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.
Highlights
IntroductionResearch on solid-state materials is increasingly attracting interest owing to their potential versatile technical applications, such as molecular sensors, switches, and data-storage devices [1,2,3,4]
Research on solid-state materials is increasingly attracting interest owing to their potential versatile technical applications, such as molecular sensors, switches, and data-storage devices [1,2,3,4].Among them, phase-transition crystalline materials are important and often cause significant changes in physical and chemical properties
The reason is that the size of the crown ether and the nature of the ammonium cation (NH4 +, RNH3 +, and R2 NH2 + ) can influence the stability of the host–guest complexes
Summary
Research on solid-state materials is increasingly attracting interest owing to their potential versatile technical applications, such as molecular sensors, switches, and data-storage devices [1,2,3,4]. The crystalline materials of inorganic-organic hybrid compounds with phase-transition or peculiar molecular packing modes display remarkable and unusual dielectric properties, ferroelectric transfer, superconductivity, and magnetic coupling [10,11,12,13]. The hybrid crystalline materials constructed by hydrogen bonds can undergo transformations, thereby leading to phase transition. The crystal displays a paraelectric-to-ferroelectric phase transition triggered by the motion of the anions or cations and proton transfer of the hydrogen bonds [20,21,22]. [(4-nitroanilinium)(18-crown-6)][BF4 ](CH3 CN), which displays a 1D supramolecular chain structure by weak hydrogen bonds between the −NH3 + moieties and −NO2 of adjacent 4-nitroanilinium interaction through the cavity of 18-crown-6 molecule [27]. The driving force of the phase transition mainly originates from the proton transfer in C–H···F–P hydrogen bonds
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