Plastic columnar mesomorphism in half-disc-shaped oxovanadium(IV) Schiff base complexes

A new series of non-disc-like oxovanadium(iv) Schiff base complexes of the type VO((4-C _n H_2n+1O)₂salcn)], where n?=?14, 16 or 18 and salcn is N,N ^′-bis-salicylidene-1,2-cyclohexadiamine, containing 4-substituted alkoxy tails in the side aromatic rings, have been synthesised and their mesogenic properties investigated. The compounds were characterised by FT–IR, ¹H NMR, ¹³C NMR, UV–Vis and FAB mass spectrometry. The mesomorphic behaviour of the compounds was studied using polarised optical microscopy and differential scanning calorimetry. The molecular organisation in the mesophase was determined by X-ray diffraction. It was found that the ligands did not show mesogenic behaviour, but their complexes exhibited a thermally stable enantiotropic highly ordered three-dimensional plastic mesophase with a columnar structure in the extended temperature range 155–166°C. The clearing temperature of the complexes was found to be lower than in the structurally analogous copper complexes. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimised structure. A square pyramidal geometry for the vanadyl complexes has been proposed.