Synthesis, structural characterization and antimicrobial activities of 4-and 6-coordinate nickel(II) complexes with three thiosemicarbazones and semicarbazone ligands

To investigate the relationship between antimicrobial activities and the mo lecular structures of nickel(II) complexes with thiosemicarbazone and semic arbazone ligands, nickel(II) complexes with ligands Hmtsc, Hatsc, Hasc and H(2)dmtsc, were prepared and characterized by elemental analysis, FT-IR, H- 1 and C-13 NMR spectroscopies, magnetic susceptibility measurements, UV-Vis absorption spectra, TG/DTA and single-crystal X-ray analysis. Their antimi crobial activities were evaluated by the MIC against four bacteria (B. subt ilis, S. aureus, E. coli and P. aeruginosa), two yeasts (C. albicans and S, cerevisiae) and two molds (A. niger and P. citrinum). The 4-coordinate, di amagnetic nickel(II) complexes showed antimicrobial activities which were d ifferent from those of free ligands or the starting nickel(II) compounds; [ Ni(mtsc)(OAc)] 1 showed selective and effective antimicrobial activities ag ainst two Gram-positive bacteria (B. subtilis and S. aureus) and modest act ivities against a yeast (S. cerevisiae), [Ni(mtsc)Cl] 3 exhibited moderate activities against a Gram-positive bacterium (S. aureus), and [Ni(atsc)(OAc )] 5 showed modest activities against two Gram-positive bacteria (B. subtil is and S. aureus). On the other hand, the 6-coordinate, paramagnetic nickel (II) complexes with two protonated or deprotonated ligands ([Ni(mtsc)(2)] 2 , [Ni(atsc)(mtsc)] 4, [Ni(atsc)(2)] 6, [Ni(Hatsc)(2)](NO3)(2)7, [Ni(Hatsc)( 2)]Cl(2)8 and [Ni(Hasc)(2)](OAc)(2)9) and the sterically crowded 4-coordina te, diamagnetic nickel(II) complex ([Ni(dmtsc)] 10) did not inhibit the gro wth of the test organisms. The structure-activity correlation in this serie s of nickel(II) complexes was discussed based on their ligand-replacement a bilities. (C) 2001 Elsevier Science B.V. All rights reserved.