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 (H(3)dpna), 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(μ(3)-Hdpna)(μ-dpey)](n)·nH(2)O (1), [Zn(4.5)(μ(6)-dpna)(3)(phen)(3)](n) (2), [Co(1.5)(μ(6)-dpna)(2,2′-bipy)](n) (3), [Zn(1.5)(μ(6)-dpna)(2,2′-bipy)](n) (4), [Co(3)(μ(3)-dpna)(2)(4,4′-bipy)(2)(H(2)O)(8)](n)·2nH(2)O (5),[Co(bpb)(2)(H(2)O)(4)](n)[Co(2)(μ(3)-dpna)(2)(H(2)O)(4)](n)·3nH(2)O (6), and [Mn(1.5)(μ(6)-dpna)(μ-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 H(3)dpna as a versatile tricarboxylate block for the fabrication of functional coordination polymers.