Structure and protonation of some indolizine derivatives studied by ab initio MO calculations

Some gauge invariant atomic orbitals-coupled-perturbed Hartree-Fock (GIAO-CPHF) calculations were performed for seven indolizine derivatives and their monoprotonated forms. Chemical shift, molecular geometry, and charge distribution data are reported for each molecule. The calculations support the results of nuclear magnetic resonance (NMR) spectroscopy measurements showing that protonation occurs preferentially at N1. The good agreement between the calculated and observed ¹³C and ¹⁵N chemical shifts show that such calculations can be used for chemical shift assignment purposes. Cation structures and probable sites for electrophilic reaction or second protonation are also discussed.     

NMR study of some sydnones,isosydnones, and isothiosydnones

Multinuclear¹H,¹³C,¹⁴N,¹⁵N, and¹⁷O NMR data are presented for some sydnones, isosydnones and isothiosydnones. The type of valence tautomerism shown in (Fig. 1) is not observed for the compounds studied. At high pH compounds2 and12 are found to undergo transformations. The more suitable NMR parameters are reported for establishing the structures of mesoionic compounds containing three heteroatoms in the five-membered conjugated ring. Someab initio GIAO calculations on a model structure of sydnones and related compounds have been performed.     

Solid-state Al NMR investigation of thermal decomposition of LiAlH4

Solid-state nuclear magnetic resonance is used to study the thermal decomposition of lithium tetrahydroaluminate into metallic aluminum, hydrogen and trilithium hexahydroaluminate. Aluminum sites in LiAlH₄ and Li₃AlH₆ were characterized using static, magic angle spinning (MAS) and multiple-quantum MAS NMR. By applying the in situ NMR method, it has been demonstrated that melting is not a prerequisite for the decomposition of LiAlH₄. Based on the observed data, a decomposition path has been established that is consistent with the concentrations of observed Al species at various stages of the thermally induced reaction.     

Tuning of particle morphology and pore properties in mesoporous silicas with multiple organic functional groups

A synthetic method has been developed that can control both multifunctionalization and morphology of the mesoporous organic-inorganic hybrid materials by introducing different molar ratios of organoalkoxysilane precursors to a base-catalyzed co-condensation of silicate.     

An improved error bound for a finite element approximation of a model for phase separation of a multi-component alloy

Using the approach of Rulla (1996 SIAM J. Numer. Anal. 33, 68-87)for analysing the time discretization error and assuming moreregularity on the initial data, we improve on the error boundderived by Barrett and Blowey (1996 IMA J. Numer. Anal. 16,257-287) for a fully practical piecewise linear finite elementapproximation with a backward Euler time discretization of amodel for phase separation of a multi-component alloy.     

Die Kristallstruktur von β-RbScO2

The Crystal Structure of β-RbScO₂ Single crystals of β-RbScO₂ have been prepared. β-RbScO₂ crystallizes hexagonal, a = 3.25₁, c = 12.78₆ Å. The structure has been refined by 4-cyclediffractometer data.     

Kristallstruktur und thermisches Verhalten von Tetrakaliumcyclo-tetraphosphat(V)-Dihydrat, (KPO3)4·2H2O

The crystal structure of (KPO₃)₄ · 2H₂O was solved by direct methods andFourier-syntheses (triclinic; P ;a=1 114.9 (2),b=821.9 (2),c=815.7 (3) pm; =88,88 (2), =84.51 (2), =82.70 (2)°;Z=2; 5910 unique reflections;R=0.052). The cyclic anions exhibit point symmetry S₄ with four terminal oxygens in axial and four in equatorial position. Thermal investigations (DTA, TGA, X-Ray-methods) show that the dehydration occurs in two steps. The anhydrous form of (KPO₃)₄ is stable above 230 °C and undergoes a second order phase transition which is complete at 515±5 °C.