Crystal structure and phase transition of the C-H…F-P-bonded supramolecular compound with 4-nitroanilinium based on 18-crown-6

Abstract

A novel inorganic-organic hybrid supramolecular macrocyclic compound, (4-nitroanilinium) (18-crown-6)(PF6)(1), was synthesized and characterized by infrared spectroscopy, thermogravimetric analysis, elemental analysis, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. Crystal 1 is found to comprise 1D C-H…F-P hydrogen-bonded chains of (4-nitroanilinium+) (18-crown-6) supramolecular cations and PF6− anions. DSC measurements confirm that 1 undergoes a reversible phase transition at 255 K with a hysteresis width of 6 K. A strong dielectric response is observed above 250 K at a low frequency (500 Hz), suggesting the occurrence of proton transfer in the C-H…F-P hydrogen bonds. A precise analysis on the main packing and structural differences, as well as the changes in the intermolecular interaction between the low- and high-temperature phases, reveals that C-H…F-P hydrogen bonds are the main factors affecting phase transition and dielectric behavior.