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 o-terphenyl units were prepared and converted to the corresponding complexes KX1 (X = halide, BF(4), PF(6), SCN) and NH(4)PF(6)1. Complexation was probed by MALDI-TOF spectrometry and NMR spectroscopy. Downfield shifts of (1)H NMR signals for complexes with soft anions Br, I, SCN, and PF(6) indicated the presence of tight ion pairs, whereas complexes with hard anions F, Cl, or BF(4) showed no or little shifts. In (13)C NMR spectra, upfield shifts were detected for soft anions. The character of the anion also influenced the mesomorphic properties of complexes MX1 (M = K, NH(4)), 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 degrees C phase widths in the case of KI1, KPF(6)1, and NH(4)PF(6)1. For complexes KSCN1 with a soft and bridging anion, the balance between mesophase stabilization and high order is shifted in favor of the plastic crystal phase.

Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

“…[12] Several methods for cyclization of the o-terphenyl-substituted derivatives 1 were investigated. First, a system of VOF 3 as oxidant and BF 3 ·OEt 2 as a Lewis acid was used, which has been successfully applied to the synthesis of triphenylene-substituted [15]crown-5 ethers.…”

“…Concentration of the filtrate and drying of the residue under high vacuum afforded the respective target complex in quantitative yield. For KX·2 c (KX = KF, KCl, KPF 6 ), KBr·2 e, and KX·2 f (KX = KCl, KBF 4 , KPF 6 ), a 1:1 ratio of salt:crown could be verified by elemental analyses, while for the other salts complexation was deduced from the MALDI-TOF mass spectra, [12,20] as exemplified for neat crown ether 2 e and its KBr complex (Figure 1). …”

“…[16] Complexes KX·2 a-f were prepared following a modification of the procedure reported by Pedersen. [12,[17][18][19] A solution of the respective crown ether 2 (1 equiv) in CH 2 Cl 2 was added to a solution of the appropriate potassium salt (1.5 equiv) in MeOH, and the resulting slurry was vigorously stirred overnight. After evaporation of the solvents, the residue was taken up in boiling CH 2 Cl 2 and the solution was filtered.…”

“…[8][9][10][11] Recently, we reported on dibenzo [18]crown-6 derivatives 1 with two lateral ortho-terphenyl units and their complexes MX·1 (M = K + , NH 4 + ). [12] It turned out that the anion X has a much stronger effect on their properties than the alkyl chain length. The anion not only caused a stabilization (soft anions such as iodide and bridging anions such as hexafluo-A C H T U N G T R E N N U N G rophosphate) or destabilization (hard anions such as fluoride, chloride, and tetrafluoroborate) of the mesophase as compared to neat crown derivatives 1, but also influenced the mesophase type.…”

“…Whereas the soft thiocyanate anion induced the formation of an ordered plastic crystal phase in KSCN·1, anions such as Hal À , PF 6 À , and BF 4 À led to the formation of columnar mesophases. [12] Previous work by Müllen on graphene-type columnar liquid crystals revealed that the temperature ranges of the columnar mesophases of propeller-shaped hexaphenylbenzenes could be significantly increased by converting them to the corresponding hexaperi-hexabenzocoronenes (HBC) with an extended flat aromatic system. [13,14] This stabilizing effect of the HBC unit was attributed to increased p-p interactions.…”