Self-assembly of luminescent 12-metal Zn–Ln planar nanoclusters with sensing properties towards nitro explosives

Abstract

Two types of Zn–Ln nanoclusters [Nd₂Zn₂L₂(L′)₂(OAc)₂(NO₃)₂(H₂O)₂] (1) and [Ln₆Zn₆L₂(L′′)₂O₂(OAc)₁₈] (Ln = Nd (2) and Sm (3)) were prepared using one long Schiff base ligand (H₂L) with a naphthyl backbone and two short polydentate ligands (H₂L′ and H₂L′′). 1 and 2–3 show linear and planar structures with sizes of approximately 10 × 10 × 30 Å and 10 × 15 × 22 Å, respectively. The chromogenic Zn/ligand components can act as efficient sensitizers for lanthanide luminescence, and thus 1–3 show visible and NIR emissions. In these clusters, the Schiff base ligands display a “U-shaped” configuration, which is suitable to form π⋯π interactions and hydrogen bonds with nitro aromatic compounds. Interestingly, Zn–Sm cluster 3 shows visible and NIR luminescence sensing of nitro explosives and exhibits high sensitivity to 1,4-DNB and TNT at the ppb level.