Lyotropic phase behaviour of disc-shaped tetra-palladium organyls in apolar organic solvents [1]

Abstract

The lyomesomorphic behaviour in apolar organic solvents of members of two series 1 and 2 of disc-shaped palladium organyls—the syntheses of four of them are new (1d, f and 2a, e) and are described here—each carrying twelve long lipophilic chains have been studied. Their lyomesomorphism appeared to be complex and has been observed here for the first time with metal organyls. As can be seen by polarizing microscopy, most of the binary mixtures investigated here exhibit nematic properties. For two members of series 1—the chloro-bridged 1b and its bromo-analogue 1c—there is even evidence for the existence of two different nematic lyomesophases side by side showing reversible transitions between them. In ternary systems, i.e. after the addition of 2,4,7-trinitrofluorenone (TNF, a strong electron acceptor), the nematic phases are stabilized, suggesting that their mesophase structures are made up by columns with intercalated TNF molecules (charge transfer complex formation). Influences of structural features of the pallado-mesogens on the one hand and of the type of solvent on the other on the molecular self-aggregation in the observed types of lyotropic mesophase formed are discussed in detail.