Construction of four low-dimensional NIR-luminescence-tunable Yb(iii) complexes

Abstract

Four low-dimensional ytterbium(III)-organic compounds through hydrothermal reactions of quinoline-2,3-dicarboxylic acid (2,3-H₂qldc) and oxalic acid (H₂ox) with Yb₂O₃, namely, [Yb(2,3-qldc)(ox)_1/2(H₂O)₃·(H₂O)₄]_n (1), [Yb(2,3-qldc)(ox)_1/2(H₂O)₂·(H₂O)₂]_n (2), [Yb(2,3-Hqldc)(ox)(H₂O)₂·(H₂O)]_n (3) and [Yb(2,3-Hqldc)(ox)(H₂O)·(H₂O)₂]_n (4), were first synthesized and characterized by elemental analysis (EA), infrared spectroscopy (IR), thermogravimetric analysis (TG), and single-crystal X-ray diffraction. When the reactant ratio of 2,3-H₂qldc : H₂ox : Yb₂O₃ is 2 : 1 : 1, 1-D chain-like complex 1 with three coordinated water molecules around the Yb(III) ion was obtained in mixed solvents of H₂O and CH₃OH (v : v = 10 : 1) at 70 °C, and with the increase of temperature to 100 °C, the same reactants gave 2-D 6³ topological layer-like complex 2 with two coordinated water molecules in the coordination sphere of the Yb(III) ion. However, when the reactant ratio was changed to 1 : 1 : 1, two 2-D 6³ topological layer-like complexes 3 (70 °C) and 4 (100 °C) were obtained at different temperatures, in which the coordination water molecules in 3 and 4 are two and one, respectively. Obviously, these results reveal that the reaction temperature and reactant ratios play critical roles in the structural direction of these low-dimensional compounds. Interestingly, with the gradual loss of coordination water molecules to the Yb(III) ion, the near infrared (NIR) emission of four Yb(III)-based compounds 1–4 can be gradually strengthened with increasing order of 1 < 3 < 2 < 4, indicating that these ytterbium(III) complexes have tunable near infrared luminescence.