Thermal diffusion with stepwise association equilibria in aqueous solutions of the ionic dyes methylene blue and methyl orange

Soret coefficients are measured conductimetrically for dilute aqueous solutions of the stepwise-associating ionic dyes methylene blue (chloride salt) and methyl orange (sodium salt) at 25°C. In contrast to the behavior of other dilute aqueous electrolytes, the Soret coefficients of the dyes increase with concentration. An approximate treatment of thermal diffusion of stepwise-associating solutes is developed to interpret the results. The analysis is used to estimate the intrinsic enthalpies of transport of the monomeric and the associated forms of the dyes. The enthalpy of association makes a large reactive contribution to the enthalpy of transport of methyl orange.     

Positive one-parameter semigroups on ordered banach spaces

In this review we describe the basic structure of positive continuous one-parameter semigroups acting on ordered Banach spaces. The review is in two parts.First we discuss the general structure of ordered Banach spaces and their ordered duals. We examine normality and generation properties of the cones of positive elements with particular emphasis on monotone properties of the norm. The special cases of Banach lattices, order-unit spaces, and base-norm spaces, are also examined.Second we develop the theory of positive strongly continuous semigroups on ordered Banach spaces, and positive weak^*-continuous semigroups on the dual spaces. Initially we derive analogues of the Feller-Miyadera-Phillips and Hille-Yosida theorems on generation of positive semigroups. Subsequently we analyse strict positivity, irreducibility, and spectral properties, in parallel with the Perron-Frobenius theory of positive matrices.     

The physical states of Fermi systems

A classification of all translationally invariant states over the algebra of anticommutation relations which satisfy criteria of finite mean density, finite mean kinetic energy, and finite mean entropy is given. It is demonstrated that these concepts can be discussed in terms of affine, semi-continuous, functionals which respect the barycentric decompositions of invariant states. Many other pertinent results, both local and global, are derived.     

Studies of cyclic acetals. XXII—limitations on the use of alkyl substituents as pseudoisotopic labels: The electron impact mass spectra of alkylated derivatives of 3,7,9- and 4,7,9-trioxabicyclo[4·2·1]nonanes

Low resolution, electron impact mass spectra are tabulated for eleven methylated derivatives of 3,7,9-trioxabicyclo[4·2·1]nonane, 4,7,9-trioxabicyclo[4·2·1]nonane and nine methylated derivatives, and 6-ethyl-3,7,9-trioxabicyclo[4·2·1]nonane. In general, a substantial proportion of the fragmentation subsequent to electron impact can be rationalized according to a few, simple decomposition pathways that are inferred from analysis of mass number shifts caused by changes in substitution; however, major alterations in fragmentation are apparent in a few of these examples, which signals that, for several of the 4,7,9-trioxabicyclo[4·2·1]nonanes, the substituent acts not as an inert label but as a fragmentation-directing group.     

Statistical mechanics of quantum spin systems

The thermodynamic limit of a quantum spin system is considered. It is demonstrated that for a large class of interactions and a wide range of the thermodynamic parameters the equilibrium state of the system is describable by an extremalZ ^v -invariant state (a single phase state) over aC* algebra of local observables. It is further shown that the equilibrium state may be obtained as the solution of a variational problem involving the mean entropy. These results extend results previously obtained for classical spin systems byGallavotti, Miracle-Sole andRuelle.     

A novel closo-type metallaundecaborane, [1,1-(PPh3)2-2,5-(OEt)2-1-RuB10H8], and its relationship to the ‘isocloso’ series of metallaborane clusters

The new ruthenaundecaborane [(PPh₃)₂RuB₁₀H₈ (OEt)₂] may be considered as an eleven-vertex member of a previously unrecognised series of metallaboranes which are formally derived by the single capping of an arachno-type (rather than a nido-type) cluster geometry with a metal centre which can be thought of as contributing four orbitals to the cluster bonding schemes.     

Gas-phase structures of dithietane derivatives, including an electron diffraction study of 1,3-dithietane 1,1,3,3-tetraoxide

The gas electron diffraction structure of 1,3-dithietane 1,1,3,3-tetraoxide has been determined using the SARACEN method to restrain parameters that otherwise could not be refined. Quantum chemical calculations for this species showed that the potential-energy surface was extremely flat, and this was also observed from the diffraction experiments. The difference in goodness of fit for the diffraction experiment between a planar ring and one puckered by up to 9° was very small. Calculations were also performed for a variety of similar species with different numbers of oxygen atoms attached to the sulphur atoms. Topological analysis of the electron density, and electron localisation function studies of the relevant molecules, have given deeper insight into the nature of their bonding, and suggested how spatial localisation of electron pairs may influence the molecular structure.     

Single crystal X-ray structural features of aromatic compounds having a pentafluorosulfuranyl (SF<Subscript>5</Subscript>) functional group

Nine pentafluorosulfuranyl (SF₅)-containing aromatic compounds have been characterized crystallographically. The SF₅ group has an umbrella geometry, and the sulfur atom in the SF₅ group is in an approximately octahedral coordination environment. All S–F bond lengths [1.572(3)–1.618(3) Å] are very similar, and the C–S–F_ax bond angles [178.94(14)–180°] are very close to each other. The angle of two adjacent F_eq is approximately 90°. The intramolecular and intermolecular interactions such as C_aryl–H···F_eq, C_aryl–H···O/N/F/Cl interactions, and π-stacking interactions play a very important role in their three-dimensional packing frameworks.     

Non-hydrolytic sol–gel synthesis of tantalum sulfides

Non-hydrolytic sol–gel synthesis provides a low temperature solution based approach to solid-state materials. In this work, reactions of TaX₅ (X = F, Cl, Br, I) with the thio-ethers di-tert-butylsulfide and hexamethyldisilathiane were carried out in chloroform or acetonitrile. The influence of synthetic parameters such as temperature, reaction time, starting sulfur to tantalum ratio, and solvent volume were explored, and optimized conditions for the preparation of phase pure crystalline TaS₂ were established. Amorphous powders were recovered for most of the samples, but crystalline 1T- and 3R-TaS₂ modifications could be selectively prepared by heat treatments of the as-recovered precursors at 700 and 800 °C, respectively. The crystallite sizes could be adjusted by tuning the starting sulfur to tantalum ratios, and by choice of solvent. For specific conditions, nanocrystalline 1T-TaS₂ was directly recovered from solution. To our knowledge, this is the first time that crystalline TaS₂ was directly obtained from low temperature solution based routes.