Reactions of cyclo-(t-Bu4Sb4) with alkali metals; syntheses and crystal structures of [M(L)n(t-Bu4Sb3)] (M=Na, K; n=1, 2) and [K(L)(t-Bu3Sb2)] (L=(Me2NCH2CH2)2NMe)

Reduction of cyclo-(t-Bu₄Sb₄) (1) with sodium or potassium in boiling tetrahydrofuran leads to the anions [t-Bu₄Sb₃]⁻ and [t-Bu₃Sb₂]⁻. Crystallization with pentamethyldiethylenetriamine (L) gives [M(L)_n(t-Bu₄Sb₃)] (n=1, M=Na (2), K (3); n=2, M=K (4)) and [K(L)(t-Bu₃Sb₂)] (5). Crystal structure analyses reveal coordination of the anionic antimony ligands on the alkali metal ions for 2, 3, and 5. In contrast, no Sb---K interactions were observed in the structure of 4.     

Komplexe mit Antimon‐Liganden: [tBu2(Cl)SbW(CO)5], [tBu2(OH)SbW(CO)5], O[SbPh2W(CO)5]2, E[SbMe2W(CO)5]2 (E = Se,Te), cis‐[(Me2SbSeSbMe2)2Cr(CO)4]

Complexes Containing Antimony Ligands: [^tBu₂(Cl)SbW(CO)₅], [^tBu₂(OH)SbW(CO)₅], O[SbPh₂W(CO)₅]₂, E[SbMe₂W(CO)₅]₂ (E = Se, Te), cis‐[(Me₂SbSeSbMe₂)₂Cr(CO)₄] Syntheses of [^tBu₂(Cl)SbW(CO)₅] ( 1 ), [^tBu₂(OH)SbW(CO)₅] ( 2 ), O[SbPh₂W(CO)₅]₂ ( 3 ), Se[SbMe₂W(CO)₅]₂ ( 4 ), cis‐[(Me₂SbSeSbMe₂)₂Cr(CO)₄] ( 5 ) Te[SbMe₂W(CO)₅]₂ ( 6 ) and crystal structures of 1 – 5 are reported.     

Structural Report for 2,5-Bis(trifluoroacetyl)cyclohexane-1,4-dione and <Emphasis Type="Italic">o</Emphasis>,<Emphasis Type="Italic">o</Emphasis>′-bis(trifluoroacetyl)-<Emphasis Type="Italic">p</Emphasis>-cresol

Abstract  

The crystal structures of 2,5-bis(trifluoroacetyl)cyclohexane-1,4-dione (1) and o,o′-bis(trifluoroacetyl)-p-cresol (2) is reported. The first compound crystallizes in monoclinic space group P2₁/n with a = 6.5040(10), b = 10.1610(10), c = 8.2420(10) ?, β = 91.690(10)° and V = 0.54445(12) nm³. Double enolization (U-structure) with a considerable electron density delocalization in the enolone backbone was established in this case. Phenol 2 crystallizes in triclinic space group P-1 with a = 7.0690(10), b = 9.4890(10), c = 9.8190(10) ?, α = 103.720(10), β = 110.760(10), γ = 102.150(10)° and V = 0.56598(12) nm³. In contrast to CDCl₃ solution, a “bifurcate” structure of 2 with jumping OH proton is quenched: only one of both trifluoroacetyl moieties is bonded by intramolecular hydrogen bond.     

Structural investigations of silicon nanostructures grown by self-organized island formation for photovoltaic applications

The self-organized growth of crystalline silicon nanodots and their structural characteristics are investigated. For the nanodot synthesis, thin amorphous silicon (a-Si) layers with different thicknesses have been deposited onto the ultrathin (2 nm) oxidized (111) surface of Si wafers by electron beam evaporation under ultrahigh vacuum conditions. The solid phase crystallization of the initial layer is induced by a subsequent in situ annealing step at 700 °C, which leads to the dewetting of the initial a-Si layer. This process results in the self-organized formation of highly crystalline Si nanodot islands. Scanning electron microscopy confirms that size, shape, and planar distribution of the nanodots depend on the thickness of the initial a-Si layer. Cross-sectional investigations reveal a single-crystalline structure of the nanodots. This characteristic is observed as long as the thickness of the initial a-Si layer remains under a certain threshold triggering coalescence. The underlying ultra-thin oxide is not structurally affected by the dewetting process. Furthermore, a method for the fabrication of close-packed stacks of nanodots is presented, in which each nanodot is covered by a 2 nm thick SiO₂ shell. The chemical composition of these ensembles exhibits an abrupt Si/SiO₂ interface with a low amount of suboxides. A minority charge carrier lifetime of 18 µs inside of the nanodots is determined.     

Structure Investigations on 4‐Halo‐1,2,3,5‐dithiadiazolyl Radicals XCNSSN• (X = F,Cl, Br): The Shortest Intradimer S···S Distance in Dithiadiazolyl Dimers

Crystals of the 4‐halo‐1,2,3,5‐dithiadiazolyl radicals (X = F, Cl, Br) were obtained by sublimation at 80 °C and 10^?2 Torr, and the structures were determined by X‐ray diffraction. The fluoro derivative crystallizes as a cisoid dimer in the space group P2₁/n, whereas the chloro and bromo derivatives crystallize isomorphous as twisted dimers in the space group C2/c. The chloro and bromo derivatives show the shortest intradimer S···S contacts of all known 1,2,3,5‐dithiadiazolyl dimers. In addition the obtained structure of ClCN₂S₂^? represents the fifth polymorph of ClCN₂S₂^? characterized by X‐ray crystallography. The structures and the packing including secondary interactions are discussed.     

Replacing suffix trees with enhanced suffix arrays

The suffix tree is one of the most important data structures in string processing and comparative genomics. However, the space consumption of the suffix tree is a bottleneck in large scale applications such as genome analysis. In this article, we will overcome this obstacle. We will show how every algorithm that uses a suffix tree as data structure can systematically be replaced with an algorithm that uses an enhanced suffix array and solves the same problem in the same time complexity. The generic name enhanced suffix array stands for data structures consisting of the suffix array and additional tables. Our new algorithms are not only more space efficient than previous ones, but they are also faster and easier to implement.     

NSF3 und NSF2NMe2 als Liganden in der metallorganischen Chemie

Thiazyltrifluoride NSF₃ and Thiazyldifluoridedimethylamide NSF₂NMe₂: Ligands in Organometallic Chemistry From the reaction of [Re(CO)₅SO₂]⁺AsF₆^? ( 1 ) and [CpFe(CO)₂SO₂]⁺AsF₆^? ( 6 ) with NSF₃ ( 2 ) and NSF₂NMe₂ ( 4 ) the complexes [Re(CO)₅NSF₃]⁺AsF₆^? ( 3 ), [Re(CO)₅NSF₂NMe₂]⁺AsF₆^? ( 5 ), [CpFe(CO)₂NSF₃]⁺AsF₆^? ( 7 ), and [CpFe(CO)₂NSF₂NMe₂]⁺AsF₆^? ( 8 ) were obtained. The compounds have been characterised by X-ray crystallography, the ligand properties of 2 and 4 are discussed.