Three-Dimensional Porous Coordination Polymer Functionalized with Amide Groups Based on Tridentate Ligand: Selective Sorption and Catalysis

Abstract

To create a functionalized porous compound, amide group is used in porous framework to produce attractive interactions with guest molecules. To avoid hydrogen-bond formation between these amide groups our strategy was to build a three-dimensional (3D) coordination network using a tridentate amide ligand as the three-connector part. From Cd(NO₃)₂·4H₂O and a three-connector ligand with amide groups a 3D porous coordination polymer (PCP) based on octahedral Cd(II) centers, {[Cd(4-btapa)₂(NO₃)₂]·6H₂O·2DMF}_n (1a), was obtained (4-btapa = 1,3,5-benzene tricarboxylic acid tris[N-(4-pyridyl)amide]). The amide groups, which act as guest interaction sites, occur on the surfaces of channels with dimensions of 4.7 × 7.3 Ų. X-ray powder diffraction measurements showed that the desolvated compound (1b) selectively includes guests with a concurrent flexible structural (amorphous-to-crystalline) transformation. The highly ordered amide groups in the channels play an important role in the interaction with the guest molecules, which was confirmed by thermogravimetric analysis, adsorption/desorption measurements, and X-ray crystallography. We also performed a Knoevenagel condensation reaction catalyzed by 1a to demonstrate its selective heterogeneous base catalytic properties, which depend on the sizes of the reactants. The solid catalyst 1a maintains its crystalline framework after the reaction and is easily recycled.