New global constraints on electronic energy hypersurfaces

Improved global energy bounds — valid for the entire electronic energy hypersurfaces of a variety of polyatomic molecular systems — are proposed. The new constraints are applicable to a larger class of molecules and are tighter than the constraints proposed earlier. The new global bounds are easily applicable using readily available energy values of atoms and atom-ions. The actual evaluation of these constraints typically involves only “back-of-the-envelope” calculations, providing both upper and lower bounds for a complete energy hypersurface, even for very large molecules. Such global energy bounds are of some importance in theoretical studies of chemical reactions and conformational changes. The proposed bounds are likely to find some practical applications in computer-based quantum-chemical synthesis planning, using multidimensional potential surfaces.     

Application of total selective solvent extraction of germanium,phosphorus and silicon to the simultaneous determination of arsenic,germanium, phosphorus and silicon

A simple rapid, accurate, and reliable method of simultaneous determination of arsenic, germanium, phosphorus, and silicon is reported. The method involves first, the determination of germanium as its phenlfluorone complex and its selective extraction with isoamyl alcohol. Phosphorus is next determined as its heteropoly blue after selective extraction of phosphomolybdic acid by isobutyl acetate at pH 1.0-0.8 and its direct reduction in this solvent. Silicon is then determined after its extraction as silicomolybdic acid by isooctyl alcohol at pH < 0.4 and direct reduction in the solvent phase. Finally, arsenic is determined in the remaining aqueous phase after reduction to its heteropoly blue.     

Dérivés lithiés et cuprolithiés du décachlorobiphényle

Exchange between decachlorobiphenyl and n-butyllithium leads to lithium derivatives. Hydrolysis affords octa- and nonachlorobiphenyls. Reaction with CuI yields aryllithium cuprates which react with acid chlorides to give the corresponding ketones.     

Protonic conduction in NH4H2PO4

The conductivity of ammonium dihydrogen phosphate has been measured as a function of temperature and dopant concentration. A previously disputed break in the log conductivity vs reciprocal temperature plots has been observed. The activation energy is in agreement with previous work on NH₄H₂PO₄. In addition, the conductivity vs concentration of NH₄HSO₄ plot is linear, permitting the calculation of the L defect mobility and indicating that the proton is the conducting species. It is concluded that the mechanism of conduction is the same as previously proposed for KH₂PO₄ and KH₂AsO₄.     

Interactions magnétiques dans des groupements binucléaires du Ruthénium +V

The cationic ordering in the $\text{Ba}\text{M}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Ru}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3\text{(M =}\text{Mg, Ca, Cd, Sr}\text{)}$ oxides which crystallize with the 6H structure gives rise to Ru⁵⁺Ru⁵⁺ pairs in (Ru₂O₉) clusters. The magnetic properties have been analyzed on the basis of the Heisenberg-Dirac-Van Vleck model: The d electrons are localized on each Ru⁵⁺ ion and interact strongly through antiferromagnetic exchange. The susceptibility curves agree with the H.D.V.V. model. The values of the exchange integrals have been determined by fitting the experimental values.     

EMF-measurements with galvanic bromine cells in the systems RBr/MBr2 (M=Sr,Ba)

The systems RbBr/SrBr₂ and RbBr/BaBr₂ were reinvestigated by DTA and X-ray-crystallography. Additionally to the known compounds RbSrBr₃, RbSr₂Br₅ and RbBa₂Br₅, the phases Rb_2.23Sr_0.885Br₄ and Rb_2.13 Ba_0.935Br₄ were found, which are structural related to the Th₃ P₄ — type. By EMF-measurements the thermodynamic functions G, H and S were determined for all compounds.

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Zusammenfassung Die Systeme RbBr/SrBr₂ und RbBr/BaBr₂ wurden mittels DTA und Röntgenaufnahmen an Kristallpulvern neu untersucht. Zusätzlich zu den schon bekannten Verbindungen RbSrBr₃, RbSr₂Br₅ und RbBa₂Br₅ wurden die Phasen Rb_2,23Sr_0,885Br₄ und Rb_2,13Ba_0,935Br₄, die sich strukturell vom Th₃P₄-Typ ableiten lassen, neu gefunden. Für alle Verbindungen wurden durch EMK-Messungen in galvanischen Feststoffzellen die thermodynamischen Funktionen G, H und S bestimmt.

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RbBr/SrBr RbBBr/BaBr₂. RbSrBr₃, Rbsr₂Br₅ RbBa₂Br₅, Rb_2,23Sr_0,885Br₄ Rb_2,I3Ba_0,935Br₄, Th₃P₄. $ G, H S.

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This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.     

Structures lamellaires: Syntaxie,polytypie et non-stoechiométrie

The paper recalls elementary principles useful for the understanding of some types of nonstoichiometry in the solid state. The structures of layered compounds are mostly characterized by the existence of layered “molecular” entities exhibiting a simple type of bonding; in between are inserted, depending on the case, cations, anions, structural frameworks, or molecules. The layers have a quaternary or a ternary symmetry; in the last case the structures can be polytypic. The phenomenon of syntaxy occurs between polymorphs or between species with different chemical compositions but with structural affinities (identical atomic planes). In some cases an ordered syntaxy between structural blocks yields the chemical compositions of the multiple phases observed for some nonstoichiometric systems, for instance rare earth ones. Ordered syntaxy and polytypism, which can occur simultaneously, give a regular repetition of structural or chemical elements over very long crystalline distances. Those phenomena of order in solids, as yet unexplained, recall ordering phenomena observed in the scope of biological chemistry.     

Confirmation of the "long-lived" tetra-nitrogen (N4) molecule using neutralization-reionization mass spectrometry and ab initio calculations

Tetra-nitrogen (N(4)), which has been the subject of recent controversy [Cacace, d. Petris, and Troiani, Science 295, 480 (2002); Cacace, Chem. Eur. J. 8, 3839 (2002); Nguyen et al., J. Phys. Chem. A 107, 5452 (2003); Nguyen, Coord. Chem. Rev. 244, 93 (2003)] as well as of great theoretical interest, has been prepared from the N(4) (+) cation and then detected as a reionized gaseous metastable molecule with a lifetime exceeding 0.8 micros in experiments based on neutralization-reionization mass spectrometry. Moreover, we have used the nature of the charge-transfer reaction which occurs between a beam of fast N(4) (+) ions (8 keV translational energy) and various stationary gas targets to identify the vertical neutralization energy of the N(4) (+) ion. The measured value, 10.3+/-0.5, most closely matches that of the lowest energy azidonitrene (4)N(4) (+)C(s)((4)A(')) ion, resulting in the formation of the neutral bound azidonitrene (3)N(4)C(s)((3)A(")). Neutralization of the global minimum (2)N(4) (+)D( infinity h)((2)Sigma(u) (+)) ion leads to a structure 166 kJ mol(-1) above the dissociation products [N(2)((1)Sigma(g) (+))+N(2)((1)Sigma(g) (+))]; moreover, it was not possible to find a minimum on the (1)N(4) neutral potential energy surface for a covalently bonded structure. Ab initio calculations at the G3, QCISD/6-31G(d), and MP2/AUG-cc-pVTZ levels of theory have been used to determine geometries and both vertical neutralization energies of ions (doublet and quartet) and ionization energies of neutrals (singlet and triplet). In addition, we have also described in detail the EI ion source for the Ottawa VG ZAB mass spectrometer [Holmes and Mayer, J. Phys. Chem. A 99, 1366 (1995)] which was modified for high-pressure use, i.e., for the production of dimer and higher number cluster ions.     

Electrophilic lactonization as a tool in acyclic stereocontrol. Synthesis of serricornin

Several electrophilic lactonization procedures have been explored as a means of functionalizing olefinic carboxylic acids with relative asymmetric induction, Iodolactonization of δ,? -unsaturated acids under conditions of thermodynamic control exhibits good 1,2- and 1,3-, but not 1,4-induction in the formation of δ-lactones. Mercurilactonization proceeds with good stereocontrol in the formation of both γ- and δ-lactones (1,2-induction), but suffers from the difficulty of elimination during reductive demercuration; phenylselenolactonization with N-(phenylseleno)phthalimide is apparently kinetically controlled, affording high induction with 10, a strongly sterically biased substrate leading to a δ-lactone, but not with 16, which leads to a γ-lactone. In contrast, hydroxymethyllactonization proceeds with good stereocontrol in the case of 26, the ester of 10, but not with the analogous ester of 16. The lactones resulting from cyclization of 10 and 13 were converted in stereospecific fashion into each of the stereoisomers of(±)-serricornin.