Formation of columnar arrangements in copper(II) complexes of 2-phenylazomethinopyridine derivatives

The synthesis and mesomorphic properties of a homologous series of 2-(3′,4′,5′-trialkoxyphenyl)-azomethinopyridines and their copper(II) complexes are reported. Liquid crystalline properties of the copper(II) complexes were studied by DSC analysis and polarized optical microscopy. The results indicated that copper complexes with six sidechains (3) exhibited columnar phases, whereas copper(II) complexes with two or four sidechains (1 and 2) formed only crystalline phases. The structures of the mesophases for copper(II) complexes 3 were characterized and confirmed as disordered hexagonal columnar phases (Col_hd) by powder X-ray diffraction. Relatively high clearing points and the short range of mesophase temperature for the copper complexes were attributed to a relatively strong interaction of pyridyl core-core groups within the columns. The EPR spectra measured at various temperatures were also examined.