Cation sensing by luminescent high-nuclearity Zn–Eu Schiff base nanoscale complexes: high sensitivity to Ag+ and Cd2+ ions at the ppm level

Abstract

Three polynuclear Zn–Ln nanoscale complexes [Ln₂Zn₂(L¹)₂(OAc)₆] (Ln = Eu (1) and Nd (2)) and [Eu₆Zn₆(L²)₂(L³)₂O₂(OAc)₁₈] (3) were constructed using two Schiff base ligands featuring Ph(CH₂)Ph (H₂L¹) and naphthyl (H₂L²) backbones. The use of the Schiff base ligand H₂L¹ leads to the formation of linear complexes 1 and 2 with molecular sizes of approximately 7 × 10 × 24 Å, while planar complex 3 (approximately 10 × 15 × 22 Å) is constructed from H₂L². In 1–3, the chromogenic Zn/ligand moieties can absorb energy from and transfer energy to lanthanide centers, and all of these complexes display the typical emissions of Ln³⁺ ions. Interestingly, 3 displays luminescence response to the addition of metal ions and has high sensitivity to Ag⁺ and Cd²⁺ ions at the ppm level.