The Limited Predictive Power of the Pauling Rules

The Pauling rules have been used for decades to rationalise the crystal structures of ionic compounds. Despite their importance, there has been no statistical assessment of the performances of these five empirical rules so far. Here, we rigorously and automatically test all five Pauling rules for a large data set of around 5000 known oxides. We discuss each Pauling rule separately, stressing their limits and range of application in terms of chemistries and structures. We conclude that only 13 % of the oxides simultaneously satisfy the last four rules, indicating a much lower predictive power than expected.     

The effect of platinum on the SnO<Subscript>2</Subscript> sorption properties

Chemisorption of SO₂ and O₂ at Pt-modified SnO₂ is studied by using the vacuum static method, with simultaneous recording of electrical conductivity, over the 22 to 300°C temperature range. The SnO₂ surface modification results in the increasing of SO₂ adsorption and weakening of the gas-surface bonding. The chemisorption enhances the samples’ electrical conductivity. The surface pretreatment with oxygen leads to the decreasing of the successive SO₂ chemisorption.     

The first steps of the Li‐B‐H cluster formation

We have theoretically investigated the formation of Li:B:H clusters from standard reactants in gas phase. Molecular electronic structure computations as well as Born‐Oppenheimer molecular dynamics have been carried out to investigate the early stages of the formation of Li:B:H clusters. We describe the thermochemical properties of the different possible reactions and the first stable structures that could initiate the growing process. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

The Correlation Between the α-γ Transition of Cast Copolyamide and the Mechanical Properties

In this work,we have examined changes in the spherulite structure of cast nylon 6 due to copolyether as a function, in particular,we focused on revealing to α-γ transition and the effect of α-γ transition on mechanical properties by the methods of X-ray diffraction and of infrared spectroscopy.     

The physics of the born–oppenheimer approximation

A new derivation of the Born–Oppenheimer separation of electronic and nuclear motion is presented. The arguments used differ from those in earlier works in not being specially designed for molecules. Instead they aim at an intuitive understanding of the qualitative behavior of the low energy bound states of any, real or hypothetical, Coulomb interacting system of particles. The virial theorem is the starting point of the discussion. After a brief explanation of how it can be used to understand atomic structure it is applied to molecules. It is found that coordinates of collective and individual motion are natural coordinates for the approximate separation, rather than nuclear and electronic. It is also shown that it is the form of the interaction between the particles that is responsible for the separation; the smallness of m_et/M_Nu is irrelevant.     

The thermodynamic characteristics of vaporization in the NaI-PrI<Subscript>3</Subscript> system

The vaporization of the NaI-PrI₃ quasi-binary system was studied by high-temperature mass spectrometry over the whole concentration range. At 623–994 K, saturated vapor contained not only (NaI) _n and (PrI₃) _n molecules (n = 1, 2) and Na⁺(NaI) _n (n = 0–4) and I^?(PrI₃) _n (n = 1–2) ions but also mixed molecular and ionic associates recorded for the first time (NaPrI₄, Na₂PrI₅, NaPrI ₃ ⁺ , Na₂PrI ₄ ⁺ , Na₃PrI ₅ ⁺ , Na₄PrI ₆ ⁺ , NaPrI ₅ ^? , and NaPr₂I ₈ ^? ). The partial vapor pressures of molecules were calculated, and the equilibrium constants of the dissociation of neutral and charged associates were measured. The enthalpies of molecular and ion-molecular reactions were determined, and the enthalpies of formation of gaseous molecules and ions were obtained.     

The thermodynamic activities of the components of NaI-PrI<Subscript>3</Subscript> system melts

The thermodynamic activities of sodium iodide and praseodymium triiodide in NaI-PrI₃ binary system melts at 900 K were determined by high-temperature mass spectrometry. The activities were used to calculate the excess integral Gibbs energy of melt formation. A negative deviation of the system from the behavior of an ideal melt was observed.     

The Origin of Life—Out of the Blue

Either to sustain autotrophy, or as a prelude to heterotrophy, organic synthesis from an environmentally available C₁ feedstock molecule is crucial to the origin of life. Recent findings augment key literature results and suggest that hydrogen cyanide—“Blausäure”—was that feedstock.     

The Stereochemical Course of the α‐Hydroxyphosphonate–Phosphate Rearrangement

The phosphonate–phosphate rearrangement is an isomerisation of α‐hydroxyphosphonates bearing electron‐withdrawing substituents at the α‐carbon atom. We studied the stereochemical course of this rearrangement with respect to phosphorus. A set of four diastereomeric α‐hydroxyphosphonates was prepared by a Pudovik reaction from two diastereomeric cyclic phosphites. The hydroxyphosphonates were separated and rearranged with Et₃N as base. In analogy to trichlorphon, which was the first reported compound undergoing this rearrangement. All four hydroxyphosphonates could be rearranged to 2,2‐dichlorovinyl phosphates. Single‐crystal X‐ray structure analyses of the α‐hydroxyphosphonates and the corresponding phosphates allowed us to show that the rearrangement proceeds with retention of configuration on the phosphorus atom.     

The antifolate trimetrexate: ­observation of the enzyme‐binding conformation

The crystal structure of the title compound contains four 2,4‐di­amino‐5‐methyl‐6‐[(3,4,5‐tri­methoxy­anilino)­methyl]­quin­az­oline mol­ecules, two di­methyl sulfoxide mol­ecules and three water mol­ecules in the asymmetric unit, i.e. 4C₁₉H₂₃N₅O₃·2C₂H₆OS·3H₂O. All four quinazoline mol­ecules adopt trans,gauche conformations. An extensive hydrogen‐bond network involving N?N base‐pairing interactions, as well as the di­methyl sulfoxide and water mol­ecules, stabilizes the crystal structure.     

The twinned structure of ferricenyl­tri­fluoro­borate

Crystals of the title compound, [Fe(C₅H₅)(C₅H₄BF₃)], are monoclinic and twinned. The twinning initially resulted in a misleading unit‐cell assignment. The formal oxi­dation state of Fe is 3+, and the crystal packing consists of intermolecular C—H...F and π–π interactions.     

The dynamics of the calcium‐induced chain–chain association in the polyuronate systems

The calcium‐induced formation of strong, hydrophilic gels is the important feature of polyuronates, connected with most of their practical applications. The insight into the molecular details of gelling process dynamics is hardly feasible for both experimental and theoretical methods. Here, the application of the transition path sampling method for studying this problem is reported; the focus was on the poly(α‐L ‐guluronate) systems, treated as the representative for all polyuronate‐containing systems. The results allowed for identifying several distinct local minima of the free energy lying on the transition paths and visited by the system during the process of chain–chain association. These minima usually correspond to the intermediate structures in which the water molecules bridge calcium ion and carboxyl groups. This work emphasizes the importance of water and provides more complete understanding of the calcium binding by the polyuronate chains. © 2012 Wiley Periodicals, Inc.     

Ti–Ni–Pd dense membranes—The effect of the gas mixtures on the hydrogen permeation

In this experimental work the influence of co-existing gases on the hydrogen permeation through a Ti–Ni–Pd membrane was studied. It was found that nitrogen, carbon dioxide and helium do not influence the hydrogen permeation through the dense membrane. However, carbon monoxide influences the hydrogen flux at each temperature investigated (400–500 °C). The results show that for low CO concentration (i.e. at H₂ upstream >80%), the hydrogen flux through the membrane decreases faster than linearly, while, at H₂ upstream <80%, the slope is linear but smaller than the theoretical one.     

The intrinsic origin of the grain-boundary resistance in Sr-doped LaGaO<Subscript>3</Subscript>

Abstract  In this paper I summarize our recent investigations (Park and Kim, Phys Chem C 111:14903, 2007; Solid State Ionics 179:1329, 2008) on the origin of the grain-boundary resistance in a doped LaGaO₃, a perovskite-structured solid electrolyte. The partial electronic and ionic resistances of the bulk and the grain boundaries, as well as the total resistance, in 1 mol% Sr-doped LaGaO₃ were measured separately by means of a dc-polarization method and ac-impedance spectroscopy. Both of the partial resistances at the grain boundaries were greater than the bulk counterparts, indicating that the grain boundaries impede the ionic as well as the electronic transport in this material. The transference number of the partial electronic conductivity at the grain boundary was however greater than that in the bulk. This fact strongly suggests that both electronic and ionic charge carriers deplete at the grain boundaries to form the space-charge zones and that the grain-boundary cores in this material are positively charged. In light of the fact that the effective charge of the oxygen vacancy (+2) is greater than that of the electron hole (+1), the oxygen vacancies deplete more sharply in the space-charge zones compared to the electron holes such that the grain boundaries become more mixed conducting relative to the bulk. These observations verify that the electrical conduction across the grain-boundaries in 1 mol% Sr-doped LaGaO₃ is governed by the space charge. Graphical Abstract        

The sequence of equilibrium phase states of the Tb-Mn-O system in the thermal dissociation of the TbMn<Subscript>2</Subscript>O<Subscript>5</Subscript> compound

Phase equilibria in the Tb-Mn-O system during the removal of oxygen from the TbMn₂O₅ compound in stages were studied by the static method on a vacuum circulation unit (973–1173 K) with subsequent X-ray analysis of quenched solid phases. The dissociation of TbMn₂O₅ was found to occur in three stages. The temperature dependences of equilibrium oxygen pressure were determined experimentally for the phase equilibria observed. The standard thermodynamic functions of the dissociation and formation from the elements of TbMn₂O₅ and TbMnO₃ were calculated.     

The dependence of the oxygen-exchange properties of Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> on the method of synthesis

The oxygen-exchange properties of Ce_0.5Zr_0.5O₂ samples prepared by the traditional coprecipitation method with the use of a biotemplate (pine wood sawdust) were studied by the temperature-programmed reduction and oxidation methods. The use of the template and the presence of alkali and alkaline-earth metal cations in it provides a high mobility of oxygen and a high capacity with respect to oxygen in the biomorphic oxide. Impurities cause the segregation of Ce- and Zr-enriched phases under high-temperature treatment conditions, which worsens the redox properties of the biomorphic sample. Nevertheless, the ability of the biomorphic sample to play the role of an “oxygen buffer” remains high compared with the coprecipitated oxide subjected to similar treatments.     

The Enantioselective Synthesis of the ‘Southern Part’ of Soraphen A

Using a series of enantioselective aldol condensations followed by an ester enolate addition, the cyclic hemiacetal 2 was prepared stereospecifically. Hemiacetal 2 represents the synthetically most challenging ‘southern part’ of the antifungal macrolide soraphen A ( 1 ). Spontaneous enolisation of 26 , the C(2) epimer of 2 , revealed that 2 is the most stable diastereoisomer at room temperature.