Columnar Mesophases Controlled by Counterions in Potassium Complexes of Dibenzo[18]crown‐6 Derivatives

Dibenzo18]crown‐6 derivatives 1 with two lateral tetraalkyloxy o‐terphenyl units were prepared and converted to the corresponding complexes KX ?1 (X=halide, BF₄, PF₆, SCN) and NH₄PF₆ ?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 ?1 (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 ?1 with a soft and bridging anion, the balance between mesophase stabilization and high order is shifted in favor of the plastic crystal phase.