M. M. Timoshenko

Study of redox reactions of bis(arene) chromium complexes by the rotating disk electrode technique. IV: Electrochemical oxidation and ionization potentials of bis(arene) chromium complexes

Abstract The reversible electrochemical oxidation of a series of bis(arene)chromium com-plexes has been studied by use of the rotating disk electrode technique The half-wave potentials E 1/2 show an excellent correlation with the meta -substituent constants. The E 1/2 values were found to correlate well with the vertical ionization potentials ( IP ) of the same complexes in the gas phase determined from their He(I) photoelectronic spectra.

Electronic structure of bis-arene-chromium complexes

Abstract Dibenzenechromium derivatives of the type (C 6 H 5 R 1 )Cr(C 6 R 5 R 2 ) have been studied by He-I photoelectron spectroscopy. Substituent parameters have been found which allow the first and second ionization potentials of the bis-arene-chromium complexes to be determined using a very precise additive scheme. It has been shown that the change in the energy of the highest occupied MOs of the molecules is determined by the electrostatic field of ligands. The molecular electrostatic potentials of a number of species (C 6 H 5 R 1 )(C 6 H 5 R 2 ) have been calculated and the equation relating IP to ϕ( R ) has been found. A scheme for constructing the energy level diagram for dibenzenechromium and its derivatives is suggested.

Photoelectron spectra and the structure of organomercury compounds

The He(I) photoelectron spectra of 30 organomercury compounds of different structural types and of some model organic compounds were investigated. Also the values of vertical ionization potentials (IP) of highest occupied molecular orbitals (HOMO) were determined. Several relationships were studied in IP in this series of compounds. A method was developed to separate the contributions of electron effects to changes in the IP of HOMO. The induction effects of HgCl and CH2HgCl groups as well as the effect of σ(CHg), π-conjugation in the alkene and benzyl derivatives of mercury were estimated. The influence of structural and other factors on the magnitude of this effect was studied.

Investigation of the mechanism of fragment coordination of aromatic molecules with transition metals by photoelectron spectroscopy-tricarbonyliron complexes

ConclusionsThe changes in the chemical shifts of organic molecules during complex formation are well known in organometallic chemistry [24]. Thus, coordinated dienes lose the olefinic characteristics; they are not hydrogenated, do not enter into the Diels-Alder reaction, and react with electrophilic reagents. At the present time the search for a link between the structure of organometallic complexes in terms of rigorous quantum-chemical calculations is beginning. The construction of experimentally substantiated models which make it possible to explain qualitatively the marked changes in the characteristics of organic compounds in the presence of the atoms of transition metals is therefore essential for a deeper understanding of the orbital mechanisms lying at the basis of catalysis.The PE spectra were measured on an ÉS 3201 electron spectrometer with an inlet system heated to 200°C. The resolution, determined from the width of the2P3/2Xe band at the half-height, amounted to 40 meV. Compounds (II) and (III) were obtained by the previously described methods [25, 26], and the analytically pure substances were used for the investigation.

Electronic structure of benzenechromium tricarbonyl derivatives: The loss of conjugation between the π-aromatic system and the substituent of the coordinated ligand

ConclusionsA study of the photoelectron spectra of benzenechromium tricarbonyl derivatives indicates the virtually complete loss of conjugation between the π-aromatic system and the substituent of the coordinated ligand.

He(I) Photoelectronic spectrum of cyclopentadienylmercury chloride

Conclusions1.The He(I) photoelectronic spectrum of C5H5HgCl was studied.2.The effectiveσ,π interaction of theσ-MO of the C-Hg bond and the 2b1-π-MO leads to a change in their energies (an increase for the first and a decrease for the second) by 0.85 eV, which within the framework of the theory of MO perturbation corresponds to a perturbation operator value of P(σ, π)=1.01 eV, whi is close to that found for allylmercury chloride.

He(I) photoelecteonic spectra of organic compounds with a mercury atom attached to AN sp2-hybeidized carbon

ConclusionThe He (I) photoelectronic spectra of some organomercury compounds of the vinyl type were studied and the nature of the electronic effects in these molecules was discussed.