Synthesis, Crystal Structure, Formation Mechanism, Theoretical Studies, and Biological Evaluation of Azine‐Based Bismuth (III) Complex

ABSTRACT The azine‐based bismuth (III) complex [Bi(H2L1)(NO3)3(H2O)2]•H2O(1a) was synthesized by an equivalent reaction between Schiff base and Bi (NO3)3•5H2O using mannitol as an auxiliary agent. During the formation of the complex (1a), the Schiff base containing 3‐methoxy group transformed into 3‐methoxysalicylaldehyde azine and further coordinated with BiIII ion to form a mononuclear BiIII complex (1a). Bismuth (III) ions were unexpectedly found to catalyze the formation of the azines from Schiff bases derived from pyrazinohydrazide, and their formation mechanism was further studied. Theoretical studies of the complex (1a) involving thermodynamic and electronic properties were done using the density functional theory (DFT) B3LYP method. Furthermore, in vitro biological evaluation showed that the antimicrobial and cytotoxic activities of the complex (1a) were much higher than those of free ligands. The obtained MIC and IC50 values of the complex (1a) were almost close to those of the reference drugs. An azine‐based bismuth (III) complex was synthesized and structurally characterized. Pyrazinohydrazide‐derived Schiff bases were first found to be catalyzed by bismuth (III) ions to the corresponding azines. The band gap between LUMO and HOMO for the complex was calculated. Compared with the free ligands, the complex displayed potential antibacterial and antitumor activities.