Ab initio calculations and normal coordinate analysis of ruthenium tris-alpha-diimine complexes

For the first time, a full scaled quantum chemical normal coordinate analysis has been performed on [Ru(LL')(3)](2+) complexes, where LL' = 2,2'-bipyrazine (bpz) or 2,2'-bipyrimidine (bpm). Geometric structures were fully optimized using density functional theory and an effective core potential basis set. The infrared and Raman spectra were calculated using the optimized geometries. The results of the calculations provide a highly satisfactory fit to the experimental infrared and Raman spectra, and the potential energy distributions allow a detailed understanding of the vibrational bands therein.     

Desoxy-nitrozucker 14. Mitteilung 1-C-Nitroglycale. Herstellung und Umsetzung mit einigen Stickstoff-Nucleophilen

1-C-Nitroglycals. Preparation and Reaction with Some Nitrogen Nucleophiles Acetylation of the 1-deoxy-1-nitromannopyranoses 2 and 6 was accompagnied by spontanous β-elimination to give the 1-C-nitroglucals 3 and 7 , respectively, while acetylation of the gluco- and galacto-configurated 1-deoxy-1-nitropyranoses 8 and 14 gave the acetates 9 and 15 , respectively (Scheme 1). The acetylation of the ribo- and arabino-configurated 1-deoxy-1-nitrofuranoses 19 and 21 also occurred without β-elimination to give the acetates 20 and 22 , respectively (Scheme 2). Mild base treatment of the previously described O-acetylnitro-β-D -glucose 4 , the O-acetylnitro-β-D -pyranoses 9 and 15 , and the O-acetylnitro-β-D -furanoses 17 , 20 , and 22 gave the 1-C-nitroglycals 3 , 10 , 16 , 18 and 23 , respectively (Scheme 1 and 2). The previously obtained 1-C-nitroglucal 3 was deacetylated by treatment with MeOH in the presence of KCN or sodium m-nitrophenolate to give the free nitroglucal 5 . Deacetylation of the benzylidene protected 1-C-nitroglucal 10 (MeOH, NaOMe) gave the 4,6-O-benzylidene-1-C-nitroglucal 11 and traces of the 2-O-methyl-1-C-nitromannoses 12 and 13 . The UV, IR, ¹H-NMR and ¹³C-NMR spectra of the 1-C-nitroglycals are discussed. In solution, the 1-C-nitroglycals 1 , 5 , 7 , 10 , 11 , and 16 adopt approximately a ⁴H_5? and 3 a flattened ⁴H₅ conformation. The structure of 5 was established by X-ray analysis. In the solid state, 5 adopts a sofa conformation, which is stabilized by an intramolecular H-bond. The β-addition of NH₃ to the 1-C-nitroglucals 7 and 10 was followed by an O→ N acetyl migration to give exclusively anomeric pairs of the N-acetyl-1-nitromannosamine derivatives 24 / 25 and 26/27 , respectively (Scheme 3). The β-addition of methylamine, octadecylamine, and tryptamine to the 1-C-nitroglucal 11 also stereoelectronically controlled and gave the crystalline N-alkyl-1-nitromannosamines 28 , 29 , and 30 , respectively. The stereoelectronically controlled β-addition of NH₃ to the 1-C-nitrogalactal 16 , followed by acetylation, yielded exclusively the talosamine derivative 31 , while the reversible β-addition of azide ions to 16 gave the anomeric 2-azido-1-nitrogalactoses 32 and 33 . The β-addition of azide ions to the 1-C-nitroglucal 1 led to the 2-azido-1-nitromannose 34 . In the presence of excess formaldehyde, this addition was followed by a Henry reaction. Chromatography of the crude product was accompagnied by solvolytic removal of the NO₂ group to give the 3-azidomannoheptulose 35 in high yields (Scheme 4).     

Resonance Raman spectroscopy and DFT calculations of the protonation of 4-(2-pyridylazo)-N,N-dimethylaniline in solution and adsorbed on oxide surfaces

The protonation of 4-(2-pyridylazo)-N,N-dimethylaniline (PYAD) in aqueous solution and its adsorption on oxide surfaces has been studied by resonance Raman (RR) spectroscopy. The gas phase structures of neutral, protonated and diprotonated forms of PYAD were modelled by SCF-DFT calculations at the B3-LYP/DZ level, enabling determination of the simulated vibrational spectra of these species, together with vibrational assignments, and providing confirmation that protonation occurs initially at the pyridyl nitrogen atom. Electronic absorption spectra were interpreted using time-dependent DFT calculations. Adsorption of PYAD on SiO₂ or Al₂O₃ surfaces is mainly via the neutral species, hydrogen bonded to surface OH groups, although a small proportion of adsorbed molecules are protonated. By contrast, adsorption on SiO₂–Al₂O₃ results in complete protonation, indicating the presence of Brønsted acidic sites with pK_a values ? 4.5, whereas adsorption on H-mordenite results in diprotonation, indicating the presence of Brønsted acidic sites with pK_a values ? 2.     

On the growth mechanism and optical properties of ZnO multi-layer nanosheets

We report multi-layer ZnO nanosheets obtained by annealing Zn polyhedral particles in pure O₂. The structure comprises a cluster core with side faces terminated with 50-nm-thick multi-layer sheets. The nanosheets were found to be (0001)-oriented single-crystalline wurtzite ZnO. By studying the early growth stages, it appears that the sheets form through a ripening process of dendritic ZnO nanostructures, during which the single-crystalline nature and crystallographic orientation are conserved. The ripening is promoted by the rapid oxidation of the Zn polyhedral microcrystals. We also show that appropriate modification of the oxidation process leads to the formation of well-defined dendritic nanowires. The optical properties (photoluminescence and Raman) of these nanostructured materials are discussed. PACS 81.07.-b; 68.70.+w; 78.67.-n; 81.05.Dz; 68.37.-d     

Lamellar zirconium phosphonates containing pendant sulphonic acid groups

The versatile sulphonic acid group has been introduced into the family of interlamellar anchored materials. Zirconium bis-3-sulphopropylphosphonate is an example of an aliphatic acid. Zirconium bis-2-(sulphophenyl)ethylphosphonate is an example with an aromatic sulphonic acid group. In general, the sulphonic acids are not as crystalline as the carboxylic acid analogs. This is probably due to the relatively large size of the sulphonic acid group compared to the available cross sectional area of the layer face. The aliphatic compounds are more crystalline than the aromatics, as is expected from size considerations. The sulphonic acid group in both crystalline and semi-crystalline examples is accessible to reaction with bases. A few preliminary experiments have demonstrated the utility of these compounds as both strong acid ion exchangers and Bronsted acid catalysts. The layered sulphonic acid—zirconium 3-sulphopropylphosphonate—is thermally stable to well over 200°C. This indicates good potential for applications in Bronsted catalysis. This stability compares favorably with organic resin based sulphonic acids.The sulphonic acid class of interlamellar anchored materials have now been established. Both aliphatic and aromatic examples have been prepared. The utility of the sulphonic acids has been demonstrated with the typical reactions of this functional group. Specifically, the acids have been shown to be strong acid cation exchangers and a Bronsted acid catalyst. In addition, we have begun to develop an insight into the structural ramifications of these compounds. The size constraints of the zirconium phosphate type backbone are evident. Further, the thermal stability of this group of compounds is encouraging relative to its applications potential.     

The molecular structure of thiocarbonylbromide

An electron diffraction investigation of SCBr₂ has yielded the following r_α⁰ parameters: r_SC= 1.597(5) Å, r_CBr = 1.894(9) Å and ?BrCBr = 111.6°. These values are compared with other carbonyl and thiocarbonyl halides.     

Microwave spectra of isotopic pyrazoles and molecular structure of pyrazole

Microwave spectra of the complete set of monosubstituted isotopic pyrazoles have been investigated and the complete r_s structure of pyrazole determined. The deuterated and ¹⁵N species of pyrazole were prepared, while the ¹³C species were examined in natural abundance. The spectrum of the parent compound was remeasured yielding rotational and centrifugal distortion constants.The mutual position of the hydrogen atoms and the direction of the dipole moment in the pyrazole principal axis system has been unambiguously established.The ¹⁴N quadrupole hyperfine structure was resolved and the quadrupole coupling constants derived by Blackman et al. [8] were confirmed.An estimated r_z structure is compared to crystal structures derived by X-ray and neutron diffraction showing the N-H bond in the crystal to be prolonged. But, otherwise no significant differences seem to develop when bringing the molecule from its isolated state into the crystal with its strong hydrogen bonds.