Synthesis, structural determination and biological evaluation of bi- and trimetallic complexes containing Pd(II) and Sn(IV) with various S-donor ligands

Abstract

This research work is concerned with the synthesis, spectroscopic characterization and biological applications of monometallic, homo/hetero bi- and tri-metallic complexes of tin and palladium with various S donor ligands. Di/triorganotin(IV) and palladium(II) salts were treated with potassium salts of ligand ((HL1, HL2 & HL3) dithiocarbamate or free ligands (HL4, HL5 & HL6) in 1:1 and 1:2 molar ratios to produce thiolates, phenolates and dithiocarbamates. Methanol, acetone, toluene or water were used as a medium for the reactions. Thin layer chromatography of the samples was carried out to monitor the progress of the reaction and to check the purity of the compounds. The characterization of the newly synthesized complexes and their parent ligands was carried out by different spectroscopic techniques, for example, IR, UV/VIS, multinuclear ( 1H,13C) NMR spectroscopy and mass spectrometry. The data obtained from these studies helped to ascertain the bonding behavior of the ligand donor sites and structural aspects of these compounds. Based on IR study, bidentate chelating mode of dithiocarbamate moieties to metals has been suggested. A distorted trigonal bipyramidal or a tetrahedral environment around tin(IV) in chlorodiorganotin(IV)/diorganotin(IV)/triorganotin(IV) phenolates, thiolates and dithiocarboxylates has been pointed out, respectively in the coordinating solvents on the basis of multinuclear NMR spectra. The absorption bands in UV/VIS spectroscopy indicated that palladium(II) complexes possessed the square planner geometry around Pd(II) center in solution. The fragmentation pattern were obtained from mass (EI-MS) spectrometry followed the suggested molecular skeletons of the synthesized complexes. Antibacterial and antifungal activities of many homo and heterometallic complexes were studied against different bacterial and fungal strains. Minimal inhibitory concentrations of complexes used to inhibit bacterial and fungal strains were also determined. Some of the compounds were found to have antimicrobial activity comparable or even more than reference drugs and may be considered for use as drugs in future. The triorganotin(IV) derivatives have strong bactericidal and fungicidal action than diorganotin(IV) complexes with few exceptions. The antimicrobial activity of homotrimetallic complexes have been higher as compared to monometallic/bimetallic and heterotrimetallic complexes. The xiv excellent behavior of trimellalic complexes as antimicrobial agent was based on the presence of greater number of tin(IV) metals in these complexes. The hemolytic activity of was also found out to study the effect of these compounds on red blood cells. The hemolytic activity of these substances have been observed in between the hemolytic activity of the Triton X-100 which was used as positive control and phosphate buffered saline (PBS) was taken as negative control during this study. These compounds can be used as antimicrobial agents as their hemolytic activity have been found low as compared to their antibacterial and antifungal activities. Two bacterial strained, B. subtilis and E. coli were used to examine the antibiofilm activity of these synthesized compounds. The complexes were also found to be good inhibitor against biofilms of bacteria. Some monometallic, homo/hetero bi- and tri-metallic complexes of tin and palladium with various sulfur donor ligands possess potent antimicrobial activities and less hemolytic effects. So it is possible to use these compounds as antibiotic drugs.