A homoleptic chromium(iii) carboxylate

The first homoleptic monomeric chromium(iii) carboxylate has been prepared using an anhydrous salt metathesis synthetic route. The carboxylate groups coordinate the chromium in a bidentate chelate yielding an aliphatic soluble complex.

Four salt phases of theophylline

The structures of two anhydrous salt phases of theophylline, namely 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium tetrafluoroborate, C7H9N4O2+·BF4−, and 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium chloride, C7H9N4O2+·Cl−, are reported together with the structures of two monohydrate salt forms, namely 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium chloride monohydrate, C7H9N4O2+·Cl−·H2O, and 1,3-dimethyl-2,6-dioxo-7H-purin-9-ium bromide monohydrate, C7H9N4O2+·Br−·H2O. The monohydrate structures are mutually isostructural, with the cations and anions lying on crystallographic mirror planes (Z′ = 1\over 2). The main intermolecular interaction motif is a hydrogen-bonding network in the same mirror plane. The tetrafluoroborate structure is based on planar hydrogen-bonded theopylline cation dimers; the anions interact with the dimers in a pendant fashion. The anhydrous chloride structure hasZ′ = 2 and in contrast to the other species it does not form planar hydrogen-bonded constructs, instead one-dimensional chains of cations and anions propagate parallel to the crystallographiccdirection. An earlier report claiming to describe an anhydrous structure of theophylline hydrochloride is re-examined in light of these results. It is concluded that the earlier structure has been reported in the wrong space group and that it has been chemically misidentified.

Thermochemical Energy Storage Using Salt Hydrates

We investigate the capability of salt hydrates, using magnesium sulfate heptahydrate as a model salt, to store thermo-chemical energy as they dissociate into anhydrous salts or lower hydrates and water vapor upon heating. When salt hydrates are heated to the temperature required to activate the dehydration reaction, water desorption occurs from the compound. While thermal diffusion governs thermal transport below this reaction temperature, the heat transfer during the dehydration process is influenced by thermochemical kinetics. An anhydrous salt that has relatively higher energy content than its hydrated counterpart can be stably stored over long durations and transported at ambient temperatures. Thus, thermal energy can be released by allowing water vapor to flow across the anhydrous salt, which transforms its chemically stored heat into a sensible form. We model the thermochemical process based on the conservation of mass and energy and a relation describing the chemical kinetics, and employ finite difference technique to solve them. Different cases are considered to provide suggestions to improve the process performance. This storage application has potential for long-term thermal applications, e.g., for storing solar heat during summer months and releasing it in the winter to warm buildings.

Preparation, Solubility, Infrared Spectra and Radiolysis of Tetramethylammonium Hydrogenselenate Monohydrate and Lithium Tetramethylammonium Selenate Tetrahydrate

Solubility in the (Me4N)2SeO4-H2SeO4-H2O and (Me4N)2SeO4-Li2SeO4-H2O systems were studied. The new compounds, tetramethylammonium hydrogenselenate monohydrate ((Me4N)HSeO4·H2O) and lithium tetramethylammonium selenate tetrahydrate (Li(Me4N)SeO4·4H2O), have been found in these systems. Both substances were characterised by chemical analysis and IR molecular spectroscopy. Both of the title substances decompose under the influence of X-radiation and, thus, their structures cannot be determined. The radiolysis of both substances was studied in greater detail. Tetramethylammonium hydrogenselenate monohydrate is dehydrated by X-radiation to form the anhydrous salt. The reaction is controlled by first-order kinetics with a rate constant of 1.30(3) × 10-3 s-1.

Aminoguanidinium(2+) Hexafluorozirconate Monohydrate: A Co-Product of Preparing the Ferroelectric Anhydrous Salt

Preparation of anhydrous aminoguanidinium(2+) hexafluorozirconate, CN4H8ZrF6, shown previously to satisfy the structural criteria for ferroelectricity [Abrahams et al. (1996). Acta Cryst. B52, 806–809], generally results in the co-formation of a series of related fluorozirconates. The structure of the monohydrate salt, one of the co-products, has been redetermined to improve understanding of the preparation pathway, locate the H atoms and compare corresponding atom positions [Gerasimenko et al. (1989). Koord. Khim. 15, 130–135]. The positions of the H atoms were not established in the latter study. All 16 H atoms in the two symmetry-independent CN4H8(2+) ions are now located and refined, with R 1 = 0.0299 and S = 1.119. Both independent water molecules are disordered. Normal probability analysis reveals uncompensated error and/or underestimated uncertainty associated with ten non-H-atom position coordinates. The relative concentrations of HF, CN4H7Cl and H2ZrF6 are among the major variables controlling the formation of the related fluorozirconates.