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New lead(II) complexes have been synthesized with Schiff bases derived from 4-methoxybenzaldehyde and amino acids (tryptophan, phenylalanine, valine, isoleucine, methionine, histidine, alanine, cysteine, serine and aspartic acid). These ligands act as monobasic bidentate species and coordinate to the lead atom through the azomethine nitrogen and carboxylate oxygen atom. The synthesized complexes have been characterized by conductance measurements, elemental analysis and molecular weight determinations. The mode of bonding of the ligands and lead(II) complexes have been confirmed on the basis of infrared, UV-visible, and 1H, and 13C NMR spectroscopic studies, and probable structures have been assigned to these complexes. The optimized structural parameters such as bond length, bond angles, HOMO orbital, LUMO orbital, dipole movement, electronegativity, global softeness, electrophilicity index and mulliken atomic charges were calculated by the methods based B3LYP on the density functional theory (DFT). The ligands and their corresponding lead(II) complexes have also been screened for antibacterial activities. [ABSTRACT FROM AUTHOR]

A new series of metal complexes [M(L)2] (where M = Sn(II), Pb(II), and HL = semicarbazone, thiosemicarbazone or phenylthiosemicarbazone) have been prepared and characterized by elemental analysis, conductance measurements, molecular weight determinations, UV–visible, infrared, and nuclear magnetic resonance (1H-,13C-, and119Sn-NMR) spectral studies. Elemental analysis of the metal complexes suggested 1 : 2 (metal–ligand) stoichiometry. Infrared spectra of the complexes agree with coordination to the metal through the nitrogen of the azomethine (>C=N−) and the oxygen/sulfur of the ketonic/thiolic group. Electronic spectra suggest a distorted tetrahedral geometry for all Schiff base complexes. The bond lengths, bond angles, highest occupied molecular orbital, lowest unoccupied molecular orbital, Mulliken atomic charges, and the lowest energy model structure of the complexes have been determined with DFT calculations. Representative Schiff base and its metal chelates have been screened for theirin vitroantibacterial activity against four bacteria, Gram-positive (Bacillus cereus,Staphylococcus aureus) and Gram-negative (Escherichia coli,Klebsiella pneumoniae) and four strains of fungus (Penicillium chrysogenum,Aspergillus niger,Rhizopus nigricans, andAlternaria alternata). The metal chelates possess higher antimicrobial activity than the free ligands. [ABSTRACT FROM PUBLISHER]