Infrared multiple-photon dissociation of N2H4 and CH3NH2 fluence dependence of the production of NH2

The multiple-photon dissociation of N₂H₄ and CH₃NH₂ by pulsed CO₂ laser light to produce NH₂(X?²B_I has been studied using the laser-induced fluorescence detection method. The relative NH₂ yield, represented by the fluorescence signal, has been measured as a function of the fluence from the threshold at about 0.1 J/cm² to about 100 J/cm², at different CO₂-laser lines and at pressures down to 10^?4 Torr.     

Synthesis, molecular structure, and catalytic activity of borohydride complexes [(Me3Si)2NC(NPri)2]2Nd(BH4)2Li(thf)2 and [(Me3Si)2NC(NPri)2]2Sm(BH4)2Li(thf)2

The reactions of lanthanide tris(borohydrides) Ln(BH₄)₃(thf)₃ (Ln = Sm or Nd) with 2 equiv. of lithium N,N′-diisopropyl-N′-bis(trimethylsilyl)guanidinate in toluene produced the [(Me₃Si)₂NC(NPrⁱ)₂]Ln(BH₄)₂Li(thf)₂ complexes (Ln = Sm or Nd), which were isolated in 57 and 42% yields, respectively, by recrystallization from hexane. X-ray diffraction experiments and NMR and IR spectroscopic studies demonstrated that the reactions afford monomeric ate complexes, in which the lanthanide and lithium atoms are linked to each other by two bridging borohydride groups. The complexes exhibit catalytic activity in polymerization of methyl methacrylate. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 441–445, March, 2007.     

Photocatalytic N2 Fixation by Plasmonic Mo-Doped TiO2 Semiconductor

Photocatalytic N₂ fixation has attracted substantial attention in recent years, as it represents a green and sustainable development route toward efficiently converting N₂ to NH₃ for industrial applications. How to rationally design catalysts in this regard remains a challenge. Here we propose a strategy that uses plasmonic hot electrons in the highly doped TiO₂ to activate the inert N₂ molecules. The synthesized semiconductor catalyst Mo-doped TiO₂ shows a NH₃ production efficiency as high as 134 μmol·g^-1·h^-1 under ambient conditions, which is comparable to that achieved by the conventional plasmonic gold metal. By means of ultrafast spectroscopy we reveal that the plasmonic hot electrons in the system are responsible for the activation of N₂ molecules, enabling improvement the catalytic activity of TiO₂. This work opens a new avenue toward semiconductor plasmon-based photocatalytic N₂ fixation.     

2∞[Yb2(NH2)2( Pz )4][Yb(NH3)2( Pz )3 Pz H]: Electride Induced Synthesis of a 2D-Ytterbium-Pyrazolate Network

Summary. ² _∞[Yb₂(NH₂)₂(Pz)₄][Yb(NH₃)₂(Pz)₃ PzH], Pz ⁻ = pyrazolate anion, PzH = pyrazole, C₃H₄N₂ is obtained by the reaction of ytterbium metal with pyrazole in liquid ammonia and subsequent increase of the temperature to 200°C resulting in the formation of colorless single crystals of the compound. The X-ray single crystal analysis reveals that the structure consists of ² _∞[Yb₂(NH₂)₂(Pz)₄] planes with neutral [Yb(NH₃)₂(Pz)₃ PzH] monomeric molecules that are located between the planes and ytterbium is trivalent. This is the first example of a two-dimensional network structure of an organic amine of the rare earth elements that derives from an electride induced synthesis. The product decomposes under release of ammonia outside its sealed reaction vessel, viz. if the NH₃ pressure is removed.     

2∞[Yb2(NH2)2(Pz)4][Yb(NH3)2(Pz)3PzH]: Electride Induced Synthesis of a 2D-Ytterbium-Pyrazolate Network

² _∞[Yb₂(NH₂)₂(Pz)₄][Yb(NH₃)₂(Pz)₃ PzH], Pz ⁻ = pyrazolate anion, PzH = pyrazole, C₃H₄N₂ is obtained by the reaction of ytterbium metal with pyrazole in liquid ammonia and subsequent increase of the temperature to 200°C resulting in the formation of colorless single crystals of the compound. The X-ray single crystal analysis reveals that the structure consists of ² _∞[Yb₂(NH₂)₂(Pz)₄] planes with neutral [Yb(NH₃)₂(Pz)₃ PzH] monomeric molecules that are located between the planes and ytterbium is trivalent. This is the first example of a two-dimensional network structure of an organic amine of the rare earth elements that derives from an electride induced synthesis. The product decomposes under release of ammonia outside its sealed reaction vessel, viz. if the NH₃ pressure is removed.     

A re-interpretation of the crystal structure of ‘(NH4)2(NH3)[Ni(NH3)2Cl4]’ in terms of (NH4)2−2z[Ni(NH3)2]z[Ni(NH3)2Cl4]

A re-interpretation and re-evaluation of single-crystal X-ray diffraction data of a previously reported ‘(NH₄)₂(NH₃)[Ni(NH₃)₂Cl₄]’ (J. Solid State Chem. 162 (2001) 254) give a new formula (NH₄)_2−2z[Ni(NH₃)₂]_z[Ni(NH₃)₂Cl₄] with z=0.152. This new formula results from defects in an idealized ‘(NH₄)₂[Ni(NH₃)₂Cl₄]’ basic structure, where two adjacent NH₄⁺ cations are replaced by one Ni(NH₃)₂²⁺ unit. Cl⁻ anions from the basic structure complete the coordination sphere of the new Ni²⁺ to [Ni(NH₃)₂Cl₄]²⁻.     

The infrared spectrum and force field of the methyl-ammonium ion in (CH3NH3)2PtCl6

Infrared spectra of the CH₃NH₃⁺, CH₃ND₃⁺, CD₃NH₃⁺ and CD₃ND₃⁺ ions in bis(methylammonium)hexachloroplatinate(IV) have been recorded. The spectra are entirely consistent with the C_3v symmetry reported for the methylammonium ion, at temperatures between room temperature and 90 K. No spectral manifestations of the phase transition, which in (CH₃NH₃)₂PtCl₆ has been reported to take place at 125 K, were observed. Assignments of the infrared-active fundamentals have been made for each ion and a normal-coordinate analysis has been performed using the observed fundamental frequencies. Comparison with the infrared spectra of other methylammonium salts shows that hydrogen bonding in (CH₃NH₃)₂PtCl₆, if present, is weak.     

(H2NC4H8NCH2CH2NH2)(HNCH2CH2NH2)3Zn2Ge2Se8: A new,templated one-dimensional ternary semiconductor stabilized by mixed organic cations

The novel, 1D semiconductor (H₂NC₄H₈NCH₂CH₂NH₂)(HNCH₂CH₂NH₂)₃Zn₂Ge₂Se₈ has been synthesized under solvothermal conditions using N-(2-aminoethyl)piperazine as solvent and templating agent at 200 °C. The material was characterized by single crystal and powder X-ray diffraction, IR and Raman spectroscopy and thermogravimetric analysis. The compound consists of 1D anionic [Zn₂Ge₂Se₈]⁴⁻ chains made of alternating edge-shared [ZnSe₄] and [GeSe₄] tetrahedra that charged balanced by one N-(2-aminoethyl)piperazinium and three piperazinium cations. The optical properties were investigated with solid state UV–Vis/near IR spectroscopy and the results show that the solid is a medium gap semiconductor with an absorption edge at 1.8 eV.     

35Cl NQR in N3P3Cl4Ph2 and N3P3Cl4(NMe2)2

³⁵Cl NQR has been investigated in two cyclotriphosphazene derivatives N₃P₃Cl₄Ph₂ and N₃P₃Cl₄(NMe₂)₂. The observed frequencies are assigned to the various chlorines and the temperature variation of the NQR frequencies studied in the range from 77 K to 300 K. The results are analysed using the Bayer-Kushida-Brown approach. Torsional (librational) frequencies are found to fall in the range 10–25 cm^?1 and are found to be only slightly temperature dependent.     

Ionization gauge sensitivities of N2, O2, N2O, NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^–1 Pap1.3·10^–3Pa. Nitrogen was used as a calibration standard.     

Laser fluorescence of NH2 and rate constant measurement of NH2 + NO

Laser induced fluorescence from the òA₁ state of the NH₂ radical, obtained by different methods, has been observed with a tunable cw dye laser as excitation source. Using pulsed photolysis of NH₃ to produce NH₂, the fluorescence technique has been employed in a first gas kinetic application to measure the rate constant of the aeronomically interesting NH₂ + NO reaction at 298 K. A value of (2.1 ± 0.2) × 10^-11 cm³ molecule^-1 s^-1 has been obtained.     

New results in the ammonolysis of hexafluoro-cyclo-triphosphazene: Crystal structure of P3N3F5–NH–P3N3F4NH2

The reaction of hexafluoro-cyclo-triphosphazene P₃N₃F₆ with ammonia in acetonitrile has been studied. New compounds, (2-imino-2,4,4,6,6-pentafluoro-2λ⁵,4λ⁵,6λ⁵-cyclo-triphosphaza-1,3,5-trienyl)-2-amino-4,4,6,6-tetrafluoro-2λ⁵,4λ⁵,6λ⁵-cyclo-triphosphaza-1,3,5-triene, P₃N₃F₅–NH–P₃N₃F₄NH₂ (2) and cis and trans isomers of non-gem-2,4-diamino-2,4,6,6-tetrafluoro-2λ⁵,4λ⁵,6λ⁵-cyclo-triphosphaza-1,3,5-triene, P₃N₃F₄(NH₂)₂ (4, 5)_, were detected by GC/MS, and ³¹P NMR spectroscopy in reaction mixtures. X-ray diffraction analysis of P₃N₃F₅–NH–P₃N₃F₄NH₂ (2) revealed two conformational polymorphs, 2A and 2B, the latter being built up of two different conformers that were further denoted as 2B_a (the same as the single conformer in 2A) and 2B_b. The compound 2 was characterized by spectroscopic methods and its 2D potential energy surface (PES) was described by density functional theory computations depending on two dihedral angles. The calculated PES spans over 30 kJ/mol in energy including 8 local minima and all first and second order saddle points. The occurrence of the two experimentally observed conformers 2B_a and 2B_b seems to be governed by crystal packing effects.     

The role of NH3 atmosphere in preparing nitrogen-doped TiO2 by mechanochemical reaction

NH₃ atmosphere in ball milling plays an important role in preparing TiO_2−XN_X by a simple mechanochemical reaction. The results show that the structure transformation of titania milled in NH₃ is greatly delayed compared with that in air. The specific surface area of titania milled in NH₃ for 2 h is two times larger than that in air. It was also found that titania prepared in NH₃ has obvious absorbance for visible light. Mechanochemical milling in NH₃ atmosphere offers a new route to prepare TiO_2−XN_X with high surface area.     

Infrared studies of the diatomic molecules O2, N2, NO and H2 adsorbed on Fe2O3

An infrared spectroscopic study of the diatomic molecules O₂, N₂, NO and H₂ adsorbed under different conditions on Fe₂O₃ has been performed.Complex patterns of absorption on both α-Fe₂O₃ and γ-Fe₂O₃ activated in O₂ at high temperature are assigned to vibrations of two different chemisorbed O₂ species.N₂ molecules do not interact with “oxygen rich” α-Fe₂O₃ surfaces, but give N₂O^? and N₂O₂^2? species when chemisorbed on evacuated surfaces.NO molecules give complex patterns of absorption, depending on the gas pressure. Three different types of nitrate structures can be identified, as well as NO, NO^? and cis-N₂O₂ chemisorbed species. Chemisorbed water molecules are formed by contact of H₂ with Fe₂O₃ surfaces even at room temperature.     

Studies on the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g)

Strongly enhanced N₂ first positive emission N₂(B ³Π_g → A ³Σ⁺_u) has been observed on addition of N atoms into a flowing mixture of Cl and HN₃. The dependence of the emission intensity on N atom concentration gave a rate constant for the reaction N + N₃ → N₂(B ³Π_g) + N₂(X ¹Σ⁺_g) of _i(1.6 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1. That for the reaction Cl + HN₃ → HCl + N₃ is (8.9 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1 from the decay of the emission. Comparison of the emission intensity in ClHN₃ with that in ClHN₃N gave the rate constant of the reaction N₃ + N₃ → N₂(B ³Π_g) + 2N₂(X ¹Σ⁺_g) as 1.4 × 10^?12 cm³ molecule^?1 s^?1 on the assumption that N + N₃ yields only N₂(B ³Π_g) + N₂(X ¹Σ⁺_g).     

Synthesis and characterisation of the amidine complexes trans-[PtCl(NH3){HNC(NH2)R}2]Cl (R = Me, Ph, CH2Ph) derived from addition of NH3 to the coordinated nitriles in trans-[PtCl2(NCR)2]

The di-nitrile complexes trans-[PtCl₂(NCR)₂] (R = Me, Ph, CH₂Ph) react with an excess of gaseous NH₃ in CH₂Cl₂ at −10 °C to form, in high yield, the corresponding di-amidine complexes trans-[PtCl(NH₃){HNC(NH₂)R}₂]Cl in which also one chlorine ligand has been displaced by NH₃. The ¹H NMR spectra in DMSO showed the formation of different species which were characterized through NOESY, TOCSY and ¹H/¹³C heteronuclear correlations as trans-[Pt(NH₃){HNC(NH₂)R}₂(DMSO)]Cl₂ and trans-[PtCl{HNC(NH₂)R}₂(DMSO)]Cl.     

Influence of coordination on N-H X hydrogen bonds. Part II. Zn(NH3)2Br2 and Ni(NH3)2X2 (X is Cl and Br)

Microcrystalline samples of Zn(NH₃)₂Br₂ and Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻) have been investigated from 100 to 293 K using X-ray diffraction and IR spectroscopy measurements (range 400–4000 cm⁻) performed with isotopically dilute (5% deuterated) samples. Values of Δν(ND)/ΔT for all compounds hint at the existence of hydrogen bonds. Zn(NH₃)₂Br₂ shows The dynamics of ammonia molecules even at 100 K, and no indications are apparent that dynamic disorder of ammonia molecules takes place in Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻). A comparison between octahedrally coordinated ammoniates [Ni(NH₃)₆]Br₂, Ni(NH₃)₂Br₂ and [Zn(NH₃)₆]Br₂ with tetrahedrally coordinated ones [Zn(NH₃)₂Br₂] leads to the conclusion that the lower coordination number increases the strength of the hydrogen bonds. Because this effect is small, it is not possible to separate the influence of the type of coordinating ions for one coordination number from the influence of the coordination number itself.     

IR and Raman spectra of two layered aluminium phosphates Co(en)3Al3P4O16 · 3H2O and [NH4]3[Co(NH3)6]3[Al2(PO4)4]2 · 2H2O

The FT IR and FT Raman spectra of Co(en)₃Al₃P₄O₁₆ · 3H₂O (compound I) and [NH₄]₃[Co(NH₃)₆]₃[Al₂(PO₄)₄]₂ · 2H₂O (compound II) are recorded and analysed based on the vibrations of Co(en)₃³⁺, Co(NH₃)₆³⁺, NH₄⁺, Al---O---P, PO₃, PO₂ and H₂O. The observed splitting of bands indicate that the site symmetry and correlation field effects are appreciable in both the compounds. In compound I, the overtone of CH₂ deformation Fermi resonates with its symmetric stretching vibration. The NH₄ ion in compound II is not free to rotate in the crystalline lattice. Hydrogen bonding of different groups is also discussed.     

1,2-Eliminations from (CH3)2NH+CH2CH3 and (CH3)2NH 2+ : Guided dissociations

1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations, elimination of CH₂=CH₂ and CH₃CH₃ from (CH₃)₂NH⁺CH₂CH₃ (1) and of CH₄ from (CH₃)₂NH₂⁺ are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from methyl to the bridging position in ethyl and then to N to reach (CH₃)₂NH₂⁺ + CH₂=CH₂ from 1. CH₃CH₃ elimination by H-transfer to C₂H₅⁺ to form CH₃NH⁺=CH₂ + CH₃CH₃ also takes place. (CH₃)₂NH₂⁺ eliminates methane by CN bond extension followed by β-H-transfer to give CH₂=NH⁺ + CH₄. Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type of reaction. As in many complex-mediated reactions, these reactions transfer H between incipient fragments. They are distinguished from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described lower energy reactions, have 1,1-like transition states, or utilize highly asynchronous 1,2 transition states. All of these avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry.