Synthesis, structural characterization and study of {[K(H2mna)2]+ · [K(μ-OH)2]− · 4H2O}n (H2mna = 2-mercapto-nicotinic acid). A supramolecular architecture of inorganic/metal-organic hybrid self-assembled by strong hydrogen bonds and π–π interactions

Crystals of a water soluble, potassium(I) complex with the heterocyclic thioamide; 2-mercapto-nicotinic acid (H2mna), of formula {[K(H2mna)2]+ · [K(μ-OH)2]− · 4H2O}n (1) were grown from the filtrate of the reaction between 2-mercapto-nicotinic acid with KOH in a molar ratio 1:1.5 in water. The complex has been characterized by elemental analysis, TG-DTA, 1H NMR and FT-IR spectroscopic techniques and X-ray powder diffraction. The single crystal structure of complex (1) has been determined by X-ray diffraction at ambient conditions. The polymeric structure of the complex is microporous, where water molecules are retained. The water molecules can be reversibly removed. The complex is ionic, containing [S–K+–S] linkages and an infinite ribbon of {[K(μ-OH)2]−}n as a counter anion. Strong hydrogen bonds and π–π interactions stabilize the supramolecular architecture of the inorganic/metal-organic hybrid formed. Heating of (1) at 100 °C for 4 h forms the {[K(H2mna)2]+ · [K(μ-OH)2]−}n (2), which retains the framework structure although the coordinated water molecules were evacuated.

A novel, water soluble, 2D metal-organic/inorganic framework was synthesized. The polymeric structure consists of infinite inorganic {[K(μ-OH)2]−}n chains, which bind {[K(H2mna)2]+} cations through strong O–H⋯O hydrogen bonds between the hydroxylic and carboxylic groups. The layers are formed due to the π⋯π interactions between the H2mna rings. Thus, a stable supramolecular pattern is established in which the removal of water molecules does not affect the structure.Figure optionsDownload as PowerPoint slide