Two series of new Schiff bases 2 (n=8, 12, 16) derived from (3-hydroxypropyl imino)propan-1, 2-diol with a hydroxyl group at C(19)/C(20)-position and their palladium complexes 1 were prepared and their mesomorphic properties investigated by DSC, POM, and XRD. The presence of both hydroxyl groups was found to be crucial in forming the liquid crystalline behavior. All compounds 2a exhibited smectic A or and C phases, in contrast, all compounds 2b formed hexagonal columnar phases. The formation of mesophases in both compounds 1-2 was probably induced by inter-molecular H-bonds. Single crystallographic data in mesogenic compound 2a (n=8) indicated that a dimeric structure with a better linear or rod-like molecular shape was formed by an inter-molecular H-bond (O4-O1', similar to 1.854 angstrom). Another inter-molecular H-bond (similar to 1.903 angstrom) between two dimeric structures was also observed. It crystallizes in a monoclinic space group P2(1)/c. On the other hand, all palladium complexes 1 formed enantiotropic smectic A phases. Single crystallographic data in mesogenic compound la (n=8) indicated that the geometry at Pd(2+) center was coordinated as slightly twisted square planar. It crystallizes in a monoclinic space group P2(1)/n. An inter-molecular H-bond (similar to 1.799 angstrom) between neighboring molecules were observed, which might have facilitated the formation of mesophases. Variable-temperature powder XRD experiments confirmed their mesophase structures. (C) 2010 Elsevier Ltd. All rights reserved.
