Nickel-catalyzed cross-couplings of organosilicon reagents with unactivated secondary alkyl bromides

A metal-catalyzed cross-coupling of organosilicon compounds with alkyl halides has been developed. Noteworthy attributes of the method are its scope (secondary electrophiles), its high functional-group compatibility, and the air stability of the catalyst components.     

Templated synthesis of the novel layered silver-antimony sulfides [H3NCH2CH2NH2][Ag2SbS3 and [H3NCH2CH2NH2]2[Ag5Sb3S8

Two new silver-antimony sulfides, [C(2)H(9)N(2)][Ag(2)SbS(3)] (1) and [C(2)H(9)N(2)](2)[Ag(5)Sb(3)S(8)] (2), have been prepared solvothermally in the presence of ethylenediamine and characterized by single-crystal X-ray diffraction, thermogravimetry, and elemental analysis. Compound 1 crystallizes in the space group Pn (a = 6.1781(1) A, b =11.9491(3) A, c = 6.9239(2) A, beta =111.164(1) degrees ) and 2 in the space group Pm (a = 6.2215(2) A, b = 15.7707(7) A, c = 11.6478(5) A, beta = 92.645(2) degrees ). The structure of 1 consists of chains of fused five-membered Ag(2)SbS(2) rings linked to form layers, between which the template molecules reside. Compound 2 contains honeycomb-like sheets of fused silver-antimony-sulfide six-membered rings linked to form double layers. The idealized structure can be considered to be an ordered defect derivative of that of lithium bismuthide, Li(3)Bi, and represents a new solid-state structure type.     

The Balian-Low theorem and regularity of Gabor systems

For any positive real numbers A, B, and d satisfying the conditions , d>2, we construct a Gabor orthonormal basis for L²(ℝ), such that the generating function g∈L²(ℝ) satisfies the condition:∫_ℝ|g(x)|²(1+|x| ^A )/log ^d (2+|x|)dx < ∞ and .     

Lifetime of the 6793-keV state in 15O

The energy derived from the CN cycle at low stellar temperatures is regulated by the 14N(p,gamma)15O reaction. A previous direct measurement of this reaction has been interpreted as showing evidence for a subthreshold resonance which makes a major contribution to the reaction rate at low temperatures. This resonance, at E(c.m.) = -504 keV would correspond to the known Ex = 6793-keV state in 15O. We have measured a mean lifetime of 1.60(+0.75)(-0.72) fs (90% C.L.) for this state using the Doppler-shift attenuation method. This lifetime is a factor of 15 longer than that inferred from the (p,gamma) data and implies that the contribution of the subthreshold resonance is negligible.     

Measurement of excitation functions in the reactions 197Au(11C, xn)208-xAt using a radioactive 11C beam

A light-element radioactive ion-beam capability has been developed at the LBNL 88-Inch Cyclotron. The system is based on the coupled-cyclotrons method and utilizes short-lived species, e.g., 11C, 14O, 13N produced by (p,n) and (p,alpha) reactions at the LBNL Biomedical Isotope Facility Cyclotron. In a first experiment, 197Au(11C,xn)208-xAt excitation functions have been measured for energies ranging from the Coulomb barrier up to 110 MeV using a beam of 11C with intensities up to (1-2)x10(8) ions/sec on target. The results of this experiment are compared to measurements of 197Au(12C, xn)209-xAt excitation functions.     

A high temperature diffraction-resistance study of chalcopyrite, CuFeS2

The electrical, magnetic and structural properties of synthetic chalcopyrite, CuFeS₂, have been studied up to 873 K using DC resistance measurements performed in-situ during neutron powder diffraction experiments. Under ambient conditions the material adopts the accepted structural model for CuFeS₂ in the space group I4?2d, with the magnetic moment of the Fe³⁺ cations aligned along [001]. The electrical resistivity is around 0.3 Ω cm under ambient conditions, consistent with semiconductor character, and decreases slightly with increase in temperature until a more abrupt fall occurs in the region 750-800 K. This abrupt change in resistivity is accompanied by a structural transition to a cubic zinc blende structured phase (space group F4?3m) in which Cu⁺ and Fe³⁺ cations are disordered over the same tetrahedral crystallographic sites and by a simultaneous loss of long-range magnetic order. The implications of these results are discussed in the context of previous studies of the chalcopyrite system.