Two-dimensional crystallization: self-assembly, pseudopolymorphism, and symmetry-independent molecules

The self-assembly of a series of 1,3-disubstituted benzenes has been scrutinized by scanning tunneling microscopy (STM) and computational modeling. Small changes in the functional groups (e.g., ester, thioester, ketone) resulted in dramatic changes in packing patterns. Remarkably, several of the molecules gave rise to monolayers with more than one molecule in the asymmetric unit and displayed multiple packing patterns. This constitutes the most complex behavior observed to date in this type of monolayer and illuminates several issues of importance in three-dimensional crystallization. Intermolecular interactions associated with the observation of multiple molecules in the asymmetric unit and stabilization of pseudopolymorphs were identified. The geometry and electrostatic properties of the isolated molecule and monolayer density were found to be critical in determining which packing motif was adopted.     

Synthese,Kristallstruktur, Elektronenstruktur,spektroskopische und magnetische Eigenschaften von [VOCl2{P(SiMe3)3}2]: Ein Phosphankomplex mit fehlgeordneter VOCl2-Einheit

Synthesis, Crystal Structure, Electronic Structure, Spectroscopic and Magnetic Properties of [VOCl₂{P(SiMe₃)₃}₂]: A Phosphane Complex with a Disordered VOCl₂ Group VOCl₃ reacts with P(SiMe₃)₃ to form blue green crystals of [VOCl₂{P(SiMe₃)₃}₂] ( 1 ). The X-ray crystal structure analysis of 1 (cubic space group P2₁3: a = 1541.4(1) pm, Z = 4) reveals a slightly distorded trigonal bipyramidal coordination environment for the disordered vanadium(IV) center. Density functional calculations on the compound [VOCl₂{P(SiH₃)₃}₂] ( 2 ) are in accord with this observation. 1 has been characterized by ESR, vibrational (IR and Raman) and electronic absorption spectroscopy and magnetic measurements. The ESR spectra of 1 in a toluene solution (293 K and frozen solution at 6 K) exhibit hyperfine interactions of the unpaired electron with the ⁵¹V center (I = 7/2) and the ³¹P centers (I = 1/2) of the two equivalent phosphane ligands. The ligand-field transitions of the VOCl₂{P}₂ chromophore observed in the electronic absorption spectrum have been assigned on the basis of density functional calculations on 2 .     

Synthese und Struktur eines zweikernigen Gadolinium(III)-Komplexes: Magnetische Austauschwechselwirkungen in alkoxyverbrückten Komplexen der Lanthanoiden

Synthesis and Structure of a Binuclear Gadolinium(III) Complex: Magnetic Exchange Interactions in Alkoxy Bridged Lanthanide Complexes The Schiff Base ligand N-salicylidene-2-(bis-(2-hydroxyethyl)amino)ethylamine (H₃sabhea) reacts with Gd(NO₃)₃ · 6 H₂O in methanol solution to yield the alkoxy bridged binuclear gadolinium(III) complex [{Gd(Hsabhea)(NO₃)}₂] · 2MeOH ( 1 ). 1 crystallizes in the monoclinic space group P2₁/c with a = 1014.8(2), b = 2059.2(4), c = 867.5(2) pm, β = 106.72(2)°, and Z = 2. The two gadolinium atoms are bridged by two alkoxide oxygen atoms with angles of 107.60(11)° at the oxygen bridgeheads and a Gd? Gd separation of 376.43(7) pm. A variable-temperature magnetic susceptibility study (2 to 280 K) of 1 revealed an antiferromagnetic coupling between the Gd(III) ions with J = ?0.198 cm^?1 (g = 1.975).     

The status of the Super-FRS at FAIR

The Super-FRS will be a large-acceptance two-stage superconducting fragment separator with three exit branches serving different experimental areas. Due to the high primary-beam intensity of up to 10¹² ions/s a challenging design of the target area and the components used in the first dipole Super-FRS is necessary. These efforts include high-power production targets, beam-dumps to catch the remaining primary beam, and radiation resistant magnets. In this contribution we summarize the recent developments on these issues.     

Capacitance humidity sensor with carbon nitride detecting element

The humidity sensitive properties of carbon nitride (CN_x) films deposited by two methods, inductively coupled plasma chemical vapour deposition utilizing transport reactions and pulsed laser deposition combined with an rf discharge, have been investigated. For this purpose capacitance humidity sensors with a CN_x detecting element have been fabricated and tested. Fast and significant responses toward moisture are registered by the changes of the electrical parameters. The CN_x films sensing mechanism has been discussed. The results obtained show unambiguously that CN_x films appear to be a promising candidate as a humidity sensitive element in up-to-date electronic noses. Received: 6 December 1999 / Accepted: 7 January 2000 / Published online: 24 March 2000