Carbon Ligands Research Articles

Hydration properties of lanthanoid(iii) carbonate complexes in liquid water determined by polarizable molecular dynamics simulations

In this work we have studied the structure and dynamics of complexes formed by three and four carbonates and a central lanthanoid(III) ion in liquid water by means of polarizable molecular dynamics simulations. With this aim we have developed a force field employing an extrapolation procedure that was previously developed for lanthanoid(III) aqua ions and then we have validated it against DFT-based data. In this way we were able to shed light on properties of the whole series, finding some similarities and differences across the series, and to help in interpreting experiments on those systems. We found that the bi-dentate tri-carbonate complexes are the most stable for all the atoms, but a variation of the number of water molecules in the first ion shell, and the associated exchange dynamics, is observed from lighter to heavier elements. On the other hand, for four-carbonate systems only one water molecule is observed in the first shell, with 10-20% probability, for La(III) and Ce(III), while for the rest of the series it seems impossible for a water molecule to enter the first ion shell in the presence of such an excess of carbonate ligands. Finally, the good performance of our extrapolation procedure, based on ionic radii, makes us confident in extending such approaches to study the structure and dynamics of other systems in solution containing Ln(III) and An(III) ions. This parametrization method results particularly useful since it does not need expensive quantum chemistry calculations for all the atoms in the series.

A laboratory study of the initial effects of dissolved carbon dioxide (CO2) on metal release from shallow sediments

Sequestration of carbon dioxide (CO2) into deep geologic reservoirs is a potential approach for controlling the rise of CO2 concentrations in the atmosphere. Proper characterization and permitting of storage sites is expected to include an assessment of the potential impacts of CO2 intrusion into overlying groundwater formations. In most natural settings, the dissolution of CO2 into groundwater will decrease the pH and can also release carbonate ligands into solution. These effects can lead to metals being mobilized from sediments through mechanisms such as ion exchange, desorption, and mineral dissolution. This laboratory-based study evaluates the extent of metal release from a groundwater system in the presence of elevated CO2 concentrations. In particular, the research investigates the geochemical mechanisms involved in metal release, with a focus on distinguishing between pH-driven processes (e.g. carbonate dissolution and ion exchange) and carbonate-driven processes (e.g. reactions enhanced by the formation of metal–carbonate complexes). Measurements from lab-scale leaching experiments and sediment characterizations are compared to data from a concurrent controlled-release field test, where CO2 was injected into a poorly buffered sandy groundwater formation at ∼50m depth. Results show that the immediate effect of the introduction of CO2 is a pH drop of ∼3 units, which leads to the quick release of some elements (e.g. Ca, Mg, Ba, Sr) by primarily pH-driven processes. The extent of metal release was different across geochemically distinct sediment types from the field site. The results suggest that it would be useful to group constituents by their pH-release trends, and to include pH and concentrations of certain indicator cations (Li, K, Na, Ba, Ca, Mg, Sr, Mn and Si) as parameters in site monitoring plans.

Control of the Escherichia coli Sialoregulon by Transcriptional Repressor NanR

NanR, one of >8,500 GntR superfamily helix-turn-helix transcriptional regulators, controls expression of the genes required for catabolism of sialic acids in Escherichia coli. It is predicted to do the same in related bacteria harboring orthologs of nanR. The sialic acids are a family of over 40 naturally occurring nine-carbon keto-sugar acids found mainly in the animal lineage, which includes starfish to humans in the deuterostome lineage. Sialic acids function in development, immunity, protein localization and stability, and homeostasis. They also serve as microbial carbon and nitrogen sources and ligands for cell recognition during host colonization. The importance of microbial sialic acid metabolism for host-microbe interactions has made it a target for therapeutic development. Exploiting this target depends on understanding sialometabolic pathways in a wide range of evolutionarily distinct bacteria. Here, we show by transcriptome, genetic, and biochemical analyses that the most common sialic acid, N-acetylneuraminate, induces the nanATEK-yhcH, yjhATS (nanCMS), and yjhBC operons by directly inactivating NanR, converting the predominantly dimeric form of the repressor to an inactive monomer of approximately 30-kDa. Additionally, other results identify critical amino acid residues and nucleotides in the regulator and operator, respectively. The combined results better define how sialic acids, acting through NanR, affect the metabolic flux of an important group of host-derived metabolites. Thus, E. coli serves as a valuable model for understanding sialocatabolic pathways in bacteria.

Tetraammine(carbonato-κ2O,O′)cobalt(III) nitrate: a powder X-ray diffraction study

Practical chemistry courses at universities very frequently propose the synthesis and characterization of [Co(CO3)(NH3)4]NO3, but this goal is never achieved since students only obtain the hemihydrated form. The anhydrous form can be prepared, however, and its structure is presented here. Similar to the hemihydrate form, the anhydrous phase contains the CoIII ion in an octahedral O2N4 coordination by a chelating carbonate group and four ammine ligands. The structure reveals an intricate array of N—H⋯O hydrogen bonds involving both the chelating and the non-chelating O atoms of the carbonate ligand as hydrogen-bond acceptors of the amine H atoms, which are also involved in hydrogen-bonding inter­actions with the nitrate O atoms. The structure of the anhydrous form is close to that of the hemihydrate phase, suggesting a probable topotactic reaction with relatively small rotations and translations of the [Co(CO3)(NH3)4]+ and NO3 − groups during the dehydration process, which produces an unusual volume increase of 4.3%.

Frontiers, opportunities, and challenges in biochemical and chemical catalysis of CO2 fixation.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTFrontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 FixationAaron M. Appel†, John E. Bercaw‡, Andrew B. Bocarsly§, Holger Dobbek∥, Daniel L. DuBois*†, Michel Dupuis†, James G. Ferry⊥, Etsuko Fujita#, Russ Hille∇, Paul J. A. Kenis○, Cheryl A. Kerfeld▲, Robert H. Morris☆, Charles H. F. Peden†, Archie R. Portis◆, Stephen W. Ragsdale*■, Thomas B. Rauchfuss*¶, Joost N. H. Reek◇, Lance C. Seefeldt△, Rudolf K. Thauer★, and Grover L. Waldrop□View Author Information† Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States‡ Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States§ Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States∥ Institut für Biologie, Strukturbiologie/Biochemie, Humboldt Universität zu Berlin, Berlin, Germany⊥ Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16801, United States# Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States∇ Department of Biochemistry, University of California, Riverside, California 92521, United States¶ ○Department of Chemical and Biochemical Engineering, ◆Departments of Crop Sciences and Plant Biology, and ¶Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States▲ DOE Joint Genome Institute, 2800 Mitchell Drive Walnut Creek, California 94598, United States, and Department of Plant and Microbial Biology, University of California, Berkeley, 111 Koshland Hall Berkeley, California 94720, United States☆ Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada■ Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States◇ van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands△ Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, Utah 84322, United States★ Max Planck Institute for Terrestrial Microbiology, Karl von Frisch Strasse 10, D-35043 Marburg, Germany□ Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, United States*E-mail: (D.L.D.) [email protected], (S.W.R.) [email protected], (T.B.R.) [email protected]Cite this: Chem. Rev. 2013, 113, 8, 6621–6658Publication Date (Web):June 14, 2013Publication History Received19 November 2012Published online14 June 2013Published inissue 14 August 2013https://doi.org/10.1021/cr300463yCopyright © 2013 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views33616Altmetric-Citations1551LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (7 MB) Get e-AlertsSUBJECTS:Catalysts,Inorganic carbon compounds,Ligands,Peptides and proteins,Redox reactions Get e-Alerts

Evolution of rodingites along stratigraphic depth in the Iti and Kallidromon ophiolites (Central Greece)

Rodingitised rocks were collected from the neighbouring Iti and Kallidromon ophiolites. They comprise metasomatic assemblages after serpentinised lherzolite and harzburgite, gabbro and dolerite dykes. The main mineral phases in the metasomatised mantle and gabbroic rocks include grossularitic garnet, chlorite and diopside whereas epidote group minerals were mainly developed at the expense of the dolerite dykes. The fluid phase involved in the metasomatic reactions was highly alkaline in the metasomatising peridotites and less alkaline in the altered gabbro and dolerite. Under such conditions, Ti is assumed to have remained immobile in the whole process while Zr remained constant in the stratigraphically upper rodingitised gabbro and dolerite. Transportation of rare earth elements, Zr, Cr and Ni from the altered mantle segment to the upper gabbro level was assisted by the presence of carbonate and hydroxyl ligands. After consequent breakdown of the carbonate complexes, these elements were deposited in the rodingitised gabbro and dolerite. Rare earths were mainly integrated in the neoblastic diopside whereas Cr and Ni likely formed insoluble hydroxides in that less reducing environment. The metasomatic event happened in the mantle wedge close to the subduction of the Pelagonian carbonates that strongly enriched the fluid phase in CO2. The entrance of an externally derived hydrothermal fluid was responsible for the reduction of pH at the higher levels and the calculated influx of Si in the system.

DFT Study of Uranyl Peroxo Complexes with H2O, F–, OH–, CO32-, and NO3–

The structural and electronic properties of monoperoxo and diperoxo uranyl complexes with aquo, fluoride, hydroxo, carbonate, and nitrate ligands have been studied using scalar relativistic density functional theory (DFT). Only the complexes in which the peroxo ligands are coordinated to the uranyl moiety in a bidentate mode were considered. The calculated binding energies confirm that the affinity of the peroxo ligand for the uranyl group far exceeds that of the F(-), OH(-), CO3(2-), NO3(-), and H2O ligands. The formation of the monoperoxo complexes from UO2(H2O)5(2+) and HO2(-) were found to be exothermic in solution. In contrast, the formation of the monouranyl-diperoxo, UO2(O2)2X2(4-) or UO2(O2)2X(4-/3-) (where X is any of F(-), OH(-), CO3(2-), or NO3(-)), complexes were all found to be endothermic in aqueous solution. This suggests that the monoperoxo species are the terminal monouranyl peroxo complexes in solution, in agreement with recent experimental work. Overall, we find that the properties of the uranyl-peroxo complexes conform to well-known trends: the coordination of the peroxo ligand weakens the U-O(yl) bonds, stabilizes the σ(d) orbitals and causes a mixing between the uranyl π- and peroxo σ- and π-orbitals. The weakening of the U-O(yl) bonds upon peroxide coordination results in uranyl stretching vibrational frequencies that are much lower than those obtained after the coordination of carbonato or hydroxo ligands.

Basic CuCO3/ligand as a new catalyst for 'on water' borylation of Michael acceptors, alkenes and alkynes: application to the efficient asymmetric synthesis of β‐alcohol type sitagliptin side chain

The efficient 'on water' β‐borylation using bis(pinacolato)diboron agent was achieved with a newly developed catalytic system based on basic copper carbonate and various ligands. The catalytic system was used for β‐borylation of various Michael acceptors, alkenes and alkynes. The presented methodology was successfully applied to the novel synthesis of β‐alcohol type sitagliptin side chain precursor via water‐based highly enantioselective β‐borylation followed by an oxidation process. Copyright © 2013 John Wiley & Sons, Ltd.

Monolayer Doping via Phosphonic Acid Grafting on Silicon: Microscopic Insight from Infrared Spectroscopy and Density Functional Theory Calculations

AbstractMonolayer doping (MLD) is a promising technique for creating ultra shallow junctions (USJs). Here, a novel self assembled monolayer (SAM) grafting technique is proposed through a single oxygen atom capable of MLD. Consequently, this approach can use simple forms of alkylphosphonic acids and avoid carbon contamination altogether during the doping process. In this paper, density functional theory (DFT) is used to explore the way how alkylphosphonic acid molecules can in just one chemical step be grafted on H‐terminated Si(111). A maximum coverage of alkylphosphonic acids is found at 2/3 due to steric constrain forces. It is further demonstrated by means of in situ infrared spectroscopy and DFT calculations that the weak link of an alkylphosphonic acid, such as octadecylphosphonic acid (ODPA), is the P‐C bond, with typical release of the carbon ligand around 500 °C. Finally, after release of the carbon ligand, an unsaturated electron configuration is driving force for the phosphorous to start the MLD process.

An unprecedented mixed valence cobalt(III)/cobalt(II) ion-pair complex ([CoCO3(bipy)2]2[Co(DCA)2]⋅16H2O) with two novel water tapes

An unprecedented mixed valence cobalt(III)/cobalt(II) ion-pair complex, [CoCO3(bipy)2]2[Co(DCA)2]⋅16H2O (1) [bipy = 2,2′-bipyridine, DCA = demethylcantharidate, exo-1,4-epoxy-cyclohexyl-2,3-dicarboxylate group, (C8H8O5)2 −], has been synthesized and characterized by elemental analysis, IR, UV–vis, Thermogravimetric analysis (TGA) and single crystal X-ray diffraction. The crystal structure of 1 consists of three independent molecular moieties: [CoCO3(bipy)2]+, [Co(DCA)2]2–, and water molecules of crystallization. Interestingly, two novel water tapes, one comprises of alternate cyclic water tetramer and octamer, the other is constructed by alternate cyclic water hexamer and carboxylate–water hybrid octamer [(H2O)2(COO)2]2 −, have been detected for the first time in the host framework of 1. The two novel water tapes are linked together by the DCA and carbonate ligands via hydrogen bonds into a 2D water layer, and then the water layers assemble complex ions ([CoCO3(bipy)2]+ and [Co(DCA)2]2 −) through hydrogen bonds, π–π interactions and electrostatic interactions to form the overall 3D metal–organic framework structure.

Structural characterization of the aqueous dimeric uranium(vi) species: (UO2)2CO3(OH)3−

A combined theoretical and spectroscopic approach was used to refine structural data of the aqueous dimeric U(VI) species, (UO2)2CO3(OH)3(-). Several isomer structures of this complex were already derived from previous X-ray absorption and NMR experiments (Szabó, Z. et al., J. Chem. Soc., Dalton Trans., 2000, 3158-3161) but due to unequivocal results a distinct structure could not be determined and uncertainties remain. In this work, the Gibbs energies and U-U distances obtained from density functional theory (DFT) calculations predict two isomers, one with a carbonate ligand and one with two hydroxo groups as bridging groups, as most likely structures. The experimental IR spectrum indicates a bidentate coordination of the carbonate ion and the presence of two spectroscopically specifiable uranyl moieties as it is also predicted by the spectra computed on the base of DFT. Taken together theoretical and experimental results the isomer with a carbonate ligand bridging the two uranyl units appears most likely to represent the predominant structure. Contributions to a small extent of an isomer with a non-bridging carbonate anion cannot be completely ruled out.

Bioavailability of Metals in Contaminated Sediments

Bioavailability controls the transfer of metals from sediments to ecological receptors and humans. It can rarely be predicted from total metal concentrations because it is affected by metal geochemistry in sediments as well as the biochemistry, physiology, and behavior of benthic organisms. There is no single approach for including bioavailability in risk assessments because of variability in site specific conditions and the difficulty of validating methods. Acid-volatile sulfide and simultaneously extracted metals are useful in predicting bioavailability in anoxic sediments containing sulfides that react to form insoluble metal complexes. This method can be improved by adjusting for organic carbon and other ligands that also bind free metals. Site-specific desorption Kd values calculated by sequential extraction methods can be useful in predicting bioavailable metal fractions in oxic and anoxic sediments. A modified desorption distribution coefficient (Kdg) can be calculated by extraction with the digestive gut fluids of sediment feeding organisms to account for the effects of ingestion on metal release from sediments. Recently developed in situ measurement technologies can accumulate dissolved metals in a controlled fashion that may correspond with bioavailable metal fractions in sediment. Successful evaluation of bioavailability requires the selection of methods suitable for the organisms and sediment environments under consideration. A weight-of-evidence approach that incorporates multiple lines of evidence can help address uncertainties and increase the likelihood of incorporating bioavailability into remedial decisions.

Dynamics of rare earth elements in water–soil systems: The case study of the Pineta San Vitale (Ravenna, Italy)

The European Union Site of Community Importance Pineta San Vitale (Ravenna, Italy) is located in a complex lagoon system nearby the Adriatic Sea. This area is affected by relevant environmental pressures related to subsidence, groundwater salinization and industrial contamination. The occurrence of rare earth elements (REE), and the characterization of processes that control their migration in the water–soil system were performed for implementing the knowledge of the present environmental status in the area.Nine soil profiles were opened in the Pineta San Vitale and each horizon was characterized. In the parent material, dominant quartz, followed by plagioclase, mica, chlorite and calcite were recognized by XRD. Topsoil samples were characterized by neutral or sub-acid pH, relatively high organic carbon content (LOI up to 43wt.%; TOC: 38÷61g/kg), and low carbonate (11÷20g/kg CaCO3). Subsoil horizons were sub-alkaline or moderately alkaline, rich in carbonate (up to 114g/kg CaCO3), and depleted in organic matter. The electrical conductivity (EC: 0.2÷4.2 mS/cm) values along the soil profiles did depend on the water table fluctuations and the salinity of groundwater. Sequential extraction tests on two soil profiles showed the highest Y and ΣREE occurrence in the residual fraction of soils, with values generally increasing at depth, and total amounts similar to values estimated in the upper continental crust (UCC). Poor fractionation of REE was observed when the bulk soil horizon was considered, but different REE patterns occurred in the organic, oxide, and carbonate soil fractions, suggesting REE fractionation during weathering and pedogenic processes.Physical–chemical parameters and concentrations of total and dissolved elements were determined in 44 water samples. Waters showed near-neutral or slightly alkaline pH (6.8÷8.0) and total dissolved solids mostly in the range of 2 to 24g/L, with values increasing with increasing seawater influence. Concentrations of ΣREE determined in waters filtered through 0.4μm pore size filters varied from 0.1 to 189μg/L (0.7·10−9÷1.3·10−6mol/L ΣREE), with the highest values observed in soil waters. REE values were not related to salinity, nor to major ions, while were positively correlated to Al concentrations. Further filtration through 0.015μm pore size filters removed about 90% of REE compared to the 0.4μm filtered samples, i.e. the studied waters showed a small quantity of truly dissolved REE species. Speciation modeling results by Visual MINTEQ indicated that truly dissolved REE species are dominated by bi-dentate organic complexes in the soil waters rich in dissolved organic carbon (up to 74mg/L DOC); aqueous complex with the carbonate and bicarbonate ligands increased in waters having low DOC. UCC-normalized patterns of REE in the colloidal fraction of soil waters showed slight enrichments in the middle REE (MREE), likely due to preferential adsorption of the MREE onto <0.4μm particles. UCC-normalized patterns of REE truly dissolved in soil waters showed slight enrichments in the heavy REE (HREE), probably due to dominant low molecular weight DOC in the truly dissolved fraction.For evaluating the potential REE contribution from the atmosphere, 12 vegetation samples (ivy leaves) were submitted to leaching tests using acidulated water as a proxy of rain water. The REE leached from leaves were in the range of 0.5 to 10μg/kg ΣREE, suggesting a significant atmospheric contribution to the water–soil system. UCC-normalized patterns of REE leached from leaves were nearly flat, possibly indicating a dominant geogenic source of atmospheric REE.

The direct dissolution of Ce2(CO3)3 and electrochemical deposition of Ce species using ionic liquid trimethyl-n-butylammonium bis(trifluoromethanesulfonyl)imide containing bis(trifluoromethanesulfonyl)imide

Ionic liquids (ILs) are solutions comprised of cation/anion pairs that are not limited by the electrochemical side reactions common to aqueous solution. The high stability of the ionic liquid provides large potential windows that can encompass the thermodynamic potentials for the reduction of f-elements such as cerium to metal. The direct dissolution of Ce2(CO3)3·xH2O into the ionic liquid trimethyl-n-butylammonium bis(trifluoromethanesulfonyl)imide [Me3NBu][TFSI] using conjugate acid bis(trifluoromethanesulfonyl)imide [HTFSI] is demonstrated. The displacement of carbonate ligand and formation of carbonic acid facilitates the in situ dissolution. The subsequent coordination of Ce with the TFSI ion in the IL is monitored using UV/vis spectroscopy and emergent ligand to metal transitions below 300nm. Further evidence of the coordination of Ce in the ionic liquid is based on changes in the IR spectra for absorbance bands related to the sulfonyl functional groups of the TFSI anion. The reduction/oxidation of soluble Ce in IL is examined at Au, Pt, and GC (glassy carbon) electrodes. Multi-wave voltammetry at all three electrodes is consistent with the reductive deposition of Ce species from the IL solution. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) confirm the deposition of Ce species at mica/Au electrodes.

Dissociation Kinetics of Open‐Chain and Macrocyclic Gadolinium(III)‐Aminopolycarboxylate Complexes Related to Magnetic Resonance Imaging: Catalytic Effect of Endogenous Ligands

The kinetics of the metal exchange reactions between open-chain Gd(DTPA)(2-) and Gd(DTPA-BMA), macrocyclic Gd(DOTA)(-) and Gd(HP-DO3A) complexes, and Cu(2+) ions were investigated in the presence of endogenous citrate, phosphate, carbonate and histidinate ligands in the pH range 6-8 in NaCl (0.15 M) at 25 °C. The rates of the exchange reactions of Gd(DTPA)(2-) and Gd(DTPA-BMA) are independent of the Cu(2+) concentration in the presence of citrate and the reactions occur via the dissociation of Gd(3+) complexes catalyzed by the citrate ions. The HCO(3)(-)/CO(3)(2-) and H(2)PO(4)(-) ions also catalyze the dissociation of complexes. The rates of the dissociation of Gd(DTPA-BMA), catalyzed by the endogenous ligands, are about two orders of magnitude higher than those of the Gd(DTPA)(2-). In fact near to physiological conditions the bicarbonate and carbonate ions show the largest catalytic effect, that significantly increase the dissociation rate of Gd(DTPA-BMA) and make the higher pH values (when the carbonate ion concentration is higher) a risk-factor for the dissociation of complexes in body fluids. The exchange reactions of Gd(DOTA)(-) and Gd(HP-DO3A) with Cu(2+) occur through the proton assisted dissociation of complexes in the pH range 3.5-5 and the endogenous ligands do not affect the dissociation rates of complexes. More insights into the interaction scheme between Gd(DTPA-BMA) and Gd(DTPA)(2-) and endogenous ligands have been obtained by acquiring the (13)C NMR spectra of the corresponding diamagnetic Y(III)-complexes, indicating the increase of the rates of the intramolecular rearrangements in the presence of carbonate and citrate ions. The herein reported results may have implications in the understanding of the etiology of nephrogenic systemic fibrosis, a rare disease that has been associated to the administration of Gd-containing agents to patients with impaired renal function.

Alumina coatings on silica powders by Fluidized Bed Chemical Vapor Deposition from aluminium acetylacetonate

A SiO2 powder has been coated by alumina using the Fluidized Bed Chemical Vapor Deposition process and a metal organic precursor, aluminium acetylacetonate (Al(acac)3 or C15H21AlO6) as single source. A range of low temperatures, i.e. 400–620°C has been explored at atmospheric pressure. Systematic characterizations were performed by Field Emission Gun Scanning Electron Microscopy (FEG-SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infra-Red (FT-IR) spectroscopy and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The process involves a first step of gas phase reactions producing reactive intermediates, themselves leading to Al2O3 and carbon containing deposits. Between 400 and 500°C, the deposits are lamellar and constituted of mixtures of Al2O3, non-decomposed Al(acac)3 and impurities, leading to a C/Al molar ratio close to 2. For this range of temperature, the precursor is not totally decomposed and the limiting parameter of the process is the deposition temperature. For 600 and 620°C, the deposits are nodular and mainly formed of Al2O3 and acetylacetone C5H8O2, one of the main intermediate species formed in the gas phase. The Al(acac)3 decomposition seems to be complete, but a deposition temperature of 620°C is not high enough to allow a complete decomposition of carbon ligands of the chemisorbing intermediate species. For these conditions, the C/Al molar ratio increases with the deposition temperature, to reach values between 4 and 6, in agreement with the observed darker colors of the deposits.

Mechanistic Investigation of the Generation of a Palladium(0) Catalyst from a Palladium(II) Allyl Complex: A Combined Experimental and DFT Study

Cross-coupling reactions can be efficiently catalyzed using palladium complexes. The formation of low-coordinated, highly reactive Pd(0), which is believed to be the catalytic species, is critical. The mechanism of the reduction of a stable and readily available allyl Pd(II) complex into Pd(0) by a combination of K2CO3 and PhB(OH)2 has been studied. We report on the characterization of the associated reactive solution using a combination of density functional theory and experimental methods. First, the stoichiometric reaction of an (allyl)(phosphine)palladium(II) complex with K2CO3 was first investigated using trandem mass spectrometry. A palladium–carbonate complex could be characterized in the electrospray mass spectrum of the reactive solution. Gas-phase infrared spectra of mass-selected complexes have been recorded, giving further information on the coordination mode (κ1) of the carbonate ligand. This structural information derived from spectroscopy is critical because the relative energy of the two κ1- and κ2-carbonate isomers is difficult to determine theoretically, presumably because of the charge transfers at play between the carbonate and the palladium. Second, the product of the stoichiometric addition of PhB(OH)2 to this carbonate complex was investigated. Both 31P and 1H NMR data provide compelling evidence for the formation of the desired 14-electron Pd(0) complex.

Binary and ternary surface complexes of U(VI) on the gibbsite/water interface studied by vibrational and EXAFS spectroscopy

The retardation of contaminants in aquifers is mainly determined by chemical reactions occurring at the solid/liquid interface. For a more detailed understanding of the molecular reactions of uranium(VI) at Al-hydroxide surfaces, the surface speciation of the radionuclide on gibbsite was studied in aqueous medium by a combined spectroscopic approach using time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. For the first time, the impact of the surface morphology and of atmospherically derived carbonate on the uranyl surface speciation was systematically investigated under environmentally relevant conditions, namely in the near neutral pH range, at maximum initial U(VI) concentrations of 20μM, and at different surface loadings. Concordantly, the formation of a monomeric binary inner-sphere surface complex is derived from vibrational and EXAFS spectroscopic data irrespective of the prevailing atmospheric condition and surface loading. In addition, from infrared spectra it was found that U(VI) surface precipitation occurs at a micromolar concentration level after a relatively short contact time in an inert gas atmosphere. However, this is circumvented by lowering the initial U(VI) concentration or in the presence of atmospheric CO2 due to the formation of ternary uranyl carbonato surface complexes. The ternary complex was identified as a dimeric inner-sphere uranyl surface species containing a bidentately coordinated carbonate ligand. The results of this work might be of relevance for a comprehensive description of the dissemination of uranium in groundwater systems.

A Theoretical Study of an Unusual Y-Shaped Three-Coordinate Pt Complex: Pt(0) σ-Disilane Complex or Pt(II) Disilyl Complex?

The unusual Y-shaped structure of the recently reported three-coordinate Pt complex Pt[NHC(Dip)(2)](SiMe(2)Ph)(2) (NHC = N-heterocyclic carbene; Dip = 2,6-diisopropylphenyl) was considered a snapshot of the reductive elimination of disilane. A density functional theory study indicates that this structure arises from the strong trans influence of the extremely σ-donating carbene and silyl ligands. Though this complex can be understood to be a Pt(II) disilyl complex bearing a distorted geometry due to the Jahn-Teller effect, its (195)Pt NMR chemical shift is considerably different from those of Pt(II) complexes but close to those of typical Pt(0) complexes. Its Si···Si bonding interaction is ~50% of the usual energy of a Si-Si single bond. The interaction between the Pt center and the (SiMe(2)Ph)(2) moiety can be understood in terms of donation and back-donation interactions of the Si-Si σ-bonding and σ*-antibonding molecular orbitals with the Pt center. Thus, we conclude that this is likely a Pt(0) σ-disilane complex and thus a snapshot after a considerable amount of the charge transfer from disilane to the Pt center has occurred. Phenyl anion (Ph(-)) and [R-Ar](-) [R-Ar = 2,6-(2,6-iPr(2)C(6)H(3))(2)C(6)H(3)] as well as the divalent carbon(0) ligand C(NHC)(2) also provide similar unusual Y-shaped structures. Three-coordinate digermyl, diboryl, and silyl-boryl complexes of Pt and a disilyl complex of Pd are theoretically predicted to have similar unusual Y-shaped structures when a strongly donating ligand coordinates to the metal center. In a trigonal-bipyramidal Ir disilyl complex [Ir{NHC(Dip)(2)}(PH(3))(2)(SiMe(3))(2)](+), the equatorial plane has a similar unusual Y-shaped structure. These results suggest that various snapshots can be shown for the reductive eliminations of the Ge-Ge, B-B, and B-Si σ-bonds.

Intrinsic Green Phosphor Containing a {Y5O22} Pentamer Unit and a Carbonate Ligand Generated In Situ from Squaric Acid

An unexpected green phosphor! The promising activator-free yttrium metal–organic framework (MOF) [Y5(OH)6(HCO2)3(CO3)2-(C4O4)] ⋅2.5 H2O consists of unique {Y5O22} pentamers and four types of ligands, the carbonate group of which was unprecedentedly in situ generated from squaric acid. This pure yttrium–MOF compound displays intrinsic green light and has proven to be the first hybrid-yttrium-host lattice to achieve near-white-light solely through Eu3+ doping (see figure). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.