Comparative Structural and Vibrational Study of 8-Hydroxyquinoline and 8-Hydroxyquinoline Succinate Compounds: A DFT Study

Quinoline based compounds efficiently form molecular complexes with various organic acids through hydrogen bonding. These compounds are classified as electron-deficient heterocyclic in nature and exhibit acceptor-donor properties with intramolecular charge transfer. 8-Hydroxyquinolinesuccinate is a π donor-acceptor molecular compound in which 8-HQ acts as donor and succinic acid as electron acceptor. The present work deals with the interaction of title compounds using Density Functional Theory (DFT) implemented in Gaussian-09 software package. All geometry optimizations, the vibrational analysis, electronic transition study of UV and NMR spectra of title compounds were interpreted with aid of normal coordinate analysis based on DFT/B3LYP using 6-311G basis set. Dihedral angles of 8-HQ varies between 0 ͦ and 180 ͦ . This shows that the molecule of 8-HQ is practically planar. 8-HQSC crystal is stabilized by the hydrogen bonds N2-H13….O22 and O22-H12….O1 formed by the existence of complementary functional groups. The negative chemical shift values of -145.5869 ppm do exist for nitrogen atom in 8-HQ. Energy gap of 8-HQ is obtained theoretically by DFT method is 4.52 eV and from HOMO-LUMO diagram is 4.53 eV. From the Mulliken atomic charges confirms the extensive intermolecular charge transfer between adsorbate and adsorbent of the title compound during the interaction. The calculated results are found to be in good agreement with the previous investigations.