Synthesis, structural characterization and antibacterial activity of 2,6-diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases and their copper(II) complexes

2,6-Diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases (L¹, L² and L³) and their Cu(II) complexes of the general formula [CuL·H₂O] were synthesized and characterized by various spectroscopic techniques. The crystal structure of [CuL³·(py)]·py was investigated by single crystal X-ray structure analysis. The Cu(II) cation has near square pyramidal, penta-coordinate geometry. The binegatively charged tetradentate Schiff base is asymmetrically coordinated to the Cu(II) ion via the pyridine N atom, the azomethine N atom, the sulfonyl O atom and the deprotonated hydrazine N atom. There is a pyridine molecule apically coordinated to the Cu(II) ion. All the Schiff bases and their copper(II) complexes were screened by the disc diffusion method against multi-drug resistant (MDR) gram-negative and gram-positive bacteria. The minimum inhibitory concentration (MIC) values were also determined. These results show that the antibacterial activity of the Schiff bases against Methicillin-resistant Staphylococcus aureus (MRSA) is enhanced when they are chelated with the copper(II) ion.     

Synthesis,Characterization and X-ray Structures of 2,6-Diacetylpyridinebis(benzenesulfonylhydrazide) and its Zinc(II) Complex

Abstract  2,6-Diacetylpyridinebis(benzenesulfonylhydrazide) (2,6-DAPBSH) and its zinc(II) complex have been synthesized and characterized by X-ray crystallography. The ligand crystallizes in the monoclinic crystal system, space group Cc, with cell parameter = 16.808(2) Ǻ, b = 16.328(2) Ǻ, c = 8.2670(11) Ǻ, β = 91.869(9)°, while the zinc(II) complex crystallizes in the orthorhombic crystal system, space group Pbcn, with cell parameters a = 14.5927(3) Ǻ, b = 9.6502(2) Ǻ, c = 20.5610(5) Ǻ. The metal center is seven-coordinate, with an approximate pentagonal bipyramidal configuration of the chelating ligand and two apically coordinated DMSO molecules. Graphical Abstract  X-ray crystallographic study on the [2,6-diacetylpyridine—bis(benzenesulfonylhydrazonato-κ⁵ N′N′′N′′′O′O′′)]bis(dimethyl sulfoxide-κO)zinc(II) (Fig. 1) shows that the complex is a seven-coordinate, with an approximate pentagonal bipyramidal configuration where the ligand coordinates to the zinc(II) ion as a pentadentate chelate via the pyridine nitrogen atom, the two azomethine nitrogen atoms and the two sulfonyl oxygen atoms.