Tuning the self-assembly and luminescence properties of lanthanide coordination polymers by ligand design

Abstract

Two new structure-related tripodal ligands featuring salicylamide pendant arms, 1,3,5-tris{[(2′-furfurylaminoformyl)phenoxyl]methyl}-2,4,6-trimethylbenzene (L^I) and 1,1,1-tris{[(2′-furfurylaminoformyl)phenoxyl]methyl}ethane (L^II) have been designed and synthesized with the ultimate aim of self-assembling lanthanide polymers with interesting luminescent properties. Among two series of Ln^III nitrate complexes (Ln = Pr, Nd, Sm, Eu, Gd, Tb or Dy) which have been characterized by elemental analyses, XRD, TGA and IR spectra, three new coordination polymers have been determined by X-ray diffraction analysis. The coordination polymer type {[Ln(NO₃)₃(L^I)]·nH₂O}_n possesses an unusual ladderlike double chain which can be further connected through π–π stacking interactions constructing a three-dimensional supramolecular structure. In contrast, the coordination polymer type {[Ln(NO₃)₃(L^II)]·nCH₃OH}_n displays a (3,3)-connected puckered two-dimensional net with 4·8² topological notation. The photophysical properties of the Sm, Eu, Tb and Dy complexes at room temperature are investigated. The present work substantiates the claim that the supramolecular structure as well as the luminescent properties of the coordination polymer can be tuned by varying either the backbone group or the terminal group of the organic ligand.