane lanthanide complexes

Abstract

The configuration of the remote amide chiral moiety determines the helicity of the metal complex in Ln(III) complexes of nonadentate N₆O₃ ligands based on triazacyclononane. Solution NMR studies revealed the presence of a dominant isomer whose proportion varies from 9 : 1 to 4 : 1 from Ce to Yb and X-ray crystallographic studies at 120 K of the Yb and two enantiomeric Eu complexes confirmed the configuration as S-Δ-λ in the major isomer. Global minimisation methods allowed magnetic susceptibility and electronic relaxation times of the lanthanide ions to be estimated by analysis of variable field longitudinal relaxation rate (R₁) data sets. A set of four europium complexes, containing different para-substituted pyridinyl-aryl groups, exist as one major isomer (15 : 1), and absorb light strongly via an ICT transition in the range 320 to 355 nm (ε = 55 to 65 000 M⁻¹ cm⁻¹). The two examples absorbing light at 332 nm, possess overall emission quantum yields of 35 and 37% in aerated water, making these systems as bright as any Eu complex in solution.