Synthesis, characterization, and X-ray studies of nonplanar mesogens: Carboxylato-bridged orthopalladated azine complexes

Article abstract of DOI:10.1021/om00157a010

The family of book-shaped orthopalladated dimers [Pd(H₂₁C₁₀OC₆H₃CH=NN=CHC ₆H₄OC₁₀H₂₁)(μ-O ₂CC_nH_2n+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.