Synthesis and structural characterization of nano‐sized metal complexes of 3‐(1‐methyl‐4‐hydroxy‐2‐oxo‐1,2‐dihydroquinolin‐3‐yl)‐2‐nitro‐3‐oxopropanoic acid. XRD, thermal, 3D modeling, and antitumor activity studies

New Co(II), Ni(II), Cu(II), Zn(II), and Fe(III) complexes of the ligand 3‐(1‐methyl‐4‐hydroxy‐2‐oxo‐1,2‐dihydroquinolin‐3‐yl)‐2‐nitro‐3‐oxopropanoic acid (H 3 L) were synthesized and characterized by various analytical and spectroscopic techniques. The obtained data confirmed the formation of 1:1 (M:L) stoichiometry for Fe(III), Co(II) complexes and 2:1 (M:L) stoichiometry for Ni(II), Cu(II), Zn(II) complexes, and the ligand, H 3 L, acts as mono‐, bi‐, tribasic bis‐, tris‐ and tetradentate towards the metal ions via the oxygen of quinolinonate, the enolic/ketonic of β‐ketoacid, and carboxylate besides of the nitro groups. All complexes showed tetrahedral geometry, except Fe(III) complex which exhibited an octahedral geometry. The X‐ray diffractograms of the ligand, H 3 L, and its metal complexes revealed a series of sharp and intense diffraction peaks which indicate their crystalline characteristic with the particle size in the nano‐scale range. Geometrical optimizations of the ligand, H 3 L, and its metal complexes were performed at the B3LYP/6‐311G(d, p) level using density functional theory (DFT) implemented in the Gaussian 09 program. The data obtained were correlated with the experimental results and suggested that the Zn(II) complex may exhibit extremely bio‐efficiency than other compounds. The antimicrobial screening results showed enhancement in the efficiency of the free ligand, H 3 L, on coordination with the metal ions. The antitumor activity was evaluated in vitro against Hepatocellular carcinoma cell line (HepG‐2 cells). The ligand, H 3 L, and its Zn(II) complex showed strong antitumor activities, especially nano‐sized Zn(II) complex that exhibited IC 50 value (2.90 μg/ml) smaller than the well‐known standard antitumor drug cis‐platin (IC 50 ~ 3.27 μg/ml), prominent it as an antitumor agent towards HepG‐2 cells.