Controlled synthesis, structures and properties of one-, two-, and three-dimensional lanthanide coordination polymers based on (8-quinolyloxy)acetate

Abstract

Hydrothermal reactions of Ln(NO3)3 and (8-quinolyloxy)acetic acid (HQOA) with auxiliary ligands resulted in a series of new one-, two- and three-dimensional (1D, 2D and 3D) coordination polymers, namely, [Ln(QOA)2 (H2O)2]·NO3·H2O [Ln = Eu (1), Gd (2)], [Ln2(QOA)4(ox)(H2O)]·3H2O [Ln = Pr (3), Er (4)], [Ln2(QOA)4(BDC) (H2O)]·4H2O [Ln = Sm (5)] and [Ln(QOA)(BDC)] [Ln = Sm (6), Eu (7)] [QOA = (8–quinolyloxy)acetate; ox = oxalate; BDC = 1, 4–benzenedicarboxylate], respectively. Compounds 1–2 possess 1D zigzag chains bridged by QOA anions and 3–4 contain 1D folded chains alternately bridged by oxalates and QOA anions. Complex 5 is an ordered (2,4)–connected 2D sheet-like structure. In compounds 6–7, four BDC anions bridge two adjacent metal atoms to form dinuclear lanthanide building blocks and these dinuclear blocks are further connected together to form an 8-connected 3D network. The progressive variation from 1D zigzag chains (1–2) to 1D folded chains (3–4) to a 2D layer network (5) and to 3D frameworks (6–7) is mainly attributed to the change of bridging ligands as well as the different coordination modes of organic carboxylic ligands. Moreover, the thermal stabilities and photoluminescent properties of these compounds show a remarkable difference due to the progressive variation of crystal structures.