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  • Title: Columnar mesophases controlled by counterions in potassium complexes of dibenzo[18]crown-6 derivatives.
    Author: Kaller M, Tussetschläger S, Fischer P, Deck C, Baro A, Giesselmann F, Laschat S.
    Journal: Chemistry; 2009 Sep 21; 15(37):9530-42. PubMed ID: 19658132.
    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.
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