scholarly journals Activation of Ammonia and Hydrazine by Electron Rich Fe(II) Complexes Supported by a Dianionic Pentadentate Ligand Platform Through a Common Terminal Fe(III) Amido Intermediate

2020 ◽  
Author(s):  
Lucie Nurdin ◽  
Yan Yang ◽  
Peter Neate ◽  
Warren Piers ◽  
Laurent Maron ◽  
...  
Keyword(s):  
Room Temperature ◽  
Ammonia Oxidation ◽  
Important Process ◽  
Hydrogen Atoms ◽  
Ammine Complexes ◽  
Ammonia Complex ◽  
Aminyl Radical ◽  
High Degree ◽  
Radical Character ◽  
Pentadentate Ligand

We report the use of electron rich iron complexes supported by a dianionic diborate pentadentate ligand system, B2Pz4Py, for the coordination and activation of ammonia (NH3) and hydrazine (NH2NH2). For ammonia, coordination to neutral (B2Pz4Py)Fe(II) or cationic [(B2Pz4Py)Fe(III)]+ platforms leads to well characterized ammine complexes from which hydrogen atoms or protons can be removed to generate, fleetingly, a proposed (B2Pz4Py)Fe(III)- NH2 complex (3Ar-NH2). DFT computations suggest a high degree of spin density on the amido ligand, giving it significant aminyl radical character. It rapidly traps the H atom abstracting agent 2,4,6-tri-tert-butylphenoxy radical (ArO•) to form a C-N bond in a fully characterized product (2Ar), or scavenges hydrogen atoms to return to the ammonia complex (B2Pz4Py)Fe(II)-NH3 (1ArNH3). Interestingly, when (B2Pz4Py)Fe(II) is reacted with NH2NH2, a fully characterized bridging diazene complex, 4Ar, is formed along with ammonia adduct 1Ar-NH3 as the spectroscopically observed (-78˚C) (B2Pz4Py)Fe(II)-NH2NH2-Fe(II)( B2Pz4Py) dimer (1Ar)2-NH2NH2 is allowed to warm to room temperature. Experimental and computational evidence is presented to suggest that (B2Pz4Py)Fe(II) induces reductive cleavage of the N-N bond in hydrazine to produce the Fe(III)-NH2 complex 3Ar-NH2, which abstracts H• atoms from (1Ar)2-NH2NH2 to generate the observed products. All of these transformations are relevant to proposed steps in the ammonia oxidation reaction, an important process for the use of nitrogen-based fuels enabled by abundant first row transition metals. <br>

scholarly journals Activation of Ammonia and Hydrazine by Electron Rich Fe(II) Complexes Supported by a Dianionic Pentadentate Ligand Platform Through a Common Terminal Fe(III) Amido Intermediate

2020 ◽  
Author(s):  
Lucie Nurdin ◽  
Yan Yang ◽  
Peter Neate ◽  
Warren Piers ◽  
Laurent Maron ◽  
...  
Keyword(s):  
Room Temperature ◽  
Ammonia Oxidation ◽  
Important Process ◽  
Hydrogen Atoms ◽  
Ammine Complexes ◽  
Ammonia Complex ◽  
Aminyl Radical ◽  
High Degree ◽  
Radical Character ◽  
Pentadentate Ligand

We report the use of electron rich iron complexes supported by a dianionic diborate pentadentate ligand system, B2Pz4Py, for the coordination and activation of ammonia (NH3) and hydrazine (NH2NH2). For ammonia, coordination to neutral (B2Pz4Py)Fe(II) or cationic [(B2Pz4Py)Fe(III)]+ platforms leads to well characterized ammine complexes from which hydrogen atoms or protons can be removed to generate, fleetingly, a proposed (B2Pz4Py)Fe(III)- NH2 complex (3Ar-NH2). DFT computations suggest a high degree of spin density on the amido ligand, giving it significant aminyl radical character. It rapidly traps the H atom abstracting agent 2,4,6-tri-tert-butylphenoxy radical (ArO•) to form a C-N bond in a fully characterized product (2Ar), or scavenges hydrogen atoms to return to the ammonia complex (B2Pz4Py)Fe(II)-NH3 (1ArNH3). Interestingly, when (B2Pz4Py)Fe(II) is reacted with NH2NH2, a fully characterized bridging diazene complex, 4Ar, is formed along with ammonia adduct 1Ar-NH3 as the spectroscopically observed (-78˚C) (B2Pz4Py)Fe(II)-NH2NH2-Fe(II)( B2Pz4Py) dimer (1Ar)2-NH2NH2 is allowed to warm to room temperature. Experimental and computational evidence is presented to suggest that (B2Pz4Py)Fe(II) induces reductive cleavage of the N-N bond in hydrazine to produce the Fe(III)-NH2 complex 3Ar-NH2, which abstracts H• atoms from (1Ar)2-NH2NH2 to generate the observed products. All of these transformations are relevant to proposed steps in the ammonia oxidation reaction, an important process for the use of nitrogen-based fuels enabled by abundant first row transition metals. <br>

scholarly journals Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate

2021 ◽  
Author(s):  
Lucie Nurdin ◽  
Yan Yang ◽  
Peter G. N. Neate ◽  
Warren E. Piers ◽  
Laurent Maron ◽  
...  
Keyword(s):  
Transition Metal ◽  
Ammonia Oxidation ◽  
Oxidation Processes ◽  
Pentadentate Ligand

Synopsis: a highly reactive Fe(iii)–NH2 complex is generated via activation of ammonia or hydrazine in reactions of relevance to fundamental steps in ammonia oxidation processes mediated by an abundant, first row transition metal.

Investigation of the Hydrogen Transport Processes in Crystalline Silicon of n-Type Conductivity

2007 ◽  
Vol 131-133 ◽  
pp. 425-430 ◽  
Author(s):  
Anis M. Saad ◽  
Oleg Velichko ◽  
Yu P. Shaman ◽  
Adam Barcz ◽  
Andrzej Misiuk ◽  
...  
Keyword(s):  
Hydrogen Concentration ◽  
Room Temperature ◽  
Crystalline Silicon ◽  
Transport Processes ◽  
Concentration Profiles ◽  
Hydrogen Transport ◽  
Hydrogen Atoms ◽  
Near Surface ◽  
Type Conductivity ◽  
Hydrogen Molecules

The silicon substrates were hydrogenated at approximately room temperature and hydrogen concentration profiles vs. depth have been measured by SIMS. Czochralski grown (CZ) wafers, both n- and p-type conductivity, were used in the experiments under consideration. For analysis of hydrogen transport processes and quasichemical reactions the model of hydrogen atoms diffusion and quasichemical reactions is proposed and the set of equations is obtained. The developed model takes into account the formation of bound hydrogen in the near surface region, hydrogen transport as a result of diffusion of hydrogen molecules 2 H , diffusion of metastable complexes * 2 H and diffusion of nonequilibrium hydrogen atoms. Interaction of 2 H with oxygen atoms and formation of immobile complexes “oxygen atom - hydrogen molecule” (O - H2 ) is also taken into account to explain the hydrogen concentration profiles in the substrates of n-type conductivity. The computer simulation based on the proposed equations has shown a good agreement of the calculated hydrogen profiles with the experimental data and has allowed receiving a value of the hydrogen molecules diffusivity at room temperature.

The photochemical and thermal decompositions of hydrogen sulphide

1953 ◽  
Vol 216 (1126) ◽  
pp. 344-361 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Quantum Yield ◽  
Hydrogen Sulphide ◽  
Low Temperatures ◽  
Room Temperature ◽  
Large Fraction ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Photochemical Decomposition ◽  
Bimolecular Mechanism

The photochemical decomposition of hydrogen sulphide has been investigated at pressures between 8 and 550 mm of mercury and at temperatures between 27 and 650° C, using the narrow cadmium line ( λ 2288) and the broad mercury band (about λ 2550). At room temperature the quantum yield increases with pressure from 1.09 at 30 mm to 1.26 at 200 mm. Above 200 mm pressure there was no further increase in the quantum yield. Temperature had little effect on the quantum yield at λ 2550, but there was a marked increase in the rate of hydrogen production between 500 and 650° C with 2288 Å radiation. This may have been caused by the decomposition of excited hydrosulphide radicals. The results are consistent with a mechanism involving hydrogen atoms and hydrosulphide radicals. The mercury-photosensitized reaction is less efficient than the photochemical decomposition, the quantum yield being only about 0.45. The efficiency increased with temperature and approached unity at high temperatures and pressures. This agrees with the suggestion that a large fraction of the quenching collisions lead to the formation of Hg ( 3 P 0 ) atoms. The thermal decomposition is heterogeneous at low temperatures and becomes homogeneous and of the second order at 650° C. The experimental evidence suggests the bimolecular mechanism 2H 2 S → 2H 2 + S 2 . The activation energies are 25 kcal/mole (heterogeneous) and 50 kcal/mole (homogeneous).

scholarly journals Room-temperature autonomous self-healing glassy polymers with hyperbranched structure

2020 ◽  
Vol 117 (21) ◽  
pp. 11299-11305 ◽  
Author(s):  
Hao Wang ◽  
Hanchao Liu ◽  
Zhenxing Cao ◽  
Weihang Li ◽  
Xin Huang ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Room Temperature ◽  
Glassy State ◽  
Glassy Polymers ◽  
Self Healing ◽  
External Branch ◽  
Healing Efficiency ◽  
High Degree ◽  
External Stimuli ◽  
Hyperbranched Structure

Glassy polymers are extremely difficult to self-heal below their glass transition temperature (Tg) due to the frozen molecules. Here, we fabricate a series of randomly hyperbranched polymers (RHP) with high density of multiple hydrogen bonds, which showTgup to 49 °C and storage modulus up to 2.7 GPa. We reveal that the hyperbranched structure not only allows the external branch units and terminals of the molecules to have a high degree of mobility in the glassy state, but also leads to the coexistence of “free” and associated complementary moieties of hydrogen bonds. The free complementary moieties can exchange with the associated hydrogen bonds, enabling network reconfiguration in the glassy polymer. As a result, the RHP shows amazing instantaneous self-healing with recovered tensile strength up to 5.5 MPa within 1 min, and the self-healing efficiency increases with contacting time at room temperature without the intervention of external stimuli.

Structure and water durability of tin(II) organosilicophosphate glasses prepared by nonaqueous acid–base reactions

2006 ◽  
Vol 21 (7) ◽  
pp. 1798-1806 ◽  
Author(s):  
Megumi Mizuno ◽  
Masahide Takahashi ◽  
Toshinobu Yoko
Keyword(s):  
Room Temperature ◽  
Orthophosphoric Acid ◽  
Chain Structure ◽  
Acid Base ◽  
Humid Atmosphere ◽  
Water Durability ◽  
Magnetic Resonance Technique ◽  
A Chain ◽  
Degree Of Condensation ◽  
High Degree

Tin(II) organosilicophosphate glasses were prepared by nonaqueous acid–base reactions using orthophosphoric acid, dimethyldichlorosilane, and tin(II)chloride as the starting materials. The structure of the methylsiloxane-phosphate copolymer (methylsilicophosphate) and tin(II) methylsilicophosphate glasses was mainly investigated by the 31P nuclear magnetic resonance technique. A chain structure composed of the –(P–O–Si–O)m– silicophosphate bonds was found as the main structural unit in the methylsilicophosphate prepared by mixing orthophosphoric acid and dimethyldichlorosilane at room temperature. Tin(II) methylsilicophosphate glasses could be prepared by introducing SnCl2 as a cross-linking agent of silicophosphate chains. By increasing the reaction temperature, it was possible to promote the reaction and then to increase the network dimensions of the resultant tin(II) methylsilicophosphate glasses. It was found that the glasses with a high degree of condensation tend to have a better water durability in a humid atmosphere.

Permeation of Electrolytically Generated Hydrogen and Tritium Atoms through Lead

1971 ◽  
Vol 49 (14) ◽  
pp. 2406-2411 ◽  
Author(s):  
Bansi L. Muju ◽  
Frank R. Smith
Keyword(s):  
Current Density ◽  
Separation Factor ◽  
Room Temperature ◽  
Alkaline Media ◽  
Gas Evolution ◽  
Hydrogen Atoms ◽  
Metal Lattice ◽  
Acidic And Alkaline Media ◽  
A Current ◽  
Lead Foil

Radiochemical and electrochemical evidence is presented that electrochemically generated tritium and hydrogen atoms permeate through lead foil at measureable rates at room temperature. The permeation process is controlled by diffusion through the metal lattice, Fick's First Law being obeyed by both H and 3H atoms. Using earlier measurements of the diffusivity of H in Pb, H and 3H concentrations of 4 × 10−7 and 9 × 10−13 g-atom cm−3 are computed for a current density of 53 mA cm−2 at the Pb cathode surface.The overall hydrogen-tritium separation factor, ST is apparently 0.3 ± 0.15, in contrast to Bockris and Srinivasan's 6.7 and 7.2 for cathodic gas evolution from acidic and alkaline media, respectively. Reasons are suggested for this large difference.

Bromine-79 NQR for uncoordinated Br– ions in trans-[CoBr2(en)2][H5O2]Br2

1992 ◽  
Vol 47 (1-2) ◽  
pp. 129-133 ◽  
Author(s):  
A. Sasane ◽  
T. Matsuda ◽  
H. Honda ◽  
Y. Mori
Keyword(s):  
Hydrogen Bond ◽  
Point Charge ◽  
Room Temperature ◽  
Bond Formation ◽  
Relative Magnitude ◽  
Hydrogen Atoms ◽  
Point Charge Model ◽  
Hydrogen Bond Formation ◽  
Charge Model ◽  
In Trans

AbstractA single 79Br NQR line showing a frequency of 19.594 MHz at room temperature has been observed in the crystals of trans-[CoBr2(en)2] [ H5O2 ] Br2 and assigned to the Br - ions which are not coordinated to the central Co(III) atom. The electric field gradient (EFG) at the Br - nuclei arises from O-H • • • Br - hydrogen bond formation between the Br - ions and the terminal O - H hydrogen atoms in [ H5O2 ] + ions. The induced EFG is greater for the present bromine complex than that for the isostructural chlorine complex. A point charge model calculation explains well the relative magnitude of the EFG in the two crystals by introducing Sternheimer's antishielding factors for the halogen ions.

Flow Phenomena in Rubber Samples

1950 ◽  
Vol 23 (1) ◽  
pp. 67-88
Author(s):  
Fritz Rössler
Keyword(s):  
Low Temperatures ◽  
Test Specimen ◽  
Room Temperature ◽  
Elastic Materials ◽  
Dead Weight ◽  
Point Change ◽  
Different Types ◽  
Flow Phenomena ◽  
High Degree ◽  
Highly Elastic Materials

Abstract A more extended investigation was made of the surprising flow phenomena which were found in an earlier study of rubber at low temperatures. The tensile apparatus was reconstructed so that a dead-weight load could be applied to the rubber test-specimen. Determinations of the dependence of the rate of flow on time of stressing, initial elongation, magnitude of the stress, and temperature showed that a simple law can be derived for expressing the flow phenomena. Yield point, change in color, and deterioration in physical properties, as well as the reversibility of these phenomena were investigated and are discussed. The phenomena of flow at room temperature are expressed by the same constants as at lower temperatures. Only the effective stress increases at low temperatures and only by this change does flow become perceptible. Different types of rubber were compared, and all showed approximately the same value for the flow constant. The essential characteristics of the flow phenomenon can be explained, on a basis of the theory of highly elastic materials, by their microliquid state of aggregation. This applies to the high degree of dependence of the mechanical properties of rubber on the temperature.

Measurement of the diffusion coefficients of reactive species in dilute gases

1982 ◽  
Vol 380 (1779) ◽  
pp. 241-258 ◽  
Keyword(s):  
Gas Phase ◽  
Diffusion Coefficients ◽  
Atmospheric Pressure ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Reactive Species ◽  
Resonance Fluorescence ◽  
Hydrogen Atoms ◽  
Chromatographic Effect ◽  
Diffusion Of Hydrogen

A technique has been developed for measuring the diffusion coefficients of atoms and other reactive species in gases below atmospheric pressure. The technique consists of measuring the rate of dispersion of a pulse of reactive species in a stream of gas flowing rapidly ( ca . 10 m s -1 ) down a quartz tube. The reactive species are observed and the profile of the pulses measured by using resonance fluorescence. The technique has been used at room temperature, but in principle measurements could be made at elevated temperatures. Measurements have been made of the rates of diffusion of hydrogen atoms in argon and nitrogen, and values for the diffusion coefficients of 1.61 ± 0.04 and 1.35 ± 0.03 cm 2 s -1 respectively, at 1 atmosphere ( ca . 10 5 Pa) and 294 K, have been obtained. Incidentally to the primary purpose of the experiment, it was observed that the hydrogen atoms spend a small fraction of their time of passage along the tube reversibly adsorbed on its walls. From the measurements, both the partition coefficient, giving the ratio of hydrogen atoms on the walls to those in the gas phase, and the rates of adsorption and desorp­tion can be obtained. This appears to be the first observation of a chromatographic effect for a highly reactive species.

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