Calculation of activation energy of electron-transfer reaction between MnO4 − and MnO 4 2− ions in aqueous medium

Conclusions The activation energy of electron transfer between the manganate and permanganate ions were calculated. The effect of the ionic strength on E _a was discussed. The calculation results were compared with experiment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 467–468, February, 1977.     

CNDO-molecular orbital calculations of MnO 4 − and MnF 6 4−

CNDO-MO calculations have been made for the tetrahedral MnO ₄ ^– ion and the octahedral MnF ₆ ^4– ion using a transferable parameter scheme for manganese. The results show that the orbital levels for both complex ions are consistent with the ligand field approach.     

Darstellung und Kristallstruktur von Ag2MnO4

Synthese and Crystal Structure of Ag₂MnO₄ Single crystals of Ag₂MnO₄ have been grown from aqueous solution. The crystal structure has been solved and refined using diffractometer data (Pnma, a = 999.8(2); b = 698.9(1); c = 547.4(2) pm). The mean bond-length Mn? O within the tetrahedral anions is 167.9 pm. In spite of similar lattice constants and identical space group, Ag₂MnO₄ is not isostructural to Olivine. The structural differences are discussed.     

Oxygen evolution from BF3/MnO4-

MnO(4)(-) is activated by BF(3) to undergo intramolecular coupling of two oxo ligands to generate O(2). DFT calculations suggest that there should be a spin intercrossing between the singlet and triplet potential energy surfaces on going from the active intermediate [MnO(2)(OBF(3))(2)](-) to the O···O coupling transition state.     

Unrestricted CNDO-MO calculations. II. MnO 4 2− and CrO 4 3−

The electronic structures of the tetrahedral molecule ions MnO ₄ ^2– and CrO ₄ ^3– have been investigated within an unrestricted CNDO-MO approximation [Theoret. Chim. Acta (Berl.)20, 317 (1971)]. Calculations assuming the unpaired electron occupies the 3a ₁, 2e, and 4t2 molecular orbitals indicate that the 3a ₁ and2e orbitals have similar orbital energies and that the 4t ₂ orbital is at a higher energy. The experimentally indicated2e orbital for the unpaired electron is obtained with expanded O^1– type atomic orbitals for oxygen and valence metal orbitals of the expanded 3d and plus one ion 4p types. The metal 4s orbitals must be held to the neutral atom type. The optimum valence orbitals above with a slightly contracted 4s type metal orbitals yield the minimum total energy and places the unpaired electron in the 3a ₁ orbital. Since the contracted 4s metal orbital produces results that are not in agreement with experimental data, the method used apparently does not adequately take into account the increased electron-electron repulsions that contracted 4s orbitals produce.     

BF3-activated oxidation of alkanes by MnO4 -

The oxidation of alkanes and arylalkanes by KMnO(4) in CH(3)CN is greatly accelerated by the presence of just a few equivalents of BF(3), the reaction occurring readily at room temperature. Carbonyl compounds are the predominant products in the oxidation of secondary C-H bonds. Spectrophotometric and kinetics studies show that BF(3) forms an adduct with KMnO(4) in CH(3)CN, [BF(3).MnO(4)](-), which is the active species responsible for the oxidation of C-H bonds. The rate constant for the oxidation of toluene by [BF(3).MnO(4)](-) is over 7 orders of magnitude faster than by MnO(4)(-) alone. The kinetic isotope effects for the oxidation of cyclohexane, toluene, and ethylbenzene at 25.0 degrees C are as follows: k(C6H12)/k(C6D12) = 5.3 +/- 0.6, k(C7H8)/k(C7D8) = 6.8 +/- 0.5, k(C8H10)/k(C8D10) = 7.1 +/- 0.5. The rate-limiting step for all of these reactions is most likely hydrogen-atom transfer from the substrate to an oxo group of the adduct. A good linear correlation between log(rate constant) and C-H bond energies of the hydrocarbons is found. The accelerating effect of BF(3) on the oxidation of methane by MnO(4)(-) has been studied computationally by the Density Functional Theory (DFT) method. A significant decrease in the reaction barrier results from BF(3) coordination to MnO(4)(-). The BF(3) coordination increases the ability of the Mn metal center to achieve a d(1) Mn(VI) electron configuration in the transition state. Calculations also indicate that the species [2BF(3).MnO(4)](-) is more reactive than [BF(3).MnO(4)](-).     

Herstellung und Eigenschaften der Verbindungen Sr2(MnO4)OH und Sr2(MnO4)OH·2H2O

Zusammenfassung Es wird die Herstellung der Verbindungen Sr₂(MnO₄)OH und Sr₂(MnO₄)OH·2H₂O beschrieben. Die Gitterkonstanten wurden aus den entsprechenden Pulverdiagrammen berechnet. Die Infrarotabsorptions-und die Reflexionsspektren im Sichtbaren sowie das magnetische und thermische Verhalten wurden untersucht und kurz besprochen.

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Preparation and properties of the compounds Sr₂(MnO₄)OH and Sr₂(MnO₄)OH·2H₂O

Methods for preparation of the anhydrous compound formulated as Sr₂(MnO₄)OH and of its dihydrate are described. Unit cell parameters, which are the same for both substances, have been calculated from X-ray powder diagramms. Infrared absorption and visible reflectance spectra as well as the magnetic and thermal properties are also reported and briefly discussed.

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Mit 4 Abbildung     

Doping effects in single-layered La0.5Sr1.5MnO4 manganite

In this paper we report the results of the synthesis and structural, transport, and magnetic characterization of pure La(0.5)Sr(1.5)MnO(4) and B-site lightly doped samples, i.e. La(0.5)Sr(1.5)Mn(0.95)B(0.05)O(4), where B = Ru, Co, and Ni. The choice was made in order to probe the charge ordering/orbital ordering ground state of the monolayered La(0.5)Sr(1.5)MnO(4) manganite as a consequence of the cation doping. It is shown that even a light doping is successful in suppressing the charge and orbital order found in pure La(0.5)Sr(1.5)MnO(4). No long-range magnetic order has been detected in any of the doped samples but the setup of a spin-glass state with a common freezing temperature ( approximately 22 K). Structural parameters show an anisotropy in the lattice constant variation, with the tetragonal distortion increasing as the cell volume reduces, which may suggest a variation in the orbital character of the e(g) electrons along with the overall cation size.     

Eine ‚Reduktive Austausch-Reaktion’︁: Einkristalle von Rb2[MnO4] aus Li[MnO4]

A ‘Reductive Exchange Reaction’: Single Crystals of Rb₂[MnO₄] from Li[MnO₄] By heating of well ground mixtures of the oxides RbO_0.9 and Li[MnO₄] (Rb:Mn = 1.5:1; Ag-tubes; 660°C, 56 d) dark-green, orthorhombic single-crystals of Rb₂[MnO₄] were obtained. The structural determination revealed the isotype to K₂[MnO₄]; a β-K₂SO₄-typ. Thus, for the first time by a pure solid-state-chemical way, via a reductive, complete alkali-metal exchange, single crystals of an oxomanganate(VI) of the alkali metals were prepared. The Madelung Part of the Lattice Energy, MAPLE, and the charge distribution were calculated.     

Synthesis and Crystal Structure of the Cesium Silver ­Permanganate Cs3Ag[MnO4]4

After successful syntheses and structural refinements of the already known permanganates of cesium (Cs[MnO₄]) and silver (Ag[MnO₄]) we started to blend aqueous solutions of both components in various molar ratios. From crystallization experiments of these mixtures only three species of crystals with different chemical compositions were obtained: tricesium monosilver tetrakispermanganate (Cs₃Ag[MnO₄]₄) and, depending upon the respective ratio, either additional silver permanganate or surplus cesium permanganate, namely. The new title compound crystallizes in the orthorhombic space group Pnnm (no. 58) with two formula units per unit cell and cell dimensions of a = 764.53(4), b = 1883.57(9) and c = 584.34(3) pm. The crystal structure of Cs₃Ag[MnO₄]₄ consists of two crystallographically distinguishable cesium cations. (Cs1)⁺ is surrounded by fourteen oxygen atoms constructing a slightly distorted bicapped hexagonal prism. These polyhedra are connected through edge‐sharing with two other polyhedra of this kind to form chains along [001]. The chains are linked to each other via sixfold coordinated Ag⁺ cations (d(Ag–O) = 238–246 pm), arranged in such a manner that they link three oxygen atoms of two cesium polyhedra, leading to a two‐dimensional layer spreading out parallel to the (001) plane. Together with the two crystallographically different tetrahedral oxomanganate(VII) anions [MnO₄]^– (d(Mn–O) = 161–162 pm) the other kind of cesium cations ((Cs2)⁺ with CN = 13) finally connect these layers three‐dimensionally.     

Synthesis and size-dependent exchange bias in inverted core-shell MnO|Mn3O4 nanoparticles

Core-shell nanoparticles of MnO|Mn3O4 with average particle sizes of 5-60 nm, composed of an antiferromagnetic (AFM) core and a ferrimagnetic (FiM) shell, have been synthesized and their magnetic properties investigated. The core-shell structure has been generated by the passivation of the MnO cores, yielding an inverted AFM-core|FiM-shell system, as opposed to the typical FM-core|AFM-shell. The exchange-coupling between AFM and FiM gives rise to an enhanced coercivity of approximately 8 kOe and a loop shift of approximately 2 kOe at 10 K, i.e., exchange bias. The coercivity and loop shift show a non-monotonic variation with the core diameter. The large coercivity and the loop shift are ascribed to the highly anisotropic Mn3O4 and size effects of the AFM (i.e., uncompensated spins, AFM domains, and size-dependent transition temperature).     

Oxidation of acetanilide by MnO 4 − in the presence of HClO4. A kinetic study

The permanganate ion oxidation of acetanilide was studied spectrophotometrically by measuring the changes in absorbance at 525 nm in perchloric acid solutions. At lower [H⁺], the formation of an intermediate was observed whereas at higher [H⁺], the nature of reaction-time curve was sigmoid. The reaction rate increases with [H⁺] and the kinetics reveals complex order dependence in [H⁺]. The kinetic data for the oxidation of acetanilide indicate that the mechanism involves two steps. The order in [acetanilide] was found to be one. Water soluble Mn(IV) has been identified as an intermediate in the reduction of MnO ₄ ⁻ by acetanilide. The hydrogen ions have been found to decrease the stability of the Mn(IV). Externally added Mn(II) (a product of the reaction) has a composite effect (inhibition and catalysis). The addition of F⁻in the form of NaF has no effect on the reaction rate. The Arrhenius equation was valid for the reaction between 40 and 60 °C. The energy of activation, enthalpy and entropy of activation have been evaluated. Mechanisms consistent with the observed kinetics results have been suggested.     

Kinetics of the reduction of MnO4− by aqueous NH3 solutions

Transition Metal Chemistry -