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

Abstract

This work explores an N,O-donor dicarboxylic acid, 5-(3-carboxyphenyl)picolinic acid (H 2 cpic), as an adjustable linker for generating diverse types of coordination polymers (CPs). Eight new compounds were hydrothermally assembled, completely characterized, and formulated as [Products 1−8 were assembled from H 2 O solutions containing the respective metal(II) chloride salts, H 2 cpic, NaOH, and an Ndonor 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 H 2 cpic for the assembly of functional coordination polymers, thus stimulating further research in this swiftly growing field.

Synthesis and Crystal Structures of Mn(II) and Co(II) Complexes as Catalysts for Oxidation of Cyclohexanone

“…This suggested the coordination of imine nitrogen to Mn(II) ion. The lowintensity peaks at 1709 cm −1 , 1256 cm −1 , and 3212 cm −1 were characteristic of ν(C=O), ν(C-O), and ν(OH) bands in 2,6-pydc, and had shifted to 1692 cm −1 and 1394 cm −1 in the spectrum of compound 1, confirming the coordination of the carboxylate oxygen atoms to the Mn(II) ion [21]. The hydrogen bond interactions between neighboring bonded atoms, i.e., imi and 2,6-pydc bearing N-H and OH groups, were confirmed by the disappearance of an ν(OH) stretching band and the appearance of an ν(C-N) weak band at 1295 cm −1 , respectively; these bands differed from those in the spectrum of 1 [22,23].…”

“…The utilization of coordination compounds, such as metal complexes, and coordination polymers (metal-organic frameworks) for highly effective catalytic reactions, has been reported [13][14][15][16][17][18][19][20][21]. Coordination compounds are various types of compounds with metal ions-such as alkali and alkaline earth metals, transitional metals, and lanthanide(III) ions-coordinated by various functional groups, such as carboxylate, hydroxyl, and amine groups [21].…”

“…The utilization of coordination compounds, such as metal complexes, and coordination polymers (metal-organic frameworks) for highly effective catalytic reactions, has been reported [13][14][15][16][17][18][19][20][21]. Coordination compounds are various types of compounds with metal ions-such as alkali and alkaline earth metals, transitional metals, and lanthanide(III) ions-coordinated by various functional groups, such as carboxylate, hydroxyl, and amine groups [21]. Several coordination compounds have shown intriguing catalytic activities owing to their flexibility, accessibility to surface acidity, possession of strong bonds between di-and trivalent metal ions and ligands pillared by nitrogen and oxygen atoms, superior stability, and resistance to decomposition upon heating.…”

“…These ligands consisted of adjustable linkers suitable for generating lower-dimensional coordination polymers. The synthesized materials were categorized into heterogeneous compounds, and as they exhibited good thermal behaviors, we selected them as being suitable for oxidizing a substrate like adipic acid [21]. Solvents were chosen from aqueous H 2 O 2 and acetonitrile, because the yields of the products were between 60% and 90% in other literatures [20,21].…”

“…The synthesized materials were categorized into heterogeneous compounds, and as they exhibited good thermal behaviors, we selected them as being suitable for oxidizing a substrate like adipic acid [21]. Solvents were chosen from aqueous H 2 O 2 and acetonitrile, because the yields of the products were between 60% and 90% in other literatures [20,21]. The effects of reaction temperature, time, and oxidants on the catalytic reactions, and the mechanism, kinetics, and thermodynamics of the reaction were studied in this research work.…”