Columnar mesophases controlled by counterions in potassium complexes of dibenzo[18]crown-6 derivatives

Abstract

Dibenzo[18]crown-6 derivatives 1 with two lateral tetraalkyloxy oterphenyl units were prepared and converted to the corresponding complexes KX·1 (X = halide, BF4, PF6, SCN) and NH4PF 6·1. Complexation was probed by MALDI-TOF spectrometry and NMR spectroscopy. Downfield shifts of 1H NMR signals for complexes with soft anions Br, I, SCN, and PF6 indicated the presence of tight ion pairs, whereas complexes with hard anions F, Cl, or BF4 showed no or little shifts. In 13C NMR spectra, upfield shifts were detected for soft anions. The character of the anion also influenced the mesomorphic properties of complexes MX-I (M = K, NH4), which were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and XRD in comparison to neat 1. Hard anions slightly stabilize or even destabilize the mesophase. Soft anions, however, improve the mesomorphic properties yielding mesophases with up to 70°C phase widths in the case of KI·1, KPF6·1, and NH4PF6· 1. For complexes KSCN-I with a soft and bridging anion, the balance between mesophase stabilization and high order is shifted in favor of the plastic crystal phase. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.