Chloroiron meso-triphenylcorrolates: Electronic ground state and spin delocalization

Article abstract of DOI:10.1016/S0020-1693(02)00929-5

Four chloroiron meso-triphenyl-substituted corrolates have been synthesized and studied by ¹H NMR spectroscopy. As in the case of the β-pyrrole-octaalkylcorrolatoiron chloride complexes studied previously [Inorg. Chem. 39 (2000) 3466], these complexes were also found to be S=3/2 Fe(III) corrolate(^2-·) π-cation radical species, where the macrocycle radical electron is antiferromagnetically coupled to the metal electrons to give an overall S=1 complex. This conclusion is based upon the large alternating-sign contact shifts observed for the meso-phenyl protons. The ¹H isotropic shifts of the pyrrole-H of these chloroiron-triphenylcorrolate complexes are similar to those of the chloroiron tri-(pentafluorophenyl)corrolate complex reported previously and said to be a S=1 Fe(IV) complex bound to a simple corrolate(^3-) ligand [Inorg. Chem. 39 (2000) 2704]. The ¹⁹F NMR spectrum of the latter complex shows that it has small (negative) phenyl-F isotropic shifts for all phenyl-F, which might suggest that this single compound has a different electronic structure than all other chloroiron corrolates investigated thus far. However, there have as yet been very few NMR investigations of paramagnetic metal macrocycles having fluorine substituents, and thus it is premature to conclude that the small phenyl-F isotropic shifts are definitive proof of small spin density at the meso positions of the corrolate ring. It is concluded that pyrrole-H chemical shifts alone cannot differentiate the two possible electron configurations, simple S=1 Fe(IV) (Corr^3-) and antiferromagnetically coupled S=3/2 Fe(III) (Corr^2-·), and that based on the ¹H investigations reported in this and two previous papers, all chloroiron corrolates reported thus far, with the exception of one, have the electron configuration S=3/2 Fe(III) (Corr^2-·), in which the corrolate unpaired electron is antiferromagnetically coupled to the three metal electrons, yielding an overall spin for the complex, S=1. The electron configuration of the one exception, the strongly electron-withdrawing tri-(pentafluorophenyl)corrolate complex of iron chloride, cannot as yet be definitively assigned.

Full text of DOI:10.1016/S0020-1693(02)00929-5

Inorganica Chimica Acta 339 (2002) 171ꢂ178
/
www.elsevier.com/locate/ica
Chloroiron meso-triphenylcorrolates: electronic ground state and spin
delocalization
Sheng Cai a, Silvia Licoccia b, Cadia D’Ottavi b, Roberto Paolesse b, Sara Nardis b,
Ve´ronique Bulach c, Bertrand Zimmer c, Tatjana Kh. Shokhireva a, F. Ann Walker a,*
a Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, USA
b Dipartimento di Scienze e Tecnologie Chimiche, Universita´ di Roma Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy
c Universite´ Louis Pasteur, Laboratoire de Chimie de Coordination Organique, Institut Le Bel, 67000 Strasbourg, France
Received 6 November 2001; accepted 1 February 2002
Abstract
1
Four chloroiron meso-triphenyl-substituted corrolates have been synthesized and studied by H NMR spectroscopy. As in the
case of the b-pyrrole-octaalkylcorrolatoiron chloride complexes studied previously [Inorg. Chem. 39 (2000) 3466], these complexes
were also found to be Sꢀ
antiferromagnetically coupled to the metal electrons to give an overall Sꢀ
alternating-sign contact shifts observed for the meso-phenyl protons. The 1H isotropic shifts of the pyrrole-H of these chloroironꢂ
triphenylcorrolate complexes are similar to those of the chloroiron tri-(pentafluorophenyl)corrolate complex reported previously
and said to be a Sꢀ
1 Fe(IV) complex bound to a simple corrolate(3ꢁ) ligand [Inorg. Chem. 39 (2000) 2704]. The 19F NMR
/
3/2 Fe(III) corrolate(2ꢁ+) p-cation radical species, where the macrocycle radical electron is
/1 complex. This conclusion is based upon the large
/
/
spectrum of the latter complex shows that it has small (negative) phenyl-F isotropic shifts for all phenyl-F, which might suggest that
this single compound has a different electronic structure than all other chloroiron corrolates investigated thus far. However, there
have as yet been very few NMR investigations of paramagnetic metal macrocycles having fluorine substituents, and thus it is
premature to conclude that the small phenyl-F isotropic shifts are definitive proof of small spin density at the meso positions of the
corrolate ring. It is concluded that pyrrole-H chemical shifts alone cannot differentiate the two possible electron configurations,
simple Sꢀ
reported in this and two previous papers, all chloroiron corrolates reported thus far, with the exception of one, have the electron
configuration Sꢀ
3/2 Fe(III) (Corr2ꢁ+), in which the corrolate unpaired electron is antiferromagnetically coupled to the three metal
electrons, yielding an overall spin for the complex, Sꢀ1. The electron configuration of the one exception, the strongly electron-
/
1 Fe(IV) (Corr3ꢁ) and antiferromagnetically coupled Sꢀ3/2 Fe(III) (Corr2ꢁ+), and that based on the 1H investigations
/
/
/
withdrawing tri-(pentafluorophenyl)corrolate complex of iron chloride, cannot as yet be definitively assigned.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Iron complexes; Corrolate complexes
1. Introduction
states for coordinated metal ions [1], and/or the possi-
bility of stabilizing a one-electron oxidized macrocycle
[2]. We have reported NMR and EPR spectroscopic
studies of two chloroiron octaalkylcorrolates ([(Me8-
Corr)FeCl] and [(7,13-Me2Et6Corr)FeCl]) and their bis-
imidazole complexes [2], as well as their complex
formation with, and autoreduction by, cyanide ion [3].
The results of these studies have shown unambiguously
that these five- and six-coordinate iron corrolates are
actually iron(III) corrolate(2ꢁ+) p-cation radicals [2,3],
and that axial ligands such as cyanide can readily
autoreduce the corrolate radical, leaving a low-spin
Fe(III) cyanide complex [3]. The nature of the magnetic
Corroles are tetrapyrrole macrocycles that are related
to porphyrins, except that they lack one meso-carbon,
and, in order to retain the same number of p electrons,
are thus, when fully deprotonated, trianionic ligands for
transition metal ions. They have unique properties,
including the capability of maintaining a planar con-
formation, the possibility of stabilizing high oxidation
* Corresponding author. Tel.: ꢃ
9300
E-mail address: awalker@u.arizona.edu (F. Ann Walker).
/
1-520-621 8645; fax: ꢃ1-520-626
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 9 2 9 - 5

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S. Cai et al. / Inorganica Chimica Acta 339 (2002) 171ꢂ178
/
coupling between the unpaired electrons on the metal
and the corrolate(2ꢁ+) p-cation radical differs, depend-
ing on the axial ligand(s) present, with very strong
antiferromagnetic coupling in the case of the chloride
complexes [2], but weak ferromagnetic coupling in the
case of the imidazole complexes [2], and much stronger
yield. UVꢂ
45 000), 504 (o 11 000) nm. LR MS (FAB): m/z 615
(Mꢃ). (TPCorr)FeClO4: 85% yield. UVꢂ
Vis: lmax 357
(o 37 000), 420 (o 45 000), 518 (o 12 000) nm. LR MS
(FAB): m/z 579 (Mꢃ Ã
ClO4). [T(4-NO2P)Corr]FeCl:
UVꢂVis: lmax 371 (o 35 000), 406 (o 47 000), 508 (o
10 000) nm. 63% yield. LR MS (FAB): m/z 750 (Mꢃ).
[T(4-MeOP)Corr]FeCl: UVꢂVis: lmax 361 (o 32 000),
410 (o 44 000), 511 (o 11 000) nm. 68% yield. LR MS
(FAB): m/z 705 (Mꢃ). NMR data are given in Table 1.
All samples for NMR spectroscopic experiments were
prepared in 5 mm NMR tubes in CD2Cl2 (Cambridge)
without degassing. 1H NMR spectra were obtained over
/
Vis: lmax 357 (o 36 000 Mꢁ1 cmꢁ1), 409 (o
/
/
/
ferromagnetic coupling in the case of the bisꢂcyanide
/
complex, [(7,13-Me2Et6Corr)Fe(CN)2]ꢁ [3]. However,
in all cases, the corrole p orbital used for the macrocycle
unpaired electron is the 7b1 orbital [4,5], which is
analogous to the 3a2u orbital of the porphyrin ring [5].
This orbital has large spin density at the meso-carbon
positions and negligible spin density at the pyrrole b-
carbons [2,4,5].
/
temperature ranges from ꢁ
/
90 to ꢃ30 8C on a Unity
/
In the present work we report a proton NMR
spectroscopic study of several meso-phenyl-substituted
300 NMR spectrometer as described previously [2]. The
temperature was calibrated using the Wilmad standard
variable temperature sample. 19F NMR spectra were
obtained at ambient temperature on the same instru-
ment. 19F chemical shifts were referenced using an
iron corrolates*
chlorate (TPCorr)FeClO4 and (5,10,15-tri-(4-X-phenyl-
corrolato))iron chloride [T(4-X)PCorr]FeCl, where Xꢀ
H, ÃNO2 and ÃOCH3. For comparison, the 5,10,15-tri-
(pentafluorophenyl)corrolatoiron chloride
[T(F5P)Corr]FeCl, claimed to be an iron(IV) corrolate
[6ꢂ8], was also investigated. As we will show, all of the
/
(5,10,15-triphenylcorrolato)iron per-
/
/
/
external sample of a,a,a-trifluorotoluene in benzine (ꢁ
/
63.73 ppm relative to CFCl ). The Mossbauer spectrum
¨
of (TPCorr)FeCl [11] was measured in zero applied field
3
/
at 4.2 K in the Institut fur Physik at the Universitat zu
¨
¨
Lubeck, Lubeck, Germany.
¨ ¨
chloroiron triphenylcorrolates, except for the tri-(penta-
fluorophenyl)corrolate complex, are unambiguously
Sꢀ
3/2 Fe(III) corrolate(2ꢁ+) p-cation radical com-
/
plexes, as reported previously for the chloroiron oc-
taalkylcorrolate analogs [2]. Additional investigations
are necessary before the electron configuration of
[T(F5P)Corr]FeCl can be defined.
3. Results and discussion
Fig. 1 shows the 1D 1H NMR spectrum of
(TPCorr)FeCl at 25 8C. The [T(4-NO2P)Corr]FeCl
compound gives similar NMR spectra, except that the
two peaks at 19.4 and 17.1 ppm in Fig. 1 are missing.
Hence these two peaks must be from the para protons of
2. Experimental
the three phenyl groups (ratioꢀ2:1, total three pro-
/
5,10,15-Triphenylcorrole (TPCorrH3), 5,10,15-Tri(4-
nitrophenyl)corrole [T(4-NO2P)Corr]H3, 5,10,15-Tri(4-
methoxyphenyl)corrole [T(4-MeOP)Corr]H3 have been
prepared as previously described [9]. 5,10,15-Tri(penta-
fluorophenyl)corrole, [T(F5P)Corr]H3, was purchased
from Strem Chemicals (Illinois). The chloroiron deriva-
tives of these meso-triarylcorroles were prepared by
reaction of FeCl2 in refluxing DMF [3,9], and the 57Fe-
labeled complex of TPCorrH3 was prepared according
to the procedure used for the corresponding 57Fe
porphyrinates [10]. The m-oxo dimer is the first product
of the reaction, and the corresponding chloroiron
complex is obtained in quantitative yield after washing
of a dichloromethane solution with diluted HCl [11].
The perchlorate complex was obtained after stirring
(TPCorr)FeCl with 1.1 equiv. of AgClO4 in dry toluene
at room temperature (r.t.) under argon for 1 h, followed
by filtration, evaporation and finally washing the
residue three times with dry hexane. Caution! Perchlo-
rate metal complexes are potentially explosive. Only
small amounts of material should be prepared and it
should be handled with caution. (TPCorr)FeCl: 82%
tons). In the COSY spectrum (Fig. 2) of (TPCorr)FeCl,
there are four pairs of cross peaks between these two
resonances and the four resonances in the upfield region
(from ꢁ
/
1 to ꢁ7 ppm). These four peaks can be assigned
/
to the meta protons of the three phenyl groups (ratioꢀ
/
2:2:1:1, total six protons). Note that the two meta
protons in each phenyl group are not equivalent, as
expected for this five-coordinate complex. The last pair
of cross peaks shown is between the 10-meta-H and a
peak at 22.7 ppm, which can thus be assigned to the two
ortho protons of the 10-phenyl group. Although they are
not equivalent, the expected two resonances are not
resolved at 300 MHz. It is reasonable to assign the other
two downfield resonances to the four 5,15-ortho protons
and the three upfield peaks to the pyrrole protons. The
fourth pyrrole-H resonance is located at 7.8 ppm (Fig.
1). No cross peaks are observed among pyrrole-H
resonances due to their short relaxation times. Only
one pair of cross peaks, between the o-H and m-H of the
10-phenyl group, is shown in the COSY spectrum
(supporting information Figure S1) of [T(4-
NO2P)Corr]FeCl, and again, no cross peaks are ob-

S. Cai et al. / Inorganica Chimica Acta 339 (2002) 171ꢂ
/178
173
Table 1
Isotropic shifts and assignments of (TPCorr)FeCl, [T(4-NO2P)Corr]FeCl, [T(4-MeOP)Corr]FeCl, (TPCorr)FeClO4 and [T(F5P)CorrFeCl
Compound
(TPCorr)FeCl, CD2Cl2, 303 K
[T(4-NO2P)Corr]FeCl, CD2Cl2, 303 K
Assignments
a
Isotropic shifts (ppm)
16.36(2H), 15.27(2H)
14.74(2H)
14.6(2H), 13.6(2H)
12.8(2H)
5,15-o-H
10-o-H
ꢁ10.18(2H), ꢁ10.56(2H)
ꢁ11.22(1H), ꢁ11.47(1H)
11.71(2H)
ꢁ9.5(2H), ꢁ9.8(2H)
ꢁ10.5(1H), ꢁ10.6(1H)
5,15-m-H
10-m-H
5,15-p-H
10-p-H
9.54(1H)
ꢁ1.95(2H), ꢁ13.67(2H), ꢁ15.26(2H), ꢁ48.06(2H) ꢁ2.2(2H) b, ꢁ14.2(2H), ꢁ15.4(2H), ꢁ46.1(2H) Pyrrole-H
Compound
[T(4-MeOP)Corr]FeCl, CD2Cl2, 293 K
(TPCorr)FeClO4, CD2Cl2, 293 K
Assignments
a
Isotropic shifts (ppm)
18.9(2H), 17.7(2H)
17.0(1H), 16.8(1H)
18.3(4H)
17.8(2H)
ꢁ12.3(4H)
ꢁ13.6(2H)
14.3(2H)
11.7(1H)
5,15-o-H
10-o-H
ꢁ11.3(2H), ꢁ11.5(2H)
ꢁ12.6(1H), ꢁ13.0(1H)
5,15-m-H
10-m-H
5,15-p-H
10-p-H
ꢁ1.9(2H) b, ꢁ12.6(2H), ꢁ16.0(2H), ꢁ50.0(2H)
ꢁ1.9(2H) b, ꢁ19.6(2H), ꢁ20.2(2H), ꢁ61.9(2H) Pyrrole-H
c
d
Compound
[T(F5P)Corr]FeCl, CD2Cl2, 294 K
[T(F5P)Corr]FeCl, C6D6, room temperature
Assignments
Pyrrole-H
a
d
Isotropic Shifts (ppm)
ꢁ5.9(2H) ꢁ12.6(2H), ꢁ21.5(2H), ꢁ45.3(2H)
ꢁ11(2H), ꢁ12(2H), ꢁ21(2H), ꢁ42(2H)
a
The isotropic shifts were calculated by subtracting the corresponding diamagnetic shifts [9,27] from the chemical shifts. The average diamagnetic
shift (8.7 ppm for triphenylcorrole free base [8], 8.9 ppm for [T(F5P)Corr]Ga(Py) [27]) was used because the pyrrole peaks of neither the free base, the
gallium complex, nor the iron complexes have been assigned.
b
Only three pyrrole proton resonances were positively detected in this case. The fourth one is located under the envelope of impurity peaks in the
region of 1ꢂ
/
9 ppm, and is tentatively assigned a chemical shift of 7.5ꢂ
/
7.8 ppm.
c
This work.
Reference [6].
d
pyrrole-H peaks happens to have same chemical shift
(ꢁ4.1 ppm) as one of the meta proton peaks (they are
/
resolved at lower temperature). In (TPCorr)FeClO4, the
perchlorate anion may exist as a dissociated counterion.
In this case, the complex would have mirror symmetry
(the corrolate plane) and the two meta protons within
each phenyl group would now be equivalent, as would
be the two ortho protons. We find that (TPCorr)FeClO4
only shows two peaks each (2:1) for phenyl meta, para
and ortho protons, respectively, hence supporting the
assumption that the perchlorate anion is not bound to
the metal, or that it exchanges rapidly between indivi-
dual iron complexes. In the COSY spectra of [T(4-
MeO)PCorr]FeCl and (TPCorr)FeClO4 (supporting in-
formation Figure S2 and S3, respectively), all cross
peaks are between para and meta protons of the phenyl
groups. Not all protons expected to be J-coupled show
cross peaks due to fast relaxation.
In Fig. 4 is shown the complete 1H NMR spectrum of
[T(F5P)Corr]FeCl at 21 8C. Although there is a promi-
nent water peak at about 2 ppm, it is clear that the
fourth pyrrole-H resonance is at 3.1 ppm, rather than at
7.8 ppm as observed for (TPCorr)FeCl (Fig. 1). For
each of these five triphenylcorrolatoiron(III) chloride
complexes the pyrrole-H resonances are slightly differ-
ently spaced (Table 1), yet all, including the perfluori-
Fig. 1. 1H NMR spectra of (TPCorr)FeCl at 298 K in CD2Cl2. The
solvent resonance is marked with S, and those peaks marked with stars
are due to impurities.
served among pyrrole-H resonances. Since this complex
has a similar spectral pattern and chemical shifts to
those of (TPCorr)FeCl, the assignments are likely the
same.
[T(4-MeOP)Corr]FeCl and (TPCorr)FeClO4 show
similar NMR spectra (Fig. 3) at 20 8C to those of
(TPCorr)FeCl and [T(4-NO2P)Corr]FeCl, and thus they
should have the same peak assignments. For [T(4-
MeOP)Corr]FeCl, four ortho (2:2:1:1) and four meta
(2:2:1:1) proton peaks were observed. One of the

174
S. Cai et al. / Inorganica Chimica Acta 339 (2002) 171ꢂ178
/
Fig. 2. COSY spectrum of (TPCorr)FeCl at 303 K. Due to fast
relaxation, not all coupled protons show cross peaks here. The cross
peaks marked with ‘M’ are between para and meta protons of phenyl
groups. The cross peaks marked with ‘O’ are between ortho and meta
protons of the meso-10 phenyl groups. The cross peaks marked with ‘I’
are from an impurity in the sample used for the COSY experiment (not
present in Fig. 1). T1 noise stripes are observed from the solvent
resonance and the impurity peak due to H2O at Â1.5 ppm.
/
Fig. 3. 1H NMR spectra of (a) [T(4-MeOP)Corr]FeCl and (b)
(TPCorr)FeClO4] at 293 K in CD2Cl2. The solvent peak is marked
with S, and stars mark impurity peaks.
nated phenyl complex, have generally similar pyrrole-H
shifts.
Table 1 lists the isotropic shifts of all peaks and their
assignments for these four compounds according to the
COSY results and relative peak areas. An important
feature concerning the isotropic shifts (see Table 1) of
the meso-phenyl protons of (TPCorr)FeCl and
(TPCorr)FeClO4 is that they alternate signs around
the phenyl ring (e.g. p-H and o-H positive, m-H
negative). This is solid evidence of large p spin density
at the meso positions [4,5]. Furthermore, the signs of
these shifts are opposite to those in [(TPP)Fe(t-
BuNC)2]ꢃ, [12] which has been shown to have large
positive p spin density on the meso carbons [5,12]. In
this latter complex, the p-H and o-H shifts are negative,
while the m-H shift is positive [12]. Hence, for the
present complexes, there is large negative p spin density
on the meso positions of (TPCorr)FeCl and
(TPCorr)FeClO4, indicating antiferromagnetic coupling
of the corrolate unpaired electron to the three unpaired
electrons of the metal. This is exactly the same electron
configuration and coupling pattern as found previously
for the octaalkyl-substituted corrolates (7,13-Me2Et6-
Corr)FeCl and (Me8Corr)FeCl [2]. Thus, we can con-
clude that these four tri-meso-phenyl-substituted
corrolatoiron chloride complexes and the octaalkylcor-
rolatoiron chloride complexes studied previously [2]
corrole unpaired electron antiferromagnetically coupled
to the unpaired electrons on the metal center.
Based on their similar NMR spectra, (TPCorr)FeCl
and (TPCorr)FeClO4 are expected to have the same
electronic structure, in both cases Sꢀ3/2 intermediate
/
spin Fe(III). This is quite different from the results for
the corresponding porphyrins: TPPFeCl is a high-spin
(Sꢀ
perchlorate ion, the spin state of the porphyrin is
lowered and changed to a spin admixed (Sꢀ3/2, 5/2)
/5/2) complex [5]. If the chloride is substituted by a
/
complex [5,13,14]. The reason why the corrolates do not
change electronic structure with change of anionic axial
ligand from chloride to perchlorate is probably that in
(TPCorr)FeCl the iron center is already intermediate-
spin (Sꢀ3/2). Thus, substitution of perchlorate ion
/
cannot lower the spin state any further.
Linear analysis of the temperature dependences of the
proton resonances (supporting information Figures S4
and S5) shows non-Curie behavior (the intercepts of the
isotropic shifts at 1/Tꢀ0 are not zero) for all four
/
complexes. This indicates that a thermally accessible
excited state also contributes to the isotropic shifts.
Using the two-level temperature-dependence fitting
program [15], the spin distribution for both the ground
state and excited state were calculated. The results,
presented in Table 2, show that the ground state has
have the same electronic structure. They are all Sꢀ
/
3/2
Fe(III) corrolate(2ꢁ+) p-cation radical species, with the

S. Cai et al. / Inorganica Chimica Acta 339 (2002) 171ꢂ
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175
Fig. 4. 1H NMR spectrum of [T(F5P)Corr]FeCl at 293 K in CD2Cl2. The solvent peak is marked with S, and impurities are marked with stars. The
‘impurity’ at 2 ppm is actually H2O.
sizable spin densities on the pyrrole positions and phenyl
rings, while the excited state has comparable spin
densities on the pyrrole positions but much smaller
spin densities on the phenyl rings (however, with some
exceptions from [T(4-MeOP)Corr]FeCl, whose phenyl
meta protons show larger spin densities for the excited
state than for the ground state). The pattern of spin
distribution for the ground state is consistent with that
expected for an iron(III) center antiferromagnetically
coupled to a p-cation radical. Based on the small spin
density at the meso positions, the excited state probably
studies of a chloroiron and a phenyliron octaalkylcor-
rolate, presented elsewhere [16], also show that because
the magnetic coupling between Fe(III) and the corrolate
radical, where present, is very strong, the magnetic
Mossbauer spectra of Fe(III)-Corr(2ꢁ+) p-cation radi-
¨
cal and Fe(IV)-Corr(3ꢁ+) are almost identical, except
for the isomer shift, and, therefore, only the latter is at
all indicative of the oxidation state of the metal. Hence,
the Mossbauer isomer shift of (TPCorr)FeCl is consis-
¨
1
tent with the conclusions reached from the H NMR
investigations discussed above, that this complex is a
Fe(III)-Corr(2ꢁ+) p-cation radical.
has an Fe(IV)Ã
/
TPCorr(3ꢁ) electron configuration. The
In their recent papers, Gross et al. [6,7], have stated
that [T(F5P)Corr]FeCl is an iron(IV) complex, but the
only experimental evidence presented to support this
excited state still has large spin density on the pyrrole
positions. The energy separation, DE, between the
ground and excited states, derived from the tempera-
ture-dependent fitting program [15], are all somewhat
statement were FeÃ/N(Corr) bond lengths [6] and the
larger than kT at room temperature (Â
200 cmꢁ1), and,
/
similarity in the one-electron oxidation potentials of the
chlorotin(IV) and chloroiron complexes (1.20 and 1.24
V, respectively) [7], neither of which is definitive proof of
the electron configuration of the complex. More re-
cently, Gross has again stated that this, as well as the
chloroiron, phenyliron and m-oxo di-iron dimer com-
plexes of all meso-triphenyl corrolates are iron(IV)
complexes [7]. In contrast, Ghosh and coworkers have
recently presented DFT calculations that favor the
except for the pentafluorophenyl complex, is largest for
the perchlorate complex, [(TPCorr)FeClO4]. This seems
reasonable based on the fact that perchlorate also
stabilizes the Sꢀ3/2 spin state of Fe(III) porphyrins
/
[14]. The perfluorophenyl complex, [T(F5P)Corr]FeCl,
exhibits generally smaller spin densities for the excited
state than for the ground state.
The Mossbauer isomer shift obtained for
¨
+
(TPCorr)FeCl is dꢀ
indicative of a Fe(III) center [16]. The quadrupole
splitting, DEQꢀ
2.93 mm sꢁ1 [11], is characteristic
of either Sꢀ3/2 Fe(III) or Sꢀ1 Fe(IV), and hence this
parameter is not useful for determining the oxidation
state of the metal. More detailed magnetic Mossbauer
/
ꢃ
/
0.19 mm sꢁ1 [11], and is
Fe(III)-Corr2ꢁ radical electron configuration for
chloroiron corrolates [17], and our own DFT calcula-
tions are also consistent with this [16]. Since corrolate
ligands in general are non-innocent [18], in the present
work we address only the electronic structure of the
/
ꢃ
/
/
/
1
chloroiron triphenylcorrolates. The H NMR spectrum
¨

176
S. Cai et al. / Inorganica Chimica Acta 339 (2002) 171ꢂ178
/
Table 2
Spin densities calculated from the two-level data fitting program for the ground state (C1) and the excited state (C2) of (TPCorr)FeCl, [T(4-
NO2P)Corr]FeCl, [T(4-MeOP)Corr]FeCl, [T(F5P)Corr]FeCl and (TPCorr)FeClO4
Compound
(TPCorr)FeCl
232
[T(4-NO2P)-Corr]FeCl
271
[T(4-MeOP)-Corr]FeCl
213
[T(F5P)Corr]-FeCl
340
(TPCorr)-FeClO4
317
DE (cmꢁ1
)
C1
o-H
ꢁ0.0140
ꢁ0.0134
ꢁ0.0124
ꢁ0.0120
ꢁ0.0110
ꢁ0.0100
ꢁ0.0150
ꢁ0.0140
ꢁ0.0140
ꢁ0.0130
ꢁ0.0130
ꢁ0.0120
p-H
ꢁ0.0110
ꢁ0.0087
0.0067
0.0071
0.0074
0.0077
0.0090
0.0090
0.0310
ꢁ0.0110
ꢁ0.0091
0.0077
m-H
0.0064
0.0068
0.0068
0.0070
0.0083
0.0100
0.0300
0.0058
0.0066
0.0068
0.0075
0.0086
0.0094
0.0330
0.0085
Pyrrole-H
0.0050
0.0063
0.0125
0.0275
0.0100
0.0110
0.0360
C2
o-H
ꢁ0.0006
0.0001
0.0005
0.0010
0.0004
ꢁ0.0003
ꢁ0.0001
0.0021
0.0021
0.0034
ꢁ0.0001
0.0012
p-H
0.0019
0.0022
0.0048
0.0036
0.0051
0.0043
0.0060
0.0100
0.0230
0.0038
0.0043
0.0052
0.0057
a
m-H
0.0041
0.0034
0.0046
0.0042
0.0099
0.0068
0.0200
0.0093
0.0075
a
a
0.0089
0.0080
a
a
Pyrrole-H
0.0047
0.0097
0.0210
ꢁ0.0050
0.0170
0.0170
0.0410
0.0099
0.0096
0.0177
DE is the energy gap between these two states.
Exceptions which are inconsistent with the spin distribution patterns on other positions of [T(4-MeOP)Corr]FeCl or for other complexes.
a
of [T(F5P)Corr]FeCl reported previously [6] shows four
pyrrole proton peaks with negative chemical shifts
expected at the b-pyrrole positions in an a2u(p)-type
orbital is expected to be quite small [5]. Thus, to
determine the electron configuration one must check
the spin density at the meso positions and the isotropic
shifts of the meso substituents.
(about ꢁ
/
2.5, ꢁ
/
3, ꢁ
/
12 and ꢁ33.5 ppm in benzene-d6
/
at room temperature). We obtain somewhat similar
chemical shifts for three of the pyrrole protons for this
complex in CD2Cl2, but the fourth (most downfield)
To probe the spin density at the meso positions of
[T(F5P)Corr]FeCl, the 19F NMR spectrum was recorded
in CD2Cl2 solution at 294 K (with a,a,a-trifluorotoluene
pyrrole-H resonance is at ꢃ
/
3.1 rather than ꢁ2.5 ppm,
/
as shown in Fig. 4, suggesting that there are important
solvent effects for this complex. Overall, the chemical
shifts of the pyrrole protons of this complex in CD2Cl2
are not significantly different than those of the other
triphenylcorrolatoiron chloride complexes of this study
(Table 1). However, whether this is an Fe(IV) complex
or an Fe(III) p-cation radical cannot be determined
based on the 1H NMR spectroscopic data, since both of
these electron configurations are expected to give large
negative pyrrole proton isotropic shifts due to one
unpaired electron being present in each of the dp
orbitals, dxz and dyz in both cases, and the spin density
(in C6D6) as external reference, ꢁ63.73 ppm vs. CFCl3),
/
as shown in Fig. 5. Since the ortho-phenyl fluorines are
closest to the metal center, they are expected to give
broad peaks due to rapid dipolar relaxation rates; [5]
thus the four broad peaks (at ꢁ
/
155, ꢁ
/
160.7, ꢁ166 and
/
ꢁ
/
169 ppm) in Fig. 4 are from the ortho-fluorines. In the
19F COSY spectrum of this complex (not shown), two
pairs of cross peaks were observed, one between para-
5,15-F and meta-5,15-F, the other one between para-10-
F and meta-10-F; these assignments are thus included in
Fig. 5 and Table 3. The ortho-F resonances relax too

S. Cai et al. / Inorganica Chimica Acta 339 (2002) 171ꢂ
/178
177
Fig. 5. 19F NMR spectrum of [T(F5P)Corr]FeCl at 293 K in CD2Cl2, externally referenced against a,a,a-trifluorotoluene in C6D6. Assignments are
based on peak intensities and COSY crosspeaks.
rapidly to give any cross peaks. Based on the COSY
results and relative peak areas, full assignments were
made, and then the 19F isotropic shifts were calculated
(Table 3).
Unlike the proton isotropic shifts of the four non-
fluorine-substituted chloroiron corrolates summarized
in Table 1, the 19F isotropic shifts of [T(F5P)Corr]FeCl
(Table 3) are all negative and smaller in magnitude
chloroiron porphyrin complex, the Sꢀ5/2 octabromo-
/
tetra-(pentafluorophenyl)porphyrinatoiron chloride, re-
ported by Birnbaum, Grinstaff and coworkers [19],
shows 19F isotropic shifts similar in magnitude, but
opposite in sign to those of [T(F5P)Corr]FeCl (Table 3).
The opposite sign could suggest that there is negative
spin density at the meso positions of this corrolate
complex, as is the case for the other chloroiron
corrolates already discussed. However, we feel that it
is not at present possible to evaluate these 19F shifts
without additional investigations of complexes for
which the electron configuration is known unambigu-
ously. This is because of the unknown importance of the
additional term, the ligand-centered dipolar shift [20,21],
which is present for all atoms having more electron
shells than hydrogen. For carbon atoms this term has
been estimated to be quite large for atoms directly
involved in a p system [20], but smaller for atoms
(decreasing in the order o ꢀ
/
pꢀm, as expected for a
/
very small contact contribution superimposed upon a
small (negative) dipolar contribution) than might be
expected possible for this nucleus. This might suggest
that the 19F shifts of this complex may not have large
contact shifts arising from large p spin delocalization to
the phenyl substituents, and hence may not have an
a2u(p) unpaired electron on the corrole macrocycle.
However, there have been very few investigations of
the 19F NMR spectra of fluorine-substituted paramag-
netic metal macrocycles, and hence the definition of
‘small’ and ‘large’ has not yet been made for 19F. One
adjacent to a p system [22ꢂ
/
24], as in the case of the
fluorine atoms of the complex of interest. Thus, addi-
Table 3
19F isotropic shifts and assignments of [T(F5P)Corr]FeCl at 293 K, and comparison to those of [Br8T(F5P)P]FeCl [19]
a
Chemical shift (ppm)
b
Diamagnetic shift (ppm)
c
Isotropic shift (ppm)
d
Assignment
ꢁ154.7, ꢁ166.0
ꢁ160.7, ꢁ170.0
ꢁ167.0
ꢁ169.4, ꢁ169.6
ꢁ166.4
ꢁ138.3
ꢁ137.7
ꢁ161.9
ꢁ162.4
ꢁ152.8
ꢁ153.4
ꢁ16.4, ꢁ27.7
ꢁ23.0, ꢁ32.3
ꢁ5.1
ꢁ7.0, ꢁ7.2
ꢁ13.6
o-5,15-F
o-10-F
m-5,15-F
m-10-F
p-5,15-F
p-10-F
ꢁ164.6
ꢁ11.2
[Br8 T(F5 P)P]FeCl
ꢁ104.4, ꢁ108
ꢁ152.5, ꢁ153.3
ꢁ141.9
e
ꢁ138.6
ꢁ163.1
ꢁ152.0
ꢃ33.9, ꢃ30.6
ꢃ10.6, ꢃ9.8
ꢃ10.1
o-F
m-F
p-F
e
e
a
19F chemical shifts of [T(F5P)Corr]FeCl in CD2Cl2 (vs. CFCl3).
b
c
19F chemical shifts of [T(F5P)Corr]H3 in CD2Cl2.
The 19F isotropic shifts were calculated by subtracting the corresponding chemical shifts (externally referenced to a,a,a-trifluorotoluene) of
diamagnetic [T(F5P)Corr]H3 from the chemical shifts of [T(F5P)Corr]FeCl.
d
Full peak assignments for [T(F5P)Corr]H3 were made based on the COSY spectrum (not shown) and relative peak areas.
Diamagnetic shifts taken from [Br8T(F5P)PFe(II)(Py)2] [19].
e

178
S. Cai et al. / Inorganica Chimica Acta 339 (2002) 171ꢂ178
/
tional investigations will be required in order to inter-
pret quantitatively the observed 19F isotropic shifts of
the chloroiron perfluorinated triphenyl corrolate, and
on the basis of the data obtained thus far, it is not
possible to reach a conclusion on the electron config-
uration of [T(F5P)Corr]FeCl. Such investigations are
currently underway in our laboratories.
Thus, we can conclude that, except in the presence of
highly electronegative fluorine substituents, and possi-
bly in that case as well, chloroiron corrolates have the
beck, Germany, for measuring the isomer shifts and
quadrupole splittings of chloroiron meso-triphenylcor-
rolate and chloroiron meso-tri-(pentafluorophenyl)cor-
rolate.
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ground state electron configuration Sꢀ3/2 Fe(III)
/
corrolate(2ꢁ+) p-cation radical, with the macrocycle
unpaired electron antiferromagnetically coupled to the
metal electrons. In the case of the meso-triphenylcorro-
lates, the Fe(IV)Corr(3ꢁ) excited state is at an energy of
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/
have more tendency to stabilize high oxidation states of
metal ions than do porphyrinate ligands. It is also not
clear that the electron configuration of any other metal
corrolate complexes can be stated without corroborating
detailed magnetic resonance investigations of each
individual complex. Rather, corrolates must be consid-
ered as non-innocent macrocyclic ligands in each of their
metal complexes, and the electron configuration cannot
be stated until each one is individually characterized by
as many physical techniques as possible, most notably
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/
1
including a careful H and other appropriate nucleus
[14] M.J.M. Nesset, S. Cai, T.K. Shokhireva, N.V. Shokhirev, S.E.
Jacobson, Kh. Jayaraj, A. Gold, F.A. Walker, Inorg. Chem. 39
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NMR spectroscopic investigation, where the isotropic
shifts are analyzed in terms of their contact, dipolar,
and, in the case of heavier nuclei, the ligand-centered
dipolar contributions, as well as theoretical calculations.
The electron configurations of additional axial ligand
complexes of iron corrolates will be addressed by this
research team in future publications using a variety of
physical and calculational techniques.
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(1995) 3632;
4. Supplementary material
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Reuben (Eds.), Biological Magnetic Resonance, vol. 12, Plenum,
Figures
S1ꢂ
/
S6:
COSY
spectra
of
[T(4-
NO2P)Corr]FeCl, [T(4-MeOP)Corr]FeCl, (TPCorr)Fe-
ClO4, Curie plots for the five complexes. This material is
available upon request from the authors (awalker@-
u.arizona.edu).
New York, 1993, pp. 299ꢂ355.
/
[22] H. Santos, D.L. Turner, FEBS Lett. 194 (1986) 73.
[23] L. Banci, I. Bertini, C. Luchinat, R. Pierattelli, N.V. Shokhirev,
F.A. Walker, J. Am. Chem. Soc. 120 (1998) 8472.
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The Porphyrin Handbook, vol. 2 (chapter 11), Academic Press,
New York, 2000, p. 201.
Acknowledgements
The support of the US National Institutes of Health,
Grant DK 31038 (F. A.W.), NATO, Grant CRG971495
(S.L.) and MURST (S.L.) is gratefully acknowledged.
The authors also wish to thank Professor Alfred X.
Trautwein and Dr. Volker Schunemann, of the Institut
fur Physik, Medizinische Universitat zu Lubeck, Lu
[26] C. Erben, S. Will, K.M. Kadish, in: K.M. Kadish, K.M. Smith, R.
Guilard (Eds.), The Porphyrin Handbook, vol. 2 (chapter 12),
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Simkhovich, Z. Gross, Angew. Chem., Int. Ed. Engl. 39 (2000)
4048.
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