SYNTHESIS, X-RAY-DIFFRACTION, DIFFERENTIAL SCANNING CALORIMETRY, AND MAGNETIC-SUSCEPTIBILITY STUDIES OF A SERIES OF BINUCLEAR RUTHENIUM(II) CARBOXYLATES GIVING LIQUID-CRYSTALLINE PHASES

A wide series of diruthenium(II,II) tetracarboxylates of general formula Ru2(RCOO)4 was prepared; the carboxylate substituents include linear alkyl chains (R = C4H9 to C19H39), unsaturated chains (R = CH2 = CH(CH2)8-, (CH3)2C = CHCH2CH2CH(CH3)CH2-) as well as a fluorinated chain (R = C7F15-). An adduct obtained by pyrazine intercalation was also characterized (R = C11H23-). The mesomorphic behavior of these compounds was investigated by differential scanning calorimetry and X-ray diffraction. A thermotropic columnar mesophase was observed above ca. 100-degrees-C for all complexes except the perfluoro compound and the pyrazine adduct. Unsaturation in the peripheral alkyl chains strongly depresses the transition temperature to the liquid-crystalline phase. The magnetic susceptibility of three members of the series was measured in the range 6-400 K. A rigorous analytical expression of the magnetic susceptibility vs temperature was derived from the (pi*)2(delta*)2 electronic configuration for the ground state of a diruthenium(II,II) core, by applying a spin-orbit Hamiltonian, and the data were successfully analyzed on this basis.