Synthesis, characterization, structural investigation, and antimicrobial studies of mononuclear Zn(II), Cd(II), and Ag(I) complexes of an N₃O Schiff base

<div><p>An N₃O Schiff base (<b>L</b>), 1 : 1 condensate of benzil monohydrazone and 4-pyridine carboxaldehyde, and its Zn(II), Cd(II), and Ag(I) complexes were synthesized and characterized by elemental analyses and various spectroscopic techniques. The crystal structures of [ZnL₂Br₂] (<b>1</b>), [CdL₂I₂]·CH₂Cl₂, (<b>2</b>)<b>·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>, and [Ag(L)_<b>2</b>]ClO₄ (<b>3</b>) have been determined using X-ray crystallography. The Zn(II) and Cd(II) complexes show a tetrahedral configuration whereas in the asymmetric unit of <b>3</b>, two independent coordination units of Ag(I) are present. Carbonyl–silver interaction, weak C–H⋯O interaction, and also π–π interaction are present in <b>3</b> in the solid state. The synthesized complexes have antibacterial activity against <i>Klebsiella pneumoniae 114</i>, <i>Escherichia coli K88</i>, <i>Salmonella typhi ATCC 34</i>, <i>Bacillus subtilis UC564,</i> and <i>Staphylococcus aureus ATCC25923</i>. The results showed that in some cases the antibacterial activities of the complexes were comparable to standard antibiotics Tetracycline and Streptomycin. The antifungal activities of the complexes were also studied for <i>Aspergillus niger</i>, <i>Aspergillus oryzae</i>, <i>Penicillium notatum,</i> and <i>Saccharomyces cerevisiae</i>. MIC values of <b>1</b>, <b>2·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>, and <b>3</b> are less than the Nystatin standard.</p></div

Geometrical isomers of [TEAH][Co(L-Se)(2)]center dot xH(2)O: synthesis, structural, spectroscopic and computational studies

Trans-1, [HNEt3][Co-III(L-Se)(2)]center dot H2O and cis-1, [HNEt3][Co-III(L-Se)(2)]center dot 3H(2)O have been synthesized and characterized by single-crystal X-ray studies. The counter ion Et3NH+ plays a crucial role in the crystal packing leading to the formation of two distinctly different supramolecular assemblies in the two complexes. In trans-1, Co-bisphenolate units and triethylamine molecules are arranged in a linear fashion leading to a supramolecular columnar assembly along the crystallographic a-axis. In this assembly, triethylammonium ions are sandwiched between successive Co-bisphenolate units and act as gluing agents joining Co-bisphenolate units on either side through C-H center dot center dot center dot pi interactions. In sharp contrast to trans-1, Co-bisphenolate units and triethylammonium ions in cis-1 are arranged in a helical supramolecular assembly through similar C-H center dot center dot center dot pi interactions along the crystallographic b-axis. The Se center dot center dot center dot Se van der Waals interactions may be responsible for the predominant occurrence of the cis-isomer. The cyclic voltammetric studies showed quasi-reversible waves for the cobalt(III) -> cobalt(II) reductions with E-1/2 = 0.635 and 0.628 V vs. Ag/AgCl for cis-1 (at similar to 5 degrees C) and trans-1 (at similar to 25 degrees C), respectively. DFT calculations show that the trans-form is the thermodynamic product with higher stability than the cis-one, which is consistent with the variable temperature H-1 NMR studie