A Nine-Coordinated Bismuth(III) Complex Derived from Pentadentate 2,6-Diacetylpyridine Bis(4N‑methylthiosemicarbazone): Crystal Structure and Both in Vitro and in Vivo Biological Evaluation

Up to now, bismuth­(III) complexes with thiosemicarbazones have been comparatively rare. Few in vivo biological studies have been carried out in comparison to the plentiful in vitro data. Here, an interesting nine-coordinated bismuth­(III) complex, [Bi­(H2L)­(NO3)2]­NO3 [1; H2L = 2,6-diacetylpyridine bis­(4N-methylthiosemicarbazone)], has been synthesized and structurally characterized. The analytical data reveal the formation of 1:1 (metal/ligand) stoichiometry. In vitro biological studies have indicated that the bismuth complex 1 has shown much higher antibacterial and anticancer activities than its parent ligand, especially with MIC = 10.66 μM against Bacillus cereus and Salmonella typhimurium and IC50 = 26.8 μM against K562 leukemia cells, respectively. More importantly, it also evidently inhibits H22 xenograft tumor growth on tumor-bearing mice (10 mg/kg; inhibitory rate = 61.6%). These results indicate that coordination to bismuth­(III) might be an interesting strategy in the discovery of new anticancer drug candidates.