Evidence of AlII Radical Addition to Benzene

Electrophilic AlIII species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low-valent AlI aluminyl anions have showcased oxidative additions towards arenes C C and/or C H bonds. Herein, we communicate compelling evidence of an AlII radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC8 in benzene furnishes a double addition to the benzene ring instead of a C H bond activation, producing the corresponding cyclohexa-1,3 (orl,4)-dienes as Birch-type reduction product. X-ray crystallographic analysis, EPR spectroscopy, and DFT results suggest this reactivity proceeds through a stable AlII radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection

Black Titania and Niobia within Ten Minutes : Mechanochemical Reduction of Metal Oxides with Alkali Metal Hydrides

Partially or fully reduced transition metal oxides show extraordinary electronic and catalytic properties but are usually prepared by high temperature reduction reactions. This study reports the systematic investigation of the fast mechanochemical reduction of rutile-type TiO2 and H-Nb2O5 to their partially reduced black counterparts applying NaH and LiH as reducing agents. Milling time and oxide to reducing agent ratio show a large influence on the final amount of reduced metal ions in the materials. For both oxides LiH shows a higher reducing potential than NaH. An intercalation of Li+ into the structure of the oxides was proven by PXRD and subsequent Rietveld refinements as well as 6 Li solid-state NMR spectroscopy. The products showed a decreased band gap and the presence of unpaired electrons as observed by EPR spectroscopy, proving the successful reduction of Ti4+ and Nb5+. Furthermore, the developed material exhibits a significantly enhanced photocatalytic performance towards the degradation of methylene blue compared to the pristine oxides. The presented method is a general, time efficient and simple method to obtain reduced transition metal oxides

Maser threshold characterization by resonator Q-factor tuning

Whereas the laser is nowadays an ubiquitous technology, applications for its microwave analog, the maser, remain highly specialized, despite the excellent low-noise microwave amplification properties. The widespread application of masers is typically limited by the need of cryogenic temperatures. The recent realization of a continuous-wave room-temperature maser, using NV− centers in diamond, is a first step towards establishing the maser as a potential platform for microwave research and development, yet its design is far from optimal. Here, we design and construct an optimized setup able to characterize the operating space of a maser using NV− centers. We focus on the interplay of two key parameters for emission of microwave photons: the quality factor of the microwave resonator and the degree of spin level-inversion. We characterize the performance of the maser as a function of these two parameters, identifying the parameter space of operation and highlighting the requirements for maximal continuous microwave emission

Maser Threshold Characterization by Resonator Q-Factor Tuning

Whereas the laser is nowadays an ubiquitous technology, applications for its microwave analogue, the maser, remain highly specialized, despite the excellent low-noise microwave amplification properties. The widespread application of masers is typically limited by the need of cryogenic temperatures. The recent realization of a continuous-wave room-temperature maser, using NV$^-$ centers in diamond, is a first step towards establishing the maser as a potential platform for microwave research and development, yet its design is far from optimal. Here, we design and construct an optimized setup able to characterize the operating space of a maser using NV$^-$ centers. We focus on the interplay of two key parameters for emission of microwave photons: the quality factor of the microwave resonator and the degree of spin level-inversion. We characterize the performance of the maser as a function of these two parameters, identifying the parameter space of operation and highlighting the requirements for maximal continuous microwave emission

The electronic structure and dynamics of the excited triplet state of octaethylaluminum(III)-porphyrin investigated with advanced EPR methods

The photoexcited triplet state of octaethylaluminum(III)-porphyrin (AlOEP) was investigated by timeresolved Electron Paramagnetic Resonance, Electron Nuclear Double Resonance and Electron Spin Echo Envelope Modulation in an organic glass at 10 and 80 K. This main group element porphyrin is unusual because the metal has a small ionic radius and is six-coordinate with axial covalent and coordination bonds. It is not known whether triplet state dynamics influence its magnetic resonance properties as has been observed for some transition metal porphyrins. Together with density functional theory modelling, the magnetic resonance data of AlOEP allow the temperature dependence of the zero-field splitting (ZFS) parameters, D and E, and the proton AZZ hyperfine coupling (hfc) tensor components of the methine protons, in the zero-field splitting frame to be determined. The results provide evidence that the ZFS, hfc and spin–lattice relaxation are indeed influenced by the presence of a dynamic process that is discussed in terms of Jahn-Teller dynamic effects. Thus, these effects should be taken into account when interpreting EPR data from larger complexes containing AlOEP