Study on the interactions of nitrophenols with bis-8-hydroxyquinolinium zinc-2,6-pyridinedicarboxylate

Abstract

An inclusion complex of bis-8-hydroxyquinolinium zinc-2,6-pyridinedicarboxylate (1) accommodating three molecules of 4-nitrophenol per complex is structurally characterized. The inclusion complex has 4-nitrophenols interacting with organo-cations knitted by hydrogen bonding of water, form a cationic layer whereas the anions are π-stacked to form anionic layer where the inter-layer separation distance is 18.942 Å. It has O⋯π interaction between an oxygen atom of the nitro group with the π-cloud of the aromatic ring of the 8-hydroxyquinolinium cation. The distance from the oxygen atom to the centroid of π cloud is 3.32 Å. The interactions of nitrophenols with complex 1 are reflected in the changes in emission properties of 8-hydroxyquinoline in solution. These changes are much different from the emission changes caused on the emission of the 8-hydroxyquinolinum by 4-nitrophenol. Due to O⋯π interactions the 4-nitrophenol inclusion complex is non-fluorescent in the solid state. The fluorescence of the complex 1 is also quenched by addition of 4-nitrophenol as well as on addition of 3-nitrophenol. The isothermal calorimetric titrations have showed that the 3-nitrophenol has larger binding ability to interact with the complex 1 than the isomer 4-nitrophenol.