SYNTHESIS, CHARACTERIZATION, AND X-RAY STUDIES OF NONPLANAR MESOGENS - CARBOXYLATO-BRIDGED ORTHOPALLADATED AZINE COMPLEXES

The family of book-shaped orthopalladated dimers [Pd(H21C10OC6H3CH═NN═CHC6H4OC10H21)(μ-O2CCnH2n+1)]2 (n = 0-11,13,15,17), which show mesogenic behavior influenced by the length of the bridging carboxylate, have been prepared. The shortest (n = 1-3) and longest (n ≥ 10) carboxylates give rise to more ordered mesophases and wider ranges of mesogenic behavior than the carboxylates of medium length. This is interpreted as a consequence of the molecular packing being disturbed on changing from short to medium chains and facilitated again when the carboxylate chains are long enough to situate themselves parallel to the azine chains. X-ray diffraction studies on monodomains give evidence of a peculiar molecular packing in these mesophases: some palladium–palladium correlations are found, which indicate the tendency to both a lateral association and a longitudinal shifting between neighboring molecules. © 1990, American Chemical Society. All rights reserved.