Dearomatization and functionalization of terpyridine by lutetium(III) alkyl complexes

Lutetium(III)-bis(alkyl) and -tris(alkyl) fragments supported by either 2,2':6',2' '-terpyridine or 4,4',4' '-tri-tert-butyl-2,2':6',2' '-terpyridine are not stable and undergo facile 1,3-alkyl migration under ambient conditions resulting in dearomatization and ortho (2' or 6') functionalization of the terpyridyl ligand, clearly demonstrating that the terpyridyl ligand framework is not as innocent as previously thought.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.     

Cation–Cation Interactions,Magnetic Communication,and Reactivity of the Pentavalent Uranium Ion [U(NtBu)2]+

Communication is important : The dimeric bis(imido) uranium complex [{U(NtBu)₂(I)(tBu₂bpy)}₂] (see picture; U green, N blue, I red) has cation–cation interactions between [U(NR)₂]⁺ ions. This f¹–f¹ system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.

     

Enhancing the reactivity of uranium(VI) organoimido complexes with diazoalkanes

Diphenyldiazomethane effects a two-electron oxidation of the uranium(IV) monoimido complex (C5Me5)2U(=N-2,4,6-t-Bu3C6H2) to give the uranium(VI) mixed bis(imido) complex, (C5Me5)2U(=N-2,4,6-t-Bu3C6H2)(=N-N=CPh2), which undergoes a rare cyclometallation reaction upon mild thermolysis to afford a uranium(IV) bis(amide) complex that results from net addition of a C-H bond of an ortho tert-butyl group across the N=U=N core.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.