Synthese und Kristallstrukturen der Phosphaniminato-Komplexe [MCl2(NPPh3)]2 mit M = Al und Ga, [SbCl2(NPMe3)(DMF)]2 sowie des Phosphanimin-Komplexes [Ph3PNH · BF3] · THF

Syntheses and Crystal Structures of the Phosphorane Iminato Complexes [MCl₂(NPPh₃)]₂ with M = Al and Ga, [SbCl₂(NPMe₃)(DMF)]₂, and of the Phosphorane Imine Complex [Ph₃PNH · BF₃] · THF The phosphorane iminato complexes [MCl₂(NPPh₃)]₂ with M = Al and Ga and [SbCl₂(NPMe₃)(DMF)]₂ are formed as colourless crystals by reactions of the anhydrous trichlorides MCl₃ (M = Al, Ga, Sb) with the corresponding silylated phosphorane imines Me₃SiNPR₃ in acetonitrile and in dimethyl formamide, respectively. The phosphorane imine derivative [Ph₃PNH · BF₃] · THF is formed from Me₃SiNPPh₃ and boron trifluoride etherate in boiling tetrahydrofuran. The compounds are characterized by their i. r. spectra and by crystal structure analyses. [AlCl₂(NPPh₃)]₂ : Space group P1 , Z = 1, structure solution with 1 585 observed unique reflections, R = 0.061. Lattice dimensions at ?70°C: a = 917.6, b = 1 053.5, c = 1 145.2 pm, α = 111.72°, β = 100.80°, γ = 109.95°. [GaCl₂(NPPh₃)]₂ : Space group P1 , Z = 1, structure solution with 2 586 observed unique reflections, R = 0.066. Lattice dimensions at ?70°C: a = 917.5, b = 1 058.3, c = 1 153.7 pm, α = 105.52°, β = 107.75°, γ = 109.88°. In both compounds the metal atoms are linked to planar M₂N₂ four-membered rings via the N-atoms of the phosphorane iminato groups. [SbCl₂(NPMe₃)(DMF)]₂ : Space group P2₁/n, Z = 4, structure solution with 3 805 observed unique reflections, R = 0.038. Lattice dimensions at ?70°C: a = 1 913.0, b = 726.8, c = 2 040.7 pm, β = 113.62°. The unit cell contains two symmetry independent dimeric molecules, in which the antimony atoms are centrosymmetricly μ₂ linked via the N-atoms of the phosphorane iminato groups. Along with the oxygen atom of the dimethyl formamide molecule the Sb atoms achieve a ψ-octahedral environment. [Ph₃PNH · BF₃] · THF : Space group C2/c, Z = 8, structure solution with 2 048 observed unique reflections, R = 0.058. Lattice dimensions at ?70°C: a = 2 460.4, b = 869.2, c = 1 978.0 pm, β = 116.35°.     

On the Existence and Hydrolytic Stability of Titanosiloxane Bonds in the System: Glycidoxypropyltrimethoxysilane-Water-Titaniumtetraethoxide

Heterometal materials based on glycidoxypropyltrialkoxysilane and titaniumalkoxide are used for optical applications and require a high homogeneity on the molecular level. The presence of heterometal titanosiloxanes, their distribution and hydrolytic stability should influence the homogeneity of these materials. 29Si and 17O NMR spectroscopy has been used to investigate sols with molar ratios Si : Ti = 1 and H2O : OR (H) = 0.5 – 2.0 and their gels after heat treatment at 130°C. The presence of Si—O—Ti bonds in sols with a low water content (H < 0.2) and in the corresponding gels was identified by the high-field shift of the 29Si NMR signals of T1 and T2 units of up to 2–3 ppm compared to corresponding signals of homo-condensed Si—O—Si bonds. The existence of Si—O—Ti bonds in the sols is supported by 17O NMR spectra which show a characteristic signal around 340 ppm. A cleavage of the Si—O—Ti bonds occurs with increasing water/OR ratio in the sols. The cleavage of the heterometal bonds and the building up of homo-condensed species leads to a separation into areas with predominantly Ti—O—Ti and Si—O—Si bonds resulting in a decreased molecular homogeneity of the materials.     

Formaldehyde Formation on Vanadium Oxide Surfaces V2O3(0001) and V2O5(001): How does the Stable Methoxy Intermediate Form?

Hydroxy‐mediated methoxy formation or stabilization is probably an important process in many methanol adsorption systems. Hydrogen atoms originating from the scission of the methanol O? H bond react with the substrate and form water. This process may result 1) in the production of additional surface defects as reactive centers for methoxy formation and 2) in the stabilization of methoxy groups by suppression of methanol formation.

     

Umweltchemie 1998

Nachdem im Trendbericht des letzten Jahres ausgewählte Beispiele aus Bereichen der Umweltchemie besprochen wurden,¹⁾ sollen in diesem Jahr Ergebnisse aus Ökotoxikologie and Humantoxikologie behandelt werden. Zunächst werden einige Arbeiten aus den Bereichen der Entsorgungsverfahren und neue Entwicklungen bei Spurenstoffen vorgestellt. Da das Gebiet der nachhaltigen Chemie immer mehr in den Brennpunkt des Interesses rückt, werden auch neue umweltfreundliche Synthesen und Produkte ausführlich diskutiert.     

Synthesis and characterization of sulfuryl diazide, O2S(N3)2

Sulfuryl diazide, O(2)S(N(3))(2), previously described as an "exceedingly explosive" compound, has been isolated and characterized by IR (Ar matrix, gas) and Raman (solid) spectroscopy, and its structure has been determined by X-ray crystallography. It has a melting point of -15 °C and can be handled in small quantities in gas, liquid, and solid states. Vibrational spectroscopic studies suggest the presence of only one conformer in both gas and solid states, and the X-ray crystallography revealed an anti conformation of the two azido groups with respect to the NSN plane. Calculations predict the anti (C(2)) conformer to be 6.6 kJ mol(-1) lower in energy than the syn (C(s)) one at the CBS-QB3 level of theory. The related chlorosulfuryl azide, ClSO(2)N(3), has also been prepared and characterized by IR and Raman spectroscopy.     

Structure of the oxygen-rich cluster cation Al2O7+ and its reactivity toward methane and water

The oxygen-rich cluster Al(2)O(7)(+) is generated in the gas phase and investigated with respect to both its structure and its reactivity toward small, inert molecules using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry and DFT-based calculations. Al(2)O(7)(+) reacts with CH(4) under ambient conditions via hydrogen atom transfer (HAT), and with H(2)O a ligand exchange occurs which gives rise to the evaporation of two O(2) molecules. The resulting product ion Al(2)O(4)H(2)(+) is also capable of abstracting a hydrogen atom from both H(2)O and CH(4). As indicated in the H(2)O/2O(2) ligand exchange and supported by collision-induced dissociation (CID) experiments, two O(2) units constitute structural elements of Al(2)O(7)(+). Further insight is provided by DFT calculations, performed at the unrestricted B3LYP/TZVP level, and reaction mechanisms are suggested on the basis of both the experimental and theoretical results.     

Regioselective synthesis of 6-aryl-5-(chloroethyl)salicylates by domino ‘[3+3] cyclization/homo-Michael’ reactions of 1,3-bis(silyloxy)-1,3-butadienes with 1-formyl- and 1-acetyl-1-aroyl-cyclopropanes

Functionalized 3-aryl-4-(chloroethyl)phenols are regioselectively prepared by domino ‘[3+3] cyclization/homo-Michael’ reactions of 1,3-bis(silyloxy)-1,3-butadienes with 1-formyl- and 1-acetyl-1-aroyl-cyclopropanes.     

Effect of structural isomerism and polymer end group on the pH-stability of hydrogen-bonded multilayers

Association of tannic acid (TA) with structurally isomeric poly(N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOX) has been examined at surfaces to understand the effect of different molecular arrangements in a polymer repeating unit of structural isomers on the construction and pH-stability of hydrogen-bonded multilayers. Films were fabricated using layer-by-layer (LbL) technique through hydrogen-bonding interactions primarily between carbonyl groups of neutral polymers and hydroxyl groups of TA molecules at pH 2. PIPOX and TA formed thinner and more stable films in the pH scale with a critical dissolution pH of 9 when compared to films of PNIPAM and TA with a critical pH of 8. The differences in the thickness and pH-stability were due to different conformational behavior of PNIPAM and PIPOX in water which affects the accessibility of carbonyl groups for participation in the hydrogen bonding and the number of binding sites between the polymer pairs. Addition of electrostatic interactions by introducing amino groups only at the PIPOX chain end shifted the critical dissolution pH to higher values and resulted in gradual dissolution of the films in a wide pH range of 9-12. Such films hold promise for use in biomedical field due to biocompatibility and lower critical solution temperature (LCST) behavior at near physiological temperature of PNIPAM and PIPOX together with the pH-response of the hydrogen-bonded films.