2g Electrons Research Articles

The electronic spectrum of μ-oxo-bis[pentammine chromium(III)] ion

The single crystal polarized spectra of μ-oxo-bis[pentammine chromium(III)] chloride and perchlorate salts are measured over the temperature range 300 to 8 K. All sharp bands are predominantly z polarized where z is the CrOCr axis. The sharp and intense near ultraviolet absorptions are assigned as symmetric double excitations of t 2g electrons allowed through a vibronically exhange — induced electric dipole mechanism. This new mechanism can explain the observed z polarization, temperature-independent intensity and relatively high values of the oscillator strengths, f ≈ 10 −4−10 −3. The pair energies calculated from H= ∑ ikj1 J a( ik)b( jl) 5a( ik) .5b( jl) do not agree with the observed values

Mixed-valence ferrocene systems temperature dependence in the mössbauer spectra of [Fe(II)Fe(III) [1.1] ferrocenophanes

57Fe Mössbauer spectra (300 and 4.2°K) have been determined for dioxidized [Fe(III)Fe(III)] biferrocenylene; a large quadrupole splitting (2.89 mm/sec at 300°K) was interpreted in terms of extensive delocalization of e 2g electrons resultant from an FeFe bonding interaction. Mössbauer and electronic absorption spectra have also been determined for two mono-oxidized [1.1] ferrocenophanes. Temperature dependence is noted in the [Fe(II)Fe(III)] ferrocenophane Mössbauer spectra and is tentatively associated with a phase transition wherein the FeFe distance is changed to permit greater FeFe exchange interaction.

A MÖSSBAUER STUDY OF A SERIES OF RUTHENIUM(II) PENTAAMINES

Abstract The Mossbauer spectra of a series of ruthenium(II) pentaammines were obtained at 4.2°K. The trends in isomer shift and quadrupole splitting parameters can be related to the relative delocalization of the ruthenium t 2g electrons (“back bonding”) by the ligand X in the complexes, [Ru(NH3)5X]4n . The delocalization associated with the CO ligand is shown to be significantly greater than that for the N2 ligand in this series of complexes.

The Jahn-Teller effect in ReF6

Calculations on the strength of the Jahn-Teller effect in ReF6 (d1) on the basis of a purely electrostatic interaction between the fluorine atoms and the non-bonding t 2g electron predict a large v 2 splitting in the Raman spectrum (130–200 cm)-1 and a small tetragonal distortion of the molecule (∼ 0·005 a).