Tetragonal low-temperature structure of LiAl

The cubic face-centered structure of LiAl (, at ) transforms into a tetragonal body-centered structure (I4₁/amd, , at ). This first-order phase transition at about during heating is probably the reason for the so-called “ anomalies” in some physical properties like specific heat, electrical resistivity and nuclear-spin lattice relaxation. This transition seems to be correlated with the composition Li:Al of the alloy and the amount of Li vacancies.     

Binucleare Nickel(0)-Komplexe mit „Schlangenliganden”︁ vom 1-Azadientyp: Modellsysteme der oxidativen Kopplung von 1-Azadienen und 1,3-Dienen am Nickel(0)

Binuclear Nickel(0) Complexes with “Snake Ligands” of 1-Azadiene Type: Model Systems of the Oxidative Coupling of 1-Azadienes and 1.3-Dienes at Nickel(0) Synthesis, properties, and reactions of dimeric nickel(0) complexes with special 1-azadiene typ ligands (“snake ligands”) are described. The X-ray analysis of a typical compound (Bis-(bis-cinnamaldehyde-N,N'-propylendiimine)-dinickel(0)) shows that both central atoms have the coordination number 3. The four 1-azadiene groups are coordinated in a different way: unidendate coordination by N-Ni(1) bond and bidendate coordination by N-Ni(1) and olefine-Ni(2) bond. The compound is a good model system for the oxidative coupling reaction of 1-azadienes with 1.3-dienes at 2 nickel(0) centres. IR and electronic spectra show other complexes with this type of ligands to have an analogous coordination sphere.     

Pentadienyls vs cyclopentadienyls and reversal of metal-ligand bonding affinity with metal oxidation state: synthesis, molecular structures, and electronic structures of high-valent zirconium pentadienyl complexes

Molecules of the form Cp(6,6-dmch)ZrX(2) (Cp = eta(5)-cyclopentadienyl, X = Cl, Br, I; 6,6-dmch = eta(5)-6,6-dimethylcyclohexadienyl) have been synthesized, and the molecular and electronic structures have been investigated. These molecules allow direct comparison of the bonding and properties of pentadienyl and cyclopentadienyl ligands in the same high-oxidation-state metal complexes. Unlike the well-known Cp(2)ZrX(2) analogues, these Cp(6,6-dmch)ZrX(2) molecules are intensely colored, indicating significantly different relative energies of the frontier orbitals. Also unusual, the average Zr-C distances to the 6,6-dmch pentadienyl ligand are about 0.1 A longer than the average Zr-C distances to the cyclopentadienyl ligand for these Zr(IV) complexes, opposite of what is observed for the Zr(II) complex Cp(2,6,6-tmch)Zr(PMe(3))(2) (tmch = eta(5)-2,6,6-trimethylcyclohexadienyl), reflecting a dramatic reversal in the favorability of the bonding depending on the metal oxidation state. The experimental and computational results indicate that the color of the Cp(6,6-dmch)ZrX(2) complexes is due to a 6,6-dmch ligand-to-metal charge-transfer band. Compared to the Cp(2)ZrX(2) analogues, the Cp(6,6-dmch)ZrX(2) molecules have a considerably less stable HOMO that is pentadienyl-based and an essentially unchanged metal-based LUMO. Also, the lowest unoccupied orbital of pentadienyl is stabilized relative to cyclopentadienyl and becomes a better potential delta electron acceptor, thus contributing to the differences in structure and reactivity of the low-valent and high-valent metal complexes.     

pH sensitivity of Si--C linked organic monolayers on crystalline silicon surfaces.

The electrochemical behavior of Si--C linked organic monolayers is studied in electrolyte-insulator-Si devices, under conditions normally encountered in potentiometric biosensors, to gain fundamental knowledge on the behavior of such Si electrodes under practical conditions. This is done via titration experiments, Mott-Schottky data analysis, and data fitting using a site-binding model. The results are compared with those of native SiO(2) layers and native SiO(2) layers modified with hexamethyldisilazane. All samples display pH sensitivity. The number of Si--OH groups on the alkylated samples is calculated to be less than 0.7 % of that of a pure SiO(2) insulator, which still causes a pH sensitivity of approximately 25 mV per pH unit in the pH range: 4-7. The alkylated samples hardly suffer from response changes during up- and down-going titrations, which indicates that very little oxide is additionally formed during the measurements. The pK(a) values of all samples with monolayers (4.0-4.4) are lower than that of native SiO(2) (6.0). The long-term drift (of approximately 1 mV h(-1)) is moderate. The results indicate that biosensors composed of alkylated Si substrates are feasible if a cross-sensitivity towards pH in the sensor signal is taken into account.     

Beiträge zur Chemie der Silicium—Stickstoff-Verbindungen, 21. Mitt.

Zusammenfassung Durch Umsetzung von Disilbercyanamid mit Organyl- und Alkoxy-halogensilanen wurden 9 bisher unbekannte zweifach silylsubstituierte Carbodiimide der Stoffgruppen (R₃SiN)₂C, [(RO)₃SiN]₂C, (R₂RSiN)₂C und R₃SiNCNSiR₃ dargestellt und in ihrer Struktur über¹⁴N- und¹H-kernmagnetische Resonanzmessungen, IR- und Raman-Spektren eindeutig als Carbodiimidderivate aufgeklärt.20. Mitt.:U. Wannagat undH. Kuckertz, Angew. Chem.75, 95 (1963).Zugleich 2. Mitt. über silylsubstituierte Carbodiimide; 1. Mitt.J. Pump undU. Wannagat, Ann. Chem.652, 21 (1962); Angew. Chem.74, 117 (1962); Österr. Chemiker-Ztg.62, 319 (1961).     

Phase Equilibria and Critical Curves of Binary Ammonia–Hydrocarbon Mixtures

Liquid or dense supercritical ammonia has been suggested as an extraction fluid. It is indeed good solvent for very different classes of compounds, as can be seen from phase diagrams. Such diagrams for binary systems of ammonia and hydrocarbons are presented and discussed on the basis of their critical curves. Apparatus and methods for the measurement of phase equilibria and equation of state data of fluid mixtures at high pressure are described.