Multi-Nuclear Palladium Organyls-Novel Structures and Properties of Disc-Like Metallomesogens¹

Abstract

The first non-calamitic/disc-shaped metal organyl series 3 and 6 containing two or even four palladium atoms and eight or twelve flexible side chains presented here have been synthesized via the novel roof-shaped/bent dimers 2 or (the thermomesomorphic) 5, respectively. In addition, from the chemical point of view the dodecaethers 5 and 6a-c are the first derivatives of four novel, uniquely structured tetrapallado-macroheterocycles. Whereas the type of mesophase of 5 is still not distinctly clear yet those ones of 6a-c are enantiotropic discotic hexagonal columnar (D_h) over a wide range of temperature. On the other hand, the dinuclear palladocompounds 3a-d represent the first (monotropic) cases of metallomesogens exhibiting the nematic-discotic (N_D) phase. This thermotropic nematic type of phase clearly gets stabilized by doping 3c, d with a strong electron acceptor; under such circumstances mesophase conversions/inductions (N_D→D_h) are observed in the cases of 3a-c. Finally, it is important to emphasize that the very large, thermotropically D_h phase displaying macroheterocycles 6a-c are also lyotropic in various organic solvents exhibiting now a nematic phase.