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

Seven mixed-ligand coordination polymers, namely [Cd-2(HPIDC)(2)(bipy)](n) (1), {[Cd-3(HPIDC)(2)(btc)(H2O)(4)]center dot H2O}(n) (2), {[Cd-2(HPIDC)(2)(bdc)(1/2)(H2O)Cl]center dot H2O}(n) (3), {[Cd-2(PIDC)(Ac)(H2O)]center dot H2O}(n) (4), [Zn-2(HPIDC)(ox)(H2O)(2)](n) (5), {[Eu(HPIDC)(ox)(1/2)H2O]center dot 2H(2)O}(n) (6), and {[Tb(HPIDC)(ox)(1/2)H2O]center dot 2H(2)O}(n) (7) (H3PIDC = 2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylic acid, bipy 2,2'-bipyridine, H(4)btc 1,2,4,5-benzenetetracarboxylic acid, H(2)bdc = 1,4-benzenedicarboxylic acid, H(2)ox = 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 ox(2-) anions bridging metal centers exhibiting the CdSO4 and alpha-Po nets, respectively. Moreover, the photoluminescent properties of 1-7 have been studied in the solid state at room temperature.