Coordination and solvation of noble metal ions: Infrared spectroscopy of Ag+(H2O)n

Vibrational spectra of mass-selected Ag⁺(H₂O)_n ions are measured by infrared photodissociation spectroscopy and analyzed with the aid of density functional theory calculations. Hydrogen bonding between H₂O molecules is found to be absent for cold Ag⁺(H₂O)₃, but detected for Ag⁺(H₂O)₄ through characteristic changes in the position and intensity of OH-stretching transitions. The third H₂O coordinates directly to Ag⁺, but the fourth H₂O prefers solvation through hydrogen bonding. The preference of the tri-coordinated form is attributed to the inefficient 5s–4d hybridization in Ag⁺, in contrast to the efficient 4s–3d hybridization in Cu⁺. For Ag⁺(H₂O)₄, however, di-coordinated isomers are identified in addition to the tri-coordinated one.     

Microhydration of the methylene blue cation in an electrospray ion source

Microhydrated methylene blue cations, MB⁺(H₂O) _n , are produced in an electrospray ion source and their size-distributions are measured as a function of the source temperature. A series of MB⁺(H₂O) _n ions is observed up to n ≃ 60. A striking feature observed in the mass spectra is that the series of hydrated ions starts at n = 4; intensities of n = 1–3 are extremely suppressed. The absence of n = 1–3 ions is well explained by the energetics concerning evaporation processes of water molecules, based on stable structures and the binding energies of MB⁺(H₂O) _n ions calculated by DFT calculations up to n = 5. MB⁺(H₂O) _n ions for n > 4 evaporate a single water molecule sequentially, while MB⁺(H₂O)₄ tends to fragment into MB⁺ and (H₂O)₄ rather than MB⁺(H₂O)₃ and an H₂O molecule. We have observed a clear magic peak at n = 24, which strongly suggests that the MB⁺(H₂O)₂₄ ion is formed by attaching a neutral (H₂O)₂₀ cage onto an MB⁺(H₂O)₄ ion.     

Syntheses and structure characterization of inorganic/organic coordination polymers: Ag(dpa), Co(O3PH)(4,4′-bpy)(H2O), Zn(O3PH)(4,4′-bpy)0.5 and Mn[O2PH(C6H5)]2(4,4′-bpy) (dpa=2,2′-dipyridylamine; 4,4′-bpy=4,4′-bipyridine)

Four novel coordination polymers: Ag(dpa) I, Co(O₃PH)(4,4′-bpy)(H₂O) II, Zn(O₃PH)(4,4′-bpy)_0.5 III and Mn[O₂PH(C₆H₅)]₂(4,4′-bpy) IV (dpa=2,2′-dipyridylamine; 4,4′-bpy=4,4′-bipyridine), were synthesized by microwave heating and characterized by X-ray crystallography. I crystallizes in monoclinic space group P21/n with a=11.576(2) Å, b=5.585(2) Å, c=15.243(4) Å, β=109.00(2)°, V=931.8(3) ų. II crystallizes in monoclinic Cc space group with a=22.477(7) Å, b=5.280(1) Å, c=10.404(4) Å, β=96.08(3)°, V=1227.8(7) ų. III crystallizes in monoclinic P21/c space group with a=9.758(2) Å, b=7.449(3) Å, c=10.277(2) Å, β=100.02(2)°, V=735.6(4) ų. IV crystallizes in monoclinic space group P2/c with a=10.174(1) Å, b=11.817(3) Å, c=18.784(4) Å, β=102.14(1)°, V=2207.8(8) ų. I consists of linear metal–metal chains wrapped by dpa ligands. II and III consist of two-dimensional M^II(O₃PH) inorganic sheets cross-linked by 4,4′-bpy ligands, while IV is formed by Mn[O₂PH(C₆H₅)]₂ sheets cross-linked by 4,4′-bpy ligands. I exhibits two-step thermal decomposition at ~200 and ~250°C, resulting in the reduction of Ag⁺ to Ag metal. II loses its coordination water at ~100°C, leaving vacant coordination sites at Co²⁺ ions, while the original framework remains intact. The removal of 4,4′-bpy in II–IV occurs at elevated temperatures above 250, 200 and 400°C respectively.     

Preparation of amorphous films of superionic conducting glasses in systems AgIAg2MoO4 and AgIAg2OB2O3

Thermal evaporation, flash evaporation and rf-sputtering techniques were applied to the preparation of amorphous films of superionic conducting glasses in the systems AgIAg₂MoO₄ and AgIAg₂OB₂O₃. The flash-evaporated films were amorphous and showed very high conductivities, about 2 × 10^?2S/cm for the AgIAg₂MoO₄ and about 5 × 10^?3S/cm for the AgIAg₂OB₂O₃ at room temperature, and gave a Ag⁺ transport number of unity. The thermal evaporation method produced crystalline-phase included films. The rf-sputtered films were amorphous by X-ray diffraction and the transport number of Ag⁺ ions was smaller than unity (about 0.9). Thus flash evaporation was concluded to be the most suitable method for preparing amorphous films of superionic conducting glasses.     

Protonic conductivity of β″ and ion-rich β-alumina. II: Ammonium compounds

The conductivity and thermal stability of NH⁺₄, H⁺(H₂O)_nβ″ and ion-rich β-alumina single crystals have been measured by the complex impedance method in the 25–700°C temperature range. Both structures have similar properties, but ion-rich β-alumina shows a higher stability and a lower activation energy (β: 0.18 eV, β″ 0.24 eV below 400°C and 250°C respectively). The room temperature conductivity is about 3×10^-5ω^-1cm^-1. The conducting properties and mechanisms are discussed and compared to other protonic or ionic conductors.     

The thermoelectric power in AgxTiS2 and AgxNiPS3. Part II. The ionic component of the thermoelectric power

The EMF of the isothermal cells: Ag/AgI/Ag_xTiS₂: 0<x<1, T=150–200°C/Ag_xNiPS₃: 0<x<3, T=150–350°C has been measured. From the EMF-x curves the existence ranges of the 2-phase (stage I and II) regions ?0.16<x<0.32 for the Ag/Ag_xTiS₂ system at 190°C; 0.20 < x < 0.50 and 1 < x < 2 for the Ag/Ag_xNiPS₃ system at 400°C - have been determined. The results are sustained by X-ray diffraction and electrical conductivity measurements. From the EMF-T curves the partial enthalpy (ΔH?_Ag) and entropy (ΔS?_Ag) of dissolution of silver in the Ag_xSSE (solid solution electrode) materials were obtained. In the case of Ag_xTiS₂, ΔH?_Ag has a low absolute value, while ΔS?_Ag is distinctly positive. The EMF of the Ag/Ag_xNiPS₃ system also has a positive temperature coefficient. Furthermore, the ionic component of the thermoelectric power, ΔE/ΔT, of the thermogalvanic cells: Ag/AgI/Ag_xSSE/AgI/Ag Ag_xTiS₂: 0 < x < 1, T = 150–200°C( T ) (T+ΔT) Ag_xNiPS₃: 0 < x < 1, T= 150–350°C has been measured. The kinetically important heat of transport of silver ions in the Ag_xSSE materials has been determined in two ways: first from the dependence of the ionic Seebeck coefficient (?_Ag+) on reciprocal temperature; and second from direct calculation, using the data for ?_Ag+ and ΔS?_Ag. The heat of transport is much smaller than the activation enthalpy for Ag⁺-conduction, indicating a high ionic polaron binding energy in these materials.     

Rigid lattice NMR spectra of proton conductors H(H2O)nSbO3

The “rigid lattice” ¹H NMR spectra of H(H₂O)_nSbO₃ have been interpreted for n=0.20, 0.92 and 1. For n?0.92 the compounds contain deformed H₃O⁺ ions and OH groups. For n=1 the real formula is (H₃O)_0.7H_0.3SbO₃,0.3 H₂O. The results are discussed in relation to the level of proton conductivity.     

Structural studies of some new lamellar magnesium,manganese and calcium phosphonates

Layered phosphonate salts of divalent metal ions (Mg, Ca and Mn) are prepared by combining solutions of soluble metal salts and alkyl- or arylphosphonic acids. In this way the compounds Mg(O₃PC_{nH2n+1)·H2O (n=1−12), Mg(O3PC6H5)·H2O, Mg(HO3PCH(C6H5)2)2·8 H2O, Mn(O3PCH3)·H2O, Mn(O3PC6H5)·H2O, Ca(O3PCnH2n+1)·H2O (n⩽5), Ca(HO3PC6H5)2 and Ca(HO3PCnH2n+1)2 (n⩾6) were prepared. The M(O3PC6H5)·H2O compounds show good thermal stability, losing lattice water at 250–300°C without further decomposition below 550°C. Compounds derived from alkylphosphonic acids decompose at lower temperatures. The Mg(O3PCnH2n+1)·H2O series, Mg(O3PC6H5)·H2O, and Mn(O3PC6H5)·H2O group Pmn21; for the latter compound unit cell dimensions (Å) are a=5.733, b=14.298, c=4.931. The structure consists of roughly coplanar layers of metal atoms coordinated by phenylphosphonate groups above and below. Each metal atom is coordinated by five phosphonate oxygens and one lattice water molecule. Mg(O3PCnH2n+1}·H₂O adopts a similar structure; infrared spectra indicate all-trans alkyl chains. In Mg(HO₃PCH(C₆H₅)₂)₂·8 H₂O, Mg(H₂O)²⁺₆ ions and lattice water lie in hydrogen-bonded sheets; the benzhydryl groups lie above and below and make van-der-Waals contacts between layers.     

In situ 1H NMR Study of Nanoreactor Interaction NH3–H2O in Zeolite Nanopores

The interaction between ammonium NH₃ and H₂O molecules in zeolitic nanopores is studied by in situ ¹H nuclear magnetic resonance (NMR) method. The powder and single crystal samples of natural zeolites, heulandites Ca₄[Al₈Si₂₈O₇₂]·24H₂O and clinoptilolite (Na, K,Ca_1/2)₆[Al₆Si₃₀O₇₂], were used as the model system. It is shown that penetration of NH₃ into the zeolitic nanopores is accompanied by disordering of the hydrogen sublattice of zeolitic water and by the fast proton exchange NH₃ + H₂O ? [NH₄]⁺ + [OH]^? characterized by correlation frequency v _c = ~40 kHz. Another nanoreactor interactions are represented by interaction of [NH₄]⁺ ions with exchangeable Na⁺ and Ca²⁺ ions of the zeolitic structure. The slow ionic exchange [NH₄]⁺ → [Na,Ca_1/2]⁺ and binding of [NH₄]⁺ in cationic sites of the framework were visualized by NMR spectroscopy along with stepwise release of (Na,Ca_1/2)OH from zeolitic pores to the external surface of zeolite grains.     

DFT(B3LYP/LanL2DZ), non-linear optical and electrical studies of a new hybrid compound: [C6H10(NH3)2]CoCl4·H2O

A new organic-inorganic material [C₆H₁₀(NH₃)₂]CoCl₄·H₂O was reported. The title compound was synthesized at room temperature by slow evaporation and then characterized by a single X-ray diffraction, spectroscopic measurements, thermal analysis and dielectric technique. It crystallizes in the non-centrosymmetric space group Pna2₁ with the following unit cell parameters: a=12.5328(1) Å, b=9.0908(1) Å, c=11.7440(1) and α=β=γ=90°. The structure can be described by the alternation of two different cationic-anionic layers. It consists of isolated H₂O, isolated [CoCl₄]²⁻ tetrahedral anions and diammoniumcyclohexane [C₆H₁₀(NH₃)₂]²⁺ cations, which are connected via N–H…Cl, N–H…O and O–H…N hydrogen bonds. The Hirshfeld surface analysis was conducted to investigate intermolecular interactions and associated 2D fingerprint plots, revealing the relative contribution of these interactions in the crystal structure quantitatively. Theoretical calculations were performed using DFT/B3LYP/LanL2DZ method for studying the molecular structure and vibrational spectra and especially to examine the non-linear optical behavior of the compound. Solid state ¹³C NMR spectrum shows three signals correspond to three different carbon environments. Thermal analysis discloses a phase transition at the temperature 315 K and the evaporation of water molecule at 327 K. A detailed dielectric study was reported and shows a good agreement with thermal measurements.     

ac conductivity of Na-Ag β” -alumina polycrystalline samples

The results of ac conductivity measurements carried out on ceramic samples of Li₂O and NiO-Li₂O-doped β7rdquo;-alumina with Na⁺, Ag⁺ and Na⁺ -Ag⁺ mobile ions are presented. The modifications of doping only slightly influenced either bulk or grain boundary conductivity in Na β” -alumina. The activation energies of conduction in Na β”-alumina equal to 0.28 eV at low temperatures decreased to 0.14–0.15 eV at temperatures above 200°C. The Arrhenius plots for Ag β” -alumina were found to be linear in whole 20–450°C temperature range with the activation energies of 0.19 eV (Li₂O) and 0.24 eV (NiO-Li₂O). The conductivity measurements done on partially exchanged samples revealed the presence of the mixed alkali effect.     

Growth of carbon nanotubes (CNTs) on metallic underlayers by diffusion plasma-enhanced chemical vapour deposition (DPECVD)

Here, we demonstrate the low-temperature (480–612 °C) synthesis of carbon nanotubes (CNTs) on different metallic underlayers (i.e., NiV, Ir, Ag, Pt, W, and Ta) using diffusion (dc) plasma-enhanced (~20 W, −600 V) chemical vapour deposition (DPECVD). The catalyst used is bi-layered Fe/Al and the feedstock used is a mixture of C₂H₂ and NH₃ (1:4). The crucial component is the diffusion of radical ions and hydrogen generated such as H₂/H⁺/H₂⁺/NH₃⁺/CH₂⁺/C₂H₂⁺ (which are confirmed by in-situ mass spectroscopy) from the nozzle, where it is inserted for most effective plasma diffusion between a substrate and a gas distributor.     

Paramagnetic silver species in irradiated Ag−NaA zeolites. An EPR and ESEEM study

Several polymeric silver clusters have been observed in Ag_x?NaA zeolite (x=1,6) of varying water content, which was exposed to x-rays at 77 K and annealed at higher temperatures.¹⁰⁹Ag₁?NaA zeolite dehydrated at 130°C yields the dimer¹⁰⁹Ag₂ ⁺ and the trimer¹⁰⁹Ag₃ ²⁺ after irradiation at 77 K and annealing at 240 K. Owing to the use of one Ag isotope the EPR spectra of these species are highly resolved exhibitingg and hyperfine anisotropy. By irradiation of¹⁰⁹Ag_x?NaA zeolite (x=1,6) in hydrated form two new trimeric silver clusters I and II are produced. The ratio between I and II depends on the initial Ag content. ESEEM spectra of these species show interaction with aluminum nuclei of the framework and with distant water molecules. If Ag₆?NaA zeolite dehydrated at 130°C is irradiated the hexameric cluster Ag₆ ⁿ⁺ is formed. The ESEEM spectrum shows interaction only to aluminum nuclei. From ESEEM experiments on Ag₆ ⁿ⁺ with added adsorbates (D₂O, CD₃OD) it could be inferred that Ag₆ ⁿ⁺ is only stable if the neighbouring cages do not contain adsorbate molecules.     

Spectre de photoélectrons et calcul des facteurs de franck-condon pour H2O,D2O,HDO

The first band of the photoelectron spectrum of HDO has been recorded. In agreement with the selection rules of the group theory, the fundamental terms of the three symmetric vibrations of HDO (C_s symmetry) have been observed. Taking the geometry of the ion as parameters, the Franck-Condon factors for the ionization of H₂O, D₂O and HDO have been calculated. The geometry of the H₂O⁺, D₂O⁺, HDO⁺ ions (ground state) have been determined accurately by comparison of the calculated results with the corresponding photoelectron spectra. This geometry is approximately the same for the three ions: r_OH  1,00 Å and < HOH  110°.     

银团簇上吸附氧原子与氢气作用的研究

The interactions between Ag_nO^-(n=1-8) and H₂ (or D₂) were explored by combination of the mass spectroscopy experiments and density function theory (DFT) calculations. The experiments found that all oxygen atoms in Ag_nO^-(n=1-8) are inert in the interactions with H₂ or D₂ at the low temperature of 150 K, which is in contrast to their high reactivity with CO under the same condition. These observations are parallel with the preferential oxidation (PROX) of CO in excess hydrogen catalyzed by dispersed silver species in the condensed phase. Possible reaction paths between Ag_nO^-(n=1-8) and H₂ were explored using DFT calculations. The results indicated that adsorption of H₂ on any site of Ag_nO^-(n=1-8) is extremely weak, and oxidation of H₂ by any kind of oxygen in Ag_nO^-(n=1-8) has an apparent barrier strongly dependent on the adsorption style of the "O". These experiments and theoretical results about cluster reactions provided molecule-level insights into the activity of atomic oxygen on real silver catalysts.     

Anregung und Schädigung der Lumineszenz von CaWO4 und ZnS/Ag durch Ionen

The luminescence-response of ZnS/Ag and CaWO₄ to ion-bombardement and the deterioration of luminescence under prolonged irradiation was determined as a function of ion-energyE, ion-massM _i and beam-densityI. The variation of lightoutput with ion-energy is of the formJ ₀=C. (E-E ₀) ⁿ withn=2 (ZnS/Ag) or lower values (CaWO₄). The luminescence-response to ions of various mass was found to decrease generally with growing mass, but to be nearly constant to ions of middle atomic weight (ZnS/Ag). The luminescence-efficiency, caused by ions of energy greater than 5 keV, is independent of beam-density within the whole range studied here (maximum 3 · 10^?7 A · cm^?2), but it diminishes in the caseE=5 keV for values ofI above 6 · 10^?8 A · cm^?2. The deterioration-effect grows, except in the case of He⁺-ions, the lightest ions used here, with ion-energy. It also increases by substituting Ne⁺- for He⁺-ions, but remains nearly independent of mass (CaWO₄) or diminishes with growing ion-mass (ZnS/Ag), if the ions are heavier than Ne⁺-ions. Increasing beam-density leads to a reduced deterioration of ZnS/Ag-luminescence, yet has no influence to that of CaWO₄.     

Silver-tracer diffusion in Cu2O

The diffusion of¹¹⁰Ag in Cu₂O has been measured by a serial-sectioning technique as a function of temperature (700–1132°C) and oxygen partial pressure (6 × 10^?6 ?8 × 10^?2 atm). The data are fit to the defect model for Cu₂O developed by the authors in the preceding paper. Silver ions have a larger impurity-vacancy binding free energy and/or a larger jump frequency for the singly charged cation vacancies relative to that for the neutral cation vacancies. The activation enthalpies for the diffusion of copper and silver ions in Cu₂O are nearly equal, but the absolute value of D¹_Ag is about three times larger than D¹_Cu even though the silver ion is 31% larger than the copper ion.     

Preparation and mechanism investigation of highly sensitive humidity sensor based on Ag/TiO2

In this paper, a high-performance silver-doped titanium dioxide (Ag/TiO₂) humidity sensor was synthesized using a hydrothermal synthesis method for respiratory monitoring. The sensing mechanism was studied by the first principles of density functional theory (DFT). Calculations show that the doping of Ag⁺ ions increases the adsorption energy of TiO₂ to water molecules. Furthermore, the Ti–O bond in TiO₂ is broken due to the doping of Ag⁺ ions, which promotes the generation of Ti³⁺ defects. Experiments show that the doping of Ag⁺ ions can increase the hydroxide groups, Ti³⁺ defects and oxygen vacancies on the surface of TiO₂, thus effectively improving the responsivity, linearity and hysteresis of the TiO₂ humidity sensor. Compared to TiO₂, the resistance of the Ag/TiO₂ (0.5 mM) humidity sensor reaches 4.5 orders of magnitude with a high response of 39707.1, maximum hysteresis rate of 4.6%, response/recovery time of 31 s/15 s and the best linearity in a range of 11%–95% RH. In addition, the Ag/TiO₂ humidity sensor has been successfully used to detect different modes of respiration and determine the respiratory rate under different respiratory states. Significantly, this work demonstrates potential application value in human healthcare and activities monitoring.     

Competitive solvation of K+ by C6H6 and H2O in the K+-(C6H6)n-(H2O)m (n = 1–4; m = 1–6) aggregates

The competitive solvation of the potassium ion by benzene and water is investigated at molecular level by means of Molecular Dynamics simulations on the K⁺-(C₆H₆) _n -(H₂O) _m (n = 1–4; m = 1–6) ionic aggregates. The preference of K⁺ to bind C₆H₆ or H₂O is investigated in the range of temperatures in which isomerisation processes are likely by adding water and benzene to the K⁺-(C₆H₆) _n and K⁺-(H₂O) _m aggregates, respectively. Hydrogen bonds and the π-hydrogen bond, in spite of their weakness with respect to the K⁺-π and K⁺-H₂O interactions, play an important role in stabilising different isomers, thus favouring isomerisation processes. Accordingly with experimental information it has been found that K⁺ bind preferably C₆H₆ rather than H₂O and that the fragmentation of C₆H₆ is only observed for aggregates containing four molecules of benzene.     

Laser ablation time-of-flight mass spectrometry (LA-TOF-MS) of “nitrogen doped diamond-like carbon (DLN) nano-layers”

Nitrogen-doped diamond-like carbon (DLC) layers (a-C:H:N, N-DLC or DLN) were prepared by the plasma-enhanced chemical vapor deposition (PECVD) technique, using a RF capacitive discharge (13.56 MHz), at low pressures (20 Pa), produced from a mixture of methane, nitrogen and hexamethyldisiloxane (HMDSO), deposited on single-crystalline silicon wafers placed on steel samples. The films, of differing deposition times, were subjected to laser ablation time-of-flight (LA-TOF) mass spectrometric measurements, using different commercial instrumentation to characterize their structures. The analysis of mass spectra was made and the following positively singly charged species were detected and identified: C_n⁺ (n=4–30), Si_n⁺ (n=2, 3), Si_nH⁺ (n=2, 3), SiOK⁺, Si₃H₄⁺, Si₂N⁺, Si₂NH₂⁺, and Si₃C⁺. The later three species could reflect the presence of nitrogen–silica and carbon–silica chemical bonds in the structure of the DLN layer. The stoichiometry of all species was confirmed by isotopic pattern simulation. In the negative detection mode, the C_n⁻ (n=2–12) clusters were observed. The findings are discussed in the light of the current research concerning analysis of the DLN thin layers and it is concluded that namely Si₂N⁺, Si₂NH₂⁺ and Si₃C⁺ species are reflecting the chemical structure of the DLN layer. LA-TOF-MS was found useful supplementary method for the characterization of DLN nano-layers.