Metal Complexes In Solution Research Articles

Electronic Structure of Ytterbium(III) Solvates-a Combined Spectroscopic and Theoretical Study.

The wide range of optical and magnetic properties of lanthanide(III) ions is associated with their intricate electronic structures which, in contrast to lighter elements, is characterized by strong relativistic effects and spin-orbit coupling. Nevertheless, computational methods are now capable of describing the ladder of electronic energy levels of the simpler trivalent lanthanide ions, as well as the lowest energy term of most of the series. The electronic energy levels result from electron configurations that are first split by spin-orbit coupling into groups of energy levels denoted by the corresponding Russell-Saunders terms. Each of these groups are then split by the ligand field into the actual electronic energy levels known as microstates or sometimes mJ levels. The ligand-field splitting directly informs on the coordination geometry and is a valuable tool for determining the structure and thus correlating the structure and properties of metal complexes in solution. The issue with lanthanide complexes is that the determination of complex structures from ligand-field splitting remains a very challenging task. In this paper, the optical spectra-absorption, luminescence excitation, and luminescence emission-of ytterbium(III) solvates were recorded in water, methanol, dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF). The electronic energy levels, that is, the microstates, were resolved experimentally. Subsequently, density functional theory calculations were used to model the structures of the solvates, and ab initio relativistic complete active space self-consistent field calculations (CASSCF) were employed to obtain the microstates of the possible structures of each solvate. By comparing the experimental and theoretical data, it was possible to determine both the coordination number and solution structure of each solvate. In water, methanol, and N,N-dimethylformamide, the solvates were found to be eight-coordinated and have a square antiprismatic coordination geometry. In DMSO, the speciation was found to be more complicated. The robust methodology developed for comparing experimental spectra and computational results allows the solution structures of homoleptic lanthanide complexes to be determined.

1,3,5-Triaza-7-Phosphaadamantane (PTA) as a 31P NMR Probe for Organometallic Transition Metal Complexes in Solution

Due to the rigid structure of 1,3,5-triaza-7-phosphaadamantane (PTA), its 31P chemical shift solely depends on non-covalent interactions in which the molecule is involved. The maximum range of change caused by the most common of these, hydrogen bonding, is only 6 ppm, because the active site is one of the PTA nitrogen atoms. In contrast, when the PTA phosphorus atom is coordinated to a metal, the range of change exceeds 100 ppm. This feature can be used to support or reject specific structural models of organometallic transition metal complexes in solution by comparing the experimental and Density Functional Theory (DFT) calculated values of this 31P chemical shift. This approach has been tested on a variety of the metals of groups 8–12 and molecular structures. General recommendations for appropriate basis sets are reported.

Transition Metal Complexes as Catalysts for the Electroconversion of CO2 : An Organometallic Perspective.

The electrocatalytic transformation of carbon dioxide has been a topic of interest in the field of CO2 utilization for a long time. Recently, the area has seen increasing dynamics as an alternative strategy to catalytic hydrogenation for CO2 reduction. While many studies focus on the direct electron transfer to the CO2 molecule at the electrode material, molecular transition metal complexes in solution offer the possibility to act as catalysts for the electron transfer. C1 compounds such as carbon monoxide, formate, and methanol are often targeted as the main products, but more elaborate transformations are also possible within the coordination sphere of the metal center. This perspective article will cover selected examples to illustrate and categorize the currently favored mechanisms for the electrochemically induced transformation of CO2 promoted by homogeneous transition metal complexes. The insights will be corroborated with the concepts and elementary steps of organometallic catalysis to derive potential strategies to broaden the molecular diversity of possible products.

Neutron Scattering Techniques for Studying Metal Complexes in Aqueous Solution.

Neutron scattering combined with ab initio calculations provides a powerful tool for studying metal complexes in different solvents and, particularly, in water. The majority of traditional characterization techniques in catalysis provide only limited information on homogeneous catalytic processes. Neutron scattering, on the other hand, thanks to its sensitivity to hydrogen atoms, and therefore water molecules, can be used to build detailed models of reaction paths and to observe, at a molecular level, the influence of solvent molecules on a catalytic process. In this Mini-Review we describe several examples on how neutron scattering combined with ab initio calculations can be used to examine the nature of the interaction of water molecules with catalytically active metal complexes in solution.

Antimicrobial activity and cytotoxicity of transition metal carboxylates derived from agaric acid

Abstract Carboxylato-type transition metal complexes with agaric acid, a bioactive natural compound derived from citric acid, were prepared, and tested in vitro for their antimicrobial activity and cytotoxicity. The products as well as agaric acid itself are amphiphilic compounds containing a hydrophilic head (citric acid moiety) and a hydrophobic tail (non-polar alkyl chain). The putative composition of the carboxylates was assigned on grounds of elemental analysis, infrared (IR) and high-resolution mass spectra (HR-MS), as well as in analogy with known complexes containing the citrate moiety. The metal carboxylates showed interesting activity in several microbial strains, especially against S. aureus (vanadium complex; MIC = 0.05 mg/ml). They were also tested for their cytotoxic activity in hepatocytes, the highest activity having been found in the copper(II) and manganese(II) complexes. Further research based on these preliminary results is needed in order to evaluate the influence of parameters like stability of the metal complexes in solution on the bioactivity of the complexes.

Activation of C–H bonds of normal alkanes in sulfuric acid solutions of Mn(III)/Mn(II)

One of the most important directions of establishing the mechanisms of activation of C–H bonds, both in saturated and aromatic hydrocarbons in aqueous and sulfuric acid solutions of oxidants, metal complexes and radicals, is to study the kinetics of reactions and the influence of temperature, environment, nature of reagents, etc. The study of mechanisms is important for the development of technologies for processing hydrocarbons into products with high added value. In this work, to determine the nature of limiting stages and mechanisms of reactions of one group of saturated hydrocarbons, normal alkanes, we use the dependences of substrate selectivity (relative rate constants) on their characteristics: ionization potentials, energy and number of primary and secondary C–H bonds. To determine the nature of the limiting stages of reactions of normal alkanes, the correlations between the logarithms of substrate selectivity of alkanes reactions in H2SO4 solutions with one of the most active manganese(III) ions and molecule properties or C–H bond type were studied by the method of correlation analysis. Comparison of the obtained results with quantum-chemically calculated enthalpy changes of different possible variants of the course of this elementary reaction allowed to clarify the mechanism and propose tests to perform the mechanism of the slow limiting stage. It is shown that for alkanes (ethane, pentane, hexane, heptane, octane) the linear dependence with the ionization potential is most accurately performed, the least accurate is the correlation with the number of secondary C–H bonds, which indicates the electron abstraction in the slow limiting stage. For the shorter pentane – octane series, correlation dependences on both the number of secondary C–H bonds and the ionization potentials are performed with almost equal accuracy, which makes it impossible to establish the nature of the slow stage. The results of quantum-chemical calculations of hexane reactions in Mn(III)/Mn(II)–H2SO4 solutions showed that the most favorable are the electron abstraction by manganese(III) and subsequent proton transfer or homolysis of the C–H bond under the action of bisulfate radical, which is likely formed in the oxidation of sulfuric acid by manganese(III).

Electroactive Metal Complexes Covalently Attached to Conductive PEDOT Films: A Spectroelectrochemical Study.

The successful covalent attachment, via copper(I)-catalyzed azide alkyne cycloaddition (CuAAC), of alkyne-functionalized nickel(II) and copper(II) macrocyclic complexes onto azide (N3)-functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films on ITO-coated glass electrodes is reported. To investigate the surface attachment of the selected metal complexes, which are analogues of the cobalt-based complex previously reported to be a molecular catalyst for hydrogen evolution, first, three different PEDOT films were formed by electropolymerization of pure PEDOT or pure N3-PEDOT, and last, 1:2N3-PEDOT:PEDOT were formed by co-polymerizing a 1:4 mixture of N3-EDOT:EDOT monomers. The successful surface immobilization of the complexes on the latter two azide-functionalized films, by CuAAC, was confirmed by X-ray photoelectron spectroscopy (XPS) and electrochemistry as well as by UV-vis-NIR and resonance Raman spectroelectrochemistry. The ratio between the N3 groups, and hence, the number of surface-attached metal complexes after CuAAC functionalization, in pristine N3-PEDOT versus 1:2N3-PEDOT:PEDOT is expected to be 3:1 and seen to be 2.86:1 with a calculated surface coverage of 3.28 ± 1.04 and 1.15 ± 0.09 nmol/cm2, respectively. The conversion, to the metal complex attached films, was lower for the N3-PEDOT films (Ni 74%, Cu 76%) than for the copolymer 1:2N3-PEDOT:PEDOT films (Ni 83%, Cu 91%) due to the former being more sterically congested. The Raman and UV-vis-NIR results were simulated using density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively, and showed good agreement with the experimental data. Importantly, the spectroelectrochemical behavior of both anchored metal complexes is analogous to that of the free metal complexes in solution. This proves that PEDOT films are promising conducting scaffolds for the covalent immobilization of metal complexes, as the existing electrochromic features of the complexes are preserved on immobilization, which is important for applications in electrocatalytic proton and carbon dioxide reduction, optoelectronics, and sensing.

Pd(II) and Rh(III) Complexes with Isoquinoline Derivatives Induced Mitochondria-Mediated Apoptotic and Autophagic Cell Death in HepG2 Cells

Nonplatinum metal complexes of [Pd(L1)Cl2] (C1), [Rh(L1)Cl3(DMSO)] (C2), [Pd(L2)Cl2] (C3), and [Rh(L3)Cl3(DMSO)] (C4) with isoquinoline derivatives have been prepared and characterized. C1–C4 exhib...

Iron's Wake: The Performance of Quantum Mechanical-Derived Versus General-Purpose Force Fields Tested on a Luminescent Iron Complex.

Recently synthetized iron complexes have achieved long-lived excited states and stabilities which are comparable, or even superior, to their ruthenium analogues, thus representing an eco-friendly and cheaper alternative to those materials based on rare metals. Most of computational tools which could help unravel the origin of this large efficiency rely on ab-initio methods which are not able, however, to capture the nanosecond time scale underlying these photophysical processes and the influence of their realistic environment. Therefore, it exists an urgent need of developing new low-cost, but still accurate enough, computational methodologies capable to deal with the steady-state and transient spectroscopy of transition metal complexes in solution. Following this idea, here we focus on the comparison between general-purpose transferable force-fields (FFs), directly available from existing databases, and specific quantum mechanical derived FFs (QMD-FFs), obtained in this work through the Joyce procedure. We have chosen a recently reported FeIII complex with nanosecond excited-state lifetime as a representative case. Our molecular dynamics (MD) simulations demonstrated that the QMD-FF nicely reproduces the structure and the dynamics of the complex and its chemical environment within the same precision as higher cost QM methods, whereas general-purpose FFs failed in this purpose. Although in this particular case the chemical environment plays a minor role on the photo physics of this system, these results highlight the potential of QMD-FFs to rationalize photophysical phenomena provided an accurate QM method to derive its parameters is chosen.

In Situ NMR Search for Spin-Crossover in Heteroleptic Cobalt(II) Complexes.

Here we report the first successful attempt to identify spin-crossover compounds in solutions of metal complexes produced by mixing different ligands and an appropriate metal salt by variable-temperature nuclear magnetic resonance (NMR) spectroscopy. Screening the spin state of a cobalt(II) ion in a series of thus obtained homoleptic and heteroleptic compounds of terpyridines (terpy) and 2,6-bis(pyrazol-3-yl)pyridines (3-bpp) by using this NMR-based approach, which only relies on the temperature behavior of chemical shifts, revealed the first cobalt(II) complexes with a 3-bpp ligand to undergo a thermally induced spin-crossover. A simple analysis of NMR spectra collected from mixtures of different compounds without their isolation or purification required by the current method of choice, the Evans technique, thus emerges as a powerful tool in a search for new spin-crossover compounds and their molecular design boosted by wide possibilities for chemical modifications in heteroleptic complexes.

Synthesis of iron-based nanoparticles from ferrocene by femtosecond laser irradiation: Suppression of the particle growth in a mixture of water and hexane

Iron-based nanoparticles show unique magnetic properties, and their syntheses from metal complex solution by pulsed lasers have been widely studied; however, the aggregation of nanoparticles is unavoidable in homogeneous solution. We report the production of water-dispersible iron-based nanoparticles in a mixture of water and ferrocene n-hexane solution by femtosecond laser irradiation without using any additive agents. The mean diameter of iron-based nanoparticles (ca. 7 nm) is independent on the concentration of ferrocene and laser irradiation time. We propose that hexane microdroplets dispersed in water act as reaction vessels and reduce the opportunity of aggregation of primary nanoparticles.

Evolution of the uranium mineralisation in the Zoujiashan deposit, Xiangshan ore field: Implications for the genesis of volcanic-related hydrothermal U deposits in South China

Volcanic-related hydrothermal U deposits from the Xiangshan ore field are situated within the Gan-Hang Metallogenic Belt in South China. These deposits are dominantly hosted in late Yanshanian felsic volcanic rocks that were emplaced during the Yanashanian post-orogenic extension. The host volcanic rocks are moderately fractionated high-K calc-alkaline A2-type volcanic rocks and are one of the possible U sources for U ore genesis in the district. Porphyroclastic rhyolite is the main host facies and contains an average of 12 ppm U, which can be released through volcanic glass devitrification and mobilised by oxidised fluids for the formation of hydrothermal mineralisation. However, REE patterns of the U mineralisation suggest multiple U sources with U mobilised from additional felsic basement rocks subjacent to the Xiangshan caldera and/or from magmatic fluids related to a late peralkaline intrusion.At the Zoujiashan deposit in the Xiangshan ore field, structurally controlled albitised zones with brannerite-dominated U mineralisation are constrained by a maximum age of 116 ± 1 Ma on hydrothermal zircon and a minimum crystallisation age of 109 ± 1 Ma on pitchblende. This constitutes the early stage of mineralisation that occurred during the early Cretaceous (ca. 120–105 Ma). The Th-Mo-P-REE-Y-Ti-Zr whole-rock geochemical signature and disseminated Th-brannerite associated with a complex mineral assemblage including hydrothermal rutile, apatite, zircon, uranothorite, sphalerite, pyrite, xenotime and REE-carbonate indicated temperatures >250 °C for the hydrothermal system. The Th-REE-Y-Nb-Zr signature of the U mineralisation concomittent with the intrusion of alkaline mafic dykes suggest that a peralkaline intrusion located at depth, postdating the Xiangshan volcanic-intrusive complex by at least 10 Ma, provided the heat source and U-Th-REE-Y-Nb-Zr-rich fluids to the hydrothermal system for the formation of the early U mineralisation. In contrast, the structurally controlled disseminated- to vein-type pitchblende-dominated U mineralisation that yielded a minimum crystallisation age of 81 ± 4 Ma represents the main stage of mineralisation (ca. 100–80 Ma) and formed during the late Cretaceous crustal extension. The mineralisation occurred at low- to moderate-temperatures (150–250 °C) as Ti-Th-Zr-rich pitchblende associated with extensive illite and fluorite alteration. Here, pitchblende that overprinted the early mineralisation stage most likely inherited the primary chemical signature of this early mineralisation, especially the high Th contents. During this episode of crustal extension, uranium was leached from the host volcanic rocks and subjacent felsic basement rocks by surface-derived oxidised fluids and transported through basement faults as carbonate and/or fluoride complexes in solution. These U-bearing solutions mixed with deep-seated magmatic-derived fluids, and the resulting destabilisation of metal complexes in solution together with pressure decrease in opening fractures promoted U deposition. Therefore, the volcanic-related hydrothermal U mineralisation in the volcanic belt formed during two major stages related to different genetic conditions.

Resolving structures of transition metal complex reaction intermediates with femtosecond EXAFS

Femtosecond-resolved Extended X-ray Absorption Fine Structure (EXAFS) measurements of solvated transition metal complexes are successfully implemented at the X-ray Free Electron Laser LCLS. Benchmark experiments on [Fe(terpy)2]2+ in solution show a signal-to-noise ratio on the order of 500, comparable to typical 100 ps-resolution synchrotron measurements. In the few femtoseconds after photoexcitation, we observe the EXAFS fingerprints of a short-lived (∼100 fs) intermediate as well as those of a vibrationally hot long-lived (∼ns) excited state.

Development of a Polyfunctional Dipodal Schiff Base: An Efficient Chelator and a Potential Zinc Sensor

A novel polyfunctional dipodal ligand, L = N,N'-bis[2-[(2-hydroxy-1-naphthyl)methyleneamino]ethyl]propanediamide (DOTA2HNAP) was developed and characterized through elemental and spectral analyses. The complexation behavior of the ligand was investigated with Co2+, Cu2+, and Zn2+ metal ions by potentiometric and spectrophotometric methods in the H2O-DMSO mixture (99:1) at µ = 0.1M KCl and 25 ± 1 °C. Four protonation constants for –OH of naphtholate groups and –N of imine were determined for the ligand. The ligand forms monomeric complexes of ML type with the metal ions, where coordination occurs through N-imine and O-naphtholate donors (N2O2). In the case of a complex of copper, an additional species, MLH-2, was formed due to ionization of the amide groups in a higher pH. The minimum energy structures of the metal complexes in solution have been obtained through molecular modeling studies by using the semi-empirical/ PM3 method. The photophysical properties of DOTA2HNAP were investigated in the presence of a wide range of biologically relevant metal ions. The fluorescence emission of the ligand at 450 nm (λex = 361 nm) exhibited a remarkable enhancement with Zn2+ ions (1 equivalent) at physiological pH amongst all metal ions. Such behavior enables the ligand to be considered as a suitable model for the detection of Zn2+ towards environmental applications.

Nematicidal Effect of Organic Extract Metal Complex on Meloidogyne incognita Infecting Groundnuts (Arachis hypogea)

Abstract The control of plant parasitic nematodes is constantly associated with environmental pollution problems which emanates from the ability of synthetic nematicides to bind strongly to different soil types owing to their hydrophilic nature. This research attempted to determine the nematicidal potential of copper, iron and zinc salts complexed with methanolic extract of Enantia chloranta on Meloidogyne incognita infecting groundnut plants on the field. Carbofuran, a synthetic nematicide was used as a reference standard. The experiment was a randomised complete block design which was conducted in two raining seasons (2017 & 2018). Two grams (2 g) of each of the metal salts were reacted with 300 ml of E. chloranta methanolic extract. Good nematicidal activity was displayed by E. chloranta crude extract copper complex (ENCT/CuSO4) close to the value obtained with carbofuran (CBFN), iron and zinc salt complexes (ENCT/FeSO4 and ENCT/ZnSO4) were also significantly (p<0.05) effective. Toxicity of the metal salt complex to M. incognita was dose dependent. Vegetative growth and yield was significantly (p<0.05) higher in plants treated with the highest concentration of the metal complex solution. Significantly lower nematode population was seen at harvest in the roots of treated plants as opposed to the untreated plants. This research has demonstrated that the E. chloranta metal complex is a promising nematicidal substance.

Nitrogen Sorption in a Transition Metal Complex Solution for N2 Rejection from Methane

Nitrogen is a ubiquitous impurity in natural gas that has to be removed for the production of liquefied natural gas (LNG). The most widely used technology for N2 rejection, cryogenic distillation, is a capital and energy intensive process. In this work, a nitrogen selective K[RuII(EDTA)] aqueous solution was prepared and tested for nitrogen sorption with the aim of reducing the N2 rejection costs by using a continuous recirculation absorption process analogous to the acid gas removal process in LNG production. The overall equilibrium amount of N2 sorption in the K[RuII(EDTA)] solution was obtained at 20 °C (0.075 mol N2/L solution at 2860 kPa), 30 °C (0.061 mol N2/L solution at 2873 kPa), and 40 °C (0.052 mol N2/L solution at 3049 kPa) using a custom-built volumetric sorption measurement apparatus. The corresponding specific N2 sorption amounts were 0.54 mol N2/mol Ru at 20 °C and 2860 kPa; 0.43 mol N2/mol Ru at 30 °C and 2873 kPa; and 0.34 mol N2/mol Ru at 40 °C and 3049 kPa. These specific N2 sorption a...

Structural study of holmium zirconate nanoparticles obtained through carbon neutral sol-gel process

The pyrochlore oxides are of potential interest as ion conducting electrolyte for intermediate temperature solid oxide fuel cell (SOFC). Nanopowders of holmium zirconate have been synthesised through ion-exchange between sodium alginate gel and metal complex solution followed by its thermal decomposition. Nanoparticles of Ho2Zr2O7 were obtained by calcining the dried gel beads at 700 °C for 2 h and 6 h duration respectively. An insight into calcination has been obtained employing simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). Thermal decomposition was also followed using High Temperature X-ray Diffraction (HTXRD) in static ambient atmosphere. Results from TGA/DSC and HTXRD corroborate with each other. Fine crystalline nanopowders of single phase Ho2Zr2O7 could be obtained after thermal decomposition at relatively low temperature (600–700 °C). Powder X-ray diffraction (XRD) revealed that the material has crystallized as single phase cubic Ho2Zr2O7 with defect fluorite structure. XRD and Raman spectroscopy were used to analyse the local structure of holmium zirconate. XRD scans of holmium zirconate and holmium hafnate prepared through identical method have been compared and the effect of cationic radius of Zr4+ and Hf4+ on B-site was studied. The crystallographic data obtained from XRD and transmission electron microscopy (TEM) are in good agreement with each other. This sol-gel method also referred as Leeds Alginate Process (LAP) is simple, cost effective, energy efficient and carbon neutral for the preparation of pyrochlore oxides (A2B2O7) solid electrolyte material for SOFC.

One-Step Route Synthesis of Siliceous Six-Line Ferrihydrite: Implication for the Formation of Natural Ferrihydrite

This paper presents a one-step route to the production of siliceous six-line ferrihydrite (6LFh) by oxidizing the aqueous Fe2+–silicate metal complex in solution. Synthetic 6LFh is analogous to nat...

Ion association with tetra-n-alkylammonium cations stabilizes higher-oxidation-state neptunium dioxocations

Extended-coordination sphere interactions between dissolved metals and other ions, including electrolyte cations, are not known to perturb the electrochemical behavior of metal cations in water. Herein, we report the stabilization of higher-oxidation-state Np dioxocations in aqueous chloride solutions by hydrophobic tetra-n-alkylammonium (TAA+) cations—an effect not exerted by fully hydrated Li+ cations under similar conditions. Experimental and molecular dynamics simulation results indicate that TAA+ cations not only drive enhanced coordination of anionic Cl– ligands to NpV/VI but also associate with the resulting Np complexes via non-covalent interactions, which together decrease the electrode potential of the NpVI/NpV couple by up to 220 mV (ΔΔG = −22.2 kJ mol−1). Understanding the solvation-dependent interplay between electrolyte cations and metal–oxo species opens an avenue for controlling the formation and redox properties of metal complexes in solution. It also provides valuable mechanistic insights into actinide separation processes that widely use quaternary ammonium cations as extractants or in room temperature ionic liquids.

Ligand exchange method for determination of mole ratios of relatively weak metal complexes: a comparative study

Ligand exchange method is introduced as an alternative to Job’s and mole ratio methods for studying the stoichiometry of relatively weak metal complexes in solutions. The method involves adding varying amounts of a ligand (L) to an excess constant amount of a colored complex (MX) with appropriate stability and molar absorptivity. The absorbance of each solution is measured at the λmax of the initial complex, MX, and plotted against the concentration of the studied ligand, L. If the newly formed complex ML does not absorb at the λmax of the initial complex, then attenuation of the absorbance of the initial complex on adding varying quantities of the investigational ligand gives an inverse calibration line that intersects with the calibration curve of initial complex at a given point. If a line parallel to the ordinate is drawn from this point to the x-axis, the ratio of the two parts of the x-axis to the left and to the right (α/β) gives the metal to ligand molar ratio in the complex formed, ML. The new method has been applied to the study of the composition of iron (III) complexes with three bisphosphonate drugs: alendronate, etidronate, and ibandronate. The mole ratio was found to be 1:1 with the three investigated bisphosphonates and results were further confirmed by Job’s and mole ratio methods. The ligand exchange method is simpler, quicker, easier to perform and more accurate than Job’s and mole ratio methods for studying weak and relatively weak complexes.