Excess enthalpies of alcohol + amine mixtures. Experimental results and theoretical description using the ERAS-model

New experimental data of the molar excess enthalpy H^E of mixtures containing eight liquids - propylamine + methanol, ethanol, propan-1-ol, butan-1-ol, butylamine + methanol, ethanol, propan-1-ol, butan-1-ol - are presented using a quasi-isothermal flow calorimeter. The results are used for testing the ERAS-model which provides a theoretical concept accounting for the self-association and cross-association of alcohol and amine molecules, as well as for non-associative intermolecular interactions. Excess molar volumes V^E are also successfully described by the model. It turns out that the strong cross-association occurring between alcohol and amine molecules is the predominant reason for the remarkably low exothermic values of H^E observed for the mixtures studied.     

Monothioindigo,determined by microcrystal structure analysis

Indigo and thioindigo pigments are used for a wide range of applications. The crystal structure of the mixed compound monothioindigo [systematic name: (E)‐2‐(3‐oxo‐2,3‐dihydro‐1‐benzothiophen‐2‐ylidene)‐2,3‐dihydro‐1H‐indol‐3‐one], C₁₆H₉NO₂S, has been determined by microcrystal structure analysis from a crystal with a size of just 1 × 2 × 10 µm. The crystal structure of monothioindigo resembles those of indigo and thioindigo. The molecules show orientational disorder, with site‐occupation factors of 0.962 (2) and 0.038 (2) for the major and minor disorder components, respectively. The indigo fragment donates an intermolecular hydrogen bond, leading to a criss‐cross arrangement of molecules similar to that in indigo, whereas the thioindigo fragment exhibits only van der Waals interactions and molecular stacking, similar to that in thioindigo.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.