Structure and photoluminescent properties of lanthanide coordination polymers based on two isomers of iminodiacetic acid substituted isophthalate and terephthalate ligands

Abstract

Two isomers, 5-aminodiacetic isophthalic (H₄adip) and 2-aminodiacetic terephthalic (H₄adtp) acid were employed for syntheses of lanthanide coordination polymers under solvothermal conditions, resulting in three isostructural two-dimensional (2D) layer-assemblies {Me₂NH₂[Ln(adip)(H₂O)]}_n (Ln = Eu (1), Tb (2), Sm (3)) and another three isomorphous three-dimensional (3D) frameworks {[Ln₂(Hadtp)₂]·3H₂O}_n (Ln = Eu (4), Tb (5), Sm (6)). Complexes 1–3 can be regarded as 3D supramolecular structures consisting of 2D anionic layers assembled by electrostatic interactions with dimethylamine cations, whereas complexes 4–6 are composed of interweaving single-stranded 4₁ helix and triple-stranded 4₃ helixes. The luminescent properties of 1–6 are discussed in detail. Due to the good match between the lowest triplet state of the ligand and the resonant energy level of the lanthanide ion, the lanthanide ions in complexes 2 and 5 can be efficiently sensitized by the ligands.