Syntheses, X-ray structures, gas adsorption and luminescent properties of three coordination polymers of Zn(ii) dicarboxylates mixed with a linear, neutral, and rigid N,N′-donor ligand

Abstract

In this article, three new zinc(II) coordination polymers have been synthesized using 4,4′-azobipyridine (azbpy) and three different aliphatic dicarboxylates. The reaction was carried out through the slow diffusion technique at room temperature giving rise to {[Zn₂(μ₃-OH)(azbpy) (suc)_1.5]·(H₂O)₂}_n (1), {[Zn(azbpy)_0.5(glut)(H₂O)]·(H₂O)}_n (2), and {[Zn₂(azbpy)₂(fum)₂]·(H₂O)}_n (3) (suc = succinate dianion, glut = glutarate dianion and fum = fumarate dianion). The structures of these complexes were determined by single-crystal X-ray diffraction analysis and also by other physicochemical methods. Compound 1 is a three-dimensional (3D) framework, whereas compound 2 shows a one-dimensional ladder-like structure which is further extended in two dimensions through supramolecular interactions (H-bonding). Compound 3 displays a three-dimensional (3D) 5-fold interpenetrated diamondoid network structure. In the case of 1 and 2, the structures contain void spaces which are occupied by guest water molecules, whereas in 3, the pores are totally blocked through interpenetration. TGA and PXRD analysis showed that all three compounds were thermally stable up to a high temperature. The desolvated framework of compounds 1 and 2 show adsorption of different gas molecules and exhibit a higher adsorption preference for CO₂ over N₂. The photoluminescence study in the solid state of compounds 1–3 indicates ligand based florescence emissions at room temperature.