Photochemische Umwandlungen. XXXVIII [1]. Synthese und Eigenschaften Methoxycarbonyl-substituierter «Quadricyclanone»

The three methoxycarbonyl-substituted quadricyclanones 7a , 7b and 7c have been synthesized in good to excellent yields. Some of their physical (UV., NMR.) and chemical properties (e.g. condensation and pyrolysis reactions) are discussed.     

Electric confinement and magnetic superconductors

Reinterpretation of the pioneering work of Nielsen and Olesen and others on magnetic confinement in (electric) superconductors leads to simple models which exhibit electric confinement of the type hoped for in quantum chromodynamics. “Electric” flux tubes joining “quarks” arise at a semi-classical level as a result of the existence of (pseudo) particles. The theory can be described in terms of a classical action principle only upon suitable modification of the action; this modification has profound topological significance as it is intimately related to the quantization condition for (pseudo) particles.     

First Cr(III)-SNS complexes and their use as highly efficient catalysts for the trimerization of ethylene to 1-hexene

Cr(III) complexes of tridentate SNS ligands have been prepared and evaluated as catalysts for ethylene trimerization, with several giving very high activity and excellent selectivity toward 1-hexene when activated with methylaluminoxane. The new complexes illustrate the potential of sulfur-based ligands on early transition metals for catalysis.     

Product measurements and fully symmetric measurements in qubit-pair tomography: A numerical study

State tomography on qubit pairs is routinely carried out by measuring the two qubits separately, while one expects a higher efficiency from tomography with highly symmetric joint measurements of both qubits. Our numerical study of simulated experiments does not support such expectations.     

Silver coordination polymers with remarkably high packing coefficients

Silver meso- and rac-tartrate and silver squarate have been synthesized, and the crystal structure of a new polymorph of the latter is reported. Three reaction products of these silver salts with pyrazine have been obtained and structurally characterized: From silver squarate, a chain polymer with linear coordination of Ag(I) by two pyrazine ligands is formed, whereas the silver tartrates yield solids in which the inner coordination sites around the metal are only partially occupied by N donors; in contrast to expectation, oxygen coordination prevails. All the four new Ag(I) coordination compounds reported show high packing coefficients in the range between 0.789 and 0.885. In order to put these results into a meaningful context, packing coefficients for the crystal structures of almost 30,000 compounds retrieved from the Cambridge Structural Database have been determined. Tartrates pack significantly closer than pyrazine complexes or metal-containing compounds in general. The exceptionally high packing coefficient of the new polymorph of silver squarate is due to stacking of anions and concomitant Ag···Ag contacts, both along the shortest lattice parameter which amounts to only 3.3990(9) ?.     

Insight into the chemical bonding and electrostatic potential: A charge density study on a quinazoline derivative

2,3-Trimethylene-3,4-dihydroquinazoline shares the heterocyclic core with natural compounds and synthetic drugs. The hydrochloride of the compound forms excellent dihydrate crystals which have allowed us to collect high-resolution X-ray diffraction data and obtain the experimental charge density. The solid may be understood as built up from pairs of heterocyclic cations and chloride anions; a direct hydrogen bond links the halide to the formally cationic pyrimidine NH group. The hydrate water molecules interact with the anions, forming an infinite chain along the crystallographic a axis between the stacks of the heterocyclic cations. Based on the experimental charge density, a dipole moment of 16.1 Debye is calculated for a pair of the hydrogen-bonded quinazolinium cation and the chloride anion in the extended crystal structure.