Lamellar columnar mesomorphism in a series of oxovanadium(IV) complexes derived from N, N/-di-(4-n-alkoxysalicylidene)diaminobenzene

Abstract

Abstract A series of new nondiscoid shaped square pyramidal oxovanadium(IV)-Schiff base complexes containing 4-substituted alkoxy chains on the aromatic rings, [VO(4-C n H 2n + 1 O) 2 salophen)] {n = 14, 16, 18; salophen = N, N/-phenylnebis(salicylideneiminato)} have been prepared and their mesogenic properties investigated. The ligands and the complexes were characterized by FT-IR, CHN, 1 H-NMR, UV–vis and FAB mass spectrometry. Presence of V═O stretching mode at ~ 980 cm − 1 indicated absence of any intermolecular … V═O ..... V═O … interactions with no dependence on the chain length. Variable temperature magnetic susceptibility measurements of the complexes also suggested lack of such exchange interaction. Cyclic voltammetry showed a quasireversible one-electron response at 0.75 V for the VO(IV)–VO(V) redox couple. DSC coupled with polarized optical microscopy showed the ligands to be nonmesogenic but the complexes exhibited an unprecedented thermally stable columnar mesophase in the 136–154 °C. X-ray diffraction technique, confirmed that the structure of the mesophase is lamellar columnar in type (Col l ). DFT studies using DMol3 were carried out to obtain the optimized geometry of the complex.