Reduction of colloidal manganese dioxide by manganese(II)

The reduction of colloidal MnO(2) by Mn(2+) in aqueous HClO(4) has been studied by a spectrophotometric method. The reaction product is Mn(III). The reaction is of first order in both colloidal MnO(2) and H(+), whereas it presents a fractional order (0.58+/-0.02) in Mn(2+). The reaction is retarded by addition of NaClO(4), but is not affected by addition of tert-butanol. The corresponding activation energy is 29.5+/-1.3 kJ mol(-1). The reaction is catalyzed by Na(4)P(2)O(7), and the pyrophosphate-catalyzed reaction is of first order in both colloidal MnO(2) and pyrophosphate and of fractional order (0.64+/-0.01) in Mn(2+), whereas its rate presents a complex dependence on the concentration of H(+). The pyrophosphate-catalyzed reaction is accelerated by addition of both NaClO(4) and tert-butanol. The corresponding activation energy is 49.7+/-3.0 kJ mol(-1). Mechanisms in agreement with the experimental data are proposed for both the parent and the pyrophosphate-catalyzed reactions.     

Isotopic exchange between manganese hydroxide and manganese ions in aqueous solution

Heterogeneous isotopic exchange between manganese hydroxide and manganese ions in aqueous solutions tagged with radioactive⁵⁴Mn has been studied at different values of α, the ratio of the quantity of exchangeable ions in the solid phase to that in the liquid phase. The aging of the precipitate in its mother liquor prior to the exchange has a significant effect on both the extent and rate of the exchange reaction. A marked feature of great interest is the appearance of two aging-times, one at about 10² and the other at about 10⁴ min. The overall reaction appears to be of the consecutive type. In the case of a fresh precipitate, “complex-surface-exchange” and “self-diffusion” mechanisms are the most probable rate-determining steps in the initial and final stages of the reaction, respectively. “Complex-surface-exchange” is a new suggested mechanism. In the case of a well-aged precipitate, “surface-exchange” and ‘self-diffusion” mechanisms are the most probable-determining steps in the initial and final stages of the reaction, respectively.     

Preparation of manganese oxide nanoparticles by thermal decomposition of nanostructured manganese carbonate

MnO and Mn₂O₃ nanoparticles were prepared in air and argon atmosphere by thermal decomposition of nanocrystalline manganese carbonate synthesized by reaction of manganese(II) nitrate with glycerol. Samples were characterized using transmission electron microscopy, simultaneous thermal analysis and X-ray diffraction analysis. Average sizes of prepared nanoparticles were calculated from XRD patterns using Scherrer equation. Also, the conditions for decomposition of manganese carbonate were optimized to obtain optimal nanoparticle sizes. Due to suitable sizes of prepared nanoparticles and the initial material, this method can be used in a wide range of industrial applications.     

Simultaneous determination of soluble manganese(III), manganese(II) and total manganese in natural (pore)waters

A new spectrophotometric protocol was developed for the simultaneous determination of soluble Mn(III), Mn(II) and total Mn [sum of soluble Mn(III) and Mn(II)] in sediment porewaters using a water soluble meso-substituted porphyrin [α,β,γ,δ-tetrakis(4-carboxyphenyl)porphine (T(4-CP)P)]. A simple kinetic rate model is used to quantify soluble Mn(II), Mn(III) and total Mn concentrations during a metal substitution reaction. Under optimized conditions, the method accurately determines soluble Mn(II) and Mn(III) within a concentration range of 100 nM-10 μM. The detection limit of total soluble Mn is 50 nM. Using this method, soluble Mn(II) and Mn(III) concentrations were determined in standard solutions within 0.4-2% of the known values and agreed closely with results of inductively coupled plasma mass spectrometric and voltammetric analyses. The procedure was successfully applied to determine soluble Mn(II), Mn(III) and total Mn in sediment porewaters of the Lower St. Lawrence Estuary. Mn(III) represented up to 85% of the total soluble Mn pool in surface sediments.     

Pillared layered manganese oxide

Keggin ion-pillared buserite was prepared by ion-exchanging the hexylammonium ion-expanded buserite with Keggin ions, [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺. The starting material was synthetic Na-buserite, which is a layered manganese oxide of composition Na₄Mn₁₄O₂₆ xH₂O. The thermal and redox properties of this oxide and its pillared derivative were compared in O₂, N₂ and H₂ environments using TG, DSC and XRD. The results indicated an improvement in thermal stability of pillared compound relative to Na-buserite in all gaseous environments. By using these compounds in catalysing the oxidation of ethane, it was found that they were very active for complete oxidation.     

Carbonyl fluorides of manganese

The first carbonyl fluorides of manganese Mn(CO)₃F₃ and [Mn(CO)₄F]₂ have been prepared by treating Mn(CO)₅Br with AgF. The compounds have been characterized by elemental analysis, conductance measurement, IR and mass spectrometric studies.     

Bis-aryldiazo complexes of manganese

The first bis-aryldiazo complexes containing manganese of the type MnX(N₂Ph)₂(PPh₃)₂ and Mn(CO)(N₂Ph)₂(PPh₃)₂⁺PF₆^? have been prepared from Mn(CO)₂(N₂Ph)(PPh₃)₂ (X  Cl, Br, NCO). In addition, the mixed aryldiazonitrosyl analogues and the dinitrosyl analogues have been prepared in order to compare their spectroscopic properties with the bis-aryldiazo complexes. The preparation of the rhenium complex Re(CO)₂(N₂Ph)(PPh₃)₂ is also reported.     

Spectrophotometric determination of manganese

Summary Manganese solution in sodium hydroxide when mixed with brucine followed by HCl produces pink color having 1g/ml as visual limit of identification and maximum absorbance at 475 nm. This color reaction has been developed for the Spectrophotometric determination of manganese in minute quantities. The maximum tolerable limit of other cations and anions is reported.

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Zusammenfassung Alkalische Manganlösungen geben nach Zusatz von Brucin und Ansäuern mit Salzsäure eine Rosafärbung mit einem Absorptionsmaximum bei 475 nm. Die Erfassungsgrenze liegt bei 1g Mn/ml. Die Farbreaktion dient zur spektrophotometrischen Bestimmung kleiner Manganmengen. Die tolerierbaren Höchstmengen anderer Ionen wurden angegeben.

     

Colorimetric determination of manganese

The colour developed, when freshly formed manganese dioxide dissolves in alkaline tellurate solution is found to be suitable for the colorimetric determination of manganese. The colour obeys Beer's law within the concentration range 1.886.10^-4 - 7.54.10^-4M. The colour is developed by oxidizing Mn(II) (in presence of 2.5M alkali) with the equivalent amount of H₂O₂ in the presence of 4 moles of telluric acid per mole Mn(II).     

30-Membered decanuclear manganese metallacrown

A new macrocyclic decanuclear manganese(III) 30-metallacrowns-10, [Mn₁₀(ipbmshz)₈(dmpmshz)₂(DMF)₁₀]. 4DMF (1) has been prepared by supramolecular self-assembly and characterized by X-ray crystal diffraction, where ipbmshz³⁻ is N-(4-isopropylbenzoyl)-3-methylsalicylhydrazide, dmpmshz³⁻ is N-(2,2-dimethylpropanoyl)-3-methylsalicylhydrazide. The single-crystal structure shows that a novel ring formed by the succession of ten structural moieties of the type [Mn(III)–N–N] through hydrazide N–N groups bridging the ring Mn ions. The ligand enforces the Mn³⁺ ions to form the stereochemistry of a propeller configuration with alternate…ΔΛΔΛ…-type chiral forms depending on the steric repulsions between the tail groups. The decanuclear systems measure ∼2.3 nm in diameter and ∼1.2 nm in thickness. The temperature-dependent magnetic properties have been studied and showed the presence of weakly antiferromagnetic couplings between Mn (III) ions.     

Natural and synthetic manganese minerals

The mineral and microelement composition and structures have been studied and a comparative analysis has been carried out for manganese minerals with the general formula [Mn(O,OH)₂]⁺[R_0.5–1(OH)_21.5] · nH₂O (R = Mn, Na, K, Ni, Co, Ca, and others) that built iron-manganese concretions raised from different areas of the Sea of Okhotsk and the Bering Sea, and their synthetic analogues. The structures of synthetic manganese species were found to better withstand temperature impacts than those of the native minerals studied under the same conditions.     

Mixed-valence tetranuclear manganese single-molecule magnets

The preparations, X-ray structures, and detailed physical characterizations are presented for two new mixed-valence tetranuclear manganese complexes that function as single-molecule magnets (SMM's): [Mn4(hmp)6Br2(H2O)2]Br2-4H2O (2) and [Mn4(6-me-hmp)6Cl4]-4H2O (3), where hmp(-) is the anion of 2-hydroxymethylpyridine and 6-me-hmp(-) is the anion of 6-methyl-2-hydroxymethylpyridine. Complex 2-4H2O crystallizes in the space group P2(1)/c, with cell dimensions at -160 degrees C of a = 10.907(0) A, b = 15.788(0) A, c = 13.941(0) A, beta = 101.21(0) degrees, and Z = 2. The cation lies on an inversion center and consists of a planar Mn4 rhombus that is mixed-valence, Mn2(III)Mn2(II). The hmp(-) ligands function as bidentate ligands and as the only bridging ligands in 2-4H2O. Complex 3-4H2O crystallizes in the monoclinic space group C2/c, with cell dimensions at -160 degrees C of a = 17.0852(4) A, b = 20.8781(5) A, c = 14.835(3) A, beta = 90.5485(8) degrees, and Z = 4. This neutral complex also has a mixed-valence Mn2(III)Mn2(II) composition and is best described as having four manganese ions arranged in a bent chain. A mu2-oxygen atom of the 6-me-hmp(-) anion bridges between the manganese ions; the Cl(-) ligands are terminal. Variable-field magnetization and high-frequency and -field EPR (HFEPR) data indicate that complex 2-4H2O has a S = 9 ground state whereas complex 3.4H(2)O has S = 0 ground state. Fine structure patterns are seen in the HFEPR spectra, and in the case of 2.4H(2)O it was possible to simulate the fine structure assuming S = 9 with the parameters g = 1.999, axial zero-field splitting of D/k(B) = -0.498 K, quartic longitudinal zero-field splitting of B4(omicron)/k(B) = 1.72 x 10(-5) K, and rhombic zero-field splitting of E/k(B) = 0.124 K. Complex 2-4H2O exhibits a frequency-dependent out-of-phase AC magnetic susceptibility signal, clearly indicating that this complex functions as a SMM. The AC susceptibility data for complex 2-4H2O were measured in the 0.05-4.0 K range and when fit to the Arrhenius law, gave an activation energy of DeltaE = 15.8 K for the reversal of magnetization. This DeltaE value is to be compared to the potential-energy barrier height of U/k(B) = absolute value DSz(2) = 40.3 K calculated for 2-4H2O.     

Triaqua­manganese sulfite revisited

Ortho­rhom­bic Mn(SO₃)(H₂O)₃ has been reinvestigated by single‐crystal X‐ray diffraction in two possible space groups, viz. P2₁2₁2₁ (with all atoms in general positions) and Pnma (with the mol­ecule bisected by a mirror plane). The results confirm the lower symmetry assigned in a previous single‐crystal neutron diffraction study. However, the refinement of the P2₁2₁2₁ model requires the introduction of racemic twinning and soft positional and displacement restraints for the H atoms. The importance of a scrupulous report on symmetry absence violations as standard policy in crystallographic work is discussed.     

The manganese(IV) oxide electrode as a manganese(II) sensor

Manganese(IV) oxide electrodes formed with a graphite/PTFE substrate are shown to have near-theoretical response to manganese(II) ions in pH-4 acetate medium and a sub-Nernstian response in 0.1M nitric acid medium. Lead and iron(III) ions interfere, and iron(II) ions even more so, but other bivalent transition metal ions have little effect. The main drawback of this type of electrode is its long response time (~ 20 min). Some attempts to use manganese(IV) oxide electrodes as the basis for phosphate electrodes by use of MnHPO(4).3H(2)O and MnNH(4)PO(4).H(2)O are also described.     

New layered manganese oxide halides

The first layered manganese(III) oxide chlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2, have been synthesised; Sr2MnO3Cl adopts a K2NiF4 type structure with sheets of MnO5 square based pyramids linked through oxygen and separated by SrCl layers; it is the end member of a new family of Ruddlesden-Popper type manganese oxide halides which includes the three-layer member Sr4Mn3O8-yCl2 also reported herein.     

A polyoxometalate-based manganese carboxylate cluster

The functionalization of a pre-formed, high oxidation state {CeIV MnIV 6} cluster with a lacunary phosphotungstate, [alpha-P2 W15 O 56]12-, exemplifies a straightforward route for grafting redox-active building blocks to existing Mn-carboxylate clusters and modeling their deposition onto metal oxide surfaces.     

Precise potentiometric titration of manganese

Summary A method for the precise automatic potentiometric titration of manganese is described. Manganese ions are titrated with permanganate as a titrant in fluoride medium. The ideal quantity to titrate is about 30 mg of manganese. The endpoint of the reaction is recorded automatically. By adding more than 98% of the titrant by weight and the remaining part by means of an automatic burette the precision of the method could be improved to 0.03%. Systematic deviations are eliminated by calibrating the reagent with well-known reference solutions.

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Genaue potentiometrische Manganbestimmung

Zusammenfassung Mangan wird mit Permanganat in Fluoridmedium titriert. Die optimale Menge für die Titration beträgt etwa 30 mg Mn. Der Endpunkt der Reaktion wird automatisch registriert. Durch Zusatz von mehr als 98% des Titrationsmittels als Einwaage und Vervollständigung der Reaktion mit Hilfe einer automatischen Bürette kann eine Genauigkeit von 0,03% erzielt werden. Systematische Fehler werden durch Eichung mit bekannten Referenzlösungen vermieden.