Schiff Base Metal Complexes Research Articles

Structure, electronic properties, and NBO and TD-DFT analyses of nickel(II), zinc(II), and palladium(II) complexes based on Schiff-base ligands

In this work we studied the structural and electronic properties of the metal-Schiff base complexes Ni[Formula: see text] (1), Pd[Formula: see text] (2), Zn[Formula: see text] (3), and Ni[Formula: see text](4), where L1 and L2 are Schiff bases synthesized from salicylaldehyde and 2-hydroxy-5-methylbenzaldehyde, respectively. Natural bond analysis showed that in complexes 1 and 2, the metal ion coordinates to the ligands through electron donation from lone pairs on ligand nitrogen and oxygen atoms to s and d orbitals on the metal ion. In complex 3, metal-N and metal-O bonds are formed through charge transfer from the lone pairs on nitrogen and oxygen atoms to an s orbital of Zn. Dimethylation of the phenolate rings in the ligands decreases the energy gap and redshifts the spectrum of the nickel complex. The main absorptions observed were assigned on the basis of singlet-state transitions. The simulated spectra of the two complexes 1 and 2 are characterized by excited states with ligand-to-ligand charge-transfer (LLCT), metal-to-ligand charge-transfer (MLCT), ligand-to-metal charge-transfer (LMCT), and metal-centered (MC) character. Graphical abstract Geometric structure of the palladium complex.

Nanographene Sheet Immobilized Transition Metal Complexes for C-C Coupling Reactions

Transition metal Schiff base complexes covalently immobilized on the surface of amino functionalized graphene sheet to catalyze C-C coupling reaction is reported. Graphene sheet which synthesized using mechanical exfoliation and then by differential oxidative reduction phenomenon of graphite. The schiff base ligand is prepared using aldehyde and amino groups containing compounds which further treated with metal salts to form metal complexes. The as-synthesized metal complexes was then incorporated into amino functionalized nanosheets which are characterized using different spectrochemical techniques. The catalytic investigation of the as-prepared catalyst were done by the cross coupling of aryl halides and aryl boronic acids to form biaryls as product in C-C cross coupling reaction. The yield of the products were high and selective which were analyzed using Gas chromatography technique. The advantage of this catalyst is high stability, recyclability easy recovery of catalyst, environmentally benign and mild reaction condition.

Fluorescence properties of some transition metal complexes of Schiff bases- A review

In the last few years there have been an increasing number of reports on the biological activity of metal complexes of Schiff bases however their applications in fluorescent probes have been scarce and largely limited to ruthenium complexes in DNA and oxygen sensing This review includes studies on the photoluminescence behavior of metal complexes of Schiff bases and the effect of different metals on the intensity of fluorescence emission The study would be beneficial for the design and development of metal based fluorescent sensors and light emitting devices

The synthesis of CuO and NiO nanoparticles by facile thermal decomposition of metal-Schiff base complexes and an examination of their electric, thermoelectric and magnetic Properties

In this study, CuO and NiO NPs have been synthesized by facile thermal decomposition of Schiff base complexes and their physical properties have been examined. The synthesized CuO and NiO NPs are crystallized in polycrystalline monoclinic and cubic structures with average particle size 17 ± 0.4 and 62 ± 1 nm, respectively. The electrical conductivity measurements confirm that the conduction in the CuO NPs is a band-to-band type while the conduction in the NiO NPs is governed by the large polaron conduction mechanism. The thermoelectric measurements confirm that the CuO and NiO NPs are P-type degenerate semiconductors with room temperature Seebeck coefficients equal to 89.9 and 12.1 mV/K, respectively. The magnetic measurements exhibit that the NPs have weak ferromagnetic ordering and antiferromagnetic to paramagnetic transition with high dipolar interaction.

Synthesis and characterization of transition metal complexes with a Schiff base derived from cephalexin and 1,2–diaminobenzene. antibacterial activity

From the reaction of 1,2-diaminobenzene 1 with cephalexin 2 antibiotic a cephalexin–based Schiff base (HL) 3, was obtained and the transition metal Schiff base complexes were synthesized. The products were characterized by physical and spectral techniques, namely, UV–Vis, FT-IR, 1H-NMR, EPR, MALDI mass spectrometry, magnetic susceptibility, molar conductance, molecular modeling, together with elemental and thermal analysis. The general composition [M(L)(OAc)(H2O)2], M(II) = Mn2+ 4, Co2+ 5, Ni2+ 6, Cu2+ 7, Zn2+ 8, where L represents deprotonated tridentate NNO Schiff base, have been assigned to the adducts. Direct calcinations of the complexes 6 and 8 at 700 °C resulted high-quality metal oxide (MO) nanoparticles. Paper disc diffusion method was used to test the bactericidal activity of the synthesized products.

Fast and reversible redox reaction of polyNi(salphen)@reduced graphene oxide/multiwall carbon nanotubes composite for supercapacitors

π-conjugated Schiff base metal complex polymer was easily synthesized onto reduced graphene oxide (rGO), multiwall carbon nanotubes (MWCNTs), polished titanium substrate and rGO/MWCNTs support electrodes from [N, N′-bis(salicylidene)-o-phenylenediamine] nickel(II) complex, Ni(salphen), by the route of Cyclic Voltammogram (CV) method, respectively. The morphologies of the polyNi(salphen) on different support electrodes was evaluated by field emission scanning electron microscopy (FESEM). X-ray photoelectron spectroscopy (XPS) measurement was carried out to shed light on the polymerization mode and energy storage mechanism. Meanwhile, the potential-step chronoamperometry was carried out to assess the charge transport dynamics. The result signals that the azomethine nitrogen group (NCH) in polyNi(salphen) with arrangement of the π-conjugated system upon the electron transfer path at intramolecular of the macrocycle instead of the Ni2+/Ni3+ process generate the energy storage capacity by reversible charge transfer. Due to the combining effect of the electrochemical double layer capacitor (EDLC) and pseudocapacitive of the polyNi(salphen) caused by faradaic capacitance, the specific capacitances of the composite electrodes exhibit 60% higher than that of the rGO/MWCNTs support electrodes. Furthermore, the strong π–π interactions between rGO/MWCNTs support electrode and the π-conjugated systems in polyNi(salphen) leads to better energy storage and kinetic behavior.

Synthesis, spectral characterization, molecular modeling, antibacterial and antioxidant activities and stability study of binuclear Pd(II) and Ru(III) complexes with novel bis-[1-(2-[(2-hydroxynaphthalen-1-yl)methylidene]amino}ethyl)-1-ethyl-3-phenylthiourea] ligand: Application to detection of cholesterol

A novel bis-[1-(2-[(2-hydroxynaphthalen-1-yl) methylidene]amino}ethyl)-1-ethyl-3-phenylthiourea] Schiff base (L) and its binuclear palladium and ruthenium complexes have been prepared and characterized by ESI-MS, elemental analysis, NMR (1H NMR, 13C NMR, COSY, NEOSY and HSQC), FT-IR, ATR, UV–Visible spectra, TGA measurements, conductivity and cyclic voltammetry. The experimental results and the molecular parameters calculated using DFT method revealed a square planar geometry around Pd and octahedral geometry around ruthenium metal.The antibacterial activity of the ligand L and its complexes was evaluated against different human bacteria. In addition, the formation constants of the synthesized Schiff base-metal complexes and the systems formed with these chelates and cholesterol were estimated using spectrophotometric technique. The detection of cholesterol using novel Pd and Ru Schiff base complexes was studied using fluorometric method, and the measurements showed that the sensitive fluorometric response towards cholesterol analysis was determined using palladium complex. The limit of detection (LOD) of cholesterol calculated using this complex (4.6 μM) is lower (better) than LOD found using ruthenium complex (19.1 μM) and different compounds previously published around linear range of 0–5 mM.

Synthesis, structural characterization, antimicrobial, antioxidant and DNA binding studies of some novel homo‐binuclear Schiff base metal (II) complexes

A novel bi‐nucleating Schiff base ligand, 6,6′‐(((1E,1′E)‐thiophene‐2,5‐diylbis (methaneylylidene))bis (azaneylylidene))bis (3,4‐dimethylaniline), and five binuclear M (II) complexes were synthesized. The bi‐nucleating Schiff base ligand and its metal complexes were characterized using various physicochemical techniques, e.g. elemental analyses, spectroscopic methods, conductivity and magnetic moment measurements. The low molar conductance of the complexes in dimethylsulfoxide shows their non‐electrolytic nature. The antibacterial activities were screened against pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Pseudomonas putida and Bacillus subtilis). The antifungal activity was screened against Aspergillus niger, Aspergillus flavus and Rhizoctonia bataicola. The antimicrobial activity data showed that the metal complexes are more potent than the parent Schiff base ligand against microorganisms. The antioxidant activities of the synthesized compounds were investigated through scavenging activity against 2,2‐diphenyl‐2‐picrylhydrazyl, superoxide anion, hydroxyl and 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulfonic acid) radicals. The complexes have superior radical scavenging activity than the free ligand and the scavenging effects of the Cu (II) complex are stronger than those of the other complexes. DNA binding studies were performed using electronic spectroscopy, fluorometric competition studies and viscosity measurements. The data indicated that there is a marked enhancement in biocidal activity of the ligand under similar experimental conditions because of coordination with metal ions.

Spectroscopic characterization and photophysical properties of schiff base metal complex

In the present work, Schiff base ligand N,N-bis(salicylidene)-(3,3′-diaminobenzidine) and its zinc complex were synthesized. The coordination of Schiff base ligand with zinc metal ion seems to occur via N azomethine followed by the deprotonation of OH group. The nuclear magnetic resonance peaks as well as important bands in the Fourier transform infra-red spectra are discussed in relation to the structure of the ligand and complex. The optical properties like absorption and fluorescence were studied to get the idea about the transition among molecular orbitals as well as quantum yield. Colour coordinates of complex fall in the blue region. HOMO-LUMO energy gap was used to determine various parameters. Thermal studies were also performed to determine the thermal stability of the complex in the range from room temperature to 500 °C.

Biological aspects of Schiff base–metal complexes derived from benzaldehydes: an overview

Schiff bases are stable imines containing C=N, where N is bonded to an alkyl or aryl group, but not with hydrogen and are prepared by condensation of aliphatic or aromatic primary amine with carbonyl compounds. They have the general formula R1R2C = NR3, where R3 ≠ H. The presence of the basic donor N atom and the stability of the imine function render Schiff bases as the most favored ligands that have the ability to stabilize metal ions in different oxidation states. The chelating environment in a Schiff base profoundly influences the electron distribution in the coordination sphere of metal in a complex and thereby regulates the property of the compounds in a big way. The structural diversity in some of the metal complexes with multidentate Schiff base ligands has triggered a wide range of applications of this class of compounds in sensors, catalysis, biology, medicines, and photonics. This review compiles the synthesis and biological activities (antimicrobial, antioxidant, anticancer, antitubercular, DNA interaction studies) of benzaldehyde-based Schiff bases and their metal complexes.

Synthesis, spectral and antimicrobial studies of amino acid derivative Schiff base metal (Co, Mn, Cu, and Cd) complexes

Amino acid derivative Schiff base was synthesized by reaction of leucine with salicyldehyde in basic medium. The Schiff base was used as a ligand which was reacted with Co, Mn, Cu and Cd metals in order to form the stable complexes. The synthesized ligand and metals complexes were characterized by using different spectroscopic tools i.e. FT-IR, Mass spectrometry and NMR. The percentages of different elements present in ligand molecule and complexes was confirmed by Elemental analyzer. All compounds including ligand and complexes were also engaged with different bacterial (Escheria coli, Staphylococcus aureus, Bacillus subbtilis) and fungal strains (Alternaria alternate, Aspergillus flavus and Aspergillus niger) in order to check the inhibitory action of titled compounds. The results showed that the metal complexes have greater antimicrobial activities than ligand.

Green synthesis of ethyl oxalate benzylidinyl hydrazides

Acylhydrazone compounds play an important role in medicine, materials and other fields. Herein we report the synthesis of ethyl oxalate benzylidinyl hydrazides by the reaction of benzaldehyde derivatives and ethyl oxalate hydrazide under catalyst-free conditions in H2O near room temperature. This green synthesis method has the advantages of mild reaction conditions, fast reaction rate, non-catalytic, good yield and easy isolation. These synthesized ethyl oxalate benzylidinyl hydrazides can be used as Schiff base metal complexes of small molecule ligands.

Antibacterial activity of transition metal complexes with a tridentate NNO amoxicillin derived Schiff base. Synthesis and characterization

From the reaction of amoxicillin (1) antibiotic with 2,6−diaminopyridine (2) an amoxicillin−based Schiff base (HL) (3) was obtained and its transition metal Schiff base complexes were synthesized. Spectroscopic and physicochemical techniques, namely, UV−Vis, FT−IR, 1H−NMR, EPR, mass spectrometry, molar conductance, magnetic susceptibility, molecular modelling, together with elemental and thermal analyses, were used to characterize the synthesized compounds. Spectral and magnetic data suggested an octahedral geometry for all the complexes and the general formulae [ML(H2O)3][PF6] (M(II) = Mn2+ (4), Co2+ (5), Ni2+ (6), Cu2+ (7), Zn2+ (8), was proposed for them, where L represents deprotonated tridentate NNO amoxycillin−derived Schiff base. All compounds were screened for antibacterial activity by using agar disc diffusion method. The zinc(II) complex exhibited promising bactericidal activity against E. coli and S. aureus.

The electric and thermoelectric properties of Cu(II)-Schiff base nano-complexes

The physical properties, such as electric and optical properties, of metal-Schiff base complexes have been widely investigated. However, their thermoelectric (TE) properties remain unreported. This work presents Cu(II)-Schiff base complexes as promising materials for TE power generation. Therefore, three Cu(II)-Schiff base complexes (namely, [Cu(C32H22N4O2)].3/2H2O, [Cu(C23H17N4O7Br)], and [Cu(C27H22N4O8)].H2O) have been synthesized in nanosized scale. The electric and TE properties have been studied and comprehensive discussions have been presented to promote the nano-complexes (NCs) practical applications in the field of TE power generation. The electrical measurements confirm that the NCs are semiconductors and the electrical conduction process is governed by intermolecular and intramolecular transfer of the charge carriers. The TE measurements reveal that the Cu(II)-Schiff base NCs are nondegenerate P-type semiconductors. The measured Seebeck coefficient values were higher compared to the values reported in previous works for other organic materials indicating that the complexes under study are promising candidates for theremoelectric applications if the electrical conductivity could be enhanced.

Synthesis of tetradentate metal Schiff base complexes towards the synthesis of novel antimicrobials

Schiff bases are molecules that carry a characteristic imine bond that are derived from carbonyl compounds and are widely studied due to the versatility of their steric and electronic properties. Schiff bases are significant because of their biologically active properties that can improve and develop agrochemicals, anti‐inflammatories, antivirals, and even radiopharmaceuticals for cancer targeting. This study is focused on synthesizing a family of novel metal Schiff base complexes that have potential to act as antimicrobials over a wide range of pathogenic species.In a previous study, a family of metal Schiff base complexes with an NN'NN coordination sphere was synthesized. This study found that antimicrobial activity using Schiff base complexes with chromium, iron, or manganese as their center showed greater inhibition of Aspergillus sp. growth than a variety of known antimicrobial drugs (Kumar et al., 2012). In an attempt to expand the antimicrobial potential of these compounds, we changed the structure of these Schiff base ligands to utilize an NN'OS coordination sphere with the same set of metal centers. We hypothesized that the chemical activity of the sulfur atom would provide an improved range of antimicrobial function.Our synthesis of NN'OS coordination sphere‐based antimicrobials began with the compound cyclopentanone. Cyclopentanone was condensed with carbon disulfide, recrystallized, protonated, and methylated with dimethyl sulfate. The resultant methylated product was aminated with two different diamines to form a set of novel primary amines. These primary amines were reacted with salicylaldehydes with different substitutions to form a family of Schiff base ligands. The last step in the synthesis process was to add a transition metal to the Schiff base ligands (chromium, iron, or manganese) through a reflux reaction. After synthesis, each metal Schiff base complex was characterized through 1H and 13C nuclear magnetic resonance, infrared, and gas chromatography‐mass spectroscopy.With synthesis complete, current work focuses on the examination of these compounds as effective antimicrobials. The compounds are being tested for these properties against Aspergillus furmigatus as a representative of a broad range of Aspergillus species. Characterized Schiff base complexes are being compared for their level of antimicrobial activity against that shown by Miconazole, an established antimicrobial used to treat an array of fungal infections. The results of these tests may establish Schiff base ligands with NN'OS coordination spheres as a novel effective means of treating an array of dangerous microbial infections.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Novel Schiff base metal complexes: synthesis, characterization, DNA binding, DNA cleavage and molecular docking studies

A novel Schiff base, 3-(((1H-1,2,4-triazol-3-yl)imino)methyl)-4H-chromen-4-one (L) was synthesized and used as ligand for the synthesis of Co(II), Ni(II), Cu(II), Zn(II) and Pd(II) complexes. The structural characterization of the ligand and its metal complexes was determined by using various physicochemical and spectroscopic methods. The IR data show that the Schiff base ligand acts as a bidentate donor coordinating through the oxygen atom of the chromone and nitrogen atom of the imine group. Based on all spectral data, tetrahedral geometry has been proposed for all the metal complexes except Cu(II) and Pd(II) complexes. However, square-planar geometry has been proposed for Cu(II) and Pd(II) complexes. DNA binding interaction of the ligand and its metal complexes was investigated by using UV–visible absorption, fluorescence and molecular docking studies. The binding constants were in the order of 104 M−1 suggesting good binding affinity towards CT-DNA. The DNA cleavage activity of the synthesized compounds was investigated by using agarose gel electrophoresis. In vitro antimicrobial activity of the synthesized compounds were screened against two gram-positive bacteria (Bacillus subtilis, Staphylococcus aureu) and two gram-negative bacteria (Escherichia coli, Proteus vulgaris) and one fungi strain Candida albicans using disc diffusion method. Antioxidant activity was carried out by DPPH radical scavenging method. In vitro anti-proliferative activity of the ligand and its metal complexes was also carried on the HEK-293, HeLa, IMR-32 and MCF-7 cancer cell lines using MTT assay.

DNA, in vitro antimicrobial/anticancer activities and biocidal based statistical analysis of Schiff base metal complexes derived from salicylalidene-4-imino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and 2-aminothiazole

New mono cationic Cu(II), Co(II), Ni(II), VO(II) and Zn(II) Schiff base complexes have been designed and synthesized from salicylalidene-4-imino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and 2-aminothiazole. The prominent structural features of synthesized compounds were studied by elemental analysis, UV–Vis., FTIR, 1H NMR, 13C NMR, EPR, Fluorescence emission, Powder XRD, FESEM and FAB-Mass spectral measurements. The IR, UV-Vis., spectra and magnetic susceptibility data of the complexes ensured that they are square planar geometry except [VOL]Cl complex which exists in square pyramidal geometry. CV profiles for [CuL]Cl and [VOL]Cl complexes in MeCN solution indicate that the redox potential of metal ions are affected by the coordinated ligand. The Spin Hamiltonian parameters calculated from the EPR spectra of [CuL]Cl and [VOL]Cl complexes were well coinciding with proposed geometries and other reported complexes. Powder XRD data and FESEM images persist that the complexes are nano size grains with polycrystalline structure. DNA interaction studies of [CuL]Cl complex reveal that the binding occurs through intercalation between complex and DNA. The in-vitro antimicrobial activities of the investigated compounds were tested against bacterial and fungal strains by well diffusion method. The minimum inhibitory concentration (MIC) values suggest that metal chelates have higher activity than the free ligand. The Schiff base and its complexes have been tested for the anticancer effect towards the human breast cancer cell line (MCF-7) by MTT assay method and % cell inhibition of compounds were reported. The comparative study of antimicrobial activities of the samples has been considered for three different parameters like Mean deviation (MD), Co-efficient of Mean Deviation (CMD) and Karl Pearson's Co-efficient of Correlation (r). These results are exhibit that the antimicrobial efficiency depends on the crystalline size and shape of the prepared samples.

Europium and terbium Schiff base peptide complexes as potential antimicrobial agents against Salmonella typhimurium and Pseudomonas aeruginosa

Eu(III) and Tb(III) Schiff base complexes are applicable in various fields such as sensing, assays, screening protocols in vitro, and imaging studies in vitro or in vivo. Fluorescent europium and terbium complexes and their interaction with cell penetrating peptide (KKKRKC) can represent an excellent key for understanding pathway of peptide transportation though cell membrane and the application of Schiff base complexes as potential antibacterial drugs. The Schiff base–metal complexes and its conjugates with peptide were tested for their antibacterial activity against Pseudomonas aeruginosa and Salmonella typhimurium. Schiff base–metal complexes conjugated with peptide show minor toxicity in normal human PNT1A cells and high antibacterial activity against P. aeruginosa and S. typhimurium, where IC50 down to 125.9 and/or 36.1 µM were found for P. aeruginosa and S. typhimurium, respectively. Our results strongly suggest that Schiff base–metal complexes conjugated with peptide have great potential to be developed into highly effective antibacterial drug.

Synthesis, Characterization and Antimicrobial Properties of Pd(II), Cr(III), Ni(II) and Co(II) Metal Complexes of Aniline and Sulphadiazine Schiff Bases as mixed Ligands

Novel Pd(II), Cr(III), Ni(II) and Co(II) metal complexes of Schiff bases were synthesized from the condensation reaction between salicylaldehyde and aniline (L1) and sulphadiazine (L2). They were characterized using FTIR and UV-Visible spectroscopy and subjected to conductivity, melting point and solubility measurements. The complexes are non-toxic, non-electrolytic and stable solids. The involvement of the azomethine nitrogen in coordination with the metals was confirmed by the IR and UV results. They showed good inhibitory activities against various microorganisms.

Efficient procedure with new fused pyrimidinone derivatives, Schiff base ligand and its La and Gd complexes by green chemistry

Synthetic strategies were developed for the construction of some newer more potent derivatives of thiobarbituric acid and its Schiff base metal complexes in both bulk and at the nanoscale.