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 · n H 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 ·2 n H 2 O ( 5 ),[Co(bpb) 2 (H 2 O) 4 ] n [Co 2 ( μ 3 - dpna) 2 (H 2 O) 4 ] n ·3 n H 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.