Influences of reaction temperature and pH on structural diversity of visible and near-infrared lanthanide coordination compounds based on bipyridyl carboxylate and oxalate ligands

Abstract

Four series lanthanide coordination compounds, [Ln(bpdc)(ox)0.5(H2O)]n·nH2O (Ln ​= ​La (1), Ce (2), Gd (3)), [Ln(bpdc)(ox)0.5(H2O)2]n (Ln ​= ​Ce (4), Pr (5), Nd (6)), [Ln2(bpdc)2(ox)(H2O)4]n·4nH2O (Ln ​= ​Nd (7), Sm (8)), [Ln2(bpdc)2(ox)(H2O)4]·H2O (Ln ​= ​Er (9), Yb (10)) (H2bpdc ​= ​2,2′-bipyridine-6,6′-dicarboxylic acid, H2ox ​= ​oxalic acid) were achieved under hydrothermal conditions by the reactions of lanthanide trichlorides with a rigid bipyridyl derivative and oxalic acid. Compounds 1–3 present a 6-connected hxl topological net with binuclear [Ln2(bpdc)2]2+ units. Compounds 4–6 display a 3-connected ths ThSi2 topological 3D framework with butterfly-like structure. Compounds 7–8 possess a ladder-shaped chain, and further linked by hydrogen bonds to form a 2D supramolecular layer. Compounds 9–10 show a binuclear molecular structure, and a 2D supramolecular layer structure is formed through hydrogen bonding interactions. Meanwhile, the reaction temperature and pH play important roles on the ultimate structures. These lanthanide compounds exhibit typical visible and near-infrared luminescence, as well as good thermal stability.