N5- in Solution: Isotopic Labeling and Further Details of Its Synthesis by Phenyl Pentazole Reduction.

The cyclopentazolate anion, N5-, has been researched extensively over the years and detected in the gas phase more than a decade ago, but was only recently measured in solution. The process whereby aryl pentazole reduction leads to the production of N5- is still not fully understood. Here, the production of N5- in solution was investigated using isotopic labeling techniques while implementing changes to the synthesis methodologies. 15N labeled phenyl pentazole produced appropriately labeled phenyl pentazole radical anions and N5- which, upon collision induced dissociation, produced the expected N3- signals. Changing to higher purity solvent and less coated Na metal allowed for a much more rapid pace, with experiments taking less time. However, the best yields were obtained with heavily coated metal and much longer reaction times. Utilization of a vacuum line and ultrapure solvents led to no products being detected, indicating the importance of a sodium passivation layer in this reaction and the possibility that sodium is too strong a reducer. These findings can lead to better production methods of N5- and also explain past failures in implementing aryl pentazole reduction techniques.

Detection of Cyclo-N5- in THF Solution.

Compelling evidence has been found for the formation and direct detection of the cyclopentazole anion (cyclo-N5- ) in solution. The anion was prepared from phenylpentazole in two steps: reduction by an alkali metal to form the phenylpentazole radical anion, followed by thermal dissociation to yield cyclo-N5- . The reaction solution was analyzed by HPLC coupled with negative mode mass spectrometry. A signal with m/z 70 was eluted about 2.1 min after injection of the sample. Its identification as N5 was supported by single and double labeling with 15 N, which yielded signals at m/z=71 and 72, respectively, with identical retention times in the HPLC column. MS/MS analysis of the m/z=70 signal revealed a dissociation product with m/z=42, which can be assigned to N3- . To our knowledge this is the first preparation of cyclo-N5- in the bulk. The compound is indefinitely stable at temperatures below -40 °C, and has a half-life of a few minutes at room temperature.

Preparation of the Cyclopentazole Anion in the Bulk: A Computational Study.

The cyclopentazole anion (cyclo-N5(-)), calculated to be a stable species, was prepared in the gas phase but attempts to synthesize it in the bulk have so far been futile. An aryl pentazole radical anion was suggested as a promising precursor in the gas phase. It is shown computationally that the radical anion (which may be prepared by reduction of the phenyl pentazole neutral) may indeed be used to form the cyclopetazolate anion in the gas phase and in liquid solution, alongside and in competition with the extrusion of N2 to produce the corresponding azide. In the gas phase, the C-N dissociation yields are very low due to much more efficient detachment of an electron. In polar solvents, ionization is suppressed and the primary yields of the two competing reactions are similar. The reaction must be carried out at low temperatures and special measures have to be taken to avoid recombination of the nascent cyclo-N5(-) with the geminate phenyl radical. A possible remedy is to use a solvent that reacts efficiently with the phenyl radical by H atom transfer.

Exceptional electrochemical performance of Si-nanowires in 1,3-dioxolane solutions: a surface chemical investigation.

The effect of 1,3-dioxolane (DOL) based electrolyte solutions (DOL/LiTFSI and DOL/LiTFSI-LiNO(3)) on the electrochemical performance and surface chemistry of silicon nanowire (SiNW) anodes was systematically investigated. SiNWs exhibited an exceptional electrochemical performance in DOL solutions in contrast to standard alkyl carbonate solutions (EC-DMC/LiPF(6)). Reduced irreversible capacity losses, enhanced and stable reversible capacities over prolonged cycling, and lower impedance were identified with DOL solutions. After 1000 charge-discharge cycles (at 60 °C and a 6 C rate), SiNWs in DOL/LiTFSI-LiNO(3) solution exhibited a reversible capacity of 1275 mAh/g, whereas only 575 and 20 mAh/g were identified in DOL/LiTFSI and EC-DMC solutions, respectively. Transmission electron microscopy (TEM) studies demonstrated the complete and uniform lithiation of SiNWs in DOL-based electrolyte solutions and incomplete, nonuniform lithiation in EC-DMC solutions. In addition, the formation of compact and uniform surface films on SiNWs cycled in DOL-based electrolyte solutions was identified by scanning electron microscopic (SEM) imaging, while the surface films formed in EC-DMC based solutions were thick and nonuniform. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were employed to analyze the surface chemistry of SiNWs cycled in EC-DMC and DOL based electrolyte solutions. The distinctive surface chemistry of SiNWs cycled in DOL based electrolyte solutions was found to be responsible for their enhanced electrochemical performances.