Temperature-induced 1D lanthanide polymeric frameworks based on Lnn (n = 2, 2, 4, 6) cores: synthesis, crystal structures and luminescence properties

Abstract

The hydrothermal reaction of the same reactive system containing Ln(NO₃)₃·6H₂O, tetrafluorophthalic acid (H₂TFPht), and 1,10-phenanthroline (phen) at different temperatures yielded coordination polymers, [Ln₂(TFPht)₃(phen)₂(H₂O)₂]·H₂O (Ln = Sm 1, Eu 2, Gd 3, Tb 4, Dy 5; at 120 °C), La(TFPht)(TFBA)(phen)(H₂O) (6; at 160 °C), Ln₃(TFPht)₄(TFBA)(phen)₃(H₂O)₃ (Ln = Dy 7, Tb 8, Yb 9; at 160 °C), and Ln₂(TFBA)₆(phen)₂ (Ln = Eu 10, Tb 11; at 180 °C). 2,3,4,5-Tetrafluorobenzoic acid (TFBA) was produced from the decarboxylation of TFPht. X-ray structural analysis reveals that these compounds contain different structural motifs. Complexes 1–5 exhibit zigzag chain structures based on the center-related tetranuclear [Ln₄] as SBUs (Secondary Building Units) with two crystallographically independent Ln³⁺ ions. Complex 6 contains a double chain structure with center-related binuclear [La₂] as SBUs. Complexes 7–9 show single chain structures involving center-related hexanuclear [Ln₆] as SBUs with three crystallographically independent Ln³⁺ ions. Complexes 10 and 11 have ribbon chain structures involving binuclear [Ln₂] as SBUs with two crystallographically independent Ln³⁺ ions. The photoluminescence properties of complexes 1–5 were studied. The Eu³⁺ and Tb³⁺ complexes exhibit bright red and green emissions with quantum yields of 15.87% for 2 and 23.82% for 4. The two-component Dy:Eu- and three-component Gd:Dy,Eu-doped complexes provided white light emission. Moreover, 2 could be a potential luminescent probe for detecting nitrobenzene and Ni²⁺ ion through significant fluorescence decrease of Eu³⁺.