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

摘要

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_nH_(2n+1)O)2salophen)] {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, ~1H-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 (Col1). DFT studies using DMol3 were carried out to obtain the optimized geometry of the complex.