Versatile lanthanide coordination assemblies due to the synergistic effect of lanthanide contraction and flexibility of a flexible tricarboxylate ligand

Abstract

Nine novel lanthanide coordination complexes with formulae {[Ln(TTTA)(H₂O)₂]·2H₂O}_n (Ln = Ce, 1·Ce; Pr, 2·Pr, Nd, 3·Nd; Sm, 4·Sm; Eu, 5·Eu and Tb, 6·Tb) and {[Ln(TTTA)(H₂O)₃]·3H₂O}_n (Ln = Dy, 7·Dy; Er, 8·Er and Yb, 9·Yb) have been synthesized by hydrothermal reactions of a new flexible ligand TTTA (2,2′,2″-[1,3,5-triazine-2,4,6-triyltris(thio)]tris-acetic acid) with corresponding lanthanide nitrate and characterized by single-crystal X-ray diffraction, IR, thermal analysis, luminescence and magnetic measurements. Due to the synergistic effect of lanthanide contraction with diverse coordination modes and conformations of the flexible ligand, they have three structural types from 3-D polymers to 0-D dimers. Type I for large ions, 1·Ce, 2·Pr and 3·Nd, possesses a rare 3-D five-connected 4⁶6⁴ network with 1-D helical inorganic Ln₂O₂ chains bridged by the organic ligands; type II for medium ions, 4·Sm, 5·Eu and 6·Tb, exhibits 1-D chains constructed from Ln₂(CO₂)₄ units connected by the V-shaped conformational ligand; and type III for small ions, 7·Dy, 8·Er and 9·Yb, is scarcely an M₂L₂ dimer structure. Fascinatingly, in the low-dimensional type II and III structures, different kinds of unusual cyclic hydrogen bonding interactions are formed which, together with other weak interactions such as S⋯H–O hydrogen bonds, noncovalent S⋯S interactions or π⋯π stacking interactions, play important roles in stabilizing the whole network. In addition, the 5·Eu and 6·Tb complexes show strong red and green photoluminescence at room temperature, respectively, and may be good candidates for potential luminescence materials. The magnetic properties for some of the structures have also been investigated.