Proton dynamics in superionic phase of Tl3H(SO4)2

Electrical properties and ¹H-NMR absorption line have been measured, in order to investigate proton dynamics in a superionic phase in Tl₃H(SO₄)₂. From the measurement of the thermoelectric power, it is found that a majority carrier in electrical conductivity is a proton. Moreover, from ¹H-NMR measurement it is also found that the activation energy 0.33 eV of the hopping motion of protons is close to 0.38 eV as observed in the electrical conductivity measurement. These results indicate that the electrical conductivity in the superionic phase is caused by the hopping motion of protons accompanied by the breaking of the hydrogen bonds.     

A study of the phase transitions and proton dynamics of the superprotonic conductor Cs5H3(SO4)4·0.5H2O single crystal with H and Cs nuclear magnetic resonance

The phase transitions and proton dynamics of Cs₅H₃(SO₄)₄·0.5H₂O single crystals were studied by measuring the NMR line shape, the spin-lattice relaxation time, T₁, and the spin-spin relaxation time, T₂, of the ¹H and ¹³³Cs nuclei. The “acid” protons and the “water” protons in Cs₅H₃(SO₄)₄·0.5H₂O were distinguished. The loss of water protons was observed above T_C1, whereas the content of water protons was found to recover above T_C2. Therefore, the water protons play a special role in the stability of the superprotonic phase at high temperatures. The mechanism of fast proton conduction was found to consist of hydrogen-bond proton transfer involving the breakage of the weak part of the hydrogen bond and the formation of a new hydrogen bond. Thus, these structural phase transitions probably involve significant reorientation of the SO₄ tetrahedra and dynamical disorder of the hydrogen bonds between them.     

双帽Keggin型杂多阴离子[H4As3Mo12O40]-和Keggin型杂多酸H3PM12O40 (M＝Mo, W)质子化的DFT研究

选用B3LYP方法在LanL2MB水平下, 对双帽α-Keggin型杂多阴离子[H₄As₃Mo₁₂O₄₀]^-的电子结构和质子的定位进行了密度泛函理论(DFT)研究. 结果表明, 双帽的形成大大影响了杂多阴离子[As₃Mo₁₂O₄₀]^5－的电子结构和性质, NBO分析显示参与成帽的三桥氧上的电子密度比双桥氧上的要大, 简单地从电荷密度来看, 质子将首先在三桥氧上定域成键, 但通过比较质子定域在几种桥氧上质子化稳定化能的大小, 发现[H₄As₃Mo₁₂O₄₀]^-中的四个质子将在八个双桥氧中的其中四个氧原子上定位, 而不是如文献中报道的在四个三桥氧上定域成键. 对杂多酸H₃PM₁₂O₄₀ (M＝Mo, W)中质子的定位也进行了理论计算并与文献进行了比较, 结果显示, H₃PMo₁₂O₄₀中质子是定位在双桥氧上; 而H₃PW₁₂O₄₀中质子将优先在双桥氧上定位, 但也可在端氧上定位; 这一结果与文献报道的相一致.     

Magnetic resonance experiments on the radical cation salt (fluoranthenyl)2+ PF6−. Correlation of proton-NMR,fluorine-NMR and ESR

The longitudinal relaxation rates of the protons and the fluorine were determined for the radical cation salt (fluoranthenyl)₂⁺PF₆^? as a function of the temperature. These data are compared with the temperature dependence of the pulsed ESR signal amplitude at the same Larmor frequency (44 MHz). Whereas the fluorines are relaxed mainly by the reorientational motion of the anions and by the interaction with fixed paramagnetic impurities, the protons are relaxed additionally above 150 K predominantly by highly mobile paramagnetic species, whose concentration could be determined directly via the signal amplitudes of the NMR and ESR signals in the same set up. The Pauli susceptibility χ_c^s = 3.1 ×10^?5 cm³/mole which is derived from this experiment and the Korringa relation (T_1H4^?)^?1 = constant of the proton relaxation leads to the assumption of a metal-like behavior of the salt above 183 K. The observation that the protons of the cation stacks, rather than the fluorines on the anions are relaxed by the mobile paramagnetic species favors the assumption of one-dimensional spin transport within the fluoranthenyl stacks, which is further supported by an ω^{$\text{?1}\text{2}$} dependence of T_1H^?1.     

1H endor investigations in tris-sarcosine-calcium chloride doped with manganese

¹H ENDOR spectra of the ferroelectric tris-sarcosine-calcium chloride doped with Mn²⁺ are reported. All identified protons are located in CH₃ groups of sarcosine molecules. From the ENDOR data, the distances of the CH₃ protons from the manganese ion were determined.     

The preparation of NbH5(Me2PCH2CH2Me2)2 and NbHL2(Me2PCH2CH2PMe2)2 (L = CO or C2H4)

MMe₅(dmpe) (M = Nb or Ta, dmpe = Me₂PCH₂CH₂PMe₂) reacts with H₂ (500 atm) and dmpe in THF at 60°C to give MH₅(dmpe)_2? NbH₅(dmpe)₂ readily reacts with two mol of CO or ethylene (L) to give NbHL₂(dmpe)₂. The exchange of the hydride ligand with the ethylene protons in NbH(C₂H₄)₂(dmpe)₂ is not rapid on the ¹H NMR time scale (60 MHz) at 95°C.     

Ba2In2O4(OH)2: Proton sites, disorder and vibrational properties

The structure of Ba₂In₂O₄(OH)₂ is analysed by the explicit full optimization of a large number of possible proton arrangements using periodic density functional theory. It is shown that the experimental assignments in which protons appear to be located at high symmetry positions with unphysical bond lengths do not correspond to minima on the potential energy hypersurface. The apparent sites are averages of a number of possible proton locations involving a set of possible local structural environments in which the internuclear separations are more realistic. Such problems with structural refinements are common where profile refinement programs place the atoms at the average position due to dynamic and/or static disorder. Thus while the calculations support a previous neutron diffraction analysis of the structure in that the average structure contains two different proton sites, they also reveal substantial information about the local environments of the protons. In all optimizations, the protons moved from the average positions suggested in the neutron diffraction study with calculated O–H and OHO distances consistent with those observed in other oxides. The energies of different proton distributions vary significantly so the protons are not randomly distributed. We also present an analysis of the vibrational properties of the O–H bonds. Since the strength of the hydrogen bonds is closely related to the local structural environments of the protons, a range of vibrational frequencies is obtained providing a prediction of the vibrational spectra. In O–HO linkages, O–H stretching modes soften with increasing HO hydrogen bond strength, while the in-plane and out-of-plane bending or libration modes stiffen. Together, our results show how modern theoretical methods can provide a clearer understanding of the structure and dynamics of a complex inorganic material.     

Comparison of H3PW12O40 and H4SiW12O40 heteropolyacids supported on silica by H MAS NMR

The H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ heteropolyacids supported on silica were studied by ¹H MAS NMR as a function of both the coverage and the dehydroxylation temperature. The signal at ca. 8 ppm attributed to the highly acidic protons of the anhydrous form of the heteropolyacid was never observed in the case of the phosphotungstic polyanion supported on silica while it was clearly present in the case of the silicotungstic species. These results explain the different activities of the two supported heteropolyacids in acid reactions involving strong acid sites. To cite this article: A. Thomas et al., C. R. Chimie 8 (2005).     

NMR study of molecular reorientations in NH4H2AsO4

Zeeman (T_1Z) and dipolar (T_1D) spin-lattice relaxation times of protons in NH₄H₂AsO₄ were measured as a function of temperature. The existence of a slow motion (τ ≈ 10^?3 see) is established, which is most probably a low frequency hindered reorientation of H₂AsO₄ groups. This motion is slowed down below the Curie point T_c. A sharp increase of the dipolar relaxation rate above T = 314°K indicates the possibility of a new high temperature phase transition in this compound.     

D-isotope-labelled n-butane cations in CF3CCl3 and in CF2ClCFCl2: Structure and reactions at low temperature

Cations of n-butane, n-butane-1,4-d₆, -d₄, -d₂ and n-butane-2,3-d4 produced by X-irradiation of CF₂ClCFCl₂ and CF₃CCl₃ 3 matrices containing 1–2 mole% of solute have been investigated by ESR spectroscopy. The measurements have been performed at 77–130 K. The results confirm that the two largest couplings are assigned to two protons on the methyl groups. Smaller couplings have been resolved in CF₃CCl₃ and assigned to specific H atoms. A geometry with a non-planar carbon skeleton is proposed. Partly deuterated methyl groups give rise to rotational isomers. Thermal and photoinduced decompositions producing 2-butyl radicals and 2-butane cations have been further studied.     

Rotational correlation times of adenosine 5′-monophosphate in solution as deduced from 1H and 13C spin-lattice relaxation times

Rotational correlation times (τ_T) of the 5′-AMP molecule deduced from spin-lattice relaxation times (T₁) of different protons in the molecule agree fairly well with each other in the temperature range of 3.5–74°C. The same is true with τ_T values deduced from ¹³CT₁ values. These results indicate that the internal motions are slow as compared to the overall rotation of the 5′-AMP molecule.     

CO2− radical in γ-irradiated single crystal of calcium formate: reinvestigation

ESR of CO₂^?, in calcium formate is reinvestigated with a view to determining the orientation of the radical in the crystal. The observed radical is associated with one of the formate sites, viz., C₁O₁O₂. Preliminary ENDOR studies confirmed that the further splittings of ESR lines observed in certain orientations are due mainly to two protons. The reasons for the assignment of the radical site together with proton interactions are discussed in relation to the crystal structure.     

Synthesis and spectral characterization of diorganodiaminosilanes [(ArNH)2SiPhMe] (Ar = 2,6-Pr2C6H3; 2,4,6-Me3C6H2) and lithium silylamide [(2,6-Et2C6H3NLi)(2,6-Et2C6H3NH)SiPh2]

Aminosilanes bearing bulky substituents on nitrogen centers, [(ArNH)₂SiPhMe] (Ar = 2,6-ⁱPr₂C₆H₃ (1), 2,4,6-Me₃C₆H₂ (2)) and half-sandwich lithium silylamide [(2,6-Et₂C₆H₃NLi)(2,6-Et₂C₆H₃NH)SiPh₂] (3) have been prepared and characterized by elemental analysis, IR, EI mass and NMR (¹H and ²⁹Si) spectroscopic studies. The solid state structures of 2 and 3 have been determined by single crystal X-ray diffraction studies. The molecule 2 has a C₁ symmetry due to the steric crowding, and the two N-H protons are approximately trans to each other. The amido nitrogen atoms in 2 show significant deviation from trigonal-planar geometry, and as a result, the observed Si-N bonds are marginally longer than those observed in aminosilanes with planar nitrogen atoms. The molecule 3 exists as discrete dimer with an inversion center. The Li ion in 3 forms intramolecular π-complex with the neighboring aryl (2,6-Et₂C₆H₃) group, to form a half-sandwich lithium silylamide.     

35Cl NQR and 1H NMR studies of [C(NH2)3]AuCl4, [C(NH2)3]2PtCl4, and [C(NH2)3]2PdCl4

The temperature dependence measurements of ³⁵Cl NQR frequencies and ¹H NMR spin-lattice relaxation time T₁ were carried out for guanidinium tetrachloro-aurate(III), -platinate(II), and -palladate(II). The gold(III) complex showed four NQR lines at various temperatures between 77 and 344 K, while the platinum-(II) and palladium(II) complexes gave two NQR lines in the temperature ranges 77–169 K and 77–220 K, respectively. An unusual phase transition was located at 363 K for the gold(III) complex. The high-temperature phase was easily supercooled. All the complexes studied yielded a T₁ minimum attributable to the reorientation of the planar cation about its C₃ axis. The motional parameters were evaluated. The Zeeman-quadrupole cross relaxation between protons and chlorine nuclei was observed for the platinum(II) and palladium(II) complexes at various temperatures below room temperature, while it was also detected for the high-temperature phase of the gold(III) complex.     

From a 3D protonic conductor VO(H2PO4)2 to a 2D cationic conductor Li4VO(PO4)2 through lithium exchange

A new phase, Li₄VO(PO₄)₂ was synthesized by a lithium ion exchange reaction from protonic phase, VO(H₂PO₄)₂. The structure was determined from neutron and synchrotron powder diffraction data. The exchange of lithium causes a stress, leading to a change in the dimensionality of the structure from 3D to 2D by the displacement of oxygen atoms. Thus, Li₄VO(PO₄)₂ crystallizes in P4/n space group with lattice parameters a=8.8204(1) Å and c=8.7614(2) Å. It consists of double layers [V₂P₄O₁₈]_∞ formed by successive chains of VO₆ octahedra and VO₅ pyramids with isolated PO₄ tetrahedra. The lithium ions located in between the layers promote mobility. Furthermore, the ionic conductivity of 10⁻⁴ S/cm at 550 °C for Li₄VO(PO₄)₂ confirms the mobility of lithium ions in the layers. On the other hand, VO(H₂PO₄)₂ exhibits a conductivity of 10⁻⁴ S/cm at room temperature due to the presence of protons in tunnels.     

(C6H6)n-kohlenwasserstoffe: Eigenschaften und darstellung einer hexacyclischen C18H18-verbindung

The synthesis of the hexacyclic C₁₈H₁₈-compound 2 and its spectroscopic and chemical properties are reported. By temperature-dependent NMR, protons H^6,7 and H^17,18 are shown to be differently influenced by the dynamic equilibrium 2a ? 2b. At 130°, 2 decomposes into benzene and tetracyclo-(5.3.2.0^2,5.0^6,8)dodeca-3 (4).     

Characteristics of Proton-Conducting Electrolytes BaCe1 ? xNdxO3 ? δ (0 ≤ x ≤ 0.16) in Moist Air

Electroconductance, overall transport number for ions, and transport number for protons in BaCeO₃ doped with neodymium in the cerium sublattice (0–16%) are measured in moist air (pH₂O = 2.6 kPa) at 550– 1000°C. Partial (by protons, oxygen, and holes) conductances and appropriate effective activation energies are determined. Literature sources are reviewed. __________ Translated from Elektrokhimiya, Vol. 41, No. 9, 2005, pp. 1125–1132. Original Russian Text Copyright ? 2005 by Sharova, Gorelov.     

Anodic dissolution of the mercury electrode by the CH3O− ions formed during the reduction of organic compounds in methanol

Anodic dissolution of the HMDE from CH₃O^? ions formed during the electrochemical reduction of organic compounds in methanol arises only if the electroreduction is non-reversible. When, however, the organic substances undergo a reversible reduction, the CH₃O^? ions formed during the reduction are neutralized by the protons released during reoxidation. The anodic dissolution of the mercury electrode is attributed to the formation of insoluble Hg₂(OCH₃)₂, as with many other ions which depolarize the mercury electrode in aqueous solution with the formation of insoluble salts.     

The structure of C2H5InBr2 · tmen,C2H5InI2 · tmen (tmen = N,N,N,′,N′-tetramethylethanediamine) and [(C6H5)4P][C2H5InI3] in solution and in the solid state

The ¹H NMR spectra of C₂H₅InBr₂ · tmen (1) C₂H₅InI₂ · tmen (2) (tmen = N,N,N′,N′-tetramethylethanediamme) and [(C₆H₅)₄P][C₂H₅InI₃] (3) show only a broad singlet for the ethyl protons at 60 MHz. Spectra run at 400 MHz resolve these into a triplet + quartet for 1 and 3. The structure of each compound has been determined by X-ray crystallography; 1 and 2 are five-coordinate species, with InC₂N₂X (X = Br, I) nuclei, while 3 consists of [(C₆H₅)₄P]⁺ cations and anions whose InCI₃ nucleus has C_3v, symmetry.     

New channel for dissociative ionization of H2

We propose a new indirect mechanism for the formation of fast protons which are observed in the dissociative ionization of H₂ at electron impact energies below 29 eV. The process involves the excitation of the molecule to doubly-excited states which autoionize to the dissociative continuum of the ground 1sσ_g state of H₂⁺.