Construction of Highly Porous Pillared Metal-Organic Frameworks: Rational Synthesis, Structure, and Gas Sorption Properties

Abstract

Different from the conventional method to construct pillared-layer metal-organic frameworks (MOFs) by using mixed bipyridyl and dicarboxylate ligands, herein, we present a new approach to build pillared-layer frameworks based on the pyridyldicarboxylate ligands which were predesigned with a certain shape. As exemplified, the ligands of 3-(2',5'-dicarboxyphenyl)benzoic acid (H₃dbba) and 3-(2',5'-dicarboxylphenyl)pyridine acid (H₂dcpy) were selected and employed to construct three pillared-layer MOFs, [Zn₃(dbba)₂(bipy)(DMF)]·3DMF·4H₂O (1) (bipy = 4,4'-bipyridine), and a pair of crystal polymorphs of [Zn(dcpy)]·1.5DMF·1.5H₂O (2 and 3), under solvothermal reactions, respectively. In the structures of 1-3, the [Zn₂(COO)₄] clusters are bridged by the terephthalate units of dbba^3-/dcpy^2- to form 2D layers; these layers are further pillared by bipy and the benzoate units of dbba^3- or the pyridine units of dcpy^2- to furnish the 3D frameworks. All of them possess high porosity characterized by N₂ adsorption and exhibit high selective adsorption of C₂H₄ and CO₂ over CH₄.