Secondary ligand-directed assembly of metal–organic coordination polymers based on a 2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylic acidligand: 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.