Reversible Phase Transition of the 1:1 Complexes of 18-Crown-6 with 4-Ethoxyanilinium Perchlorate

Abstract

The solid structure of the crystalline 1:1 complexes of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclo-octadecane) with 4-ethoxyanilinium perchlorate [1] has been determined at 298 and 93 K, respectively. The measurements of the unit cell parameters versus temperature show that the values of a axis and crystal volume change abruptly and remarkably at ∼163 K, indicating that this phase character may be a first-order. The crystal structural analysis of both two temperatures shows that in addition to van der Waals' forces, conventional N-H 3 3 3 O, C-H 3 3 3 O hydrogen bonds, and C-H 3 3 3 π interaction are the main molecular interactions. The most distinct differences between the structures in room-temperature phase and low-temperature phase are of the twist of molecules viewing along a-axis. DSC measurements further confirm that this inclusion compound undergoes a reversible structural phase transition at about 163 K with a thermal hysteresis of 3.6 K in which relatively large latent heat (H) makes 1 a good candidate for PCMs (phase change materials). As usual, the physical properties, such as dielectric constant and specific heat (C p ), will change a lot near phase transition temperature (T c ). No distinct dielectric constant anomaly was observed in frequency and temperature ranges of 10-1000 kHz and 100-298 K.

Unusual Sequential Reversible Phase Transitions Containing Switchable Dielectric Behaviors in Cyclopentyl Ammonium 18-Crown-6 Perchlorate

“…11−14,17−21 Recently, our research groups and others discovered that some order−disorder of host−guest molecules in crown-ether clathrates can cause reversible structural phase transitions, depending on temperature. [11][12][13][14]25 Using this methodology, we have discovered two new ferroelectrics: ([Hcha-(18-crown-6)] + [BF 4 ] − and [Hcha-(18-crown-6)] + [ClO 4 ] − (Hcha = protonated cyclohexyl ammonium), with high Curie temperatures and large spontaneous polarization. 25 Xiong et al found that the slowing of the rotation of the 18-crown-6 molecule and the tumbling of the BF 4 anion causes the symmetry breaking; the relative displacement between the cationic and anionic sublattices can induce spontaneous polarization.…”

N-Methylpyrrolidinium hydrogen tartrate (NMPHT): an above-room-temperature order–disorder molecular switchable dielectric material

“…[1][2][3][4][5][6][7][8][9][10] The architecture and design of such stimuli-responsive structural phase-transition materials (SPTMs) are not only imperative for nding multifunctional materials with novel properties but also very valuable for studying the structure-property relationships. [11][12][13][14][15] Such materials are capable of switching between two or more states, which can thus be employed for multiple purposes 16 including rewritable data storage, [17][18][19][20] memory devices, [21][22][23] switchable dielectric, magnetic and optical functionalities. 24 Generally, these physical responses undergo abrupt changes around the phase transition temperature (T c ).…”

Switchable Dielectric Phase Transition Induced by a Twisting Transformation in Diglycine Methanesulfonate

“…Similar examples have been found in the 1:1 complex of [18]crown-6 with 4-ethoxyanilinium perchlorate and 1:2 complex of a-d-glucose with p-tolylboronic acid, and such structural transformation phenomenon is supposed to be defined as structure (or phase) modulation. [13] The reversible phase transition with structural transformation leads not only to a thermal entropy change, but also usually to a dielectric anomaly. Here, dielectric measurements were performed on crystals of 1.…”