Coordination Polymers Driven by Carboxy Functionalized Picolinate Linkers: Hydrothermal Assembly, Structural Multiplicity, and Catalytic Features

This work explores an N,O-donor dicarboxylic acid, 5-(3-carboxyphenyl)picolinic acid (H2cpic), as an adjustable linker for generating diverse types of coordination polymers (CPs). Eight new compounds were hydrothermally assembled, completely characterized, and formulated as [Mn(μ3-cpic)(H2O)2]n (1), [Cd2(μ3-cpic)(μ4-cpic)(H2O)2]n (2), [Cd(μ4-cpic)]n (3), [Mn(μ-cpic)(phen)(H2O)]n (4), [Zn(μ-cpic)(phen)]n·nH2O (5), [Cd2(μ-cpic)2(phen)2(H2O)]·3H2O (6), [Cd(μ3-cpic)(phen)]n (7), and [Zn2(μ-cpic)2(bipy)(H2O)2]n·4nH2O (8). Products 1-8 were assembled from H2O solutions containing the respective metal(II) chloride salts, H2cpic, NaOH, and an N-donor crystallization mediator (optional: 1,10-phenanthroline, phen; or 2,2′-bipyridine, bipy). The structural types of 1-8 include a dimer complex (6), one-dimensional (1, 4, 5, 7, 8) and two-dimensional (2) CPs, and a three-dimensional (3) metal-organic framework. Hydrothermal reaction temperature, type of metal(II) center, and presence of mediators of crystallization are the factors responsible for structural diversity of 1-8. Thermal behavior, topological features, and catalytic properties of these products were studied. Notably, CP 1 acts as an effective, stable, and recyclable catalyst for the heterogeneous cyanosilylation of different aldehydes under mild conditions, resulting in quantitative conversion of aldehyde substrates to respective cyanohydrin products (99% product yields). Compounds 1-8 expand the usage of H2cpic for the assembly of functional coordination polymers, thus stimulating further research in this swiftly growing field. © 2021 American Chemical Society.