Mn Compounds Research Articles

A combination of super-resolution fluorescence and magnetic resonance imaging using a Mn(ii) compound

Two manganese(ii) complexes supported by terpyridyl-based ligands were synthesized; they showed an enhanced fluorescence, including a two-photon signal and magnetic contrast, and were used in multi-modal imaging.

Interaction of Co, Mn, and Fe Atoms with Calcite: An X-Ray Photoelectron Spectroscopy Study

Adsorption of Co, Mn, and Fe atoms on the surface of calcite in ultrahigh vacuum and the interaction of the generated adsorption systems with water were studied by X-ray photoelectron spectroscopy. It is demonstrated that Mn and Fe atoms form CaCO3/Mn(Fe)CO3 solid solutions on calcite surface, whereas the dominant compounds of adsorbed Co atoms are CoО and Co3О4. When interacting with water, the Mn and Fe surface compounds are not appreciably modified, whereas the Co compounds are partly transformed into soluble hydroxylated complexes.

Effect of Dopant Concentrations on Magnetic States of Ti, Mn, And Ni Doped Iii-V Zincblende Compounds

The effect of Ti, Mn, and Ni dopants concentration on various magnetic states of III-V zincblende compounds (Al1-xTx)M is presented by calculation of multiple scattering theory based on Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA), where T denotes Ti, Mn, and Ni atoms and M represents As and P atoms. The calculations reveal the phase changes in various magnetic states, which are solely controlled by dopant concentrations. The turning points of these behaviors are reported, which are responsible for the change of stable ferromagnetic (FM) state to unstable disordered local moment (DLM) state. The Curie temperature, magnetic moments, and density of states at different concentrations of the dopants are calculated and explain the concurrency with magnetic phase stability.
 Journal of Bangladesh Academy of Sciences, Vol. 42, No. 2, 177-182, 2018

Slime from sulfuric acid shop of Balkhash copper-smelting factory – alternative source for production of selenium at the enterprise. Review

The article covers the problems of possibility for involving selenium from the slime of the sulfuric acid shop of the Balkhash Copper Smelting Plant (BCSP) into the sphere of its production. At pyrometallurgical processing of copper charge, selenium is sublimated and distributed among four waste products: washing sulfuric acid, slimes of sulfuric acid and electrolyte shop, and electrofilter dust. In the world, the main raw material for the production of selenium is copper electrolytic sludge (90 %) and sludge of sulfuric acid production of the chemical and pulp and paper industry (10 %). A comparative analysis of selenium content in the slimes of the metallurgical, chemical and pulp and paper industries showed that the content of selenium in the slimes of the sulfuric acid shops of the BCSP and “Kola Company” JSC is identical and much higher than in copper electrolytic slimes – the main source of selenium in the world. The qualitative, quantitative, granulometric and material compositions of the slime of the BCSP’s sulfuric acid shop are presented. It contains Pb, Se, Re, Al, Si, S, Ca, Fe, Cu, Zn, Sr, Cd, I, Hg, Ni, Br, Bi, As, Sb, Ag, Cr, Mg, Mo, Ti, Mn, and organic compounds (presumably, aliphatic acids). The content of some elements is several tens of percent, others – hundredths of a percent. Interest for the recovery is Se (4.6–32.3 5 wt. %), and furthermore are Re (0.14 wt. %), I (0.33 wt. % Hg (0.57 wt. %). Slime-forming element is lead in the form of its sulfate. Into the size class -0.4 + 0 the following are recovered Pb – 47.84 %, Se – 47.45 %, Re 55.31 %. The content of the elements in classes of different sizes is almost identical: Pb (56.7-58.1 wt. %), Se (4.00-4.51 wt. %), Re (0.10-0.16 wt. %.). Selenium in the slime is in the forms of the elemental – of three modifications, lead selenate and a substance containing the selenite anion. With the slime disposed to sewage treatment plants, 30-40 % of selenium, produced from copper electrolyte slime in Balkhash, is lost. Following facts are a strong argument for involving these slimes into the sphere of selenium production. They are the high content of selenium in slime of sulfuric acid shop, in perspective taken out as an independent product when introducing the technology of rhenium extraction from washing solutions, the presence of selenium production at the plant and the predicted selenium deficit in the world due to introduction of new technologies.

Hybrid improper ferroelectricity in B-site substituted Ca3Ti2O7: The role of tolerance factor

Hybrid improper ferroelectricity is induced by the coupling of oxygen octahedral rotation and tilting, and a promising way to create multiferroic materials with a strong magnetoelectric effect can be proposed. Although some hybrid improper ferroelectric materials with Ruddlesden-Popper structures have been discovered experimentally, the small polarizations and high coercive fields will severely limit their practical applications. To deal with this issue, an alternative way is proposed by the first-principles calculations in the present work. By calculating the energies of phases with oxygen octahedral rotation and tilting in Ca3TiMO7 (M = Si, Ge, Mn, Sn, Hf, and Zr) compounds with five B-site ordering configurations, it is found that the tolerance factor has a considerable impact on their ferroelectric properties. The energy barriers and ferroelectric polarizations increase with decreasing tolerance factor. Moreover, the individual-layer contributions to the total polarizations depend on the space group, which is also decided by the tolerance factor of the compound. Therefore, to enhance the ferroelectric polarization in B-site substituted Ca3Ti2O7, the tolerance factor should be decreased according to the calculation results of this work.

Non-Pincer Mn(I) Organometallics for the Selective Catalytic Hydrogenation of Nitriles to Primary Amines

We report herein selective catalytic hydrogenation of nitriles to primary amines with the use of the non-pincer Mn(I) compound fac-[(CO)3Mn{iPr2P(CH2)2PiPr2}(OTf)] (2) as a catalytic precursor (3 mol %) in the presence of KOtBu (10 mol %) and 2-BuOH as solvent. Benchmark benzonitrile and electron-rich aromatic and aliphatic nitriles were hydrogenated under rather mild conditions (7 bar, 90 °C, 15 min) to produce the corresponding amines in excellent to very good isolated yields (83–97%, six examples). Increasing the H2 pressure and time (35 bar, 30 min) allowed for the production of (di)amines in excellent yields (94–98%, three examples) from electron-deficient aromatic nitriles and terephthalonitrile. Notably, adiponitrile was reduced to hexamethylenediamine in 53% isolated yield. Finally, mechanistic insights were performed and suggested unsaturated Mn-hydride species performing the elementary steps during catalytic turnover.

Structure and properties of Mn3O4 thin films grown on single crystal substrates by chemical vapor deposition

Mn3O4 thin films were fabricated on SrTiO3(111) and Y3Al5O12(100) substrates by chemical vapor deposition (CVD) under O2 atmospheres, starting from a fluorinated Mn(II) diketonate-diamine adduct. The obtained systems were investigated by a multi-technique characterization in order to elucidate the interplay between preparation conditions and their chemico-physical properties. The results highlighted the formation of phase-pure and homogeneous α-Mn3O4 (haussmannite) films, characterized by a smooth morphology, an appreciable Vis light absorption and structural features directly dependent on the used substrate. The target systems were uniformly doped with fluorine, due to the used Mn compound acting as a single-source precursor for both Mn and F. In addition, magnetic force microscopy measurements revealed the formation of spin domains and long-range magnetic order in the target materials, paving the way to their future implementation as magnetic media toward device integration for data storage.

Synthesis, crystal structure and properties of Cd(NCS)2 coordination compounds with two different Cd coordination modes

Abstract Reaction of Cd(NCS)2 with 4-methoxypyridine leads to the formation of four new compounds, of which one crystallizes in two different polymorphs. In Cd(NCS)2(4-methoxypyridine)4·(4-methoxypyridine)2 (1) and Cd(NCS)2(4-methoxypyridine)4 (2-I and 2-II) discrete complexes are found, in which the Cd cations are octahedrally coordinated by four 4-methoxypyridine co-ligands and two terminally N-bonded thiocyanate anions. For the polymorphs 2-I and 2-II no single crystals are available and therefore, the corresponding Mn(II) compound (2-I-Mn) was prepared, which is isotypic to 2-I, as proven by a Rietveld refinement. The crystal structure of 2-II was solved and refined from XRPD data. In [Cd(NCS)2(4-methoxypyridine)2] n (3), the Cd cations are also octahedrally coordinated but linked into linear chains by pairs of thiocyanate anions with all ligands in trans-position. {[Cd(NCS)2]3(4-methoxypyridine)5} n (4) also consists of chains but two different Cd coordination modes are observed. Two of the three crystallographically independent Cd cations show an octahedral coordination with a trans- or cis-arrangement of the N and S atoms of the anionic ligands, whereas the third one is in a distorted square-pyramidal coordination, with cis-coordination of the thiocyanate N and S atoms. Measurements using simultaneous thermogravimetry and differential scanning calorimetry of 2-I and 2-II show different heating rate dependent mass steps, in which the co-ligands are removed. In some of the residues obtained after the respective TG steps compound 3 was detected but no phase pure samples could be obtained.

A New Mixed-Valence Mn(II)Mn(III) Compound With Catalase and Superoxide Dismutase Activities.

The synthesis, X-ray molecular structure, physico-chemical characterization and dual antioxidant activity (catalase and superoxide dismutase) of a new polymeric mixed valence Mn(III)Mn(II) complex, containing the ligand H2BPClNOL (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)] propylamine) is described. The monomeric unit is composed of a dinuclear Mn(II)Mn(III) moiety, [Mn(III)(μ-HBPClNOL)(μ-BPClNOL)Mn(II)(Cl)](ClO4)·2H2O, 1, in which the Mn ions are connected by two different bridging groups provided by two molecules of the ligand H2BPClNOL, a phenoxide and an alkoxide group. In the solid state, this mixed valence dinuclear unit is connected to its neighbors through chloro bridges. Magnetic measurements indicated the presence of ferromagnetic [J = +0.076(13) cm−1] and antiferromagnetic [J = −5.224(13) cm−1] interactions. The compound promotes O dismutation in aqueous solution (IC50 = 0.370 μmol dm−3, kcat = 3.6x106 M−1 s−1). EPR studies revealed that a high-valent Mn(III)-O-Mn(IV) species is involved in the superoxide dismutation catalytic cycle. Complex 1 shows catalase activity only in the presence of a base, e.g., piperazine or triethylamine. Kinetic studies were carried out in the presence of piperazine and employing two different methods, resulting in kcat values of 0.58 ± 0.03 s−1 (detection of O2 production employing a Clark electrode) and 2.59 ± 0.12 s−1 (H2O2 consuption recorded via UV-Vis). EPR and ESI-(+)-MS studies indicate that piperazine induces the oxidation of 1, resulting in the formation of the catalytically active Mn(III)-O-Mn(IV) species.

Seasonal dynamics of manganese and iron compounds in the superficial waters of Vidsichne water intake of Teteriv River

Research aim – to determine features of the season dynamics of concentrations of manganese (Мn) and iron (Fe) in the surface waters of Vidsichne water intake, Teteriv river in 2012–2014 and clarification of their correlations with the water temperature, hydrogen index (рН), content of dissolved oxygen (DO), and also by the number of dominating associations of planktonic algae.Methods. Water samples (1 dm3) were taken from the water intake (at realizing arrangements for cleaning and deepening its bottom part), and Mn and Fe compounds concentrations were determined in them by colorimetric methods, DO – by DO 4000 measurer, hydrogen index – by рН-meter, temperature – by the mercury thermometer. For studying the phytoplankton content, there was realized the hydrobiological analysis. The statistical processing of data was realized by MO Excel 2003 program.Research results. Mn compounds concentration in water exceeded MPCw and had two peak values in summer. Fe compounds were also observed in increased amounts, but their peak was in another season every year. There were revealed reliable correlations of strong and middle Mn concentrations in water with a temperature and DO. The tendency to strengthening correlations of concentrations of these compounds with blue-green algae and weakening – with green ones was demonstrated. Mutual connections of Fe with these parameters were in whole weaker comparing with Mn, especially with рН and planktonic algae. And only in 2014 coefficient values of correlation between iron and temperature and DO essentially grew.Conclusions. It was established, that concentrations of Mn and Fe compounds in water of the water intake exceeded MPCw during most seasons (0,1 and 0,3 mg/dm3 respectively) in 2-8 times. The most content of Mn was observed especially in summer months, and Fe – in different seasons. Changes of Mn concentrations were much stronger connected with the water temperature (0,7029, р≤0,01 – in 2012 and 0,6702, р≤0,05 – 2013 years) and DO (-0,6272, р≤0,05 – in 2012, -0,8752, р≤0,0001 – 2013 and -0,6349, р≤0,05 – 2014 years), than ones of Fe concentrations. Correlations of Fe compounds with these parameters reaches reliability only in 2014 year (0,7326 and -0,7469 respectively, р≤0,01). Mn and Fe compounds had reliable connections only with blue-green algae (cyanogen bacteria) among all phytoplankton associations: Mn (0,6808, р≤0,05) – in 2014 and Fe (0,7410, р≤0,01) – in 2012. During the three year period of the studies there was fixed weakening connections between Mn and water temperature (by 28,54 %) and amounts of green algae (by 65,63 %) and strengthening – with amounts of blue-green ones (by 77,95 %), and also the growing dependence of Fe compounds concentrations on the temperature (by 79,12 %) and DO (by 95,77 %). Most revealed tendencies (except season dynamics of Mn and its correlations with the temperature, DO and amounts of blue-green ones) were atypical for the water intake and appeared, most probably, as a result of arrangements for cleaning the bottom part of the water body and its deepening that resulted in disorders in the condition of the water environment, including the abnormal increase of blue-green algae amounts in December of 2012 (up to 91,06 thousand cl/dm3)

Coordination behaviour, molecular docking, density functional theory calculations and biological activity studies of some transition metal complexes of bis‐Schiff base ligand

Coordination compounds of Mn (II), Fe (III), Co (II), Ni (II), Cu (II) and Cd (II) ions were synthesized from reaction with Schiff base ligand 4,6‐bis((E)‐(2‐(pyridin‐2‐yl)ethylidene)amino)pyrimidine‐2‐thiol (HL) derived from the condensation of 4,6‐diaminopyrimidine‐2‐thiol and 2‐(pyridin‐2‐yl)acetaldehyde. Microanalytical data, magnetic susceptibility, infrared and 1H NMR spectroscopies, mass spectrometry, molar conductance, powder X‐ray diffraction and thermal decomposition measurements were used to determine the structure of the prepared complexes. It was found that the coordination between metal ions and bis‐Schiff base ligand was in a molar ratio of 1:1, with formula [M (HL)(H2O)2] Xn (M = Mn (II), Co (II), Ni (II), Cu (II) and Cd (II), n = 2; Fe (III), n = 3). Diffuse reflectance spectra and magnetic susceptibility measurements suggested an octahedral geometry for the complexes. The coordination between bis‐Schiff base ligand and metal ions was through NNNN donor sites in a tetradentate manner. After preparation of the complexes, biological studies were conducted using Gram‐positive (B. subtilis and S. aureus) and Gram‐negative (E. coli and P. aeruginosa) organisms. Metal complexes and ligand displayed acceptable microbial activity against both types of bacteria.

New insight into the reactivity of Mn(III) in bisulfite/permanganate for organic compounds oxidation: The catalytic role of bisulfite and oxygen

A recently discovered bisulfite(HSO3−)/permanganate(MnO4−) system was reported to produce highly reactive free Mn(III) that can oxidize organic compounds in milliseconds. However, this characteristic reactivity was not found in all other known reaction systems that can also produce free Mn(III). Why can Mn(III) in NaHSO3/KMnO4 be so active? Here, we found NaHSO3 and O2 acted as catalysts for the reaction between Mn(III) and organic compounds. Without O2, 0% of organic compounds were oxidized in NaHSO3/KMnO4, indicating the absence of O2 inactivated Mn(III) reactivity. When the reaction between NaHSO3 and KMnO4 was monitored in air, Mn(III) catalyzed rapid oxidation of NaHSO3 by O2. Then, the Mn(III) that could oxidize organic compounds was found to be the ones involved in the catalytic reaction between NaHSO3 and O2, thus the link between O2 and Mn(III) reactivity was established. Finally, NaHSO3/O2 can be viewed as catalysts for the reaction between Mn(III) and organic compounds because 1) when Mn(III) was involved in oxidizing organic compounds, it stopped being the catalyst for the reaction between NaHSO3 and O2 so that they were consumed to a much smaller extent; and 2) without NaHSO3 and O2, Mn(III) lost its oxidation ability. To the best of our knowledge, this is the first report on “catalytic role exchange” where Mn(III) is the catalyst for NaHSO3/O2 reaction while NaHSO3/O2 are the catalysts for Mn(III)/organic compounds reaction. Understanding the critical role of oxygen in NaHSO3/KMnO4 will enable us to apply this technology more efficiently toward contaminant removal.

Magnetic structure and spin correlations in magnetoelectric honeycomb Mn4Ta2O9

The coupling between magnetic ordering and electric polarization in magnetoelectrics is technically relevant and not yet completely understood. The elucidation of this requires a comprehension of underlying magnetic interactions and the electronic structure. Here, the authors investigate the magnetoelectric honeycomb compound Mn${}_{4}$Ta${}_{2}$O${}_{9}$, by means of neutron scattering and electronic structure calculations, to reveal the ingredients that determine the ground state. For this compound, the ground state is determined by an electron correlation assisted magnetic dipole-dipole interaction. The investigation here offers detailed insight into the factors that determine the ground-state manifold and the role of electron correlation on the strength of anisotropy.

Syntheses and Crystal Structures of Mn(II), Ni(II) and Cu(II) Coordination Compounds Assembled by Maleato and Dimethyl-2,2′-bipyridines

Three complexes: {[Mn(H2O)(mal)(5dmb)·H2O}n] (1); [Ni2(H2O)6(mal)2(4dmb)2]·3H2O (2); [Cu2(mal)2(4dmb)2]·3H2O (3); where mal = maleato, 4dmb = 4,4′-dimethyl-2,2′-bipyridine, and 5dmb = 5,5′-dimethyl-2,2′-bipyridine; have been synthesized, using self-assembly solution reactions at ambient conditions. Crystallographic studies show that 1 crystallizes in an orthorhombic system, space group Pna21, with a = 17.4067(4) A, b = 11.9672(2) A, c = 8.2075(2) A; V = 1709.70(6) A3. Complex 2 has a monoclinic system, space group C2/c, with a = 21.206(8) A, b = 7.523(3) A, c = 25.399(10) A; β = 109.755(8)°; V = 3813(2) A3. Complex 3 crystallizes in a monoclinic system, space group C2/c, with a = 14.6976(12) A, b = 11.3849(10) A, c = 22.1638(18) A; β = 101.2998(17)°; V = 3636.8(5) A3. Complex 1 is a one-dimensional (1D) polymer, where the Mn centers are six-coordinated in a distorted octahedral geometry. 2 is a dinuclear complex, generated by supramolecular interactions, where Ni ions are six-coordinated in a distorted octahedral geometry. 3 is a dinuclear complex with five-coordinated Cu ions having a distorted square pyramidal geometry. All three complexes exhibit hydrogen bonding interactions, which generate 2D supramolecular structures in 1 and 2, whereas in complex 3 a 3D supramolecular array is formed. These novel complexes prove that the self-assembly of a dicarboxylate ligand (mal) with three different first-row transition metals, can afford coordination compounds with diverse structural characteristics and dimensionality, which can be attributed to the different ligand coordination modes and the coordination properties of the employed metals. Divergent coordination compounds of three different transition metals have been obtained due to the versatility in the coordination modes of maleato ligand.

Magnetic, electronic, and transport properties of the high-pressure-synthesized chiral magnets Mn1−xRhxGe

We report on structural, magnetic and transport properties of a new set of the high-pressuresynthesized compounds Mn$_{1-x}$Rh$x$Ge ($0 \leq x \leq 1$) with the chiral magnetic ordering. The magnetic and transport properties depend substantially on the concentration of rhodium (x) and the pressure. The saturation magnetic moment corresponds to a known high-spin value for pristine MnGe (x = 0) and decreases almost linearly with increasing concentration $x$. In addition, XMCD spectra taken at 10 K and 2 T indicate magnetic polarization of the Rh 4d electron states and Ge $4p$ states, which decreases with $x$, too. In rhodium rich compounds ($x \geq 0.5$) the temperature of the magnetic ordering increases significantly with pressure, whereas in manganese rich compounds ($x < 0.5$) the temperature decreases. Three different tendencies are also found for several structural and transport properties. In the intermediate range ($0.3 \leq x \leq 0.7$) samples are semiconducting in the paramagnetic phase, but become metallic in the magnetically ordered state. We carried out ab initio density-functional calculations of Mn$_{1-x}$Rh$_x$Ge at various concentrations $x$ and traced the evolution of electronic and magnetic properties. The calculation results are in good agreement with the measured magnetic moments and qualitatively explain the observed trends in transport properties.

Effect of Mn and AlTiB Addition and Heattreatment on the Microstructures and Mechanical Properties of Al-Si-Fe-Cu-Zr Alloy.

The microstructure and mechanical properties of as-extruded Al-0.1 wt%Si-0.2 wt%Fe- 0.4 wt%Cu-0.04 wt%Zr-xMn-xAlTiB (x = 1.0 wt%) alloys under various annealing processes were investigated and compared. After the as-cast billets were kept at 400 °C for 1 hr, hot extrusion was carried out with a reduction ratio of 38:1. In the case of the as-extruded Al-Si-Fe-Cu-Zr alloy at annealed at 620 °C, large equiaxed grain was observed. When the Mn content is 1.0 wt%, the phase exhibits a skeleton morphology, the phase formation in which Mn participated. Also, the volume fraction of the intermetallic compounds increased with Mn and AlTiB addition. For the Al-0.1Si-0.2Fe-0.4Cu-0.04Zr alloy with Mn and AlTiB addition from 1.0 wt%, the ultimate tensile strength increased from 100.47 to 119.41 to 110.49 MPa. The tensile strength of the as-extruded alloys improved with the addition of Mn and AlTiB due to the formation of Mn and AlTiB-containing intermetallic compounds.

Heat treatment of MnCO3: An easy way to obtain efficient and stable MnO2 for humid O3 decomposition

The competitive water adsorption in the practical environment usually causes severe deactivation of the O3 decomposition catalysts. In this study, MnCO3 was used as precursor to prepare efficient and stable MnO2 catalyst for gaseous O3 decomposition in humid stream. The sample S-300, prepared by calcining MnCO3 at 300 °C for 6 h, exhibited 63% (80%) of removal efficiency for 120 (43) ppm of O3 under a high space velocity of 600 L g−1 h−1 and 50% (40%) of relative humidity at 25 °C, which is superior to the commercial O3 scrubber (oxide compound of Cu and Mn) and α-MnO2. However, even lower or higher treatment temperature did not further promote humid O3 decomposition. Thorough characterizations, especially by the temperature programmed and in situ DRIFTs experiments, demonstrate that the large amount of active oxygen vacancies and strong Lewis-acid sites together with the easy recovery of the occupied oxygen vacancies and weak interaction with water molecules accounted for the excellent O3 decomposition activity in humid stream. Besides, the developed pores by thermal decomposition of MnCO3 might also facilitate O3 removal. This study provides an easy and rational design of affordable and efficient catalysts for environmental application.

Structure-Property Relations in Multiferroic [(CH3)2NH2] M(HCOO)3 ( M = Mn, Co, Ni).

We bring together magnetization, infrared spectroscopy, and lattice dynamics calculations to uncover the magnetic field-temperature ( B- T) phase diagrams and vibrational properties of the [(CH3)2NH2] M(HCOO)3 ( M = Mn2+, Co2+, Ni2+) family of multiferroics. While the magnetically driven transition to the fully saturated state in [(CH3)2NH2]Mn(HCOO)3 takes place at 15.3 T, substitution with Ni or Co drives the critical fields up toward 100 T, an unexpectedly high energy scale for these compounds. Analysis of the infrared spectrum of the Mn and Ni compounds across TC reveals doublet splitting of the formate bending mode which functions as an order parameter of the ferroelectric transition. By contrast, [(CH3)2NH2]Co(HCOO)3 reveals a surprising framework rigidity across the order-disorder transition due to modest distortions around the Co2+ centers. The transition to the ferroelectric state is thus driven by the dimethylammonium cation freezing and the resulting hydrogen bonding. Under applied field, the Mn (and most likely, the Ni) compounds engage the formate bending mode to facilitate the transition to their fully saturated magnetic states, whereas the Co complex adopts a different mechanism involving formate stretching distortions to lower the overall magnetic energy. Similar structure-property relations involving substitution of transition-metal centers and control of the flexible molecular architecture are likely to exist in other molecule-based multiferroics.

Kα X-ray Emission Spectroscopy on the Photosynthetic Oxygen-Evolving Complex Supports Manganese Oxidation and Water Binding in the S3 State.

The unique manganese-calcium catalyst in photosystem II (PSII) is the natural paragon for efficient light-driven water oxidation to yield O2. The oxygen-evolving complex (OEC) in the dark-stable state (S1) comprises a Mn4CaO4 core with five metal-bound water species. Binding and modification of the water molecules that are substrates of the water-oxidation reaction is mechanistically crucial but controversially debated. Two recent crystal structures of the OEC in its highest oxidation state (S3) show either a vacant Mn coordination site or a bound peroxide species. For purified PSII at room temperature, we collected Mn Kα X-ray emission spectra of the S0, S1, S2, and S3 intermediates in the OEC cycle, which were analyzed by comparison to synthetic Mn compounds, spectral simulations, and OEC models from density functional theory. Our results contrast both crystallographic structures. They indicate Mn oxidation in three S-transitions and suggest additional water binding at a previously open Mn coordination site. These findings exclude Mn reduction and render peroxide formation in S3 unlikely.

New room-temperature ferromagnet: B-added [formula omitted] alloy

Mn-based room-temperature ferromagnets attract considerable attention due to their high ordered Mn moment. We have found that a Pd0.75Mn0.25 alloy with added B (Pd0.75Mn0.25Bx) shows room-temperature soft ferromagnetism, whereas the parent Pd0.75Mn0.25 alloy is a spin-glass system. The saturated Mn moment at room temperature systematically increases to 2.68μB/Mn as x increases to 0.125. The maximum Curie temperature of 390 K is also realized at an x of 0.125. The experimental results suggest a tunable soft ferromagnetism, which is governed only by the boron concentration. Our results will pave the way in chemical control of room-temperature bulk ferromagnetism in Mn compounds based on the addition of an atom with a small atomic radius.