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(1 3.IV. 95) The thermal properties of two ferrocene derivatives, substituted by either one or two cholesteryloxycarbonyl units, were investigated. While the monosubstituted ferrocene derivative 1 was found to be non-mesomorphic, the disubstituted ferrocene derivative 2 exhibited a crystal smectic-B phase. This result shows that ferrocene-containing thermotropic liquid crystals, despite the bulkiness of the metallocene core, are not limited to disordered calamitic phases.

The two series I and 11 of 1,l'-disubstituted ferrocenes which differ by the direction of the ester function included in the rigid organic part were synthesized and their liquid crystal properties examined. These latter were found to be strongly dependent on the orientation of the connecting ester group and on the alkyl chain length.Introduction. -Much interest is currently devoted to metallomesogens [ 11. First, these compounds, which combine the properties of liquid crystals and the characteristics of metals, have allowed fundamental studies at the interface of chemistry, physics, molecular electronics, and material science. New technologies could emerge from this interdisciplinary field of research. Secondly, a specific arrangement of organic frameworks around a metallic core opens the way to new geometries and new topologies, in comparison with purely organic liquid crystals, thus allowing to explore more deeply the relationship between structure and mesogenic properties.Most of the metallomesogens studied so far are coordination complexes built up from one or two transition-metal centers coordinated to monodentate or chelating ligands. Mononuclear Ni, Cu [7] complexes containing liquid crystals were reported and generated much enthusiasm. Much less attention was devoted to organotransition metallomesogens. Monosubstituted [S] and 1, 1'-disubstituted [9] ferrocene-containing liquid crystals were reported, and the first family of mesogenic (butadiene)iron-tricarbonyl derivatives was recently described [lo].Ferrocene-containing liquid crystals are interesting for three major reasons: i) they have a high thermal stability, giving rise to reversible transitions without decomposition, ii) they are soluble in common organic solvents, making their characterization straightforward, and iii) their three-dimensional structure offers multiple possibilities for the design of substituted derivatives. These properties prompted us to undertake a systematic study to exploit the ferrocene as a valuable organometallic unit to be incorporated into mesogenic materials.Recently, we reported the first 1,3-disubstituted ferrocene-containing metallomesogens and showed, by comparison of their mesomorphic properties with those of the

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