On the Electronic Structure and Photochemistry of Coordinatively Unsaturated Complexes: The Case of Nickel Bis‐dinitrogen,Ni(N2)2

The electronic ground and excited states of the coordinatively unsaturated complex Ni(η¹‐N₂)₂, isolated in an Ar matrix, are analyzed in detail by vibrational and electronic absorption and emission spectroscopies allied with quantum chemical calculations. The bond force constants are determined from a normal coordinate analysis and compared with those of the isoelectronic carbonyl complex. The consequences for the bond properties are discussed, and the trend in the force constants is compared with the standard formation enthalpies. The linear complex Ni(η¹‐N₂)₂ with two terminal dinitrogen ligands can be photoisomerized to two isomeric, metastable forms Ni(η¹‐N₂)(η²‐N₂) and Ni(η²‐N₂)₂, with one and two side‐on coordinated dinitrogen ligands, respectively.     

Counting of Oxygen Defects versus Metal Surface Sites in Methanol Synthesis Catalysts by Different Probe Molecules

Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N₂O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N₂O, temperature programmed desorption of H₂, and kinetic experiments. The presence of ZnO dramatically influences the N₂O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu‐ZnO interface and can be used to easily quantify the intensity of Cu‐Zn interaction. N₂O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H₂.     

Aromatic Foldamer Helices as α-Helix Extended Surface Mimetics

Helically folded aromatic oligoamide foldamers have a size and geometrical parameters very distinct from those of α-helices and are not obvious candidates for α-helix mimicry. Nevertheless, they offer multiple sites for attaching side chains. It was found that some arrays of side chains at the surface of an aromatic helix make it possible to mimic extended α-helical surfaces. Synthetic methods were developed to produce quinoline monomers suitably functionalized for solid phase synthesis. A dodecamer was prepared. Its crystal structure validated the initial design and showed helix bundling involving the α-helix-like interface. These results open up new uses of aromatic helices to recognize protein surfaces and to program helix bundling in water.     

New engineering polymers for blow-moulding

The combination of using high performance flexible engineering polymers and their processing by blow moulding technology allows traditional rubber and rubber-metal composite parts to be replaced to obtain improved performance, lower cost and greater design freedom. Two examples of automobile applications are detailed to support this concept - constant velocity joint boots and engine air ducting.     

Green,purple, blue — [Cu(N-Methylimidazole)<Subscript>n</Subscript> (OOCCH<Subscript>3</Subscript>)<Subscript>2</Subscript>]<Subscript>m</Subscript>, what is in a colour

Starting from the paddlewheel complex copper(II)acetate, the green N-methylimidazole adduct of copper(II)acetate is formed and transformed into the monomeric and dimeric N-methylimidazole adducts of copper(II)acetate [Cu(C₄H₆N₂)₂(CH₃COO)₂]_n·xH₂O (n = 1,2; x = 0, 6). The formation of the blue dimer or the purple monomer depends on the solvent and the presence or absence of water.     

Eight and seven point degenerations of Miquel's Theorem in Laguerre planes

For M?bius planes Schaeffer [9] has proved that all seven point degenerations of Miquel's Theorem characterize miquelian M?bius planes. For Laguerre planes we have several degenerations of Miquel's Theorem with eight and seven points. We prove that all except one of these degenerations characterize miquelian Laguerre planes. The remaining degeneration characterizes elation Laguerre planes. Received 14 September 2001; revised 1 September 2002.     

Deformations of the nilpotent infinite-dimensional Lie algebraL 2

Moscow Institute of New Technologies, Twente University (Netherlands). Translated from Funktsional'nyi Analiz i Ego Prilozheniya, Vol. 26, No. 4, pp. 90–92, October–December, 1992.