FeII Species Research Articles

Synthesis, general physicochemical behaviour and magnetic studies of the macrocyclic bis-pyridine derivatives [TTDPzM(py)2]·2H2O (M = MnII, CoII, NiII)

In our extensive work on phthalocyanine-like macrocycles carrying peripherally attached strongly electron-withdrawing 1,2,5-thia/selenodiazol rings we recently reported on the FeII species of formula [TTDPzFe(py)2].2H2O (TTDPz = tetrakis(thiadiazole)porphyrazinato dianion). The present work deals with the synthesis and extended physicochemical studies of the series of related macrocycles [TTDPzM(py)2].2H2O (M = MnII, CoII, NiII). The diffractograms of three solid samples of the NiII complex [TTDPzNi(py)2]·2H2O, obtained from different synthetic procedures, indicate that the species is reproducibly obtained. All three samples are isomorphous with each other as shown by their X-ray powder diffractograms. Based on the comparison of the IR spectra of [TTDPzNi(py)2].2H2O and the related desolvated [TTDPzNi], the IR absorption peaks belonging to the pyridine molecules could be identified. The systematic presence of the two water molecules in all three species suggests that forms of contact do exist in the form of hydrogen bonds between them and the S and N atoms present peripherally in the thiadiazole groups of the macrocyclic units. As regard to the elimination of water, the thermograms (in inert atmosphere in the range 25–600 °C) indicate in all cases that loss of water occurs below 100 °C but loss of pyridine occurs over a broad range 100–300 °C for the MnII and CoII species whereas for the NiII complex it takes place in the narrow range 200–220 °C. In relation to the parallel series of metallophthalocyanines, i.e. [PcM] (M = MnII, FeII, CoII), it is noted that the NiII analog has not been reported in the literature and in a direct experiment it has been proved that [PcNi] heated in pyridine is obtained unchanged, the different behavior for the NiII TTDPz derivative due to the electron withdrawing effect of the external thiadiazole substituents, which makes favorable axial pyridine coordination in the complex. Completely insoluble in water, the triad of TTDPz derivatives is extremely low-soluble in non-donor or low donor solvents. This precluded any attempt to isolate single crystals for single-crystal X-ray work. Their UV–visible spectra show essential similarities in whatever organic solvent is used with clearly positioned Soret (300–400 nm) and Q-band absorptions (630–650 nm). Variable temperature magnetic susceptibility and magnetization studies reveal that the [TTDPzM(py)2].2H2O complexes all show paramagnetism with ground state spins of 3/2 (MnII), ½ (CoII) and 1 (NiII), supported by fitting the data to spin Hamiltonian formalism, vide infra. Comparisons are made with the magnetism of [PcM] analogues with key differences noted for M = NiII.

The role of iron(II) excess and phosphate to synthesize hydroxychloride green rust

Green rust (GR) is a chemically reactive mineral of interest for environmental remediation. However, the lack of stability of this compound is a major drawback for practical applications. In this study, the precipitation of hydroxychloride green rust type 1 (GR1Cl) from soluble FeII and FeIII species was studied by analyzing pH titration curves and employing XRD, Raman and Mössbauer spectroscopies to find optimal conditions for synthesizing GR1Cl. Using the stoichiometric condition for FeII-FeIII corresponding to the [FeII3FeIII(OH)8]Cl compound, FeIIIO(OH)2.9Cl0.1 was formed in a first step during the addition of NaOH and then transformed into a mixture of GR1Cl and Fe3O4. The addition of phosphate anions (PO4) at a molar ratio PO4: Fe = 1: 10 in the initial solution was shown to avoid the formation of undesired magnetite. Interestingly, GR1Cl was also the only product without adding PO4 using an excess of FeII species in solution, i.e. for an initial ferric molar fraction x = FeIII: Fetot of 0.2. First experimental evidences of a hydroxyphosphate green rust type 2 GR2PO4 were also provided by XRD and Raman spectroscopy. Therefore, this work may attract interest for a better understanding of the geochemical cycle of iron and phosphate in natural environments such as hydromorphic soils or hydrothermal chimneys where fougerite, the mineral homologue of synthetic GR, is supposed to play a significant role.

X-ray chemical imaging for assessing redox microsites within soils and sediments

Redox reactions underlie several biogeochemical processes and are typically spatiotemporally heterogeneous in soils and sediments. However, redox heterogeneity has yet to be incorporated into mainstream conceptualizations and modeling of soil biogeochemistry. Anoxic microsites, a defining feature of soil redox heterogeneity, are non-majority oxygen depleted zones in otherwise oxic environments. Neglecting to account for anoxic microsites can generate major uncertainties in quantitative assessments of greenhouse gas emissions, C sequestration, as well as nutrient and contaminant cycling at the ecosystem to global scales. However, only a few studies have observed/characterized anoxic microsites in undisturbed soils, primarily, because soil is opaque and microsites require µm-cm scale resolution over cm-m scales. Consequently, our current understanding of microsite characteristics does not support model parameterization. To resolve this knowledge gap, we demonstrate through this proof-of-concept study that X-ray fluorescence (XRF) 2D mapping can reliably detect, quantify, and provide basic redox characterization of anoxic microsites using solid phase “forensic” evidence. First, we tested and developed a systematic data processing approach to eliminate false positive redox microsites, i.e., artefacts, detected from synchrotron-based multiple-energy XRF 2D mapping of Fe (as a proxy of redox-sensitive elements) in Fe-“rich” sediment cores with artificially injected microsites. Then, spatial distribution of FeII and FeIII species from full, natural soil core slices (over cm-m lengths/widths) were mapped at 1–100 µm resolution. These investigations revealed direct evidence of anoxic microsites in predominantly oxic soils such as from an oak savanna and toeslope soil of a mountainous watershed, where anaerobicity would typically not be expected. We also revealed preferential spatial distribution of redox microsites inside aggregates from oak savanna soils. We anticipate that this approach will advance our understanding of soil biogeochemistry and help resolve “anomalous” occurrences of reduced products in nominally oxic soils.

Catechol‐Isolated Atomically Dispersed Nanocatalysts for Self‐Motivated Cocatalytic Tumor Therapy

AbstractNanocatalytic tumor therapy based on Fenton nanocatalysts has attracted considerable attention because of its therapeutic specificity, enhanced outcomes, and high biocompatibility. Nevertheless, the rate‐determining step in Fenton chemistry, which involves the transition of a high‐valence metallic center (FeIII) to a Fenton‐active low‐valence metallic center (FeII), has hindered advances in nanocatalyst‐based therapeutics. In this study, we constructed mesoporous single iron atomic nanocatalysts (mSAFe NCs) by employing catechols from dopamine to coordinate and isolate single iron atoms. The catechols also serve as reductive ligands, generating a field‐effect‐based cocatalytic system that instantly reduces FeIII species to FeII species within the mSAFe NCs. This self‐motivated cocatalytic strategy enabled by mSAFe NCs accelerates the kinetics of the Fenton catalytic reaction, resulting in remarkable performance for nanocatalytic tumor therapy both in vitro and in vivo.

Catechol-Isolated Atomically Dispersed Nanocatalysts for Self-Motivated Cocatalytic Tumor Therapy.

Nanocatalytic tumor therapy based on Fenton nanocatalysts has attracted considerable attention because of its therapeutic specificity, enhanced outcomes, and high biocompatibility. Nevertheless, the rate-determining step in Fenton chemistry, which involves the transition of a high-valence metallic center (FeIII ) to a Fenton-active low-valence metallic center (FeII ), has hindered advances in nanocatalyst-based therapeutics. In this study, we constructed mesoporous single iron atomic nanocatalysts (mSAFe NCs) by employing catechols from dopamine to coordinate and isolate single iron atoms. The catechols also serve as reductive ligands, generating a field-effect-based cocatalytic system that instantly reduces FeIII species to FeII species within the mSAFe NCs. This self-motivated cocatalytic strategy enabled by mSAFe NCs accelerates the kinetics of the Fenton catalytic reaction, resulting in remarkable performance for nanocatalytic tumor therapy both in vitro and in vivo.

Synthesis of the new bis-pyridine adduct [TTDPzFe(py)2]⋅2H2O, and its detailed solid state properties examined by its magnetic behavior

The air-stable hydrated FeII species [TTDPzFe(py)2]⋅2H2O (1; TTDPz = tetrakis(thiadiazole)- porphyrazinato dianion) is reproducibly obtained by reaction of the corresponding unmetalated species [TTDPzH2] with the FeII salt (NH[Formula: see text]Fe(SO[Formula: see text]⋅6H2O. Experimental interconnection between the bis-pyridine derivative 1 and the bis-adduct of known crystal structure [TTDPzFe(DMSO)2] (2) and the desolvated complex [TTDPzFe] (3) has been observed possible, with the formation in the air from the latter of the hydrated species [TTDPzFe]⋅2H2O (4). Reported here are the general properties of complex 1 accurately examined as a solid in terms of its physicochemical properties, in comparison with those of the phthalocyanine analog [PcFe(py)2], in terms of the magnetic behavior examined via Mössbauer spectra and magnetic susceptibility measurements under specified experimental conditions over a large range of temperature (300-4 K).

Developing the Ascorbic Acid Test: A Candidate Standard Tool for Characterizing the Intrinsic Reactivity of Metallic Iron for Water Remediation

Granular metallic iron (gFe0) materials have been widely used for eliminating a wide range of pollutants from aqueous solutions over the past three decades. However, the intrinsic reactivity of gFe0 is rarely evaluated and existing methods for such evaluations have not been standardized. The aim of the present study was to develop a simple spectrophotometric method to characterize the intrinsic reactivity of gFe0 based on the extent of iron dissolution in an ascorbic acid (AA—0.002 M or 2 mM) solution. A modification of the ethylenediaminetetraacetic acid method (EDTA method) is suggested for this purpose. Being an excellent chelating agent for FeII and a reducing agent for FeIII, AA sustains the oxidative dissolution of Fe0 and the reductive dissolution of FeIII oxides from gFe0 specimens. In other words, Fe0 dissolution to FeII ions is promoted while the further oxidation to FeIII ions is blocked. Thus, unlike the EDTA method that promotes Fe0 oxidation to FeIII ions, the AA method promotes only the formation of FeII species, despite the presence of dissolved O2. The AA test is more accurate than the EDTA test and is considerably less expensive. Eight selected gFe0 specimens (ZVI1 through ZVI8) with established diversity in intrinsic reactivity were tested in parallel batch experiments (for 6 days) and three of these specimens (ZVI1, ZVI3, ZVI5) were further tested for iron leaching in column experiments (for 150 days). Results confirmed the better suitability (e.g., accuracy in assessing Fe0 dissolution) of the AA test relative to the EDTA test as a powerful screening tool to select materials for various field applications. Thus, the AA test should be routinely used to characterize and rationalize the selection of gFe0 in individual studies.

Highly Efficient Electroenzymatic Cascade Reduction Reaction For The Conversion of Nitrite to Ammonia

AbstractThe electrochemical nitrite reduction reaction provides an alternative approach to offer sustainable ammonia source routes for repairing imbalances in the global nitrogen cycle. In this work, electrocatalysis is combined with enzymatic catalysis to provide an efficient and clean process for recoverable ammonia production. NO2− is reduced to NH3 by electroenzymatic cascade reduction reaction on a bioconjugate, in which 1‐butyl‐3‐methylimidazolium bromide (ILBMB) modified chloroperoxidase (CPO) is fixed on polyethyleneimine (PEI) modified multi‐walled carbon nanotubes (MWCNT) to from bioconjugate (CPO‐ILBMB/MWCNT‐PEI). 15N and 14N isotope labeling reveal that the NH3 species is derived from NO2− reduction. Density functional theory calculations identify that the FeII species in heme center of CPO serve as the key active site for NO2− reduction. The amino groups derived from MWCNT‐PEI not only serve as a bridge to covalently immobilize CPO but also enrich the NO2− ion at electrode/solution interface through electrostatic interactions. The low energy barrier of NO2− reduction and low adsorption free energy of the intermediate result in high Faradaic efficiency (96.4%), NH3 yield (112.7 mg h−1 mgCPO−1), and high selectivity in pH 5.0 solution. The highly efficient electroenzymatic reaction ensurespromising applications in the conversion of NO2− to NH3.

Fe(II) complexes of pyridine-substituted thiosemicarbazone ligands as catalysts for oxidations with hydrogen peroxide.

The reaction of three [FeII(TSC)2] complexes, where TSC is a pyridine-substituted thiosemicarbazone of the HDpT or HBpT families, with H2O2 in acetonitrile solution does not result in the accumulation of the corresponding [FeIII(TSC)2]+ complexes. Instead, a mixture of diamagnetic low-spin FeII species is generated. According to the MS spectra, those species result from the sequential addition of up to five oxygen atoms to the complex. This capability for the addition of oxygen atoms suggested that oxygen atom transfer to external substrates may be possible, and these TSC complexes were tested in the oxidation of thioanisole and styrene with H2O2. As hypothesized, the complexes are active in both the oxidation of thioanisole to its sulfoxide and styrene to benzaldehyde, with time scales indicating the participation of the species containing added oxygen atoms. Interestingly, the free thiosemicarbazone ligands and the [Zn(Dp44mT)2] complex also catalyse the selective sulfoxidation of thioanisole, but they are ineffective in catalysing styrene oxidation to benzaldehyde. These findings open up new directions for the development of thiosemicarbazone-based metal catalysts for oxidation processes.

Low-temperature Mössbauer spectroscopy of organs from 57Fe-enriched HFE(−/−) hemochromatosis mice: an iron-dependent threshold for generating hemosiderin

Hereditary hemochromatosis is an iron-overload disease most often arising from a mutation in the Homeostatic Fe regulator (HFE) gene. HFE organs become overloaded with iron which causes damage. Iron-overload is commonly detected by NMR imaging, but the spectroscopic technique is insensitive to diamagnetic iron. Here, we used Mössbauer spectroscopy to examine the iron content of liver, spleen, kidney, heart, and brain of 57Fe-enriched HFE(−/−) mice of ages 3–52 wk. Overall, the iron contents of all investigated HFE organs were similar to the same healthy organ but from an older mouse. Livers and spleens were majorly overloaded, followed by kidneys. Excess iron was generally present as ferritin. Iron–sulfur clusters and low-spin FeII hemes (combined into the central quadrupole doublet) and nonheme high-spin FeII species were also observed. Spectra of young and middle-aged HFE kidneys were dominated by the central quadrupole doublet and were largely devoid of ferritin. Collecting and comparing spectra at 5 and 60 K allowed the presence of hemosiderin, a decomposition product of ferritin, to be quantified, and it also allowed the diamagnetic central doublet to be distinguished from ferritin. Hemosiderin was observed in spleens and livers from HFE mice, and in spleens from controls, but only when iron concentrations exceeded 2–3 mM. Even in those cases, hemosiderin represented only 10–20% of the iron in the sample. NMR imaging can identify iron-overload under non-invasive room-temperature conditions, but Mössbauer spectroscopy of 57Fe-enriched mice can detect all forms of iron and perhaps allow the process of iron-overloading to be probed in greater detail.Graphical

Engineering Single-Atom Iron Nanozymes with Radiation-Enhanced Self-Cascade Catalysis and Self-Supplied H2O2 for Radio-enzymatic Therapy.

Single-atom nanozymes (SAzymes), with individually isolated metal atom as active sites, have shown tremendous potential as enzyme-based drugs for enzymatic therapy. However, using SAzymes in tumor theranostics remains challenging because of deficient enzymatic activity and insufficient endogenous H2O2. We develop an external-field-enhanced catalysis by an atom-level engineered FeN4-centered nanozyme (FeN4-SAzyme) for radio-enzymatic therapy. This FeN4-SAzyme exhibits peroxidase-like activity capable of catalyzing H2O2 into hydroxyl radicals and converting single-site FeII species to FeIII for subsequent glutathione oxidase-like activity. Density functional theory calculations are used to rationalize the origin of the single-site self-cascade enzymatic activity. Importantly, using X-rays can improve the overall single-site cascade enzymatic reaction process via promoting the conversion frequency of FeII/FeIII. As a H2O2 producer, natural glucose oxidase is further decorated onto the surface of FeN4-SAzyme to yield the final construct GOD@FeN4-SAzyme. The resulting GOD@FeN4-SAzyme not only supplies in situ H2O2 to continuously produce highly toxic hydroxyl radicals but also induces the localized deposition of radiation dose, subsequently inducing intensive apoptosis and ferroptosis in vitro. Such a synergistic effect of radiotherapy and self-cascade enzymatic therapy allows for improved tumor growth inhibition with minimal side effects in vivo. Collectively, this work demonstrates the introduction of external fields to enhance enzyme-like performance of nanozymes without changing their properties and highlights a robust therapeutic capable of self-supplying H2O2 and amplifying self-cascade reactions to address the limitations of enzymatic treatment.

Unmasking the Iron-Oxo Bond of the [(Ligand)Fe-OIAr]2+/+ Complexes.

ArIO (ArI = 2-(tBuSO2)C6H4I) is an oxidant used to oxidize FeII species to their FeIV-oxo state, enabling hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions at low energy barriers. ArIO, as a ligand, generates masked Fen=O species of the type Fe(n-2)-OIAr. Herein, we used gas-phase ion–molecule reactions and DFT calculations to explore the properties of masked iron–oxo species and to understand their unmasking mechanisms. The theory shows that the I–O bond cleavage in [(TPA)FeIVO(ArIO)]2+ (12+, TPA = tris(2-pyridylmethyl)amine)) is highly endothermic; therefore, it can be achieved only in collision-induced dissociation of 12+ leading to the unmasked iron(VI) dioxo complex. The reduction of 12+ by HAT leads to [(TPA)FeIIIOH(ArIO)]2+ with a reduced energy demand for the I–O bond cleavage but is, however, still endothermic. The exothermic unmasking of the Fe=O bond is predicted after one-electron reduction of 12+ or after OAT reactivity. The latter leads to the 4e– oxidation of unsaturated hydrocarbons: The initial OAT from [(TPA)FeIVO(ArIO)]2+ leads to the epoxidation of an alkene and triggers the unmasking of the second Fe=O bond still within one collisional complex. The second oxidation step starts with HAT from a C–H bond and follows with the rebound of the C-radical and the OH group. The process starting with the one-electron reduction could be studied with [(TQA)FeIVO(ArIO)]2+ (22+, TQA = tris(2-quinolylmethyl)amine)) because it has a sufficient electron affinity for electron transfer with alkenes. Accordingly, the reaction of 22+ with 2-carene leads to [(TQA)FeIIIO(ArIO)]2+ that exothermically eliminates ArI and unmasks the reactive FeV–dioxo species.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Photoactive Fe Catalyst for Light-Triggered Alkyd Paint Curing.

Herein, we show that the photoactive complexes [(Cp)Fe(arene)]+ (Cp = cyclopentadienyl; arene = C6H6, C6H5Me) act as latent catalysts that allow for photochemical control over the onset of alkyd paint curing, without the need for antiskinning agents such as the volatile 2-butanone oxime normally used to prevent curing during paint storage. The highly soluble neutral complexes [(Cp)Fe(Ch)] and [(Cp)Fe(Ch′)] (Ch = cyclohexadienyl, Ch′ = methylcyclohexadienyl) readily convert to the photoactive complexes [(Cp)Fe(arene)]+ upon oxidation in alkyd, allowing the latter to be dosed in a wide range of concentrations. Infrared and Raman studies show similar spectral changes of the alkyd paint matrix as have been observed in alkyd curing mediated by well-known, industrially applied cobalt- and manganese-based catalyst Co(neodecanoate)2 and [(Me3TACN)2Mn2(μ-OOCR)3](OOCR). The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]+ system performs equally well as these cobalt- and manganese-based catalysts in terms of drying time and outperform the manganese catalyst by showing a hardness development (increase) similar to that of the cobalt-based catalyst. Based on electron paramagnetic resonance and light–activity studies, we propose that photolysis of [(Cp)Fe(arene)]+ generates short-lived active FeII species, explaining the desired latency. The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]+ alkyd curing systems presented herein are unique examples of intrinsically latent paint curing catalysts that (1) are based on an abundant and harmless transition metal (Fe), (2) do not require any antiskinning agents, and (3) show favorable performance in terms of drying times and hardness development.

Co-existence of five- and six-coordinate iron(II) species captured in a geometrically strained spin-crossover Hofmann framework.

Inclusion of an angular bridging ligand, 4,2':6',4''-terpyridine (TPy), into a Hofmann-type framework produces an irregular network in which six- and five-coordinate FeII species co-exist. The octahedral sites show thermally-induced spin-crossover (SCO) and the rare five-coordinate FeII sites are high-spin.

Active in Sleep: Iron Guanidine Catalyst Performs ROP on Dormant Side of ATRP.

Copolymers are the answer to property limitations of homopolymers. In order to use the full variety of monomers available, catalysts active in more than one polymerization mechanism are currently investigated. Iron guanidine catalysts have shown to be extraordinarily active in ROP of lactide and herein prove their versatility by also promoting ATRP of styrene. The presented iron complex is the first polymerizing lactide and styrene simultaneously to a defined block copolymer in a convenient one‐pot synthesis. Both mechanisms work hand in hand with ROP using the dominantly present FeII species on the dormant side of the ATRP equilibrium. This orthogonal copolymerization by a benign iron catalyst opens up new pathways to biocompatible polymerization procedures broadening the scope of ATRP applications.

Relevance of Single-Transmetalated Resting States in Iron-Mediated Cross-Couplings: Unexpected Role of σ-Donating Additives.

Control of the transmetalation degree of organoiron(II) species is a critical parameter in numerous Fe-catalyzed cross-couplings to ensure the success of the process. In this report, we however demonstrate that the selective formation of a monotransmetalated FeII species during the catalytic regime counterintuitively does not alone ensure an efficient suppression of the nucleophile homocoupling side reaction. It is conversely shown that a fine control of the transmetalation degree of the transient FeIII intermediates obtained after the activation of alkyl electrophiles by a single-electron transfer (SET), achievable using σ-donating additives, accounts for the selectivity of the cross-coupling pathway. This report shows for the first time that both coordination spheres of FeII resting states and FeIII short-lived intermediates must be efficiently tuned during the catalytic regime to ensure high coupling selectivities.

Enzymatic Cascade Reactions Mediated by Highly Efficient Biomimetic Quasi Metal-Organic Frameworks.

The integration of chemo- and enzymatic catalysis for effective multistep cascades has presented critical challenges for decades. In this work, the biomimetic quasi NH2-MIL-101 (qNM) with highly efficient peroxidase-like activity was synthesized via a palmitic acid-induced strategy followed by pyrolysis. The effects of the amount of palmitic acid and calcination temperature on the synthesis of qNM were optimized. It was found that qNM was an excellent catalyst for oxidations of various peroxidase substrates, and a possible mechanism was proposed, i.e., the presence of FeII species in qNM was responsible for its excellent activity, which facilitated the transition between FeII and FeIII species to produce more hydroxyl radicals by H2O2 decomposition. The qNM served as the potential matrix for enzyme immobilization through a cross-linking method, and kinetic studies revealed that the catalytic efficiency (kcat/Km) for the immobilized GOx (23.7 mM-1 s-1) is comparable to that of free GOx (26.9 mM-1 s-1). The immobilized GOx also showed improved stability against high temperatures and organic solvents compared to free GOx, and analysis of the secondary structure of GOx indicated that the improved stability resulted from enzyme rigidity by the intense covalent linkage with qNM. Furthermore, qNM contributed its biomimetic activity to cooperate with a single enzyme (GOx) or two enzymes (β-Gal and GOx) for the enzymatic cascade reactions. Compared with the mixture of each component in the solution, the combination of the single-enzyme system (GOx) or the two-enzyme system (β-Gal and GOx) in qNM achieved 2.67-fold and 1.83-fold enhancements in the activity of catalytic cascades, respectively. This study provides new insights into the construction of effective and synergistic cascade reactions by integrating biomimetic MOF with natural enzyme, which holds potential for applications in biotechnology and ecofriendly and biomimetic catalysis.

Tuning the electronic properties of tetradentate iron-NHC complexes: Towards stable and selective epoxidation catalysts

Two sets of bio-inspired non-heme iron complexes, each comprising of an FeII and FeIII species, bearing 16-membered macrocyclic tetradentate N-heterocyclic carbene ligands are reported. The complexes exhibit trans labile coordination sites, are characterized by means of NMR, ESI-MS, elemental analysis, SC-XRD and cyclic voltammetry and assessed as olefin epoxidation (pre-)catalysts applying H2O2 as oxidant. Sc(OTf)3 and AcOH are evaluated as Lewis and Brønsted acidic additives, respectively, resulting in partially noticeable improvement in catalytic performance. Hereby, complex 2b shows high stability (TON = 1000 at 20 °C), high temperature tolerance and advances in the more challenging epoxidation of terminal and functionalized olefins. Furthermore, in-depth DFT calculations are conducted to put the catalysts’ structural and electronic features into relation with the catalytic results.

Birnessite: A New Oxidant for Green Rust Formation.

Iron and manganese are ubiquitous in the natural environment. FeII-FeIII layered double hydroxide, commonly called green rust (GR), and MnIII-MnIV birnessite (Bir) are also well known to be reactive solid compounds. Therefore, studying the chemical interactions between Fe and Mn species could contribute to understanding the interactions between their respective biogeochemical cycles. Moreover, ferromanganese solid compounds are potentially interesting materials for water treatment. Here, a {Fe(OH)2, FeIIaq} mixture was oxidized by Bir in sulphated aqueous media in the presence or absence of dissolved O2. In oxic conditions for an initial FeII/OH− ratio of 0.6, a single GR phase was obtained in a first step; the oxidation kinetics being faster than without Bir. In a second step, GR was oxidised into various final products, mainly in a spinel structure. A partial substitution of Fe by Mn species was suspected in both GR and the spinel. In anoxic condition, GR was also observed but other by-products were concomitantly formed. All the oxidation products were characterized by XRD, XPS, and Mössbauer spectroscopy. Hence, oxidation of FeII species by Bir can be considered as a new chemical pathway for producing ferromanganese spinels. Furthermore, these results suggest that Bir may participate in the formation of GR minerals.