The dimensional reduction of solids into smaller fragments provides a route to achieve new physical properties and gain deeper insight into the extended parent structures. Here, we report the ...synthesis of CuTOTP-OR (TOTP n– = 2,3,6,7-tetraoxidotriphenylene), a family of copper-based macrocycles that resemble truncated fragments of the conductive two-dimensional (2D) metal–organic framework Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene). The planar metal–organic macrocycles self-assemble into ordered nanotubes with internal diameters of ∼2 nm and short interlayer distances of ∼3.20 Å. Strong π–π stacking interactions between macrocycles facilitate out-of-plane charge transport, and pressed pellet conductivities as high as 2(1) × 10–3 S cm–1 are observed. Peripheral alkyl functionalization enhances solution processability and enables the fabrication of thin-film field-effect transistor devices. Ambipolar charge transport is observed, suggesting that similar behavior may be operative in Cu3(HHTP)2. By coupling the attractive features of metal–organic frameworks with greater processability, these macrocycles enable facile device integration and a more nuanced understanding of out-of-plane charge transport in 2D conductive metal–organic frameworks.
Aqueous Zn-ion batteries (ZIBs) are emerging candidates for safe and eco-friendly large-scale energy storage, but the critical challenge is to develop stable and robust cathode materials for ...reversible and fast Zn2+ intercalation. In the present work, the drawbacks of pure hydrated vanadium oxides (VOH), including low ion mobility and cycling instability, are mitigated by modifying the local atomic environment and increasing the amount of tetravalent vanadium cations. These effects are achieved by introducing trivalent Al-ions during a one-step hydrothermal synthesis. The expanded lattice spacing and improved conductivity of the synthesized Al–VOH enable rapid Zn2+ diffusion and electron transfer, leading to a high capacity of 380 mAh·g−1 at 50 mA g−1, as well as the excellent long-term cycling stability (capacity maintained over 3000 cycles). Further investigations of the reaction kinetics and mechanism reveal the effects of introducing Al-ions, and the role of Zn2+ trapped upon initial charging plays in promoting the subsequent electrochemical process and preventing the structural degradation.
Display omitted
•Al-ions were introduced into hydrated vanadium oxide through hydrothermal reaction.•The lattice spacing of the product is expanded.•Improved ion diffusion rate and conductivity result in a higher capacity.•Al-ions and trapped Zn-ions assist in stabilizing the structure.
Detailed measurements of the electron densities, temperatures, and ionization states of compressed CH shells approaching pressures of 50 Mbar are achieved with spectrally resolved x-ray scattering. ...Laser-produced 9 keV x-rays probe the plasma during the transient state of three-shock coalescence. High signal-to-noise x-ray scattering spectra show direct evidence of continuum depression in highly degenerate warm dense matter states with electron densities ne>1024 cm-3. The measured densities and temperatures agree well with radiation-hydrodynamic modeling when accounting for continuum lowering in calculations that employ detailed configuration accounting.
Photosynthetic water oxidation is a fundamental process that sustains the biosphere. A Mn
Ca cluster embedded in the photosystem II protein environment is responsible for the production of ...atmospheric oxygen. Here, time-resolved x-ray emission spectroscopy (XES) was used to observe the process of oxygen formation in real time. These experiments reveal that the oxygen evolution step, initiated by three sequential laser flashes, is accompanied by rapid (within 50 μs) changes to the Mn Kβ XES spectrum. However, no oxidation of the Mn
Ca core above the all MnIV state was detected to precede O-O bond formation, and the observed changes were therefore assigned to O-O bond formation dynamics. We propose that O-O bond formation occurs prior to the transfer of the final (4th) electron from the Mn
Ca cluster to the oxidized tyrosine Y
residue. This model resolves the kinetic limitations associated with O-O bond formation, and suggests an evolutionary adaptation to avoid releasing of harmful peroxide species.
X-ray emission (XES) spectroscopy is an attractive technique for analysis of the electronic structure of molecules, materials, and metalloproteins. However, a better understanding of XES results is ...required. Using a combination of experiment and ground-state density functional theory analysis, we rationalize differences in the X-ray emission spectra of multinuclear Mn complexes. Model compounds, including dinuclear Mn2O2L′4(ClO4)3 (L′= 2,2′-bipyridyl, 1) and two examples from the Mn4O4L6 “cubane” family of model compounds (L = (p-R-C6H4)PO2 −, R = OCH3 2, CH3 3 ), were compared with the Oxygen Evolving Complex of Photosystem II. Our analysis shows that changes in the structure of the Mn complexes, resulting in changes to the spin polarization, can introduce significant spectral shifts in compounds of the same formal redox state. The implications of changes in spin polarization for understanding photosynthetic water-splitting catalysis is discussed.
Understanding the function of Mn ions in biological and chemical redox catalysis requires precise knowledge of their electronic structure. X-ray emission spectroscopy (XES) is an emerging technique ...with a growing application to biological and biomimetic systems. Here, we report an improved, cost-effective spectrometer used to analyze two biomimetic coordination compounds, MnIV(OH)2(Me2EBC)2+ and MnIV(O)(OH)(Me2EBC)+, the second of which contains a key MnIVO structural fragment. Despite having the same formal oxidation state (MnIV) and tetradentate ligands, XES spectra from these two compounds demonstrate different electronic structures. Experimental measurements and DFT calculations yield different localized spin densities for the two complexes resulting from MnIV–OH conversion to MnIVO. The relevance of the observed spectroscopic changes is discussed for applications in analyzing complex biological systems such as photosystem II. A model of the S3 intermediate state of photosystem II containing a MnIVO fragment is compared to recent time-resolved X-ray diffraction data of the same state.
Recently developed instrumentation at the University of Washington has allowed for nonresonant x-ray emission spectra (XES) to be measured in a laboratory-setting with an inexpensive, easily operated ...system. We present a critical evaluation of this equipment by means of Kβ and valence-level XES measurements for several Co compounds. We find peak count rates of ∼5000 s for concentrated samples and a robust relative energy scale with reproducibility of 25 meV or better. We furthermore find excellent agreement with synchrotron measurements with only modest loss in energy resolution. Instruments such as ours, based on only conventional sources that are widely sold for elemental analysis by x-ray fluorescence, can fill an important role to diversify the research applications of XES both by their presence in non-synchrotron laboratories and by their use in conjunction with XAFS beamlines where the complementarity of XAFS and XES holds high scientific potential.
PDF
