Template synthesis, characterization and antibacterial activity of d10 (Zn2+, Cd2+, Hg2+) Schiff base complexes: A novel supramolecular Cd2+ complex with two 1D helical chains, and its Hirshfeld surface analysis

Abstract

Three new macroacyclic Schiff base complexes were prepared via condensation of N,N,N',N'-tetrakis(2-aminoethyl) ethylenediamine hydrobromide with 5-bromo salicylaldehyde in the presence of metal ions (Zn2+, Cd2+, Hg2+) as template agents. The compounds were studied with elemental analysis, FT-IR, and 1H, 13C NMR spectroscopy. The structure of the Cd(II) complex, [Cd(H2L)] .2H2O (1), (H4L = N,N,N',N'-tetrakis(5-bromo salicylidene) N,N,N',N'-tetrakis(2-aminoethyl) ethylenediamine), was determined by single crystal X-ray crystallography. The X-ray diffraction analysis revealed that 1 crystallizes in monoclinic space group P21/c. Intermolecular O–H⋯O and C–H⋯Br hydrogen bonds linked [Cd(H2L)] monomers to a 2D network structure along the ac plane. The Br⋯Br halogen bonding interactions further expand the structure and construct a 3D supramolecular network with 1D right-handed and left-handed helical chains along the b axis in a 1:1 ratio. Furthermore, 1 is self-assembled through hydrogen bonding between the lattice water molecules with the phenolic oxygen atoms and phenolato oxygen atoms to form a 1D helical chain perpendicular to bc plane. The impact of the intermolecular contacts on the crystal packing of 1 has been further studied using Hirshfeld surface analysis and corresponding 2D fingerprint plots. Antibacterial activities of the compounds were screened by the disc diffusion method against three Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 23212 and S. epidermidis ATCC 34384), and three Gram-negative bacteria (Eschericha coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Klebsiella pneumonia ATCC 70063). All compounds demonstrated good antibacterial activities, and in three cases, the antibacterial activity of the Hg(II) complex exceeded the one of sulfisoxazole used as a standard.