Coordination Polymers Constructed from an Adaptable Pyridine-Dicarboxylic Acid Linker: Assembly, Diversity of Structures, and Catalysis.

4,4'-(Pyridine-3,5-diyl)dibenzoic acid (H 2 pdba) was explored as an adaptable linker for assembling a diversity of new manganese(II), cobalt(II/III), nickel(II), and copper(II) coordination polymers (CPs): [Mn(μ 4 -pdba)(H 2 O)] n ( 1 ), {[M(μ 3 -pdba)(phen)]·2H 2 O} n (M = Co ( 2 ), Ni ( 3 )), {[Cu 2 (μ 3 -pdba) 2 (bipy)]·2H 2 O} n ( 4 ), {[Co(μ 3 -pdba)(bipy)]·2H 2 O} n ( 5 ), [Co 2 (μ 3 -pdba)(μ-Hbiim) 2 (Hbiim)] n ( 6 ), and [M(μ 4 -pdba)(py)] n (M = Co ( 7 ), Ni ( 8 )). The CPs were hydrothermally synthesized using metal(II) chloride precursors, H 2 pdba, and different coligands functioning as crystallization mediators (phen: 1,10-phenanthroline; bipy: 2,2'-bipyridine, H 2 biim: 2,2'-biimidazole; py: pyridine). Structural networks of 1 - 8 range from two-dimensional (2D) metal-organic layers ( 1 - 3 , 5 - 8 ) to three-dimensional (3D) metal-organic framework (MOF) ( 4 ) and disclose several types of topologies: sql (in 1 ), hcb (in 2 , 3 , 5 ), tfk (in 4 ), 3,5L66 (in 6 ), and SP 2-periodic net (6,3)Ia (in 7 , 8 ). Apart from the characterization by standard methods, catalytic potential of the obtained CPs was also screened in the Knoevenagel condensation of benzaldehyde with propanedinitrile to give 2-benzylidenemalononitrile (model reaction). Several reaction parameters were optimized, and the substrate scope was explored, revealing the best catalytic performance for a 3D MOF 4 . This catalyst is recyclable and can lead to substituted dinitrile products in up to 99% product yields. The present study widens the use of H 2 pdba as a still poorly studied linker toward designing novel functional coordination polymers.