Isostructural triazenido complexes of first row transition metals. Part 1. Synthesis and properties of (η5-C5H5)(L)(RN3R) FeII,L = PPh3, P(OMe)3, P(OPh)3 or CO

Summary The complexes ( ⁵-C₅H₅)L(RN₃R)Fe, where L = PPh₃, P(OMe)₃, P(OPh)₃ or CO and R,R=p-MeC₆H₄ orp-ClC₆H₄, have been prepared by reaction of suitable iron halides with Ag(RN₃R). The mechanism of formation of the Fe(RN₃R) group is thought to involve, initially, an Fe-Ag bond. The bonding mode of the triazenido ligand is chelating in a six coordinate configuration. The spectroscopic results are discussed in relation to variations in the environment of the metal atom.     

Ab initio Calculations on the thermal ring closure of acrolein

The electrocyclic reaction which interconverts acrolein and oxetene is investigated by ab initio calculations, using a 4-31G basis set. Like the transition state of the thermal ring closure of cisbutadiene, the transition state of this reaction shows a torsion of about 18 ° around the central bond, in spite of the absence of H-H repulsion. The resulting oxetene is 43 kcal/mol endothermic with regard to acrolein. The calculated activation energies for ring closure and -opening are 3.4 and 1.0 eV. The conformational result of the ring opening reaction is discussed.     

Dynamic modulation transfer function: a method to characterize the temporal performance of liquid-crystal displays

A method to measure the dynamic modulation transfer function (DMTF) of a liquid-crystal display (LCD) is proposed to characterize its performance when rendering motion images. The method includes a measurement system to capture the temporal luminance variation of a LCD while using a well-designed input data sequence and a simulation model based on smooth pursuit eye tracking and temporal light integration at the human retina. It predicts the perceived performance of a moving sine wave pattern on a LCD and subsequently calculates the DMTF. With this approach, several technologies to reduce motion blur were evaluated and discussed.     

Retrieving the elastodynamic Green's function of an arbitrary inhomogeneous medium by cross correlation

A correlation-type reciprocity theorem is used to show that the elastodynamic Green's function of any inhomogeneous medium (random or deterministic) can be retrieved from the cross correlation of two recordings of a wave field at different receiver locations at the free surface. Unlike in other derivations, which apply to diffuse wave fields in random media or irregular finite bodies, no assumptions are made about the diffusivity of the wave field. In a second version, it is assumed that the wave field is diffuse due to many uncorrelated sources inside the medium.     

Ligand exchange reactions between copper(II)- and nickel(II)- chelates of different sulphur- and selenium-containing ligandsIII: Single-crystal ESR study on the mixed-ligand chelate (n-Bu4N) [63Cu(mnt) (et2dsc)] and crystal and molecular structure of (n-Bu4N) [Ni(mnt) (et2dsc)]

A single-crystal ESR study of the mixed-ligand complex tetra - n - butylammonium - (maleonitriledithiolato)(diethyl - di - selenocarbamato)cuprate(II) diamagnetically diluted by the corresponding Ni(II) complex, and the crystal and molecular structure of the host complex determined by a single-crystal X-ray diffraction study, is reported. (n-Bu₄N)[Ni(mnt)(et₂dsc)] is monoclinic, space group C2/c, with eight molecules in the unit cell; a = 19.932(9) Å, b = 9.597(3) Å, c = 37.580(13) Å and β = 101.32(3)°. Based on the structure the spin Hamiltonian parameters have been calculated from the results of extended Hückel molecular orbital calculations and compared with the experimentally obtained values. The principal axes of the g? and the metal hyperfine tensor do not coincide reflecting the large influence of the et₂dsc^? ligand for which this behaviour was found to be typical. A comparison between the ESR parameters and the Mulliken spin densities of the mixed-ligand chelate and the corresponding parent complexes shows that in the former one spin density appears to be transfered from the S atoms to the Se atoms of the et₂dsc^? part of the complex resulting in an increased CuSe covalency. Back-bonding effects were considered in discussing the bonding properties.     

Application of HPLC column-switching in pesticide residue analysis

Summary An overview is given of the applicability of HPLC with column-switching in pesticide residue analysis. The main advantage of HPLC with column-switching is the enhancement of both sensitivity and selectivity combined with a high potential for automation. The selection of optimal conditions such as column dimensions, mobile phase compositions and multi step gradient elution is discussed.