H. Rabah et al., MOSSBAUER STUDY AND MOLECULAR-ORBITAL CALCULATIONS ON SOME BIMETALLICDERIVATIVES OF FERROCENE AND FERRICINIUM, Hyperfine interactions, 77(1-2), 1993, pp. 51-66
We have studied by absorption Mossbauer spectroscopy, some bridged der
ivatives of biferrocene, unoxidized (Fe(II)-Fe(II)) and mono-oxidized
(Fe(II)-Fe(III)). The mixed-valence species exhibits a quasi-delocaliz
ed behavior at the Mossbauer timescale (approximately 10(-8) s), with
a splitting of the lines which is interpreted in terms of a partial va
lence trapping. This in turn reveals intramolecular properties at vari
ance from those of the unbridged cation. SCC-Xalpha MO calculations ha
ve been performed; they correctly reproduce the measured quadruple spl
ittings and provide evidence that the HOMO of the mixed-valence comple
x is of d(xy), d(x2-y2) type. Some consequences on the mixed-valence p
roperties are discussed.