NEXAFS spectra of model sulfide chains: implications for sulfur networks obtained from inverse vulcanization.

Inverse vulcanization is a promising route to stabilize sulfur in lithium-sulfur batteries, but the resulting sulfur strand lengths in the materials are elusive. We address the strand length by characterization via sulfur near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Theoretical predictions of NEXAFS spectra for model molecules containing strands with up to three sulfur atoms are verified by experiment. The near perfect agreement between simulation and experiment on the absolute energy scale allows for the predictions for larger chain lengths also. Inspection and interpretation of NEXAFS spectra from real battery materials on this basis reveals the appearance of single connecting sulfur atoms for very low sulfur content, and of longer strands when the sulfur fraction increases.

Sulfide-Bridged Covalent Quinoxaline Frameworks for Lithium-Organosulfide Batteries.

The chelating ability of quinoxaline cores and the redox activity of organosulfide bridges in layered covalent organic frameworks (COFs) offer dual active sites for reversible lithium (Li)-storage. The designed COFs combining these properties feature disulfide and polysulfide-bridged networks showcasing an intriguing Li-storage mechanism, which can be considered as a lithium-organosulfide (Li-OrS) battery. The experimental-computational elucidation of three quinoxaline COFs containing systematically enhanced sulfur atoms in sulfide bridging demonstrates fast kinetics during Li interactions with the quinoxaline core. Meanwhile, bilateral covalent bonding of sulfide bridges to the quinoxaline core enables a redox-mediated reversible cleavage of the sulfursulfur bond and the formation of covalently anchored lithium-sulfide chains or clusters during Li-interactions, accompanied by a marked reduction of Li-polysulfide (Li-PS) dissolution into the electrolyte, a frequent drawback of lithium-sulfur (Li-S) batteries. The electrochemical behavior of model compounds mimicking the sulfide linkages of the COFs and operando Raman studies on the framework structure unravels the reversibility of the profound Li-ion-organosulfide interactions. Thus, integrating redox-active organic-framework materials with covalently anchored sulfides enables a stable Li-OrS battery mechanism which shows benefits over a typical Li-S battery.

Steric and Electronic Effects in Gold N-Heterocyclic Carbene Complexes Revealed by Computational Analysis.

A computational analysis of a series of cationic and neutral gold imidazolylidene and benzimidizolylidene complexes is reported. The Bond Dissociation Energies of the various ligands in the complexes calculated at the PBE0-D3/def2-TZVP level of theory increase with increasing ligand volume, except for those of complexes containing t-butyl-substituted ligands, which are anomalously low particularly for the benzimidazolylidene species. Atoms in Molecules studies show the presence of a variety of weak intramolecular interactions, characterised by the presence of bond critical points with a range of different properties. Energy Decomposition Analysis and calculation of Electrostatic Surface Potentials indicate that some interactions are weakly attractive dispersion-type interactions, while others are repulsive. The octanol/water partition coefficients (log P values) were calculated as a measure of the lipophilicities of the complexes and were found to increase with increasing volume.