Intrachain energy transfer in silylene-spaced alternating donor-acceptor divinylarene copolymers

Silylene-spaced donor-acceptor divinylarene copolymers are synthesized by hydrosilylation of bisalkynes 7 with bisvinylsilanes 3; efficient intrachain energy transfer between donor-acceptor chromophores is observed.     

The radiation hardness property of dry oxide grown by postoxidation cooling in oxygen ambient

The radiation behavior of silicon oxides prepared under various postoxidation conditions is studied by⁶⁰CO irradiation with a total dose of 10⁶ rad. Before irradiation, it was shown that the sample obtained by postoxidation cooling in N₂+O₂ exhibited more positive initial oxide charges and larger negative charge-temperature instability than that obtained by postoxidation annealing in N₂. But after considering the initial oxide field effect on the irradiation result, the former one is less sensitive to irradiation than the latter one. Surprisingly, this hardness ability is significantly enhanced when the orientation of silicon substrate is gradually tilted from [100] to [O11]. Possible explanations are given for these observations. It is supposed that the postoxidation cooling in N₂+O₂ provides a possible way for the oxide to become more radiation hard.     

Low-temperature crystal growth of Cs2LiLuCl6-II and Cs2KScCl6 under reducing conditions and their structural refinement

Cs₂LiLuCl₆ (form II, metastable at room temperature) and Cs₂KScCl₆ were obtained as single crystals from reaction of CsLu₂Cl₇: Li = 1:1 and Cs₃Sc₂Cl₉: K = 1:2 in arc-welded tantalum tubes at 500°C. They crystallize with the cubic face-centered K₂NaAlF₆-type structure (elpasolite, Fm3m, Z = 4) with a = 1040.9 pm, x(Cl) = 0.2483(4) [Cs₂LiLuCl₆-II] and a = 1087.3(3) pm, x(Cl) = 0.2263(6) [Cs₂KScCl₆].     

1,2-Eliminations in a novel reductive coupling of nitroarenes to give azoxy arenes by sodium bis(trimethylsilyl)amide

[reaction: see text]. Symmetric azoxy arenes were successfully prepared in one step from 2 equiv of the corresponding nitroarenes by use of sodium bis(trimethylsilyl)amide as the deoxygenating agents in THF at 150 degrees C in a sealed tube.     

Interaction between 3-(p-tolylamino)-1,5-azulenequinone and the deoxyguanosine residue in various oligonucleotides upon photolysis.

Eight single-stranded oligodeoxyribonucleotides 32P-labeled at the 5'-end were synthesized; they were annealed with the complementary oligodeoxyribonucleotides to form the corresponding double-stranded helices. These duplexes possessed standard Watson-Crick base pairs, locally perturbed sites of a base mismatch, or a bulge. Further, 5'-32P-labeled oligodeoxyribonucleotides with a hairpin loop were also synthesized. Cleavage of these single- and double-stranded oligodexyribonucleotides selectively at the deoxyguanosine residue was accomplished by use of 3-(p-tolylamino)-1,5-azulenequinone 1 upon irradiation with 350 nm UV light. The single strands were cleaved more efficiently than the double-helices. For the helices containing a deoxyguanosine residue at a bulge, at a hairpin loop or toward the end, the cleaving efficiency was increased. Computation results indicate that two possibilities exist for agent 1 to form two "Watson-Crick type" hydrogen bonds with guanine in single-stranded oligodeoxyribonucleotides; yet, only one possibility exists in duplexes.     

Photoelectron spectroscopy of silver clusters

A comparison of x-ray photoemission from Ag clusters deposited on polygraphite and highly oriented pyrolitic graphite shows the influence of the support both on the valence band and on the core 3d level of the metal. Positive shifts have been obtained with respect to the bulk for the Fermi edge and the 3d peaks depending on the number of silver atoms deposited on the substrates. When the deposition is very small (cluster regime) the positive shifts of the binding energies are quite different for different substrates and cannot have a common origin. In contrast with recent work, we show that several effects contribute to these shifts: initial state effects like charge redistribution as well as final state effects like the hole-electron interaction.     

β-BaV2(P2O7)2: A New Polymorph of Barium Vanadium (III) Pyrophosphate Characterized by Intersecting Tunnels

Investigation into the synthesis of reduced vanadium phosphate has led to the formation of a new form of the barium vanadium (III) pyrophosphate compound β-BaV₂(P₂O₇)₂. It is a polymorph of the previously known BaV₂(P₂O₇)₂, which is now labeled as the α-phase. The title compound crystallizes in the P-1 (No. 2) space group with a = 6.269(1) Å, b = 7.864(3) Å, c = 6.1592(9) Å, α = 101.34(2)°, β = 105.84(1)°, and γ = 96.51(2)°. The structure consists of corner-shared VO₆ octahedra and PO₄ tetrahedra that are connected in V-O-P-O-V and V-O-P-O-P-O-V bonding arrangements. This interesting three-dimensional framework is characterized by seven types of intersecting tunnels, three of which are occupied by the barium cation, while the others are empty. It is important to know that one of the empty tunnels has a relatively large window with a minimum diagonal distance of 4.41 Å, which facilitates a possible framework for a lithium ion insertion reaction. The barium atom has a 10-coordination sphere, BaO₁₀, in which the oxygen atoms can be viewed as forming two intersecting pseudohexagonal planes. β-BaV₂(P₂O₇)₂ appears to form at a relatively higher temperature than its polymorph, α-BaV₂(P₂O₇)₂. A detailed structural analysis and structural comparison with the α-phase, as well as a brief comparison with SrV₂(P₂O₇)₂, are presented.     

Thermal- and photo-induced transformations of N-aryl-N-nitrosohydroxylamine ammonium salts to azoxy compounds

Heating of an ethanolic solution containing N-aryl-N-nitrosohydroxylamine ammonium salts at 78 °C produced the desired azoxy compounds in 80–93% yields. Furthermore, irradiation with UV light (λ≥300 nm) of ethanolic solutions of those ammonium salts at room temperature also provided the desired azoxy compounds in 51–72% yields.