Liquid-crystalline, polycatenar complexes of silver(I): dependence of the mesomorphism on the ligand and the anion

Abstract

We have synthesised several series of poly(alkoxy)stilbazole ligands, and investigated the thermal behaviour of their complexes with some silver salts. Most of the complexes, with the general formula [AgL₂][X], where X=dodecyl sulfate (DOS) or trifluoromethanesulfonate (OTf), and L=poly(alkoxy)stilbazole, were found to be liquid-crystalline over a wide-temperature range, the vast majority of them being low-melting. The mesomorphic properties were mainly dominated by the formation of hexagonal columnar (Col_h) phases and to a lesser extent, of bicontinuous Iad cubic phases; monotropic nematic and smectic C phases were also seen for one structural type of compound only. The mesophases were assigned on the basis of their optical textures under polarised optical microscope (POM) prior to being identified by X-ray diffraction (XRD). The temperatures and enthalpies of the transitions were determined by differential scanning calorimetry (DSC). The mesomorphism was found to be strongly dependent on the substitution pattern of the ligand, that is on the number, position and length of alkoxy chains, as well as on the type of the counter anion. We explain the mesomorphism in terms of ionic interactions and in terms of mean interfacial curvature between the hydrophobic, aliphatic chains and the rigid, aromatic, central core, by analogy to lyotropic systems.