Structural and vibrational spectral studies on hydrogen bonded salts: 4-chloroanilinium maleate and nitrate

In the present study, proton transfer from nitric and maleic acids to amine group (4-chloroaniline) led to hydrogen bonded crystals of 4-chloroanilinium maleate (4CAM) and 4-chloroanilinium nitrate (4CAN) which are investigated by the experimental and theoretical approaches. The molecular structures of these two compounds were optimized with the Density Functional Theory (DFT) using B3LYP function and the Hartree-Fock (HF) level with a6-311 ++G(d,p) basis set. Geometrical parameters of the molecules were also analyzed along with their intermolecular hydrogen bond, which tailors the ions. These analyses show that present molecules are stabilized through the N-H a <-O and O-H a <-O hydrogen bonds. The vibrational modes were computed by quantum chemical methods. Further, these modes are investigated by FT-IR and FT-Raman spectroscopy in the range of 4000-400 cm(-1). The optimized molecular geometry and computed vibrational spectra are compared with experimental results, which show significant agreement. The natural bond orbital (NBO) analysis was carried out to interpret hyperconjucative interaction and intramolecular charge transfer (ICT). This analysis gives the precise insight into the nature of H-bond interactions. The chemical hardness, electronegativity and chemical potential of the molecules were determined by HOMO-LUMO plot. The frontier molecular orbitals have small band gap value, which signify the possible biological/pharmaceutical activity of the compounds.