Pyridine-and imidazoledicarboxylates of zinc: hydrothermal synthesis, structure, and properties

Abstract

The reaction of hetrocyclic dicarboxylic acids, such as pyridine-2,5-dicarboxylic acid and imidazole-4,5-dicarboxylic acid, under hydrothermal conditions in the presence of an appropriate zinc salt yields three new zinc coordination polymers ⁰_∞[{Zn₂(H₂O)₄}{C₅H₃N(COO) ₂}₂] (1), ¹_∞ [{Zn(C1₂H₈N₂)}{C₅H₃N(COO) ₂}·0.5H₂O] (2), and ¹_∞ [{Zn(C1₂H₈N₂)}{C₃HN₂(COO) ₂}] (3). While 1 forms with a zero-dimensional molecular rectangular box structure, 2 and 3 have zig-zag one-dimensional chain structures. The Zn²⁺ ions are coordinated by both the carboxylate oxygen atoms and also by the nitrogen atoms of the heterocycles. The 1,10-phenanthroline molecules in 2 and 3 act as a secondary ligands and occupy the inter-chain spaces. The moderate hydrogen-bond interaction energy in 1 and the π···π interactions in 2 and 3 appear to play an important role for the structural stability. The structures of 2 and 3 appear to be related, even though they are formed with different carboxylic acids. All three compounds exhibit photoluminescence at room temperature.