Smectogenic Copper(II) Complexes of N-Salicylideneaniline Derivatives. A Comparative Study of Homologous Series Carrying Alkoxy and/or Alkanoyloxy Substituents

A series of bis[4-alkoxy- N -(4-ethoxyphenyl)salicylaldiminato]copper(II) complexes have been prepared and shown to possess smectic A phases with isotropization temperatures ranging from 157 to 182 °C over butoxy to octadecyloxy homologues. Corresponding series of the ligands have also been isolated and characterized for their mostly nematogenic properties. Analogous series of bis[4-alkoxy- N -(4-acetoxyphenyl)salicylaldiminato]copper(II) complexes and their ligands have also proved to be mesomorphic; both of the phase type and the thermal stability are similar to those of the N -(4-ethoxyphenyl) counterparts. On the other hand, a series of bis[4-alkanoyloxy- N -(4-ethoxyphenyl)salicylaldiminato]copper(II) complexes, in which terminal alkyl groups are attached to the 4-oxysalicylidene groups via carbonyl groups, have been shown to melt at high temperatures (184−228 °C) and not mesogenic at all, while the phase behavior of the ligand series is very similar to that of the above 4-alkoxy series. An X-ray powder diffraction study of the two series of metallosmectic phases has led to a common structural model, in which layers of bis[ N -phenylsalicylaldiminato]copper(II) cores are intervened by fully interdigitated alkyl chains. The thermodynamic parameters for the first series have been analyzed for their dependence on the terminal alkyl chain length and partial ordering of short chains is suggested.