Metal Ion Ligand Research Articles

Electrochemical assessment of water|ionic liquid biphasic systems towards cesium extraction from nuclear waste

A room temperature ionic liquid (IL) composed of a quaternary alkylphosphonium (trihexyltetradecylphosphonium, P66614+) and tetrakis(pentafluorophenyl)borate anion (TB−) was employed within a water|P66614TB (w|P66614TB or w|IL) biphasic system to evaluate cesium ion extraction in comparison to that with a traditional water|organic solvent (w|o) combination. 137Cs is a major contributor to the radioactivity of spent nuclear fuel as it leaves the reactor, and its extraction efficiency is therefore of considerable importance. The extraction was facilitated by the ligand octyl(phenyl)-N,N′-diisobutylcarbamoylphosphine oxide (CMPO) used in TRans-Uranium EXtraction processes and investigated through well established liquid|liquid electrochemistry. This study gave access to the metal ion to ligand (1:n) stoichiometry and overall complexation constant, β, of the interfacial complexation reaction which were determined to be 1:3 and 1.6×1011 at the w|P66614TB interface while the study at w|o elicited an n equal to 1 with β equal to 86.5. Through a straightforward relationship, these complexation constant values were converted to distribution coefficients, δα, with the ligand concentrations studied for comparison to other studies present in the literature; the w|o and w|IL systems gave δα of 2 and 8.2×107, respectively, indicating a higher overall extraction efficiency for the latter. For the w|o system, the metal ion-ligand stoichiometries were confirmed through isotopic distribution analysis of mass spectra obtained by the direct injection of an emulsified water–organic solvent mixture into an electron spray ionization mass spectrometer.

The C-Terminal Regions Have an Important Role in the Activity of the Ferroxidase Center and the Stability of Chlorobium tepidum Ferritin

The recombinant Chlorobium tepidum ferritin (rCtFtn) is able to oxidize iron using ferroxidase activity but its ferroxidase activity is intermediate between the H-chain human ferritin and the L-chain human ferritin. The rCtFtn has an unusual C-terminal region composed of 12 histidine residues, as well as aspartate and glutamate residues. These residues act as potential metal ion ligands, and the rCtFtn homology model predicts that this region projects inside the protein cage. The rCtFtn also lacks a conserved Tyr residue in position 19. In order to know if those differences are responsible for the altered ferroxidase properties of rCtFtn, we introduced by site-directed mutagenesis a stop codon at position 166 and a Tyr residue replaced Ala19 in the gene of rCtFtn (rCtFtn 166). The rCtFtn166 keeps the canonical sequence considered important for the activity of this family of proteins. Therefore, we expected that rCtFtn 166 would possess similar properties to those described for this protein family. The rCtFtn 166 is able to bind, oxidize and store iron; and its activity is inhibit by Zn(II) as was described for other ferritins. However, the rCtFtn 166 possesses a decrease ferroxidase activity and protein stability compared with the wild type rCtFtn. The analysis of the Ala19Tyr rCtFtn shows that this change does not affect the kinetic of iron oxidation. Therefore, these results indicate that the C-terminal regions have an important role in the activity of the ferroxidase center and the stability of rCtFtn.

Synthesis of rare earth metal-organic frameworks (Ln-MOFs) and their properties of adsorption desulfurization

The rare earth metal-organic frameworks (Ln-MOFs) materials, Ln(BTC)(H2O)·(DMF), were synthesized using the rare earth metal (Ln=Sm, Eu, Tb, Y) and 1,3,5-trimesic acid (BTC) as a metal ion center and ligand, respectively. X-ray diffraction (XRD) and infrared spectroscopy (FT-IR) were employed to characterize the Ln-MOFs structural features. The property of adsorption desulfurization of Ln-MOFs materials was evaluated with thiophene/n-octane as model oil. The results showed that Ln-MOFs with rare earth metals Sm, Eu, Tb and Y had perfect crystalline and good adsorption desulfurization ability. Y(BTC)(H2O)·(DMF) material had a comparatively better activity for the adsorption desulfurization with desulfurization rate up to 80.7% and the sulfur adsorption capacity was found 30.7 mgS/g(Y-MOFs). The Ln-MOFs materials had excellent reusability.

Role of the LEXE Motif of Protein-primed DNA Polymerases in the Interaction with the Incoming Nucleotide

The LEXE motif, conserved in eukaryotic type DNA polymerases, is placed close to the polymerization active site. Previous studies suggested that the second Glu was involved in binding a third noncatalytic ion in bacteriophage RB69 DNA polymerase. In the protein-primed DNA polymerase subgroup, the LEXE motif lacks the first Glu in most cases, but it has a conserved Phe/Trp and a Gly preceding that position. To ascertain the role of those residues, we have analyzed the behavior of mutants at the corresponding ϕ29 DNA polymerase residues Gly-481, Trp-483, Ala-484, and Glu-486. We show that mutations at Gly-481 and Trp-483 hamper insertion of the incoming dNTP in the presence of Mg(2+) ions, a reaction highly improved when Mn(2+) was used as metal activator. These results, together with previous crystallographic resolution of ϕ29 DNA polymerase ternary complex, allow us to infer that Gly-481 and Trp-483 could form a pocket that orients Val-250 to interact with the dNTP. Mutants at Glu-486 are also defective in polymerization and, as mutants at Gly-481 and Trp-483, in the pyrophosphorolytic activity with Mg(2+). Recovery of both reactions with Mn(2+) supports a role for Glu-486 in the interaction with the pyrophosphate moiety of the dNTP.

G-Quadruplexes as Sensing Probes

Guanine-rich sequences of DNA are able to create tetrastranded structures known as G-quadruplexes; they are formed by the stacking of planar G-quartets composed of four guanines paired by Hoogsteen hydrogen bonding. G-quadruplexes act as ligands for metal ions and aptamers for various molecules. Interestingly, the G-quadruplexes form a complex with anionic porphyrin hemin and exhibit peroxidase-like activity. This review focuses on overview of sensing techniques based on G-quadruplex complexes with anionic porphyrins for detection of various analytes, including metal ions such as K+, Ca2+, Ag+, Hg2+, Cu2+, Pb2+, Sr2+, organic molecules, nucleic acids, and proteins. Principles of G-quadruplex-based detection methods involve DNA conformational change caused by the presence of analyte which leads to a decrease or an increase in peroxidase activity, fluorescence, or electrochemical signal of the used probe. The advantages of various detection techniques are also discussed.

Using low-frequency IR spectra for the unambiguous identification of metal ion–ligand coordination sites in purpose-built complexes

One of the aims of our long-term research is the identification of metal ion–ligand coordination sites in bioinspired metal ion–C- or N-protected amino acid (histidine, tyrosine, cysteine or cystine) complexes immobilised on the surface of chloropropylated silica gel or Merrifield resin. In an attempt to reach this goal, structurally related, but much simpler complexes have been prepared and their metal ion–ligand vibrations were determined from their low-frequency IR spectra. The central ions were Mn(II), Co(II), Ni(II) or Cu(II) and the ligands (imidazole, isopropylamine, monosodium malonate) were chosen to possess only one-type of potential donor group. The low-frequency IR spectra were taken of the complexes for each ion–ligand combination and the typical metal ion-functional group vibration bands were selected and identified. The usefulness of the obtained assignments is demonstrated on exemplary immobilised metal ion-protected amino acid complexes.

Synthesis, crystal structures and complexing properties of tetramethoxyresorcinarene functionalized tetraacylhydrazones

In this work, the syntheses, crystal structures and complexing properties of novel tetramethoxyresorcinarenes with functional tetraacylhydrazones were described in detail. Tetramethoxyresorcinarenes were alkylated with α-chloroacetate in the system of K2CO3/KI/acetone to give active O-acetates, which in turn were reacted with hydrated hydrazine to give the corresponding acylhydrazine derivatives. Then by condensation with salicylaldehyde, the expected tetramethoxyresorcinarene acylhydrazones were efficiently prepared in satisfactory yields. The single crystal analysis of eight products shows that tetramethoxyresorcinarenes existed in chair conformation. The complexing properties of these polydentated ligands for transition metal ions were studied with UV–Vis and fluorescence spectroscopy. The results suggested that tetramethoxyresorcinarene tetraacyl hydrazones exhibited a more efficient fluorescent sensing ability to Zn2+.

New lanthanide complexes of 1,1`-bis[(2-thienylmethylidene)hydrazono-1-ethyl]-ferrocene and 1,1`-bis(2,3-dihydro-2-methylbenzo[d]thiazol-2-yl)ferrocene: Synthesis, characterization and antimicrobial properties

In this paper; synthesis, characterization and biocidal properties of new prepared Sc(III), Y(III), La(III) and Ce(III) complexes with the two ferrocenyl ligands of 1,1`- bis [(2-thienylmethylidene)hydrazono-1-ethyl]ferrocene and 1,1`- bis (2,3-dihydro-2-methylbenzo[ d ] thiazol-2-yl)ferrocene are reported. These organometallic compounds are potential ligands for lanthanide metal ions. The composition of these complexes is discussed on the basis of elemental analysis, IR, NMR, magnetic moments, electronic absorption spectra and conductivity measurements. In vitro antimicrobial activity of the prepared complexes was screened. All complexes showed remarkable antibiotic activity. Scandium complexes are very effective towards Salmonella spp . Sc-L 2 complex found to have inhibition activity against B. subtilis more than the standard drugs.

ChemInform Abstract: Click to Bind: Metal Sensors.

AbstractReview: 54 refs.

A Method for Improving the Optical Properties of a Fluoregenic Di-metal Chelator as a Zn2+Ion Fluorescent Probe by Using a Bridging Substrate

Fluorescent probe based detection methods for metal ions are indispensable tools in many fields, including medical diagnostics, environmental monitoring, living cell studies, and electronics. These methods have multiple advantages over other methods, such as high sensitivity, low cost, ease of application, and versatility. Numerous fluorescent metal ion probes have been designed using many strategies, including fluorogenic metal chelators, fluorescent dye tagged oligonucleotides, catalytic signal amplification, and chemodosimetors. Fluorogenic metal chelators, which consist of a fluorogenic unit (signaling site) covalently linked to chelating moieties (receptor units) with an appropriate spacer, are a general type metal ion probe. The recognition of chelating moieties with metal ions induces a change in the photophysical properties of the fluorescent probe. This is converted into an optical signal expressed as an enhancement or quenching of the fluorophore emission. The recognition can be enhanced to utilize additive reagents that provide additional binding sites for metal ions. For example, 8-aminoquinolino-β-cyclodextrin, developed by Liu et al., exhibited cooperative binding to Zn ion with 1-adamatanoic acid. It also detected Zn ions more efficiently than without 1adamatanoic acid because 1-adamatanoic acid bound to βcyclodextrin to provide additional binding site for Zn ions. This strategy can easily expand to improve the optical properties of metal ion sensors with two metal binding sites. Di-metal complexes may include bridging substrates to complete the metal coordination sphere, and bridging substrates can modulate the properties of the resulting cascade complexes. In particular, bridging substrates provided additional metal ion binding sites and enhanced the binding properties of metal ions to metal ion ligands. Various fluorescent molecules with two metal binding sites have been synthesized as efficient probes for detecting metal ions, such as Zn and Ag. Scaffolds of di-metalic fluoregenic probes have also been devised to detect anions. Most of these molecules can be used as metal ion probes. The optical properties of these molecules can be improved by bridging substrates, which provide additional metal ion binding sites. To validate this concept, (9,10-bis[(2,2-dipicolylamino)methyl]anthracene) (1) was adapted as a Zn ion probe because [Zn2(1)] 4+ efficiently detects phosphate derivatives as potential bridging substrates to provide additional metal binding sites. In various phosphate derivatives, ATP was adapted as a bridging substrate to provide additional metal binding sites because [Zn2(1)] 4+ fluorescence is most enhanced by binding with ATP. Therefore, a combination of 1 and ATP (1/ATP) was prepared as a Zn fluorescent probe. The optical properties of 1/ATP, compared to those of 1, can be improved by providing additional binding sites for metal ions using ATP, as depicted in Scheme 1. To determine the optimal ratio of 1 and ATP, fluorescence titration of ATP was conducted using a 5 μM solution of 1 with 2 equivalents of Zn ions. The fluorescence emission spectra of [Zn2(1)] 4+ in the presence of varied ATP concentrations were evaluated. [Zn2(1)] 4+ fluorescence increased nearly proportionally to ATP concentration and was maximized at one equivalent of ATP (see Supporting information). A sensing system (1/ATP) consiting of 1 (5 μM) and ATP (5 μM) was prepared to evaluate the cooperative binding effect of the bridging substrate by providing additional binding sites for Zn ions. Fluorescence changes of 1/ATP in the presence of various concentrations of Zn were examined. The addition of Zn ions induced greatly enhanced fluorescence. The binding zinc ions within the bis-(2-picolyl)amine in 1 prevents the photo induced electron transfer process

ChemInform Abstract: Coordination Polymer Gels with Important Environmental and Biological Applications

AbstractReview: 45 refs.

Integrated and Passive 1,2,3-Triazolyl Groups in Fluorescent Indicators for Zinc(II) Ions: Thermodynamic and Kinetic Evaluations

In addition to being a covalent linker in molecular conjugation chemistry, the function of a 1,2,3-triazolyl moiety resulting from the copper(I)-catalyzed azide-alkyne cycloaddition reaction as a ligand for metal ions is receiving considerable attention. In this work, we characterize the thermodynamic and kinetic effects of incorporating a 1,2,3-triazolyl group in a multidentate ligand scaffold on metal coordination in the context of fluorescent zinc(II) indicator development. Ligands L14, BrL14, and FL14 (1,4-isomers) contain the 1,4-disubstituted-1,2,3-triazolyl group that is capable of binding with zinc(II) in conjunction with a di(2-picolylamino) (DPA) moiety within a multidentate ligand scaffold. Therefore, the 1,2,3-triazolyl in the 1,4-isomers is "integrated" in chelation. The 1,5-isomers L15, BrL15, and FL15 contain 1,2,3-triazolyls that are excluded from participating in zinc(II) coordination. These 1,2,3-triazolyls are "passive linkers". Zinc(II) complexes of 2:1 (ligand/metal) stoichiometry are identified in solution using (1)H NMR spectroscopy and isothermal titration calorimetry (ITC) and, in one case, characterized in the solid state. The 1:1 ligand/zinc(II) affinity ratio of L14 over L15, which is attributed to the affinity enhancement of a 1,2,3-triazolyl group to zinc(II) over that of the solvent acetonitrile, is quantified at 18 (-1.7 kcal/mol at 298 K) using an ITC experiment. Fluorescent ligands FL14 and FL15 are evaluated for their potential in zinc(II) sensing applications under pH neutral aqueous conditions. The 1,4-isomer FL14 binds zinc(II) both stronger and faster than the 1,5-isomer FL15. Visualization of free zinc(II) ion distribution in live HeLa cells is achieved using both FL14 and FL15. The superiority of FL14 in staining endogenous zinc(II) ions in live rat hippocampal slices is evident. In summation, this work is a fundamental study of 1,2,3-triazole coordination chemistry, with a demonstration of its utility in developing fluorescent indicators.

Click To Bind: Metal Sensors

The copper-catalyzed azide-alkyne "click" cycloaddition reaction is an efficient coupling reaction that results in the formation of a triazole ring. The wide range of applicable substrates for this reaction allows the construction of a variety of conjugated systems. The additional function of triazoles as metal-ion ligands has led to the click reaction being used for the construction of optical sensors for metal ions. The triazoles are integral binding elements, which are formed in an efficient modular synthesis. Herein, we review recent examples of triazoles as a metal-binding element in conjugated metal-ion sensors.

Research Front on Coordination Polymers

Coordination polymers, which are also widely known as metalorganic frameworks (MOFs), are infinite solid-state networks that can be synthesised from combinations of organic links and metals or metal oxide clusters. By careful choice of both precursor metal salt and the bridging organic ligand, materials with varying 1-D, 2-D, and 3-D topologies; tailored pore sizes, pore shapes, and internal pore chemistry; and properties can be synthesised. Research into the field of coordination polymers and MOFs appears to know no limits. A Web of Science search of both terms as part of the title of published manuscripts (Fig. 1) shows a continual and notable growth over the past 20 years; first of the term ‘coordination polymer’ and then more recently the term ‘metal-organic framework’ or ‘MOF’. This Research Front inAust. J. Chem. highlights examples of the current state of research in the field of coordination polymer or MOF chemistry and indicates briefly where some of the future challenges and opportunities in the field may lie. Australasia has strong links to the field of coordination polymers with Hoskins and Robson publishing one of the seminal papers in this area. By combining tetrahedral organic links and tetrahedral Cu metals ions, Hoskins and Robson were able to form a 3-D coordination polymer with a diamond-like cationic framework. This primary contribution outlined a strategy by which judicious choice of both metal ion and organic ligand could lead to the synthesis of coordination polymers with 1-D, 2-D, and 3-D topologies (Scheme 1). By modifying the structure metrics of a link or ligand, the pore size and chemistry could be systematically manipulated to generate desirable materials. A flurry of activity in the field has elucidated numerous structurally novel materials from a vast array of metal and ligand combinations, along with the observation of various fundamental phenomenon such as the mechanical interlocking – catenation or interpenetration – of the polymeric structures and the intrinsic physical properties of the frameworks, for example, magnetism and non-linear optics. The appreciation that such materials could be made permanently porous altered the focus of the field to the properties of coordination polymers that take advantage of the high surfaces areas and large pore volumes; to on-board gas storage initially and hence to separations, catalysis, sensing, and delivery, for example. The identification of a third class of coordination polymers, namely materials with dynamic structures, has added a further focus to the field with the ability to tie changes in the properties of a material to structural changes that occur in the framework. As noted, the robust frameworks obtained from combinations of metal ions, or metal-oxide clusters, and organic ligands possess high surfaces areas and large pore volumes that make them suitable for gas storage. Potential for onboard storage of gases such as hydrogen and methane for transportation has been investigated in considerable detail, with control over surface areas and pore volume by extension of the ligands, control of catenation, and generation of open metal sites having been shown to enhance gas uptake. More recently considerable attention has been directed towards the use of coordination polymers for gas separations, particularly for the separation of CO2 frommixtures of gases that include predominantlymethane (natural gas sweetening), hydrogen (pre-combustion CO2 capture), or nitrogen (post-combustion CO2 capture) to counter the increasing levels of CO2 in the atmosphere. [13] Two main strategies have been used to enhance the gas separation performance ofMOFs: increasing the affinity of the framework for the gas (e.g. generation of exposed metal sites, post-synthetic metallation, and functionalising pores with Lewis basic sites), or by separating on the basis of different kinetic diameters. Other separations that have been studied included olefin/alkane separations, capture of organosulfur compounds, and enantioseparations. The open, crystalline structures of coordination polymers have also led to studies of their potential as catalytic materials, including as shape-selective catalysts, framework catalysts (e.g. Lewis acid catalysis due to structural metal ions), and for heterogenising – embedding – existing homogenous catalysts. Properties of the frameworks such as luminescence, solvatochromism, or vapochromism, and localised Surface Plasmon Resonance have been utilised for sensing, while the large pore volumes have been explored for delivery of pharmaceutical

Coordination polymer gels with important environmental and biological applications

Coordination Polymer Gels (CPGs) constitute a subset of solid-like metal ion and bridging organic ligand structures (similar to metal-organic frameworks) that form multi-dimensional networks through a trapped solvent as a result of non-covalent interactions. While physical properties of these gels are similar to conventional high molecular weight organic polymer gels, coordination polymer gel systems are often fully reversible and can be assembled and disassembled in the presence of additional energy (heat, sonication, shaking) to give a solution of solvated gelators. Compared to gels resulting from purely organic self-assembled low molecular weight gelators, metal ions incorporated into the fibrilar networks spanning the bulk solvent can impart CPGs with added functionalities. The solid/liquid nature of the gels allows for species to migrate through the gel system and interact with metals, ligands, and the solvent. Chemosensing, catalysis, fluorescence, and drug-delivery applications are some of the many potential uses for these dynamic systems, taking advantage of the metal ion's coordination, the organic polydentate ligand's orientation and functionality, or a combination of these properties. By fine tuning these systems through metal ion and ligand selection and by directing self-assembly with external stimuli the rational synthesis of practical systems can be envisaged.

Evaluation of quantitative probes for weaker Cu(i) binding sites completes a set of four capable of detecting Cu(i) affinities from nanomolar to attomolar

Copper plays essential roles in biology, but abnormal interactions are damaging. Reliable quantification of copper-protein interactions will underpin the molecular understanding of copper nutrition and toxicity. We have previously established two high affinity probes, Bathocuproine disulfonate (Bcs) and Bicinchoninate (Bca) anions, that are capable of in vitro quantification of Cu(i) binding with affinities from pico- to atto-molar concentrations. Quantitative probes are required for Cu(i) binding of lower affinity for proteins and peptides typically associated with neurodegenerative diseases. The present work evaluates two classic Fe(ii) ligands Ferene S (Fs) and Ferrozine (Fz) as quantitative probes for Cu(i). Both react with Cu(i) quantitatively to yield well-defined complex anions [Cu(I)(Fs)2](3-) (λmax = 484 nm, ε = 6700 cm(-1) M(-1)) and [Cu(I)(Fz)2](3-) (λmax = 470 nm, ε = 4320 cm(-1) M(-1)). These complexes are sensitive to aerial oxidation (E1/2∼ +0.36 V vs. SHE) and to substitution by other ligands (e.g., Cl(-), MeCN). However, they can be protected effectively under anaerobic conditions by suitable reductants and an excess of the free probe ligands. Formation constants β2 were determined by two approaches: direct metal ion titration and ligand competition. They provided estimates which differed by ∼3 orders of magnitude. The sources of these differences were examined carefully to consolidate the affinities of the two probes to a unified standard (10(15.1) M(-2) for Fz and 10(13.7) M(-2) for Fs). It is apparent that application of direct metal ion titrations to quantification of Cu(i) binding affinities is problematical and should be avoided. The four ligands Bcs, Bca, Fz and Fs in combination form a set of versatile probes for ligand competition experiments and are capable of detecting and differentiating an extended spectrum of Cu(i) binding affinities from nano- to atto-molar concentrations. Selected examples of quantification of weaker Cu(i) binding in proteins and peptides are provided, including that of an amyloid-β peptide.

A comparative investigation of copper and cobalt imprinted polymers: evidence for retention of the solution-state metal ion–ligand complex stoichiometry in the imprinted cavities

A copper imprinted polymer (CuVbMIP) was synthesised using a well characterised 1 : 1 complex of Cu2+ with vinylbenzyliminodiacetic acid (VbIDA). The sorption behaviour of CuVbMIP was compared with that of cobalt imprinted polymer (CoVbMIP) synthesised using the 1 : 2 complex of Co2+ and VbIDA. The complexation properties of the imprinted polymers were investigated using EPR and batch sorption studies. The results indicated that the complexation geometry in the sorption sites were different in the imprinted polymers. The sorption sites generated in the imprinted polymers were found to complex with the metal ions strictly according to the stoichiometry maintained in solution during the preparation of the imprinted polymers.

Aggregation-induced emission logic gates based on metal ion sensing of phenanthroline–tetraphenylethene conjugates

Phenanthroline–tetraphenylethene (Phen–1TPE) was synthesized by a typical Suzuki coupling. The aggregation-induced emission (AIE) properties and interactions with metal ions in THF–water (fw = 90%) and in THF were investigated. Aggregation-induced emission logic gates were fabricated based on the metal ion sensing of Phen–1TPE conjugates via control of the metal ions and solvents. In THF–water with fw = 90%, Phen–1TPE exhibits a strong AIE effect, while the fluorescence is almost totally quenched upon the addition of Cu2+ compared to other metal ions. Phen–1TPE works as an “INHIBIT” logic gate, with Cu2+ and aggregation (“Agg”) as the inputs and the fluorescence as the output. The fluorescence can also be quenched in fw = 90% by the addition of metal ions (Cd2+, Zn2+, Sn2+ and In3+). In THF, Phen–1TPE exhibits a metal ion–ligand charge transfer (MLCT)-caused fluorescence enhancement by the addition of metal ions (Cd2+, Zn2+, Sn2+ and In3+). Thus it is established that Phen–1TPE works as a dual “XOR” logic gate with metal ions (Cd2+, Zn2+, Sn2+ and In3+) and “Agg” as the inputs. The INHIBIT and XOR logic gates were manipulated by utilizing different metal ions and water–THF volume ratios as the inputs, and the fluorescence of Phen–1TPE as the output.

A multispectroscopic study of 3d orbitals in cobalt carboxylates: the high sensitivity of 2p3d resonant X-ray emission spectroscopy to the ligand field.

Determination of the ligand coordination number and symmetry of a transition metal ion is important to understand reaction mechanisms in inorganic chemistry. The problem can be addressed through diffraction techniques or by spectroscopy. Here we limit ourselves to the latter and note that, historically, the problem has been studied with UV/Vis, or optical absorption or electronic spectroscopy.1 Recently however the field of resonant X-ray emission spectroscopy (RXES) developed at a high pace.2 Here we show that metal 2p3d RXES is highly sensitive to the metal ion ligand field. We present a comparison of UV/Vis, 2p X-ray absorption spectroscopy (XAS), and 2p3d RXES on a series of cobalt(II) carboxylates. The X-ray data were acquired at the state-of-the-art ADRESS beamline.3 We show that 2p XAS and UV/Vis have a limited discriminative power compared to 2p3d RXES. Through ligand field multiplet (LFM) calculations we show that 2p3d RXES allows the most judicious analysis of the ligand field. While previous 2p3d RXES studies on metal oxides revealed its d–d sensitivity,4 this is the first such observation on inorganic complexes. More importantly, the notion that 2p3d RXES measures element-selective, more as well as more intense d–d excitations than UV/Vis, and that this allows a more reliable determination of the ligand field, is novel. 2p3d RXES will allow unraveling reaction mechanisms of important 3d-metal-mediated chemical processes.

New insights in the bonding regime and ligand field in Wernerian complexes. A density functional study

We advance challenging new observations about the bonding regime and ligand field (LF) effects in the Wernerian complexes, with the help of several computer experiments realized exploiting the specific leverages of the ADF (Amsterdam density functional) code. Assembling the molecular systems from preliminarily prepared metal ion and individual ligand fragments and analyzing the components of the total bonding energy (Pauli repulsion, electrostatic interactions and orbital part), we noticed interesting correlations between the orbital part and the simple formulas of the qualitatively defined ligand field stabilization energy (LFSE). The facts are beyond the obvious or predictable comprehension, since the orbital components incorporate the subtle balance of intra- and inter-fragment density rearrangements, charge transfer and orbital mixing. The energy decomposition analysis was performed considering metal ions and ligand sets in their nominal oxidation states, or with fractional charges, resulted after a preliminary step of electronegativity equalization driven charge transfer. We worked on series of prototypic simple octahedral units: [MqF6]q−6 , [Mq(CN)6]q−6 and [Mq(H2O)6]q complexes with MII and MIII ions selected from the M=Cr to Cu 3d series. Besides, as illustration of observed regularities in the case of more complex ligands and intermediate symmetries, we considered [Mq(bpca)2]q−2 complexes (Hbpca=bis(2-pyridilcarbonyl)amine) with D2d symmetry. Using the ADF facilities of orbital population control and fractional occupation schemes, we devised two simple ways to estimate 10Dq parameters by numerical experiments that simulate the effects of Ligand Field stabilization and electron promotion. To the best of our knowledge, though simple, such considerations on bonding regime or methodological procedures designed to meet the phenomenological demands of LF models have not been discussed before. Interesting new aspects can yet be discovered exploring the subtle details of coordination bonding as intermediate between ionic and covalent bonding regime.