Systematic study on the structures of salen type lanthanide complexes tuned by lanthanide contraction and corresponding luminescence

Abstract

Two types of N,N′-bis(salicylidene)-1,3-propanediamine (H₂L) lanthanide complexes, viz. [Ln(NO₃)₃(H₂L)₂]·0.2CH₃OH [Ln = La (1), Ce (2) and Pr (3)] and [Ln(NO₃)₃(H₂L)₂]₂·CH₂Cl₂·CH₃OH [Ln = Nd (4), Sm (5), Eu (6), Gd (7), Tb (8) and Yb (9)], have been isolated by reactions of H₂L with Ln(NO₃)₃·6H₂O. X-ray crystallographic and PXRD analysis reveal that 1–3 are isomorphic possessing a novel one-dimensional (1D) ladder-like double-chain structure. Complexes 4–9 are isostructural exhibiting a discrete dinuclear structure. Luminescent analysis reveals the lanthanide ion and ligand-centered co-luminescence for 5, 6 and 8, which are attributed to the incomplete energy transfer from the triplet state of H₂L to the resonance energy level of the corresponding Ln(III) ion. Further, the characteristic near infrared (NIR) luminescence of Nd(III) and Yb(III) ions for complexes 4 and 9 have been revealed.