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

4,4 '-(Pyridine-3,5-diyl)dibenzoic acid (H2pdba) 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(mu 4-pdba)(H2O)]n (1), {[M(mu 3-pdba)(phen)]center dot 2H2O}n (M = Co (2), Ni (3)), {[Cu2(mu 3- pdba)2(bipy)]center dot 2H2O}n (4), {[Co(mu 3-pdba)(bipy)]center dot 2H2O}n (5), [Co2(mu 3-pdba)(mu-Hbiim)2(Hbiim)]n (6), and [M(mu 4-pdba)(py)]n (M = Co (7), Ni (8)). The CPs were hydrothermally synthesized using metal(II) chloride precursors, H2pdba, and different coligands functioning as crystallization mediators (phen: 1,10-phenanthroline; bipy: 2,2 '-bipyridine, H2biim: 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 H2pdba as a still poorly studied linker toward designing novel functional coordination polymers.

Automated summary

The study explores the use of H2pdba as a versatile linker for assembling various metal coordination polymers, with particular focus on the catalytic potential of the resulting polymers in Knoevenagel condensation reactions. The 3D MOF 4 showed the best catalytic performance, leading to high product yields in the condensation reaction.