Diagnosis of the redox levels of TCNQF4 compounds using vibrational spectroscopy

The vibrational spectroscopy of TCNQF4, TCNQF41- and TCNQF42- has been investigated by means of density functional theory. Band assignments in infrared and Raman spectra have been clarified and a series of diagnostics developed for redox level characterisation of TCNQF4 compounds. In the C£C stretching region (1460-1600 cm-1), TCNQF40 and TCNQF 41- show two bands, with the more energetic being at 1600 cm-1 in TCNQF40 and at approximately 1535 cm-1 in TCNQF41-; in TCNQF42- both modes absorb below 1500 cm-1, often merging to give a single band. In the C-F and endocyclic C-C stretching region (1290 and 1360 cm-1), TCNQF40 and TCNQF41- show strong bands, whereas TCNQF42- absorbs weakly or not at all. (Additional bands, e.g. from co-crystallised solvent molecules, may complicate this region.) In the nitrile stretching region (2000-2250 cm-1), modes are highly sensitive to nitrile coordination by metal cations. All three redox levels can produce bands above 2200 cm -1, however bands below 2150 cm-1 are usually due to TCNQF42-. This sensitivity to coordination is likely to affect the spectra of many organic molecular ions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Some unusual applications of the `Error-bar` feature in Excel spreadsheets

This paper demonstrates how the "error-bar" feature can be used to extend the utility of "worldware" spreadsheet packages in producing high-quality graphs for university teaching and learning, and for research. To further utilize the advantages of spreadsheets in university education, this paper seeks to overcome some of the earlier reservations about the lack of scientific plotting capabilities of spreadsheet applications. Specific examples of educational material in the areas of enzyme kinetics, vibrational spectroscopy, vibronic spectroscopy, and mass spectrometry are discussed. It is argued that, where practical, university educators should use "worldware" packages to prepare teaching aids, since these would better prepare their students for future employment. The use of software features for purposes that were not envisioned by the programmers has additional educational benefits in fostering flexibility and innovation. Other graphing packages can also use the "error-bar" feature in a manner similar to that described here for Excel.

The effect of nano-particle TiO2 fillers on structure and transport in polymer electrolytes

Nano-particle oxide fillers including TiO₂, SiO₂ and Al₂O₃ have previously been shown to have a significant affect on the properties of polymer electrolytes, especially those based on polyether–lithium salt systems. In some cases, conductivity increases of more than one order of magnitude have been reported in crystalline PEO-based complexes. In this work, we report on the effects of TiO₂ on a completely amorphous polyether-based system to remove the complication of multiple phases presented by the semi-crystalline nature of PEO. Multinuclear magnetic resonance spectroscopy has shown that the lithium ion environment is changed by the addition of filler. Vibrational spectroscopy shows that the filler influences the disordered-longitudinal acoustic modes (DLAM) in the case of an amorphous polyether and suggests an interaction between the filler surface and the polymer. Positron annihilation lifetime spectroscopy indicates an increase in free volume upon addition of filler to an amorphous polyether–salt complex, coinciding with an apparent increase in polymer mobility as determined from ¹H T₂ NMR measurements. Impedance spectroscopy has shown clear evidence of an inter-phase region that may be more or less conductive than the bulk polymer electrolyte itself. The data support a model which includes conduction through an interfacial region in addition to the bulk polymer

Reactions with oleum under harsh conditions : characterization of the unique [M(S2O7)3]2- ions (M=Si, Ge, Sn) in A2[M(S2O7)3] (A=NH4, Ag)

The reactions of group 14 tetrachlorides MCl4 (M=Si, Ge, Sn) with oleum (65 % SO3) at elevated temperatures lead to the unique complex ions [M(S2O7)3]2−, which show the central M atoms in coordination with three chelating S2O72− groups. The mean distances M[BOND]O within the anions increase from 175.6(2)–177.5(2) pm (M=Si) to 186.4(4)–187.7(4) pm (M=Ge) to 201.9(2)–203.5(2) pm (M=Sn). These distances are reproduced well by DFT calculations. The same calculations show an increasing positive charge for the central M atom in the row Si, Ge, Sn, which can be interpreted as the decreasing covalency of the M[BOND]O bonds. For the silicon compound (NH4)2[Si(S2O7)3], 29Si solid-state NMR measurements have been performed, with the results showing a signal at −215.5 ppm for (NH4)2[Si(S2O7)3], which is in very good agreement with theoretical estimations. In addition, the vibrational modes within the [MO6] skeleton have been monitored by Raman spectroscopy for selected examples, and are well reproduced by theory. The charge balance for the [M(S2O7)3]2− ions is achieved by monovalent A+ counter ions (A=NH4, Ag), which are implemented in the syntheses in the form of their sulfates. The sizes of the A+ ions, that is, their coordination requirements, cause the crystallographic differences in the crystal structures, although the complex [M(S2O7)3]2− ions remain essentially unaffected with the different A+ ions. Furthermore, the nature of the A+ ions influences the thermal behavior of the compounds, which has been monitored for selected examples by thermogravimetric differential thermal analysis (DTA/TG) and XRD measurements.

A study of phase behavior and conductivity of mixtures of the organic ionic plastic crystal N-methyl-N-methyl-pyrrolidinium dicyanamide with sodium dicyanamide

We report on the thermal, structural and conductivity properties of the organic ionic plastic crystal (OIPC) N-methyl-N-methyl-pyrrolidinium dicyanamide [C1mpyr][N(CN)2] mixed with the sodium salt Na[N(CN)2]. The DSC thermal traces indicate that an isothermal transition, which may be a eutectic melting, occurs at ~ 89 °C, below which all compositions are entirely in the solid phase. At 20 mol% Na[N(CN)2], this transition is the final melt for this mixture, and a new liquidus peak grows beyond 20 mol% Na[N(CN)2]. The III- > II solid-solid phase transition continues to be evident at ~- 2 °C. The microstructure for all the mixtures indicated a phase separated morphology where precipitates can be clearly observed. Most likely, these precipitates consist of a Na-rich second phase. This was also suggested from the vibrational spectroscopy and the 23Na NMR spectra. The lower concentrations of Na[N(CN)2] present complex 23Na MAS spectra, suggesting more than one sodium ion environment is present in these mixtures consistent with complex phase behavior. Unlike other OIPCs where the ionic conductivity usually increases upon doping or mixing in a second component, the conductivity of these mixtures remains relatively constant and above 10- 4 S cm- 1 at ∼ 80 °C, even in the solid state. Such high conductivities suggest these materials may be promising to be used for all solid-state electrochemical devices.

Synthesis of Sodium Poly[4-styrenesulfonyl(trifluoromethylsulfonyl)imide]-co-ethylacrylate] Solid Polymer Electrolytes

Sodium-based batteries are being considered to replace Li-based batteries for the fabrication of large-scale energy storage devices. One of the main obstacles is the lack of safe and conductive solid Na-ion electrolytes. A Na-ion polymer based on the (4-styrenesulfonyl(trifluromethylsulfonyl) imide anion, Na[STFSI], has been prepared by a radical polymerization process and its conductive properties determined. In addition, a number of multi-component polymers were synthetized by co-reaction of two monomers: Na[STFSI] and ethyl acrylate (EA) at different ratios. The structural and phase characterizations of the polymers were probed by various techniques (DSC, TGA, NMR, GPC, Raman, FTIR and Impedance spectroscopy). Comparative studies with blends of the homopolymers Na[PSTFSI] and poly(ethylacrylate) (PEA) have also been performed. The polymers are all thermally stable up to 300°C and the ionic conductivity of EA copolymers and EA blends are about 1-3 orders of magnitude higher than that of Na[PSTFSI]. The highest conductivity measured at 100°C was found for Na[PSTFSI-blend-5EA] at 7.9 × 10^-9 S cm^-1, despite being well below its Tg. Vibrational spectroscopy indicates interaction between Na⁺ and the EA carbonyl groups, with a concomitant decrease in the sulfonyl interaction, facilitating Na⁺ motion, as well as lowering Tg.

Bond length dependence on quantum states as shown by spectroscopy

Undergraduate students often have the misconception that molecules have fixed, unchanging bond lengths. This article discusses how linear-molecule rotational band spacings in infrared spectroscopy can be used as a qualitative, visual demonstration of the elongation of average bond lengths on vibrational excitation. The method does not depend on a detailed mathematical analysis of the spectra. In UV–vis spectroscopy, the rotational band spacings give rise to distinctive linear-molecule rotational contours, which easily show whether the average bond length has increased or decreased. The method is based on a spreadsheet simulation of the vibration–rotation or rovibronic (electronic–vibration–rotation) spectrum and is applied to hydrogen chloride IR, iodine UV–vis, and nitrogen UV–vis spectra in this article.

Direct observation of defect levels in hexagonal BN by soft X-ray absorption spectroscopy

Formation of defects in hexagonal boron nitride under low-energy argon bombardment has been studied by near-edge X-ray absorption fine structure (NEXAFS) around B and N K-edges. Breaking of B-N bonds and creation of nitrogen vacancies has been identified from the B K-edge, followed by the formation of molecular nitrogen, N2, at interstitial positions. The presence of N2 produces a sharp resonance in the low-resolution NEXAFS spectra around N K-edge, showing the characteristic vibrational fine structure in high-resolution measurements. Several new peaks in NEXAFS spectra have been assigned to boron or nitrogen interstitials, in good agreement with theoretical predictions. © 2009 Elsevier B.V. All rights reserved.