Hydrothermal Assembly, Structural Multiplicity, and Catalytic Knoevenagel Condensation Reaction of a Series of Coordination Polymers Based on a Pyridine-Tricarboxylic Acid

A pyridine-tricarboxylic acid, 5-(3 ',5 '-dicarboxylphenyl)nicotinic acid (H3dpna), was employed as a adjustable block to assemble a series of coordination polymers under hydrothermal conditions. The seven new coordination polymers were formulated as [Co(mu 3-Hdpna)(mu-dpey)]n center dot nH2O (1), [Zn4.5(mu 6-dpna)3(phen)3]n (2), [Co1.5(mu 6-dpna)(2,2 '-bipy)]n (3), [Zn1.5(mu 6-dpna)(2,2 '-bipy)]n (4), [Co3(mu 3-dpna)2(4,4 '-bipy)2(H2O)8]n center dot 2nH2O (5),[Co(bpb)2(H2O)4]n[Co2(mu 3-dpna)2(H2O)4]n center dot 3nH2O (6), and [Mn1.5(mu 6-dpna)(mu-dpea)]n (7), wherein 1,2-di(4-pyridyl)ethylene (dpey), 1,10-phenanthroline (phen), 2,2 '-bipyridine(2,2 '-bipy),4,4 '-bipyridine(4,4 '-bipy),1,4-bis(pyrid-4-yl)benzene (bpb), and 1,2-di(4-pyridyl)ethane (dpea) were employed as auxiliary ligands. The structural variation of polymers 1-7 spans the range from a 2D sheet (1-4, 6, and 7) to a 3D metal-organic framework (MOF, 5). Polymers 1-7 were investigated as heterogeneous catalysts in the Knoevenagel condensation reaction, leading to high condensation product yields (up to 100%) under optimized conditions. Various reaction conditions, substrate scope, and catalyst recycling were also researched. This work broadens the application of H3dpna as a versatile tricarboxylate block for the fabrication of functional coordination polymers.