Die Kristallstruktur von TlFeSe2 und TlFeS2

TlFeSe₂ is monoclinic, space groupC2/m–C _2h ³ ,a=11.973 Å,b=5.490 Å,c=7.110 Å, =118.2°,Z=4.TlFeS₂ is isotypic witha=11.636 Å,b=5.304 Å,c=6.799 Å, =116.7°.The crystal structure of TlFeSe₂ has been determined from single crystal diffractometer data. Isotypy of the sulfide has been confirmed from powder diffraction data. The crystal structure containing infinite linear chains of edgesharing FeX ₄-tetrahedra, and its relationship to the thio- and selenoferrates of the alkali metals are discussed. The mineral raguinite is very probably isotypic to synthetic TlFeS₂.

     

Synthesis and Characterization of β‐Diketiminate Aluminum Compounds and Their Use in the Ring‐Opening Polymerization of ε‐Caprolactone

Four aluminum alkyl compounds, [CH{(CH₃)CN‐2,4,6‐MeC₆H₂}₂AlMe₂] ( 1 ), [CH{(CH₃)CN‐2,4,6‐MeC₆H₂}₂AlEt₂] ( 2 ), [CH{(CH₃)CN‐2‐iPrC₆H₄}₂AlMe₂] ( 3 ), and [CH{(CH₃)CN‐2‐iPrC₆H₄}₂AlEt₂] ( 4 ), bearing β‐diketiminate ligands [CH{(Me)CN‐2,4,6‐MeC₆H₂}]₂ (L¹H) and [CH{(Me)CN‐2‐ⁱPrC₆H₄}]₂ (L²H) were obtained from the reactions of trimethylaluminum, triethylaluminum with the corresponding β‐diketiminate, respectively. All compounds were characterized by ¹H NMR and ¹³C NMR spectroscopy, single‐crystal X‐ray structural analysis, and elemental analysis. Compounds 1 – 4 were found to catalyze the ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) with good activity.     

Implementation of an analogue model of a memristor based on a light-dependent resistor

In this paper,an analogue model of a memristor using a light-dependent resistor(LDR) is presented.This model can be simplified into two parts:a control circuit and a variable resistor.It can be used to easily verify theoretical presumptions about the switching properties of memristors.This LDR-based memristor model can also be used in both simulations and experiments for future research into memristor applications.The paper includes mathematical models,simulations,and experimental results.     

Amphiphilic cationic block copolymers via controlled free radical polymerization

N-oxyl terminated vinylbenzyl chloride macromonomers, available via controlled free radical polymerization, were used to synthesize AB-block copolymers of vinylbenzyl chloride and styrene with low polydispersity and different block lengths and block length ratios. The vinylbenzyl chloride blocks were quantitatively converted into cationic polyelectrolytes by reactions with tertiary amines. The micellization of the synthesized amphiphilic cationic block copolymers was investigated using different techniques such as static light scattering, ultracentrifugation and size exclusion chromatography.     

Effect of donor-acceptor substitution on the nonlinear optical properties of oligo(1,4-phenyleneethynylene)s studied by third harmonic generation spectroscopy

Third-harmonic generation (THG) spectroscopy was performed for oligo(1,4-phenyleneethynylene)s (OPEs) with terminal donor-acceptor (DA) substitution and compared to the results of merely donor substituted OPEs and regular OPE chains with 2,5-dipropoxy benzene rings. Both, extension of the conjugation and push-pull effect enhance the molecular hyperpolarizability gamma, even for the DAOPEs, which exhibit a hypsochromic shift of the long-wavelength absorption for increasing length L of the conjugated chain.     

Extraction and derivatization of polar herbicides for GC-MS analyses

A sample preparation procedure including a simultaneous microwave-assisted (MA) extraction and derivatization for the determination of chlorophenoxy acids in soil samples is presented. For a selective and sensitive measurement, an analytical technique such as GC coupled with MS needs to be adopted. For GC analyses, chlorophenoxy acids have to be converted into more volatile and thermally stable derivatives. Derivatization by means of microwave radiation offers new alternatives in terms of shorter derivatization time and reduces susceptibility for the formation of artefacts. Extraction and derivatization into methyl esters (ME) were performed with sulphuric acid and methanol. Due to the novelty of the simultaneous extraction and derivatization assisted by means of microwave radiation, a careful investigation and optimization of influential reaction parameters was necessary. It could be shown that the combination of sulphuric acid and methanol provides a fast sample preparation including an efficient clean up procedure. The data obtained by the described method are in good agreement with those published for the reference material. Finally, compared to conventional heating and also to the standard procedure of the EPA, the sample preparation time could be considerably shortened.     

An [(NHC)(NHCEWG)RuCl2(CHPh)] Complex for the Efficient Formation of Sterically Hindered Olefins by Ring‐Closing Metathesis

NHC with EWGs for RCM : Ruthenium complexes with two N‐heterocyclic carbenes (NHCs), one of them substituted with electron‐withdrawing groups (EWGs), are highly efficient (pre)catalysts for the synthesis of tetrasubstituted olefins and trisubstituted olefins by ring‐closing metathesis reactions (RCM, see scheme).

     

Highly Enantioselective Intramolecular 1,3‐Dipolar Cycloaddition: A Route to Piperidino‐Pyrrolizidines

Enantioselective catalytic intermolecular 1,3‐dipolar cycloadditions are powerful methods for the synthesis of heterocycles. In contrast, intramolecular enantioselective 1,3‐dipolar cycloadditions are virtually unexplored. A highly enantioselective synthesis of natural‐product‐inspired pyrrolidino‐piperidines by means of an intramolecular 1,3‐dipolar cycloaddition with azomethine ylides is now reported. The method has a wide scope and yields the desired cycloadducts with four tertiary stereogenic centers with up to 99 % ee. Combining the enantioselective catalytic intramolecular 1,3‐dipolar cycloaddition with a subsequent diastereoselective intermolecular 1,3‐dipolar cycloaddition yielded complex piperidino‐pyrrolizidines with very high stereoselectivity in a one‐pot tandem reaction.     

Heteronuclear dipolar recoupling in solid-state nuclear magnetic resonance by amplitude-, phase-, and frequency-modulated Lee-Goldburg cross-polarization

This paper presents a theoretical, numerical, and experimental study of phase- and frequency-switched Lee-Goldburg cross-polarization (FSLG-CP) under magic-angle spinning conditions. It is shown that a well-defined amplitude modulation of one of the two radio-frequency (rf) fields in the FSLG-CP sequence results in highly efficient heteronuclear dipolar recoupling. The recoupled dipolar interaction is gamma-encoded and, under ideal conditions, the effective spin Hamiltonian is equivalent to that in continuous-wave Lee-Goldburg CP. In practice, however, FSLG-CP is less susceptible to rf field mismatch and inhomogeneity, and provides better suppression of (1)H spin diffusion. The performance of FSLG-CP is experimentally demonstrated on liquid-crystalline samples exhibiting motionally averaged dipolar couplings.