Segregation into Layers: A General Problem for Structural Instability under Pressure,Exemplified by SnH4

When a molecular compound is thermodynamically unstable (but kinetically persistent) with respect to the elements, structures that contain segregated layers of the elements may be favored at moderate pressures, as a compromise between the potential stability of novel electronic configurations and decomposition into the elements (or other stable compounds). We use stannane, SnH₄, to approach this quite general problem theoretically, since the heat of formation of SnH₄ is so positive. Our ground‐state DFT searches for optimal structures begin with slabs formed from 1–4 layers of tin atoms in the β‐Sn and bcc configurations, and also slabs of molecular hydrogen or hydrogen atoms, preserving the overall SnH₄ stoichiometry. As argued, segregated layers are an important structural feature in the lower‐ and moderate‐pressure regime (0 and 50 GPa). By 140 GPa (V/V₀=0.21) the coordination of tin and hydrogen increases and the slabs disappear, as judged from the optimized structures.     

Investigation into factors influencing stereoselectivity in the reactions of heterocycles with donor-acceptor-substituted rhodium carbenoids

Rhodium-catalyzed decomposition of aryldiazoacetates in the presence of pyrroles or furans results in mono- or biscyclopropanation of the heterocycle, but with opposite enantioinduction. In the absence of sterically encumbering groups, the cyclopropanation of furan occurs with initial bond formation at the 2-position. If this pathway is sterically blocked, cyclopropanation can occur with initial bond formation at the 3-position of the furan ring; in this case, the cyclopropanation reaction takes place on the opposite face of the heterocycle, and the opposite enantioinduction is observed. Upon extension of this methodology to benzofurans, a highly enantioselective monocyclopropanation reaction occurs to furnish a product derived from initial bond formation at the 2-position of the benzofuran. When this reaction pathway is inhibited by sterically encumbering substituents on the benzofuran, no cyclopropanation of the furan ring is observed, and instead, double cyclopropanation of the benzene ring occurs. Double cyclopropanation of the benzene ring was also observed in reactions with indoles.     

Disclosing the thermal behaviour,electrochemical and optical properties of synthetic Fe3(PO4)2(OH)2 materials

Journal of Thermal Analysis and Calorimetry - In this research paper, the thermal behaviour of the mixed valence iron oxides Fe3(PO4)2(OH)2 is presented in both air and vacuum atmosphere. The...     

Quotients of internally quasicontinuous functions<Superscript>*</Superscript>

In this paper, we characterize the family of quotients of internally quasicontinuous functions. Moreover, we study cardinal invariants related to quotients in the case of internally quasicontinuous functions and the complement of this family.