The preparation and characterization of the π-cation
radical derivatives of [Fe(OEP)(X)] (X =
Cl-, Br-) is reported.
Three different derivatives have been prepared:
[Fe(OEP•)(Cl)]ClO4,
[Fe(OEP•)(Cl)][SbCl6], and
[Fe(OEP•)(Br)][SbCl6]. All derivatives have been characterized by
UV−vis, IR, and Mössbauer spectroscopy. In
addition,
[Fe(OEP•)(Cl)]ClO4 has been
characterized by a single-crystal structure determination, and
[Fe(OEP•)(Cl)][SbCl6]
and [Fe(OEP)(Br)][SbCl6] have been
studied by temperature-dependent magnetic susceptibility
measurements
and Mössbauer measurements in an applied magnetic field. The
X-ray structure of
[Fe(OEP•)(Cl)]ClO4
reveals
a five-coordinate porphyrinate species that forms tight cofacial
π−π dimers in which the two porphyrin rings are
almost exactly overlapped with an inter-ring separation of 3.24 Å, a
lateral shift of 0.2 Å, and a twist angle
between the two rings of 31.2°; the two iron atoms are 4.112 Å
apart. Crystal data:
C37H46FeCl4O4N4,
a =
27.454(7) Å, b = 15.322(3) Å, c =
19.802(3) Å, β = 116.14 (2)°, monoclinic,
C2/c, Z = 8. Iron(III) is
found
to be in the high-spin state in all derivatives. The magnetic data
(susceptibility and Mössbauer) have been interpreted
in terms of two spin coupling models. Both models give a picture
of strong coupling between the various spins
in the dimeric species. In the model judged to best fit all data
with a physically meaningful zero-field splitting,
there are three terms in the total Hamiltonian: an axial zero-field
splitting parameter D for the high-spin iron,
an
intramolecular antiferromagnetic coupling
−2J
Fe
-
r(S⃗·s⃗)
between the iron spin S = 5/2 and
the π-cation radical s
= 1/2 spin, and an intermolecular
antiferromagnetic coupling
−2J
R
-
R(S⃗
+ s⃗)·(S⃗‘ +
s⃗‘) between the total spins on
each half of the dimer.
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