Secondary ligand-directed assembly of metal–organic coordination polymers based on a 2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylic acid ligand: Syntheses, structures and photoluminescent properties

Abstract

Seven mixed-ligand coordination polymers, namely [Cd2(HPIDC)2(bipy)]n (1), {[Cd3(HPIDC)2(btc)(H2O)4]·H2O}n (2), {[Cd2(HPIDC)2(bdc)1/2(H2O)Cl]·H2O}n (3), {[Cd2(PIDC)(Ac)(H2O)]·H2O}n (4), [Zn2(HPIDC)(ox)(H2O)2]n (5), {[Eu(HPIDC)(ox)1/2H2O]·2H2O}n (6), and {[Tb(HPIDC)(ox)1/2H2O]·2H2O}n (7) (H3PIDC = 2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylic acid, bipy = 2,2′-bipyridine, H4btc = 1,2,4,5-benzenetetracarboxylic acid, H2bdc = 1,4-benzenedicarboxylic acid, H2ox = aoxalic acid) have been synthesized under hydrothermal conditions. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric analyses (TGA). Complexes 1 and 2 display a two-dimensional (2D) layer formed by the inter-linking helices and ligands connecting di-metal units, respectively. Both 3 and 4 assume a 3D covalent framework built up from mixed ligands linking two types of rod-shaped SBUs with trinodal (3,4)-connected and (3,4,5)-connected nets. Complexes 5–7 feature a 3D network constructed from HPIDC2− and ox2− anions bridging metal centers exhibiting the CdSO4 and α-Po nets, respectively. Moreover, the photoluminescent properties of 1–7 have been studied in the solid state at room temperature.