Study on the self-assembly behaviors based on aromatic carboxylic acids and dibenzo-diaza-crown ether salts

Abstract

Pyromellitic acid (pmaH4) with N,N′-dibutyl-diaza-18-crown-6 (3), N,N′-di(2-ethoxyethyl)-diaza- 18-crown-6 (4), N,N′-di(2-butoxyethyl)-diaza-18-crown-6 (5), N,N′-di(2-(2-butoxyethoxy)ethyl)-diaza-18- crown-6 (6) and picric acid (paH) with N,N′-di(2-(2-butoxyethoxy)ethyl)-diaza-18-crown-6 (6) have been obtained as single crystals in crystallization solvent acetone-water. Single crystal X-ray diffraction studies show that organic acid-aza crown ether co-crystals are proton-transfer organic salts. In every pyromellitic acid with aza-crown ether organic salts, acid and base are present in a 1:1 ratio, and the charge-assisted ((N+) N–H⋯O (COO−)) hydrogen bonds and aromatic stacking interactions (π···π stacking) provides the main forces to direct the packing modes of molecules together. Acid and base are present in a 2:1 ratio in the picric acid with compound 6 organic salts, and aromatic stacking interactions provide direct binding of pa anions with aza-crown ether cations. The supramolecular structures of organic salts are also supported by other non-covalent interactions, such as O···π stacking, C–H···π interaction and C–H⋯O interactions. Small molecules (water or acetone) wrapped in the crystals can effectively help to build the supramolecular structures of these organic salts.