Trimeric cluster of lithium amidoborane—the smallest unit for the modeling of hydrogen release mechanism

A detailed first‐principle DFT M06/6‐311++G(d.p) study of dehydrogenation mechanism of trimeric cluster of lithium amidoborane is presented. The first step of the reaction is association of two LiNH₂BH₃ molecules in the cluster. The dominant feature of the subsequent reaction pathway is activation of H atom of BH₃ group by three Li atoms with formation of unique Li₃H moiety. This Li₃H moiety is destroyed prior to dehydrogenation in favor of formation of a triangular Li₂H moiety, which interacts with protic H atom of NH₂ group. As a result of this interaction, Li₂H₂ moiety is produced. It features N^?? H⁺? H^? group suited near the middle plane between two Li⁺ in the transition state that leads to H₂ release. The transition states of association and hydrogen release steps are similar in energy. It is concluded that the trimer, (LiNH₂BH₃)₃, is the smallest cluster that captures the essence of the hydrogen release reaction. © 2016 Wiley Periodicals, Inc.     

A localised orbital study of bond properties in LiNH+3, LiNH2 and Li2NH

In this paper we report Boys-localised MO's for LiNH⁺₃, LiNH₂ and Li₂NH and an analysis of their one-electron properties and population analysis indices.     

Amminelithium Amidoborane Li(NH3)NH2BH3: A New Coordination Compound with Favorable Dehydrogenation Characteristics

The monoammoniate of lithium amidoborane, Li(NH₃)NH₂BH₃, was synthesized by treatment of LiNH₂BH₃ with ammonia at room temperature. This compound exists in the amorphous state at room temperature, but at ?20 °C crystallizes in the orthorhombic space group Pbca with lattice parameters of a=9.711(4), b=8.7027(5), c=7.1999(1) Å, and V=608.51 ų. The thermal decomposition behavior of this compound under argon and under ammonia was investigated. Through a series of experiments we have demonstrated that Li(NH₃)NH₂BH₃ is able to absorb/desorb ammonia reversibly at room temperature. In the temperature range of 40–70 °C, this compound showed favorable dehydrogenation characteristics. Specifically, under ammonia this material was able to release 3.0 equiv hydrogen (11.18 wt %) rapidly at 60 °C, which represents a significant advantage over LiNH₂BH₃. It has been found that the formation of the coordination bond between ammonia and Li⁺ in LiNH₂BH₃ plays a crucial role in promoting the combination of hydridic B? H bonds and protic N? H bonds, leading to dehydrogenation at low temperature.     

Synthesis and Photocatalytic Activity of Poly(triazine imide)

Poly(triazine imide) was synthesized with incorporation of Li⁺ and Cl^? ions (PTI/Li⁺Cl^?) to form a carbon nitride derivative. The synthesis of this material by the temperature‐induced condensation of dicyandiamide was examined both in a eutectic mixture of LiCl–KCl and without KCl. On the basis of X‐ray diffraction measurements of the synthesized materials, we suggest that a stoichiometric amount of LiCl is necessary to obtain the PTI/Li⁺Cl^? phase without requiring the presence of KCl at 873 K. PTI/Li⁺Cl^? with modification by either Pt or CoO_x as cocatalyst photocatalytically produced H₂ or O₂, respectively, from water. The production of H₂ or O₂ from water indicates that the valence and conduction bands of PTI/Li⁺Cl^? were properly located to achieve overall water splitting. The treatment of PTI/Li⁺Cl^? with [Pt(NH₃)₄]²⁺ cations enabled the deposition of Pt through ion exchange, demonstrating photocatalytic activity for H₂ evolution, while treatment with [PtCl₆]^2? anions resulted in no Pt deposition. This was most likely because of the preferential exchange between Li⁺ ions and [Pt(NH₃)₄]²⁺ cations.     

Studies of layered uranium (VI) compounds. VI. Ionic conductivities and thermal stabilities of MUO2PO4 · nH2O,where M = H,Li,Na,K,NH4 or 12Ca, and where n is between 0 and 4

We have measured the ionic conductivities of pressed pellets of the layered compounds MUO₂PO₄ · nH₂O, and correlated the results with TGA data. The conductivities (in ohm^?1 m^?1), at temperatures increasing with decreasing water content over the range 20 to 200°C, were approximately as follows: Li⁺4H₂O, 10^?4; Li⁺, Na⁺, K⁺, and NH₄⁺3H₂O, 10^?4, 10^?2, 10^?4, and 10^?4; H⁺, Li⁺, and Na⁺1.5H₂O, 10^?2, 10^?4, and 10^?4; Na⁺1H₂O, 10^?5; H⁺, K⁺, and NH₄⁺0.5H₂O, all 10^?5; and H⁺, Li⁺, Na⁺, K⁺, NH⁺₄, and $\text{1}\text{2}\text{Ca}{}^{\mathrm{2+}}\text{}\text{OH}{}_2\text{O}$, 10^?5, 10^?5, 10^?4, 10^?5, 10^?5, and 10^?6. A ring mechanism is proposed to account for the high conductivity found in NaUO₂PO₄ · 3.1H₂O. The accurate TGA data showed that most of the hydrates had water vacancies of the Schottky type, and should be represented as MUO₂PO₄(A ? x)H₂O, where x can be between 0 and 0.3.     

5,5′‐Hydrazinebistetrazole: An Oxidation‐stable Nitrogen‐rich Compound and Starting Material for the Synthesis of 5,5′‐Azobistetrazolates

All 5,5′‐hydrazinebistetrazoles reported in the literature are sensitive to oxidation and react with atmospheric oxygen to yield the corresponding 5,5′‐azobistetrazolates on time. Herewith, we report on the synthesis of the free acid 5,5′‐hydrazinebistetrazole (HBT) which showed to be stable on air for extended periods of time. The compound was fully characterized by analytical and spectroscopic methods and its X‐ray structure was determined by diffraction techniques. Besides, we determined its explosive properties by BAM methods and calculated its heat of formation (+414 kJ mol^?1), detonation velocity (8523 m s^?1) and detonation pressure (27.7 GPa). HBT proved to be very safe to handle (impact sensitivity: >30 J, friction sensitivity: ～108 N) and was used as a starting material for the synthesis of some already reported 5,5′‐azobistetrazolates: NH₄⁺, NH₂NH₃⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺.     

Application of Nafion／Cobalt Hexacyanoferrate Chemically Modified Electrodes for the Determination of Electroinactive Cations by Ion Chromatography

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On the complexation of some univalent cations with beauvericin in nitrobenzene saturated with water

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M⁺(aq)?+?1·Cs⁺(nb) ? 1·M⁺(nb)?+?Cs⁺(aq) taking place in the two-phase water–nitrobenzene system (M⁺?=?Li⁺, Na⁺, K⁺, Rb⁺, H₃O⁺, NH₄ ⁺, Tl⁺; 1?=?beauvericin; aq?=?aqueous phase, nb?=?nitrobenzene phase) were determined. Moreover, the stability constants of the 1·M⁺ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the series of Rb^+?<?Na⁺, H₃O^+?<?Tl^+?<?NH ₄ ^+? <?K^+?<?Li⁺.     

Applying the polarization model to selected ionic substances

The polarization model is applied to Li⁺ and F^? in their interactions with water and with themselves. The model is also applied to NH₃ and NH₄⁺ in their interactions with water. Results on applying the polarization model to PO₄^3?, HPO₄^2?, H²PO₄^? and H₃PO₄ in their interactions with water are reported. Finally, results on CO₃^2?, HCO₃^?, H₂CO₃ and CO₂ are reported.     

Li2Br(NH2): Das erste ternäre Alkalimetallamidhalogenid

Li₂Br(NH₂): The First Ternary Alkali Metal Amide Halide The pseudobinary system LiNH₂/LiBr was investigated by X-ray methods. The crystal structure of the compound Li₂Br(NH₂) was solved by single crystal data: Li₂Br(NH₂): Pnma, Z = 8, a = 12.484(2) Å, b = 7.959(1) Å, c = 6.385(1) Å, Z(F_o) with (F_o)² ≧ 3σ(F_o)² = 348, Z (parameter) = 51, R/R_w = 0.019/0.021 Li₂Br(NH₂) crystallizes in a new type of structure. To one another isolated chains of [Li₂Li_4/2(NH₂)₂²⁺] show the motif of closest rod packing. They are connected via bromide ions in a distorted cubic primitive arrangement.     

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N₂ to N^3? with high efficiency. It had been proposed that this could be coupled with H₂ oxidation in an electrolytic cell to produce NH₃ at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li₃N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N^3? to NH₃ is grossly over‐simplified. We find that Li₃N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H₂ (H oxidation state 0) into H^? (H oxidation state ?1) and H⁺ in the form of NH^2?/NH₂^?/NH₃ (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH₃. It is further observed that NH^2? and NH₂^? possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li₃N, N₂ can be reduced to N^3? while stoichiometric amounts of H^? are oxidised to H₂. The H₂ can then react spontaneously with N^3? to form NH₃, regenerating H^? and closing the catalytic cycle. Initial tests show a peak NH₃ synthesis rate of 2.4×10^?8 mol cm^?2 s^?1 at a maximum current efficiency of 4.2 %. Isotopic labelling with ¹⁵N₂ confirms the resulting NH₃ is from catalytic N₂ reduction.     

Guanidinium-selective PVC membrane electrodes based on crown ethers

Guanidinium-selective membrane electrodes were constructed with dibenzo-24-crown-8, dibenzo-27-crown-9, tribenzo-27-crown-9 or dibenzo-30-crown-10. The detection limits and selectivity coefficients towards different interfering ions, such as Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺ and Ca²⁺ were determined. The electrode with dibenzo-27-crown-9 shows linear response over the range 10^?1–10^?4 M, with selectivity coefficients about 10^?2 for most alkali and alkaline earth metal ions.     

The properties of the ion associates of benzophenone in DMF

The properties of the ion associates of benzophenone (BP) free radicals with Na⁺ and Li⁺ have been investigated polarographically in dimethylformamide. It was found that BP^? forms ion pairs with Na⁺ (K_ass=69 M^?1) and two types of associates with Li⁺: BP^?...Li⁺ (K_ass,1=330 M^?1) and BP^?...(Li⁺)₂(K_ass,2M^?2). The influence of temperature on the equilibria was also discussed. The ion associates with Li⁺ disappear in a disproportionation reaction; the mechanism and kinetics of that reaction were studied. It was found that the main contribution to the overall kinetics are made by the pairs (a) BP^?...Li⁺+BP^?...Li⁺, (b) BP^?+BP^?...(Li⁺)₂ (c) BP^?...Li⁺+BP^?...(Li⁺)₂.     

The nature of the bonding of Li+ to H2O and NH3; A3 initio studies

Ab initio wavefunctions have been calculated for the complex of Li⁺ with NH₃ and H₂O in order to better characterize the nature of the bonding. Hartree—Fock and generalized valence bond calculations were performed using a double zeta basis plus polarization functions. The binding energies obtained at the GVB level are D_e (Li⁺ — NH₃) = 40.4 kcal/mol and D_e (Li⁺ ? H₂O) = 37.6 kcal/mol, in reasonable agreement with experimental values. Model calculations indicate that the Li⁺ ? base bond is basically electrostatic. Small basis sets were found to lead to D_e as large as 75 kcal/mol for Li⁺ — NH₃, a significant overestimation. Repulsions due to the Li⁺ core are responsible for keeping the Li⁺ too far away for significant relaxation effects.     

The [CH5NO]+ ˙ potential energy surface: Distonic ions,lon-dipole complexes and hydrogen-bridged radical cations

By combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision-induced dissociative ionization, neutralization-reionization spectrometry, ²H, ¹³C and ¹⁸O isotopic labelling and appearance energy measurements) and high-level ab initio molecular orbital calculations, the potential energy surface of the [CH₅NO]^{+ ˙} system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH₃ONH₂]^{+ ˙} and [HO? CH₂? NH₂]^{+ ˙}, the distonic ions [O? CH₂? NH₃]^{+ ˙}, [O? NH₂? CH₃]^{+ ˙}, [CH₂? O(H)? NH₂]^{+ ˙}, [HO? NH₂? CH₂]^{+ ˙}, and the ion-dipole complex CH₂?NH₂⁺ …? OH˙. Surprisingly the distonic ion [CH₂? O? NH₃]^{+ ˙} was found not to be a stable species but to dissociate spontaneously to CH₂?O + NH₃^{+ ˙}. The most stable isomer is the hydrogen-bridged radical cation [H? C?O …? H …? NH₃]^{+ ˙} which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH₂?O …? H …? NH₂]^{+ ˙}, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H₂N? C(?O)? OCH₃ and the proposed mechanism involves a 1,4-H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH₂?O …? H …? NH₂]^{+ ˙} product ions fragment exothermically, but via a barrier, to NH₄^{+ ˙} HCO^…? and to H₃N? C(H)?O^{+ ˙} H˙. Metastable ions [CH₃ONH₂]^+…? dissociate, via a large barrier, to CH₂?O + NH₃⁺ + and to [CH₂NH₂]⁺ + OH˙ but not to CH₂?O^{+ ˙} + NH₃. The former reaction proceeds via a 1,3-H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2-CH₃ shift to produce excited [O? NH₂? CH₃]^{+ ˙}, which rearranges to excited [HO? NH₂? CH₂]^{+ ˙} via a 1,3-H shift after which dissociation follows.     

Kinetics and mechanism of the iodine oxidation of hydroxylamine

Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH₂OH + 2I₂ = N₂O + 4I^? + H₂O + 4H⁺. Since the reaction is first-order in [I₂] + [I₃^?], the specific rate law, k₀, is k₀ = (k₁ + k₂/[H⁺]) {[NH₃OH⁺]₀/(1 + K_p[H⁺])} {1/(1 + K_I[I^?])}, where [NH₃OH⁺]₀ is total initial hydroxylamine concentration, and k₁, k₂, K_p, and K_I are (6.5 ± 0.6) × 10⁵ M^?1 s^?1, (5.0 ± 0.5) s^?1, 1 × 10⁶ M^?1, and 725 M^?1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH₂OH) and molecular iodine (I₂) as reactive species, with intermediates NH₂OI₂^?, HNO, NH₂O, and I₂^?, is proposed.     

über den Mechanismus der Extraktion von Gold(III) mit gesÄttigten aliphatischen Monoketonen

It has been found, that gold(III) is extracted by way of a hydrate-solvated mechanism from a hydrochloric acid medium with aliphatic ketones (in the presence or absence of a solvent). When the methylethylketone is used as an extractant, the solvate has the following composition:M ⁺(H₂O)_3–14 (MEK)₇AuCl₄ ^?, whereM ⁺=H⁺, Li⁺, K⁺, Na⁺, NH₄ ⁺. If the cation is a heavy non-solvated ion, for instance N(C₂H₅)₄ ⁺, the solvate is free of water. The active extractant solvates also the anion AuCl₄ ^?, a fact which could explain the high values of the coefficient of distribution.     

Relationship between the Physicochemical Properties of Electrolytes and the Electronic Structure of Solvated Alkali Metal Cations

Group theoretical analysis and linear combinations of molecular orbitals of the cation and solvent are used to establish the nature and stability of bonds and hence the electric mobility of the cation and the viscosity of the electrolyte depending on the type of cation (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and molecules (H₂O, NH₃, H₂CO, (CH₃)₂CO, CH₃CN). Solvation effects on the UV photoelectron and intramolecular vibrational IR and NMR spectra are revealed.     

A theoretical approach to substituent effects: Interaction between directly bonded groups in the isoelectronic series XNH3+, XCH3, and XBH3−

Ab initio molecular orbital theory including full geometry optimization at the 4-31G level is used to examine the interactions between substitutents X(X = Li, BeH, BH₂, CH₃, NH₂, OH and F) and substrates Y(Y = NH₃⁺, CH₃, BH₃^?) in the isoelectronic series XNH₃⁺, XCH₃ and XBH₃^?. The results indicate that the interaction energies are dominated by σ-effects. NH₃⁺ is found to interact favorably with the σ-donors (e.g. Li, BeH and BH₂) and unfavorably with the σ-acceptors (e.g. F, OH, NH₂). The reverse pattern a observed for XBH₃^?. The range of interaction energies for XCH₃ is considerably smaller than for XNH₃⁺ and XBH₃^?.     

Investigations on the solid state interaction between LiAlH4 and NaNH2

In this paper, two LiAlH₄-NaNH₂ samples with LiAlH₄ to NaNH₂ molar ratio of 1/2 and 2/1 were investigated, respectively. It was observed that both samples evolved 2 equiv H₂ in the ball milling process, however, the reaction pathways were different. For the LiAlH₄-NaNH₂ (1/2) sample, Li₃Na(NH₂)₄ and NaAlH₄ were formed through cation exchange between reactants. The NaAlH₄ formed further reacts with Li₃Na(NH₂)₄ and NaNH₂ to give H₂, NaH and LiAlN₂H₂. For the LiAlH₄-NaNH₂ (2/1) sample, Li₃Na(NH₂)₄, LiNH₂ and NaAlH₄ were formed firstly through the same cation exchange process. The resulting LiNH₂ reacts with the remaining LiAlH₄ and produces H₂ and Li₂AlNH₂.