Influence of Br − /S 2− site-exchange on Li diffusion mechanism in Li 6 PS 5 Br: a computational study

We investigate how low degrees of Br − / S 2 − site-exchange influence the Li + diffusion in the argyrodite-type solid electrolyte Li 6 PS 5 Br by ab initio molecular dynamics simulations. Based on the atomic trajectories of the defect-free material, a new mechanism for the internal Li + reorganization within the Li + cages around the 4 d sites is identified. This reorganization mechanism is highly concerted and cannot be described by just one rotation axis. Simulations with Br − / S 2 − defects reveal that Li + interstitials ( L ii . ) are the dominant mobile charge carriers and originate from Frenkel pairs. These are formed because B rS . defects on the 4 d sites donate one or even two L ii . to the neighbouring cages. The L ii . then carry out intercage jumps via interstitial and interstitialcy mechanisms. With that, one single B rS . defect enables Li + diffusion over an extended spatial area explaining why low degrees of site-exchange are sufficient to trigger superionic conduction. The vacant sites of the Frenkel pairs, namely V Li ′ , are mostly immobile and bound to the B rS . defect. Because S Br ′ defects on 4 a sites act as sinks for L ii . they seem to be beneficial only for the local Li + transport. In their vicinity T4 tetrahedral sites start to get occupied. Because the Li + transport was found to be rather confined if S Br ′ and B rS . defects are direct neighbours, their relative arrangement seems to be crucial for effective long-range transport. This article is part of the Theo Murphy meeting issue ‘Understanding fast-ion conduction in solid electrolytes’.

Interplay between Single-Ion and Two-Ion Anisotropies in Frustrated 2D Semiconductors and Tuning of Magnetic Structures Topology

The effects of competing magnetic interactions in stabilizing different spin configurations are drawing renewed attention in order to unveil emerging topological spin textures and to highlight microscopic mechanisms leading to their stabilization. The possible key role of the two-site exchange anisotropy in selecting specific helicity and vorticity of skyrmionic lattices has only recently been proposed. In this work, we explore the phase diagram of a frustrated localized magnet characterized by a two-dimensional centrosymmetric triangular lattice, focusing on the interplay between the two-ion anisotropy and the single-ion anisotropy. The effects of an external magnetic field applied perpendicularly to the magnetic layer, are also investigated. By means of Monte Carlo simulations, we find an abundance of different spin configurations, going from trivial to high-order Q skyrmionic and meronic lattices. In closer detail, we find that a dominant role is played by the two-ion over the single-ion anisotropy in determining the planar spin texture; the strength and the sign of single ion anisotropy, together with the magnitude of the magnetic field, tune the perpendicular spin components, mostly affecting the polarity (and, in turn, the topology) of the spin texture. Our analysis confirms the crucial role of the anisotropic symmetric exchange in systems with dominant short-range interactions; at the same time, we predict a rich variety of complex magnetic textures, which may arise from a fine tuning of competing anisotropic mechanisms.

Binding site exchange kinetics revealed through efficient spin–spin dephasing of hyperpolarized 129Xe

Localized detection of hyperpolarized, exchanging Xe spins enables quantitative insights at unprecedented sensitivity for characterizing chemical exchange kinetics in various contexts such as host–guest interactions and displacement assays.

Ligand Effects on Structural, Protophilic and Reductive Features of Stannylated Dinuclear Iron Dithiolato Complexes

The synthesis and characterization of Fe2(CO)5(L){μ-(SCH2)2}SnMe2 (L = PPh3 (2) and P(OMe)3 (3) derived from the parent hexacarbonyl complex Fe2(CO)6{μ-(SCH2)2}SnMe2 (1) is reported. Whereas 1 exhibits a unique planar structure, X-ray crystallography showed that the apical orientation of L in complexes 2 and 3 results in a chair/boat conformation of the Fe2S2C2Sn fused six-membered rings, which is typical for diiron dithiolato complexes. In solution, NMR and FTIR spectroscopic techniques provide evidence for a dynamic process of apical-basal site exchange of the ligand L in 2 and 3. Protonation experiments on 2 and 3 in MeCN using CF3CO2H, HCl or HBF4·Et2O suggest enhanced protophilicity of the Fe-Fe bond due to the presence of the electron donor ligands L as well as the stannylation effect. While the carbonyl ligands in 2 stretch at lower wavenumbers ν(CO) than those in 3, the cyclic voltammetric reduction of 2 unpredictably occurs at less negative potential than that of 3. In contrast to 1, the presence of PPh3 and P(OMe)3 in 2 and 3, respectively, allows protonation prior to reduction as shown by FTIR spectroscopy and cyclic voltammetry.

Ligand Effects on Structural, Protophilic and Reductive Features of Stannylated Dinuclear Iron Dithiolato Complexes

The synthesis and characterization of Fe2(CO)5(L){μ-(SCH2)2}SnMe2 (L = PPh3 (2) and P(OMe)3 (3) derived from the parent hexacarbonyl complex Fe2(CO)6{μ-(SCH2)2}SnMe2 (1) is reported. Whereas 1 exhibits a unique planar structure, X-ray crystallography showed that the apical orientation of L in complexes 2 and 3 results in a chair/boat conformation of the Fe2S2C2Sn fused six-membered rings, which is typical for diiron dithiolato complexes. In solution, NMR and FTIR spectroscopic techniques provide evidence for a dynamic process of apical-basal site exchange of the ligand L in 2 and 3. Protonation experiments on 2 and 3 in MeCN using CF3CO2H, HCl or HBF4·Et2O suggest enhanced protophilicity of the Fe-Fe bond due to the presence of the electron donor ligands L as well as the stannylation effect. While the carbonyl ligands in 2 stretch at lower wavenumbers ν(CO) than those in 3, the cyclic voltammetric reduction of 2 unpredictably occurs at less negative potential than that of 3. In contrast to 1, the presence of PPh3 and P(OMe)3 in 2 and 3, respectively, allows protonation prior to reduction as shown by FTIR spectroscopy and cyclic voltammetry.