Fluoroalkylated mononuclear ortho-metallated mesogens: new molecules at the calamitic-discotic cross-over point

The first examples of liquid crystalline mononuclear palladium and platinum organyls carrying semiperfluorinated alkyl chains at their peripheries have been synthesised. The phase behaviour of the semifluorinated compounds was investigated by optical polarizing microscopy, differential scanning calorimetry and X-ray scattering. By increasing the number of chains from five to seven a discontinuous transition from smectic to columnar organization of the molecules was observed. A re-entrant isotropic phase and a nematic phase could be detected as intermediate phases at this transition. In addition, increasing the number of fluorine atoms in the fluoroalkyl chains leads to a stabilisation of smectic and columnar mesophases and in one case a smectic phase with an additional short range periodicity within the layers was observed.