Studies of thermotropic properties and the mesophase of mixtures of n-alkanoates and perfluoro-n-alkanoates of dimolybdenum (M(4)under-barM)

Mixtures of Mo-2(O2C(CH2)(n)CH3)(4), where n = 6 (=Oct) and 7 (=Non), form a columnar mesophase upon heating and the crystal-to-liquid crystal phase transition temperatures differ Little from those predicted by the Shroder-van Laar equation for an ideal mixture. The XRD of the solid sample obtained from cooling a 1:1 mixture of MO2(Oct)(4) and Mo-2(Non)(4) conformed to a triclinic cell with lattice parameters intermediate between those of the pure compounds. Similarly in the mesophase the intercolumnar separation (d) was an intermediate distance. The phase behavior of mixtures of Mo-2(non)(4) and Mo-2(O2C(CH2)(10)CH3)(4) [Mo-2(Dod)(4)] were more complex, but in all instances a mesophase was observed whereas that of the pure Mo-2(Dod)(4) shows only a crystalline solid to isotropic phase transition. Mixtures of Mo-2(Oct)(4) and Mo-2(O2C(CF2)(6)CF3)(4) [Mo-2(Oct(f))(4)] were also shown to form a columnar mesophase with an intercolumnar separation intermediate between that of the pure compounds. The mesophase is an optically positive material with the largest component of the index of refraction coincident with the columnar axis. The solid to mesophase transition temperatures varied significantly from that predicted for an ideal mixture. These results are discussed on the basis of facile carboxylate scrambling to produce Mo-2(O2CR)(4-n)(O2CR')(n), where n = 0-4 in both the mesophase and the resultant solid solution.