Topotactic reversible phase transition between room-temperature and a new low-temperature modification in the MCl3(THF)3 system

Both single crystals of VCl₃(THF)₃ as well as isotypic cocrystals of the composition MCl₃(THF)₃, M=Ti/V 1/3, undergo a topotactic reversible phase transition to a hitherto unknown low-temperature modification. The close relationship between this new structure and the room-temperature phase determined by Cottonet al. is discussed from the molecular and the intermolecular point of view: Both modifications are built up by conformationally very similar molecules which change their arrangement during the phase transition. Lattice energy calculations confirm that these two alternative arrangements correspond to minima of almost the same packing energy.Dedicated to Professor Dr. G. E. Herberich on the occasion of his 60th birthday.     

Exploiting C3-symmetry in the dynamic coordination of a chiral trisoxazoline to copper(II): improved enantioselectivity, and catalyst stability in asymmetric lewis acid catalysis

Chiral C3-symmetric trisoxazolines are highly efficient stereodirecting ligands in enantioselective Cu(II) Lewis acid catalysis which is based on the concept of a stereoelectronic hemilability of the divalent copper; in direct comparison with the analogous bisoxazoline systems they are more efficient in the enantioselective alpha-amination as well as the enantioselective Mannich reaction of prochiral beta-ketoesters.     

EXAFS Spectroscopy of the Alkoxide Precursor Zr(O n Bu)4 and its Modification in Solution

Summary. The molecular structure of the transition metal alkoxide Zr(OⁿBu)₄ in toluene and its modification by addition of i-propanol, tetrahydrofurane, and the coordinating ligand pentane-1,3-dione (Hacac) were investigated by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. Zr(OⁿBu)₄ dissolved in toluene forms dimers. It was proved that cluster size is a function of the number of added equivalents ligand. In contrast, the addition of i-propanol or tetrahydrofurane caused no structural changes observable by EXAFS spectroscopy. A detailed discussion of the structural models is given in terms of possible alternatives and errors within the EXAFS analysis.     

The potential of composite pyrolysis gas chromatographic mass spectra in the study of lignocellulosics

The objective of this work was to evaluate the use of composite mass spectral (CMS) data from pyrolysis gas chromatography/mass spectrometry (PY–GC/MS) for lignocellulosic materials. Various forages, by-products and fiber fractions derived from them were examined as CMS by PY–GC/MS. The PY–GC/MS system consisted of a heated platinum filament, a capillary gas chromatograph and an ion trap detector (ITD) mass spectrometer operated under electron impact conditions. Mass spectra were then composited in several ways by summing all the mass spectra acquired within retention times corresponding to major product classes. CMS data were entered in a dedicated library and compared using the ITD library editor software. The usefulness of such a simple procedure for studies related to lignocellulose analysis, such as forage recognition, development of analytical methods and digestibility/maturity correlation, is discussed.     

Cyanidverbrückte Koordinationspolymere aus cis‐ oder trans‐[Ru(tBuNC)4(CN)2] und MnCl2: Zum Einfluß unterschiedlicher Topologien auf die magnetischen Eigenschaften von Materialien

Cyanide Bridged Coordination Polymers from cis‐ or trans‐[Ru(^tBuNC)₄(CN)₂] and MnCl₂: About the Influence of Different Topologies on the Magnetic Properties of Materials The reaction of cis‐ or trans‐[Ru(^tBuNC)₄(CN)₂] with MnCl₂ as an additional transition metal fragment yields the one dimensional coordination polymers {cis‐[Ru(CN)₂(^tBuNC)₄] MnCl₂}_n, ( 1 ), and {trans‐[Ru(CN)₂(^tBuNC)₄]MnCl₂}_n, ( 2 ), with a different arrangement of the metal centers caused by the different stereochemistry of the starting compounds. The variation of the Ru‐C‐N‐Mn geometry nevertheless leads to significant differences in the magnetic properties of 1 and 2 . The coordination polymer derived from trans‐[Ru(^tBuNC)₄(CN)₂] shows a more efficient antiferromagnetic intrachain interaction between the manganese centers compared to the cis‐derivative.     

Orientation and order in thin films of a combined liquid crystalline polymer

The order in thin films of a combined liquid crystalline polymer is studied by X-ray reflection. Films of thicknesses of less than 200 nm on float glass are investigated as a function of temperature. The polymer with mesogenic groups in the main and side-chains exhibits smectic and cholesteric mesophases. Measurements in the smectic phases show a Bragg peak and smectic layers are oriented parallel to the substrate. The sample is thus macroscopically ordered by the influence of substrate and free surface. The film surface is very smooth after spincoating; surface roughness is typically 0.8 nm. First annealing of samples leads to a significant roughening of the free surface; roughness increases to 2.1 nm. Order as a function of film thickness depends on the interaction of the polymer with the substrate and free surface. These interactions give rise to a typical correlation length of perturbations in smectic ordering.     

InIII-Phthalocyanine: Darstellung,Eigenschaften und Kristallstruktur von Tetra(n-butyl)ammonium-cis-di(nitrito-O,O′)phthalocyaninato(2–)indat(III)

In^III-Phthalocyanines: Synthesis, Properties, and Crystal Structure of Tetra(n-butyl)ammonium-cis-di(nitrito-O,O')phthalocyaninato(2–)indate(III) [In(Cl)Pc^2?] reacts with (ⁿBu₄N)NO₂ in acetone yielding green-blue (ⁿBu₄N)^cis[In(NO₂)₂Pc^2?], which crystallizes in the monoclinic space group P2₁/n (No. 14). Both nitrite anions are coordinated as chelating nitrito-O,O'(NO₂) ligands to In^III in cis-geometry. Consequently In^III is octa-coordinated within a distorted “quadratic” antiprism and directed towards the Pc^2?-ligand. One of the NO₂ ligands has equivalent N? O bonds similar to free nitrite, while the other has asymmetric N? O bonds. Both (In,O,N,O) rings are approximately planar with a dihedral angle of 80°. The Pc^2? ligand is distorted in an asymmetrically convex manner. Partially overlapping pairs of Pc^2? ligands related by an inversion center form double layers, which are separated by layers containing the (ⁿBu₄N)⁺ cations. The cyclic voltammogram shows three electrode processes, which are assigned to the redox pairs: Pc^3?/Pc^2? (?0.94 V) < In^I/In^III (-0.78 V) < Pc^2?/Pc^? (0.64 V). The UV-VIS-NIR spectra and vibrational spectra are discussed.