Role of the solvent in the activation of LiS as cathode material: a DFT study.

Lithium-sulfur batteries are considered one of the possible next-generation energy-storage solutions, but to be commercially available many drawbacks have yet to be solved. One solution with great potentiality is the use of lithium sulfide as cathode material since it can be coupled to Li-free anodes, such as graphite, Si or Sn. Nevertheless, LiS, like sulfur, is electronically and ionically insulating, with a high activation potential for its initial oxidation step.

Mechanochemical disulfide reduction reveals imprints of noncovalent sulfuroxygen chalcogen bonds in protein-inspired mimics in aqueous solution.

The surprisingly rich chemistry of mechanically activated cleavage of disulfide bonds has been uncovered only recently. Using a disulfide protein mimic together with Cleland's reagent (DTT) as the attacking nucleophile in aqueous solution, our isotensional ab initio simulations add another surprise to the list. They unveil that noncovalent chalcogen-chalcogen 1,5-type SO interactions involving the S-S bridge and γ-carbonyl O are controlling the mechanochemical reactivity of disulfides at very low forces, thus adding a third reactivity regime to the hitherto known ones.

Selective Nanomechanics of Aromatic versus Aliphatic Thiolates on Gold Surfaces.

Thiolated gold nanointerfaces play a key role in numerous fields of science, technology, as well as modern medicine to coat, functionalize, and protect. Our computational study reveals that the mechanical vs thermal stabilities of aliphatic thiolates on gold surfaces are strikingly different from those of aromatic thiolates. The aliphatic thiolates feature, at the same time, a higher thermal desorption energy but a lower mechanical rupture force than thiophenolates.

Nanomechanics of bidentate thiolate ligands on gold surfaces.

The effect of the chain length separating sulfur atoms in bidentate thiols attached to defective gold surfaces on the rupture of the respective molecule-gold junctions has been studied computationally. Thermal desorption always yields cyclic disulfides. In contrast, mechanochemical desorption leads to cyclic gold complexes, where metal atoms are extracted from the surface and kept in tweezer-like arrangements by the sulfur atoms.

Nucleophilic substitution in ionizable Fischer thiocarbene complexes: steric effect of the alkyl substituent on the heteroatom.

A detailed kinetic study has been carried out for the aminolysis of ionizable Fischer thiocarbene complexes (CO)5M[double bond, length as m-dash]C(SR)CH3 (M = Cr, W; R = iPr, nBu, cHex, tBu) with five primary amines and one secondary amine in aqueous acetonitrile solutions (50% MeCN-50% water (v/v)). The observed rate constants for the reaction with primary amines showed a first-order dependence on the amine concentration, while with morpholine, the rate constant has second-order dependence. The general base catalysis process was confirmed by the variation of the rate constants with the concentration of an external catalyst and the pH.

Anchoring sites to the STM tip can explain multiple peaks in single molecule conductance histograms.

Accelerated molecular dynamics and quantum conductance calculations are employed to shed light onto the electrochemical properties of the Au|1,8-octanedithiol|Au junction. Widely different contact geometries with varying degrees of roughness are examined. Strikingly, the two extreme situations considered in this work, tip-tip and tip-perfect surface junctions, give almost indistinguishable conductances.

Configurational Behavior and Conductance of Alkanedithiol Molecular Wires from Accelerated Dynamics Simulations.

An accelerated dynamics scheme is employed to sample the configurational space of a system consisting of an alkanedithiol molecule confined to the gap between a metal tip and a perfect metal surface. With this information and by means of nonequilibrium green functions techniques (NEGF), conductance calculations are performed. The present results show that even for this system, which is one of the most simple conceivable because of the perfectness of the surface, a complex behavior appears due to the occurrence of an unexpected tip-molecule-surface arrangement, where the insertion of one of the molecular ends into the tip-surface gap generates configurations with strongly enhanced conductance.

Role of the hydrophobicity on the thermodynamic and kinetic acidity of Fischer thiocarbene complexes.

Rate constants for the reversible deprotonation of (CO)(5)W=C(SR)CH(3) (W-SR) by OH(-), water and a number of primary aliphatic and secondary alicyclic amines, have been determined in 50% MeCN:50% water at 25 degrees C. In addition, solvation energy and proton affinities values for M-SR (M = Cr and W) in the gas phase and in acetonitrile have been computed at DFT level. Although there is not a linear correlation between the calculated proton affinities and the measured pK(a)s, the calculations reveal that when solvent effects are taken into account the substituted compounds studied show differences in their proton affinities.

Kinetics of the reactions of [p-nitrophenoxy(phenyl)carbene]pentacarbonylchromium(0) with aryloxide ions, hydroxide ion, and water in aqueous acetonitrile. Concerted or stepwise?

The main question addressed in this paper is whether the nucleophilic substitution of the p-nitrophenoxy group in (CO)5Cr=C(OC6H4-4-NO2)Ph (1-NO2) by a series of substituted phenoxide ions is concerted or stepwise. Rate constants, kArO, for these substitution reactions were determined in 50% MeCN-50% water (v/v) at 25 degrees C. A Brønsted plot of log kArO versus pKa(ArOH) s consistent with a stepwise mechanism.

Hydrolysis of Fischer carbene complexes. Steric effects of the pi-donor group.

Rate constants for the hydrolysis of Fischer carbenes (CO)5Cr=C(OR)Ph (R = n-propyl, neopentyl, isopropyl, and menthyl) in 50% MeCN-50% water (v/v) at 25 degrees C are reported. The rate constants for the addition of -OH to the carbene carbon are 5.3, 3.