Formation Of Manganese Research Articles

Formation of manganese–alkyne complexes mediated by trialkylmanganates and their application

Treatment of dodec-6-yne with triallylmanganate in the presence of 1,3,5-trimethylbenzene provides (Z)-dodec-6-ene. An addition of D2O before quenching the reaction affords the corresponding dideuterated alkene. The result suggests the existence of the manganese–alkyne complex as an intermediate. Treatment of methyl propargyl ethers as alkynes with tributylmanganate generates propargylmanganese species. The reaction of non-2-ynyl tetrahydropyran-2-yl ether with tributylmanganate provides tetradec-7-yn-1,5-diol and 6-hexylocta-6,7-dien-1,5-diol.

Laser flash photolysis formation and direct kinetic studies of manganese(V)-oxo porphyrin intermediates.

Irradiation of porphyrin-manganese(III) perchlorate complexes in acetonitrile with 355 nm laser light gave MnV-oxo intermediates that were characterized by their UV-vis spectra and reactivities. The MnV-oxo species of tetrakis(pentafluorophenyl)porphyrin (2), tetraphenylporphyrin (4), and tetra-(4-(N-methylpyridiniumyl))porphyrin (6) were generated. Second-order rate constants for reactions of 2 with substrates were as follows: 6.1 x 105 M-1 s-1 (cis-stilbene), 1.3 x 105 M-1 s-1 (diphenylmethane), 1.3 x 105 M-1 s-1 (ethylbenzene), and 0.55 x 105 M-1 s-1 (ethylbenzene-d10). In oxidations of cis-stilbene and diphenylmethane, the order of reactivity of the MnV-oxo species was 2 > 6 > 4.

Diverse microbial communities inhabiting ferromanganese deposits in Lechuguilla and Spider Caves.

Lechuguilla Cave is an ancient, deep, oligotrophic subterranean environment that contains an abundance of low-density ferromanganese deposits, the origin of which is uncertain. To assess the possibility that biotic factors may be involved in the production of these deposits and to investigate the nature of the microbial community in these materials, we carried out culture-independent, small subunit ribosomal RNA (SSU rRNA) sequence-based studies from two sites and from manganese and iron enrichment cultures inoculated with ferromanganese deposits from Lechuguilla and Spider Caves. Sequence analysis showed the presence of some organisms whose closest relatives are known iron- and manganese-oxidizing/reducing bacteria, including Hyphomicrobium, Pedomicrobium, Leptospirillum, Stenotrophomonas and Pantoea. The dominant clone types in one site grouped with mesophilic Archaea in both the Crenarchaeota and Euryarchaeota. The second site was dominated almost entirely by lactobacilli. Other clone sequences were most closely related to those of nitrite-oxidizing bacteria, nitrogen-fixing bacteria, actinomycetes and beta- and gamma-Proteobacteria. Geochemical analyses showed a fourfold enrichment of oxidized iron and manganese from bedrock to darkest ferromanganese deposits. These data support our hypothesis that microorganisms may contribute to the formation of manganese and iron oxide-rich deposits and a diverse microbial community is present in these unusual secondary mineral formations.

The photochemical metal organic deposition of manganese oxide films from films of manganese(II) 2-ethylhexanoate: a mechanistic study

The photochemistry of thin films of manganese(II) 2-ethylhexanoate to produce manganese oxide films is presented. Thin films of manganese(II) 2-ethylhexanoate can be cast onto silicon wafers by spin coating. The FTIR spectroscopy of these films suggests they exist as chains or clusters with the manganese(II) centers linked by bridging 2-ethylhexanoate ligands. The initial photochemical reaction results in the loss of the bridging 2-ethylhexanoate ligands and the formation of monomeric manganese(II) 2-ethylhexanoate. In this process approximately 60% of the bridging 2-ethylhexanoate ligand is converted to chelating 2-ethylhexanoate while the other 40% fragments to form CO 2, heptane and heptene. Further photolysis resulted in the conversion of the remaining 2-ethylhexanoate ligand to form CO 2, heptane and heptene. The film consisted of manganese(II) oxide although the surface of the film was more oxidized and had carbon impurity on it. Annealing the film resulted in the conversion to polycrystalline α-Mn 2O 3.

Phase transformations in the thermoactivated MnO x–Al 2O 3 catalytic system

The phenomenon of the sharp increase of activity in reactions of deep oxidation found for the manganese oxide–alumina system calcined at 900–1000 °C was named as thermoactivation effect. This effect was shown to be associated with phase transformations in this system. Peculiarities of phase transformations in the MnO x /Al 2O 3 system after its calcination at 950 °C for 1–10 h were studied with XRD, TEM, XPS methods; the catalysts activity in deep oxidation of n-pentane was measured in a flow-circuit setup. It was found that a set of phase transformations occurred in the system, starting from the formation of the metastable nonstoichiometric manganese–alumina cubic spinel (after 1–2 h calcination) and nonequilibrium solid solution of Mn 3+ ions in the structure of γ-Al 2O 3 which decomposes producing high-temperature aluminas modified by manganese ions and particles of imperfect β-Mn 3O 4 phase doped with aluminium ions. Increase of the calcination time to 10 h and more results in the formation of biphasic system composed of α-Al 2O 3 and nanocrystalline β-Mn 3O 4 modified by Al 3+ ions. These transformations are associated with the maximum activity showed by catalysts calcined for 5–6 h in the reaction of n-pentane combustion.

Oxidative precipitation of arsenic(III) with manganese(II) and iron(II) in dilute acidic solution by ozone

Oxidative precipitation using ozone has been examined for removal of arsenic with manganese from dilute acidic sulfate solution under the following conditions: the initial concentrations of arsenic(III) and arsenic(V)=1–100 mg/L, the initial mole ratio of Mn/As=10–100, pH=0.4–5.0 and temperature=15–80 °C. The oxidation–reduction potential (ORP) of the system was continuously measured to monitor the process of oxidation reactions. The O 3–O 2 gas mixture (ozone partial pressure=0.010–0.031 atm, feed rate=500 mL/min) was found to produce an adequately high potential to oxidize arsenic(III) and then manganese(II). By formation of manganese(III) arsenate and uptake of arsenic by manganese dioxide formed by ozone oxidation, arsenic entities are removed to a sufficiently low concentration to meet the regulation against arsenic contaminant level for industrial waste water in Japan (0.1 mg/L) in the pH range 1.0–3.0 at 25 °C, where coprecipitation with ferric hydroxide is not very effective to remove arsenic. Furthermore, coexistence of an appropriate amount of iron(II) promotes significantly removal of arsenic with manganese at pH below 3 by ozonation.

Surfactant-mediated synthesis of metal substituted hexaaluminate from alumina sol

Manganese substituted hexaaluminate has been prepared using environmentally benign surfactants such as Triton X-100, under ambient condition with a commercial alumina sol and metal acetate precursors. The surface area of the pure alumina can be controlled to 10–70m2g−1 using cetyltrimethylammonium chloride after heating in oxygen flow at 1200°C for 6h. The crystal structure of the obtained alumina was high purity θ-Al2O3. Incorporation of La and Mn leads to the formation of the high purity manganese substituted hexaaluminate with a surface area of 30–40m2g−1 which is also controllable using organic additives such as urea. The catalytic activity of the manganese substituted hexaaluminate was comparable to the sol–gel derived hexaaluminate catalyst from metal alkoxides.

Thermodynamic and structural aspects of manganese(II) complexes with polyaminopolycarboxylic ligands based upon 1,4,7,10-tetraazacyclododecane (cyclen). Crystal structure of dimeric [MnL]2·2CH3OH containing the new ligand 1,4,7,10-tetraazacyclododecane-1,4-diacetate

The formation of manganese(II) complexes with polyaminopolycarboxylic ligands based upon 1,4,7,10-tetraazacyclododecane (cyclen) has been studied in aqueous solution by means of potentiometric and microcalorimetric techniques affording log K, ΔH° and TΔS° values for the complexation reactions. The ML complexes present high stability constants, due to both favourable enthalpic and entropic contributions; with the unique exception of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), the entropic term is prevalent. The new ligand 1,4-DO2A (1,4,7,10-tetraazacyclododecane-1,4-diacetic acid) forms a more stable complex than the 1,7-DO2A isomer. The thermodynamic results are discussed in terms of ligand characteristics: number and type of donor atoms, overall charge, substituent location. The crystal structure of [MnL]2·2CH3OH (H2L = 1,4-DO2A), obtained by single crystal X-ray analysis, displays a centrosymmetric dimeric [Mn2L2] unit in which each manganese atom is seven-coordinated by four nitrogen atoms of a cyclen macrocycle, one oxygen atom of each of the acetate groups linked to this macrocyclic unit, and one oxygen atom pertaining to an acetate group of the other cyclen molecule in the same dimeric unit and bridging the two metal centers. The resulting binuclear complex contains a doubly bridged bimetallic core with Mn ⋯ Mn distance of 3.537(1) A.

A review of the geology of the dolomite-dominated carbonatite complexes of the Kalahari Craton, southern Africa

Drill core and outcrop samples of pure marine chemical sediments (banded iron formation (BIF), manganese formation (MnF), jaspilites, lutites, and cherts) from the transition of the ~2426 Ma old Ongeluk Formation into the 2413 Ma old Hotazel Formation, Transvaal Supergroup, South Africa, reveal remarkable changes of seawater chemistry in the Transvaal Ocean. Similar to pre-Ongeluk chemical sediments, the shale-normalized rare earths and yttrium (REYSN) patterns of jaspilites intercalated with the volcanic rocks of the Ongeluk large igneous province and directly overlying cherts do not show positive EuSN anomalies, indicating that high-temperature (>250 °C) hydrothermal fluids did not contribute significantly to the REY budget of ambient waters. However, a 10 cm drill core section in the lower Hotazel Formation is characterized by conspicuous positive EuSN anomalies, revealing temporary inflow of water masses strongly affected by high-temperature hydrothermal fluids. After this short episode, the REYSN pattern of Transvaal seawater returned to that of pre-Ongeluk times, showing heavy REYSN enrichment, positive LaSN, GdSN and YSN anomalies, but no CeSN or EuSN anomalies. Higher up in the stratigraphy, the Hotazel Formation shows negative CeSN anomalies in some of the lutites, BIFs and MnFs, reflecting Ce depletion in ambient seawater. All Hotazel lutite, BIF, and MnF samples studied show unradiogenic εNd(t) values (−0.5 ± 0.2 to −2.4 ± 0.2), indicating a mostly continental REY source. The REY distribution and Nd isotope data combined suggest that oxidative terrestrial weathering of this continental crustal source supplied most of the dissolved REY to local “Transvaal seawater”. Precipitation of the Hotazel lutites, BIFs and MnFs with negative CeSN anomalies, therefore, suggests that oxic conditions prevailed on the Kaapvaal Craton and in Hotazel seawater already at ~2.413 Ga, i.e. 80 m.y. before the disappearance of mass-independent sulfur isotope fractionation (MIF-S) that defines the Great Oxidation Event at ~2.33 Ga.

First example of electroassisted biomimetic activation of molecular oxygen by a (salen)Mn epoxidation catalyst in a room-temperature ionic liquid

A first example of electroassisted activation of molecular oxygen by Jacobsen′s epoxidation catalyst in an ionic liquid at room temperature has been achieved and showed the formation of the postulated high-valent manganese–oxo active intermediate.

Ionic Processes in Saturated Solutions of MgCl2·6H2O in Solutions of Other Divalent Metals

Solubility isotherms of MgCl2·6H2O at 25 °C in solutions of chlorides of bivalent beryllium, calcium, manganese, iron, cobalt, zinc and mercury were treated by the hydration analysis. In addition to the usual procedure, the recently developed modified transfer energy Ξ was used to characterize the situation in saturated solutions. As a result, the following ionic processes were established in the saturated solutions under consideration: competition for water in solutions of MgCl2·6H2O containing beryllium and calcium chloride, complex formation in solutions of MgCl2·6H2O containing manganese, cobalt, zinc and mercury ions and formation of ions with heterogeneous coordination sphere in solutions of MgCl2·6H2O containing iron or copper ions. In the last case, the ability of the formed ions to crystallize from solution was found to be reduced in comparison with the other cases. Activity coefficients of MgCl2 were calculated along the solubility curves under consideration.

Electrochemical synthesis of neutral Mn(III) complexes with asymmetrical N 2O 2 Schiff base ligands

Interaction of new potentially tetradentate trianionic chelating ligands [H 3-4Me-amsal-R=3-aza-4-(2-hydroxyphenyl)-N-(2-hydroxy-4-methylphenyl)but-3-enamide, R=H; 5Cl; 5Br; 3OEt; 3OMe,5Br; 3,5Cl; 3,5Br; 3Br,5Cl; 3Br,5NO 2] with manganese has been investigated employing an electrochemical method. This method leads to the formation of neutral manganese(III) complexes in high yield and purity. These neutral manganese complexes have been thoroughly characterised by elemental analysis, infrared and paramagnetic 1H NMR spectroscopy, fast atom bombardment (FAB) mass spectrometry, magnetic susceptibility measurements and cyclic voltammetry.

THE MANGANESE FORMATION OF THE NEOPROTEROZOIC PENGANGA GROUP, INDIA—REVISION OF AN ENIGMA—A REPLY

Sir : We welcome the opportunity to reply to criticism raised by Roy to our publication on the origin of the Neoproterozoic Penganga manganese formation (Gutzmer and Beukes, 1998). Roy’s strong misgivings with our contribution center on only one point, namely our conclusion that the todorokite-rich oxide ores mined from shallow trenches by artisan miners is of supergene origin and formed at the expense of a carbonate protore that we discovered. Our interpretation is in obvious contrast to the results of work by Roy and coworkers (Roy, 1981; Bandopadhyay, 1988, 1989, 1996; Roy et al., 1990) who have classified the todorokite-rich ore to be of primary sedimentary origin. We believe that Roy, with his discussion of our publication, enters into a dispute that has been resolved for many manganese deposits originally thought to comprise primary oxide ores that were later found to be the product of supergene alteration of a carbonate protore. The best example for such supergene development is the economically very important Nsuta manganese deposit, Ghana. This deposit, which has been exploited continuously for over 80 years, was originally thought to be composed of primary manganese oxides (Kitson and Junner, 1927; Service, 1943; Bates, 1958). The manganese carbonate protore was discovered beneath the lateritic oxide cap only after more than 40 …

Mass-spectrometric study of formation and stability of manganese and manganese oxide cluster anions

We present a mass-spectrometric investigation of the reactions of manganese cluster anions Mn x − (in the size range x = 2–12) with molecular oxygen in the gas phase. The manganese and manganese oxide cluster anions are studied in a pulsed supersonic molecular beam experiment and generated in a conventional laser vaporization cluster source with an additional flow tube reactor. Relative reactivities are determined at near room temperature as a function of oxygen partial pressure, cluster size, and composition. We observed for the first time the controlled formation of at least four stable manganese oxide series: Mn x O −, Mn x O 2 −, Mn x O 3 −, and Mn x O 4 − ( x = 2–12). The reactivities decrease rapidly with cluster size reaching a minimum around Mn 4 − and Mn 5 −. They increase smoothly with further increasing cluster size and show no significant pressure dependence for clusters of x > 5. The adsorption of molecular oxygen on the cluster surface most probably takes place in a dissociative way resulting in the formation of distinct Mn–O bonds. The Mn 5 − cluster exhibits a special behavior. It has the highest intensity in mass spectra and shows the lowest reactivity towards oxygen. Another interesting feature is the evolution of an intense Mn 2O − peak with increasing oxygen pressure.

Effects of hydrogen on carbon and manganese containing steels at high temperature

Hydrogen promotes the decarburization of carbon containing alloys. However, our results show that manganese partially retains carbon in the substrate probably due to the formation of stable manganese containing carbides. The decarburization rate also depends upon the metallic structure : between 600 and 900°C, a two phase metal (ferrite + perlite or ferrite + austenite) leads to a linear weight loss kinetic regime limited by an interfacial reaction. Above 1000°C, the austenite structure induces a parabolic weight loss regime showing that the process is limited by the carbon diffusion in the alloy. The effect of hydrogen on pure iron, a carbon free specimen, leads us to conclude that iron swelling at 700°C is due to the di-hydrogen recombination from atomic hydrogen dissolved inside the substrate.

Increase of Oxygen in the Earth's Atmosphere and Hydrosphere between −2.5 and −2.4 Ga B.P.

Currently, two competing concepts that both are based on (amongst others) the Fe-Ti systematics of palaeosols, try to describe the evolution of the oxygen content of the Precambrian Earth's atmosphere. One model favours a rapid and significant increase of atmospheric oxygen levels during the Palaeoproterozoic (summarized in Holland, 1994), whereas another suggests that only minor changes of less than _ 50% occurred throughout Earth's history (summarized in Ohmoto, 1997). Although the former is currently more widely accepted than the latter, it suffers from two shortcomings: (i) the validity of the conclusions derived from the palaeosol record rely heavily on the assumption of absence of organic matter from Archaean and Palaeoproterozoic weathering profiles, and (ii) the time of the postulated increase of atmospheric oxygen is rather poorly constrained due to large uncertainties of some palaeosol ages; nevertheless, however, the rapid increase is suggested to have occurred between c. 2.2 and 1.9 Ga B.P. (Holland, 1994). Thus, there is need for (i) other redox-indicators that are able to provide at least qualitative evidence for a rather constant or an increasing redox-level of the Precambrian atmosphere-hydrosphere system, but which are rather insensitive to the presence or absence of organic matter, and (ii) evidence from samples that originate from well-dated profiles with a (for Precambrian standards) reasonably good time resolution. Hence, we studied the distribution of Mn and rareearth elements (REEs) in only slightly metamorphosed chemical platform sediments from the Kuruman and Griquatown Iron-Formations (IFs) and the Hotazel Manganese-Formation (MnF), and in palaeoweathering products in the Transvaal Supergroup, South Africa. While the only abundant primary oxide minerals in the Kuruman and Griquatown IFs are Fe(III) oxides, the Hotazel MnF is the oldest largescale deposit of Mn(III) oxides in the geological record. The results bear clear evidence for a rapid increase of the oxygen content of both, the Earth's ocean and atmosphere between -2.5 and -2.4 Ga B.P.

40Ar/39Ar Dating of African Manganese Pisolites: Implication for Cenozoic Climatic Changes

Chemical and mechanical weathering-derived processes are among the most efficient factors in modifying the Earth surface. Weathering gradients are strongly dependent upon temperature, rainfall and tectonic stability over geological time. In this way, the upper part of tropical and sub-tropical cratonic lithosphere has been transformed into thick supergene lateritic mantles with frequent metal accumulations. In West Africa, the lateritic weathering episodes have developed from early Tertiary successive crusts that have controlled the local geomorphology. These indurated formations are evidence of the successive weathering and erosion cycles. In this way, laterites that constitutes the rain forest substratum, may trace the palaeoclimate evolution. One of the best opportunities to date weathering events is to apply the 4~ method on isotopically closed supergene K-bearing minerals such as K-Mn oxides from the hollandite group (AxBsO16, nH20 , where A represents K +, Ba 2+, pb2+or Na + and B represents Mn 3§ Mn 4+, Fe3+,). Initiated by Chukhrov et aI. (1966), using the K-Ar dating method, direct dating of potassium-rich manganese oxides was widely facilitated by the recent development of the 4~ laser probe method as shown by the studies of Vasconcelos et al. (1992 and 1994) and Ruffet et al. (1996). Cryptomelane is well represented in numerous lateritic manganese weathering profiles over the tropical belt. Then radiochronological study may help to understand the genesis of the Mn-lateritic systems and to correlate them to the development of Fe-laterites. This work presents analytical performances of the 4~ argon-ion laser probe method in 'dating' K-rich samples of the pisolitic manganese formation and the underlying manganese crust of the Tambao deposit (northern Burkina Faso).

Stereoelectronic Aspects of Inter-Metal Nitrogen Atom Transfer Reactions between Nitridomanganese(V) and Chromium(III) Porphyrins

Reactions of nitridomanganese(V) porphyrins with chromium(III) porphyrins resulted in the irreversible formation of nitridochromium(V) porphyrins and manganese(III) porphyrins. The progress of these reactions has been followed spectrophotometrically, electrochemically, and spectroscopically by EPR. Kinetic analysis of the spectrophotometric data obtained during these reactions for a variety of substituted porphyrins showed the reactions to be first order in each of the reactants. Rate constants were dependent upon the electronic and steric effects of the porphyrin substituent, upon the identity of the anion bound to the chromium(III) reactant, and upon the solvent dielectric constant. We propose that the mechanism of these nitrogen atom transfer reactions involves the nucleophilic attack of the nitridomanganese porphyrin donor on the cationic chromium(III) porphyrin acceptor facilitating a net, two-electron redox process mediated by a heterobimetallic μ-nitrido intermediate. This report represents the first systematic study of the stereoelectronic effects involved in the complete, inter-metal nitrogen atom transfer between two metalloporphyrins.

Environmental Contamination and Human Exposure to Airborne Total and Respirable Manganese in Montreal

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organometallic compound used as an octane improver in unleaded gasoline. The combustion of MMT leads to the formation of manganese (Mn) oxides, mainly Mn3O4. The objective of this study is to assess the variations over time and space of respirable (MnR) and total (MnT) Mn in the urban atmosphere and to evaluate human exposure by inhalation. Two sampling sites were selected on the island of Montreal based on their local traffic density (municipal botanical garden, C-= 10,000–15,000 vehicles d-1; Montreal Waterworks, C+= 100,000–130,000 vehicles d-1). Air samplings were made during the day at stations located 10 m from the road using portable pumps, some of which were equipped with a cyclone. MnR and MnT and other metals were measured on Teflon filters by neutron activation. Mn exposure doses by inhalation were calculated using Monte–Carlo simulations. MnR and MnT average concentrations were significantly higher at site C+ (MnR = 0.024 µg m-3; MnT = 0.050 µg m-3) than at site C- (MnR= 0.015 µg m-3; MnT= 0.027 µg m-3). Temporal profiles at sites C+ and site C-were similar, with a coefficient of correlation of 0.24 for MnR and 0.26 for MnT. Trend analyses (ARIMA) also showed that the period of the week (work days vs. off days) was significantly related to MnR and MnT variations at both sites. The average exposure dose by inhalation to MnR and MnT ranged from 0.001 to 0.030 µg kg-1 day-1 and 0.001 to 0.05 µg kg-1 day-1. MnR and MnT concentrations reflected a positive relationship with traffic density. However, it remains difficult to attribute these results directly to the combustion of MMT in unleaded gasoline. On average, the MnR and MnT inhalation doses were 2 to 15 times lower than the reference dose (RfC) proposed by the U.S. Environmental Protection Agency (EPA) for the general population.

Kinetic investigations into the mechanism of peroxosulfate oxidation of Calmagite dye catalysed by manganese(II) ions

Manganese(II) ions were found to be capable of catalysing the peroxosulfate (KHSO5) oxidation of Calmagite, a dye containing the o,o′-dihydroxy azo structural motif at pH 10 but not the more common monohydroxy azo dyes or those that contain no o-hydroxy group. The catalysed decomposition of Calmagite results in decomposition profiles that resemble an autocatalytic process, i.e. the reaction rate increases as dye concentration decreases. Spectroscopic investigations indicated that two complexes are formed between MnII and Calmagite (D), having 1∶1 and 1∶2 stoichiometries, i.e. [MnD] and [MnD2]. Under experimental conditions [KHSO5] ≫ [D] ≫ [MnII] so the catalyst exists in the form [MnD2] and it is shown that the unusual kinetics are due to a reaction of order -1 in [D]. This negative order is explained by attributing [MnD] as the active catalyst, formed from the inert [MnD2], with which it is in equilibrium, by the loss of one dye molecule. The experimental data were found to conform to the rate expression –d[D]/dt = k0[MnII][KHSO5]/[D] and the rate constant k0 can be determined from plots of [D]2 against time. It is concluded that a key factor for promoting catalysis is specific complexation of MnII to the dye substrate, and that the o,o′-dihydroxy azo structural unit is specifically required for efficient manganese catalysis. Some insight into the mechanism of catalysis was obtained by investigating MnIII as catalyst and from studies where H2O2 was employed as the oxidant. It is proposed that the mechanism involves nucleophilic attack by oxidant on the metal centre followed by peroxide-bond scission, leading to formation of manganese-(III) or -(IV) species which subsequently initiate dye oxidation via an inner-sphere reaction mechanism.