Properties Of Metal Complexes Research Articles

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.

Development of approximate spin projection method and its application for elucidation of electronic structures, molecular structures and physical properties of polynuclear metal complexes

Development of approximate spin projection method and its application for elucidation of electronic structures, molecular structures and physical properties of polynuclear metal complexes

Ultrafiltration for the Determination of Cu Complexed with Dissolved Organic Matters of Different Molecular Weight from a Eutrophic River, China.

The molecular weight of dissolved organic matter (DOM) is one of the essential factors controlling the properties of metal complexes. A continuous ultrafiltration experiment was designed to study the properties of Cu complexes with different molecular weights in a river before and after eutrophication. The results showed that the concentration of DOM increased from 26.47 to 38.20mg/L during the eutrophication process, however, DOM was still dominated by the small molecular weight fraction before and after eutrophication. The amount of Cu-DOM complexes increased with the increasing of molecular weight, however, the amounts of DOM-Cu complexes before eutrophication were higher than those after eutrophication. This is because DOM contained more -COOH and -OH before eutrophication and these functional groups are the active sites complexed with Cu.

Mercury in fish from Norwegian lakes: The complex influence of aqueous organic carbon

Mercury (Hg) concentrations in water and biota are often positively correlated to organic matter (OM), typically measured as total or dissolved organic carbon (TOC/DOC). However, recent evidence suggests that higher OM concentrations inhibit bioaccumulation of Hg. Here, we test how TOC impacts the Hg accumulation in fish in a synoptic study of Methyl-Hg (MeHg) in water and total Hg (THg) in perch (Perca fluviatilis) in 34 boreal lakes in southern Norway. We found that aqueous MeHg (r2 = 0.49, p < 0.0001) and THg (r2 = 0.69, p < 0.0001), and fish THg (r2 = 0.26, p < 0.01) were all positively related with TOC. However, we found declining MeHg bioaccumulation factors (BAFMeHg) for fish with increasing TOC concentrations. The significant correlation between fish THg concentrations and aqueous TOC suggests that elevated fish Hg levels in boreal regions are associated with humic lakes. The declining BAFMeHg with increasing TOC suggest that increased OM promotes increased aqueous Hg concentrations, but lowers relative MeHg bioaccumulation. A mechanistic understanding of the response from OM on BAFMeHg might be found in the metal-complexation properties of OM, where OM complexation of metals reduces their bioavailability. Hence, suggesting that MeHg bioaccumulation becomes less effective at higher TOC, which is particularly relevant when assessing potential responses of fish Hg to predicted future changes in OM inputs to boreal ecosystems. Increased browning of waters may affect fish Hg in opposite directions: an increase of food web exposure to aqueous Hg, and reduced bioavailability of Hg species. However, the negative relationship between BAFMeHg and TOC is challenging to interpret, and carries a great deal of uncertainty, since this relationship may be driven by the underlying correlation between TOC and MeHg (i.e. spurious correlations). Our results suggest that the trade-off between Hg exposure and accumulation will have important implications for the effects of lake browning on Hg transport, bioavailability, and trophodynamics.

Spectrophotometric properties of azo dye metal complex and its possible use as radiation dosimeter

The current work describes the physico-chemical studies of two dosimetry systems. Aqueous solution of 1, 5 diphenyl carbazone (DPC) incorporating with chromium (III) to form a colored azo dye metal complex in two methods liquid and gel. Under the effect of γ-irradiation, the colored complex undergoes visual color change from red to colorless. The prepared complex can be used as a dosimeter and applicable in dose range 0.2–6; 0.02–1 kGy for both dosimetry systems. Electrical conductivity was measured and reflecting its application as sensor. The dosimetric characteristics of this complex solution were investigated spectrophotometrically at גmax at 540 nm. Complex sensitivity for γ-radiation, pre and post-irradiation storage under different conditions were illustrated. Moreover, the applications of these results of metal uptake resembles to dosimeter.

Effect of the type of metal on the electrical conductivity and thermal properties of metal complexes: The relation between ionic radius of metal complexes and electrical conductivity

Co(II) complexes (1–4) and Ni(II) complexes (5–8) were prepared and characterized by elemental analysis, IR spectra and thermal analysis data. Thermal decomposition of all complexes was discussed using thermogravimetric analysis. The dielectric properties and alternating current conductivity were investigated in the frequency range 0.1–100 kHz and temperature range 300–660 K. The thermal activation energies of electrical conductivity (ΔE1 and ΔE2) values for complexes were calculated and discussed. The values of ΔE1 and ΔE2 for complexes (1–8) were found to decrease with increasing the frequency. Ac electrical conductivity (σac) values increases with increasing temperatures and the values of σac for Co(II) complexes are greater than Ni(II) complexes. Co(II) complexes showed a higher conductivity than other Ni(II) complexes due to the higher crystallinity as confirmed by X-ray diffraction analysis.

Exciton Localization on Ru-Based Photosensitizers Induced by Binding to Lipid Membranes

The characterization of electronic properties of metal complexes embedded in membrane environments is of paramount importance to develop efficient photosensitizers in optogenetic applications. Molecular dynamics and QM/MM simulations together with quantitative wave function analysis reveal a directional electronic redistribution of the exciton formed upon excitation of [Ru(bpy)2(bpy-C17)]2+ when going from water to a lipid bilayer, despite the fact that the media influence neither the metal-to-ligand charge-transfer character nor the excitation energy of the absorption spectra. When the photosensitizer is embedded into the DOPC lipid membrane, exciton population is mainly located in the bypyridyl sites proximal to the positively charged surface of the bilayer due to electrostatic interactions. This behavior shows that the electronic structure of metal complexes can be controlled through the binding to external species, underscoring the crucial role of the environment in directing the electronic flow upon excitation and thus helping rational tuning of optogenetic agents.

Computational insight into magnetic behavior and properties of the transition metal complexes with redox-active ligands: a DFT approach

Abstract Various aspects related to the use of DFT method for the study of magnetic, geometry and energetic properties of transition metal complexes with redox-active ligands are considered. Particular attention is given to the correct choice of model compounds and methodology of the calculations.

The nature of frontier orbitals under systematic ligand exchange in (pseudo-)octahedral Fe(ii) complexes.

Understanding and controlling properties of transition metal complexes is a crucial step towards tailoring materials for sustainable energy applications. In a systematic approach, we use resonant inelastic X-ray scattering to study the influence of ligand substitution on the valence electronic structure around an aqueous iron(ii) center. Exchanging cyanide with 2-2'-bipyridine ligands reshapes frontier orbitals in a way that reduces metal 3d charge delocalization onto the ligands. This net decrease of metal-ligand covalency results in lower metal-centered excited state energies in agreement with previously reported excited state dynamics. Furthermore, traces of solvent-effects were found indicating a varying interaction strength of the solvent with ligands of different character. Our results demonstrate how ligand exchange can be exploited to shape frontier orbitals of transition metal complexes in solution-phase chemistry; insights upon which future efforts can built when tailoring the functionality of photoactive systems for light-harvesting applications.

Synthesis, X-ray structure, in silico calculation, and carbonic anhydrase inhibitory properties of benzylimidazole metal complexes

Three coordination compounds of formula {M(bmim)2Cl2} were synthetised (M = Co, Zn, and Hg) and fully characterised. Each complex incorporates 1-benzyl-2-methylimidazole (bmim) as ligand. The coordination polyhedron around the metal center for all complexes has a quasi-regular tetragonal geometry. Density functional theory calculations were carried out on the title compounds and as well on hypothetical complexes (Cu, Ni), in order to elucidate their electronic and molecular structure. The calculations reproduced the Co, Zn, and Hg experimental structures and could predict stable complexes in the case of Ni(II) and Cu(II) ions. The carbonic anhydrase (CA, EC 4.2.1.1) inhibitory effects of the three complexes were investigated. Only compound {Hg(bmim)2Cl2} (3) exhibited a modest inhibitory effect against hCA I, probably due to the affinity of Hg(II) for His residues at the entrance of the active site cavity.

Synthesis, fluorescent studies, antioxidative and α-amylase inhibitory activity evaluation of some lanthanide(III) complexes

A novel heterocyclic ligand, viz. 1,2-dihydro-1,5-dimethyl-4-[[1-2- -oxo-2H-1-benzopyran-3-yl)ethylidene]amino]-2-phenyl-3H-pyrazol-3-one, was prepared by condensing 3-acetylcoumarin with 4-aminoantipyrine. This ligand is versatile in forming complexes with lanthanum(III), praseodymium(III), samarium(III), gadolinium(III) and dysprosium(III) ions. The ligand and the metal complexes were characterized through various physicochemical and spectral studies. The spectral studies revealed that the ligand is coordinated to the metal ion in a bidentate fashion, through the azomethine nitrogen and the oxygen atom of the pyrazolone ring. The powder XRD patterns of ligand and the dysprosium(III) complex were studied. The photoluminescent properties of ligand and metal complexes were evaluated and the relative quantum yields were determined. It was observed that in all cases the metal ions enhanced the luminescence intensity. The ?-amylase inhibitory activity of the ligand and the metal complexes was evaluated using the method of Apostolidis. The metal complexes exhibited increased activity compared to the ligand. The antioxidant property was also examined using the DPPH assay and the metal complexes were found to be more potent antioxidants than the ligand.

New insight into the effects of N^N ligand isomerization and methyl modification on the phosphorescence properties of Cu(i) complexes with (1-(2-pyridyl)pyrazole/imidazole) ligands

The influence of ligand isomerization and methylation modification on the phosphorescence properties of metal complexes has been attracting great interest owing to the significant improvement of phosphorescence efficiency.

Effect of magnetic fields on the methyl rotation in a paramagnetic cobalt(ii) complex. Quasielastic neutron scattering studies.

Molecular dynamics is a fundamental property of metal complexes. These dynamic processes, especially for paramagnetic complexes under external magnetic fields, are in general not well understood. Quasielastic neutron scattering (QENS) in 0-4 T magnetic fields has been used to study the dynamics of Co(acac)2(D2O)2 (1-d4, acac = acetylacetonate). At 80-100 K, rotation of the methyl groups on the acac ligands is the dominant dynamical process. This rotation is slowed down by the magnetic field increase. Rotation times at 80 K are 5.6(3) × 10-10 s at 0 T and 2.04(10) × 10-9 s at 4 T. The QENS studies suggest that methyl groups in these paramagnetic Co(ii) molecules do not behave as isolated units, which is consistent with results from earlier magnetic susceptibility studies indicating the presence of intermolecular interactions. DFT calculations show that unpaired electron spin density in 1 is dispersed to the atoms of both acac and H2O ligands. Methyl torsions in 1-d4 have also been observed at 5-100 K in inelastic neutron spectroscopy (INS). The QENS and INS results here help understand the dynamics of the compound in the solid state.

Changing π-Interactions and Conformational Adjustments of N-(Isonicotinylhydrazide)-1,8-naphthalimide by Hydration and Complexation Affect Photophysical Properties

Noncovalent self-assemblies of different forms of a 1,8-naphthalimide derivative N-(isonicotinylhydrazide)-1,8-naphthalimide adopt different conformational adjustments due to the interplay of weak interactions. In such assemblies stacking interactions significantly contribute to direct the orientations of tether, which also influenced packing patterns. Effects of weak noncovalent interactions are reflected in the physicochemical properties of solvate and metal complexes of this naphthalimide derivative. Dual fluorescence emissions were observed from hydrate and silver complex of N-(isonicotinylhydrazide)-1,8-naphthalimide, which was not observed in anhydrous form of the compound. These results are compared with fluorescence emission study performed with solution of N-(isonicotinylhydrazide)-1,8-naphthalimide. Aggregation induced fluorescence emission of a solution in DMSO was caused by adding water. This emission in solution occurred at a much different emission wavelength than the emission observed from ...

A DFT computational study of the magnetic behaviour of cobalt dioxolene complexes of tetraazamacrocyclic ligands

Density functional theory computational modelling (UTPSSh/6-311++G(d,p)) of the structural and magnetic characteristics of the cobalt dioxolene complexes of 2,11-diaza[3.3](2,6)pyridinophane and tris(2-pyridylmethyl)amine) ligands has been performed. By means of quantum-chemical calculations it has been shown that the nature of exchange interactions between the metal ion and semiquinonate form of the redox-active ligand is determined by the structural peculiarities of tetraazamacrocyclic ligand. The structural parameters responsible for the possibility of the occurrence of spin-crossover and/or valence tautomeric rearrangements have been identified. The calculations testified that correct theoretical representation of magnetic properties of the salt-like transition metal complexes of redox-active ligands requires detailed accounting for their exterior counter-ions.

Four unprecedented 2D trinuclear Mn(II)-complexes with adenine nucleobase controlled by solvent or co-ligand: Hydrothermal synthesis, crystal structure and magnetic behaviour

Four unique infinite 2D Mn(II) aggregates, [Mn3(μ3-ade)2(OAc)4X]n (X = DMF for 1, DMA for 2 and C2H5O− for 3), [Mn3(μ3-ade)2(ap)2DMF]n (4) (Hade = adenine; DMF = N,N-dimethylformamide; DMA = N,N-dimethylacetamide, OAc− = acetate ion, H2ap = adipic acid) with trinuclear Mn(II) as secondary building units (SBUs), have been successfully synthesized by the assembly of Hade nucleobase and manganese acetate under solvothermal conditions. The resultant complexes can be applied to explore the influence of solvent or co-ligands on the self-assembly and properties of metal complexes based on adenine. The Hade represent tridentate μ3-N3, N7, N9 bridging coordination modes. The acetate anions exhibit μ2-η1:η1 bidentate, μ2-η1:η2 tridentate mode, and μ2-η0:η2 bidentate mode. The adipate anions in complex 4 adopt two coordination modes: one is μ4-η2:η1:η1:η1 pentadentate mode, the other one is μ3-η1:η2:η2:η1 hexadentate mode. Their magnetic behaviors exhibit interesting variations, in which the local net magnetization at low temperature increases from 1 to 3. The MnII3 SBUs in 1–3 are symmetric with an inversion center, whereas that in 4 has three crystallographically independent MnII atoms. Thus, the magnetic behaviors of 4 are different from complex 1–3.

Synthesis, characterization and catalytic properties of some transition metal complexes of new phenoxy-imine ligand

In this study a new Schiff base ligand was synthesized by the reaction of salicylaldehyde, 1,2-bis(bromomethyl)benzene and 4-nitrobenzenamine. [Cr(L)Cl2]Cl·H2O, [Fe(L)Cl2]Cl·2H2Oand [Ru(L)Cl2]Cl complexes were synthesized with this ligand and Cr(III), Fe(III) and Ru(III) chloride salts. The structures of the ligand and the obtained complexes were characterized using Elemental Analysis, FT-IR, 1H-NMR, 13C-NMR, UV-Vis, Magnetic Susceptibility and Thermogravimetric Analysis. The synthesized phenoxy-imine ligand is a ligand of the O2N2 type. The resulting metal complexes are mononuclear and have octahedral geometry. Preliminary studies have also been carried out on the catalytic effects of complexes in cycloalkane oxidation and in cycloalkene epoxidation. In the general sense, the catalyst that triggers the highest product formation in the synthesized catalysts are the Ru(III) complex. It is suggested that Ru(III) complexes can be used in such catalysis reactions since they exhibit a high catalytic effect on cyclohexane oxidation.

Modulation of the Photophysical, Photochemical, and Electrochemical Properties of Re(I) Diimine Complexes by Interligand Interactions.

The photophysical and photochemical properties of transition metal complexes have attracted considerable attention because of their recent applications as photocatalysts in artificial photosynthesis and organic synthesis, as light emitters in electroluminescent (EL) devices, and as dyes in solar cells. The general control methods cannot be always used to obtain transition metal complexes with photochemical properties that are suitable for the above-mentioned applications. In the fields of solar energy conversion, strong metal-to-ligand charge-transfer (MLCT) absorption of redox photosensitizers and/or photocatalysts in the visible region with long wavelength is essential. However, the usual methods, i.e., introduction of electron-withdrawing groups into the electron-accepting ligand and/or weak-field ligands into the central metal, have several drawbacks, including shorter excited-state lifetime, lower emission efficiency, and lower oxidation and reduction power. Herein we describe a new method to control the photophysical, photochemical, and electrochemical properties of Re(I) diimine carbonyl complexes that have been widely used in various fields such as photocatalysts for CO2 reduction and emitters in EL devices and sensors. This method involves the introduction of interligand interactions (π-π and CH-π interactions) into the Re(I) complexes; the aromatic diimine ligand coordinating to the Re center approaches the aryl groups on the phosphine ligand or ligands at the cis position, which "compulsorily" induces a weak interaction between these aromatic groups. As a result of this interligand interaction, the Re complexes with the aromatic diimine ligand and the arylphosphine ligand(s) exhibit red-shifted 1MLCT absorption but afford blue-shifted emission from the triplet metal-to-ligand charge-transfer (3MLCT) excited state. This increases the oxidation power and lifetime of the 3MLCT excited state. These unique property changes are favorable, particularly for redox photosensitizers. The interligand interaction is strongly expressed by the ring-shaped multinuclear Re(I) complexes (Re-rings). In the case of Re-rings with high steric hindrance due to a small inner cavity, the lifetime of the 3MLCT excited state is up to 8 μs and the emission quantum yield is up to 70%. These properties cannot be obtained by the corresponding mononuclear Re(I) complexes, which generally exhibit shorter lifetimes (<1 μs) and lower emission quantum yields (<10%). Some of the Re-rings could be successfully applied as efficient photosensitizers in photocatalytic systems for CO2 reduction; the highest quantum yields for CO2 reduction were achieved by using photocatalytic systems composed of Re-rings as the photosensitizers and Re(I) (82%), Ru(II) (58%), and Mn(I) (48%) complexes as catalysts. This interligand interaction potentially provides unique and useful methods for controlling the photophysical, photochemical, and electrochemical functions of various metal complexes, paving the way to create new functions for metal complexes.

Suitability of in vivo and in vitro models for assessing on the safety of natural and industrial products

The excellent thermal and chemical stability and robustness of ECE-pincer metal complexes make these species promising candidates as medical and therapeutics tools; tools such as: biomarkers, sensors, anticarcinogenic agents, surface plasmon resonance enhancers, etc. In this sense, one of the main interests is the hybridization of organometallic species anchored or incorporated in biological molecules, i.e., mainly in enzymes. Also of interest is the preparation of dendritic ECE-pincer metal complexes as potential drug carriers. Thus far, several papers describing dendrimeric skeletons (e.g., PAMAM) have been reported with promising drug delivery abilities. However, to the best of our knowledge, there are no reports describing the utilization of dendritic ECE-pincer metal complexes as drug carriers.In addition, an incipient development of bioorganometallic conjugates, combining the properties of ECE-pincer metal complexes covalently anchored to diverse biological molecules (peptides, aminoacids, carbohydrates, anticarcinogenic agents, proteins, enzymes, etc.), have been synthetized in an effort to generate potential sensors or biomarkers, exploiting the properties of the biomolecules used (water solubility, size, chiral environment, etc.).In this chapter, we describe the development of metallopincer dendrimers and the potential applications of more compact metallopincer species in medical, therapeutic, and other fields.

Highly Potent Antibacterial Organometallic Peptide Conjugates.

Resistance of pathogenic bacteria against currently marketed antibiotics is again increasing. To meet the societal need for effective cures, scientists are faced with the challenge of developing more potent but equally bacteria-specific drugs. Currently, most efforts are directed toward the modification of existing antibiotics, but ideally, compounds with a new mode of action are required. In this Account, we detail our findings in the area of novel metal-based antibiotics. Our strategy is based on the modification of simple antimicrobial peptides (AMPs) with organometallic agents, resulting in organometallic AMPs (OM-AMPs). Since bacteria have most likely never encountered these synthetically prepared unnatural organometallic agents, we anticipated that such agents could well become potentiating players in the antibiotics arena. Moreover, exploiting some of the particular properties of metal complexes should also help to elucidate the mode of action of small cationic AMPs, the molecular details of which have remained elusive despite intensive efforts. Using standard Fmoc/tBu-based solid-phase peptide synthesis approaches, we have prepared various organometallic-peptide conjugates with covalently linked group 8 and 9 metallocenes (ferrocene, ruthenocene, osmocene, and cobaltocenium). As a starting point we took the (RW)3 antibacterial hexapeptide lead structure. After modifying the peptide sequence (generations 1 and 2), changing the nature and position of the organometallic group (generation 3), and optimizing the amino acid chirality (generation 5), we identified several organometallic antibacterial peptides that are currently among the most active synthetic AMPs (synAMPs) that have ever been prepared. Through these rational and systematic optimizations, we were able to increase the antibacterial activity of a short non-organometallic synAMP 18-fold to submicromolar activity, rivaling the activity of vancomycin (often the drug of last resort) against methicillin-resistant Staphylococcus aureus (MRSA). Moreover, by making use of the unique physicochemical properties of ruthenocene, we were able to determine the mode of action of these short AMPs in unprecedented detail. We propose that the OM-AMP integrates into the bacterial membrane and changes its biophysical properties, which ultimately results in detachment of vital enzymes for respiration and cell-wall biosynthesis such as specifically cytochrome c and MurG from their locations in the membrane. Further explorations of these small OM-AMP derivatives that are summarized in this Account include lipid substitution, multivalent display of metalated di- or tripeptides on a trivalent scaffold with different linkers, and increasing the metal-to-peptide ratio such that every tryptophan in the (RW)3 scaffold is eventually replaced by a metalated lysine. While initial experiments with our OM-AMPs for systemic applications were largely disappointing, these OM-AMPs turned out to be potent antibiotics for topical applications. In this sense, two applications are described as examples in this Account, namely, bacterial decontamination of wastewater by reverse osmosis membranes (coated with our OM-AMPs by Cu-catalyzed azide-alkyne cycloaddition reaction) and synergistic activities of one of our synAMPs with colistin and tobramycin for the treatment of Pseudomonas aeruginosa infections that are associated with cystic fibrosis.