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

ABSTRACT The azine‐based bismuth (III) complex [Bi(H 2 L 1 )(NO 3 ) 3 (H 2 O) 2 ]•H 2 O( 1a ) was synthesized by an equivalent reaction between Schiff base and Bi (NO 3 ) 3 •5H 2 O 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 Bi III ion to form a mononuclear Bi III 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 IC 50 values of the complex ( 1a ) were almost close to those of the reference drugs.