Molecular Motions and Hydrogen-Bonding Networks in (o-Aminoanilinium)–(Crown Ethers)–[PMo12O40]4− Crystals

Abstract

Abstract Single crystals formed from hydrogen-bonding supramolecular cations of o-aminoanilinium (HOPD+)–crown ethers, (HOPD+)([12]crown-4), (HOPD+)([15]crown-5), and (HOPD+)([18]crown-6), and one-electron-reduced [PMo12O40]4− Keggin-type clusters were synthesized. The crystal structures and dielectric responses of the three new compounds (HOPD+)4([12]crown-4)4[PMo12O40]4−·4CH3CN (1), (HOPD+)4([15]crown-5)4[PMo12O40]4− (2), and (HOPD+)4([18]crown-6)4[PMo12O40]4−·8CH3CN (3) were examined. The CH3CN molecules in salts 1 and 3 were included in zero-dimensional pores and one-dimensional channels, respectively; higher thermal stability was observed in the former lattice because of its extended hydrogen-bonding network. Large frequency- and temperature-dependent dielectric responses were confirmed in salts 2 and 3, whereas the dielectric response of salt 1 was quite small. The fixed orientation of HOPD+ because of the hydrogen-bonding network was consistent with the dielectric property of salt 1. In contrast, large magnitudes of dielectric responses in the temperature range above 280 K were observed for salt 3. Thermal motions of CH3CN molecules in the channel were the origin of such dielectric responses. In salt 2, the thermally activated coupled motion of the orthogonally arranged HOPD+ pair along the C–NH3+-axis with the potential energy barrier of ca. 80 kJ mol−1 resulted in large dielectric responses.