Synthesis, characterization, X-ray crystallography, and antimicrobial activities of Ni(II) and Cu(II) complexes with a salicylaldehyde-based thiosemicarbazone ligand

<div><p>A new salicylaldehyde-based ‘ONS’ tridentate salicylaldehyde-N(4)-diethylthiosemicarbazone (H₂SANEt₂) has been synthesized and characterized by elemental analyses, mass, IR, and ¹H NMR spectral parameters. The coordination mode of the synthesized ligand is reported by solid state isolation and physico-chemical identification of Ni(II) and Cu(II) complexes, [Ni(SANEt₂)]₂ (<b>1</b>) and [Cu(SANEt₂)]₂ (<b>2</b>). Both complexes are neutral and oxygen-bridged dinuclear species. The ligand is bideprotonated ‘ONS’ tridentate in both complexes. IR spectral data indicate that coordination of each metal of the two complexes occurs through phenolic oxygen, azomethine nitrogen, and thiolato sulfur. X-ray crystallographic data of <b>1</b> and <b>2</b> (both monoclinic, <i>P2</i>_<i>1</i><i>/c</i>) show a MONSO (where M=Ni and Cu) square-planar coordination around each metal. Magnetic studies of <b>2</b> show that the two Cu(II) centers are strongly antiferromagnetically coupled via the bridging phenoxo O. All the synthesized compounds were tested for their <i>in vitro</i> antimicrobial activities against pathogenic bacteria. The inhibition power of the complexes was greater than the parent ligand.</p>