Density functional calculations have been performed to explore the sextet, quartet, and doublet potential energy surfaces of methane dehydrogenation by gas-phase Os+ for understanding the reaction mechanism. The minimum energy reaction path is found to involve the spin inversion three times in the different reaction steps. Totally, three spin states (sextet, quartet, and doublet) are involved in the whole reaction. Specifically, the reaction is most likely to proceed through the following steps:  6 Os+ + CH4 → OsCH4 + ( 6 1) → HOsCH3 ( 4 2) → HOsH(CH2)+ ( 2 3) → (H2)Os(CH2)+ ( 4 4) → Os(CH2)+ ( 4 5) + H2. The overall reaction is calculated to be exothermic by 4.2 kcal/mol, which is in good agreement with the available experimental results. The first spin inversion, from the sextet state to the quartet state, makes the activation of the first C−H bond energetically spontaneous. The second transition from the quartet state to the doublet state facilitates the cleavage of the second C−H bond, lowering the barrier from 25.9 kcal/mol to 16.1 kcal/mol. The third spin inversion occurs from the doublet state to the quartet state in the reductive elimination step of H2, and this spin inversion leads to a decrease in the barrier height from 41.0 to 30.4 kcal/mol.

Unrestricted density functional calculations with spin-projection procedures have been performed for a series of m-phenylene-bridged diradicals to investigate the effects of substitution on the singlet-triplet (S-T) energy gaps and the ground-state multiplicities. Our calculations show that the introduction of electron-donating (or electron-withdrawing) substituents on 4,6-positions of the m-phenylene moiety or on the radical centers, or on both positions, generally leads to a triplet ground state, although the S-T energy gaps are smaller than that of the parent m-xylylene diradical to some extent. However, the simultaneous substitution of electrondonating and electron-withdrawing groups at m-phenylene and radical centers, and Vice Versa, will result in a singlet ground state or a very small positive S-T gap. A perturbative analysis based on the SOMO-SOMO energy splittings, the spatial distributions of SOMOs, and the population of the spin densities calculated for the triplet state has been presented to elucidate factors determining the S-T gap and ground-state multiplicity in studied diradicals.

Currently adding a suitable additive in the electrolyte is one of the most effective strategies to improve the electrochemical performance for a lithium-ion battery, especially under high temperature. In this work, N,Ndimethylformamide (DMF) as an electrolyte additive was introduced to improve the battery performance of LiFePO 4 at 60 °C. The addition of DMF can effectively increase the specific capacity, cycling performance, and rate performance of batteries using LiFePO 4 as cathode material. X-ray diffraction results reveal that for the electrode cycled in the electrolyte without additive, Fe 2 O 3 , FePO 4 , and other impurity peaks appear under high temperature. scanning electron microscopy/transmission electron microscopy results indicate that some deposits are generated on the electrode surface without additive under high temperature due to the decomposition of electrolyte in the reaction between electrolyte and electrode materials. The Fourier transform infrared spectroscopy/NMR/X-ray photoelectron spectroscopy results demonstrate that DMF as a lewis base can capture lewis acidic PF 5 from the decomposition of LiPF 6 as well as block the chain reaction of LiFePO 4 with hydrogen fluoride, which alleviates the electrolyte decomposition and electrode dissolution at high temperature.

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Recently, single-atom catalysts (SACs) have been used to construct biosensors for the determination of organophosphorus pesticides (OPs). However, most nanozymes including SACs are peroxidase-like enzymes and require highly toxic and unstable hydrogen peroxide (H 2 O 2 ) as a co-reactant to generate reactive oxygen species. Inspired by the heme site of cytochrome c oxidases (Ccos), the construction of Fe-N 5 -coordinated SACs by introducing axial N ligands is expected to bind O 2 to generate active metal−oxygen intermediates. Herein, a SAC with an Fe-N 5 active center confined by hierarchically porous carbon nanoframes (Fe SAs/N 5 -pC-4) was prepared by a polymerization−pyrolysis− evaporation−etching strategy, and its underlying enzyme-like mechanism was uncovered through experiments and density functional theory calculations. The 100% metal atom utilization, increased accessible active sites, accelerated mass transfer, excellent hydrophilicity, and an electron-driven mechanism of axial N endow the SAC with enhanced oxidase-like activity. Notably, its catalytic rate constant (0.398 s −1 ) is 569 times greater than that of the commercial Pt/C catalyst. Similar to the catalytic mechanism of Ccos, O 2 can be converted into reactive oxygen species, avoiding the use of co-reactant H 2 O 2 effectively. In addition, based on the inhibitory effect of thiols on the active site of Fe SAs/N 5 -pC-4, a biosensor was constructed and applied to the colorimetric analysis of OPs. This provides a facile, cost-effective method for efficient OP screening at sites to help control their contamination.