X‐ray Photoelectron Spectroscopy of Pyridinium‐Based Ionic Liquids: Comparison to Imidazolium‐ and Pyrrolidinium‐Based Analogues

We investigate eight 1‐alkylpyridinium‐based ionic liquids of the form [C_nPy][A] by using X‐ray photoelectron spectroscopy (XPS). The electronic environment of each element of the ionic liquids is analyzed. In particular, a reliable fitting model is developed for the C 1s region that applies to each of the ionic liquids. This model allows the accurate charge correction of binding energies and the determination of reliable and reproducible binding energies for each ionic liquid. Shake‐up/off phenomena are determinedfor both C 1s and N 1s spectra. The electronic interaction between cations and anions is investigated for both simple ionic liquids and an example of an ionic‐liquid mixture; the effect of the anion on the electronic environment of the cation is also explored. Throughout the study, a detailed comparison is made between [C₈Py][A] and analogues including 1‐octyl‐1‐methylpyrrolidinium‐ ([C₈C₁Pyrr][A]), and 1‐octyl‐3‐methylimidazolium‐ ([C₈C₁Im][A]) based samples, where X is common to all ionic liquids.     

Towards a Molecular Understanding of Cation–Anion Interactions—Probing the Electronic Structure of Imidazolium Ionic Liquids by NMR Spectroscopy,X‐ray Photoelectron Spectroscopy and Theoretical Calculations

Ten [C₈C₁Im]⁺ (1‐methyl‐3‐octylimidazolium)‐based ionic liquids with anions Cl^?, Br^?, I^?, [NO₃]^?, [BF₄]^?, [TfO]^?, [PF₆]^?, [Tf₂N]^?, [Pf₂N]^?, and [FAP]^? (TfO=trifluoromethylsulfonate, Tf₂N=bis(trifluoromethylsulfonyl)imide, Pf₂N=bis(pentafluoroethylsulfonyl)imide, FAP=tris(pentafluoroethyl)trifluorophosphate) and two [C₈C₁C₁Im]⁺ (1,2‐dimethyl‐3‐octylimidazolium)‐based ionic liquids with anions Br^? and [Tf₂N]^? were investigated by using X‐ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While ¹H NMR spectroscopy is found to probe very specifically the strongest hydrogen‐bond interaction between the hydrogen attached to the C² position and the anion, a comparative XPS study provides first direct experimental evidence for cation–anion charge‐transfer phenomena in ionic liquids as a function of the ionic liquid’s anion. These charge‐transfer effects are found to be surprisingly similar for [C₈C₁Im]⁺ and [C₈C₁C₁Im]⁺ salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions.     

X‐Ray Photoelectron Spectroscopy and Electron Microscopy of Hydralazinium Ion‐Selective Electrode Membrane's Surface

New hydralazinium (Hz) plastic membrane electrodes of either conventional or coated‐wire type were constructed based on incorporation of Hz‐phosphotungstate (Hz‐PT) ion associate or Hz‐reineckate (Hz‐Rn) ion‐pair in poly(vinyl chloride) membranes. The (Hz‐PT)‐based electrodes required 30 minutes conditioning time to exhibit nearly Nernstian response over the concentration range 1.58×10^?5–1.7×10^?2 M HzCl. They also showed life span of 17 days, working pH range of 3.2 to 9.4 and high selectivity for Hz towards Na⁺, K⁺, Mg²⁺ and Ca²⁺. The electrodes have not lost their efficiency at temperatures elevated up to 60 °C. They were successfully employed to assaying HzCl in a pharmaceutical preparation. The electrode containing (Hz‐Rn) ion‐pair required 30 minutes conditioning time to show response for Hz over the concentration range 2.5×10^?5–5.6×10^?2 M. The life span of the electrode was only 8 h. X‐ray photoelectron spectroscopy was applied to investigate the effect of prolonged soaking on the membrane's surface of both types of electrodes. The surfaces of fresh and expired membranes containing Hz‐PT were also examined by electron microscopy. The results indicated that the limitation of the life span of plastic membrane electrodes is attributed to leaching of the ion exchanger from the membrane to the test solution in addition to deformation at the surface of the expired electrode.     

MoO_3电致变色薄膜的XPS研究

近年来 ,随着人们提倡节能和使用洁净能源 ,无机电致变色材料在建筑物采光控制系统和反射率可调表面的应用研究 ,已成为材料领域的一个新热点 .WO3、 MoO3等过渡金属氧化物薄膜具有良好的电致变色效应 ,是人们研究的重点 .其中 MoO3的电致变色效果要好于 IrO2、 TiOx、 CoO及 NiOx等电致变色材料 [1],而且它在可见光区有比 WO3更柔和的色彩 ,使人眼更易于适应其颜色变化 .着色态的 MoO3称为钼青铜 ,其开路记忆也好于钨青铜 [2].故 MoO3电致变色薄膜是极有潜力用于实用化的电致变色器件 .MoO3薄膜常用的制备方法有真空蒸 发、化学气…     

In Situ Solid‐State Reactions Monitored by X‐ray Absorption Spectroscopy: Temperature‐Induced Proton Transfer Leads to Chemical Shifts

The dramatic colour and phase alteration with the solid‐state, temperature‐dependent reaction between squaric acid and 4,4′‐bipyridine has been probed in situ with X‐ray absorption spectroscopy. The electronic and chemical sensitivity to the local atomic environment through chemical shifts in the near‐edge X‐ray absorption fine structure (NEXAFS) revealed proton transfer from the acid to the bipyridine base through the change in nitrogen protonation state in the high‐temperature form. Direct detection of proton transfer coupled with structural analysis elucidates the nature of the solid‐state process, with intermolecular proton transfer occurring along an acid‐base chain followed by a domino effect to the subsequent acid‐base chains, leading to the rapid migration along the length of the crystal. NEXAFS thereby conveys the ability to monitor the nature of solid‐state chemical reactions in situ, without the need for a priori information or long‐range order.     

Structure of Glancing Incidence Deposited TiO2 Thin Films as Revealed by Grazing Incidence Small‐Angle X‐ray Scattering

For the first time, grazing incidence small‐angle X‐ray scattering (GISAXS) analysis is used to characterize the morphology of TiO₂ thin films grown by glancing angle physical vapor deposition (GLAD). According to cross‐section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO₂ columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the tilted geometry of the TiO₂ columns. The patterns also show the existence of two populations of columns in these GLAD‐TiO₂ films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.     

Thin‐Film Infrared Spectroscopy of Acetonitrile

Acetonitrile and [D₃]acetonitrile in the vicinal region of a planar AgX fiber contain linear dipole–dipole linked oligomers as shown by 1) comparison of infrared band intensity ratios in the gaseous and condensed phases and 2) remarkable plots of absorbance (C? N stretch) versus time during evaporation from an AgX planar fiber element. The plots (CH₃CN 2252 cm^?1, CD₃CN 2262 cm^?1) reveal the presence of octamers, hexamers, tetramers, and dimers along with some heptamer, trimer, and monomer structures. A novel isotope effect arises from the somewhat smaller size of the CD₃CN resulting in an increase in the CN band intensity. The organized oligomers may be termed pseudocrystals and are the main components responsible for absorption intensity in the infrared spectrum of acetonitrile, on the AgX planar fiber or in an IR cell.     

Conformational Analysis by Photoelectron Spectroscopy

The conformation of organic molecules may be determined by means of photoelectron (PE) spectroscopy if there are orbital interactions present which depend on a dihedral angle. Straightforward application of the method requires that all ionization bands of interest can be assigned unambiguously and that inductive effects and secondary orbital interactions do not occur or can be accounted for appropriately. In many cases, this method complements conventional methods of conformational analysis. PE conformational analysis is particularly suited to compounds containing vicinal lone pairs or π systems.     

用X—射线光电子能谱对钇的配位化合物价态的研究

二价的配合物3p能级分裂间距大于三价Y的化合物,二价Y的4s多重分裂也是鉴别Y的价态指纹。     

Microsecond X‐ray Absorption Spectroscopy Identification of CoI Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution

Rational development of efficient photocatalytic systems for hydrogen production requires understanding the catalytic mechanism and detailed information about the structure of intermediates in the catalytic cycle. We demonstrate how time‐resolved X‐ray absorption spectroscopy in the microsecond time range can be used to identify such intermediates and to determine their local geometric structure. This method was used to obtain the solution structure of the Co^I intermediate of cobaloxime, which is a non‐noble metal catalyst for solar hydrogen production from water. Distances between cobalt and the nearest ligands including two solvent molecules and displacement of the cobalt atom out of plane formed by the planar ligands have been determined. Combining in situ X‐ray absorption and UV/Vis data, we demonstrate how slight modification of the catalyst structure can lead to the formation of a catalytically inactive Co^I state under similar conditions. Possible deactivation mechanisms are discussed.     

Molecule‐Enhanced Surface‐Enhanced Infrared Absorption Spectroscopy (MOSEIRA)

Surface‐enhanced infrared absorption spectroscopy (SEIRA) of methanol, ethanol, 1‐propanol, and 2‐propanol in thin films on planar silver halide (AgX) fibers under slow N₂ flow using 1 sec scans reveals structure in absorbance–time plots. The absorption intensities show extra enhancements (3×) in the absorbance (O? H stretch) ascribed to oligomers present at the AgX surface (molecule enhanced, thus MOSEIRA).This is above those due to amplification (40×, 20 reflections) and enhancement (30×, image dipoles or surface phonon polaritons). In the case of ethanol an excellent initial pentamer spectrum evolves over 8–10 min to a mixture of pentamer, tetramer, and trimer spectra that within another minute forms small oligomers and monomers. We use a new type of cell for infrared spectroscopy containing an AgX planar fiber. The optical configuration leads to a vicinal region at the surface defined by evanescent waves. Within this region are surface‐induced organized species such as ethanol oligomers. The planar AgX fiber supports 20 reflections and transmits light over a wide visible–infrared wavelength range. Short scan times permit the study of volatile substrates or solvents, including the effects of solvent polarity.     

X‐ray photoelectron analysis of surface functional groups on diamond‐like carbon films by gas‐phase chemical derivatization method

Oxygen‐related surface functional groups on diamond‐like carbon (DLC) films were derivatized with fluorine‐ and nitrogen‐related groups by the gas‐phase chemical derivatization (GCD) method, and the groups were analyzed quantitatively by X‐ray photoelectron spectroscopy (XPS). It is desirable that a derivatization reaction is unique to the target group; however, it usually causes undesirable side reactions which affect other groups. This diversity of the reactions has complicated the analysis. In this report, we have overcome the problem by applying a mathematical treatment which takes the side reactions into account. This improved analysis shows that it is no longer necessary to have derivatization reactions unique to the target groups. As a result, it is demonstrated that the carbonyl (C?O) group is the dominant surface functional group on both the DLC and its wet‐oxidized films, the carboxyl (COOH) group plays a minor role, and the presence of the hydroxyl (OH) group is logically denied. Considering the oxidation steps of these oxygen‐related surface functional groups, it is suggested that the C?O group on the DLC films requires the cleavage of the carbon–carbon bond with a relatively high activation energy barrier to change into the COOH group. Copyright © 2010 John Wiley & Sons, Ltd.