Crystal Structure of the Orthorhombic Modification of a Mononuclear Peroxotitanium(IV) Dipicolinate

The deep red diaquoperoxotitanium dipicolinate [TiO₂(C₇H₃O₄N) (H₂O)₂]2H₂O crystallises in a pleochroic triclinic and a nonpleochroic orthorhombic modification. The structure of the former has been reported earlier. The structure of the latter, described in this paper, has been determined from X-ray diffractometer data and refined to R = 0.034. In both forms the complex occurs as the free acid, but the modes of packing are completely different. Bond lengths and angles agree closely. As in the other peroxotitanium(IV) chelate structures so far determined, titanium has an approximately pentagonal bipyramidal coordination with the peroxo group and the chelate ligand occupying equatorial sites and the waters forming the apices. The relationship proposed earlier between the basicity of the ligands and the bond lengths and colours of the related compounds is substantiated. The final difference Fourier maps obtained with normal and modified refinement procedures clearly reveal bonding electron densities. They indicate a pentagonal bipyramidal sp³d³ hybridisation of titanium with bent Ti-O_peroxo bonds, again in agreement with the triclinic form and other peroxotitanium chelates.     

Szintillationseigenschaften dotierter organischer Molekül-Einkristalle bei Beschüß mit α-Teilchen

Scintillation anisotropy of organic crystals containing impurities was measured. Single crystals oft-stilben with impurities of anthracene and naphthacene and single crystals ofp-terphenyl containing anthracene were bombarded withα-particles in order to investigate their scintillation response as function of direction ofα-particles and concentration of guest molecules. The relations between the results and the polarization of the fluorescence light of the corresponding molecules are discussed.     

Die Kristallstruktur eines dinuklearen Peroxotitan(IV)-nitrilotriacetatkomplexes

Crystal Structure of a Dinuclear Peroxotitanium(IV)-Nitrilotriacetate Complex The structures of four peroxotitanium(IV) dipicolinates, with colours ranging from deep red to yellow orange, have been reported earlier, and a correlation between their colours and the variations of certain bond lengths has been proposed. This paper describes the pale yellow dinuclear peroxotitanium nitrilotriacetate complex Na₄[Ti₂O₅(C₆H₆O₆N)₂]11 H₂O. The monoclinic structure, space group B2/b, contains 25 independent non-hydrogen atoms and 17 hydrogen atoms. It has been determined from diffractometer data and refined to R = 3.2%. Titanium is again coordinated approximately pentagonal-bipyramidally. The μ-oxygen bridge occupies an axial position. The short (1.819 Å), nearly linear Ti–O–Ti bonds show double bond character. The titaniumperoxide bonds, however, are relatively long, thus confirming the rule proposed before: the more basic the axial ligands, the higher is the frequency of the absorption band, the longer are the Ti-peroxide bonds and the shorter are the axial distances. This is confirmed by electron density maps, which are to be discussed elsewhere in detail, showing bent Ti-peroxide bonds enclosing an angle of about 70° and a strong electron bridge on the μ-oxygen bond. Hydrogen bonding and the packing of the complexes is discussed.     

A computer system for structural identification of organic compounds from 13C NMR data

A computerised library search system for ¹³C NMR data is described. Given the spectral data of an unknown compound, the system will retrieve from the library those reference compounds exhibiting similar spectra. For comparison the spectral data are converted into a binary code, designed to reflect the underlying structure rather than exact values for chemical shifts. Thus, the ability of the system to retrieve compounds similar to the unknown (as opposed to identical) is greatly enhanced. A sophisticated search strategy adapting itself automatically to the problem at hand makes the system highly efficient.     

New liquid crystalline di- and tetra-acrylates for network formation

New liquid crystalline diacrylates and tetra-acrylates containing four to six aromatic rings were synthesized and characterized, and their mesophase behaviour was investigated. They are designed to be used in combination with chiral molecules to form cholesteric mesophases which can be crosslinked by photopolymerization. The acrylates presented exhibit broad mesophase ranges since mesogenic moieties longer than three are employed. Most diacrylates show no isotropization, due to premature thermal polymerization above 180°C. Additionally, liquid crystalline dipropionates were synthesized as reference compounds which cannot be crosslinked, and selected examples of these exhibit isotropization temperatures as high as 238°C prior to thermal degradation. Substituents at the mesogenic moiety have a great influence on the mesophase characteristics. Bulky substituents such as the tert-butyl group, induce a nematic mesophase, whereas compounds with small substituents (e.g. OCH3) or unsubstituted molecules also exhibit smectic phases. Tetra-acrylates with unsubstituted and substituted mesogenic units feature nematic mesophases only as a result of the additional spacers attached. Here isotropization was observed without polymerization at temperatures around 120-160°C.     

Charge qubit purification by an electronic feedback loop

We propose the manipulation of an isolated qubit by a simple instantaneous closed-loop feedback scheme in which a time-dependent electronic detector current is directly back-coupled into qubit parameters. As a specific detector model, we employ a capacitively coupled single-electron transistor. We demonstrate the stabilization of pure delocalized qubit states above a critical detector-qubit coupling. This electronic purification is independent of the initial qubit state and is accomplished after few electron jumps through the detector. Our simple scheme can be used for the efficient and robust initialization of solid-state qubits in quantum computational algorithms at arbitrary temperatures.     

Pyroxene‐type compounds NaM3+Ge2O6, with M = Ga,Mn, Sc and In

The four title compounds, namely sodium gallium germanate, NaGaGe₂O₆, sodium manganese vanadate germanate, NaMnV_0.1Ge_1.9O₆, sodium scandium germanate, NaScGe₂O₆, and sodium indium germanate, NaInGe₂O₆, adopt the high‐temperature structure of the pyroxene‐type chain germanates, with monoclinic symmetry and space group C2/c. The lattice parameters, the individual and average bond lengths involving M1, and the distortion parameters scale well with the ionic radius of the M1 cation. NaGaGe₂O₆ has more distorted M1 sites and more extended tetrahedral chains than NaInGe₂O₆, in which a high degree of kinking is required to maintain the connection between the octahedral and tetrahedral building units of the pyroxene structure. An exceptional case is NaMnGe₂O₆, in which the strong Jahn–Teller effect of Mn³⁺ results in more distorted octahedral sites than expected according to linear extrapolation from the other NaM³⁺Ge₂O₆ pyroxenes. In contrast with the literature, minor incorporations of V⁵⁺ in the tetrahedral site and a corresponding reduction of Mn³⁺ to Mn²⁺ in the octahedral sites in the present sample lower the Jahn–Teller distortion and stabilize the Mn‐bearing pyroxene, even allowing its synthesis at ambient pressure.