Hydrogeochemical and isotope study of perched aquifers in the Cuvelai-Etosha Basin,Namibia

A hydrogeochemical and stable isotope study (²H and ¹⁸O) was carried out in the Cuvelai-Etosha Basin in order to characterize available groundwater and to identify possible recharge mechanisms for the perched aquifers. Data were collected during seven field campaigns between 2013 and 2015 from a total of 24 shallow and deep groundwater hand-dug wells. In the investigated groundwaters, hydrogencarbonate is the dominating anion in both well types, whereas cations vary between calcium and magnesium in deep wells, and sodium and potassium in shallow wells. Groundwater chemistry is controlled by dissolution of carbonate minerals, silicate weathering and ion exchange. Stable isotopic composition suggests that deep groundwater is recharged by high-intensity/large rainfall events, whereas the shallow wells can even be recharged by less-intense/small rainfall events. Water in deep wells reflect a mixture of water influenced by evaporation during or before infiltration and water that infiltrated through fast preferential pathways, whereas shallow wells are strongly influenced by evaporation. The findings of this research contribute to improve the understanding of hydrogeochemistry, recharge paths and temporal variations of perched aquifers.     

Cationic Platinum(II) σ‐SiH Complexes in Carbon Dioxide Hydrosilation

The low‐electron‐count cationic platinum complex [Pt(ItBu’)(ItBu)][BAr^F], 1 , interacts with primary and secondary silanes to form the corresponding σ‐SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η¹‐SiH. The reaction of 1 with Et₂SiH₂ leads to the X‐ray structurally characterized 14‐electron Pt^II species [Pt(SiEt₂H)(ItBu)₂][BAr^F], 2 , which is stabilized by an agostic interaction. Complexes 1 , 2 , and the hydride [Pt(H)(ItBu)₂][BAr^F], 3 , catalyze the hydrosilation of CO₂, leading to the exclusive formation of the corresponding silyl formates at room temperature.     

Taming C60 fullerene: tuning intramolecular photoinduced electron transfer process with subphthalocyanines

Two subphthalocyanine–C₆₀ conjugates have been prepared by means of the 1,3-dipolar cycloaddition reaction of (perfluoro) or hexa(pentylsulfonyl) electron deficient subphthalocyanines to C₆₀. Comprehensive assays regarding the electronic features – in the ground and excited state – of the resulting conjugates revealed energy and electron transfer processes upon photoexcitation. Most important is the unambiguous evidence – in terms of time-resolved spectroscopy – of an ultrafast oxidative electron transfer evolving from C₆₀ to the photoexcited subphthalocyanines. This is, to the best of our knowledge, the first case of an intramolecular oxidation of C₆₀ within electron donor–acceptor conjugates by means of only photoexcitation.     

On theT(1) theorem on product domains

The direct proof by R. R. Coifman and Y. Meyer of theT(1) Theorem of G. David and J. L. Journé is based on the following result. LetT be an operator associated to a kernelk(x, y) satisfying

Decarbonylative radical cyclization of alpha-amino selenoesters upon electrophilic alkenes. A general method for the 6-azabicyclo[3.2.1]octane synthesis

alpha-Amino selenoester-tethered electronically poor alkenes on treatment with tributyltin hydride or TTMSS undergo intramolecular radical cyclization to provide 6-azabicyclo[3.2.1]octanes through 1-aminomethyl radical intermediates.     

Ru(eta3-2-C3H4Me)(CO)(dppf)][SbF6]: a mononuclear 16e - ruthenium(II) catalyst for propargylic substitution and isomerization of HC[triple bond]CCPh2(OH)

The 16e(-) derivative [Ru(eta3-2-C3H4Me)(CO)(dppf)][SbF6] catalyzes: (i) the propargylic substitution reaction of 1,1-diphenyl-2-propyn-1-ol with alcohols to produce propargylic ethers, and (ii) the formal isomerization of 1,1-diphenyl-2-propyn-1-ol into 3,3-diphenyl-2-propenal.     

Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder

KCl coated denuders were employed for the measurement of divalent mercury (Hg²⁺) species in the air. Laboratory tests show that gaseous Hg²⁺ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg²⁺ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl₂ reduction-CVAFS determination. Hg²⁺ concentrations of 0.04–0.15 ng m^–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations. Received: 24 September 1996 / Revised: 14 January 1997 / Accepted: 18 January 1997     

Kristall- und Molekülstruktur von Bis[N-(diethylaminothiocarbonyl)-N′-phenylbenzamidinato]nickel(II)

Crystal and Molecular Structure of Bis[N-(diethylaminothiocarbonyl)-N′-phenyl-benz-amidinato]nickel(II) The structure of bis[N-(diethylaminothiocarbonyl)-N′-phenyl-benzamidinato]-nickel(II) has been determined by X-ray structure analysis. The compound crystallizes in orthorhombic space group P2₁2₁2₁ with a = 16.36, b = 16.94, c = 12.96 Å and Z = 4. The solution of the structure was performed by heavy atom technique and gave a final R value of R = 0.055 for 1764 observed reflections. The coordination polyhedron has a tetrahedrally distorted shape. The ligator atoms are arranged in cis position. The chelate rings deviate clearly from planarity. Against the chelate rings the phenyl rings are appreciably twisted. The title compound is compared regarding its structure with the analogous copper chelate.