Synthesis, crystal structure, and in vitro biological evaluation of bismuth (III) complexes incorporating pyrazinohydrazide‐derived Schiff bases

Two new Schiff‐base bismuth (III) complexes were prepared by an equivalent reaction between Schiff‐base ligand and Bi (NO3)3•5H2O with the assistance of Mannitol. The chemical structures of the two complexes were characterized by spectroscopic studies (FT‐IR, NMR, and MS), elemental analysis, and single‐crystal X‐ray diffraction. The ligand‐to‐metal ion ratio was found to be 1:1 in the complexes. During the formation of the complexes, Schiff bases changed from the amidic forms to the iminol forms, and the resulting tautomers could coordinate with bismuth (III) ions to produce dinuclear BiIII complexes(1a and 2a). Structural analyses showed that each Bi (III) ion held a distorted capped octahedron geometry with a seven‐coordinate mode in two complexes. Screening in vitro biological activities revealed that two bismuth (III) complexes exhibited much higher antimicrobial and cytotoxic activity than their parent ligands. The cytotoxic activity of the complex(1a) was close to that of the known anticancer drug (Doxorubicin) by evaluating against SGC7901 cells, with the IC50 value 0.59 μM. The complex(1a) could effectively induce SGC7901 cell apoptosis and its oral acute toxicity for LD50 value was found to be 576 mg kg−1. The content of bismuth (III) in mitochondria was higher than that in the nucleus. Two Schiff‐based bismuth(III) complexes have been synthesized and characterized. During the formation of two complexes, Schiff bases could change from the amidic forms to the iminol forms. Two complexes possess much higher antibacterial and antitumor activities than their parent ligands. The complex(1a) could effectively induce gastric cancer SGC7901 cell apoptosis.