Iron Chemistry Research Articles

Динаміка змін фізіологічного стану і гематологічних показників райдужної форелі під час запуску біофільтра в установках замкненого водовикористання

Наведено результати змін фізіологічного стану і гематологічних показників райдужної форелі у воді установок замкненого водопостачання. Показано, що під час запуску біофільтра УЗВ найбільша загибель малька райдужної форелі виникає з 16 по 20 добу досліду і становить 14,9% від усієї риби. При цьому вся жива риба плавала у верхніх шарах води, у ≈ 50% риби спостерігалося нервове тремтіння тіла та плавників, вона масово підпливала до місця подавання води, у ≈ 90% риби ввідмічали потемніння тіла і плавників, які були ущільнені, у ≈ 90% риби колір зябер змінювався з червоного на коричневий.З моменту запуску біофільтра і до 25 доби у крові риби знижувалася кількість еритроцитів, яка виявилася вірогідною у період з 16 по 20 добу (Р ≤ 0,05) і з 21 по 25 добу, а також вірогідно знижувався рівень гемоглобіну на 16–20 і 21–25 доби (Р ≤ 0,05).Із запуском біофільтра в присутності малька райдужної форелі у крові риб, порівняно із початком запуску біофільтра, зростає вміст метгемоглобіну: на 6–10 добу досліду на 8,8%, 11–15 добу – на 15,0%, 16–20 добу – на 26,4%, 21–25 добу – на 16,8%, 26–30 добу – на 12,8% і 31–35 добу – на 2,1%.

Near-field iron and carbon chemistry of non-buoyant hydrothermal plume particles, Southern East Pacific Rise 15°S

Abstract Iron (Fe)-poor surface waters limit phytoplankton growth and their ability to remove carbon (C) from the atmosphere and surface ocean. Over the past few decades, research has focused on constraining the global Fe cycle and its impacts on the global C cycle. Hydrothermal vents have become a highly debated potential source of Fe to the surface ocean. Two main mechanisms for transport of Fe over long distances have been proposed: Fe-bearing nanoparticles and organic C complexation with Fe in the dissolved (dFe) and particulate (pFe) pools. However, the ubiquity and importance of these processes is unknown at present, and very few vents have been investigated for Fe-Corg interactions or the transport of such materials away from the vent. Here we describe the near-field contributions (first ~100 km from ridge) of pFe and Corg to the Southern East Pacific Rise (SEPR) plume, one of the largest known hydrothermal plume features in the global ocean. Plume particles (>0.2 μm) were collected as part of the U.S. GEOTRACES Eastern Pacific Zonal Transect cruise (GP16) by in-situ filtration. Sediment cores were also collected to investigate the properties of settling particles. In this study, X-ray absorption near edge structure (XANES) spectroscopy was used in two complementary X-ray synchrotron approaches, scanning transmission X-ray microscopy (STXM) and X-ray microprobe, to investigate the Fe and C speciation of particles within the near-field non-buoyant SEPR plume. When used in concert, STXM and X-ray microprobe provide fine-scale and representative information on particle morphology, elemental co-location, and chemical speciation. Bulk chemistry depth profiles for particulate Corg (POC), particulate manganese (pMn), and pFe indicated that the source of these materials to the non-buoyant plume is hydrothermal in origin. The plume particles at stations within the first ~100 km down-stream of the ridge were composites of mineral (oxidized Fe) and biological materials (organic C, Corg). Iron chemistry in the plume and in the core-top sediment fluff layer were both dominated by Fe(III) phases, such as Fe(III) oxyhydroxides and Fe(III) phyllosilicates. Particulate sulfur (pS) was a rare component of our plume and sediment samples. When pS was detected, it was in the form of an Fe sulfide mineral phase, composing ≤0.4% of the Fe on a per atom basis. The sediment fluff layer contained a mixture of inorganic (coccolith fragments) and Corg bearing (lipid-rich biofilm-like) materials. The particle morphology and co-location of C and Fe in the sediment was different from that in plume particles. This indicates that if the Fe-Corg composite particles settle rapidly to the sediments, then they experience strong alteration during settling and/or within the sediments. Overall, our observations indicate that the particles within the first ~100 km of the laterally advected plume are S-depleted, Fe(III)-Corg composites indicative of a chemically oxidizing plume with strong biological modification. These findings confirm that the Fe-Corg relationships observed for non-buoyant plume particles within ~100 m of vent sites are representative of particles within the first ~100 km of the advecting non-buoyant plume, and demonstrate that the export of hydrothermal pFe is facilitated through physical-chemical association with Corg.

Seasonal variation and speciation of dissolved iron in an artificial surface water body

Abstract The aquatic chemistry of iron is an important issue since iron is a micronutrient for the growth of phytoplankton. Its concentration in surface waters involves many environmental aspects, from the quality of a particular water to the control of atmospheric carbon dioxide. Dissolved iron can exist in water as ferrous and ferric iron, and the equilibrium between these two forms, as well as the precipitation and solubilization of iron, depends on many natural and anthropic factors. We studied the variation for an year of Fe(II) and total iron concentration into Poarta Alba - Midia Navodari Canal, an artificial surface water which connects Danube River with Black Sea. The results indicate a high iron concentration in surface water and a seasonal variation of iron concentration and speciation, which can be correlated with the oxidable matter content.

Mercury transformations in resuspended contaminated sediment controlled by redox conditions, chemical speciation and sources of organic matter

Mercury (Hg) contaminated sediments can be significant sources of Hg in aquatic ecosystems and, through re-emission processes, to the atmosphere. Transformation and release of Hg may be enhanced by various sediment perturbation processes, and controlling biogeochemical factors largely remain unclear. We investigated how rates of Hg transformations in pulp-fiber enriched sediment contaminated by Hg from chlor-alkali industry were controlled by (i) transient redox-changes in sulfur and iron chemistry, (ii) the chemical speciation and solubility of Hg, and (iii) the sources and characteristics of organic matter (OM). Sediment-bottom water microcosm systems were exposed to four combinations of air and nitrogen gas for a total time of 24 h. The treatments were: 24 h N2, 0.5 h air + 23.5 h N2, 4 h air + 20 h N2 and 24 h of air exposure. As a result of these treatments, microcosms spanned a wide range of redox potential, as reflected by the dissolved sulfide concentration range of ≤0.3–97 µM. Four different chemical species of inorganic divalent Hg (HgII) and methyl mercury (MeHg), enriched in different Hg isotope tracers, were added to the microcosms: 201Hg(NO3)2(aq), 202HgII adsorbed to OM (202HgII-OM(ads)), 198HgII as microcrystalline metacinnabar (β-198HgS(s)) and Me204HgCl(aq). Microcosm systems were composed of bottom water mixed with sediment taken at 0–2, 0–5 and 0–10 cm depth intervals. The composition of OM varied with sediment depth such that compared to deeper sediment, the 0–2 cm depth-interval had a 2-fold higher contribution of labile OM originating from algal and terrestrial inputs, serving as metabolic electron-donors for microorganisms. The potential methylation rate constant (kmeth) of Hg tracers and net formation of ambient MeHg (MeHg/THg molar ratio) increased up to 50% and 400%, respectively at intermediate oxidative conditions, likely because of an observed 2-fold increase in sulfate concentration stimulating the activity of sulfate reducing bacteria with a capability of methylating HgII. Due to differences in HgII water-sediment partitioning, kmeth varied by a factor of 11–70 for the different isotope-enriched Hg tracers. The chemical form of HgII was a major controlling factor for kmeth and its response to the resuspension-oxidation of the system. The β-198HgS(s) tracer had the lowest kmeth and it was mainly constrained by redox-driven HgII solubility. The 202HgII-OM(ads) tracer showed an intermediate value on kmeth. It was controlled by both HgII solubility and availability of electron donors and acceptors, regulating bacterial activity. The 201Hg(NO3)2(aq) tracer had the highest value on kmeth which was limited mainly by bacterial activity. The kmeth was up to a factor of 3 higher in the 0–2 cm sediment depth-interval than in 0–5 and 0–10 cm intervals due to a larger contribution of labile OM in the 0–2 cm sediment. Reduction of HgII to Hg0 followed by volatilization exclusively occurred at high sulfidic conditions in the top 0–2 cm sediment. Aromatic moieties of terrestrial OM, present mainly in the top sediment, is suggested to control the reduction of HgII. The Hg0 volatilization rate constant for the 202HgII-OM(ads) tracer exceeded that for β-198HgS(s) by one order of magnitude. Our results suggest that contaminated sediments posing a high risk for reactivation of legacy Hg following transient redox resuspension events are characterized by depletion of sulfate in the sediment porewater prior to resuspension, predominance of HgII species with solubility exceeding that of crystalline β-HgS(s), and conditions promoting in situ formation and/or import of labile OM from algal and terrestrial sources.

Nanoscale Imaging Reveals Big Role for Iron in Alzheimer’s Disease

In this issue of Cell Chemical Biology, Telling etal. (2017) apply advanced X-ray microscopy techniques to reveal magnetite iron species in plaques from a mouse model of Alzheimer's disease. The characterization of abnormal iron chemistry in the disease model highlights the potential for iron to combine with the β-amyloid peptide and accelerate the disease process.

(Invited) The Molten Air Battery and the Multiple Electron Storage Advantage

We’ve demonstrated multiple electron per molecule processes yield higher battery storage capacity, introducing a variety of novel storage chemistries including high efficiency in-situ photoelectrochemical solar cells,1,2 aluminum sulfur battery,3 super-iron battery,4 ammonia useful for fuel cells,5 and zirconia on VB2 batteries.6 Unusual multiple electron opportunities abound. For example, not only redox active oxygen from air, but also redox active carbon dioxide from air can be utilized for charge storage.7,8 The Licht group has recently introduced a new class of multiple electrons per molecule battery: Molten Air Batteries.9-14 These new batteries use multi-electron charge storage, a molten electrolyte, are quasi-reversible (rechargeable), and have amongst the highest intrinsic battery storage capacities. This talk will focus on advances in the molten air class of rechargeable batteries including carbon (4 electron storage), iron (3 electron storage) and VB2 (11 electron storage). For example, uncommonly, the carbon molten air battery can utilize carbon dioxide directly from the air or from industrial smoke stacks: charging: CO2(g) -> C(solid) + O2(g) (1) discharging: C(solid) + O2(g) -> CO2(g) (2) 1) S. Licht, G. Hodes, R. Tenne, J. Manassen, A Light Variation Insensitive High Efficiency Solar Cell" Nature , 326, 863-864 (1987). 2) S. Licht, "A Description of Energy Conversion in Photoelectrochemical Solar Cells" Nature , 330, 148-151 (1987). 3) D. Peramunage, S. Licht, "A Novel Solid Sulfur Cathode for Aqueous Batteries" Science , 261, 1029-1032 (1993). 4) S. Licht, B. Wang, S. Ghosh, "Energetic Iron(VI) Chemistry: The Super-Iron Battery," Science , 285, 1039-1042 (1999). 5) S. Licht, B. Cui, B, Wang, F.-F. Li, J. Lau, S, Liu, "Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3," Science, 345 , 637-640, (2014). 6) S. Licht, H. Wu, X. Yu, Y. Wang, "Renewable Highest Capacity VB2/Air Energy Storage," Chemical Communication , 2008, 3257-3259 (2008). 7) S. Licht, A. Douglas, R. Carter, M. Lefler, C. L. Pint, C. “Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes,” ACS Central Science , 2, 162-168 (2015). 8)J. Ren, S. Licht, “Tracking airborne CO2 mitigation and low cost transormation into valuable carbon nanotubes,” Scientific Reports, 6, 27760-1-11 (2016). 9) S. Licht, B. Cui, J. Stuart, B. Wang, J. Lau, "Molten Air Batteries - A new, highest energy class of rechargeable batteries," Energy & Environmental Science ,6, 3646-3657, with 2 pages supplementary information (2013). 10) B. Cui, S. Licht, "A Low Temperature Iron Molten Air Battery," Journal of Materials Chemistry A , 2, 10577-10580, with 3 pages supplementary (2014). 11) S. Liu, X. Li, B. Cui, X. Liu , Y. Hao, Q. Guo, P. Xu, S. Licht, "Critical advances for the iron molten air battery: A new lowest temperature, rechargeable, ternary electrolyte domain," Journal of Materials Chemistry A, 3, 21039-21043, with 2 page Supplementary Info (2015). 12) B. Cui, X. Xiang, S. Liu, H. Xin, X. Liu, and Stuart Licht, "A novel rechargeable zinc-air battery with molten salt electrolyte," Journal of Power Sources, 342, 435-441. (2017). 13) B. Cui, H. Xin, S. Liu, Xianjun Liu, Y. Hao, Q. Guo, and S. Licht, "Improved cycle iron molten air battery performance using a robust fin air electrode," Journal of the Electrochemical Society , 164, A88-A92 (2017). 14) Baochen Cui, Wei , Xiang, Shuzhi Liu, Hongyu Xin, Xianjun Liu, and Stuart Licht, "A long cycle life, high coulombic iron molten air battery," Sustainable Energy & Fuels , cover article, in press (2017).

Environmental Chemistry of Iron——A Frontier in Environmental Chemistry and Geochemistry

Environmental Chemistry of Iron——A Frontier in Environmental Chemistry and Geochemistry

Iron nutrition in plants: an overview

Plants require iron for a large number of metabolic processes. Due to its low availability in high pH soils, and the impaired acquisition by roots, iron chlorosis is one of the most important limiting factors on plant development in many countries. This editorial paper gives an overview of the latest aspects related to iron nutrition presented at the 18th International Symposium on Iron Nutrition and Interaction in Plants: (i) Iron chemistry and dynamics in soils; (ii) Agronomic practices to correct Fe deficiency, from diagnosis to fertilizer development and genetic approaches; (iii) Physiology of the Fe acquisition, transport and distribution in plants, including microorganism-rhizosphere interactions; (iv) Molecular regulation of Fe homeostasis; (v) Iron and plant metabolism; (vi) Iron interaction with other elements and (vii) Iron fortification of crops for a better human nutrition. The outcomes of the meeting will allow a step forward on the understanding of iron nutrition and open new approaches to cope the iron deficiency problem.

Insights from post-test examination of three packages from the MiniCan test series of copper-cast iron canisters for geological disposal of spent nuclear fuel: impact of the presence and density of bentonite clay

ABSTRACTMiniCan is a field test designed to highlight certain aspects of corrosion in a KBS-3 type repository for spent nuclear fuel. Five experimental packages containing miniature copper-cast iron canisters were installed in the Äspö Hard Rock Laboratory in 2006. Three packages have been retrieved, MiniCan 3 in 2011 and MiniCan 4 and 5 in 2015. The packages were examined regarding surface chemistry, microbiology and corrosion of copper and iron. The main difference in design between the retrieved packages was the presence and density of bentonite clay. Black deposits of sulphides were visually noted during dismantling of both MiniCan 3 (low density clay) and MiniCan 5 (no clay), but not in MiniCan 4 (high density clay). Extensive corrosion of cast iron specimens was observed in all three packages, with local attacks corresponding to the loss of hundreds of µm/y. Sulphate reducing bacteria (SRB) were found to be present in ground water, in bentonite clay and on surfaces of various specimens of iron and copper, and it is suggested that the SRB activity had a pronounced influence on the corrosion observed. Copper surfaces display a roughness at the µm level and the integrated corrosion rate of copper mass-loss specimens was generally low.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Scaling Considerations in All-Iron Flow Batteries

In recent years, the deployment of renewable energy sources, development of smart grid technology and advances in electrified transportation have resulted in a surge in markets for large-scale stationary energy storage. Several factors contribute to the demand for large-scale energy storage, including capital costs of managing peak demands, integration of renewable energy sources and investments needed for grid reliability. Although hydroelectric is one of the most common types of energy storage, flow batteries offer a much more desirable alternative, due to scalability and location flexibility. A number of studies and demonstration projects have been carried out in the field of flow batteries, in particular with the vanadium [1,4], and iron/chromium[2-4] chemistries and these and other systems are in the first stages of commercial deployment. In this presentation we will discuss the scale-up an all iron flow battery, focusing on two issues in particular, flow distribution and hydrogen generation/recombination. Flow distribution is a scaling concern in all flow battery systems both on a cell to cell level within a stack and within an individual cell. This investigation utilizes the all iron chemistry to investigate the effects of flow distribution within a single cell on cell performance and the pressure drop associated pumping costs of achieving a more even flow distribution within a cell. These effects are considered in the context of transitioning from a 50cm2 lab scale cell to a 1100cm2 commercial scale prototype. An optimization can be achieved between flow uniformity and pumping losses. Hydrogen evolution is a parasitic reaction in many chemistries that can have a significant effect on lifetime. We have developed a simple in-tank system that captures and re-oxidizes hydrogen to maintain electrolyte stability and demonstrated this concept on a laboratory scale.[5] This investigation looks into scaling considerations and their effect on the hydrogen recombination system. Specifically, the relationship between head space, gas recirculation and the effectiveness of the reactor are considered. [1] G. Codina, J. Perez, M. Lopez-Atalaya, J. Vasquez, and A. Aldaz, J. Power Sources, 48, 293 (1994). [2] S. Takahashi and T. Hiramatsu, J. Power Sources, 17, 55 (1986). [3] M. Futamata, S. Higuchi, O. Nakamura, I. Ogino, Y. Takada, and S. Okazaki, J. Power Sources, 24, 137 (1988). [4] M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mjalli and M. Saleem, J. Electrochem.Soc., 158, 8 (2011). [5] S, Selverston, R. F. Savinell and J. S. Wainright, J. Power Sources., 324, 674, (2016).

Mössbauer spectroscopy: epoch-making biological and chemical applications

Abstract Iron is one of the most abundant elements on Earth and also in Mössbauer research. The present study is a summary of our search for iron compounds that now play an important role in the development of specific areas of inorganic chemistry of iron, biological applications and pigment for various types of artworks. The different catalytic or biologically active systems were studied in particular of the Mössbauer spectrometry, including temperature dependencies of the biological tissue and the synthetic vivianite. Mössbauer spectrometry was chosen as the main investigation tool for identification of Fe2+ and Fe3+. We are identified divalent and trivalent iron in the samples and we found their mutual ratio. The iron sandwich complexes exhibit a linear dependence between quadrupole splitting and number of methyl groups. We also determined temperature of transformation of divalent to trivalent iron for vivianite sample that are used in painting. The transformation temperature is about 90°C.

Impact of Organics and Carbonates on the Oxidation and Precipitation of Iron during Hydraulic Fracturing of Shale

Hydraulic fracturing of unconventional hydrocarbon reservoirs is critical to the United States energy portfolio; however, hydrocarbon production from newly fractured wells generally declines rapidly over the initial months of production. One possible reason for this decrease, especially over time scales of several months, is the mineralization and clogging of microfracture networks and pores proximal to propped fractures. One important but relatively unexplored class of reactions that could contribute to these problems is oxidation of Fe(II) derived from Fe(II)-bearing phases (primarily pyrite, siderite, and Fe(II) bound directly to organic matter) by the oxic fracture fluid and subsequent precipitation of Fe(III)-(oxy)hydroxides. The extent to which such reactions occur and their rates, mineral products, and physical locations within shale pore spaces are unknown. To develop a foundational understanding of potential impacts of shale iron chemistry on hydraulic stimulation, we reacted sand-sized (150–250 ...

Iron chemistry at the service of life.

Iron is an essential element for almost all organisms on Earth. It is necessary for a number of crucial processes such as hemoglobin and myoglobin transport and storage of oxygen in mammals; electron transfer support in a variety of iron-sulfur protein or cytochrome reactions; and activation and catalysis of reactions of a wide range of substrate like alkanes, olefins, and alcohols. Living organisms adopted iron as the main metal to carry out all of these functions due to the rich coordination chemistry of its two main redox states, Fe2+ and Fe3+ , and because of its abundance in the Earth's crust and oceans. This paper presents an overview of the coordination chemistry of iron that makes it suitable for a large variety of functions within biological systems. Despite iron's chemical advantages, organisms were forced to manage with some drawbacks: Fe3+ insolubility and the formation of toxic radicals, especially the hydroxyl radical. Iron chemistry within biology is an example of how organisms evolved by creating molecular machinery to overcome these difficulties and perform crucial processes with extraordinary elegance and efficiency. © 2017 IUBMB Life, 69(6):382-388, 2017.

Indefinitely stable iron(IV) cage complexes formed in water by air oxidation

In nature, iron, the fourth most abundant element of the Earth’s crust, occurs in its stable forms either as the native metal or in its compounds in the +2 or +3 (low-valent) oxidation states. High-valent iron (+4, +5, +6) compounds are not formed spontaneously at ambient conditions, and the ones obtained synthetically appear to be unstable in polar organic solvents, especially aqueous solutions, and this is what limits their studies and use. Here we describe unprecedented iron(IV) hexahydrazide clathrochelate complexes that are assembled in alkaline aqueous media from iron(III) salts, oxalodihydrazide and formaldehyde in the course of a metal-templated reaction accompanied by air oxidation. The complexes can exist indefinitely at ambient conditions without any sign of decomposition in water, nonaqueous solutions and in the solid state. We anticipate that our findings may open a way to aqueous solution and polynuclear high-valent iron chemistry that remains underexplored and presents an important challenge.

Diazoalkanes in Low-Coordinate Iron Chemistry: Bimetallic Diazoalkyl and Alkylidene Complexes of Iron(II).

The addition of (trimethylsilyl)diazomethane and its conjugate base to iron β-diketiminate precursors gives novel dinuclear complexes in which the bridges are either diazomethane derivatives or an alkylidene. One product is an unusual bridging alkylidene complex containing two three-coordinate iron(II) centers. On the other hand, syntheses using the deprotonated diazomethane give two bridging diazomethyl species with binding modes that have not been observed in iron complexes previously. In the presence of a coordinating tetrahydrofuran solvent, a diiron(II) compound with μ-N bridges rearranges to a more stable isomer with μ-N,C bridges, a process that is accompanied by a 1,3-shift of a silyl group.

Binding of ligands containing carbonyl and phenol groups to iron(iii): new Fe6, Fe10 and Fe12 coordination clusters.

The initial use of ligands 2'-hydroxyacetophenone (HL1), 2-hydroxybenzophenone (HL2) and 2,2'-dihydroxybenzophenone (H2L3) in iron(iii) chemistry is described. The syntheses and crystal structures are reported for five iron(iii) clusters: [Fe10O4(OMe)14(L1)6(MeOH)2](NO3)2·3MeOH (1·3MeOH), [Fe12O4(OH)(OMe)17(L1)8](ClO4)2·2H2O (2·2H2O), [Fe10O4(OMe)14Cl4(L2)4(MeOH)2] (3), [Fe10O4(OMe)14(L2)6(py)2](ClO4)2·MeOH (4·MeOH), where py = pyridine, and [Fe6O2(OEt)6(O2CMe)2(L3)2(HL3)2] (5). The molecular structures of the decanuclear clusters 1, 3 and 4 are organized around a {Fe10(μ4-O)4(μ3-OMe)2(μ-OMe)12}8+ core consisting of ten {Fe3O4} face-sharing defective cubane units. The core of 2 consists of a {Fe12(μ4-O)4(μ3-OMe)4(μ-OH)(μ-OMe)13}10+ unit composed of twelve {Fe3O4} face-sharing defective cubanes. The ligands (L1)- and (L2)- in 1-4 adopt the O,O'-bidentate chelating coordination mode and their roles are to terminate the further aggregation of the FeIII/O2-/RO- cores. Complex 5 contains the {Fe6(μ4-O)2(μ-OEt)6(μ-Ocarbonyl)2}4+ core, where the μ-Ocarbonyl atoms are the bridging carbonyl oxygens of the two η1:η2:η1:μ (L3)2- ligands; the (HL3)- groups behave as Ophenolate, Ocarbonyl-bidentate chelating ligands with the neutral hydroxyl group being unbound to the FeIII atoms. The core is composed of four {Fe3O4} face-sharing defective cubanes. The FeIII atoms in 1-5 are all six-coordinate with distorted octahedral geometries. The IR spectra of the complexes are discussed in terms of the known coordination modes of the ligands and the ionic character of nitrates and perchlorates. Variable-temperature magnetic susceptibility and variable-field magnetization measurements establish that 2, 3 and 5 have S = 3, 0 and 5 ground states, respectively. The susceptibility data for 5 were fitted using a 3-J model indicating the simultaneous presence of both antiferromagnetic and ferromagnetic FeIIIFeIII exchange interactions. Known magnetostructural correlations in oxido-bridged iron(iii) systems have been applied to rationalise the magnetic behaviour of the three clusters. The results of the present study demonstrate the utility of HL1, HL2 and H2L3 in the stabilisation of robust iron(iii)/oxido/alkoxido clusters.

Asymmetrically substituted triazenes as poor electron donor ligands in the precursor chemistry of iron(ii) for iron-based metallic and intermetallic nanocrystals.

Triazene ligands are introduced, for the first time, in the precursor chemistry for their ability to afford oxygen-free molecular precursors of Fe0 nanoparticles. For this purpose, we synthesized new asymmetric triazene ligands t-BuN[double bond, length as m-dash]N-NHR (R = Et, i-Pr, n-Bu) featuring different alkyl substituents at 1,3-N centers, as well as a symmetric ligand t-BuN[double bond, length as m-dash]N-NHt-Bu and used them to develop novel heteroleptic monomeric FeII triazenide derivatives [Fe(t-BuN3R)2(TMEDA)] (where TMEDA = tetramethylethylenediamine). A range of physico-chemical studies such as FT-IR, TG-DTA, 1H & 13C NMR, mass spectrometry, single crystal X-ray structure analysis, cyclic voltammetry and Mössbauer spectroscopy were used to characterize these newly synthesized ligands and FeII derivatives. One representative derivative [Fe(t-BuN3Et)2(TMEDA)] was evaluated as a precursor for the synthesis of metallic Fe0 and intermetallic Al13Fe4 nanoparticles by the chemical solution deposition method.

The Two Faces of Tetramethylcyclam in Iron Chemistry: Distinct Fe-O-M Complexes Derived from [FeIV(Oanti/syn)(TMC)]2+ Isomers.

Tetramethylcyclam (TMC, 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) exhibits two faces in supporting an oxoiron(IV) moiety, as exemplified by the prototypical [(TMC)FeIV(Oanti)(NCCH3)](OTf)2, where anti indicates that the O atom is located on the face opposite all four methyl groups, and the recently reported syn isomer [(TMC)FeIV(Osyn)(OTf)](OTf). The ability to access two isomers of [(TMC)FeIV(Oanti/syn)] raises the fundamental question of how ligand topology can affect the properties of the metal center. Previously, we have reported the formation of [(CH3CN)(TMC)FeIII-Oanti-CrIII(OTf)4(NCCH3)] (1) by inner-sphere electron transfer between Cr(OTf)2 and [(TMC)FeIV(Oanti)(NCCH3)](OTf)2. Herein we demonstrate that a new species 2 is generated from the reaction between Cr(OTf)2 and [(TMC)FeIV(Osyn)(NCCH3)](OTf)2, which is formulated as [(TMC)FeIII-Osyn-CrIII(OTf)4(NCCH3)] based on its characterization by UV-vis, resonance Raman, Mössbauer, and X-ray absorption spectroscopic methods, as well as electrospray mass spectrometry. Its pre-edge area (30 units) and Fe-O distance (1.77 Å) determined by X-ray absorption spectroscopy are distinctly different from those of 1 (11-unit pre-edge area and 1.81 Å Fe-O distance) but more closely resemble the values reported for [(TMC)FeIII-Osyn-ScIII(OTf)4(NCCH3)] (3, 32-unit pre-edge area and 1.75 Å Fe-O distance). This comparison suggests that 2 has a square pyramidal iron center like 3, rather than the six-coordinate center deduced for 1. Density functional theory calculations further validate the structures for 1 and 2. The influence of the distinct TMC topologies on the coordination geometries is further confirmed by the crystal structures of [(Cl)(TMC)FeIII-Oanti-FeIIICl3] (4Cl) and [(TMC)FeIII-Osyn-FeIIICl3](OTf) (5). Complexes 1-5 thus constitute a set of complexes that shed light on ligand topology effects on the coordination chemistry of the oxoiron moiety.

Effect of Fe (III) on Pseudokirchneriella subcapitata at circumneutral pH in standard laboratory tests is explained by nutrient sequestration.

The complex chemistry of iron (Fe) at circumneutral pH in oxygenated waters and the poor correlation between ecotoxicity results in laboratory and natural waters have led to regulatory approaches for iron based on field studies (US Environmental Protection Agency Water Quality Criteria and European Union Water Framework Directive proposal for Fe). The results of the present study account for the observed differences between laboratory and field observations for Fe toxicity to algae (Pseudokirchneriella subcapitata). Results from standard 72-h assays with Fe at pH 6.3 and pH 8 resulted in similar toxicity values measured as algal biomass, with 50% effect concentrations (EC50) of 3.28 mg/L and 4.95 mg/L total Fe(III), respectively. At the end of the 72-h exposure, however, dissolved Fe concentrations were lower than 30 μg/L for all test concentrations, making a direct toxic effect of dissolved iron on algae unlikely. Analysis of nutrient concentrations in the artificial test media detected phosphorus depletion in a dose-dependent manner that correlated well with algal toxicity. Subsequent experiments adding excess phosphorus after Fe precipitation eliminated the toxicity. These results strongly suggest that observed Fe(III) toxicity on algae in laboratory conditions is a secondary effect of phosphorous depletion. Environ Toxicol Chem 2017;36:952-958. © 2016 SETAC.

The impact of reactive surface area on brine-rock-carbon dioxide reactions in CO2 sequestration

Injection of carbon dioxide into saline aquifers is one the most promising methods for mitigating the increase in atmospheric CO2 concentrations. Reactions of CO2 with brine and formation rocks are important in determining the ultimate fate of CO2. Rates of reactions of the different relevant minerals are dependent on rate constants and mineral surface area. It is important to quantify the effect of surface area on reaction rates when different types of rock samples are employed in experiments. Batch experiments with different forms of the Berea sandstone were set up and performed at high pressure (2000 psi) and reservoir temperature (60°C) for two-week under reservoir CO2 sequestration conditions. Experiments were performed with markedly different samples (cores, rock chips, and powdered) with progressively increased surface areas. Experiments with the different forms of sandstones showed similar trends in major minerals dissolution with increase in cation concentrations of iron, magnesium, and calcium in the effluent brine. Under realistic aquifer pressure and temperature conditions, iron chemistry plays an important role in the dissolution reactions in the Berea sandstone. Reactivities increased leading to larger cationic concentrations in brine (as determined using ICP-MS) as the surface areas increased. Morphology of the reacted volume was viewed using QEMSCAN and Micro-CT for core plug samples. These experiments helped quantity the effect of surface area (higher surface area leading to more dissolution) and revealed that reactions appear to be limited more to the surface in Berea sandstone. It was shown that the factor used to obtain geometric surface area from a core decreased when samples with higher surface areas were used. This indicated that some internal surface area became available for fragmented (fractured), and powdered samples. Mineral dissolution caused the growth and expansion of pores in Berea sandstone and surface area measurements (BET) showed that the new porosity generated was characterized by a smaller pore size distribution in comparison to the unreacted one.