Switchable Mesomorphic Materials Based on the Ferrocene−Ferrocenium Redox System:  Electron-Transfer-Generated Columnar Liquid-Crystalline Phases

Oxidation of the non-mesomorphic ferrocene derivative <b>1</b> with silver toluene-4-sulfonate gave the ferrocenium derivative <b>2</b>, which showed a monotropic columnar phase. The latter two-dimensional phase is composed of ribbons, in which derivative <b>2</b> is organized into bilayers, and has a centered rectangular symmetry with <i>a</i> = 318.3 Å and <i>c</i> = 94.9 Å. The Mössbauer spectra of the ferrocene derivative <b>1</b> yields hyperfine parameters that are typical of these derivatives and are, as expected, virtually independent of temperature. In a similar fashion, the hyperfine parameters of the ferrocenium derivative <b>2</b> are typical of these derivatives, but in this case at both 78 and 4.2 K slow paramagnetic relaxation of the magnetic moment associated with the rather well isolated paramagnetic ferrocenium ion is observed. The temperature-dependent magnetic susceptibilities of <b>2</b> are in agreement with those expected for weakly interacting ferrocenium cores. No magnetic-field-induced orientation was observed upon cooling the sample from the isotropic phase down to the columnar phase. Ferrocene and ferrocenium are valuable units for the design of liquid-crystalline switches.