Lithium superoxide encapsulated in a benzoquinone anion matrix

2021 ◽  
Vol 118 (51) ◽  
pp. e2019392118
Author(s):  
Matthew Nava ◽  
Shiyu Zhang ◽  
Katharine S. Pastore ◽  
Xiaowen Feng ◽  
Kyle M. Lancaster ◽  
...  
Keyword(s):  
Solid State ◽  
Lithium Ion ◽  
Spectroscopic Characterization ◽  
Blue Color ◽  
Paramagnetic Resonance ◽  
Deep Blue ◽  
Lithium Peroxide ◽  
X Ray Absorption ◽  
Electron Paramagnetic ◽  
Lithium Air Batteries

Lithium peroxide is the crucial storage material in lithium–air batteries. Understanding the redox properties of this salt is paramount toward improving the performance of this class of batteries. Lithium peroxide, upon exposure to p–benzoquinone (p–C6H4O2) vapor, develops a deep blue color. This blue powder can be formally described as [Li2O2]0.3 · [LiO2]0.7 · {Li[p–C6H4O2]}0.7, though spectroscopic characterization indicates a more nuanced structural speciation. Infrared, Raman, electron paramagnetic resonance, diffuse-reflectance ultraviolet-visible and X-ray absorption spectroscopy reveal that the lithium salt of the benzoquinone radical anion forms on the surface of the lithium peroxide, indicating the occurrence of electron and lithium ion transfer in the solid state. As a result, obligate lithium superoxide is formed and encapsulated in a shell of Li[p–C6H4O2] with a core of Li2O2. Lithium superoxide has been proposed as a critical intermediate in the charge/discharge cycle of Li–air batteries, but has yet to be isolated, owing to instability. The results reported herein provide a snapshot of lithium peroxide/superoxide chemistry in the solid state with redox mediation.

scholarly journals Lithium Ion Battery Materials as Tunable, Redox Non-Innocent Catalyst Supports

2021 ◽  
Author(s):  
Alon Chapovetsky ◽  
Ryan J. Witzke ◽  
Robert Kennedy ◽  
Evan Wegener ◽  
Fulya Dogan ◽  
...  
Keyword(s):  
Lithium Ion ◽  
Catalyst Supports ◽  
Paramagnetic Resonance ◽  
Battery Materials ◽  
X Ray ◽  
Electronic Tuning ◽  
Microscopy Techniques ◽  
Nickel Species ◽  
X Ray Absorption ◽  
Electron Paramagnetic

The development of general strategies for the electronic tuning of a catalyst’s active site is an ongoing challenge in heterogeneous catalysis. To this end we report the application of cathode and anode materials as redox non-innocent catalyst supports that can be continuously modulated as a function of lithium intercalation. A zero valent nickel complex was oxidatively grafted onto the surface of lithium manganese oxide (Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>) to yield single-sites of Ni<sup>2</sup><sub>­</sub><sup>+</sup> (Ni/Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>). Its activity for olefin hydrogenation was found to be a function of the redox state of the support material, with the most lithiated variant showing the most activity. X-ray absorption, X-ray photoelectron, solid-state nuclear magnetic resonance and electron paramagnetic resonance spectroscopies, and electron microscopy techniques established the nature of the nickel species on Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>. Catalyst control through support redox non-innocence was extended to an organotantalum complex on lithium titanium oxide (Li<sub>x</sub>TiO<sub>2</sub>), demonstrating the generality of this phenomenon.

scholarly journals Lithium Ion Battery Materials as Tunable, Redox Non-Innocent Catalyst Supports

2021 ◽  
Author(s):  
Alon Chapovetsky ◽  
Ryan J. Witzke ◽  
Robert Kennedy ◽  
Evan Wegener ◽  
Fulya Dogan ◽  
...  
Keyword(s):  
Lithium Ion ◽  
Catalyst Supports ◽  
Paramagnetic Resonance ◽  
Battery Materials ◽  
X Ray ◽  
Electronic Tuning ◽  
Microscopy Techniques ◽  
Nickel Species ◽  
X Ray Absorption ◽  
Electron Paramagnetic

The development of general strategies for the electronic tuning of a catalyst’s active site is an ongoing challenge in heterogeneous catalysis. To this end we report the application of cathode and anode materials as redox non-innocent catalyst supports that can be continuously modulated as a function of lithium intercalation. A zero valent nickel complex was oxidatively grafted onto the surface of lithium manganese oxide (Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>) to yield single-sites of Ni<sup>2</sup><sub>­</sub><sup>+</sup> (Ni/Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>). Its activity for olefin hydrogenation was found to be a function of the redox state of the support material, with the most lithiated variant showing the most activity. X-ray absorption, X-ray photoelectron, solid-state nuclear magnetic resonance and electron paramagnetic resonance spectroscopies, and electron microscopy techniques established the nature of the nickel species on Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>. Catalyst control through support redox non-innocence was extended to an organotantalum complex on lithium titanium oxide (Li<sub>x</sub>TiO<sub>2</sub>), demonstrating the generality of this phenomenon.

scholarly journals CH4-to-CH3OH on Mononuclear Cu(II) Sites Supported on Al2O3: Structure of Active Sites from Electron Paramagnetic Resonance

2021 ◽  
Author(s):  
Jordan Meyet ◽  
Anton Ashuiev ◽  
Gina Noh ◽  
Mark Newton ◽  
Daniel Klose ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Organometallic Chemistry ◽  
Active Sites ◽  
Spectroscopic Characterization ◽  
Paramagnetic Resonance ◽  
Transition Alumina ◽  
Selective Conversion ◽  
Conversion Of Methane ◽  
Electron Paramagnetic ◽  
Alumina Supports

The selective conversion of methane to methanol remains one of the holy grails of chemistry, where Cu-exchanged zeolites have been shown to selectively convert methane to methanol under stepwise conditions. Over the years, several active sites have been proposed, ranging from mono-, di- to trimeric Cu(II). Herein, we report the formation of well-dispersed monomeric Cu(II) species supported on alumina using surface organometallic chemistry and their reactivity towards the selective and stepwise conversion of methane to methanol. Extensive studies using various transition alumina supports combined with spectroscopic characterization, in particular electron paramagnetic resonance (EPR), show that the active sites are associated with specific facets, which are typically found in gamma- and eta-alumina phase, and that their EPR signature can be attributed to species having a tri-coordinated [(Al<sub>2</sub>O)Cu<sup>II</sup>O(OH)]<sup>-</sup>,T-shape geometry. Overall, the selective conversion of methane to methanol, a two-electron process, involve two of these isolated monomeric Cu(II) sites that play in concert.

scholarly journals Towards Blue AIE/AIEE: Synthesis and Applications in OLEDs of Tetra-/Triphenylethenyl Substituted 9,9-Dimethylacridine Derivatives

Molecules ◽  
2020 ◽  
Vol 25 (3) ◽  
pp. 445 ◽  
Author(s):  
Monika Cekaviciute ◽  
Aina Petrauskaite ◽  
Sohrab Nasiri ◽  
Jurate Simokaitiene ◽  
Dmytro Volyniuk ◽  
...  
Keyword(s):  
Solid State ◽  
Quantum Yields ◽  
Yellow Emission ◽  
Blue Color ◽  
Television System ◽  
Fluorescence Quantum Yields ◽  
Deep Blue ◽  
Wide Range ◽  
Cyano Groups ◽  
High Yields

Aiming to design blue fluorescent emitters with high photoluminescence quantum yields in solid-state, nitrogen-containing heteroaromatic 9,9-dimethylacridine was refined by tetraphenylethene and triphenylethene. Six tetra-/triphenylethene-substituted 9,9-dimethylacridines were synthesized by the Buchwald-Hartwig method with relatively high yields. Showing effects of substitution patterns, all emitters demonstrated high fluorescence quantum yields of 26–53% in non-doped films and 52–88% in doped films due to the aggregation induced/enhanced emission (AIE/AIEE) phenomena. In solid-state, the emitters emitted blue (451–481 nm) without doping and deep-blue (438–445 nm) with doping while greenish-yellow emission was detected for two compounds with additionally attached cyano-groups. The ionization potentials of the derivatives were found to be in the relatively wide range of 5.43–5.81 eV since cyano-groups were used in their design. Possible applications of the emitters were demonstrated in non-doped and doped organic light-emitting diodes with up to 2.3 % external quantum efficiencies for simple fluorescent devices. In the best case, deep-blue electroluminescence with chromaticity coordinates of (0.16, 0.10) was close to blue color standard (0.14, 0.08) of the National Television System Committee.

scholarly journals The binuclear cluster of [FeFe] hydrogenase is formed with sulfur donated by cysteine of an [Fe(Cys)(CO)2(CN)] organometallic precursor

2019 ◽  
Vol 116 (42) ◽  
pp. 20850-20855 ◽  
Author(s):  
Guodong Rao ◽  
Scott A. Pattenaude ◽  
Katherine Alwan ◽  
Ninian J. Blackburn ◽  
R. David Britt ◽  
...  
Keyword(s):  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Carbon And Nitrogen ◽  
Binuclear Cluster ◽  
Organometallic Precursor ◽  
Pulse Epr ◽  
X Ray Absorption ◽  
Electron Paramagnetic

The enzyme [FeFe]-hydrogenase (HydA1) contains a unique 6-iron cofactor, the H-cluster, that has unusual ligands to an Fe–Fe binuclear subcluster: CN−, CO, and an azadithiolate (adt) ligand that provides 2 S bridges between the 2 Fe atoms. In cells, the H-cluster is assembled by a collection of 3 maturases: HydE and HydF, whose roles aren’t fully understood, and HydG, which has been shown to construct a [Fe(Cys)(CO)2(CN)] organometallic precursor to the binuclear cluster. Here, we report the in vitro assembly of the H-cluster in the absence of HydG, which is functionally replaced by adding a synthetic [Fe(Cys)(CO)2(CN)] carrier in the maturation reaction. The synthetic carrier and the HydG-generated analog exhibit similar infrared spectra. The carrier allows HydG-free maturation to HydA1, whose activity matches that of the native enzyme. Maturation with 13CN-containing carrier affords 13CN-labeled enzyme as verified by electron paramagnetic resonance (EPR)/electron nuclear double-resonance spectra. This synthetic surrogate approach complements existing biochemical strategies and greatly facilitates the understanding of pathways involved in the assembly of the H-cluster. As an immediate demonstration, we clarify that Cys is not the source of the carbon and nitrogen atoms in the adt ligand using pulse EPR to target the magnetic couplings introduced via a 13C3,15N-Cys–labeled synthetic carrier. Parallel mass-spectrometry experiments show that the Cys backbone is converted to pyruvate, consistent with a cysteine role in donating S in forming the adt bridge. This mechanistic scenario is confirmed via maturation with a seleno-Cys carrier to form HydA1–Se, where the incorporation of Se was characterized by extended X-ray absorption fine structure spectroscopy.

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