Nanostructured Palladacycle and its Decorated Ag@NP Composite: Synthesis, Morphological Aspects, Characterization, Quantum Chemical Calculation and Antimicrobial Activity

We herein report the synthesis of nanostructured cyclopalladated complex and its nanosilver composite for the first time. The reaction between Schiff base ligand 4-methyl-N-(3,4-dimethoxybenzylidene)] benzenamine (L) and palladium acetate gave the cyclopalladted complex (Pd1) in nanoscale. Thermal treatment of silver oxalate with Pd1 resulted in the formation of novel nanostructured composite, silver nanoparticle-decorated palladacycle (Pd2). The synthesized compounds were characterized using spectroscopic analysis (FT-IR and 1H NMR), thermal analysis (TGA), XRD and morphological analysis (SEM and TEM). The spectral analysis revealed that complex Pd1 has dimeric structure bridged with acetate ligands between two monomers. SEM images exhibited that Ag-NPs loaded on complex surface in decorated form. TEM photographs showed the particle sizes of composite ≈ 29 nm. Quantum chemical analysis of ligand and complex Pd1 has been carried out by DFT/B3LYP method. There are two suggested isomers for cyclopalladated complex named Pd1 and Pd1* which are theoretically studied and correlated with practical results. HOMO, LUMO energy values, chemical hardness–softness, electronegativity and electrophilic index were calculated. The theoretical data obtained have been confirmed that the Pd1 isomer is more stable than Pd1* isomer which correlated well with practical results. The ligand and complexes screened for antimicrobial activity against five medically important microorganisms, namely Staphylococcus aureus, Proteus mirabilis, Pseudomonas aeruginosa, Escherichia coli and Candida albicans. The results showed that complex Pd2 displayed the highest activity against the tested microorganisms.