Synthesen von Heterocyclen, 93. Mitt.

Zusammenfassung Malonsäure und monosubstit. Malonsäuren reagieren in Acetanhydrid mit Cyclanon-anilen in guter Ausbeute zu Spiro-1,3-oxazinen (3–6 bzw.9–13). Diese labilen Verbindungen lassen sich mit POCl₃ leicht in 4-Hydroxy-5,6-polymethylen-pyridone-(2) umwandeln. Analog verhält sich Acetophenonanil.

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Malonic acid and monosubstituted malonic acids react in acetic anhydride with cyclanon-aniles yielding the spiro-1.3-oxazines3–6 and9–13. These compounds are readily converted with POCl₃ to 4-hydroxy-5.6-polymethylene-pyrid-2-ones. Acetophenon-anil reacts in the same manner.

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Herrn Prof. Dr.F. Wessely, Universität Wien, mit den besten Wünschen zum 70. Geburtstag gewidmet.     

The atomic-level structure of bandgap engineered double perovskite alloys Cs2AgIn1−xFexCl6

Although lead-free halide double perovskites are considered as promising alternatives to lead halide perovskites for optoelectronic applications, state-of-the-art double perovskites are limited by their large bandgap. The doping/alloying strategy, key to bandgap engineering in traditional semiconductors, has also been employed to tune the bandgap of halide double perovskites. However, this strategy has yet to generate new double perovskites with suitable bandgaps for practical applications, partially due to the lack of fundamental understanding of how the doping/alloying affects the atomic-level structure. Here, we take the benchmark double perovskite Cs₂AgInCl₆ as an example to reveal the atomic-level structure of double perovskite alloys (DPAs) Cs₂AgIn_1−xFe_xCl₆ (x = 0–1) by employing solid-state nuclear magnetic resonance (ssNMR). The presence of paramagnetic alloying ions (e.g. Fe³⁺ in this case) in double perovskites makes it possible to investigate the nuclear relaxation times, providing a straightforward approach to understand the distribution of paramagnetic alloying ions. Our results indicate that paramagnetic Fe³⁺ replaces diamagnetic In³⁺ in the Cs₂AgInCl₆ lattice with the formation of [FeCl₆]³⁻·[AgCl₆]⁵⁻ domains, which show different sizes and distribution modes in different alloying ratios. This work provides new insights into the atomic-level structure of bandgap engineered DPAs, which is of critical significance in developing efficient optoelectronic/spintronic devices.

Through Fe³⁺-alloying, the bandgap of benchmark double perovskite Cs₂AgInCl₆ can be tuned from 2.8 eV to 1.6 eV. The atomic-level structure of Cs₂AgIn_1−xFe_xCl₆ was revealed by solid-state nuclear magnetic resonance (ssNMR).     

Solid-State NMR Study of Phase Separation and Order of Water Molecules and Silanol Groups in Polysiloxane Networks

Homogeneity and structure of organically modified polysiloxane networks prepared by sol-gel co-condensation, as well as location and nature of water molecules and silanol groups were studied by 1D and 2D solid-state NMR. ¹H–²⁹Si and ¹H–¹H interatomic distances were estimated from variable contact-time CP/MAS experiments, ¹H NMR chemical shifts and off-resonance WISE NMR. A structure model of these networks is proposed and discussed. The fraction of proton-inaccessible units Q⁴ in the networks decreases with increasing amounts of dimethylsiloxane (D) and methylsiloxane (T) units. In contrast to systems prepared by co-condensation of tetraethoxysilane (TEOS) with dimethyl(diethoxy)silane (DMDEOS), proton-inaccessible units form essential fraction in networks prepared by co-condensation of TEOS with methyl(triethoxy)silane (MTEOS). The proton-accessible part of the networks with high O/Si ratios is nano-heterogeneous phase, which is composed of water containing Q ⁱ particles separated by copolymer domains. The overall homogeneity and uniformity of binding sites around silanol groups increases by co-condensation TEOS with DMDEOS or MTEOS, while the amount of physisorbed water as well as the hydrogen bond strength decreases, as compared with neat silica gel prepared by polycondensation of TEOS.     

Variable electron-phonon coupling in isolated metallic carbon nanotubes observed by Raman scattering

We report the existence of broad and weakly asymmetric features in the high-energy (G) Raman modes of freely suspended metallic carbon nanotubes of defined chiral index. A significant variation in peak width (from 12 cm(-1) to 110 cm(-1)) is observed as a function of the nanotube's chiral structure. When the nanotubes are electrostatically gated, the peak widths decrease. The broadness of the Raman features is understood as the consequence of coupling of the phonon to electron-hole pairs, the strength of which varies with the nanotube chiral index and the position of the Fermi energy.     

Structure and in vitro antifungal activity of [2,6‐bis(dimethylaminomethyl)phenyl]diphenyltin(IV) compounds

A set of seven [2,6‐bis(dimethylaminomethyl)phenyl]diphenyltin(IV) ({[(CH₃)₂NCH₂]₂(C₆H₃)}­(C₆H₅)₂Sn⁺X^?) ionic organotin(IV) compounds (X = Br, NO₃, CN, SCN, SeCN, BF₄ and PF₆) has been prepared and characterized by electrospray ionization mass spectrometry, ¹H NMR spectroscopy in CDCl₃,¹¹⁹Sn NMR in CDCl₃ and DMSO‐d₆ solution, as well as by ¹³C and ¹¹⁹Sn CP/MAS NMR spectroscopy and X‐ray diffraction techniques in the solid state. The in vitro antifungal activity of these water‐soluble ionic organotin(IV) compounds was compared with starting compounds and the antifungal drugs currently in clinical use. Copyright © 2002 John Wiley & Sons, Ltd.     

UV laser deposition of nanostructured Si/C/O/N/H from disilazane precursors and evolution to silicon oxycarbonitride

Megawatt ArF laser photolysis of gaseous methyldisilazanes [(CH₃)_nH_3?nSi]₂NH (n = 2, 3) in excess of Ar yields hydrocarbons (major volatile products), methylsilanes (minor volatile products) and allows chemical vapour deposition of solid amorphous Si/C/O/N/H powder containing Si? X (X? C, H, O, N) bonds. The incorporation of O is due to a high reactivity of the primarily formed products towards air moisture. The resulting solid materials possess nanometer‐sized texture and high specific area, contain Si‐centered radicals and anneal under argon to silicon oxycarbonitride, whose structure is described as a network of O‐ and N‐interconnected Si and C atoms. Copyright © 2006 John Wiley & Sons, Ltd.     

Structure of Framework Aluminum Lewis Sites and Perturbed Aluminum Atoms in Zeolites as Determined by 27Al{1H} REDOR (3Q) MAS NMR Spectroscopy and DFT/Molecular Mechanics

Zeolites are highly important heterogeneous catalysts. Besides Brønsted SiOHAl acid sites, also framework Al_FR Lewis acid sites are often found in their H‐forms. The formation of Al_FR Lewis sites in zeolites is a key issue regarding their selectivity in acid‐catalyzed reactions. The local structures of Al_FR Lewis sites in dehydrated zeolites and their precursors—“perturbed” Al_FR atoms in hydrated zeolites—were studied by high‐resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)₃AlOH groups and are characterized by a broad ²⁷Al NMR resonance (δ_i=59–62 ppm, C_Q=5 MHz, and η=0.3–0.4) with a shoulder at 40 ppm in the ²⁷Al MAS NMR spectrum. Dehydroxylation of (SiO)₃AlOH occurs at mild temperatures and leads to the formation of Al_FR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)₃Al Lewis sites exhibit an extremely broad ²⁷Al NMR resonance (δ_i≈67 ppm, C_Q≈20 MHz, and η≈0.1).     

Quantum crystallites and nonlinear optics

This is a review and analysis of the optical properties of quantum crystallites, with principal emphasis on the electro-optic Stark effect and all optical third order nonlinearity. There are also introductory discussions on physical size regimes, crystallite synthesis, quantum confinement theory, and linear optical properties. The experiments describe CdSe crystallites, exhibiting strong confinement of electrons and holes, and CuCl crystallites, exhibiting weak confinement of the exciton center of mass. In the CdSe system, neither the Stark effect nor the third order nonlinearity is well understood. The Stark shifts appear to be smaller than calculated, and field inducted broadening also occurs. The third order nonlinearity is only modestly stronger than in bulk material, despite theoretical prediction. Unexpectedly large homogeneous widths, due to surface carrier trapping, in the nominally discrete crystallite excited states appear to be involved. The CuCl system shows far narrower spectroscopic homogeneous widths, and corresponds more closely to an ideal quantum dot in the weak confinement limit. CuCl also exhibits exciton superradiance at low temperature. Surface chemistry and crystallite encapsulation are critical in achieving the predicted large Stark and third order optical effects in II-VI and III-V crystallites.