Synthesis, spectroscopic characterization, DFT-D2 analysis and BSA binding studies of Co(II), Ni(II) and Cu(II) complexes with a novel Benzothiazole-based ligand

An equimolar mixture of 2-amino-6-methoxybenzothiazole and 2-hydroxy-4-methoxybenzaldehyde was used to produce a Schiff base ligand 5-methoxy-2-(((6-methoxybenzothiazol-2-yl)imino)methyl)phenol, HL, which was then examined by elemental analysis, IR, ¹H NMR, ¹³C NMR and ESI-mass spectrometry. The Co(II), Ni(II) and Cu(II) chlorides, acetates and ligands were combined in ethanol in a molar ratio of 1:1 to create the metal complexes [1-C₁₆H₁₉CoClN₂O₆S, 2- C₁₈H₂₂CoN₂O₈S, 3- C₁₆H₁₅NiClN₂O₄S, 4- C₁₈H₁₈NiN₂O₆S, 5- C₁₆H₁₅CuClN₂O₄S and 6- C₁₈H₁₈CuN₂O₆S]. To identify the structure of all metal complexes 1–6, elemental analysis, molar conductance, electronic spectra and IR spectra were used. The ligand HL functions as an uninegative bidentate via phenolic O- and azomethine N- atoms, according to spectral data. Theoretical studies were performed to investigate the interaction between the metal ions and the ligand HL. This included analysis of the HOMO–LUMO gap to assess electronic properties, Hirshfeld charge distribution to understand electron density changes upon complexation and calculation of the binding energy to evaluate the stability of the metal–ligand complexes. The Co(II) complexes have been given an octahedral geometry, Ni(II) complexes a tetrahedral geometry and Cu(II) complexes a square planar geometry. Studies of the binding of the metal complex to bovine serum albumin (BSA) have been undertaken with the aid of fluorescence and circular dichroism spectrometry.