Thermotropic mesomorphism of mixed-valent diruthenium aliphatic carboxylates with axial anion bearing two aliphatic chains

Abstract

A homologous series of binuclear mixed-valent diruthenium tetracarboxylates, Ru2(O2C(CH2)n-2CH3)DHDP, (DHDP=di(hexadecyl)phosphate axial anion, n=10,12,14,16 and 18), have been synthesized and characterized, and liquid crystallines properties of these compounds were examined. All the compounds exhibit a room-temperature crystallines lamellar phase and a high temperature (above 140º) Col_h mesophase. Another, probably semi-crustallines lamellar intermediate phase has also been found for all the studied compounds but for the n=18 derivative. Comparison with related mesogenic homologous series where the equatorial ligands are alsolinear carboxylates, but the axial anion bear just one aliphatic chain (carboxylates, octylslfonate, and dodecylsulfate), shows that the presence of a second aliphatic chain in the axial anion both lowers the transition temperatures and modifies the nature of the intermediate lamellar phase. Structural models at the molecular level are suggested for the crystallines lamellar en the Col_h phases.