Testing the triple network structure of the cubic Im3m (I) phase by isomorphous replacement and model refinement

Abstract

This study provides further tests of the validity of the triple network structure of the body-centred Imm (I) cubic phase in polycatenar (phasmidic) liquid crystals, proposed by Zeng et al., Nat. Mater., 2005, 4, 562. New hemiphasmid compounds were synthesised, two of which (6 and 7) display the above phase, while 8 shows the hexagonal columnar phase. Comparison of 3-d electron density maps based on small-angle X-ray diffraction of two compounds with different proportions of high and low electron density regions (aliphatic and aromatic) helped with phasing the X-ray reflections of the cubic structure. This variant of the isomorphous replacement technique gave further support to the triple network structure proposed earlier.