Cobalt(II) and Nickel(II) Complexes of a New 2,6‐Di(pyrazin‐2‐yl)pyridine Ligand: Synthesis, Crystal Structures, Serum Albumin Interactions, and Antiproliferative Activity

Two new transition‐metal complexes based on a dipyrazinylpyridine (dppy) ligand, 4‐( tert ‐butoxyphenyl)‐2,6‐di(pyrazin‐2‐yl)pyridine ( L ), namely {[Co L 2 ](ClO 4 ) 2 ( 1 ) and [Ni L 2 ](ClO 4 ) 2 ( 2 )}, were synthesized and characterized using various spectroscopic techniques. Single‐crystal X‐ray diffraction analysis revealed that complexation occurs in a 1:2 metal‐to‐ligand stoichiometry and both complexes exhibit distorted octahedral geometries. Furthermore, the binding studies with serum albumins (human serum albumin [HSA] and bovine serum albumin [BSA]) revealed that the complex 2 shows greater affinity than complex 1. Emission spectra showed binding constants of 3.83 × 10 4 M −1 and 2.63 × 10 7 M −1 for complex 1 and 2 , respectively, with BSA, whereas the corresponding values for HSA were 2.57 × 10 3 M −1 and 1.41 × 10 7 M −1 , respectively. Fluorescence quenching tests revealed a static quenching mechanism. The anticancer activity of the complexes was evaluated against Dalton’s lymphoma (DL) cells by MTT assay after 24–96 h of treatment at half IC 50 concentrations. Complexes 1 and 2 showed IC 50 values of 45 and 157 µM, respectively, indicating enhanced cytotoxic potency of complex 1 against DL cells.