A three-dimensional mesophase with rhombohedral structure formed by double-swallow-tailed compounds

In five double-swallow-tailed compounds a weakly birefringent high temperat ure phase occurs which exhibits a characteristic optical texture. On the ba sis of X-ray diffraction measurements on well oriented monodomains, the str ucture of this phase could be described by a rhombohedral lattice of space group R3c or R32/c; the lattice parameters are not far from a cubic lattice . In spite of the three dimensional superstructure with long range characte r, the lateral packing of the molecules is liquid-like-similar to the well known cubic mesophases.