Bonding, Hyperfine Interactions, and Lattice Dynamics of Cationic and Neutral Ferrocenyl-Substituted Allylic and Cumulenic Compounds

The synthesis and spectroscopic characterization (by mass,
UV−visible, IR, NMR and 57Fe Mössbauer
spectroscopy)
of three new compounds related to seven recently published
ferrocenyl-substituted allylic and cumulenic compounds
are reported and have made it possible to effect a systematic
evaluation of the parameters extractable from
temperature-dependent γ ray resonance studies. For the neutral
species, the hyperfine parameters (IS and QS) of
the σ-bonded ferrocenyl groups are insensitive to the structural
details of the allylic or cumulenic carbon framework.
The temperature dependence of the recoil-free fraction is
dominated by the Cp ring−iron atom interaction, and
is not diagnostic of the detailed molecular architecture. In the
case of the carbocationic complexes, two distinct
iron sites are resolvable from the Mössbauer data. The
detailed temperature-dependent behavior of the hyperfine
parameters and recoil-free fraction for 10 complexes with either
equivalent termini, linked by similar, but different
types of bridges (neutral 1−5), or with
inequivalent moieties linked by related or identical connectors
(cationic
6−10), has been elucidated over the temperature
range 90 ≤ T ≤ 300 K. An X-ray crystallographic study
of
(R,S)-ferroceno[2,3-a]inden-1-one
proved the racemic nature of this progenitor of compound
10:  monoclinic,
P21/c, a =
9.29.3(2) pm, b = 1083.7(2) pm, c =
1345.7(3) pm, β = 108.41(3), V =
1.2859(5) nm3, Z = 4,
R(Fo)
= 0.0574, Rw
(Fo2) = 0.1394.