Mechanism of the Reaction of Xenon Tetraoxide with Hydrogen: A Photochemical Reaction

The dependence of the rate of a photochemical reaction of XeO₄with H₂on the concentrations of H₂and the diluent gases He and CO₂is studied at room temperature. The results are compared with the data for the dark reaction. A mechanism with the elementary energetic branched-chain reaction OH (v) + XeO₄OH + O + XeO₃is proposed to explain the results of the study.     

Non-catalyzed oscillation reaction in the aniline-KBrO3?H2SO4 system. II. Reaction products and their oscillating behavior

By means of thin-layer and gas chromatography the reaction products have been determined in the oscillation system of aniline, KBrO₃ and H₂SO₄. These products include: 2-bromoaniline, 4-bromoaniline, 2,4-dibromoaniline, 2,4,6-tribromoaniline, 1,4-benzoquinone, 2-bromo-1,4-benzoquinone, 2,6-dibromo-1,4-benzoquinone and a brominated oxidation product. The brominated aniline derivatives do not exhibit an oscillating behavior, and the addition of these substances to an oscillating mixture damps the course of other oscillations.

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, KBrO₃ H₂SO₄. : 2-, 4-, 2,4-, 2,4,6-, 1,4-, 2--1,4-, 2,6--1,4- . , , , .

     

Principal vectors of crystallographic groups and applications

For a crystallographic group acting on ann-dimensional Euclidean space we consider the -invariant linear elliptic differential operatorP with constant coefficients and to it the -automorphic eigenvalue problemP [] + = 0. N() is the number of all eigenvalues smaller than or equal to the frequency bound ^q (q: order ofP). Earlier we found the asymptotic estimationN() c₀ · ⁿ + c₁ · ^n–1 (c ₀,c ₁: certain volumina). Furthermore,N() was interpreted as the number of so-called principal classes of principal lattice vectors within a convex domain. In this paper we demonstrate these results for the casen = 2 for two representative crystallographic groups and the assigned lattices. Above all we demonstrate a counting method for an exact estimation ofN() if a is not too big. In an analogous way we can treat all the 230 space groups of crystallography. It will be seen that these applications are brought about by the so-called principal vectors of these lattices.     

Thermometric study of the dissociation equilibria of the maleinimidodioxime

The values of the dissociation constants of the maleinimidodioxime are potentiometrically determined at various ionic strengths, and extrapolated to zero ionic strength (pK ₁ ^T =10.41;pk ₂ ^T =11.60). From these values and from the thermometric titration curves the enthalpies of neutralization (H _N1=–21.76,H _N2=–23.77 kJ/mol) and the thermodynamic parameters of dissociation of this substance at 25.0 °C are determined ( G ₁ =59.41, G ₂ =66.23, H ₁ =34.06, H ₂ =32.05 kJ/mol; S ₁ =–85.06, S ₂ =–114.64 J/(K mol)).

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Zusammenfassung Die Werte der Dissoziationskonstanten von Maleinimidodioxim wurden potentiometrisch bei verschiedenen Ionenstärken bestimmt und auf die Ionenstärke Null extrapoliert (pK ₁ ^T =10.41;pK ₂ ^T =11.60). Aus diesen Werten und aus den thermometrischen Titrierungskurven wurden die Neutralisierungsenthalpien (H _N1=–21.76,H _N2=–23.77 kJ/mol) und die thermodynamischen Dissoziationsparameter dieser Substanz bei 25 °C bestimmt ( G ₁ =59.41, G ₂ = 66.23, H ₁ =34.06 kJ/mol, H ₂ = 32.05 kJ/mol; S ₁ =–85.06, S ₂ =–114.64 J/Kmol.

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( ₁ =10.41 ₂ =11.60) . H _N1=–21.76 H _N2=–23.77 / 25.0°:G ₁ ⁰ =59.41;G ₂ ⁰ =66.23.H ₁ ⁰ =34.06₂ H ₂ ⁰ = 32.05 /,S ₁ ⁰ =–85.06;S ₂ ⁰ =–114.64 /.

     

Intramolecular Rearrangements of >Si(O–C·=O)(CH2–CH3) and >Si(CH2–CH·–CH3)(CH2–CH3) Radicals

Using ESR and IR spectroscopy, the structures of >Si(O–C^·=O)(CH₂–CH₃) (1) and >Si(CH₂–CH^·–CH₃)(CH₂–CH₃) (2) radicals were deciphered. The directions and kinetic parameters of reactions of intramolecular rearrangements in these radicals were determined. The reactions of hydrogen atom abstraction in radical (1) from the CH₂ and CH₃ groups were studied. It was found that the endothermic reaction of hydrogen atom abstraction from the methyl group occurs at a higher rate than the exothermic reaction with the methylene group. The differences are determined by changes in the size of a cyclic transition state. Based on the experimental data, the strengths of separate C–H bonds in surface fragments are compared. The rearrangement >Si(CH₂–CH^·–CH₃)(CH₂–CH₃) >Si(C^·(CH₃)₂)(CH₂–CH₃) was discovered and its mechanism was determined. One of its steps is the skeletal isomerization Si- (2)- _. (1)Si- (1)- _. (2). Experimental data are analyzed using the results of quantum-chemical calculations of model systems.     

Influence of substituents on rate constants for recombination of tertiary peroxy radicals

A linear correlation between the logarithm of rate constant (2k_t) for recombination of tertiary peroxy radicals (ROO)^* and ^* constants of substituents R was found to be 1g 2k_t=lg 2k _t ^° . The calculated values are 1g 2k _t ^° =4.59±0.08 and ^*=5.56±0.35.

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I (2k_t) (ROO) R: 1g 2k_t=lg 2k _t ^° . , 1g 1g 2k _t ^° =4,59±0,08 =5,56±0,35

     

Bimolecular Reactions of Radical Generation Involving Nitrogen-Containing Compounds with Multiple Bonds

Retrodisproportionation reactions R"C=NR" + HY R" NHR" + , RCN + HY R =NH + , RN=NR + HY R NHR + , RNO + HY R OH + , and RNO₂ + HY RN( )OH + (where HY represents hydrocarbons, alcohols, phenols, amines, thiophenols, etc.) are considered as sources of radical generation. The enthalpies of these reactions are calculated. The parabolic model is used to calculate the rate constants for 254 such reactions. Various HY compounds acting as hydrogen-atom donors are compared with nitrogen-containing compounds acting as hydrogen-atom acceptors. The PhN(O) and PhNO₂ compounds exhibit the highest activity among the studied acceptors.     

Thermodynamic and magnetic resonance studies on the hydration of polymers: I. Interactions of water in a synthetic cation-exchange resin

Measurements of NMR spin-lattice relaxation times T ₁ were performed for sorbed H₂O and D₂O in a sulfonated ion-exchange resin at varying degrees of hydration with alkaline cations as counter ions. From the sorption isotherms at three different temperatures the partial molar enthalpies and entropies of sorption show a minimum for all alkaline cations at water concentrations of n 0.8, i.e., there are 0.8 water molecules per –SO ₃ ^– group. The first water molecules sorbed in the ion-exchange resin matrix are characterized by anisotrtopic rotational diffusion processes with correlation times of the order of ₁ 50 ns and ₂ 30 ps, respectively. This indicates that they are located in the electrostatic field between the corresponding ion pair. Although these two correlation times are very similar at a given temperature for all alkaline cations studied in the present investigation, the existence of a second spin-lattice relaxation time for sorbed H₂O at n=0.8 indicates that for Cs about 50% of the sorbed water diffuses between locations in the resin. This fraction decreases with ionic radii and with falling temperatures. For Li the amount is less than 20%.     

Propos sur l'interpretation de l'energie d'activation experimentale

Résumé Les résultats de divers travaux montrent que la valeurE _e de l'énergie activation expérimentale tirée des diagrammes d'Arrhénius varie avec la pression, dans le cas de réactions de décompositions endothermiques.L'analyse de divers modèles permet d'expliquer cette constatation en montrant que la grandeurE _e n'a pas le sens d'une énergie d'activation mais est une fonction de nombreux paramètres. Deux d'entre eux ont été retenus dans le cadre de cette étude: le terme d'écart à l'équilibre et le terme de gradient thermique, provoqué par l'endothermicité du phénomène.Cette analyse permet d'établir une prévision de la fonctionE _e (P) conforme aux résultats expérimentaux.

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The results from various investigations show that the experimental activation energy valueE _e derived from the Arrhenius diagrams varies with pressure for endothermic decomposition reactions.The analysis of various models allows this fact to be accounted for by showing thatE _e should be regarded not in its fundamental formulation, but as being a function of numerous parameters. Two of these were taken into account in the present study, i.e. deviation from equilibrium and a thermal gradient due to the fact that the phenomenon is endothermic.FunctionE _e (P) fitting the experimental results may be predicted by such an analysis.

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Zusammenfassung Die Ergebnisse verschiedener Untersuchungen zeigen, dass die aus den Arrhenius-Diagrammen abgeleiteten experimentellen Werte der AktivierungsenergieE _e bei endothermen Zersetzungsreaktionen mit dem Druck variieren.Die Analyse verschiedener Modelle ermöglicht eine Erklärung dieser Tatsache, indem gezeigt wird, dassE _e nicht in ihrer grundliegenden Formulierung betrachtet werden darf, sondern als Funktion einer Anzahl von Parametern. Zwei dieser Parameter wurden in der vorliegenden Untersuchung berücksichtigt d.h. die Abweichung von dem Gleichgewicht und der thermische Gradient, welcher infolge der endothermen Beschaffenheit der Erscheinung auftritt.Eine den Versuchsergebnissen entsprechende FunktionE _e (P) kann mittels einer solchen Analyse vorausgesagt werden.

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, _e, , . , _ee , . , : , , . _e (), , .

     

Changes in the surface characteristics of residues from the thermal decomposition of nickel oxysalts

The changes in surface area and density which occur during the decomposition of eight nickel oxysalts have been reported. Surface area peaks were observed in the temperature range 473 K to 673 K. An equation relating to the number of product particles (n) produced from a single particle of original material has been derived. Logn was shown to vary linearly with temperature, wheren is the number of product particles formed from one original reactant particle.

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Zusammenfassung Es wird über die Veränderungen der Oberfläche und Dichte berichtet, welche bei der Zersetzung von acht Nickeloxysalzen auftreten. Oberflächenpeaks wurden im Temperaturbereich von 473 K bis 673 K beobachtet. Eine Gleichung wurde abgeleitet, welche sich auf die Zahl (n) der sich aus einem einzigen Partikel der Ausgangssubstanz bildenden Produktpartikel bezieht. Es wurde bewiesen, daß sich logn linear zur Temperatur ändert, wobein die Zahl der sich aus einem reagierenden Ausgangspartikel bildenden Produktpartikel ist.

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Résumé Etude des changements de surface spécifique et de densité pendant la décomposition de huits oxysels du nickel entre 473 K à 673 K. En désignant parn le nombre de particules issues d'une particule unique du matériau initial, on montre que logn varie linéairement avec la température.

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8 - , . , , 473–673 . , (), . logn .

     

Study of the thermal decomposition of solids in a fluidized bed,II

In order to eliminate the errors of the TG method with a static layer, and to determine the influence of the heating rate, the composition of the carrier gas and the particle size of the solids, a method of thermal gas evolution from a fluidized bed (FTGE) with continuous and linear increase of temperature was worked out and the thermal decomposition of diammonium hydrogen phosphate was followed. This method gives reproducible results and makes possible the determination of the apparent activation energies and kinetic parameters.

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Zusammenfassung Um die Fehler der TG Methode unter fixierten Verhältnissen zu eliminieren, den Einfluß der Temperaturerhöhung, der Zusammensetzung des Trägergases und des Ausmaßes der Festkörper zu klären, wurde eine thermogasanalytische Methode im fluidisierten Bett (FTGE) mit kontinuierlichem und linearem Temperaturanstieg entwickelt und die thermische Zersetzung des Diammonium-biphosphates verfolgt. Man erhielt mit dieser Methode reproduzierbare Ergebnisse. Sie ist zur Bestimmung der scheinbaren Aktivierungsenergien und kinetischer Parameter geeignet.

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Résumé Dans le but d'éliminer les erreurs des procédés thermogravimétriques avec couches fixes, et de mettre en évidence l'influence de la vitesse d'échauffement de la composition du gaz porteur et de la dimension des solides, on a développé une méthode d'analyse des gaz dégagés, avec lit fluidifié et élévation de la température continue et linéaire. On a suivi ainsi la décomposition thermique de (NH₄)₂HPO₄. Cette méthode donne des résultats reproductibles et rend possible la détermination des énergies d'activation apparentes et des paramètres cinétiques.

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, , . . , .

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Some parts presented at the IIIrd Analytical Conference, Budapest, 1970     

Thermal behaviour of transition metal complexes of dithiocarbazic esters. II

A thermal study (simultaneous TG and DTA measurements) was carried out on the dithiocarbazic ester complexes M[N³CH₂R₁N²C¹(S)SCH₃]₂, where M=Ni, Pt; R₁=C₆H₅. The following disproportionation reaction occurs in the solid state: II is formed through deprotonation of the CH₂ group bound to N³, whereas III is formed through protonation of N³.The influence of inductive and/or steric effects on the mechanism of this reaction is discussed, taking into account the electrochemical and X-ray data on the complexes Pt[NRNC(S)SR']₂ with differentR substituents: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃; R=CH₃, CH₂Ph.These results accord with the behaviour of the same complexes in solution.

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Zusammenfassung Dithiokarbamidsäureesterkomplexe M[N³CH₂R₁N²C¹(S)SCH₃]₂ mit M=Ni, Pt und R₁=C₆H₅ wurden thermisch untersucht. Im festen Zustand spielt sich folgende Disproportionierungsreaktion ab: II wird durch Deprotonierung der an N³ gebundenen CH₂ Gruppe und III durch Protonierung des Atoms N² gebildet. Unter Zuhilfenahme der elektrochemischen und Röntgendaten der Komplexe Pt[NRNC(S)SR']₂ mit verschiedenen Substituenten R: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃ und R=CH₃ bzw. CH₂Ph wurde der Einfluß von induktiven und/or sterischen Effekten auf den Reaktionsmechanismus diskutiert. Diese Ergebnisse stehen in Übereinstimmung mit dem Verhalten der Komplexe in Lösung.

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M[N³CH₂R₁N²C¹(S)SCH₃]₂, M= Ni, Pt,R ₁=C₆H₅. : II CH₂ , N³, III N². () , Pt[NRNC(S)SR]₂, R= , aR= . .

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We thank prof. A. La Ginestra for many helpful discussions on the various aspects of this work.     

Molecular isotope exchange of14CO in surface carbonyl complexes of rhodium

Molecular isotope exchange of CO with¹⁴CO for Rh₆(CO)₁₆/Sn(II)–SiO₂, Rh₆(CO)₁₆/Al₂O₃, Rh(I)(CO)₂/Al₂O₃, Rh₄(CO)₁₂/Al₂O₃ carbonyl complexes of rhodium has been studied. Estimates of the activation energies and a mechanism of the CO exchange are suggested.

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, (Rh₆(CO)₁₆/Sn(II)–SiO₂, Rh₆(CO)₁₆/Al₂O₃, Rh^I(CO)₂/Al₂O₃, Rh₄(CO)₁₂/Al₂O₃), ¹⁴CO. CO .

     

Thermal and some other properties of the complexes crystallizing from the system Ni(II)-en-[Ni(CN)4]2−-H2O

Seven complex compounds exhibiting the compositions Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) and-Ni(en)₂Ni(CN)₄ (VII) were prepared from the system Ni-en-[Ni(CN)₄]^2–-H₂O. These compounds were examined by the methods of infrared spectroscopy, X-ray powder diffractometry, UV-VIS reflectance spectroscopy, and also by the measurement of magnetic moments. The thermal stability, the stoichiometry of thermal decomposition and the mutual transformations were investigated with a derivatograph. The reactions proceeding according to the following schemes were observed if the system was heated to appropriate temperature: (I)(II)(III)(V)(IV) and (VI)(VII)(III)(V)(IV) Process (VII)(III) represents isomerization. The reversibility of the process (V)(IV) is due to the high hygroscopicity of the anhydrous complex. The changes in structure in the course of the individual processes are discussed.

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Zusammenfassung Aus einem System Ni-en-[Ni(CN)₄]^2–-H₂O wurden sieben Komplexe der Formeln Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) und-Ni(en)₂Ni(CN)₄ (VII) hergestellt. Diese Verbindungen wurden mittels IR-Spektroskopie, Röntgenpulverdiffraktometrie, UV-Reflexionsspektroskopie und durch Messungen des magnetischen Momentes untersucht. Die Wärmestabilität, die Stöchiometrie des thermischen Zerfalles und die gegenseitigen Umwandlungen wurden mittels eines Derivatographen untersucht. Wird das System auf geeignete Temperaturen erhitzt, kann der Reaktionsverlauf durch folgendes Schema dargestellt werden: (I)(II)(III)(V)(IV) und (VI)(VII)(III)(V)(IV).Der Prozeß (VII)(III) verkörpert eine Isomerisierung. Die Umkehrbarkeit von Prozeß (V)(IV) ist auf die ausgeprägten Hygroskopieeigenschaften des wasserfreien Komplexes zurückzuführen. Es werden die im Ablaufe der einzelnen Prozesse vorgehenden Strukturveränderungen besprochen.

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Ni- -[No(N)]² -₂ Ni(en)₃Ni(CN)₄ · ₂ (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄-2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2,5H₂O (VI) -Ni(en)₂Ni(CN)₄ (VII). , , - , . , . (I)(II)(III)(V)(IV) (VI)(VII)(III)(V)(IV). (VII)(III) . (V)(IV) . .

     

Crystal Structures and Properties of New Mixed-Ligand Complexes of Nickel(II) Diisobutyldithiophosphinate with Imidazole and 3,5-Dimethylpyrazole

The reaction of Ni{(i-C₄H₉)₂PS₂}₂ with imidazole and 3,5-dimethylpyrazole in ethanol gave paramagnetic (_ef = 3.02 and 3.11 BM) mixed-ligand complex compounds [Ni(Im)₂{(i-C₄H₉)₂PS₂}₂] (I) and [Ni(Pyr){(i-C₄H₉)₂PS₂}₂] (II). Single crystals were grown and the crystal structures of I and II were determined from X-ray diffraction data (CAD-4 diffractometer, Mo radiation, 1483 , R = 0.0344 for I and 2630 , R = 0.0486 for II). The crystals are monoclinic with cell dimensions a = 12.845(2), b = 10.250(1), c = 13.431(1) , = 115.89(1)°, V = 1591(1) ³, Z = 2, d _calc = 1.281 g/cm³, space group (for I); a = 11.152(3), b = 12.483(2), c = 23.389(4) , = 100.78(1)°, V = 3199(2) ³, Z = 4, d _calc = 1.191 g/cm³, space group (for II). The structures consist of discrete monomer molecules. The coordination polyhedron of the Ni atom is a compressed octahedron NiN₂S₄ (in I) and a tetragonal pyramid NiNS₄ (in II) formed by four S atoms of the two cyclic bidentate ligands i-Bu₂ and the N atoms of two monodentate ligands (Im molecules in trans-positions) or the N atom of the monodentate Pyr ligand in complexes I and II, respectively. The character of interaction between molecules I and II and molecular packing modes are considered. The electronic spectra of the complexes are consistent with the symmetry of chromophores found from X-ray data.     

Interaction of Nitromethane with Modified Paramagnetic Defects on a Thermochemically Activated Silica Surface

It was found that the interaction of the modified paramagnetic defects SiO(CH₂) _n H₂ (n = 0.1) with nitromethane on a thermochemically activated silica surface at 300 K results in the formation of the following nitroxyl radicals: SiO(CH₂) _n CH₂ON( )CH₃ and SiO(CH₂) _n CH₂N( )CH₃. It was suggested that these radicals are the products of two different reactions of the modified paramagnetic defects: the first results from a reaction with free nitromethane; the second, from a reaction with nitromethane bound as complexes with diamagnetic surface defects.     

Vibrational isotope effect of linear and planar molecules: Deuterated bromoethenes

Linear (planar) molecules A and B which are identical except for isotopic substitutions at the atomic sites are considered. Stretching (bending, out-of-plane) frequencies _k and normal modes _k of the isotopically perturbed molecule B are expressed in terms of stretching (bending, out-of-plane) frequencies _i and the corresponding normal modes _i of the unperturbed molecule A. Complete specification of the unperturbed normal modes is not required. All that is needed are stretching (bending, out-of-plane) amplitudes | _i of the normal modes _i at those sites that are affected by isotopic substitution. The rule which interlaces frequencies _k of molecule A with frequencies _i of molecule B is derived. Given two isotopic molecules A and B that differ by a single isotopic substitution at site , the inversion relation is derived. This relation expresses unperturbed stretching (bending, out-of-plane) amplitudes at the site in terms of stretching (bending, out-of-plane) frequencies of molecules A and B . As an example, out-of-plane vibrations of deuterated bromoethene were considered. In the simplest method 12 out-of-plane frequencies of four polydeuterated bromoethenes were calculated from 12 out-of-plane frequencies of bromoethene and three monodeuterated bromoethenes. Standard deviation of thus calculated frequencies from experimental frequencies is =2.74 cm^–1. In another method, 15 out-of-plane frequencies of four polydeuterated bromoethenes and selected monodeuterated bromoethene are calculated from 9 out-of-plane frequencies of bromoethene and the remaining two monodeuterated bromoethenes. Depending on which monodeuterated bromoethene is selected (1-, cis- or trans-), standard deviation of thus obtained frequencies from experimental frequencies is 1=2.84 cm^–1, c=2.96 cm^–1 and t=2.72 cm^–1.     

Thermal and spectroscopic study of the solid complexes of furan-2-hydroxamic acid and several divalent metallic cations

Solid crystalline complexes of furan-2-hydroxamic acid (FHA) and six metallic divalent cations (Ca(II), Ba(II), Co(II), Ni(II), Cu(II), and Cd(II)) were prepared. In all cases the stoichiometry was 2(FHA)1 (cation). The solids were characterized by elemental analysis, TG, DSC and IR techniques.

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Zusammenfassung Es wurden feste, kristalline Komplexe von Furan-2-hydroxamsäure (FHA) und sechs verschiedenen bivalenten Metallkationen hergestellt: Ca(II), Ba(II), Co(II), Ni(II), Cu(II) und Cd(II). Die stöchiometrische Zusammensetzung betrug in allen Fällen 2(FHA)1(Kation). Die Feststoffe wurden mittels Elementaranalyse, TG-, DSC- und IR-Techniken charackterisiert.

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-2- , , , , . : 21. , , .

     

The classification of tensor surface harmonic functions for clusters and coordination compounds

A simple method for enumerating theL and functions for polyhedral cluster and coordination molecules, within Stone's tensor surface harmonic methodology, is described. The nature of theL orbitals which are generated depends on the polyhedral topology and in particular the number of layers of vertices and the number of vertices within each layer. The functions are enumerated from theL 's by a number of spherical harmonic multiplication rules.     

Catalytic Mechanism of the “Noncatalytic” Autooxidation of Sulfite

Iron ions are shown to play a special role among transition metal ions in the oxidation of sulfite by oxygen. The thermodynamically favorable formation of chain carriers S : FeOH²⁺+ HSO₃ ^– Fe²⁺+ H₂O + , H _{r 298} ⁰ –250 kJ/mol accompanied by the regeneration of the active Fe(III) form in the reactions of Fe(II) with and HSO₅ ^–provides the efficient catalytic mechanism for sulfite consumption even at [Fe]₀ 10^–8mol/l. Any aqueous solution contains iron ions in this amounts. Thus, the noncatalytic oxidation of sulfite is in fact the catalytic reaction involving unavoidable microadmixtures of iron ions. Other transition metal ions (Mn²⁺, Co²⁺, etc.) can only enhance the catalytic effect of iron admixture.