Vanadyl(IV) complexes of 4-alkoxy substituted [N,O] donor salicylaldimine Schiff bases derived from chloro-/nitro-aniline: synthesis, mesomorphism, and DFT study

Abstract

Oxovanadium(IV)-Schiff-base complexes, [VOL₂] {L = N,N′-bis-(4-X-amino phenyl (4′-n-alkoxy)-salicylaldiminato), n = 10, 18; X = Cl, NO₂}, have been synthesized from the interaction of vanadyl (VO²⁺) and the bidentate [N,O] donor in methanol/ethanol. The compounds were characterized by FT–IR, ¹H- and ¹³C-NMR, FAB-mass spectra, elemental analyses, and solution electrical conductivity. Mesomorphic behavior of the ligands and their vanadyl complexes were probed by polarizing optical microscopy and differential scanning calorimetry. The compounds are thermally stable and exhibit enantiotropic smectic A mesomorphism over the temperature range of 57–231°C. The mesophase–isotropic transition temperatures for the complexes are much higher than the ligands. Melting and clearing points of the compounds did not show any definitive trend with regards to alkoxy chain length or electronegative substituent. Variable temperature magnetic susceptibility measurements of the vanadyl complexes clearly show the absence of exchange interactions among the vanadyl spin centers. Non-electrolytic natures of the complexes were shown by conductometric measurements. A ν(V=O) of ∼970 cm⁻¹ corroborated the absence of any V=O ··· V=O interactions. Density functional theory study carried out using DMol3 at BLYP/DNP level to determine the energy-optimized structure revealed a distorted square pyramidal geometry for the vanadyl complexes.

Keywords:

• Metallomesogen
• Schiff bases
• Vanadyl
• DFT

Acknowledgments

The authors thank SAIF, NEHU, and CDRI, Lucknow, for providing analytical and spectral data. G. Das acknowledges the financial support from DST and UGC, Government of India. Dr R.C. Deka, Tezpur University, India, is acknowledged for providing the computational facility.