Lanthanide(III) dodecanoates: Structure, thermal behaviour, and ion-size effects on the mesomorphism

Rare-earth salts of dodecanoic acid (lauric acid) have been prepared and ch aracterized. The compounds have the stoichiometry Ln(C11H23COO)(3), where L n = Y, La, Ce-Lu (except Pm). The thermal behaviour of these rare-earth dod ecanoates has been investigated by hot-stage polarized optical microscopy, differential scanning calorimetry (DSC), thermogravimetry (TG), and high-te mperature X-ray diffraction analysis. The compounds have a lamellar bilayer structure in the solid state, with the alkyl chains in an all-trans confor mation normal to the ionic sublayer. The size of the trivalent lanthanide i on has proved to be a critical factor with regard to the existence of mesop hases of this type of metallomesogens bearing carboxylate ligands. Thus, it was found that a mesophase can only be formed with the light lanthanide io ns having large ionic radii. The mesophase stability range decreases rapidl y on traversing the lanthanide series. Whereas a smectic A phase has been o bserved for the La-III, Ce-III, Pr-III, and Nd-III dodecanoates, no mesomor phism is apparent for the other lanthanide complexes.