Metal-ligand Complexes Research Articles

One-pot three-step mechanically assisted synthesis and catalytic performance of tripodal metallic complexes

All-green matters. Synthesis of the ligand and metal–ligand complexes and a model catalytic oxidation reaction can be sequentially processed under solventless conditions using a planetary ball mill, via fast, high yielding and selective processes.

Eco-friendly and Efficient Composition, Diagnosis Theoretical, kinetic studies, Antibacterial and Anticancer Activities of Mixed Some Metal Complexes of Tridentate Schiff base Ligand

Eco-friendly and Efficient Composition, Diagnosis Theoretical, kinetic studies, Antibacterial and Anticancer Activities of Mixed Some Metal Complexes of Tridentate Schiff base Ligand

Coordination of trivalent lanthanum and cerium, and tetravalent cerium and actinides (An = Th(IV), U(IV), Np(IV)) by a 4-phosphoryl 1H-pyrazol-5-olate ligand in solution and the solid state.

Structural investigations of three actinide(iv) 4-phosphoryl 1H-pyrazol-5-olate complexes (An = Th(iv), U(iv), Np(iv)) and their cerium(iv) analogue display the same metal coordination in the solid state. The mononuclear complexes show the metal centre in a square antiprismatic coordination geometry composed by the two O-donor atoms of four deprotonated ligands. Detailed solid state analysis of the U(iv) complex shows that dependent on the solvent used altered arrangements are observable, resulting in a change in the coordination polyhedron of the U(iv) metal centre to bi-capped trigonal prismatic. Further, single crystal analyses of the La(iii) and Ce(iii) complexes show that the ligand can also act as a neutral ligand by protonation of the pyrazolyl moiety. All complexes were comprehensively characterized by NMR, IR and Raman spectroscopy. A single resonance in each of the 31P NMR spectra for the La(iii), Ce(iii), Ce(iv), Th(iv) and Np(iv) complex indicates the formation of highly symmetric complex species in solution. Extended X-ray absorption fine structure (EXAFS) investigations provide evidence for the same local structure of the U(iv) and Np(iv) complex in toluene solution, confirming the observations made in the solid state.

Solvent-dependent fac/mer-isomerization and self-assembly of triply helical complexes bearing a pivot part.

Tris–chelate metal complexes of unsymmetrical bidentate ligands can form two geometric stereoisomers, facial (fac) and meridional (mer) isomers. Due to the small difference in their properties, the highly-selective synthesis of one of the isomers is challenging. We now designed a series of tripodal ligands with a tris(3-(2-(methyleneoxy)ethoxy)phenyl)methane pivot. Surprisingly, the ratio of the fac/mer isomers of the triply helical FeII complexes significantly changed depending on the solvents. To the best of our knowledge, this is the first example of fac/mer isomerism of a labile tris(2,2′-bipyridine) FeII complex governed by the solvent. Furthermore, well-defined self-assemblies were quantitatively produced by imine bond formation with a suitable diamine. The supramolecular assemblies contained only the fac isomer even though a mixture of the two isomers existed in solution before the condensation reaction. Namely, the self-assembly formation effectively adjusted the geometries of the building unit that results in the suitable supramolecular structure.

Recent advances in organophosphorus-chalcogen and organophosphorus-pincer based macrocyclic compounds and their metal complexes.

The design and development of phosphorus based macrocycles containing one or more other heteroatoms is of crucial importance for the enhancement of modern synthetic chemistry. In recent years focus on phosphorus based macromolecules has led to intriguing and innovative structures with a variety of applications, including photophysical and host-guest properties, and in organic synthesis. This article summarizes the recent advancements in the synthesis of macrocycles that consist of organophosphorus-chalcogen (P-E, P[double bond, length as m-dash]E; E = O, S, Se) and organophosphorus-pincer based macrocyclic ligands and their transition metal complexes with emphasis given to synthetic methodologies. The reactions involve the modification of simple macrocycles with phosphorus sources or phosphorus-based chalcogenating reagents. Transition metal complexes of phosphine-based macrocyclic pincer ligands and their reactivity are also included.

Synthesis, cytotoxic, anticancer and antimicrobial activities of some metal complexes of a novel tetradentate Schiff base ligand, (E)-3-((2-((E)-(1-(2-hydroxyphenyl)ethylidene)amino)ethyl)imino)-N-phenylbutanamide

A novel tetradentate Schiff base ligand, (E)-3-((2-((E)-(1-(2-hydroxyphenyl)ethylidene)amino)ethyl)imino)-N-phenylbutanamide (HEAc) and its VO(IV), Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes have been synthesized. Ligand, HEAc was characterized analytically and spectroscopically. Physico-chemical methods like elemental analysis, molar conductance, magnetic susceptibility measurement and IR- and UV–vis spectral measurements were employed for the characterization of the complexes. The cytotoxic activities of ligand and its Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes have been evaluated. In-vitro cytotoxicity studies on ligand and its metal complexes showed potential cytotoxicity against Dalton’s Lymphoma Ascites (DLA) cell lines. Antitumour activities of this Cu(II) complex was studied using Daltons Lymphoma Ascites cell-induced solid tumour model and Ehrlich's Ascites Carcinoma cell-induced ascites tumour model. Treatment with the Cu(II) complex at three different concentrations (15, 10 and 5 mg/kg body weight) subdued the solid tumour growth in experimental mice and increased the mean survival rate and the life span of Ascites tumour bearing mice in a concentration dependent manner. The copper complex showed highest antitumor activity and cytotoxicity with an IC50 value of 47 μg/ml. It was observed that all the metal complexes were more potent bactericides and fungicides than the free ligand, HEAc and copper complex showed high antimicrobial activity than the others.

Main-group metal complexes of α-diimine ligands: structure, bonding and reactivity.

α-Diimine ligands, in particular 1,4-diazabutadiene (dad) and bis(iminoacenaphthene) (bian) derivatives, have been widely used for coordination with various metals, including main-group, transition, and lanthanide and actinide metals. In addition to their tunable steric and electronic properties, the dad and bian ligands are redox-active and can readily accept one or two electrons, converting into the radical-anionic (L˙-) or dianionic (enediamido, L2-) form, respectively. This non-innocence brings about rich electronic structures and properties of the ligands and complexes thereof. For example, the dad ligands in their three redox levels can effectively stabilize a series of metal centers in different oxidation states, including low-valent metals. Moreover, these ligands can serve as electron reservoirs and can participate in reactions toward other molecules with or without metals. Therefore, such ligands are extremely useful in the areas of low-valent complexes and small molecule activation. Herein, we will discuss the use of dad (and bian) ligands in the stabilization of metal-metal-bonded compounds, in particular those of main-group metals, as well as small molecule activation by these (low-valent) metal coordination species where the non-innocence of the ligands plays a key role.

Predicting ligand removal energetics in thiolate-protected nanoclusters from molecular complexes.

Thiolate-protected metal nanoclusters (TPNCs) have attracted great interest in the last few decades due to their high stability, atomically precise structure, and compelling physicochemical properties. Among their various applications, TPNCs exhibit excellent catalytic activity for numerous reactions; however, recent work revealed that these systems must undergo partial ligand removal in order to generate active sites. Despite the importance of ligand removal in both catalysis and stability of TPNCs, the role of ligands and metal type in the process is not well understood. Herein, we utilize Density Functional Theory to understand the energetic interplay between metal-sulfur and sulfur-ligand bond dissociation in metal-thiolate systems. We first probe 66 metal-thiolate molecular complexes across combinations of M = Ag, Au, and Cu with twenty-two different ligands (R). Our results reveal that the energetics to break the metal-sulfur and sulfur-ligand bonds are strongly correlated and can be connected across all complexes through metal atomic ionization potentials. We then extend our work to the experimentally relevant [M25(SR)18]- TPNC, revealing the same correlations at the nanocluster level. Importantly, we unify our work by introducing a simple methodology to predict TPNC ligand removal energetics solely from calculations performed on metal-ligand molecular complexes. Finally, a computational mechanistic study was performed to investigate the hydrogenation pathways for SCH3-based complexes. The energy barriers for these systems revealed, in addition to thermodynamics, that kinetics favor the break of S-R over the M-S bond in the case of the Au complex. Our computational results rationalize several experimental observations pertinent to ligand effects on TPNCs. Overall, our introduced model provides an accelerated path to predict TPNC ligand removal energies, thus aiding towards targeted design of TPNC catalysts.

Synthesis, structural characterization, and coordination chemistry of imidazole-based alkylidene ketenes.

Alkylidene ketenes typically display high intrinsic reactivity, impeding isolation on a preparative scale. Herein, we report the synthesis of alkylidene ketenes by reaction of imidazole-based diazoolefins with carbon monoxide. The good thermal stability of these heterocumulenes allows for characterization by single crystal X-ray diffraction. N-Heterocyclic alkylidene ketenes can be used as C-donor ligands for transition and main group metals, as evidenced by the isolation of complexes with AuCl, RhCl(CO)2, PdCl(C3H5) and GaCl3.

Controllable DNA strand displacement by independent metal-ligand complexation.

Introduction of artificial metal–ligand base pairs can enrich the structural diversity and functional controllability of nucleic acids. In this work, we revealed a novel approach by placing a ligand-type nucleoside as an independent toehold to control DNA strand-displacement reactions based on metal–ligand complexation. This metal-mediated artificial base pair could initiate strand invasion similar to the natural toehold DNA, but exhibited flexible controllability to manipulate the dynamics of strand displacement that was only governed by its intrinsic coordination properties. External factors that influence the intrinsic properties of metal–ligand complexation, including metal species, metal concentrations and pH conditions, could be utilized to regulate the strand dynamics. Reversible control of DNA strand-displacement reactions was also achieved through combination of the metal-mediated artificial base pair with the conventional toehold-mediated strand exchange by cyclical treatments of the metal ion and the chelating reagent. Unlike previous studies of embedded metal-mediated base pairs within natural base pairs, this metal–ligand complexation is not integrated into the nucleic acid structure, but functions as an independent toehold to regulate strand displacement, which would open a new door for the development of versatile dynamic DNA nanotechnologies.

Solvent manipulation of the pre-reduction metal-ligand complex and particle-ligand binding for controlled synthesis of Pd nanoparticles.

Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. In this study, we show that the nucleation and growth rates are correlated with the thermodynamics of metal-ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability. The results show that the nucleation rate decreased, while the growth rate increased in the following order, toluene, piperidine, 3,4-lutidine and pyridine, leading to a large increase in the final nanoparticle size (from 1.4 nm in toluene to 5.0 nm in pyridine). Using density functional theory (DFT), complemented by 31P nuclear magnetic resonance and X-ray absorption spectroscopy, we calculated the reduction Gibbs free energies of the solvent-dependent dominant pre-reduction complex and the solvent-nanoparticle binding energy. The results indicate that lower nucleation rates originate from solvent coordination which stabilizes the pre-reduction complex and increases its reduction free energy. At the same time, DFT calculations suggest that the solvent coordination affects the effective capping of the surface where stronger binding solvents slow the nanoparticle growth by lowering the number of active sites (not already bound by trioctylphosphine). The findings represent a promising advancement towards understanding the microscopic connection between the metal-ligand thermodynamic interactions and the kinetics of nucleation and growth to control the size of colloidal metal nanoparticles.

The Effects of Oxidation States and Spin States of Chromium Interaction with <i>Sargassum Sp</i>.: A Spectroscopic and Density Functional Theoretical Study

The study of various oxidation states of chromium with Sargassum sp. is of particular interest since hexavalent chromium is reduced to trivalent chromium in an aqueous solution. In this study, a systematic density functional theory (DFT) calculations were performed to study the interactions of transition metal chromium ion with different oxidation states and spin states with the Sargassum sp. decorated with carboxylate (acetate) at the wB97XD/6-311++ G(d,p) level of theory. The structures and binding energies of chromium metal-carboxylate complexes at various oxidation states and spin states in gas phase were examined. The coordination strength of Cr(VI) with the acetate ligand was predominantly the strongest compared to the other oxidation states. Vibrational frequency analysis, for the homoleptic monomers of tris [CrIII(AC)3]0 and [CrVI(AC)3]3+ complexes, illustrate good harmony with the experimental and theoretical calculated frequencies. Using the time-dependent DFT (TD-DFT) at the level of CAM-B3LYP/6-311++G(d,p), the vertical excitation energies were obtained. The stabilization energies derived using the second order perturbation theory, Eij(2), of NBO analysis confirmed the greater charge transfer for the observed trends in the metal binding. The calculated binding energies (ΔE) and interactions energies SEij(2) favor the formation of [CrVI(AC)3]3+ complexes. The findings of this study identify efficient electronic factors as major contributors to the metal binding affinities, with promising possibilities for the design of metal-ligand complexes and sensing of the metal ions.

Synthesis, crystal structures and antimicrobial activity of palladium metal complexes of sulfonyl hydrazone ligands

Palladium complexes of sulfonyl hydrazone based ligands have been prepared by refluxing with the corresponding ligands and Pd(II) salt in 2:1 ratio. The compounds have been characterized by FT-IR and UV-Vis spectroscopic methods. The crystal structure of the prepared palladium complexes has been determined by single-crystal X-ray crystallographic technique. Crystal data for C40H50N4O6PdS2 (PMHT-Pd(II) complex): triclinic, space group P-1 (no. 2), a = 7.1561(6) Å, b = 12.1300(11) Å, c = 12.6117(17) Å, α = 63.498(11)°, β = 86.694(9)°, γ = 81.451(7)° and Z = 1. The final R1 was 0.0699 (I > 2σ(I)) and wR2 was 0.1834 (all data). Crystal data for C36H42N4O6PdS2 (PTHC-Pd(II) complex): monoclinic, space group P21/n (no. 14), a = 8.6726(2) Å, b = 20.8824(4) Å, c = 10.3351(2) Å, β = 104.429(2)° and Z = 2. The final R1 was 0.0344 (I > 2σ(I)) and wR2 was 0.0840 (all data). Crystal data for C36H42N4O6PdS2 (PTHT-Pd(II) complex): monoclinic, space group P21/n (no. 14), a = 9.7658(2) Å, b = 10.0488(3) Å, c = 18.7714(4) Å, β = 99.602(2)° and Z = 2. The final R1 was 0.0334 (I > 2σ(I)) and wR2 was 0.0832 (all data). Crystal data for C40H50N4O6PdS2 (PMHC-Pd(II) complex): triclinic, space group P-1 (no. 2), a = 10.2070(9) Å, b = 12.1841(13) Å, c = 16.8879(19) Å, α = 109.005(6)°, β = 90.061(5)°, γ = 99.032(5)° and Z = 2. The final R1 was 0.0822 (I > 2σ(I)) and wR2 was 0.2293 (all data). The single-crystal structure data showed a good agreement with the experimental results. The synthesized complexes were screened for their in vitro antibacterial activity against one Gram-negative (Escherichia coli) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in vitro antifungal activity against Aspergillus niger, Aspergillus flavus and Aspergillus fumigatus. The PTHC-Pd(II) complex possesses the nearby significant antifungal activity analogous to the standard drug fluconazole against selected fungal strains Aspergillus niger, Aspergillus Flavus and Aspergillus fumigatus as well as the same complex showed the antibacterial activity for Staphylococcus aureus as comparable to standard ofloxacin drug.

Synthesis and characterization of substituted acetophenone-4, 4-dimethyl-3-thiosemicarbazone derivatives with an evaluation of antimicrobial and antioxidant activities

Thiosemicarbazones are organic compounds; these are widely used in the medical field. It is primarily in the manufacture of pharmaceutical drugs and bio molecules. These compounds have the azomethine functional group (-N=CH-) used to derive organic open chain and heterocyclic compounds. Thiosemicarbazones are similar to semicarbazones, and carbonyl group oxygen is replaced by sulphur. Thiosemicarbazone contains nitrogen and sulfur atoms, so they are used as ligands in coordination chemistry and form metal complexes. Thiosemicarbazone and its metal complexes are used in a variety of ways. It is especially widely used in the preparation of polymers and biochemicals products. Thiosemicarbazone and its metal complexes are closely correlated with biological properties and act as antioxidants, antifungals, antimicrobials and anticancer. Subsequently, in the current study, substituted thiosemicarbazones were synthesized and examined for their antimicrobial and antioxidant activity. Newly substituted thiosemicarbazones were obtained from the respective acetophenones and thiosemicarbazides. The structure of the newly prepared compounds was confirmed by spectroscopic studies such as IR, 1H, 13C NMR, Mass and elemental analysis. The antimicrobial activity of all the new compounds showed significant activity against the selected bacteria and fungi in the studies. The compound TZ04 exhibited good antioxidant activity compared with standard ascorbic acid and butylated hydroxytoluene.

Synthesis, characterization, ADMET, in vitro and in vivo studies of mixed ligand metal complexes from a curcumin Schiff base and lawsone

Complexes are currently synthesized from plant origin because of their therapeutic effect against certain diseases with toxicity. Hence, in this work, four new transition metal(II) mixed ligand complexes have been synthesized using a curcumin Schiff base (primary ligand) and lawsone (as co-ligand). The geometry of these complexes was explored by elemental analyses, molar conductance, thermal analysis, magnetic moment values, IR, NMR, Mass, electronic and EPR spectral studies. Electronic absorption titrations, viscosity measurements and molecular docking studies reveal that all the metal complexes interact with the CT DNA by groove binding. Among all the complexes, the copper(II) complex (complex 1) exhibits a higher Kb value (3.5 × 10−4 M) which reveals that it has a strong binding efficiency toward the CT DNA. The complexes also possess strong DNA cleavage efficiency. Cytotoxicity investigations on Artemia salina show that all the complexes possess higher cytotoxic effect than the ligand. Moreover, all the metal complexes have better antimicrobial efficacy than the ligand. Swiss ADME, PASS and pkCSM online softwares are helpful to predict the pharmacokinetic and biological actions of the curcumin Schiff base. Theoretical results obtained from the in silico study are experimentally corroborated by in vivo anti-inflammatory screening study. All the above studies demonstrate that the copper complex possesses biological activity similar to that of the drug like molecules. Research Highlights Synthesis and characterization of four novel transition mixed ligand complexes using plant moieties Promising in vivo anti-inflammatory agents and in vitro DNA metallonucleases Cytotoxicity investigation on Artemia salina Higher cytotoxic effect for the complexes than the ligand Identification of copper(II) complex as lead like molecule among all

The anti-malignant activity of Macrotyloma uniflorum mediated green synthesized Cu and Zn metal-ligand nano complexes

The green biological route has been employed to convert macro-sized zinc and copper metal complexes into nano-sized metal complexes. These bioactive metal complexes were synthesized by template condensation process in the chemistry laboratory. The newly synthesized biologically active complexes were converted into nano range from phytochemical aqueous extract of Macrotyloma uniflorum (horse gram). Biologically converted nano complexes have been characterized by physicochemical as well as spectroscopic techniques such as UV-visible spectrophotometer and FTIR. The reduced Cu and Zn metal nanoparticles were analyzed with SEM for shape and size, which showed most of the nanoparticles, were nearly spherical with nano range size. To estimate the potentiality of newly manufactured copper and zinc nanoparticles in vitro and in in vivo studies, i.e. antifungal and antibacterial and anti-cancer activities were performed. The biogenic nanoparticles of Cu and Zn were evaluated for their activity on cancer A-549 cell lines by standard MTT assay for metabolically active mitochondria and cell viability. Further flow cytometric studies showed Cu, and Zn nano complexes had inhibition efficacy of cancer cells compared to normal cells. This study elevates that biosynthesized Cu & Zn nano complexes can be an alternative for the treatment of cancer.

Masking Ability of Various Metal Complexing Ligands at 1.0 mM Concentrations on the Potentiometric Determination of Fluoride in Aqueous Samples.

Fluoride is a common anion present in natural waters. Among many analytical methods used for the quantification of fluoride in natural waters, potentiometric analysis is one of the most widely used methods because of minimum interferences from other ions commonly present in natural waters. The potentiometric analysis requires the use of ionic strength adjusting buffer abbreviated as TISAB to obtain accurate and reproducible data. In most of the reported literature, higher concentrations of strong metal chelating ligands are used as masking agents generally in the concentration range of 1.0 to 0.01 M. In the present study, effectiveness of the masking agents, phosphate, citrate, CDTA ((1,2-cyclohexylenedinitrilo)tetraacetic acid), EDTA (ethylenediaminetetraacetic acid) HE-EDTA ((hydroxyethyl)ethylenediaminetriacetic acid)), triethanolamine, and tartaric acid at 1.0 mM in TISAB solutions was investigated. The experimental data were compared with a commercially available WTW 140100 TISAB solution as the reference buffer. According to the experimental data, the reference buffer always produced the highest fluoride concentrations and the measured fluoride concentrations were in the range of 0.611 to 1.956 mg/L. Out of all the masking agents investigated, only CDTA performed marginally well and approximately a quarter of the samples produced statistically comparable data to the reference buffer. All the other masking agents produced significantly low concentrations compared to the reference buffer. The most probable reasons for the underestimation of fluoride concentrations could be shorter decomplexing time and lower masking agent concentrations.

Theoretical and experimental studies of novel histidine derived Schiff base metal complexes, active towards biomedical and MCF 7 cell lines

Novel tri-dentate ligand-metal complexes [Mn(II), Co(II), Cu(II), Ni(II) and Zn(II) ( 1-5 )] have been synthesized using L-histidine amino acid derived Schiff base ligand and characterized using analytical and spectral methods like UV-visible, FT-IR and ESI-MS techniques. The antioxidant studies of the Schiff base ligand and 1-5 complexes reveal that complexes exhibit significant free radical scavenging activity against the free radical DPPH. In vitro cytotoxic activity of the 1-5 complexes evaluated against the breast cancer cell lines (MCF-7), reveal that complex 3 exhibits higher cytotoxicity than any other synthesized metal complexes. The docking studies have been carried out using BSA protein and DNA biomolecules with synthesized metal complexes. Antimicrobial studies has demonstrated that Cu(II) complexes possess higher activity against both Gram positive and Gram negative bacteria as well as Fungi.

Coordination Polymers Integrating Metalloimmunology with Immune Modulation to Elicit Robust Cancer Chemoimmunotherapy

Nanoscale coordination polymers (NCPs) constructed by metal ions and organic ligands via metalligand bonds have attracted great attention for their biomedical application. Herein, a new type of NCP...

Synthesis, characterization and antimicrobial activity of transition metal complexes of 4-[(2-hydroxy-4-methoxyphenyl)methyleneamino]-2,4-dihydro-3H-1,2,4-triazole-3-thione

A novel nitrogen containing 3 H -1, 2, 4-triazole-3-thione-2, 4-dihydro-4-[(2-hydroxy-4-methoxyphenyl) methylene]-amino ligand (H 2 L) was synthesized using an equimolar ratio of 4-amino-1, 2, 4-triazole-3-thione and 2-hydroxy-4-methoxybenzaldehyde. A series of Mn (II), Fe (II), Co (II), Ni (II), Cu (II), Zn (II), Cd (II) transition metal complexes were synthesized using the ligand. The synthesized ligand and transition metal complexes were characterized by using IR, 1 H NMR, 13 C NMR, Mass spectrometry, UV, XRD and TGA investigation methods. Spectral data suggests that the ligand acts as a tridentate SNO donor. Further, the synthesized H 2 L ligand and their metal complexes were screened for antimicrobial activity. The results of biological activities showed that the metal complexes have higher antifungal as well as antibacterial activity as compared to the parent H 2 L ligand against the tested microbes.