Synthesis of 2‐Pyridyl Based N(1)‐Substituted Thiosemicarbazonates of Nickel(II) as Bioactive Materials against MRSA, <i>S. aureus</i> , <i>S. typhimurium 2</i> , and <i>K. pneumonia</i>

Abstract In this investigation, the bio‐activity and biosafe potential of thiosemicarbazonates of nickel(II) as well as that of ligands are described. Reactions of nickel(II) acetate with a series of thiosemicarbazones, {R 1 (py)C 2 =N 3 ‐N 2 (H)‐C 1 (=S)‐NHR; R 1 =py, Me, H and Ph; R=H, Me, Et, Ph}, led to the loss of acidic hydrazinic N 2 (H) protons, and resulted in the formation of six‐coordinated complexes of stoichiometry, [Ni(N,N,S−L) 2 ], where anionic N,N,S−L=py 2 tsc‐NHR, 1 – 4 ; apytsc‐NHR, 5 – 8 ; pytsc‐NHR, 9 – 12 and bpytsc‐NHR, 13 – 16 . All these complexes have been characterized using analytical data, IR and UV‐visible spectroscopy and ESI‐mass spectrometry. The single crystal X‐ray crystal structure of several complexes { 2 (Me), 7 (Et), 11 (Et), 12 (Ph), 13 (H), 14 (Me) and 15 (Et)} were also determined. Thio‐ligands coordinate to nickel(II) through pyridyl nitrogen‐N 4 , azomethine nitrogen‐N 3 and thiolato sulfur atoms, resulting in the formation of homoleptic complexes with octahedral structures. Complexes 1 – 16 and uncoordinated thiosemicarbzones, were evaluated for their antimicrobial activity, in terms of ZOI, MIC, time kill assay and in vitro percent cell viability MTT assay, against clinical isolate methicillin‐resistant Staphylococcus aureus (MRSA), Staphylococcus aureus (MTCC740), Klebsiella pneumonia (MTCC109), Salmonella typhimurium (MTCC1251), and Candida albicans (MTCC227), a yeast. Both the ligands and their metal complexes exhibited moderate to high bioactivity, and were found to be biosafe with high cell viability, 88–92 %, in several cases.