Theoretical and spectroscopic studies of 5-fluoro-isatin-3-(N-benzylthiosemicarbazone) and its zinc(II) complex

The molecular parameters (bond lengths, bond angles, the highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), the energy gap between EHOMO and ELUMO (ΔEHOMO–LUMO), dipole moment, charges on the atoms of 5-fluoro-isatin-3-(N-benzylthiosemicarbazone)) (H2FLB) as monomer were studied by HF and B3LYP methods using several basis sets. The cyclic trimer form of H2FLB was also reproduced. w zinc(II) complex with H2FLB has been synthesized and characterized using elemental analysis, Fourier transform infrared spectroscopy (FT-IR), UV and 1H NMR spectra. Theoretical calculations have also been performed by HF method using 6-31G(d,p) and LanL2DZ basis sets. The assignments of bands observed in FT-IR spectrum for H2FLB and its Zn(II) complex have been made using ab initio and DFT methods. Some significant differences in vibrational structures between ligand and Zn(HFLB)2 have been observed and discussed.