Arndt Simon

Eine Methode zur Untersuchung extrem luftempfindlicher Substanzen mit der Guinier-Methode

Powder patterns of an extremely air sensitive substance can be prepared in a modified Guinier type camera, the substance being introduced in a closed glass capillary. The capillary is situated on the focusing circle of the camera parallel to the focal line of the monochromator and is rotated during exposure to X-rays. Line broadening and line shifts due to specimen geometry are discussed.

Synthesis of a Möbius aromatic hydrocarbon.

The defining feature of aromatic hydrocarbon compounds is a cyclic molecular structure stabilized by the delocalization of π electrons that, according to the Hückel rule, need to total 4n + 2 (n = 1,2,…); cyclic compounds with 4n π electrons are antiaromatic and unstable. But in 1964, Heilbronner predicted on purely theoretical grounds that cyclic molecules with the topology of a Möbius band—a ring constructed by joining the ends of a rectangular strip after having given one end half a twist—should be aromatic if they contain 4n, rather than 4n + 2, π electrons. The prediction stimulated attempts to synthesize Möbius aromatic hydrocarbons, but twisted cyclic molecules are destabilized by large ring strains, with the twist also suppressing overlap of the p orbitals involved in electron delocalization and stabilization. In larger cyclic molecules, ring strain is less pronounced but the structures are very flexible and flip back to the less-strained Hückel topology. Although transition-state species, an unstable intermediate and a non-conjugated cyclic molecule, all with a Möbius topology, have been documented, a stable aromatic Möbius system has not yet been realized. Here we report that combining a ‘normal’ aromatic structure (with p orbitals orthogonal to the ring plane) and a ‘belt-like’ aromatic structure (with p orbitals within the ring plane) yields a Möbius compound stabilized by its extended π system.

Untersuchungen mit einer neuen Röntgenkamera: Phasenumwandlungen in festem Bromwasserstoff

For X-ray investigations of structural changes in solids (including extremely air sensitive substances, frozen liquids or condensed gases) as a function of temperature a moving film camera has been developed on the basis of a modified Guinier technique. Temperatures can be maintained to within ±0.05°C from −1190° to 400 °C. The phase transitions occurring in solid hydrogen bromide have been investigated with the new camera. HBr is shown to crystallize in two orthorhombic low temperature and two face-centered cubic high temperature phases.

β-Nb3Br8 und β-Nb3J8 darstellung, eigenschaften und struktur☆

Zusammenfassung Bei Temperaturen oberhalb 500°C reagiert metallisches Niob mit der stochio-metrischen Menge NbBr5 unter Bildung von β-Nb3Br8. Unter analogen Bedingungen entsteht β-Nb3J8. Die durch chemischen Transport bei 800 760 °C gereinigten und kristallisierten Verbindungen bilden schwarze sechsseitige Blattchen. Die Verbindungen β-Nb3Br8 und β-Nb3J8 sind isotyp. Ihre Struktur wurde aus Einkristalldaten bestimmt. Sie ist nicht mit der des Nb3Cl8 identisch. Bromid und Jodid kristallisieren hexagonal-rhomboedrisch in der Raumgruppe D53d-R−3m: ah = 7.080, c h = 38.975 A , c a = 5.505 fur das Bromid, ah = 7.600, c h = 41.715 A , c a = 5.489 fur das Jodid. Die Nb3X8-Strukturen mit X = Cl, Br, J enthalten trigonale Nb3-Gruppen mit verkurzten Nb-Nb-Abstanden (Me-Me-Bindung). Die Grosse dieser Abstande (2.81; 2.88; 3.00 A) wie auch der Betrag der Verkurzung hangt von der jeweiligen Anionengrosse ab.

Empty, filled, and condensed metal clusters*

Aspects of structure, bonding, physical, and chemical properties are discussed for (a) compounds containing discrete empty clusters and clusters with interstitial H atoms: Nb 6 I 11 , HNb 6 I 11 , HCsNb 6 I 11 , (b) metal-rich lanthanide halides and halide carbides,-nitrides and -hydrides, focusing on the role of interstitial atoms: Gd 2 Br 2 C 2 , Gd 2 Br 2 C, Gd 3 Cl 3 C, Gd 10 Cl 18 C 4 , Gd 10 Il 17 C 4 , Gd 10 I 16 C 4 , GD 2 Cl 3 N, Gd X H n ( X =Cl, Br, I; 0.6 n 2 ; (c) metal-rich oxides of the alkali metals rubidium and cesium. Chemical bonding in the suboxide clusters Rb 9 O 2 and Cs 11 O 3 is discussed along the lines valid for (a) and (b) and covers recently described “hypervalent” species as Li 6 C, Li 4 O, etc.

Group 1 and 2 suboxides and subnitrides — Metals with atomic size holes and tunnels

Abstract Alkali metal suboxides and the closely related subnitrides of alkaline earth metals represent a unique class of compounds. Their structures are composed of discrete clusters (Rb9O2, Cs11O3, Ba6N,Ba14CaN6) which form stoichiometric compounds with alkali metals like Rb9O2Rb3 = Rb6O, Cs11O3Cs10 = Cs7O, Cs11O3Rb7, Na16Ba6N, or Na22Ba14CaN6. In the structures of NaBa3N and Na5Ba3N chains of condensed clusters are embedded in alkali metal. All compounds are metalic. Due to the cumulation of negative charges by O2− and N3− ions inside the clusters the conduction electrons reside in the space between the clusters. Electronic confinement in space leads to interesting physical properties.

Structures of nanometre-size crystals determined from selected-area electron diffraction data

The structure of a new modification of Ti2Se, the beta-phase, and several related inorganic crystal structures containing elements with atomic numbers between 16 and 40 have been solved by quasi-automatic direct methods from single-crystal electron diffraction patterns of nanometre-size crystals, using the kinematical approximation. The crystals were several thousand times smaller than the minimum size required for single-crystal X-ray diffraction. Atomic coordinates were found with an average accuracy of 0.2 A or better. Experimental data were obtained by standardized techniques for recording and quantifying electron diffraction patterns. The SIR97 program for solving crystal structures from three-dimensional X-ray diffraction data by direct methods was modified to work also with two-dimensional electron diffraction data.

Raman scattering in the high Tc superconductors MBa2Cu3O7-x

Abstract We report Raman scattering measurements of MBa 2 Cu 3 O 7 ( M = Y , Sm , Eu ) polycrystalline superconductors in the region of Cu-O stretching vibrations. Four peaks are seen. On the basis of the factor group analysis given here they are assigned to two Raman allowed and two ir-allowed LO modes. The latter are probably induced by disorder (e.g. O-vacancies).

CRYSTAL AND ELECTRONIC STRUCTURES OF SCAUGE, CEAUGE, AND LUAUGE: A TRANSITION FROM TWO- TO THREE-DIMENSIONAL AUGE POLYANIONS

Abstract New germanides ScAuGe, TmAuGe, and LuAuGe were prepared by melting mixtures of the elements in an arc furnace and subsequent annealing at 1070 K. The structures of ScAuGe and LuAuGe were refined from X-ray single-crystal diffractometer data: P6 3 mc (No. 186), Z = 2, a = 430.82(5) pm, c = 684.58(10) pm, V = 0.1100(1) nm 3 , wR 2 = 0.0688, 275 F o 2 values, ten variables for ScAuGe; P6 3 mc (No. 186), Z = 2, a = 437.75(4) pm, c = 711.38(6) pm, V = 0.1181(1) nm 3 , wR 2 = 0.0340, 355 F o 2 values, 11 variables, and a batch scale factor of 0.47(3) for LuAuGe. The lattice constants for TmAuGe are a = 439.08(4) pm, c = 716.59(7) pm, and V = 0.1196(1) nm 3 . The crystal structures of these germanides are derived from the CaIn 2 -type structure by an ordered arrangement of Au and Ge atoms at the indium position. The crystal chemistry of ScAuGe and LuAuGe is compared with that of the recently reported cerium compound. Although the AuGe intralayer distances at 259.6 pm in CeAuGe, 260.5 pm in LuAuGe, and 257.6 pm in ScAuGe are similar, the AuGe interlayer distances at 364.2 pm in CeAuGe, 292.7 pm in LuAuGe, and 275.2 pm in ScAuGe differ significantly. Thus, the [AuGe] polyanions are changed from two-dimensional layers in CeAuGe to a three-dimensional network of distorted tetrahedra in ScAuGe. Chemical bonding within the structures was investigated by TB-LMTO-ASA band structure calculations. The energy bands, the densities of states and the valence charge densities are discussed. Bonding is characterized by intralayer bonds between Au and Ge within the puckered AuGe hexagons. In addition, in the case of ScAuGe strong bonds are directed from the Au atoms of one layer to the Ge atoms of the neighbouring layer. Weaker interlayer bonding is observed in LuAuGe and no interlayer interaction in CeAuGe, as already indicated by the pronounced increase of the interlayer distances.

An inorganic complex of silver (III): K5Ag(IO5OH)2 · 8H2O

Abstract The chemical preparation and crystal structure of the trivalent silver salt K5Ag(IO5OH)2 · 8H2O are described (monoclinic, space group Cc; a = 21.79(4), b = 6.320(3), c = 15.16(3) A, β = 96.14(4); four formula units per unit cell). The structure is refined until R = 0.033 for 2718 reflections. Isolated Ag(IO5OH)5−2 units occur, which contain trivalent silver ions surrounded by four oxygen atoms from two IO6 octahedra in rectangular configuration. The differences in the IO bond lengths, as well as the small deviations of the crystal structure from centrosymmetry, are in agreement with an antiperiplanar position of the OH groups in both octahedra.