Determination of aliphatic amines in air by membrane enrichment directly coupled to a gas chromatograph

Summary A method is described for the determination of shortchain aliphatic amines in ambient air based on impinger sampling in dilute H₂SO₄, selective enrichment across a PTFE gas membrane and quantification by gas chromatography. The enrichment step is carried out in a flow system directly connected to the chromatograph. The separation is performed on a packed column with nitrogen selective detection. The enrichment per sample volume was in the range 7.3 to 8.2 mL^–1 for C₁–C₆ amines. Detection limits were ca 3–10 nM with enrichment of a 2.9 mL liquid sample. After impinger sampling of 5 m³ air in 10 mL absorption solution, this corresponds, to 0.4–0.8 ng/m³ (ca 0.2–0.5 ppt by volume) in air.     

Observation of paramagnetic lightscattering from EuO,EuS, Eu0.005Sr0.995S and Gd

We report on lightscattering from the thermal spin precession in paramagnets. The effect had for the first time been reported for CrBr₃, by Sandercock [1] but is now also observed in EuO, EuS, highly Sr diluted EuS and in metallic Gd. It is the same kind of phenomenon as usually studied by means of EPR-experiments where the spin precession is excited by means of microwave absorption. The lightscattering experiments senses the thermal motion of the spins. We have studied the effect as a function of decreasing temperature down into the ferrogmagnetic states of the samples.     

Pair interaction of dislocations in two-dimensional crystals

The pair interaction between crystal dislocations is systematically explored by analyzing particle trajectories of two-dimensional colloidal crystals measured by video microscopy. The resulting pair energies are compared to Monte Carlo data and to predictions derived from the standard Hamiltonian of the elastic theory of dislocations. Good agreement is found with respect to the distance and temperature dependence of the interaction potential, but not regarding the angle dependence where discrete lattice effects become important. Our results on the whole confirm that the dislocation Hamiltonian allows a quantitative understanding of the formation and interaction energies of dislocations in two-dimensional crystals.     

(Im-)possible ISOL beams

Refractory elements, i.e. elements with very high melting point and low vapor pressure, cannot be released in atomic form from an ISOL target. Therefore most of these elements are presently not available as ISOL beams. However, when reactive gases are introduced into the target, they may form volatile compounds with the refractory elements, allowing for an easier transport to the ion source. Particularly useful are high-temperature stable fluorides and oxides. By these chemical evaporation methods so far ISOL beams of the refractory elements C, Zr, Hf and Ta have been produced. We discuss how ISOL beams of B, Ti, Nb, Mo, Tc, Ru, W, Re, Os and Ir could be produced in a similar way.     

Solid‐State NMR Characterization of Wilkinson’s Catalyst Immobilized in Mesoporous SBA‐3 Silica

The Wilkinson’s catalyst [RhCl(PPh₃)₃] has been immobilized inside the pores of amine functionalized mesoporous silica material SBA‐3 and The structure of the modified silica surface and the immobilized rhodium complex was determined by a combination of different solid‐state NMR methods. The successful modification of the silica surface was confirmed by ²⁹Si CP‐MAS NMR experiments. The presence of the T_n peaks confirms the successful functionalization of the support and shows the way of binding the organic groups to the surface of the mesopores. ³¹P‐³¹P J‐resolved 2D MAS NMR experiments were conducted in order to characterize the binding of the immobilized catalyst to the amine groups of the linkers attached to the silica surface. The pure catalyst exhibits a considerable ³¹P‐³¹P J‐coupling, well resolvable in 2D MAS NMR experiments. This J‐coupling was utilized to determine the binding mode of the catalyst to the linkers on the silica surface and the number of triphenylphosphine ligands that are replaced by coordination bonds to the amine groups. From the absence of any resolvable ³¹P‐³¹P J‐coupling in off‐magic‐angle‐spinning experiments, as well as slow‐spinning MAS experiments, it is concluded, that two triphenylphosphine ligands are replaced and that the catalyst is bonded to the silica surface through two linker molecules.     

Darstellung und Kristallstruktur der Kupfer(I)-chalkogenolat-2,2′-Bipyridin-Komplexe [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 und [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2

Synthesis and Structure of Copper(I)Chalcogenolate-2,2′-Bipyridine Complexes [CuS(2,4,6-iPr₃C₆H₂)]₄(Bipy)₂ and [CuSe(2,4,6-iPr₃C₆H₂)]₂(Bipy)₂ The oligomeric homoleptical copper(I) chalcogenolate compounds [CuS(2,4,6-iPr₃C₆H₂)]_x=4,8 and [CuSe(2,4,6-iPr₃C₆H₂)]₆ react with 2,2′-bipyridine (Bipy) to yield the tetranuclear complex [CuS(2,4,6-iPr₃C₆H₂)]₄(Bipy)₂ ( 4 ) and the dinuclear complex [CuSe(2,4,6-iPr₃C₆H₂)]₂(Bipy)₂ ( 5 ). The structures of 4 and 5 were determined by X-ray analysis. In the eight-membered Cu₄S₄ core of 4 with chair conformation the copper atoms are linked by μ₂-bridging selenolate ligands. Only two copper atoms are coordinated by 2,2′bipyridine. The corresponding copper(I) selenolate complex ( 5 ) forms a folded four-membered Cu₂Se₂ ring with μ₂-bridging selenolate ligands. The Cu? Cu distance of 2.52 Å is relatively short. In contrast to the reaction performed with 2,2′-bipyridine, addition of phenantroline to 1 respectively 2 yields a dinuclear complex [CuS(2,4,6-iPr₃C₆H₂)]₂(Phen)₂ ( 10 ). NMR spectroskopic and cryoscopic measurement of 4 show that this complex dissociates into smaller fragments in solution which undergo rapid exchange reactions. However, corresponding investigations performed on 5 indicate that the solid state structure is maintained in solution. The electrochemical behaviour of 4, 5 and 10 was studied in CH₂Cl₂ and in any case no reversible redox processes could be observed.     

Thermodynamic and kinetic data for adduct formation, cis-trans isomerization and redox reactions of ML4 complexes: a case study with rhodium- and iridium-tropp complexes in d8, d9 and d10 valence electron configurations (tropp=dibenzotropylidene phosphanes)

The formation of adducts of the square-planar 16-electron complexes trans-[M(tropp(ph))(2)](+) and cis-[M(tropp(ph))(2)](+) (M=Rh, Ir; tropp(Ph)=5-diphenylphosphanyldibenzo[a,d]cycloheptene) with acetonitrile (acn) and Cl(-), and the redox chemistry of these complexes was investigated by various physical methods (NMR and UV-visible spectroscopy, square-wave voltammetry), in order to obtain some fundamental thermodynamic and kinetic data for these systems. A trans/cis isomerization cannot be detected for [M(tropp(ph))(2)](+) in non-coordinating solvents. However, both isomers are connected through equilibria of the type trans-[M(tropp(ph))(2)](+)+L<==>[ML(tropp(ph))(2)](n)<==>cis-[M(tropp(ph))(2)](+)+L, involving five-coordinate intermediates [ML(tropp(ph))(2)](n) (L=acn, n=+1; L=Cl(-), n=0). Values for K(d) (K(f)), that is, the dissociation (formation) equilibrium constant, and k(d) (k(f)), that is, the dissociation (formation) rate constant, were obtained. The formation reactions are fast, especially with the trans isomers (k(f)>1x10(5) m(-1) s(-1)). The reaction with the sterically more hindered cis isomers is at least one order of magnitude slower. The stability of the five-coordinate complexes [ML(tropp(ph))(2)](n) increases with Ir>Rh and Cl(-)>acn. The dissociation reaction has a pronounced influence on the square-wave (SW) voltammograms of trans/cis-[Ir(tropp(ph))(2)](+). With the help of the thermodynamic and kinetic data independently determined by other physical means, these reactions could be simulated and allowed the setting up of a reaction sequence. Examination of the data obtained showed that the trans/cis isomerization is a process with a low activation barrier for the four-coordinate 17-electron complexes [M(tropp(ph))(2)](0) and especially that a disproportionation reaction 2 trans/cis-[M(tropp(ph))(2)](0)-->[M(tropp(ph))(2)](+)+[M(tropp(ph))(2)](-) may be sufficiently fast to mask the true reactivity of the paramagnetic species, which are probably less reactive than their diamagnetic equilibrium partners.     

Mikrochemie

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