In this perspective, we highlight the issue of meridional (mer) and facial (fac) orientation of asymmetrical diimines in tris-chelate transition metal complexes. Diimine ligands have long been the ...workhorse of coordination chemistry, and whilst there are now good strategies to isolate materials where the inherent metal centered chirality is under almost complete control, and systematic methodologies to isolate heteroleptic complexes, the conceptually simple geometrical isomerism has not been widely investigated. In systems where the two donor atoms are significantly different in terms of the σ-donor and π-accepting ability, the fac isomer is likely to be the thermodynamic product. For the diimine complexes with two trigonal planar nitrogen atoms there is much more subtlety to the system, and external factors such as the solvent, lattice packing and the various steric considerations play a delicate role in determining the observed and isolable product. In this article we discuss the possibilities to control the isomeric ratio in labile systems, consider the opportunities to separate inert complexes and discuss the observed differences in their spectroscopic properties. Finally we report on the ligand orientation in supramolecular systems where facial coordination leads to simple regular structures such as helicates and tetrahedra, but the ability of the ligand system to adopt a mer orientation enables self-assembled structures of considerable beauty and complexity.
A series of cationic rhodium(I) and iridium(I) complexes of the type M(Lsymbol: see textL)(C2)BAr(F)24 (where M = Rh or Ir, Lsymbol: see textL = bis(pyrazol-1-yl)methane (bpm), ...bis(N-methylimidazol-2-yl)methane (bim) or 1-(2-(diphenylphosphino)ethyl)-3,5-diphenylpyrazole (Ph2PyP), C2 = 1,5-cyclooctadiene (COD) or (CO)2 and BAr(F)24 = tetrakis3,5-bis(trifluoromethyl)phenylborate) were synthesised in good yields. The solid-state structure of a number of complexes, including Ir(Ph2PyP)(COD)BAr(F)24, Ir(bpm)(COD)BAr(F)24 and Ir(bim)(COD)BAr(F)24 was determined using X-ray crystallography. The efficiency of the complexes as catalysts for the intramolecular hydroamination of 4-phenyl-3-butyn-1-amine, 4-pentyn-1-amine and 2-(2-phenylethynyl)aniline was established. The incorporation of the BAr(F)24- counter-ion in the Rh(I) and Ir(I) complexes was found to significantly improve the catalytic activity of the complexes, compared to the analogous Rh(I) and Ir(I) complexes containing BPh4- as the counter-ion. Excellent conversions were achieved for the cyclisation of 2-(2-phenylethynyl)aniline to 2-phenylindole using Rh(bpm)(CO)2BAr(F)24 as a catalyst. The use of a microwave reactor for enhancing the catalysed reactions was also investigated.
The methylhydrazine complex Ru(NH2NHMe)(PyP)2Cl(BPh4) (PyP=1‐2‐(diphenylphosphino)ethylpyrazole) was synthesised by addition of methylhydrazine to the bimetallic complex Ru(μ‐Cl)(PyP)22(BPh4)2. The ...methylhydrazine ligand of the ruthenium complex has two different binding modes: side‐on (η2‐) when the complex is in the solid state and end‐on (η1‐) when the complex is in solution. The solid‐state structure of Ru(PyP)2(NH2NHMe)Cl(BPh4) was determined by X‐ray crystallography. 2D NMR spectroscopic experiments with 15N at natural abundance confirmed that in solution the methylhydrazine is bound to the metal centre by only the ‐NH2 group and the ruthenium complex retains an octahedral conformation. Hydrazine complexes RuCl(PyP)2(η1‐NH2NRR′)OSO2CF3 (in which R=H, R′=Ph, R=R′=Me and NRR′=NC5H10) were formed in situ by the addition of phenylhydrazine, 1,1‐dimethylhydrazine and N‐aminopiperidine, respectively, to a solution of the bimetallic complex Ru(μ‐Cl)(PyP)22(OSO2CF3)2 in dichloromethane. These substituted hydrazine complexes of ruthenium were shown to exist in an equilibrium mixture with the bimetallic starting material.
Monodentate, bidentate or both? The first example of an η2‐hydrazine complex of ruthenium is described (see figure). The binding mode of the methylhydrazine ligand is dependent on whether the complex is in solution or the solid state.
A module of the ATLAS electromagnetic barrel liquid argon calorimeter was exposed to the CERN electron test-beam at the H8 beam line upgraded for precision momentum measurement. The available ...energies of the electron beam ranged from 10 to 245
GeV. The electron beam impinged at one point corresponding to a pseudo-rapidity of
η
=
0.687
and an azimuthal angle of
φ
=
0.28
in the ATLAS coordinate system. A detailed study of several effects biasing the electron energy measurement allowed an energy reconstruction procedure to be developed that ensures a good linearity and a good resolution. Use is made of detailed Monte Carlo simulations based on GEANT4 which describe the longitudinal and transverse shower profiles as well as the energy distributions. For electron energies between 15 and 180
GeV the deviation of the measured incident electron energy over the beam energy is within 0.1%. The systematic uncertainty of the measurement is about 0.1% at low energies and negligible at high energies. The energy resolution is found to be about 10%
·
E
for the sampling term and about 0.2% for the local constant term.
Electronics calibration board for the ATLAS liquid argon calorimeters Colas, J.; Dumont-Dayot, N.; Marchand, J.F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2008, Letnik:
593, Številka:
3
Journal Article
Recenzirano
To calibrate the energy response of the ATLAS liquid argon calorimeter, an electronics calibration board has been designed; it delivers a signal whose shape is close to the calorimeter ionization ...current signal with amplitude up to 100
mA in 50
Ω with 16
bit dynamic range. The amplitude of this signal is designed to be uniform over all calorimeters channels, stable in time and with an integral linearity much better that the electronics readout. The various R&D phases and most of the difficulties met are discussed and illustrated by many measurements. The custom design circuits are described and the layout of the ATLAS calibration board presented. The procedure used to qualify the boards is explained and the performance obtained illustrated: a dynamic range up to 3
TeV in three energy scales with an integral linearity better than 0.1% in each of them, a response uniformity better than 0.2% and a stability better than 0.1%. The performance of the board is well within the ATLAS requirements. Finally, in situ measurements done on the ATLAS calorimeter are shown to validate these performances.
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