Synthesis, Structural Analysis and Antimicrobial Screening of Mn(II) Complexes of Schiff Bases

Mn(II) complexes of Schiff bases 4-((3-ethoxy-2-hydroxybenzylidene)amino)-N-(pyridin-2-yl)benzenesulfonamide (HL2) and 4-((3-ethoxy-2-hydroxybenzylidene)amino)-N-(pyrimidin-2- yl)benzenesulfonamide (HL3) were synthesized. The Schiff bases HL2 and HL3 and their complexes were characterized by analytical, conductance, magnetic susceptibility measurements, infrared, ultraviolet-visible, thermal analysis, and EI mass techniques. The spectral data of the complexes have revealed the bidentate complexing nature of the Schiff base ligand through phenoxide ion and azomethine nitrogen atoms. The antibacterial activities of complexes were tested against gram-positive bacterial species Pseudomonas aeruginosa (NCIM 2036) and fungal species Aspergillus niger (NCIM 105) and Mucor sp. (NCIM 108) by disc diffusion method. Keywords: Schiff bases; Mn(II) complex; antibacterial; antifungal. Resumen. Los complejos de Mn(II) de las bases de Schiff 4-((3-etoxi-2-hidroxibencilideno)amino)-N-(piridin-2-il)bencenosulfonamida (HL2) y 4-((3-etoxi-2-hidroxibencilideno)amino)-N-(pirimidin-2- il)bencenosulfonamida (HL3) fueron sintetizados. Las bases de Schiff HL2 and HL3 y sus complejos fueron caracterizados por métodos analíticos, conductancia, susceptibilidad magnética, espectroscopia infrarroja y UV-vis, termogravimetría, y espectrometría de masas por impacto enectrónico. Los datos espectroscópicos obtenidos para los complejos corroboraron la coordinación bidentada de los ligantes de base de Schiff a través del ion fenóxido y el átomo de nitrógeno del grupo azometino. La actividad antibacterial de los complejos se evaluó contra cepas bacterianas gram-positivas Pseudomonas aeruginosa (NCIM 2036) y contra especies fúngicas Aspergillus niger (NCIM 105) y Mucor sp. (NCIM 108) utilizando el método de difusión en disco.

SYNTHESIS AND CHARACTERIZATION OF COPPER(II) COMPLEX WITH 2,6-DIACETYLPYRIDINE-BIS(PHENYLHYDRAZONE)

The syntheses, physicochemical and structural properties of the novel Cu(II) complex with 2,6-diacetylpyridine bis(phenylhydrazone) (L), of the formula [CuL2]Br2 are presented. In the reaction of warm MeOH solutions of the ligand, 2,6-diacetylpyridine bis(phenylhydrazone) and CuBr2 in molar ratio 2:1 resulted in formation of black single crystals of the bis(ligand) complex. This is the first Cu(II) complex with this ligand that is characterized by SC-XRD. Two ligand molecules are coordinated in the usual tridentate mode, via nitrogen atoms of the pyridine ring, and two azomethine nitrogen atoms, forming distorted octahedral environments of the metal ion.

Synthesis, Characterization and corrosion Inhibition Studies on Mn (II) and Co (II) Complexes Derived from 1-{(Z)-[(2-hydroxyphenyl) imino]methyl}naphthalen-2-ol in 1M HCl Solution

Schiff base derived from the reaction of 2-amino phenol and 2-hydroxy-1-naphthaldehyde and its Co (II), and Mn (II) complexes have been synthesized and characterized by solubility test, melting point/ decomposition temperatures, molar conductance, IR and magnetic susceptibility. The number of ligands coordinated to the metal ion was determined using Job’s method of continuous variation. Their molar conductance values indicate that all the complexes are non-electrolytes. Magnetic moment values of the complexes showed that both Mn (II) and Co (II) are paramagnetic. The spectroscopic data of metal complexes indicated that the metal ions are complexed with azomethine nitrogen and deprotonated oxygen atom. Corrosion inhibition of the schiff base and Mn (II) and Co (II) complexes were evaluated using the weight loss method in a 0.1MHCl solution for copper metal. The inhibition efficiency increased with increasing inhibitors concentration. The negative values of Gibb’s free energy of adsorption (ΔGads) confirmed the spontaneity and physical adsorption of the inhibition process which is inconsistent with Langmuir adsorption isotherm.

Solvent-Induced Formation of Novel Ni(II) Complexes Derived from Bis-Thiosemicarbazone Ligand: An Insight from Experimental and Theoretical Investigations

In this work, we report solvent-induced complexation properties of a new N2S2 tetradentate bis-thiosemicarbazone ligand (H2LI), prepared by the condensation of 4-phenylthiosemicarbazide with bis-aldehyde, namely 2,2’-(ethane-1,2-diylbis(oxy)dibenzaldehyde, towards nickel(II). Using ethanol as a reaction medium allowed the isolation of a discrete mononuclear homoleptic complex [NiLI] (1), for which its crystal structure contains three independent molecules, namely 1-I, 1-II, and 1-III, in the asymmetric unit. The doubly deprotonated ligand LI in the structure of 1 is coordinated in a cis-manner through the azomethine nitrogen atoms and the thiocarbonyl sulfur atoms. The coordination geometry around metal centers in all the three crystallographically independent molecules of 1 is best described as the seesaw structure. Interestingly, using methanol as a reaction medium in the same synthesis allowed for the isolation of a discrete mononuclear homoleptic complex [Ni(LII)2] (2), where LII is a monodeprotonated ligand 2-(2-(2-(2-(dimethoxymethyl)phenoxy)ethoxy)benzylidene)-N-phenylhydrazine-1-carbothioamide (HLII). The ligand LII was formed in situ from the reaction of LI with methanol upon coordination to the metal center under synthetic conditions. In the structure of 2, two ligands LII are coordinated in a trans-manner through the azomethine nitrogen atom and the thiocarbonyl sulfur atom, also yielding a seesaw coordination geometry around the metal center. The charge and energy decomposition scheme ETS-NOCV allows for the conclusion that both structures are stabilized by a bunch of London dispersion-driven intermolecular interactions, including predominantly N–H∙∙∙S and N–H∙∙∙O hydrogen bonds in 1 and 2, respectively; they are further augmented by less typical C–H∙∙∙X (where X = S, N, O, π), CH∙∙∙HC, π∙∙∙π stacking and the most striking, attractive long-range intermolecular C–H∙∙∙Ni preagostic interactions. The latter are found to be determined by both stabilizing Coulomb forces and an exchange-correlation contribution as revealed by the IQA energy decomposition scheme. Interestingly, the analogous long-range C–H∙∙∙S interactions are characterized by a repulsive Coulomb contribution and the prevailing attractive exchange-correlation constituent. The electron density of the delocalized bonds (EDDB) method shows that the nickel(II) atom shares only ~0.8|e| due to the σ-conjugation with the adjacent in-plane atoms, demonstrating a very weak σ-metalloaromatic character.

Mn(II), Co(II), Ni(II), and Cu(II) complexes of amino acid derived Schiff base ligand: Synthesis, characterization and in-vitro antibacterial investigations

Four complexes of Mn(II), Co(II), Ni(II) and Cu(II) with Schiff base ligand (H3L) derived from 2-amino-3-methylbutanoic acid and acetylacetonate were synthesized. All complexes were characterized by elemental analysis, Fourier-transform infrared spectroscopy and electronic spectroscopy. The results confirmed the coordination of the ligand to metals in tridentate fashion via the hydroxyl oxygen, the azomethine nitrogen and the enolic acetylacetonate oxygen. Antimicrobial activities were established for all complexes, free ligand and ciprofloxacin for comparison. Both the ligand and its metal complexes were active against Gram-positive and negative bacterial strains. The Cu(II) complex, showed highest antibacterial activity among the complexes screened. Other complexes displayed considerable antibacterial activity. Octahedral geometry was proposed for the metal(II) complexes with the Schiff base. KEY WORDS: Schiff base, Amino acid, Metal Complexes, Antibacterial agents Bull. Chem. Soc. Ethiop. 2021, 35(1), 97-106. DOI: https://dx.doi.org/10.4314/bcse.v35i1.8

Synthesis, characterization, and biological evaluation of some 4-((thiophen-2-yl-methylene)amino)benzenesulfonamide metal complexes

Background Sulfonamides (sulfa drugs) and the metals like mercury, copper, and silver bear antimicrobial properties. The discovery of broad-spectrum antibiotics such as penicillins, cephalosporins, and fluoroquinolones has reduced their use. However, in some instances these drugs are the first-line treatment. The metal-based sulfonamide (e.g., silver sulfadiazine) is considered as first choice treatment in post-burn therapy while the use of silver nanoparticle-cephalexin conjugate to cure Escherichia coli infection explains the synergistic effect of sulfa drugs and their metal conjugates. With growing interest in metal-based sulfonamides and the Schiff base chemistry, it was decided to synthesize sulfonamide Schiff base metal complexes as antioxidant and antimicrobial agent. Results The Fe (III), Ru (III), Co (II), Ni (II), Cu (II), Pd (II), Zn (II), Cd (II), and Hg (II) metal complexes of 4-((thiophen-2-ylmethylene)-amino)-benzenesulfonamide (TMABS) were prepared and studied for thermal stability, geometry, and other electronic properties. The ligand TMABS (Schiff base) and its metal complexes were screened in-vitro for 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and antimicrobial properties against Gram-positive (+ve) Bacillus subtilis (MTCC-441), Staphylococcus aureus (MTCC 7443), Gram-negative (-ve) Escherichia coli (MTCC 40), Salmonella typhi (MTCC 3231), and fungal strains Aspergillus niger (MTCC-1344) and Penicillium rubrum by agar well diffusion method. Results summarized in Tables 3, 4, and 5 represent the inhibitory concentration (IC50) in micromole (μM). The zone of inhibition (ZI) in millimeter (mm) represents antimicrobial properties of TMABS and its metal complexes. Conclusions The synthesized sulfanilamide Schiff base (TMABS) behaved as a neutral and bidentate ligand coordinating with metal ions through its azomethine nitrogen and thiophene sulfur to give complexes with coordination number of 4 and 6 (Fig. 3). The nucleophilic addition of sulfanilamide amino group (–NH2) group to carbonyl carbon (>C=O) of benzaldehyde gave sulfanilamide Schiff base (imine) (Fig. 2). All the metal complexes were colored and stable at room temperature. With IC50 of 9.5 ± 0.1 and 10.0 ± 0.7 μM, the Co, Cu, and Pd complexes appeared better antioxidant than the ligand TMABS (155.3±0.1 μM). The zone of inhibition (ZI) of Hg (28 mm) and Ru complexes (20 mm) were similar to the ligand TMABS (20 mm) against Aspergillus niger (MTCC-1344) as in Figs. 4, 5, and 6. None of the synthesized derivatives had shown better antimicrobial properties than the standard streptomycin sulfate and fluconazole.

Preparation and Characterization of Biacetyl Monoxime Hydrazone Salicylidene Complexes of Lanthanoid (III) Ions

The 1:3 complexes of lanthanoid (III) ions as Nd(III), Sm(III), Tb(III) and La(III) with biacetyl monoxime hydrazone salicyalidene have been prepared and characterized by elemental analysis, IR, PMR, electronic spectra, molar conductance and magnetic properties. All these complexes of Ln(III) complexes are found to be unique in infrared and solubility to the methanol, chloroform, DMF, DMSO solvents. The results show that the biacetyl monoxime hydrazone salicyalidene ligand acts as a bidentate monobasic donor, coordinating through the azomethine nitrogen and deprotonated oximino proton.

Theoretical and Spectroscopic Studies of SN Donor Thiosemicarbazone Ligand and Its Pt(II) Complex

Sulphur-nitrogen(SN) donor thiosemicarbazone ligand [(Z)-N-ethyl-2-(5-methyl-2-oxoindolin-3-ylidene)hydrazinecarbothioamide] and its Pt(II) complex were synthesized by condensation method. The compounds were structurally characterized by elemental analysis CHNS, FT-IR, and NMR analysis. The elemental analyses data for the compounds were in good agreement with the theoretical values. The melting point of the complex was higher than the ligand, as expected. The FT-IR spectral data reflect a bidentate bonding of thiosemicarbazone ligand to Pt(II) ion through thioketo sulfur and azomethine nitrogen. The docking results (theoretical results) of these compounds show that the binding energy between DNA and Pt(II) complex was found to be less than that of the Schiff base ligand (L) in the sense that it has higher stability at various stages and angles. The strength of docking between DNA and Pt(II) complex was also found to be that stronger than the Schiff base ligand (L).

Ruthenium(III) Based Diimine Complexes; Synthesis, Characterization, PXRD Study and Catalytic Hydrogenation of Cyclohexene

This study deals with preparation and characterization of a group of RuIII-chelates contains tetradentate diimine ligands. These quadridentate ligands are derived from 2-OH-1-naphthaldehyde and a number of aliphatic diamines where the number of methylene groups between the two azomethine nitrogen donors varied from two to six are the components of quadridentate ligands. The pure isolated compounds were subjected to several physicochemical investigations to assign their structures. Spectral and magnetic measurements suggested a distorted octahedral arrangement of the six coordinate diimine ruthenium(III) complexes. The structural optimization for one of the current RuIII-complexes was determined based on the processing of powder X-ray diffraction (PXRD) data by the computer program Expo 2014 PXRD. As well DFT calculations were applied to optimize the geometry in the case of complexes 1. The newly synthesized ruthenium(III) diimines were tested as catalysts for hydrogenation of cyclohexene. The effect of the catalyst structure and the type of catalysis as well as the nature and amount of the solvent used on the catalytic performance of the current catalysts were studied. Catalytic experiments reported that the ongoing ruthenium(III) complexes are promising precatalysts that have successfully catalyzed hydrogenation of cyclohexene by hydrogen gas under moderate process conditions. The results obtained allowed to establish a mechanism for the studied catalytic hydrogenation reactions.

Synthesis, characterization, and antimicrobial activity of 4-imidazolecarboxaldehyde thiosemicarbazone and its Pt(II) and Pd(II) complexes

Schiff bases are versatile ligands, synthesized via condensation of primary amines with carbonyl compounds. In this study, equimolar amounts of 4-imidazolecarboxaldehyde and thiosemicarbazide were combined and the Schiff base 4-imidazolecarboxaldehyde thiosemicarbazone was prepared as a new bidentate complexing agent. The synthesized ligand was reacted with palladium (II) and platinum (II) ions yielding air-stable complexes. For characterization purpose, infrared spectra, mass spectra, electronic spectra, thermal analysis, proton nuclear magnetic resonance and 13-carbon nuclear magnetic resonance spectra studies were carried out on the obtained complexes and ligand. The characterization data showed that the ligand acts as a bidentate coordinate to the metal ions through azomethine nitrogen and sulfur atoms. An in vitro antimicrobial investigation was also carried out for the free ligand and its metal complexes against four bacteria; Bacillus cereus, Staphylococcus aureus (Gram-positive), Escherichia coli and Salmonella typhimurium (Gram-negative) and one Fungi; Candida albicans, to assess their antimicrobial properties by disc diffusion technique. Antimicrobial activity of the prepared complexes showed higher activity than the free ligand.