Formation and characterization of five- and six-coordinate iron(III) corrolazine complexes

Article abstract of DOI:10.1142/S1088424612500460

Electronic structures of five- and six-coordinate iron(III) corrolazine complexes are determined by means of ¹H NMR, ¹³C NMR, EPR, and M?ssbauer spectroscopy as well as SQUID magnetometry. A series of five-coordinate complexes, [Fe^III(TBP₈Cz)(L)]* where the axial ligands(L) are cyanide(CN^-), imidazole(HIm), 1-methylimidazole(1-MeIm), 4-(N,N-dimethylamino)pyridine(DMAP), pyridine(Py), 4-cyanopyridine(4-CNPy), and tert-butylisocyanide(^tBuNC), are obtained by the addition of 1 to 2 equiv. of the ligands to the dichloromethane solutions of Fe^III(TBP₈Cz) at 298 K: TBP₈Cz is a trianion of 2,3,7,8,12,13,17,18-octakis(4-tert-butylphenyl)corrolazine. These complexes commonly show the S = 3/2 at 298 K. By contrast, formation of the six-coordinate complexes depends on the nature of the axial ligands. While the addition of 3 equiv. of CN^- has completely converted Fe ^III(TBP₈Cz) to (Bu₄N)₂[Fe ^III(TBP₈Cz)(CN)₂] at 298 K, the conversion to the bis-adduct is only attained below ca. 200 K in the case of HIm, 1-MeIm, and DMAP even in the presence of 50 equiv. of the ligands. If the axial ligand is Py, 4-CNPy, or ^tBuNC, the formation of [Fe^III(TBP ₈Cz)(L)₂] is confirmed only at an extremely low temperature (15 K). Close inspection of the ¹H NMR and EPR spectra has revealed that all the bis-adducts adopt the (d_xy) ²(d_xz, d_yz)³ ground state. While Fe^III(TBP₈Cz) forms paramagnetic bis- and mono-adduct in toluene solution at 298 K in the presence of excess amount of CN^- and ^tBuNC, respectively, the corresponding porphyrazine complex, [Fe^III(TBP₈Pz)]Cl, forms diamagnetic bis-CN and bis- ^tBuNC under the same conditions: TBP₈Pz is a dianion of 2,3,7,8,12,13,17,18-octakis(4-tert-butylphenyl)-porphyrazine. Thus, the iron(III) ion of porphyrazine complex is more easily reduced than that of the corresponding corrolazine complex.

Full text of DOI:10.1142/S1088424612500460

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 518–529
DOI: 10.1142/S1088424612500460
Published at http://www.worldscinet.com/jpp/
Formation and characterization of five- and six-coordinate
iron(III) corrolazine complexes
Satoshi Kurahashib◊◊, Takahisa Ikeue*a◊, Tamotsu Sugimoric, Masashi Takahashid,e,
Masahiro Mikuriyab, Makoto Handaa◊, Akira Ikezakif◊ and Mikio Nakamura*e,f,g◊
a Department of Material Science, Interdisciplinary Faculty of Science and Engineering, Shimane University, 1060
Nishikawatsu, Matsue 690-8504, Japan
b Department of Chemistry and Research Center for Coordination Molecule-Based Devices, School of Science and
Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan
c Division of Chemistry, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama
930-0194, Japan
d Department of Chemistry, Faculty of Science, Toho University, Funabashi 274-8510, Japan
e Research Center for Materials with Integrated Properties, Toho University, Funabashi 274-8510, Japan
f Department of Chemistry, School of Medicine, Toho University, Ota-ku, Tokyo 143-8540, Japan
g Division of Chemistry, Graduate School of Science, Toho University, Funabashi 274-8510, Japan
Dedicated to Professor Emanuel Vogel in memoriam
Received 28 September 2011
Accepted 21 November 2011
ABSTRACT: Electronic structures of five- and six-coordinate iron(III) corrolazine complexes are
1
determined by means of H NMR, 13C NMR, EPR, and Mössbauer spectroscopy as well as SQUID
magnetometry. A series of five-coordinate complexes, [FeIII(TBP8Cz)(L)]* where the axial ligands(L) are
cyanide(CN-), imidazole(HIm), 1-methylimidazole(1-MeIm), 4-(N,N-dimethylamino)pyridine(DMAP),
pyridine(Py), 4-cyanopyridine(4-CNPy), and tert-butylisocyanide(tBuNC), are obtained by the addition
of 1 to 2 equiv. of the ligands to the dichloromethane solutions of FeIII(TBP8Cz) at 298 K: TBP8Cz is
a trianion of 2,3,7,8,12,13,17,18-octakis(4-tert-butylphenyl)corrolazine. These complexes commonly
show the S = 3/2 at 298 K. By contrast, formation of the six-coordinate complexes depends on the nature
of the axial ligands. While the addition of 3 equiv. of CN- has completely converted FeIII(TBP8Cz) to
(Bu4N)2[FeIII(TBP8Cz)(CN)2] at 298 K, the conversion to the bis-adduct is only attained below ca. 200
K in the case of HIm, 1-MeIm, and DMAP even in the presence of 50 equiv. of the ligands. If the axial
ligand is Py, 4-CNPy, or tBuNC, the formation of [FeIII(TBP8Cz)(L)2] is confirmed only at an extremely
low temperature (15 K). Close inspection of the 1H NMR and EPR spectra has revealed that all the bis-
adducts adopt the (dxy)2(dxz, dyz)3 ground state. While FeIII(TBP8Cz) forms paramagnetic bis- and mono-
adduct in toluene solution at 298 K in the presence of excess amount of CN- and tBuNC, respectively,
the corresponding porphyrazine complex, [FeIII(TBP8Pz)]Cl, forms diamagnetic bis-CN and bis-tBuNC
under the same conditions: TBP8Pz is a dianion of 2,3,7,8,12,13,17,18-octakis(4-tert-butylphenyl)-
porphyrazine. Thus, the iron(III) ion of porphyrazine complex is more easily reduced than that of the
corresponding corrolazine complex.
KEYWORDS: corrolazine, iron(III) complexes, spin state, electron configuration.
SPP full and ◊◊student member in good standing
*Correspondence to: Takahisa Ikeue, email: ikeue@riko.
shimane-u.ac.jp and Mikio Nakamura, email: mnakamu@med.
toho-u.ac.jp
Copyright © 2012 World Scientific Publishing Company

FORMATION AND CHARACTERIZATION OF FIVE- AND SIX-COORDINATE IRON(III) CORROLAZINE COMPLEXES
519
iron(III) ions, where the 1H NMR chemical shifts are less
INTRODUCTION
useful because of the absence of the meso-carbon atoms
[30]. Recently, Goldberg and co-workers have disclosed
the synthesis of corrolazine, H3(TBP8Cz), a new member
of the porphyrinoid family having triazacorrole structure,
and have extensively studied the catalytic activities of its
manganese and iron complexes, i.e. MnIII(TBP8Cz) and
FeIII(TBP8Cz) [31–42]. We are very much interested in
the electronic ground state of the iron(III) complexes of
this new porphyrinoid. In this paper, we will describe
the formation and electronic structures of a series
of five- and six-coordinate [FeIII(TBP8Cz)(L)]* and
[FeIII(TBP8Cz)-(L)2]*(4) carrying typical nitrogen bases
such as HIm, 1-MeIm, DMAP, Py, and 4-CNPy as well
Electronic structures of iron(III) porphyrin complexes
can be modulated by various factors which include the
field strength of the axial ligand, electronic effect of
the peripheral substituent, deformation of the porphyrin
ring, hydrogen bonding to the axial ligand, etc. [1–3].
By manipulating these factors, we are now able to obtain
various iron(III) complexes with different electronic
structures, i.e. S = 1/2 with the (dxy)2(dxz, dyz)3, S = 1/2 with
4
1
2
2
1
2
the (dxz, dyz) (dxy) , S = 3/2 with the (dxy) (dxz, dyz) (dx ) ,
3
1
1
2
and S = 3/2 with the (dxz, dyz) (dxy) (dx ) [4–8]. As an
extension of our on going studies on determining the
factors that control the electronic structure of iron(III)
porphyrins, we have expanded the system from the
porphyrins to the porphyrin analogues. Such studies have
revealed that iron(III) porphycene core stabilizes the S =
3/2 state as compared with other iron(III) complexes of
the corresponding porphyrin and porphyrin isomers such
as corrphycene and hemiporphycene [9–12]. As is well
known, the chemistry of these porphyrin isomers has
been developed by the pioneering work of the late Prof.
Vogel and others [13–21]. Not only the spin states, but
also the electron configuration of low-spin complexes
is perturbed by the core modification. For example, the
chlorin core stabilizes the (dxz, dyz)4(dxy)1 ground state as
compared with the corresponding porphyrin core [22–
25]. In contrast, replacement of the meso-carbon atoms by
one or two nitrogen atoms greatly stabilizes the (dxy)2(dxz,
dyz)3 ground state. Thus, the six-coordinate S = 1/2
complexes of substituted monoazaporphyrin (H2MAzP)
and diazaporphyrin (H2DAzP) such as [FeIII(MAzP)(L)2]
(1)and [FeIII(DAzP)(L)2] (2) shown in Chart 1 adopt the
(dxy)2(dxz, dyz)3 ground state even if the axial ligand(L) is
tBuNC [26, 27]. The result is quite unusual since almost
all the low-spin iron(III) complexes reported previously
adopt the (dxz, dyz)4(dxy)1 electronic ground state if the
t
as carbon bases such as CN- and BuNC by means of
1
UV-vis, H NMR, 13C NMR, Mössbauer, EPR spectra,
and SQUID measurement. The electronic structures of
the corrolazine complexes (4) are compared with those
of the corresponding porphyrazine complexes (3).
EXPERIMENTAL
Measurements
UV-vis spectra were recorded for the CH2Cl2
solutions from 300 to 900 nm on a Shimazu UV-3100
spectrophotometer. The UV-vis spectra at low temperatures
were recorded from 300 to 800 nm on a Shimadzu
MultiSpec-1500 spectrophotometer equipped with a
UNISOKU liquid nitrogen cryostat, CoolSpec UV USP-
203-A. 1H and 13C NMR spectra were recorded either on a
JEOL LA 400 spectrometer operating at 400.1 MHz or on
a JEOL ECS-500SS spectrometer operating at 500.0 MHz
for1H.Chemicalshiftswerereferencedtotheresidualpeaks
of CD2Cl2(d = 5.32 and 52.3 ppm for the 1H and 13C signals,
respectively). EPR spectra were recorded in frozen toluene
solution at 15 K on a Bruker E500 spectrometer operating
at X band and equipped with an Oxford helium cryostat.
Some samples were measured in frozen CH2Cl2 solution or
in the solid. Iron-57 Mössbauer spectra were measured on
a Wissel Mössbauer spectrometer system consisting of an
MDU-1200 function generator, a DFG-1200 driving unit,
and an MVT-100 velocity transducer, incorporating with a
t
axial ligand is BuNC [27–29]. We have also found that
the 13C NMR chemical shifts of the pyrrole-Ca signals
in substituted porphyrazine H2(TBP8Pz) complexes such
as five-coordinate FeIII(TBP8Pz)X (X = Cl-, Br-, and I-)
and six-coordinate [FeIII(TBP8Pz)(L)2]* (3) shown also in
Scheme 1 are the excellent probe to determine the subtle
change in the spin state and electron configuration of the
∗
Ar
Ar
Et
Me
Ar
Et
Me
Ar
N
N
N
L
N
L
N
L
Ar
Et
Et
Bu
Bu
Ar
Ar
Ar
Ar
Et
Et
Bu
Bu
Ar
Ar
L
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Fe
N
N
Fe
Fe
Fe
L
L
L
L
Ar
N
N
Et
Me
Ar
Ar
Ar
Et
Me
Ar
1
2
3
4
Chart 1. Six-coordinate iron(III) complexes of monoazaporphyrin(MAzP) (1), diazaporphyrin(DAzP) (2), tetraazaporphyrin or
porphyrazine(Pz) (3), and triazacorrole or corrolazine(Cz) (4)
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 519–529

520
S. KURAHASHI ET AL.
model 7800 multichannel analyzer form Seiko EG&G Co.
Ltd. The samples were kept in a Heli-Tran LT-3 gas-flow
cryostat from Advanced Research System Inc. equipped
with a 9620 digital temperature controller from Scientific
Instruments Inc., and the 57Co(Rh) source was kept at room
temperature. The data were analyzed on a MossWinn 3.0 i
Software. The isomer shift is given relative to a-iron foil
at room temperature. MALDI-TOF-MS spectra were
recorded on a Bruker Daltonics pAutoflex-T1. The solid
state magnetic susceptibilities were measured over the
temperature range 4.5–300 K in a magnetic field of 0.5 T
with a SQUID magnetometer (Quantum Design MPMS).
The measured data were corrected for diamagnetic
contributions. The effective magnetic moment (m1eff) of
[FeIII(TBP8Cz)(L)]* was determined in solution relative
to that of intermediate-spin FeIII(TBP8Cz) (m2eff = 3.89 mB)
by the Evans method [43], using CH2Cl2 as the chemical
[FeII(TBP8Pz)(tBuNC)2]. To the CD2Cl2 solution
t
of FeIII(TBP8Pz)I was added 3 equiv. of BuNC. The
spectrum immediately changed to form diamagnetic
[FeII(TBP8Pz)(tBuNC)2]. Similar reaction occurred in
1
toluene-d8 solution. H NMR (toluene-d8, 298 K): dH,
ppm 8.62 (16H, o-H), 7.58 (16H, m-H), 1.46 (p-tBu),
-0.78 (coord-tBuNC). EPR spectrum taken for frozen
CH2Cl2 solution at 4 K was silent.
(Bu4N)2[FeII(TBP8Pz)(CN)2]. To the toluene-d8
solution of FeIII(TBP8Pz)I was added 5 equiv. of
1
Bu4N(CN). The H NMR spectrum changed to give
diamagnetic (Bu4N)2[FeII(TBP8Pz)(CN)2]. 1H NMR
(toluene-d8, 298 K): dH, ppm 8.46 (16H, o-H), 7.57 (16H,
m-H), 1.48 (p-tBu). The chemical shift of 2.51 reported
for p-tBu protons in our previous paper was mistyped and
should be corrected to 1.48 [30].
shift reference according to the following equation; m1eff
=
RESULTS AND DISCUSSION
(Dn1/ Dn2)1/2m2eff [44]. In this equation, Dn1 and Dn2 are the
differences in chemical shifts of CH2Cl2 in [FeIII(TBP8Cz)-
(L)]* and FeIII(TBP8Cz), respectively. The effective
magnetic moments of [FeIII(TBP8Cz)(L)2]* were similarly
determined.
Spin state of four-, five, and six-coordinate iron(III)
corrolazine complexes
By using the method developed by Goldberg and
co-workers [41], we have obtained four-coordinate
FeIII(TBP8Cz), five-coordinate [FeIII(TBP8Cz)(L)]*, and
six-coordinate [FeIII(TBP8Cz)(L)2]*. In the following
section, we will report the spectroscopic and magnetic
data of these complexes and discuss mainly the spin-state
of these complexes.
Synthesis
H3(TBP8Cz). Free-base corrolazine was prepared from
the corresponding porphyrazine H2(TBP8Pz) [45], via
phosphrous corrolazine [P(TBP8Cz)OH](OH), according
to the method developed by Goldberg and co-workers
[31, 46]. Since the solvents used for the NMR and
UV-vis measurements are different from those reported
by Goldberg and co-workers, the chemical shifts and
absorption maxima are given below. 1H NMR (400 MHz;
CD2Cl2; 298 K): dH, ppm 8.21 (4H, br s), 8.11 (4H, br s),
7.80 (4H, br s), 7.67 (4H, d, JH-H = 7.3 Hz), 7.65 (4H, d,
JH-H = 7.9 Hz), 7.51 (4H, d, JH-H = 8.2 Hz), 7.44 (4H, d,
JH-H = 8.2 Hz), 7.16 (4H, d, JH-H = 8.2 Hz), 1.49 (18H, s),
1.48 (18H, s), 1.42 (18H, s), 1.34 (18H, s). MALDI-TOF
MS: m/z 1358.84 (calcd. for C96H107N7 1358.92). UV-vis
(CHCl3): lmax, nm (e 104 M-1.cm-1) 465 (8.58), 625 (1.97),
686 (3.94). IR (KBr): n, cm-1 3359, 2960, 2903, 2867,
2356, 1476, 1459, 1393, 1361, 1267, 1213, 1107, 982, 969,
836, 772, 739, 565. Anal. calcd. for C96H107N7: C, 84.85; H,
7.94; N, 7.22%. Found: C, 84.35; H, 7.59; N, 7.08.
UV-visible spectra
i) Addition of CN to FeIII(TBP8Cz). Figure 1(a) shows
the UV-vis spectral change of FeIII(TBP8Cz) measured in
CH2Cl2 solution at 298 K after the addition of 0–1.0 equiv.
of tetrabutylammonium cyanide (Bu4NCN). As the CN-
ion was added, the absorption band at 433 nm showed
a bathochromic shift to 437 nm. By the further addition
of CN- up to 120 equiv., the band at 437 nm decreased
and the new band at 477 nm increased in intensity as
shown in Fig. 1(b). The results strongly indicate that the
CN- ions bind to the iron(III) ions of FeIII(TBP8Cz) in a
stepwise fashion to form firstly the mono-adduct (Bu4N)-
[FeIII(TBP8Cz)(CN)] with Soret band at 437 nm and then
the bis-adduct (Bu4N)2[FeIII(TBP8Cz)(CN)2] with Soret
band at 477 nm.
[PV(TBP8Cz)(OH)]OH(13Ca). Phosphorus corrola-
zine complex where pyrrole-Ca is 13C enriched was
prepared by the reaction between PBr3 and H2(TBP8Pz)
(13Ca) in refluxed pyridine solution. 13C NMR (CD2Cl2,
298 K): dC, ppm 146.3 (Ca), 145.0 (Ca), 142.8 (Ca),
ii) Addition of various ligands to FeIII(TBP8Cz).
Other ligands such as HIm, DMAP, Py, 4-CNPy, and
tBuNC were similarly added to the CH2Cl2 solutions
of FeIII(TBP8Cz). The spectral change was similar to
that of the CN- case; the Soret band showed a small
bathochromic shift in each case. However, in contrast to
the case of the cyanide addition, no further change was
observed in UV-vis spectra even by the addition of larger
excess of ligand. Figure 1(c) shows the UV-vis spectra
observed when ca. 50 equiv. of the ligands were added to
the CH2Cl2 solutions of FeIII(TBP8Cz). The spectra were
126.4 (Ca). MALDI-TOF MS: m/z 1410.68 (calcd. for
12
C
13C8H105N7OP 1411.82).
88
FeIII(TBP8Cz)(13Ca). Insertion of iron was carried
out by the addition of 20 equiv. of FeIII(acac)3 according
to the Goldberg’s method [41]. 13Ca-enriched complex
was similarly prepared. MALDI-TOF MS: m/z 1419.82
(calcd. for 12C8813C8H104FeN7 1419.69).
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 520–529

FORMATION AND CHARACTERIZATION OF FIVE- AND SIX-COORDINATE IRON(III) CORROLAZINE COMPLEXES
521
for CuIIICz [47]. Since the complex belongs
to the C2v group, the symmetries of the
iron dxz and dyz orbitals, which are labeled
as eg in D4h complex, are lowered to the b1
and a2, respectively. Thus, these orbitals
can interact with the nearly degenerated
corrolazine HOMO-1(b1) and HOMO(a2). In
contrast, the iron dxy orbital has b2 symmetry
and is therefore orthogonal to any of the
corrolazine orbitals. The dxy orbital could
interact with some corrolazine orbitals if
the corrolazine core deforms as frequently
observed in porphyrin complexes. However,
all the X-ray crystallographic analysis of
corrolazine complexes reported previously
exhibited the relatively planar structure [31,
32, 38–40]. Furthermore, recent theoretical
study has also revealed that the parent corrole
ring does not ruffle [49]. Taken together,
it should be reasonable to suppose that the
half-occupied dxy orbital is orthogonal to
Fig. 1. UV-vis spectral change when (a) 0–1equiv and (b)1–120 equiv of
any of the corrolazine p orbitals. Thus, if
the complex exhibits large isotropically
shifted signals, it should indicate that the
complex has half-occupied iron dxz and/or
dyz orbitals. Although the electron densities
among the eight Ca and eight Cb atoms are
not much different in the HOMO(a2), they
Bu4NCN was added to the CH2Cl2 solution of FeIII (TBP8Cz). Red, green, and
blue lines show the UV-vis spectra of FeIII(TBP8Cz), (Bu4N)[FeIII(TBP8Cz)-
(CN)], and (Bu4N)2[FeIII(TBP8Cz)(CN)2], respectively. (c) UV-vis spectra
of FeIII(TBP8Cz) measured after the addition of 50 equiv of ligands(L) such
t
as Hlm, 1-MeIm, DMAP, Py, 4-CNPy, and BuNC at ambient temperature.
(d) UV-Vis spectra spectra at 298 and 213 K are shown in green and blue
lines, respectively.
are quite inhomogeneous in the HOMO-1(b1), i.e. two of
the Cb and two of the Ca atoms have zero coefficients.
Thus, we can expect a large spread of the isotropically
shifted Ca, o-H, and m-H signals if the complex has half-
essentially the same as those obtained by the addition of
1.0 equiv. of the ligands. On the basis of these results, it
is concluded that the complexes carrying HIm, 1-MeIm,
DMAP, Py, 4-CNPy, and BuNC maintain the five-
coordinate structure at least at ambient temperature even
in the presence of large amount of the ligand.
1
occupied dxz orbital. The H and 13C NMR spectra have
t
to be interpreted on the basis of the orbital interactions
mentioned here.
1
ii) FeIII(TBP8Cz). Figure 3(a) shows the H NMR
In order to see if six-coordinate complex can be
formed at lower temperature, the UV-vis spectra of the
CH2Cl2 solution of FeIII(TBP8Cz) containing 1000 equiv.
of HIm was examined. At ambient temperature, the
spectrum was essentially the same as that obtained in the
presence of 50 equiv. of HIm. As the temperature was
lowered, however, the Soret band at 440 nm showed a
bathochromic shift together with the Q-band at 614 nm as
shown in Fig. 1(d). The presence of the isosbestic points
is a clear indication that the spectral change corresponds
to the conversion from five- to six-coordinate complex
as the temperature is lowered. The absorption maxima of
the bis-HIm complex were 451, 619, and 745 nm. Thus,
the Soret band was by 26 nm shorter than that of the
corresponding bis-CN complex.
spectra of FeIII(TBP8Cz) taken in CD2Cl2 solution at
298 K. Poorly resolved signals appeared at 11–13 ppm
together with the four broad signals at around 8 ppm; 7.5,
7.9, 8.2, and 8.8 ppm. Goldberg and co-workers confirmed
that the complex adopts the intermediate-spin (S = 3/2)
1H NMR spectra
i) Orbital consideration. DFT calculations revealed
that corrolazine has closely located HOMO and HOMO-1
labeled as a2 and b1, respectively [47, 48]. Figure 2 shows
the a2 and b1 HOMOs reported by Tangen and Ghosh
Fig. 2. The a2 HOMO and b1 HOMO-1 of CuIIICz adapted from
E. Tangen and A. Ghosh, J. Am. Chem. Soc. 2002, 124, 8117–
8121, with permission from the American Chemical Society.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 521–529

522
S. KURAHASHI ET AL.
the phenyl protons. Namely, the Cb atom having larger
spin density induces more upfield and downfield shifts
of the o-H and m-H signals, respectively. The average
chemical shifts of the o-H and m-H signals were 2.07
and 10.22 ppm, respectively. The presence of the upfield
shifted o-H and the downfield shifted m-H signals
suggests that the S = 3/2 state is maintained during the
addition of 1.0 equiv. of the CN- ion.
By the further addition of CN- to the mono-CN
complex, four new signals appeared and increased their
intensities. When 3.0 equiv. of CN- was added, the signals
for the mono-CN complex completely disappeared and
only the signals for bis-CN complex were observed as
shown in Fig. 3(c). On going from the mono-CN to the
bis-CN complex, the four m-H signals shifted upfield
and appeared at 11.21, 9.39, 6.33, and 6.07 ppm. The
four broad o-H signals also showed appreciable shifts
and appeared at 9.28, 6.51, 4.64, and -7.00 ppm. As in
the case of the mono-CN complex, the COSY spectrum
given in Fig. S1(b) showed the correlation between the
o-H and m-H signals at 4.64 and 9.39 ppm, 6.51 and 6.07
ppm, and 9.28 and 6.33 ppm. Although no correlation
peak was observed between the o-H signal at -7.00 ppm
and the m-H signal at 11.21 ppm, they should belong to
the same phenyl ring. Thus, the average chemical shifts
of the o-H and m-H signals changed from 2.07 and 10.22
ppm, respectively, in the mono-CN complex to 3.33
and 8.25 ppm, respectively, in the bis-CN complex. The
results suggest that the spin densities on the Cb atoms
have decreased by the addition of the second CN- ion,
which in turn indicates that the spin-state has changed
from the S = 3/2 to the S = 1/2. Whether this complex
adopts the (dxy)2(dxz, dyz)3 or (dxz, dyz)4(dxy)1 ground state
will be discussed later.
Fig. 3. 1H NMR spectra of (a) FeIII(TBP8Cz), (b) (Bu4N)-
[FeIII(TBP8Cz)(CN)] and, (c) (Bu4N)2[FeIII(TBP8Cz)(CN)2]
taken in CD2Cl2 at 298 K. Red and green circles indicate the
o-H and m-H signals, respectively.
state in frozen toluene solution at 77 K on the basis of the
EPR spectrum; the g^ and g∥ values were determined to
be 4 and 2.0, respectively [41]. As mentioned later, we
have also confirmed by the Mössbauer spectra that the
microcrystalline sample of FeIII(TBP8Cz) maintains the
S = 3/2 spin state in the temperature range 77–295 K.
We and others reported that structurally analogous
porphyrazine complexes such as FeIII(TBP8Pz)X adopt
the S = 3/2 spin state if X is Cl-, Br-, or I- [30, 50, 51].
In the case of the iodide complex FeIII(TBP8Pz)I, the o-H
and m-H signals were observed at 6.10 and 11.74 ppm,
respectively [30]. The downfield shift of the m-H signal
in FeIII(TBP8Pz)I is ascribed to the sizable amount of spin
density on the pyrrole-Cb atoms, which in turn indicates
that the dxz and/or dyz orbitals are half-occupied. In the
present case, the m-H signals at 11–13 ppm strongly
indicate that FeIII(TBP8Cz) adopts the S = 3/2 spin state
in CD2Cl2 solution at 298 K.
Figure 4(a) shows the Curie plots of the m-H signals
of [(TBP8Cz)FeIII(CN)]-(green lines) and [(TBP8Cz)-
FeIII(CN)2]2-(black lines). The averaged Curie slopes
for the m-H signals were +770 and +230 ppm K,
·
iii) Addition of CN- to FeIII(TBP8Cz). Figure 3(b)
shows the 1H NMR spectrum when 1.0 equiv. of Bu4NCN
was added to the CD2Cl2 solution of FeIII(TBP8Cz). The
four sharp signals observed at 12.64, 11.08, 9.88, and
7.28 ppm at 298 K can be assigned to the m-H signals of
(Bu4N)[FeIII(TBP8Cz)(CN)]. The three broad o-H signals
were observed at much more upfield positions; 8.50, 2.85,
and -4.58 ppm. The chemical shift of the fourth signal,
though hidden by the strong butyl signals of Bu4NCN,
was determined to be 2.07 ppm from the Curie plots. The
COSY spectrum shown in Fig. S1(a) of the Supporting
information exhibits the correlation peak between 12.64
and -4.58 ppm. Similarly, the m-H signals at 11.08, 9.88,
and 7.28 ppm correlate with the o-H signals at 1.50,
2.85, and 8.50 ppm, respectively. Thus, the chemical
shifts (ppm) of the (o-H, m-H) signals of four phenyl
rings are (-4.58, 12.64), (1.50, 11.08), (2.85, 9.88), and
(8.50, 7.28), which clearly indicates that the spin density
at the Cb atom mainly determines the chemical shifts of
respectively, while those of the o-H signals (not shown)
were -2200 and -1400 ppm·K, respectively. The decrease
in the absolute values of the Curie slopes on going from
the mono-CN to the bis-CN complex again indicates
that the spin densities on the Cb atoms have decreased in
this order and supports the change in spin-state from the
S = 3/2 to the S = 1/2.
iv) Addition of various ligands to FeIII(TBP8Cz).
Figure 4(a) also shows the Curie plots of the m-H
signals (red symbols) of the complex obtained by the
addition of 50 equiv. of HIm to the CD2Cl2 solutions
of FeIII(TBP8Cz). The Curie plots showed curvature
in the temperature range between 300 and 250 K. As
the temperature was further lowered, the plots showed
reasonably good linearity. The results can be explained in
terms of the change in spin state from the five-coordinate
S = 3/2 to the six-coordinate S = 1/2. Similar curvature
was observed in the Curie plots of the DMAP complexes
(red symbols) as shown in Fig. 4(b) though the curvature
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 522–529

FORMATION AND CHARACTERIZATION OF FIVE- AND SIX-COORDINATE IRON(III) CORROLAZINE COMPLEXES
523
Py, 4-CNPy, and tBuNC at 298 and 193 K. As is
revealed from the Curie plots, all the complexes
except for bis-CN adopt the five-coordinate S = 3/2
state at 298 K. Characteristic feature of the 1H NMR
spectra of the S = 3/2 complexes is the downfield
shifts of three of the m-H signals; the fourth one
appears quite close to the diamagnetic positions.
In contrast, the bis-CN complex adopting the S
= 1/2 at 298 K exhibit two of the m-H signals at
the downfield positions; other two signals appear
at slightly upfield positions. As the temperature is
lowered to 193 K, the HIm, 1-MeIm, and DMAP
complexes adopt the six-coordinate low-spin state
as is revealed from the presence of two downfield
Fig. 4. Curie plots of the m-H signals in (Bu4N)[FeIII(TBP8Cz)(CN)]
(green lines) and (Bu4N)2[FeIII(TBP8Cz)(CN)2] (black lines) together
with those of the complex obtained by the addition of 50 equiv of (a)
Him (red symbols) and (b) DMAP (red symbols)
shifted and two slightly upfield shifted m-H signals;
the m-H chemical shifts of these complexes are
quite close to those of the bis-CN complex. In
t
contrast, the Py, 4-CNPy, and BuNC complexes
maintain the five-coordinate S = 3/2 state even at 193 K
as is revealed by the similarity in chemical shifts to those
of the mono-CN complex. Spin states of these complexes
at 298 and 193 K are summarized in Table 1.
was observed at much lower temperature, i.e. below
250 K, as compared with the HIm complex. The Curie
plots of the Py complex started to curve below 200 K as
shown in Fig. S2. Thus, the change in spin state occurs at
much lower temperature as the axial ligand changes from
HIm to DMAP, and then to Py. In contrast, the 4-CNPy
13C NMR
Figure 5(a,b) shows the 13C NMR spectra of
13Ca-enriched five-coordinate (Bu4N)[FeIII(TBP8Cz)-
(CN)] and six-coordinate (Bu4N)2[FeIII(TBP8Cz)(CN)2]
taken in CD2Cl2 solution at 298 K. For comparison,
the 13C NMR spectra of 13Ca-enriched porphyrazine
complexes such as [FeIII(TBP8Pz)(I)] (298 K) and (Bu4N)-
[FeIII(TBP8Pz)(CN)2] (273 K) taken in CD2Cl2 solution
are also given in Figs 5(c) and 5(d), respectively [30].
t
and BuNC complexes shown also in Fig. S2 exhibited
good straight line in the temperature range examined, i.e.
308–193 K, indicating that the complexes maintain the
five-coordinate S = 3/2 spin state.
v) Chemical shifts. Table 1 shows the 1H NMR
chemical shifts of mono-CN and bis-CN complexes as
well as those of FeIII(TBP8Cz) taken in the presence of
50 equiv. of the ligands such as HIm, 1-MeIm, DMAP,
Table 1. 1H NMR chemical shifts of [FeIII(TBP8Cz)(L)]* and [FeIII(TBP8Cz)(L)2]* at 298 and 193 K together with their spin state
Ligands
1H NMR (298 K, CD2Cl2)
m-H
Spin state
1H NMR (193 K, CD2Cl2)
m-H
tBu
Spin state
o-H
tBu
o-H
8.13
-3.31 -11.91 11.56 6.79 1.53 1.30
10.15 5.27 13.26 10.31 1.67 1.30
2.31 -14.82 5.73 5.26 1.20 0.54
8.50 2.85 12.64 11.08 1.82 1.80
1.50 -4.58 9.88 7.28 1.55 1.49
9.28 6.51 11.21 9.39 1.70 1.40
4.64 -7.00 6.33 6.07 1.28 0.90
-0.83 15.27 12.96 1.89 1.83
CN-
S = 3/2
S = 1/2
S = 3/2
S = 3/2
S = 1/2
S = 1/2
(CN-)2
HIm
8.03
0.28 -5.52 9.71 7.14 1.52 1.40
8.75 13.18 11.22 1.86 1.80
1.01 -6.12 9.22 1.52 1.45
9.46 13.94 11.85 2.10 1.88
0.04 -6.02 10.31 7.51 1.68 1.62
14.74 12.38 2.16 1.89
-1.25 -7.70 10.40 1.68 1.59
—
13.21 11.34 1.83 1.71
9.74
—
—
12.44 10.29 1.60 1.19
-11.56 5.68 5.31 1.08 0.51
5.79 12.94 10.39 1.15 1.61
-13.53 5.68 5.26 1.22 0.52
—
10.04
—
1-MeIm
DMAP
S = 3/2
S = 1/2
—
—
9.41
—
13.74 11.10 1.35 1.66
5.84 1.26 0.72
0.88 17.04 13.68 2.16 1.89
-4.48 -16.02 10.04 6.48 1.51 1.38
8.25 -1.71 19.32 15.33 2.54 2.00
-7.56 -18.00 12.09 7.08 1.65 1.65
10.22 17.46 14.09 2.08 1.93
-5.31 -16.58 9.97 6.34 1.62 1.47
S = 3/2
S = 3/2
S = 3/2
S = 3/2
S = 1/2(major)
S = 3/2(major)
S = 3/2
0.78 -14.00
9.22
—
—
—
Py
—
4-CNPy
8.05 3.48 15.46 12.88 2.26 1.93
-2.36 -9.22 10.51 7.39 1.71 1.60
tBuNC
10.01
—
14.83 12.44 2.15 1.89
—
S = 3/2
-1.41 -8.21 10.23 7.34 1.65 1.58
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 523–529

524
S. KURAHASHI ET AL.
Fig. 6. EPR spectra of the samples consisting of FeIII(TBP8Cz)
and 50 equiv of various ligands(L) taken in frozen toluene
solution at 15 K.
spectra taken in frozen toluene solution at 15 K exhibited
the clearly separated rhombic type spectra for all the
complexes examined, indicating the formation of six-
coordinate low-spin [FeIII(TBP8Cz)(L)2]*. The g values
of these complexes are listed in Table 2. The g values of
the Py and DMAP complexes are essentially the same as
those reported by Goldberg and co-workers [41].
Fig. 5. 13C NMR spectra of 13Ca-enriched (a) (Bu4N)
[FeIII(TBP8Cz)-(CN)], (b) (Bu4N)2[FeIII(TBP8Cz)(CN)2], (c)
[FeIII(TBP8Pz)(I)] taken in CD2Cl2 solution at 298 K, and (d)
(Bu4N)[FeIII(TBP8Pz)-(CN)2] taken in CD2Cl2 solution at 273 K
We have considered that the addition of much smaller
amount of ligands(L) should form five-coordinate
FeIII(TBP8Cz)(L) at 15 K and that they exhibit the EPR
spectra characteristic to the intermediate-spin state.
However, the EPR spectra of FeIII(TBP8Cz) taken in the
presence of 3 equiv. of the ligands such as CN-, HIm,
and tBuNC showed the rhombic-type spectra that are the
same to those shown in Fig. 6.
The Ca signals of (Bu4N)2[FeIII(TBP8Cz)(CN)2] were
widely spread; they appeared at 162, 50, -79, and -625
ppm. Similarly, the Ca signals of (Bu4N)2[FeIII(TBP8Cz)-
(CN)2]were observed at 163, 105, 40, and -87 ppm. Thus,
the average Ca chemical shifts of the mono- and bis-CN
complexes were calculated to be -123 and 55 ppm,
respectively. In the case of the porphyrazine complexes,
the Ca chemical shift of the iodide complex with S = 3/2
was -252 ppm while that of the bis-CN complex with S =
1/2 was 53 ppm. These results clearly indicate that (Bu4N)-
[FeIII(TBP8Cz)(CN)] and (Bu4N)2[FeIII(TBP8Cz)-(CN)2]
adopt the S = 3/2 and S = 1/2, respectively [51, 52].
Table 2. EPR
g
values of
[FeIII(TBP8Cz)(L)2]* determined in
frozen toluene solution at 15 K
Ligand (L)
g1
g2
g3
EPR spectra
HIm
2.47
2.46
2.48
2.44
2.40
2.38
2.36
2.21 1.89
2.22 1.88
2.22 1.89
2.26 1.89
2.22 1.90
2.21 1.90
2.21 1.92
Figure 6 shows the EPR spectra of the complexes
obtained by the addition of 50 equiv. of a wide variety of
ligands(L) to the toluene solutions of FeIII(TBP8Cz). As
is revealed by the UV-vis spectra at ambient temperature,
only CN- ion binds the iron(III) of FeIII(TBP8Cz) to form
the bis-adduct; all the other ligands examined in this
study bind the iron to form only the mono-adducts. EPR
1-MeIm
DMAP
CN-
Py
4-CNPy
tBuNC
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 524–529

FORMATION AND CHARACTERIZATION OF FIVE- AND SIX-COORDINATE IRON(III) CORROLAZINE COMPLEXES
525
In the case of the low-spin iron(III) complexes with
axial symmetry(D4h or C4v), the EPR spectra can be
classified into three categories [3]. The complex that
adopts the (dxy)2(dxz, dyz)3 ground state exhibits either
the large gmax or the rhombic type spectrum depending
on the orientation of the axial ligands. Thus, the low-
spin complexes having either perpendicularly aligned
planar ligands or linear ligands exhibit the large gmax type
spectra, while the low spin complexes having parallel
aligned planar ligands exhibit the rhombic type spectra.
In contrast, the complex that adopts the (dxz, dyz)4(dxy)1
ground state exhibits the axial type spectrum with g^
value less than 2.6 [53]. In the present case, however,
the rhombic type spectra are expected regardless of
the electronic ground states because corrolazine does
not possess C4 axis perpendicular to the ring. Thus, we
cannot determine the electronic ground state simply from
the spectral type.
co-workers on the basis of the EPR spectroscopy [41].
In the case of (Bu4N)2[FeIII(TBP8Cz)(CN)2], the IS values
were 0.07–0.10 and QS values were 2.72–2.75 mm s-1,
though the QS values are slightly larger than the typical
values for the low-spin complexes. The results could be
interpreted in terms of the unsymmetrical coordination
field caused by the triaza-corrole structure.
Effective magnetic moments
Effective magnetic moments of FeIII(TBP8Cz) were
measured by the Evans method in CD2Cl2 solution
in the presence of 50 equiv. of each ligand [43]. As
shown in Fig. 8(a), the effective magnetic moments of
(Bu4N)2[FeIII(TBP8Cz)(CN)2] were 2.0 0.1 mB in the
temperature range 193–298 K. The results indicate that
the complex maintains the S = 1/2 in CD2Cl2 solution.
Consistent with the Curie plots in Fig. 4, both the DMAP
and 1-MeIm complexes showed the conversion of spin
state from the S = 3/2 to the S = 1/2 as the temperature
is lowered, suggesting the change in structure from five-
to six-coordination. In contrast, the 4-CNPy complex
maintains the five-coordinate S = 3/2 structure even at
193 K as in the case of the mono-CN complex.
Figure 8(b) shows the temperature dependence of the
effective magnetic moments of the mono-CN and bis-CN
complexes measured for the microcrystalline samples at 4.5
to 300 K by SQUID magnetometry. The effective magnetic
moments for the microcrystalline sample obtained from
the solution containing FeIII(TBP8Cz) and HIm (3 equiv.) is
also given in Fig. 8(b). As expected, the mono-CN complex
showed the effective magnetic moments
expected for the S = 3/2 in the wide range of
temperature. The bis-CN complex showed
the low-spin state below 150 K. However, the
effective magnetic moment of this complex
increased gradually as the temperature was
raised above 150 K and reached 2.42 mB at 300
K. The result suggests that the spin state partly
changed to the S = 3/2 as the temperature was
raised from 150 to 300 K. The result should be
ascribed to the spin crossover phenomenon in
the bis-CN complex rather than to the change
in coordination structure from six- to five-
coordinate complex in the solid state. In contrast
tothesolutiondata, theHImcomplexmaintained
the S = 1/2 spin state in the temperature range
examined. The result suggests that the bis(HIm)
complex was crystallized preferentially from the
solution containing FeIII(TBP8Cz) and 3 equiv.
HIm. Thus, the CD2Cl2 solution prepared from
the microcrystalline sample used for the SQUID
measurement showed the 1H NMR signals
indicative of the S = 3/2 spin state at ambient
temperature due to the conversion from the six-
Mössbauer spectra
Figure 7 shows the Mössbauer spectra of (a)
FeIII(TBP8Cz) and (b) (Bu4N)2[FeIII(TBP8Cz)(CN)2]
taken for the microcrystalline sample from 77 to 295 K
(or 292 K in the latter complex). Tables S1 and S2 in the
Supporting information list the Mössbauer parameters. In
the case of FeIII(TBP8Cz), the QS values were temperature
independent and they were maintained at 3.91 mm s-1.
The large QS values together with the IS values of 0.45–
0.56 mm s-1 strongly indicate that the complex adopts
the S = 3/2 [54–57], as pointed out by Goldberg and
Fig. 7. Mössbauer spectra of (a) FeIII(TBP8Cz) and (b) (Bu4N)2[FeIII-
(TBP8Cz)(CN)2] taken for the microcrystalline samples.
coordinate to the five-coordinate complex in
solution.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 525–529

526
S. KURAHASHI ET AL.
Electron configurations of six-coordinate low-spin
corrolazine complexes
shown in Fig. 2. These interactions should increase the
spin densities on the Cb atoms. Consequently, the o-H
and m-H signals shift upfield and downfield, respectively.
The large spread of these signals can be another good
evidence for the (dxy)2(dxz, dyz)3 ground state. If, on the
other hand, the complex adopts the (dxz, dyz)4(dxy)1 ground
state, the unpaired electron in the dxy orbital, which is
labeled as b2 in the six-coordinate complex with C2v
symmetry, has no suitable corrolazine orbitals to interact.
Thus, every signal should appear quite close to its
diamagnetic position.
As listed in Table 1, both the o-H and m-H signals
of (Bu4N)2[FeIII(TBP8Cz)(CN)2] showed large spread, i.e.
the amounts of the spread for the o-H and m-H signals
were 16.28 and 5.14 ppm, respectively, at 298 K. The
result indicates that the spin densities of the peripheral Cb
atoms are quite inhomogeneous, which can be explained
if the dxz orbital is half-occupied. In addition, the Ca
signals of the bis-CN complex also spread widely, i.e.
from -87 to +163 ppm. These results strongly indicate
that the bis-CN complex adopts the (dxy)2(dxz, dyz)3 ground
state.
In the previous section, we have discussed mainly
the spin states of four-, five-, and six-coordinate
corrolazine complexes on the basis of various
spectroscopic and magnetic data. We now consider the
electron configurations of the six-coordinate corrolazine
complexes.
(Bu4N)2[FeIII(TBP8Cz)(CN)2]. Among the six-
coordinate corrolazine complexes examined in this
study, the bis-CN complex (Bu4N)2[FeIII(TBP8Cz)(CN)2]
has been most extensively studied. This is because the
complex is easily formed by the addition of 3 equiv. of
CN- into the CH2Cl2 solutions of FeIII(TBP8Cz) even at
the ambient temperature.
As
mentioned
in
the
previous
section,
(Bu4N)2[FeIII(TBP8Cz)(CN)2] adopts mainly the S = 1/2
both in solution and in the solid state in a wide range
of temperature on the basis of the EPR (frozen toluene
solution, 15 K) and Mössbauer (solid, 77–295 K)
spectroscopy as well as the magnetic susceptibility data
obtained by the SQUID (solid, 4.5–300 K) and Evans
method (CD2Cl2 solution, 213–313 K); the SQUID data
has suggested a presence of small amount of the S = 3/2
complex at 300 K. The question is how to determine the
electronic ground state of the low-spin complex.
[FeIII(TBP8Cz)(L)2]*. Complexes carrying HIm,
1-MeIm, and DMAP adopt the six-coordinate low-
spin state only at the low temperature as revealed by
the temperature dependence of the effective magnetic
moments shown in Fig. 8 and the 1H NMR chemical shifts
listed in Table 1. The similarity of the 1H NMR chemical
shifts to those of the bis-CN complex suggests that these
complexes also adopt the (dxy)2(dxz, dyz)3 ground state.
If the corrolazine complexes adopt the (dxy)2(dxz, dyz)3
ground state, the unpaired electron in the dxz or dyz orbital
can interact with the corrolazine HOMO-1 or HOMO
Fig. 8. (a) Effective magnetic moments of FeIII(TBP8Cz) determined by the Evans method in the presence of 50 equiv of CN-,
1-MeIm, DMAP, and 4-CNPy in CD2Cl2 solution. Mono-CN complex (Bu4N)[FeIII(TBP8Cz)(CN)] is obtained by the addition of
1.0 equiv of Bu4N(CN) to the CD2Cl2 solution of FeIII(TBP8Cz). (b) Temperature dependence of the effective magnetic moments
determined by the SQUID magnetometry for the microcrystalline samples of (Bu4N)2[FeIII(TBP8Cz)(CN)2], (Bu4N)[FeIII(TBP8Cz)-
(CN)], and [FeIII(TBP8Cz)(Him)2]
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 526–529

FORMATION AND CHARACTERIZATION OF FIVE- AND SIX-COORDINATE IRON(III) CORROLAZINE COMPLEXES
527
The amounts of the spread of the o-H signals reached
as much as 21.12, 23.66, and 23.41 ppm for the HIm,
1-MeIm, and DMAP complexes, respectively, at 193 K.
Complexes carrying Py, 4-CNPy, and tBuNC form the
low-spin bis-adducts only at extremely low temperature
as confirmed by the EPR spectra taken in frozen toluene
solution at 15 K. The rhombic EPR spectra clearly
indicates that these complexes are in the S = 1/2 state.
In the absence of the NMR data, it is very difficult to
conclude whether the complex adopts the (dxy)2(dxz, dyz)3
or (dxz, dyz)4(dxy)1 ground state. We speculated that these
complexes should also adopt the (dxy)2(dxz, dyz)3 ground
state because the EPR spectrum of each complex is quite
similar to that of the bis-CN complex. For example, the
g values of the bis-tBuNC complex were 2.36, 2.21, and
1.92, which are close to those of the bis-CN complex, i.e.
2.44, 2.26, and 1.89. As mentioned in the Introduction,
low-spin bis-tBuNC complexes almost always adopt the
(dxz, dyz)4(dxy)1 ground state because tBuNC has low-lying
p* orbital and stabilizes the dp orbitals. The exceptional
complexes showing the (dxy)2(dxz, dyz)3 ground state are
1 and 2 having one and two nitrogen atoms at the meso-
positions, respectively, as shown in Chart 1 [26, 27].
Thus, it seems to be a reasonable assumption to consider
that [FeIII(TBP8Cz)(tBuNC)2] having three nitrogen atoms
at the meso-positions of the corrole structure adopts the
(dxy)2(dxz, dyz)3 ground state.
amount of tBuNC to the CD2Cl2 (or toluene-d8) solution
of FeIII(TBP8Pz)Cl led to the formation of the bis-tBuNC
complex even at the ambient temperature. However,
1
the H NMR spectrum has revealed that the complex is
diamagnetic [FeII(TBP8Pz)(tBuNC)2]; the chemical shifts
for the o-H, m-H and tBu-H were determined to be 8.62,
7.58, and 1.59 ppm, respectively, which are quite close
to those of diamagnetic [FeII(TBP8Pz)(CN)2] mentioned
above. The 13C NMR spectrum of the complex obtained
from 13Ca-enriched FeIII(TBP8Pz)Cl exhibited the Ca
signal at the diamagnetic position in CD2Cl2 solution, i.e.
151 ppm. The diamagnetic nature was further confirmed
by the EPR spectrum, which showed no signal in frozen
CH2Cl2 solution at 4 K. These results suggest that the
iron(III) ion in FeIII(TBP8Pz)Cl was reduced to iron(II)
in the presence of excess amount of tBuNC to form low-
spin diamagnetic [FeII(TBP8Pz) (tBuNC)2].
Facile reduction of FeIII(TBP8Pz)Cl in the presence
t
of excess CN- (in toluene) and BuNC (both in toluene
and CH2Cl2) to form diamagnetic [FeII(TBP8Pz)(CN)2]
and [FeII(TBP8Pz)(tBuNC)2], respectively, suggests
that FeIII(TBP8Pz)Cl is much more easily reduced
than FeIII(TBP8Cz), which should be one of the major
differences between these two ring systems.
CONCLUSION
Spin states and electron configurations of four-,
five- and six-coordinate corrolazine complexes have
been examined. In CH2Cl2 (or CD2Cl2) solution, the
spectroscopic data have unambiguously shown that the
five-coordinate [FeIII(TBP8Cz)(L)]* (L = CN-, HIm,
Comparison of the electronic structures with those
of porphyrazine complexes
In the previous paper, we have reported that the low-
spin porphyrazine complex, (Bu4N)[FeIII(TBP8Pz)(CN)2],
adopts the (dxy)2(dxz, dyz)3 ground state on the basis of the
large gmax type signal in EPR, the upfield shift of the Ca
signal in 13C NMR, and the downfield shifted m-H signal
t
1-MeIm, DMAP, Py, 4-CNPy, and BuNC) adopt the
S = 3/2 spin state at ambient temperature. As for the
six-coordinate cyanide complex, (Bu4N)2[FeIII(TBP8Cz)-
(CN)2], the spectroscopic and magnetic data have shown
that the complex adopts the S = 1/2 both in solution and
in the solid in a wide range of temperature; the population
of the S = 3/2 increases slightly as the temperature is
raised. The large spread of the o-H, m-H, and pyrrole Ca
signals in the 1H and 13C NMR spectra has indicated that
the complex adopts the (dxy)2(dxz, dyz)3 electronic ground
state. Other six-coordinate [FeIII(TBP8Cz)(L)2] (L = HIm,
1-MeIm, and DMAP), which are the major components
at least below 200 K, also adopt the low-spin (dxy)2(dxz,
dyz)3 ground state. Thus, the electronic structure of six-
coordinate corrolazine complexes is similar to that of the
porphyrazine bis-CN complex [(TBP8Pz)FeIII(CN)2]-. In
toluene solution, however, some differences are observed
between corrolazine and porphyrazine complexes. The
addition of excess amount of CN- and tBuNC to the toluene
solutions of FeIII(TBP8Pz)Cl has led to the formation of
diamagnetic [FeII(TBP8Pz)(CN)2]2- and [FeII(TBP8Pz)-
(tBuNC)2]-. These results suggest that the iron(III) ion
of the porphyrazine complex is much more easily reduced
than that of the corresponding corrolazine complex.
1
in H NMR spectra [30]. Thus, the electronic ground
state of (Bu4N)2[FeIII(TBP8Cz)(CN)2] is the same as that
of (Bu4N)[FeIII(TBP8Pz)(CN)2] as far as the solvent is
CH2Cl2.
In toluene solution, however, the porphyrazine
complex exhibited a completely different NMR spectra.
The o-H and m-H signals appeared at 8.46 and 7.57
ppm, respectively. Similarly, the Ca signal appeared
at 151 ppm. These chemical shifts are quite close to
those of the diamagnetic complexes. Furthermore, the
EPR spectrum was silent at 4.2 K. Thus, the complex
is not paramagnetic (Bu4N)[FeIII(TBP8Pz)(CN)2] but
diamagnetic (Bu4N)2[FeII(TBP8Pz)(CN)2], indicating
that the porphyrazine core is more easily reduced than
the corresponding corrolazine core especially in toluene
solution.
As mentioned, the bis-tBuNC complex of corrolazine,
[FeIII(TBP8Cz)(tBuNC)2], was formed only when the
temperature was lowered to 15 K as revealed by the EPR
spectrum taken in frozen toluene solution. In the case of
theporphyrazinecomplex, however, theadditionofexcess
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 527–529

528
S. KURAHASHI ET AL.
Acknowledgements
12. Ohgo Y, Neya S, Takahashi M, Takeda M, Funasaki
N and Nakamura M. Chem. Lett. 2003; 32: 526–527.
13. Sessler JL, Gebauer A and Vogel E. The Porphyrin
Handbook, Vol. 2, Kadish KM, Smith KM and
Guilard R. (Eds.) Academic Press: San Diego,
2000; pp 1–54.
14. Vogel E, Köcher M, Schmickler H and Lex J.
Angew. Chem. Int. Ed. Engl. 1986; 25: 257–259.
15. Vogel E, Balci M, Pramod K, Koch P, Lex J and
Ermer O. Angew. Chem. Int. Ed. Engl. 1987; 26:
928–931.
16. Wehrle B, Limbach H-H, Kocher M, Ermer O and
Vogel E. Angew. Chem. Int. Ed. Engl. 1987; 26:
934–936.
17. Sessler JL, Brucker EA, Weghorn SJ, Kisters M,
Schafer M, Lex J and Vogel E. Angew. Chem. Int.
Ed. Engl. 1994; 33: 2308–2312.
This work was supported by the Grant-in-Aid for
Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan (Grant
22750052 to T.I. and Grant 22550157 to M.N.). Thanks
are due to the Research Center for Molecular-Scale
Nanoscience, the Institute for Molecular Science (IMS).
This work was also supported by the Research Center for
Materials with Integrated Properties, Toho University.
Supporting information
COSY spectra and Mössbauer parameters (Figs S1–S2
and Tables S1–S2) are given in the supplementary
material. This material is available free of charge via the
Internet at http://www.worldscinet.com/jpp/jpp.shtml.
18. Aukauloo MA and Guilard R. New J. Chem. 1994;
18: 1205–1207.
REFERENCES
19. Callot HJ, Rohrer R and Tschamber T. New
J. Chem. 1995; 19: 155–159.
‡ Abbreviations: TBP8Cz: trianion of 2,3,7,8,12,13,
17,18-octakis(4-tert-butylphenyl)corrolazine,
TBP8Pz: dianion of 2,3,7,8,12,13,17,18-octakis-
(4-tert-butyl-phenyl)porphyrazine, MAzP: dianion
of 2,3,7,8,12,13,17,18-octaethyl-5-azaporphyrin,
DAzP: dianion of 2,8,12,18-tetrabutyl-3,7,13,17-
tetramethyl-5,15-diazaporphyrin, HIm: imidazole,
1-MeIm: 1-methylimidazole, DMAP: 4-(N,N-
dimethylamino)pyridine, Py: pyridine, 4-CNPy:
4-cyanopyridine, tBuNC: tert-butylisocyanide.
1. Nakamura M. Coord. Chem. Review. 2006; 250:
2271–2294.
20. Vogel E, Broring M, Scholz P, Deponte R, Lex
J, Schmickler H, Schaffner K, Braslavsky SE,
Muller M, Porting S, Weghorn SJ, Fowler CJ and
Sessler JL. Angew. Chem. Int. Ed. Engl. 1997; 36:
1651–1654.
21. Waluk L. Handbook of Porphyrin Science, Vol.
7, Kadish KM, Smith KM and Guilard R. (Eds.)
World Scientific: Singapore, 2010; pp 359–435.
22. Kobeissi M, Toupet L and Simonneaux G. Inorg.
Chem. 2001; 40: 4494–4499.
23. Astashkin AV, Raitsimring AM and Walker FA.
J. Am. Chem. Soc. 2001; 123: 1905–1913.
24. Cai S, Lichtenberger L and Walker FA. Inorg.
Chem. 2005; 44: 1890–1903.
2. Nakamura M, Ohgo Y and Ikezaki A. Handbook of
Porphyrin Science, Vol. 7, Kadish KM, Smith KM
and Guilard R. (Eds.) World Scientific: Singapore,
2010; pp 1–146.
25. IkezakiA, Nakamura M, Juillard S and Simonneaux
G. Inorg. Chem. 2006; 45: 6728–6739.
26. Nakamura K, Ikezaki A, Ohgo Y, Ikeue T, Neya
S and Nakamura M. Inorg. Chem. 2008; 47:
10299–10307.
3. Walker FA. The Porphyrin Handbook, Vol. 5,
Kadish KM, Smith KM and Guilard R. (Eds.)
Academic Press: San Diego, 2000; pp 81–183.
4. Evans DR and Reed CA. J. Am. Chem. Soc. 2000;
122: 4660–4667.
27. Ohgo Y, Neya S, Uekusa H and Nakamura M.
Chem. Commun. 2006; 4590–4592.
28. Simonneaux G, Hindre F and Le Plouzennec M.
Inorg. Chem. 1989; 28: 823–825.
29. Simonneaux G, Schunemann V, Morice C, Carel
L, Toupet L, Winkler H, Trautwein AX and Walker
FA. J. Am. Chem. Soc. 2000; 122: 4366–4377.
30. Ikeue T, Kurahashi S, Handa M, Sugimori T and
Nakamura M. J. Porphyrins. Phthalocyanines
2008; 12: 1041–1049.
5. Sakai T, Ohgo Y, Ikeue T, Takahashi M and
Nakamura M. J. Am. Chem. Soc. 2003; 125:
13028–13029.
6. Cheng R-J, Wang Y-K, Chen P-Y, Han Y-P and
Chang C-C. Chem. Commun. 2005; 1312–1314.
7. Ling Y and Zhang Y. J. Am. Chem. Soc. 2009; 131:
6386–6388.
8. Ikezaki A, Ohgo Y, Watanabe T and Nakamura M.
Inorg. Chem. Commun. 2008; 11: 1199–1202.
9. Neya S, Ohgo Y, Nakamura M and Funasaki N.
Bull. Chem. Soc. Jpn. 2000; 73: 2759–2765.
10. Ikeue T, Ohgo Y, Takahashi M, Takeda M, Neya S,
Funasaki N and Nakamura M. Inorg. Chem. 2001;
40: 3650–3652.
11. OhgoY,Neya S, Ikeue T, Funasaki N, Takahashi M,
Takeda M and Nakamura M. Inorg. Chem. 2002;
41: 4627–4629.
31. Ramdhanie B, Stern CL and Goldberg DP. J. Am.
Chem. Soc. 2001; 123: 9447–9448.
32. Ramdhanie B, Zakharov LN, Reingold AL and
Goldberg DP. Inorg. Chem. 2002; 41: 4105–4107.
33. Mandimutsira BS, Ramdhanie B, Todd RC, Wang
H, Zareba AA, Czernuszewicz RS and Goldberg
DP. J. Am. Chem. Soc. 2002; 124: 15170–15171.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 528–529

FORMATION AND CHARACTERIZATION OF FIVE- AND SIX-COORDINATE IRON(III) CORROLAZINE COMPLEXES
529
34. Wang SH, Mandimutsira BS, Todd R, Ramdhanie
B, Fox JP and Goldberg DP. J. Am. Chem. Soc.
2004; 126: 18–19.
35. Grybo DT, Fox JP and Goldberg DP. J. Porphyrins
Phthalocyanines 2004; 8: 1091–1105.
47. Tangen E and Ghosh A. J. Am. Chem. Soc. 2002;
124: 8117–8121.
48. Kobayashi N, Yokoyama M, Muranaka A and
Ceulemans A. Tetrahedron Lett. 2004; 45:
1755–1758.
36. Kerber WD and Goldberg DP. J. Inorg. Biochem.
2006; 100: 838–857.
49. Thomas KE, Conradie J, Hansen LK and Ghosh A.
Inorg. Chem. 2011; 50: 3247–3251.
37. Lansky DE and Goldberg DP. Inorg. Chem. 2006;
45: 5119–5125.
50. Fitzgerald JP, Haggerty BS, Rheingold AL,
May L and Brewer GA. Inorg. Chem. 1992; 31:
2006–2013.
51. Stuzhin PA, Hamdush M and Ziener U. Inorg.
Chim. Acta 1995; 236: 131–139.
52. Ikeue T, Ohgo Y, Saitoh T, Yamaguchi T and
Nakamura M. Inorg. Chem. 2001; 40: 3423–3434.
53. Ikeue T, Ohgo Y, Saitoh T, Nakamura M, Fujii H
and Yokoyama M. J. Am. Chem. Soc. 2000; 122:
4068–4076.
54. Reed CA and Guiset F. J. Am. Chem. Soc. 1996;
118: 3281–3282.
55. Ikeue T, Saitoh S, Yamaguchi T, OhgoY, Nakamura
M, Takahashi M and Takeda M. Chem. Commun.
2000; 1989–1990.
56. Debrunner P. Iron Porphyrins (part 3), Lever ABP
and Gray HB. (Eds.) VCH: Weinheim, 1983; pp
139–234.
57. Gütlich P and Ensling J. Inorganic Electronic
Structure and Spectroscopy, Solomon EI and
Lever ABP. (Eds.) Wiley: New York, 1999;
pp 161–211.
38. Lansky DE, Kosack JR, Narducci Sarjeant AA and
Goldberg DP. Inorg. Chem. 2006; 45: 8477–8479.
39. Lansky DE, Narducci Sarjeant AA and Goldberg
DP. Angew. Chem. Int. Ed. 2006; 45: 8214–8217.
40. Kerber WD and Goldberg DP. J. Inorg. Biochem.
2006; 100: 838–857.
41. Kerber WD, Ramdhanie B and Goldberg DP.
Angew. Chem. Int. Ed. 2007; 46: 3718–3721.
42. McGown AJ, Kerber WD, Fujii H and Goldberg DP.
J. Am. Chem. Soc. 2009; 131: 8040–8048.
43. Evans DF and James TA. J. Chem. Soc. 1979;
723–726.
44. Groves JT, Quinn R, McMurry TJ, Nakamura M,
Lang G and Boso B. J. Am. Chem. Soc. 1985; 107:
354–360.
45. Nie H, Barret AGM and Hoffman BM. J. Org.
Chem. 1999; 64: 6791–6796.
46. Fox JP, Ramdhanie B, Zareba AA, Czemuszewicz
RS and Goldberg DP. Inorg. Chem. 2004; 43:
6600–6608.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 529–529