Pyridine-2-Carbaldehyde Thiosemicarbazone and its Cobalt(II) Complex: Synthesis, Characterization, and Spectrophotometric Study

This study reports the synthesis, spectroscopic characterization, and analytical application of Pyridine-2-carbaldehyde thiosemicarbazone (Py-2-TSC) and its cobalt(II) complex. The ligand Py-2-TSC was synthesized and characterized using UV-visible spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD), confirming its structural features and purity. The complexation between Co(II) and Py-2-TSC was optimized at pH 3, where a stable 1:1 metal-to-ligand complex formed, exhibiting maximum absorbance at 510 nm with a molar extinction coefficient of 2.77 × 10³ L mol⁻¹ cm⁻¹. The complex remained stable for up to 24 hours and followed Beer’s law over the Co(II) concentration range of 8.48 × 10⁻⁶ to 8.48 × 10⁻⁵ M. Both Job’s method of continuous variation and the mole ratio method confirmed the 1:1 stoichiometry. The low dissociation constant (7.07 × 10⁻⁸) and high stability constant (1.41 × 10⁷) indicated strong and stable complex formation. Interference studies showed good selectivity, with notable interference only from EDTA and acetate ions. The antimicrobial activity of Py-2-TSC was evaluated against Klebsiella pneumoniae, a gram-negative bacterium, and showed promising inhibitory effects. These findings are consistent with literature reports that highlight thiosemicarbazone ligands as bioactive compounds with potential antimicrobial, antifungal, antitumor, and antitubercular activities. Overall, this study establishes Py-2-TSC as a sensitive and selective ligand for the spectrophotometric determination of cobalt(II), while also demonstrating its potential in medicinal chemistry.