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

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.