A pyrolysis mechanism for ammonia

The mechanism of NH₃ pyrolysis was investigated over a wide range of conditions behind reflected shock waves. Quantitative time-history measurements of the species NH and NH₂ were made using narrow-linewidth laser absorption. These records were used to establish an improved model mechanism for ammonia pyrolysis. The risetime and peak concentrations of NH and NH₂ in this experimental database have also been summarized graphically. Rate coefficients for several reactions which influence the NH and NH₂ profiles were fitted in the temperature range 2200 K to 2800 K. The reaction and the corresponding best fit rate coefficients are as follows: with a rate coefficient of 4.0 × 10¹³ exp(?3650/RT) cm³ mol^?1 s^?1, with a rate coefficient of 1.5 × 10¹⁵T^?0.5 cm³ mol^?1 s^?1 and with a rate coefficient of 5.0 × 10¹³ exp(?10000/RT) cm³ mol^?1 s^?1. The uncertainty in rate coefficient magnitude in each case is estimated to be ±50%. The temperature dependences of these rate coefficients are based on previous estimates. The experimental data from four earlier measurements of the dissociation reaction were reanalyzed in light of recent data for the rate of NH₃ + H → NH₂1 + H₂, and an improved rate coefficient of 2.2 × 10¹⁶ exp(?93470/RT) cm³ mol^?1 s^?1 in the temperature range 1740 to 3300 K was obtained. The uncertainty in the rate coefficient magnitude is estimated to be ± 15%.     

Synthesis and Crystal Structure of Tetraamminelithium-Rubidiumtriselenide, Li(NH3)4RbSe3, and Pentaamminesodium-Rubidiumtriselenide-Ammonia(1/3), Na(NH3)5RbSe3 · 3NH3

Summary. The ammoniates Li(NH₃)₄RbSe₃ and Na(NH₃)₅RbSe₃·3NH₃ were prepared by the reduction of Rb₂Se₅ with lithium or sodium in liquid ammonia. Single crystals were isolated and characterized by X-ray structure analysis using low temperature techniques. Both compounds contain triselenide anions Se₃^2–, which coordinate to rubidium cations forming ¹[RbSe₃]^– or ¹[Rb(NH₃)₂Se₃]^– chains. The chains are separated in the crystal structures by the homoleptic ammine complexes Li(NH₃)₄⁺ and Na(NH₃)₅⁺.     

Studies on the Chemistry of Tetraamminezinc(II) Dipermanganate ([Zn(NH3)4](MnO4)2): Low‐Temperature Synthesis of the Manganese Zinc Oxide (ZnMn2O4) Catalyst Precursor

Tetraamminezinc(II) dipermanganate ([Zn(NH₃)₄](MnO₄)₂; 1 ) was prepared, and its structure was elucidated with XRD‐Rietveld‐refinement and vibrational‐spectroscopy methods. Compound 1 has a cubic lattice consisting of a 3D H‐bound network built from blocks formed by four MnO anions and four [Zn(NH₃)₄]²⁺ cations. The other four MnO anions are located in a crystallographically different environment, namely in the cavities formed by the attachment of the building blocks. A low‐temperature quasi‐intramolecular redox reaction producing NH₄NO₃ and amorphous ZnMn₂O₄ could be established occurring even at 100°. Due to H‐bonds between the [Zn(NH₃)₄]²⁺ cation and the MnO anion, a redox reaction took place between the NH₃ and the anion; thus, thermal deammoniation of compound 1 cannot be used to prepare [Zn(NH₃)₂](MnO₄)₂ (contrary to the behavior of the analogous perrhenate (ReO ) complex). In solution‐phase deammoniation, a temperature‐dependent hydrolysis process leading to the formation of Zn(OH)₂ and NH₄MnO₄ was observed. Refluxing 1 in toluene offering the heat convecting medium, followed by the removal of NH₄NO₃ by washing with H₂O, proved to be an easy and convenient technique for the synthesis of the amorphous ZnMn₂O₄.     

Copper(II)–Ammonia Complexation Equilibria in Aqueous Solutions at Temperatures from 30 to 250°C by Visible Spectroscopy

The spectra of copper(II)–ammonia solutions in 2 mol-kg^–1 NH₄NO₃(aq) were recorded as a function of pH with a new UV–visible flow cell, capable of operating at conditions up to 325°C and 300 bars. Equilibrium constants for the formation of copper(II)–ammonia complexes Cu(NH₃)_n ²⁺, 1 n 4, from 30 to 150°C were determined by evolving factor analysis and nonlinear least-squares regression. Measurements at higher temperatures were limited by thermal decomposition of NH₄NO₃(aq). The formation constants of Cu(NH₃)_n ²⁺ decrease with temperature, consistent with extrapolations of literature data from measurements below 100°C. Measurements above 150°C were carried out in 0.5 mol-kg^–1 CF₃SO₃H (aq), at the very high ammonia concentrations required to avoid the precipitation of CuO(s). The spectra are consistent with Cu(NH₃)₄ ²⁺ as the predominant species, based on extrapolations of peak maxima and molar absorptivities from lower temperatures. Shifts in the spectra of Cu²⁺ and the Cu(NH₃)_n ²⁺ species to higher wavelength and increases in molar absorbance with increasing temperature are discussed in terms of the structure of the complexes.     

AlCl3 · 3NH3 — eine Verbindung mit der Kristallstruktur eines Tetraammindichloroaluminium-diammintetrachloroaluminats: [AlCl2(NH3)4]+[AlCl4(NH3)2]−

AlCl₃ · 3NH₃ — a Compound with the Crystal Structure of a Tetraammine Dichloro Aluminium-Diammine Tetrachloro Aluminate: [AlCl₂(NH₃)₄]⁺[AlCl₄(NH₃)₂]^? . AlCl₃ · 3 NH₃ ? [AlCl₂(NH₃)₄]⁺ [AlCl₄(NH₃)₂]^? forms during the reaction of two mole NH₃ with AlCl₃(NH₃) at T ≥ 200°C. Repeated heating and cooling within 48 h between 200°C and 250°C gives a homogeneous product with total uptake of the necessary amount of NH₃. Slow sublimation in a vacuum line apparatus at 200°C gives crystals of the triammoniate sufficient for a X-ray structure determination: The compound contains elongated [AlCl₂(NH₃)₄]⁺ octahedra and compressed [AlCl₄(NH₃)₂]^? octahedra. Besides ionic bonding hydrogen bridge bonds with 3.369 Å ? d(N—H … Cl) ? 3.589 Å stabilize the atomic arrangement.     

Interaction of bivalent transition metal ions with iminodiacetato-(pentaammine/tetraammine)cobalt(III) ions. A kinetic and equilibrium study

Summary The kinetics of reversible complexation of Ni^II and Co^II with iminodiacetato(pentaammine)cobalt(III), [(NH₃)₅-Co(idaH₂)]³⁺ and Ni^II with iminodiacetato(tetraammine)-cobalt(III), [(NH₃)₄Co(idaH)]²⁺, have been investigated by the stopped-flow technique at 25 °C, pH = 5.7–6.9 and I = 0.3 mol dm ^–3. The reaction paths (NH₃)₅Co(idaH)²⁺+M²⁺(NH₃)₅Co(ida)M³⁺+H⁺ (NH₃)₅Co(ida)⁺+M²⁺(NH₃)₅Co(ida)M³⁺ (NH₃)₄Co(ida)⁺+Ni²⁺(NH₃)₄Co(ida)Ni³⁺ have been identified (idaH = N⁺H₂(CH₂CO₂)₂H, ida = NH(CH₂COO)^2–]. The rate parameters for the formation and dissociation of the binuclear species are reported. The data are essentially consistent with an I _d mechanism. The dissociation rate constants of the binuclear species indicate that Ni²⁺ and Co²⁺ are chelated by the coordinated iminodiacetate moiety.     

Arrangement and Diffusive Mobility of Extraframework Species in the Hydrated Ammonium Forms of Zeolites Clinoptilolite and Chabazite

The location and diffusive mobility of ammonium ions and water molecules in the channels of the NH₄substituted forms of the natural zeolites clinoptilolite (NH₄)_6.5[Al_6.5Si_29.5O₇₂] · 12.6H₂O and chabazite (NH₄)_9.6Ca_0.6Na_0.3[Al_11.1Si_24.9O₇₂] · 25.8H₂O were studied by Xray diffraction analysis and ¹H NMR spectroscopy. The arrangement of the extraframework subsystem was shown to be largely determined by hydrogen bonds N—H...O(H₂O) of length 2.7–2.9 . The diffusive mobility of the ions was found to correspond to abnormally low energy barriers, similar to those for H₂O diffusion. The activation parameters for the diffusion jumps of the ions and molecules are E(NH₄) = E(H₂O) = 31(2) kJ/mole, ₀(NH₄) = 2 · 10¹¹ sec^-1, ₀(H₂O) = 4 · 10¹² sec^-1 in NH₄chabazite and E(NH₄) = E(H₂O) = 25(1) kJ/mole, ₀(NH₄) = 2 · 10¹⁰ sec^-1, ₀(H₂O) = 3 · 10¹¹ sec^-1 in NH₄clinoptilolite. It is suggested that the development of ion and molecular diffusion is caused by the same defects, whose formation with temperature rise is controlled by Hbond rearrangement.     

Die Fällung des PdII als [Pd(NH3)2Cl2] sowie das Verhalten verschiedener Begleitelemente

Precipitation of Pd^II as [Pd(NH₃)₂Cl₂] and the Behaviour of Various Impurities The dependence of [Pd(NH₃)₂Cl₂] precipitation upon reaction conditions (pH, Cl^? content, reaction time, temperature) has been studied. The dependence of residual Pd content in the mother liquor upon these parameters was found to be significant only for the precipitation temperature (c_Pd at 20°C: 1.65 ± 0.11 mM; at 50°C: 6.70 ± 0.58 mM). The increase of Pd concentration was due to the formation of Pd(NH₃)Cl₃^?. Among the impurities studied Cr, Ru, and Au were largely precipitated in the NH₃ medium. In subsequent precipitation of [Pd(NH₃)₂Cl₂] the following order of coprecipitation was found: The first four elements could be separated only incompletely by repeated reprecipitation. The coprecipitation of the platinum-group metals and of Au was highly dependence upon preceding formation of ammine complexes of these elements. The considerable coprecipitation of Pt^IV is presumably due to the formation of mixed Pd/Pt compounds, whereas the other impurities are adsorbed by [Pd(NH₃)₂Cl₂].     

L'action de l'ammoniac sur l'oxyde cuivrique. et les hydroxo-complexes de cuivre (II)

Using a new mathematical treatment, the nature and stability constants of the simple and mixed complex-species of copper(II) with hydroxyde and ammonia as ligands have been determined. The solubility curves of CuO in heterogeneous equilibrium have been identified in function of pH only and in function of pH and pNH_3tot at 25° and unit ionic strength (NaClO₄). The predominent species in the relatively dilute system limited by the ionic strength are [Cu²⁺], [Cu(OH)₂], [Cu(OH)], [Cu(OH)], [Cu(NH₃)], [Cu(NH₃)], [Cu(NH₃)], [Cu(NH₃) (OH)⁺], [Cu(NH₃)₃(OH)⁺] and [Cu(NH₃)₂(OH)₂].     

Oxofluorovanadates(V). IV. Dioxotetrafluorovanadates

Preparation and properties of the salts of the series MVO₂F₄, where M = NH, Na⁺, K⁺, 1/2 Ni²⁺, and 1/3 [Co(NH₃)₆]³⁺ are described. Molecular conductivity of Na₃VO₂F₄ at different dilutions indicates that Na₃VO₂F₄ dissociates into 3 Na⁺ and VOaF ions. Ion exchange study of (NH₄)₃VO₂F₄ solution through cation exchange resin (H⁺ form) suggests that the corresponding acid decomposes partly to vanadium pentoxide. Reaction between (NH₄)₃VO₂F₄ with BaCl₂ and AgNO₃ solutions shows the formation of BaVO₂F₃ and AgVO₃ respectively. Thermogravimetric study of (NH₄)₃VO₂F₄ shows the formation of impure vanadium pentoxide as the ultimate product on heating up to 450°C. X-ray powder diffraction data are given for (NH₄)₃VO₂F₄ and Na₃VO₂F₄.     

Internal Mobility, Phase Transitions, and Ionic Conductivity in Na(NH4)6Zr4F23 and Li(NH4)6Zr4F23

The dynamics of fluoride and ammonium ions in Na(NH₄)₆Zr₄F₂₃ (I) and Li(NH₄)₆Zr₄F₂₃ (II) was studied by ¹H and ¹⁹F NMR in the temperature range 170-440 K. Types of ionic motion were determined, and their activation energies were evaluated. In I, phase transitions were found in the temperature ranges 360-370 and 410-415 K. The experimental values of conductivity of Na(NH₄)₆Zr₄F₂₃ and Li(NH₄)₆Zr₄F₂₃ ( 4 × 10^-3 S/cm at T = 420 K) permit one to attribute these fluorides to the class of superionic conductors.     

Synthese und Kristallstruktur von Mangan(II)‐ und Zinkamid,Mn(NH2)2 und Zn(NH2)2

Synthesis and Crystal Structure of Manganese(II) and Zinc Amides, Mn(NH₂)₂ and Zn(NH₂)₂ Metal powders of manganese resp. zinc react with supercritical ammonia in autoclaves in the presence of a mineralizer Na₂Mn(NH₂)₄ resp. Na₂Zn(NH₂)₄_.0.5NH₃ to well crystallized ruby‐red Mn(NH₂)₂ (p(NH₃) = 100 bar, T = 130°C, 10 d) resp. colourless Zn(NH₂)₂ (p(NH₃) = 3.8 kbar, T = 250°C, 60 d). The structures including all H‐positions were solved by x‐ray single crystal data: Mn(NH₂)₂: I4₁/acd, Z = 32, a = 10.185(6) Å, c = 20.349(7) Å, N(F_o) with F > 3σ (F) = 313, N(parameter) = 45, R/R_w = 0.038/0.043. Zn(NH₂)₂: I4₁/acd, Z = 32, a = 9.973(3) Å, c = 19.644(5) Å, N(F_o) with F > 3σ (F) = 489, N(parameter) = 45, R/R_w = 0.038/0.043. Both compounds crystallize isotypic with Mg(NH₂)₂ [1] resp. Be(NH₂)₂ [2]. Nitrogen of the amide ions is distorted cubic close packed. One quarter of tetrahedral voids is occupied by Mn²⁺‐ resp. Zn²⁺‐ions in such an ordered way that units M₄(NH₂)₆(NH₂)_4/2 occur. The H‐atoms of the anions have such an orientation that the distance to neighboured cations is optimum.     

Manganese cationic pyrazolylamidino complexes

The reactions of fac-[MnBr(CO)₃(NHC(CH₃)pz^∗-κ²N,N)] (pz^∗ = pz, dmpz; pzH = pyrazole; dmpzH = 3,5-dimethylpyrazole) with wet AgBF₄ in a 1:1 ratio lead to the cationic pyrazolylamidino complexes fac-[Mn(OH₂)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]BF₄. The aquo ligand is readily substituted by 2,6-xylylisocyanide (CNXyl) to give fac-[Mn(CNXyl)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]BF₄. The pyrazole complexes fac-[Mn(pz^∗H)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]BF₄ are obtained by treating fac-[MnBr(CO)₃(NCMe)₂] with AgBF₄ and then with pyrazole (pzH or dmpzH), in a 1:1:2 ratio. A similar reaction using 1:1:1 ratio and AgClO₄ leads to the acetonitrile complexes fac-[Mn(NCMe)(CO)₃(NHC(CH₃)pz^∗-κ²N,N)]ClO₄. The X-ray structures of the complexes show moderate hydrogen bonds interactions between the N-bond hydrogen of the pyrazolylamidino ligand and the anion. In the aquo complex, one of the hydrogens of the coordinated water molecule is also involved in a hydrogen bond.     

About the stability of Au(NH3) 4 3+ in aqueous solution

The transformations of Au(OH) ₄ ^? in aqueous solutions (T = 20°C, I = 1) containing NH₃ and NH ₄ ⁺ (pH 8.1–8.5) were studied. The most pronounced changes in the system occur in the range 0 > log [NH ₄ ⁺ ] > ?2.0 (c _Au = (1?10) × 10^?4 mol/L, the monitoring time was about two weeks). When log [NH ₄ ⁺ ] > 0, Au(NH₃) ₄ ³⁺ dominates together with the amido form Au(NH₃)₃NH ₂ ²⁺ ; when log [NH ₄ ⁺ ] < ?2.0, no changes in the spectra are observed, probably, because of the very low rate of the processes. As c _Au increases in the indicated range, the polymerization rate grows. The equilibrium constant for Au(NH₃)₃OH²⁺ + NH₃ = Au(NH₃) ₄ ³⁺ + OH is log $ K_{4 OH, NH_3 } The transformations of Au(OH)₄⁻ in aqueous solutions (T = 20°C, I = 1) containing NH₃ and NH₄⁺ (pH 8.1–8.5) were studied. The most pronounced changes in the system occur in the range 0 > log [NH₄⁺] > −2.0 (c _Au = (1−10) × 10⁻⁴ mol/L, the monitoring time was about two weeks). When log [NH₄⁺] > 0, Au(NH₃)₄³⁺ dominates together with the amido form Au(NH₃)₃NH₂²⁺; when log [NH₄⁺] < −2.0, no changes in the spectra are observed, probably, because of the very low rate of the processes. As c _Au increases in the indicated range, the polymerization rate grows. The equilibrium constant for Au(NH₃)₃OH²⁺ + NH₃ = Au(NH₃)₄³⁺ + OH is log = −4.2 ± 0.3. This constant was used together with other constants, taking into account possible ligand effects, to estimate the formation constant of Au(NH₃)₄³⁺: logβ₄ = 47 ± 1, E _3/0 = 0.64 ± 0.02 V, log = −8.5 ± 1 (substitution of 4 NH₃ for 4 OH⁻ in Au(OH)₄⁻), log = 17.5 ± 1 (substitution of 4NH₃ for 4Cl⁻ in AuCl₄⁻). Original Russian Text ? I.V. Mironov, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 4, pp. 711–715.     

Synthese und Kristallstruktur von Na10[P4(NH)6N4](NH2)6(NH3)0,5 mit dem adamantanartig aufgebauten Anion [P4(NH)6N4]4−

Synthesis and Crystal Structure of Na₁₀[P₄(NH)₆N₄](NH₂)₆(NH₃)_0.5 with an Adamantane-like Anion [P₄(NH)₆N₄]^4? Crystals of Na₁₀[P₄(NH)₆N₄](NH₂)₆(NH₃)_0.5 were obtained by the reaction of P₃N₅ with NaNH₂ (molar ratio 1:20) within 5 d at 600°C in autoclaves. The following data characterize X-ray investigations: Fm3 m, Z = 8, a = 15.423(2) Å, Z(F) = 261 with F ≥ 3 σ(F) Z(Variables) = 27, R/R_w = 0.086/0.089 The compound contains the hitherto unknown anion [P₄(NH)₆N₄]^4?, which resembles adamantane. The total structure can be described as follows: The centers of gravity of units of [Na₈(NH₂)₆(NH₃)]²⁺ – 8Na⁺ on the corners of a cube, 6NH₂^? on the ones of an inscribed octahedron with NH₃ in the center – follow the motif of a cubic-closest packed arrangement. Units of [Na₁₂(NH₂)₆]⁶⁺ – 12Na⁺ on the corners of a cuboctahedron and 6NH₂^? on the ones of an inscribed octahedron – occupy all octahedral and those of [P₄(NH)₆N₄]^4? all tetrahedral sites.     

Nickel(II) and copper(II) complexes of macrocyclic and acyclic Schiff-base ligands derived from new asymmetrical tripodal tetraamines and 2,6-diacetylpyridine

The asymmetrical tripodal 4,2,2-tetraamine N{(CH₂)₄NH₂}{(CH₂)₂NH₂}₂ bee, 3,2,2-tetraamine N{(CH₂)₃NH₂} {(CH₂)₂NH₂}₂ pee, and 3,3,2-tetraamine N{(CH₂)₃NH₂}₂{(CH₂)₂NH₂} ppe ligands have been prepared. In the presence of Cu^II or Ni^II ions, these ligands condense with 2,6-diacetylpyridine. In some cases, cyclization occurs and new isomers of CR-type with a pendant primary amine group are formed. In the other cases ring closure does not occur and coordinated acyclic hexadentate ligands have been isolated. At room temperature and in absolute methanol the latter acyclic complexes are usually the only products. I.r., u.v.–vis., reflectance spectra and magnetic moments for the complexes were recorded.     

The2 E↔4 A 2 transition in tetragonal Cr3+ complexes

The² E⁴ A ₂ absorption and emission spectra of [Cr(NH₃)₅(NO₃)](NO₃)₂, [Cr(NH₃)₅(NO₂)] ·(NO₃)₂, and [Cr(NH₃)₅(H₂O)](NO₃)₃ microcrystals have been recorded at 77°K. Tetragonal²E splittings are 209, 188 and 87 cm^–1, respectively. An analysis of the limited vibronic structure has been made and compared to the results for the parent octahedral complex, [Cr(NH₃)₆](NO₃)₃. Vibrations of approximately 270 and 700 cm^–1 are prominent.

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Zusammenfassung Die² E⁴ A ₂ Absorptions- und Emissionsspektren von [Cr(NH₃)₅(NO₃)](NO₃)₂-, [Cr(NH₃)₅ (NO₂)](NO₃)₂- und [Cr(NH₃)₅(H₂O)](NO₃)₃-Mikrokristallen werden für 77° angegeben. Die tetragonalen² E Aufspaltungen sind209, 188 bzw. 87 cm^–1. Eine Analyse der begrenzten vibronischen Struktur wurde vorgenommen und mit den Resultaten für den oktaedrischen Stammkomplex, [Cr(NH₃)₆](NO₃)₃ verglichen. Schwingungen von etwa 270 und 700 cm^–1 treten besonders hervor.

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Résumé Les spectres d'émission et d'absorption² E⁴ A ₂ de microcristaux de [Cr(NH₃)₅(NO₃)](NO₃)₂, [Cr(NH₃)₅(NO₂)](NO₃)₂ et [Cr(NH₃)₅(H₂O)](NO₃)₃ ont été enregistrés à 77° K. Les écartements tétragonaux² E sont respectivement 209, 188 et 87 cm^–1. Une analyse de la structure vibronique limitée a été effectuée et comparée aux résultats pour le complexe octaédral parent [Cr(NH₃)₆](NO₃)₃. Les vibrations au voisinage de 270 et 700 cm^–1 émergent.

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This contribution is dedicated to the memory of Prof. Hans-Ludwig Schläfer, a stimulating colleague and valued friend.     

Nitride protonation and NH3 binding versus N–H bond cleavage in uranium nitrides

The conversion of metal nitrides to NH₃ is an essential step in dinitrogen fixation, but there is limited knowledge of the reactivity of nitrides with protons (H⁺). Herein, we report comparative studies for the reactions of H⁺ and NH₃ with uranium nitrides, containing different types of ancillary ligands. We show that the differences in ancillary ligands, leads to dramatically different reactivity. The nitride group, in nitride-bridged cationic and anionic diuranium(iv) complexes supported by –N(SiMe₃)₂ ligands, is resistant toward protonation by weak acids, while stronger acids result in ligand loss by protonolysis. Moreover, the basic –N(SiMe₃)₂ ligands promote the N–H heterolytic bond cleavage of NH₃, yielding a “naked” diuranium complex containing three bridging ligands, a nitride (N³⁻) and two NH₂ ligands. Conversely, in the nitride-bridged diuranium(iv) complex supported by –OSi(O^tBu)₃ ligands, the nitride group is easily protonated to afford NH₃, which binds the U(iv) ion strongly, resulting in a mononuclear U–NH₃ complex, where NH₃ can be displaced by addition of strong acids. Furthermore, the U–OSi(O^tBu)₃ bonds were found to be stable, even in the presence of stronger acids, such as NH₄BPh₄, therefore indicating that –OSi(O^tBu)₃ supporting ligands are well suited to be used when acidic conditions are required, such as in the H⁺/e⁻ mediated catalytic conversion of N₂ to NH₃.

Ancillary ligands alter the reactivity of U-nitrides with H⁺, relevant to N₂ conversion to NH₃. The amides lead to complete ligand loss and NH₃ activation, while for siloxides, the nitride is protonated to NH₃ leaving the ancillary ligands intact.