Synthesis, characterization, and antibacterial and anticancer screening of {M2+–Co3+–M2+} and {Co3+–M2+} (M is Zn, Cd, Hg) heterometallic complexes

The cobalt(III) complexes Et4N[Co(L1)2] and [Co(L2)3] [H2L1 is 2,6-bis(N-(2-pyridyl)carbamoyl)pyridine and HL2 is 2-(N-(2-pyridyl)carbamoyl)pyridine] were used as the building blocks for preparing a series of {M2+–Co3+–M2+} (where M is Zn, Cd, or Hg) and {Co3+–M2+} (where M is Zn or Cd) heterometallic complexes. All heterometallic complexes were characterized using a host of spectroscopic methods (IR, NMR, and UV/vis spectroscopy and mass spectrometry), elemental analysis, and conductivity measurements. One of the representative compounds, {Hg2+–Co3+–Hg2+}, was characterized crystallographically, and it was revealed that two Hg(II) ions are coordinated within the clefts created by the building block Et4N[Co(L1)2]. The results of screening for anticancer activity against the human brain tumor U87 cell line and antibacterial activity against a range of resistant (Pseudomonas aeruginosa and Proteus vulgaris) as well as standard (Staphylococcus aureus SA 96, P. aeruginosa MTCC 1688, Klebsiella planticola MTCC 2272, and Escherichia coli T7) bacterial strains indicate promising activities. Notably, the observed activity was found to vary with the type of building block and the secondary metal ion present in the heterometallic complex. Treatment-induced cell death [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, MTT and macrocolony assay), growth inhibition, cytogenetic damage, cell cycle delay, and apoptosis were studied as the parameters for cellular response.