The effect of low molecular weight organosiloxane substituents on mesophase formation and structure in non-symmetric nickel(II) complexes

Organosiloxane groups have been used as components of metal-containing liquid crystals (metallomesogens). It has been found that the disiloxane unit aids mesophase formation, stabilising an enantiotropic smectic A phase over a wide temperature range. The overall effect of an organodisiloxane unit is to lower the melting point relative to an alkyl substituted complex while increasing the clearing temperature, or leaving it unchanged, and so increasing mesophase temperature range. A model for the mesophase is proposed based on thermo-optical polarized light microscopy and small angle X-ray scattering studies. This proposes that weak nickel-nickel interactions, which are observed in the solid state, are maintained in the mesophase. The unusual steric shape of the organosiloxane group stabilizes the smectic A structure, allowing more efficient packing of the flexible chains. (C) 1998 Elsevier Science S.A.