Series Of Transition Metal Complexes Research Articles

Synthesis, Characterization and Biological Activity of Transition Metals Schiff Base Complexes Derived from 4,6-Diacetylresorcinol and 1,8-Naphthalenediamine

The tridentate Schiff base ligand was prepared via condensation of 4,6-diacetylresorcinol and 1,8-naphthalenediamine in 1:1 molar ratio using conventional method. Additionally, a new series of transition metal complexes of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal ions were prepared and fully characterized by elemental analysis, FT-IR, 1H NMR, UV–vis, conductivity and magnetic susceptibility measurements and theoretically through density function theory (DFT). Spectral studies suggested that, the Schiff base coordinated to the metal ions through the azomethine N, N-amine and phenolic oxygen atoms. From the elemental, magnetic susceptibility and spectroscopic data, the complexes were suggested to have octahedral geometry. The Schiff base and its metal complexes were screened for their in vitro antimicrobial activities and showed that Cd(II), Cu(II) and Cr(III) complexes have high activity against Escherichia coli, while Ni(II) and Cd(II) complexes have the highest activity against Bacillus Subtilis, Co(II) complex has the highest activity against Staphylococcus aureus and Cd(II) complex has the highest activity against Pseudomonas aeruginosa. In addition, the molecular docking study was performed to explore the possible ways for binding to crystal structure of Staphylococcus aureus nucleoside diphosphate kinase complexed with ADP (PDB ID: 3Q8U).

Preparation and Characterization of Some Complexes with New (Azo-Schiff base) Ligand and Study of Complex as Anticancer

Anew series of transition metal complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), Au(III) and Pt(II) have been preparation and characterization using anew azo-Schiff base ligand derived from schiff base (N1Z,N2Z)-N1,N2-bis(4-amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-ylidene)benzene-1,2-diamine with 5-methyl-imidazole.The structures of the new ligand azo-schiff base and their transition metal complexes are characterized using several techniques,including analysis(C.H.N),molar conductance,magnetic measurements, electronic spectral,IR spectral studies,13CNMR,1HNMR and mass spectra The data show that these complexes have composition of[MLCl2] where M=Co(II),Ni(II), Cu(II),Zn(II),Cd(II) and Hg(II),[ML] Cl3 where M=Au(III) and[ML]Cl2 ,where M=Pt(II).The electronic spectral, and magnetic susceptibility data of the complexes suggest octahedral geometry of all complexes,except the Au(III) and Pt(II) complex suggest a square planar geometry.The IR results demonstrate that the co-ordination sites are the azomethine nitrogen and azo nitrogen atoms of the ligand.The ligand behaves natural tetra dentate manner.The biological screening effect of the Pt(II) complex are tested against human breast cancer cell line MCF-7and normal cells( cell line WRL68).The results show the highest inhibitory effect for complex.

Synthesis and characterization of a series of acylpyrazolone transition metal complexes: Crystal structures and catalytic performance in the epoxidation of cyclooctene

A series of transition metal complexes of 4-acetyl-3-methyl-1-phenyl-2-pyrazoline-5-one with Ni(II), Cu(II), Fe(III) and Mn (II) central metal ions have been synthesized and characterized by X-ray crystallography, UV–Vis and FTIR spectroscopy, and elemental analysis. The complexes were used as a catalyst for epoxidation of cyclooctene with tert-butylhydroperoxide. Various parameters, including catalyst type and amount, solvent type and amount, oxidant/substrate ratio and time, have been optimized. The highest catalytic activity was found for Cu(II) complex at the optimized conditions. Very high selectivity for the epoxide product (cyclooctene oxide) was also obtained.

Synthesis, Characterization and Biological Evaluation of Schiff Base Transition Metal Complexes Derived from 4-Nitrobenzene-1,2-diamine and 5-Chloroisatin

A series of transition metal complexes of the type [MLX2], where M = Mn(II), Fe(II), Co(II), Ni(II), X = Cl–/CH3COO– and L = Schiff base derived from 4-nitrobenzene-1,2-diamine and 5-chloroisatin have been synthesized and characterized by elemental analysis, molar conductance, IR, UV-visible, magnetic moments measurement, 1H & 13C NMR and mass spectral studies. On the basis of physico-chemical studies and spectral evaluation, an octahedral geometry have been proposed for all metal(II) complexes. The antimicrobial activity of ligand and its metal complexes have been additionally screened against bacteria and fungi. Metal(II) complexes show good activity as compared to ligand towards studied microorganisms and also metal complexes checked for their catalytic properties for benzoylation of phenol.

Enhanced biological properties of taurine metal complexes via binding active sites

A simple preparation of Taurine metal complexes (TauMC) were carried out by general precipitation technique using binary solvent (DMF-Water) in 1:1 ratio. Taurine-metal complex formation were confirmed by the shift in the absorption peaks of UV–Visible spectrum. The role of Taurine played as a vital ligand to form the series of metal complexes with transition metal ions (Mn, Cu, Zn) were clearly observed as the M-O stretching vibration in FT-IR spectroscopy. Thermal stability and crystalline structure of these taurine metal complexes were well characterized by TGA and XRD studies. Co-ordination complex ratio of metal to ligand (1:2) were absolutely determined via XPS analysis. Especially, among the prepared taurine based series of transition metal complexes, Taurine-Cu complex (TauCC) emerged out as binding active sites than ligand which significantly enhanced its biological properties.

NMR absolute shielding scales and nuclear magnetic dipole moments of transition metal nuclei.

This work reports new, accurate nuclear magnetic dipole moments for NMR-active transition metal nuclei where the long-standing systematic error due to obsolete diamagnetic correction has been eliminated by ab initio calculations of absolute NMR shielding constants. The error of the diamagnetic correction reaches ≈ -14 000 ppm for rhenium, which results in magnetic dipole moment corrections of about -3 × 10-2μN for the 185Re and 187Re nuclei. Such extreme values are one to two orders of magnitude larger than the corrections reported in the literature so far. These findings may help to resolve discrepancies in hyperfine splitting experiments involving rhenium ions. To obtain the corrected transition metal nuclear magnetic dipole moments, NMR shielding constants for a series of transition metal complexes defined as NMR standards [Harris et al., Pure Appl. Chem., 2001, 73, 1795] were calculated using the non-relativistic coupled cluster method and four-component relativistic density functional theory. To reproduce the experimental conditions of the NMR standards, the solvent effects were incorporated by explicit and implicit solvent models.

Double core hole valence-to-core x-ray emission spectroscopy: A theoretical exploration using time-dependent density functional theory.

With the help of newly developed X-ray free-electron laser (XFEL) sources, creating double core holes (DCHs) simultaneously at the same or different atomic sites in a molecule has now become possible. DCH X-ray emission is a new form of X-ray nonlinear spectroscopy that can be studied with a XFEL. Here, we computationally explore the metal K-edge valence-to-core (VtC) X-ray emission spectroscopy (XES) of metal/metal and metal/ligand DCH states in a series of transition metal complexes with time-dependent density functional theory. The simulated DCH VtC-XES signals are compared with conventional single core hole (SCH) XES signals. The energy shifts and intensity changes of the DCH emission lines with respect to the corresponding SCH-XES features are fingerprints of the coupling between the second core hole and the occupied orbitals around the DCHs that contain important chemical bonding information of the complex. The difference between delocalized/localized core hole models on DCH VtC-XES is also briefly discussed. We theoretically demonstrate that DCH XES provides subtle information on the local electronic structure around metal centers in transition metal complexes beyond conventional linear XES. Our predicted changes from calculations between SCH-XES and DCH-XES features should be detectable with modern XFEL sources.

Helicene Bis(pyrazol‐1‐yl)pyridine Ligands for Luminescent Transition‐Metal Complexes

We describe herein the synthesis of 2,6‐bis(pyrazol‐1‐yl)pyridine (1‐bpp) ligands substituted by helicene units in the 4‐position of the pyridine ring. The two‐step procedure afforded the molecules bpp[n]helicene (n = 4, 5 and 6) and methyl‐bpp[4]helicene, abbreviated as 4, 5, 6 and 4m respectively, with overall good yields. This series of ligands shows fluorescence in the violet region, with a red shift of the emission when increasing the number of aromatic rings in the helicene unit. The tridentate fluorophores have been reacted with Re(CO)5Cl and [Ru(terpy)Cl3] to prepare a series of transition metal complexes formulated as [ReI(n)(CO)3Cl] (n = 4 and 5) and [RuII(n)(terpy)](PF6)2 (n = 4, 4m, 5 and 6). The compounds [ReI(4)(CO)3Cl]·(CH2Cl2)0.5(H2O) and [RuII(4m)(terpy)](PF6)2 crystallized in the centrosymmetric space groups P21/n and P1 respectively, and thus present both M and P helicene units in their crystal structures. The absorption and emission properties of the complexes have been studied. All complexes show luminescence at 77 K in frozen DCM solution. The tricarbonyl complex [ReI(5)(CO)3Cl] shows a strong emission band with two peaks at 540 nm and 580 nm, which could be attributed to ligand‐localized π–π* phosphorescence due to the extended π system of the ligand. The heteroleptic RuII complexes show emission bands above 600 nm attributed to the terpyridine‐based 3MLCT state.

Efficient calculations of a large number of highly excited states for multiconfigurational wavefunctions.

Electronically excited states play important roles in many chemical reactions and spectroscopic techniques. In quantum chemistry, a common technique to solve excited states is the multiroot Davidson algorithm, but it is not designed for processes like X-ray spectroscopy that involves hundreds of highly excited states. We show how the use of a restricted active space wavefunction together with a projection operator to remove low-lying electronic states offers an efficient way to reach single and double-core-hole states. Additionally, several improvements to the stability and efficiency of the configuration interaction (CI) algorithm for a large number of states are suggested. When applied to a series of transition metal complexes the new CI algorithm does not only resolve divergence issues but also leads to typical reduction in computational time by 70%, with the largest savings for small molecules and large active spaces. Together, the projection operator and the improved CI algorithm now make it possible to simulate a wide range of single- and two-photon spectroscopies. © 2019 Wiley Periodicals, Inc.

In silico and in vitro studies of transition metal complexes derived from curcumin–isoniazid Schiff base

A series of transition metal complexes have been synthesized from biologically active curcumin and isoniazid Schiff base. They are characterized by various spectral techniques like UV–Vis, Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and mass spectroscopies. Moreover, elemental analysis, magnetic susceptibility and molar conductivity measurements are also carried out. All these data evidence that the metal complexes acquire square planar except zinc(II) which adopts a tetrahedral geometry, and they are non-electrolytic in nature. Groove mode of binding between the calf thymus DNA (CT DNA) and metal complexes is confirmed by electronic absorption titration, viscosity and cyclic voltammetry studies. In addition to that, all the metal complexes are able to cleave pUC 19 DNA. Optimized geometry and ground-state electronic structure calculations of all the synthesized compounds are established out by density functional theory (DFT) using B3LYP method which theoretically reveals that copper(II) complex explores higher stability and higher biological accessibility. This is experimentally corroborated by antimicrobial studies. In silico Absorption, Distribution, Metabolism, Excretion (ADME) studies reveal the biological potential of all synthesized complexes, and also biological activity of the ligand is predicted by PASS online biological activity prediction software. Molecular docking studies are also carried out to confirm the groove mode of binding and receptor–complex interactions.

Synthesis, characterization, biological activity, and QSAR studies of transition metal complexes derived from piperonylamine Schiff bases

A series of transition metal complexes of Co(II), Ni(II), Cu(II), and Zn(II) metal ions with various uninegative bidentate Schiff base ligands derived from condensation of piperonylamine and 2-hydroxy-1-naphthaldehyde/substituted salicylaldehyde derivatives were synthesized and were well characterized by different spectroscopic techniques (FT-IR, UV–Vis, NMR, fluorescence, mass, and ESR), molar conductance measurements, elemental analysis and by various physical studies like thermal (TGA, DTG, and DTA) and magnetic susceptibility measurements. The characterization data revealed that Schiff bases’ coordinates via azomethine nitrogen and deprotonated phenolic oxygen (NO) with metal centres in 2:1 molar ratio with octahedral geometrical arrangement for Co(II), Ni(II), and Zn(II) complexes and square planar geometry for Cu(II) complexes. The synthesized compounds were evaluated for their in vitro antimicrobial activities against two Gram-positive bacteria (Staphylococcus aureus and Streptococcus gordonii); two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa); and two fungal strains (Aspergillus niger and Candida albicans). Comparative biological study indicated that metal complexes were more noxious as compared to free ligands and Zn(II) complexes were found to be most potent antimicrobial agents among all the synthesized complexes. The complexes 23–30 showed excellent activity against tested microorganisms. Quantitative structure–activity relationship study of compounds was made for antimicrobial assessment which exposed that metal complexes with high molecular weight were more potent against E coli.

Synthesis, spectroscopic, thermal properties, Calf thymus DNA binding and quantum chemical studies of M(II) complexes

A new series of transition metal complexes of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) were prepared from the ligand of 5‐(4‐benzenesulfonic acid azo)‐2‐thioxo‐4‐thiazolidinone (H2L). The M(II) complexes were structurally elucidated by elemental analysis, infrared spectra, spectral studies, thermal analysis, magnetic measurements and X‐ray diffraction analysis. Elemental analysis and IR result suggested the ligand was bonded to the metal ions in monobasic/neutral bidentate through the nitrogen atom of the hydrazone group and oxygen atom of carbonyl group. The bond length, bond angle, HOMO, LUMO and quantum chemical parameters were calculated to confirm the geometry of the ligand and the M(II) complexes. In vitro antimicrobial behavior of ligand (H2L) and its M(II) complexes (1‐5) was screened with targeted bacterial and fungal strains. Spectroscopic (UV‐vis) technique was employed in order to study the binding mode and binding strength of the ligand (H2L) and its M(II) complexes to Calf thymus DNA (CT‐DNA). Intercalation is the most possible mode of interaction of the ligand (H2L) and its M(II) complexes with CT‐DNA and the determined binding constants. Molecular docking was used to predict the binding between the starts (4‐aminobenzenesulfonic acid (start 1) and 2‐thioxo‐4‐thiazolidinone (start 2)) and tautomers (A‐C) of ligand (H2L) with the receptors of prostate cancer mutant (PDB code: 2Q7K) and breast cancer mutant (PDB code: 3HB5).

Synthesis, Spectroscopic Characterization, DNA Binding Ability and Biological Activities of Transition Metal Complexes Containing Tridentate Schiff base

A new series of transition metal complexes of Cu(II),Ni(II),Co(II),and Zn(II) have been synthesized from the Schiff base (L) derived from1,3- isopthaldehyde with 2-amino phenol and 4-Nitroaniline. Its Cu(II), Co(II), Ni(II), Zn(II) complexes have also been synthesized in ethanol medium. The structural features have arrived from their elemental analyses, molar conductance, magnetic susceptibility, IR, UV–Vis, mass, ESR and 1H NMR spectral studies. The data show that the complexes have composition of ML2 type. The electronic absorption spectral data of the complexes suggest an octahedral geometry around the central metal ion. The interaction of the complexes with calf thymus (CT) DNA has been studied using absorption spectra, and Cyclic Voltammetric measurement. The metal complexes exhibit effective cleavage of pBR 322 DNA from the super coiled form to the open circular form. These complexes also show enhanced antifungal and antibacterial activities compared with the free ligand

Mixed ligand complexes of the novel nanoferrocene based Schiff base ligand (HL): Synthesis, spectroscopic characterization, MOE studies and antimicrobial/anticancer activities

A series of transition metal complexes of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with (Z)-4-(1-((2-carboxycyclohexa-2,4-dien-1-yl)imino)-ethyl)[bis(η5-cyclopenta-1,3-dien-1-yl)]iron (HL) mixed with 1,10-phenanthroline (Phen.) have been synthesized and successfully characterized using various spectrochemical techniques: elemental analyses, molar conductance, IR, 1H NMR, mass spectroscopy, SEM, thermal analysis (TG/DTG), MOE, biological and anticancer activities. The molecular structures of the HL ligand and its Fe(III) complex were determined by SEM studies. HL ligand acts as a bidentate ligand and coordinates to metal ion center via deprotonated carboxylate oxygen atom and azomethine nitrogen. Also, 1,10-phenanthroline acts as a neutral bidentate ligand coordinates to the metal ion center via two nitrogen atoms. Additionally, mixed ligand complexes were screened against pathogenic antibacterial and antifungal strains: two Gram (+) bacteria; Streptococcus pneumoniae and Bacillis subtilis, two Gram (−); Pseudomonas aeruginosa and Escherichia coli and four fungi; Aspergillus fumigatu, Syncephalastrum racemosum, Geotricum candidum and Candida albicans. The breast cancer cell line MCF7 anticancer activity was studied and a moderate result was the main observation. Molecular docking studies of the HL ligand and its mixed Fe(III), Ni(II) and Cu(II) metal complexes with 1,10-phenanthroline showed the nature of binding energy, H-bond and hydrophobic interactions with the crystal structure of: Tyrosine kinase auto-inhibitor (PDB: 1T46), Staphylococcus aureus nucleoside (PDB: 3Q8U), Human papillomavirus (HPV) pro-apoptotic tumor suppressor (PDB: 4XR8) and breast cancer mutant oxidoreductase (PDB ID: 3HB5).

Structural, theoretical investigations and biological evaluation of Cu(II), Ni(II) and Co(II) complexes of mercapto-pyrimidine schiff bases

A new series of transition metal complexes of mercapto pyrimidine Schiff base complexes has been studied and characterized using various spectral techniques like single crystal XRD, FT-IR, electronic, EDX and TGA. The molecular properties of the ligand and the complexes have been derived from HOMO-LUMO calculations using Gaussian software. The biological evaluation of the ligands and the complexes has been studied and compared. The DNA binding studies of the complexes has been carried out and the binding constants are in the order of 104 M−1. The DNA cleavage activity of the complexes proves the mechanism of cleavage is through non-hydrolytic pathway.

Geometrical structures, thermal properties and spectroscopic studies of Schiff base complexes: Correlation between ionic radius of metal complexes and DNA binding

A novel series of transition metal complexes of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) were prepared from Schiff base derived from 4-aminoantipyrine and quinoline-2-carbaldehyde to give 4-((quinolin-2-yl)methyleneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (QMP). The structural features were derived from elemental analysis, mass spectroscopy, X-ray, IR, 1H NMR, electronic spectra, molar conductance magnetic susceptibility and thermogravimetric studies. On the basis of the studies the coordination sites were proven to be through oxygen of the ring CO and nitrogen of the azomethine (HCN) group. The thermodynamic parameters were calculated using Coats–Redfern and Horowitz–Metzger methods. From the values of the thermal activation energy of decomposition (Ea) of Schiff base (QMP) and its metal complexes (1–5), it was found that the Ea value for the complex (3) is higher compared to the other complexes. The Gibbs free energy of decomposition (ΔG⁎) for Schiff base (QMP) and its metal complexes is positive value which indicates that the processes are non-spontaneous. The interaction between Schiff base (QMP) and its metal complexes and calf thymus DNA shows hypochromism effect coupled with obvious bathochromic shift. From the values of binding constant (Kb) we noted that the highest value of Kb is belong complex (3) and these indicated that the Ni(II) is highly binding with CT-DNA and these due to the lower ionic radius. Furthermore, quantum chemical parameters of Schiff base and its complexes were calculated and discussed. The antimicrobial activity of Schiff base (QMP) and its M(II) complexes were studied and compared with the standard antibacterial and antifungal drugs.

Trigonal Prismatic Tris-pyridineoximate Transition Metal Complexes: A Cobalt(II) Compound with High Magnetic Anisotropy.

High magnetic anisotropy is a key property of paramagnetic shift tags, which are mostly studied by NMR spectroscopy, and of single molecule magnets, for which magnetometry is usually used. We successfully employed both these methods in analyzing magnetic properties of a series of transition metal complexes, the so-called clathrochelates. A cobalt complex was found to be both a promising paramagnetic shift tag and a single molecule magnet because of it having large axial magnetic susceptibility tensor anisotropy at room temperature (22.5 × 10-32 m3 mol-1) and a high effective barrier to magnetization reversal (up to 70.5 cm-1). The origin of this large magnetic anisotropy is a negative value of zero-field splitting energy that reaches -86 cm-1 according to magnetometry and NMR measurements.

Synthesis, crystal structures, biological screening and electrochemical analysis of some salen-based transition metal complexes

A new series of transition metal complexes with (1) Mn(III), (2) Co(II), (3) Ni(II) and (4) Cu(II) have been synthesized by the reaction of [6,6′-((1E,1′E)-(propane-1,3-diylbis(azanylylidene))bis(methanylylidene))bis(5-isopropyl-2-methylphenol)] with suitable metal salts. The synthesized complexes have been characterized by elemental analysis and spectroscopic techniques. The results of single crystal structures show that the metal is bonded to the ligand through the phenolic oxygens and imino nitrogens. Synthesized complexes have been evaluated for antibacterial activity and antioxidant activity, which shows considerable results.

New complexes with 19-membered pyridine-based macrocycle ligand

A novel series of transition metal complexes with 19-membered pyridine-based macrocycle ligand [L], i.e., 1,5,12,16-tetraaza-3,4:7,10:13,14-tribenzo1,16(2,6-pyrido)cyclononadecan-5,11 diene 2,15 dione, has been isolated and characterized. The mode of bonding and overall geometry of the complexes has been inferred through elemental analysis, spectral, thermal as well as magnetic and molar conductivity measurements. On basis of IR, MS, UV–Vis and EPR spectral studies, an octahedral geometry has been proposed for all complexes except Co(II) chloride and acetate and Cu(II) nitrate complexes that adopt tetrahedral or square planar geometry, respectively. The complexes were also screened for its in vitro anticancer activity against the breast cell line (MFC7) and human hepatocarcinoma cell line (HepG2); the results obtained show that they exhibit potent antitumor activity.

Amidinatogermylene Metal Complexes as Homogeneous Catalysts in Alcoholic Media

A series of transition-metal complexes containing the bulky amidinatogermylene Ge(tBu2bzam)tBu (1; tBu2bzam = N,N′-bis(tert-butyl)benzamidinate) as a ligand have been prepared and characterized. While the hydrolytic degradation of the germylene ligand of the square-planar complexes [MCl(η4-cod){Ge(tBu2bzam)tBu}] (M = Rh (2), Ir (3); cod = 1,5-cyclooctadiene) and [PdCl(η3-metallyl){Ge(tBu2bzam)tBu}] (4; metallyl = 2-methylallyl) is slow but clearly evident in carefully dried aprotic solvents, the octahedral complexes [RuCl2(η6-cym){Ge(tBu2bzam)tBu}] (5; cym = p-cymene) and [IrCl2(η5-Cp*){Ge(tBu2bzam)tBu}] (6; Cp* = pentamethylcyclopentadienyl) have proven to be stable even in alcoholic solvents. These latter complexes have been tested as catalyst precursors of reactions involving alcohols as substrates and/or solvents, and remarkably, they have been found to be active in the transfer hydrogenation of cyclohexanone with isopropyl alcohol (5 and 6), the N-alkylation of aniline with benzyl alcohol (5 and 6), ...