Chloro(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)iron(III): A high-spin complex

Article abstract of DOI:10.1039/b202842p

The crystal structures of diamagnetic (methanol)(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)zinc(II) methanol solvate Zn(N-p-NCOC₆H₄NO₂-tpp)(MeOH)·MeOH [or 4(MeOH)·MeOH] and paramagnetic chloro-(N-p-nitrobenzoylimi

Full text of DOI:10.1039/b202842p

View Article Online / Journal Homepage / Table of Contents for this issue
Chloro(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)iron(III):
a high-spin complex†
Ching-Huei Chen,a Yu-Yi Lee,a Bing-Chuang Liau,a Shanmugham Elango,a Jyh-Horung Chen,*a
Hsi-Ying Hsieh,b Feng-Ling Liao,c Sue-Lein Wangc and Lian-Pin Hwangd
a Department of Chemistry, National Chung-Hsing University, Taichung 40227, Taiwan
b Chung Hwa College of Medical Technology, Tainan 717, Taiwan
c Department of Chemistry, National Tsing-Hua University, Hsin-Chu 30043, Taiwan
d Department of Chemistry, National Taiwan University and Institute of Atomic and Molecular
Sciences, Academia Sinica, Taipei 10764, Taiwan
Received 20th March 2002, Accepted 29th May 2002
First published as an Advance Article on the web 4th July 2002
The crystal structures of diamagnetic (methanol)(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)zinc()
methanol solvate Zn(N-p-NCOC6H4NO2-tpp)(MeOH)ؒMeOH [or 4(MeOH)ؒMeOH] and paramagnetic chloro-
(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)iron() Fe(N-p-NCOC6H4NO2-tpp)Cl (5), were determined.
Both are pentacoordinate complexes where the p-nitrobenzoylimido (NNB) moiety is inserted into a zinc–pyrrole
(or iron–pyrrole) bond. The coordination geometry of the zinc (or iron) center is best described as a distorted
trigonal bipyramid with the N(2), N(5), and O(4) [or N(2), N(5), and Cl(1)] atoms lying in the equatorial plane. The
plane of the three pyrrole nitrogen atoms [i.e., N(1), N(2) and N(3)] strongly bonded to Zn2ϩ in 4(MeOH)ؒMeOH
(or Fe3ϩ in 5) is adopted as a reference plane, 3N. The porphyrin ring is severely distorted and the pyrrole ring N(4) is
bonded to the NNB ligand making a dihedral angle of 30.0Њ (or 27.8Њ) with the 3N plane for 4(MeOH)ؒMeOH (or 5).
Solid state magnetic susceptibility and the effective magnetic moment data were measured for 5 from 300 to 5 K. In
the higher temperature range (T > 50 K), the effective magnetic moment is constant and is equal to 5.87 µB. This µeff
value confirms that there is a high-spin ferric (S = 5/2) state for the iron atom in 5. The g values of 9.5 0.4, 4.2 and
1.1 measured from X-band EPR spectra were also consistent with a high-spin ferric iron in 5. The magnitude of zero
field splitting, D, and the rhombicity parameter, λ (= E/D), in 5 were determined approximately as 0.79 cmϪ1 and 0.29,
respectively, by EPR spectroscopy and paramagnetic susceptibility measurements.
tetraphenylporphyrinato)zinc() methanol solvate Zn(N-p-
NCOC6H4NO2-tpp) [or 4(MeOH)ؒMeOH] and paramagnetic
chloro-N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato-
iron() Fe(N-p-NCOC6H4NO2-tpp)Cl (5). Compound 5, like a
Introduction
Metalloporphyrins with a bridged structure between the central
metal and one of the four pyrrole nitrogens are of great interest
since an iron() porphyrin with an oxygen atom inserted
wide variety of neutral five-coordinate ferric porphyrin com-
into an Fe–N bond is postulated as one of the possible struc-
plexes, Fe(por)X (XϪ = an anionic ligand), can have a low- (S =
tures for the highly oxidized forms of some hemoproteins.1
1/2), intermediate- (S = 3/2) or high-spin (S = 5/2), or quantum
Many bridged metalloporphyrins with metal–NTs–N linkages
mechanically spin-admixed (S = 3/2, 5/2) ground state, depend-
(metal = Zn,2 Ni,3 Fe,4 Hg,5 Ga,6 Tl;6 Ts = tosyl) have so far been
ing on the ligand field strength of the anion.8 Although the data
reported. Callot et al.3 reported the synthesis and spectroscopic
for Fe(N–NTs–tpp)Cl was published 14 years ago by Mansuy
characterization of the metallation of N-p-nitrobenzoylamido-
meso-tetraphenylporphyrin [N-p-HNCOC6H4NO2-Htpp] (tpp =
the dianion of meso-tetraphenylporphyrin) leading to mono-
nuclear complexes of (N-p-nitrobenzoylimido-meso-tetra-
and co-workers,4 there was some ambiguity in the intepretation
and assignment of their EPR data. Futhermore, the replace-
ment of tosylimido (NTs) substituents in Fe(N-NTs-tpp)Cl by
N-p-nitrobenzoylimido (NNB) ligand in compound 5 provides
phenylporphyrinato)nickel() Ni(N-p-NCOC6H4NO2-tpp) (1)
a route to observe the zero-field splitting parameter, D, and the
and (N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)-
copper() Cu(N-p-NCOC6H4NO2-tpp) (2). We have recently
reported the X-ray structures of two diamagnetic, mono-
nuclear, and bridged metal complexes i.e., the four-coordinate
rhombicity parameter, λ (= E/D), for 5 by X-band EPR
spectroscopy and paramagnetic susceptibility mesurements. We
report herein the X-ray structures of 4(MeOH)ؒMeOH and 5
and the analysis of the electronic and magnetic properties of
compound of 1 and the six-coordinate complex of cis-
5 from magnetic susceptibility mearsurements and EPR and 1H
acetato(N-p-nitrobenzoylimido-meso-tetraphenylporphyrinato)-
NMR spectroscopic studies. Complex 5 is the first example of
thallium() Tl(N-p-NCOC6H4NO2-tpp)(OAc) (3).7
In this paper, we present the results obtained upon replacing
Ni() with Zn() and Fe() in 1 forming new compounds
an iron() porphyrin with high-spin (S = 5/2) which has the
FeIII–N–(p-COC6H4NO2)–N (or Fe–NNB–N) linkage.
4(MeOH)ؒMeOH and 5, respectively. This replacement
increases the coordination number (CN) from 4 of 1 to 5
forming diamagnetic (methanol)(N-p-nitrobenzoylimido-meso-
Experimental
Preparation of Zn(N-p-NCOC6H4NO2-tpp) (4)
Compound 4 was prepared in the same way as described for
Ni(N-p-NCOC6H4NO2-tpp) using Zn(OAc)2.3 Compound 4
† Dedicated to Professor Rob Dunbar (Case Western Reserve
University) on the occasion of his 60th birthday.
DOI: 10.1039/b202842p
J. Chem. Soc., Dalton Trans., 2002, 3001–3006
This journal is © The Royal Society of Chemistry 2002
3001

View Article Online
Table 1 Crystal data for 4(MeOH)ؒMeOH and 5ؒCHCl3
Empirical formula
Formula weight
C53H40N6O5Zn [4(MeOH)ؒMeOH]
906.28
C52H33Cl4FeN6O3 [5ؒCHCl3]
987.49
Space group
Crystal system
P2(1)/n
P2(1)2(1)2(1)
Orthorhombic
10.027(1)
17.277(2)
26.645(3)
90
Monoclinic
14.865(3)
18.088(3)
16.773(3)
97.200(4)
4474(1)
a/Å
b/Å
c/Å
β/Њ
V/Å3
4615.8(9)
4
Z
4
F(000)
1880
6.06
2020
6.10
µ(Mo Kα)/cmϪ1
Crystal size/mm
T /K
0.63 × 0.50 × 0.25
295(2)
0.32 × 0.25 × 0.25
295(2)
No. of reflections measured
No. of reflections observed
R
26251
9991 [I > 2σ(I )]
0.0709
29828
11062 [I > 2σ(I )]
0.0501
Rw
0.2223
0.1115
was dissolved in CHCl3 and layered with MeOH and dark blue
through one-bond coupling and HMBC (heteronuclear mult-
iple bond coherence) for two- and three-bond proton–carbon
coupling.
The positive-ion fast atom bombardment mass spectrum
(FAB MS) was obtained in a nitrobenzyl alcohol (NBA) matrix
using a JEOL JMS–SX/SX 102A mass spectrometer. UV/
Visible spectra were recorded at 25 ЊC on a HITACHI U-3210
spectrophotometer.
crystals of 4(MeOH)ؒMeOH were obtained for single crystal
1
X-ray analysis. H NMR (200.00 MHz, CDCl3, 25 ЊC): δ 9.10
3
[d, Hβ(5,14), J(H–H) = 4.6 Hz], Hβ(a,b) represents the two
equivalent β-pyrrole protons attached to carbons a and b,
respectively; 8.92 [d, Hβ(4,15), 3J(H–H) = 4.6 Hz]; 8.87 [s,
Hβ(9,10)]; 7.75–8.40 (m, phenyl protons); 7.79 [s, Hβ(19,20)];
3
6.63 [d, HNB(48,50) or NB–H3,5, J(H–H) = 8.8 Hz], HNB(c,d)
represents the two equivalent protons attached to carbons c
and d of p-nitrobenzoyl (NB) group respectively; 4.08 [d,
Magnetic susceptibility measurements
3
HNB(47,51) or NB–H2,6, J(H–H) = 8.8 Hz]. 13C (150.92 MHz,
The solid-state magnetic susceptibilities were measured under
helium on a Quantum Design MPMS5 SQUID susceptometer
from 5 to 300 K at a field of 1 T. The sample was held in a Kel-F
bucket. The bucket had been calibrated independently at the
same field and temperatures. The raw data for 5 were corrected
for the molecular diamagnetism. The diamagnetic contribution
of the sample was measured from an analogous diamagnetic
metal complex, i.e. 4(MeOH)ؒMeOH.
CDCl3, 25 ЊC): 162.3 [s, CO]; 151.4 (s) and 148.8 (s) for Cα(6,13)
and Cα(3,16); 150.1 [s, Cα(8,11)]; 149.1 [s, Cα(1,18)]; 134.1 [s,
Cβ(5,14)]; 132.6 [s, Cβ(9,10)]; 132.0 [s, Cβ(4,15)]; 118.8 [s,
Cβ(19,20)]; 142.1 (s) and 141.9 (s) for phenyl-C1[i.e., C(21),
C(27), C(33), and C(39)]; 135.5 (s), 135.1 (s), 134.4 (s), 128.5 (s),
128.0 (s), 127.5 (s), 126.9 (s) and 126.5 (s) for phenyl C2,6, C3,5
,
and C4; 147.0 [s, CNB(49) or NB–C4]; 139.9 [s, CNB(46) or NB–
C1]; 125.5 [s, CNB(47,51) or NB–C2,6]; 121.4 [s, CNB(48,50) or
NB–C3,5]; 124.2 (s) and 122.9 (s) for Cm. MS, m/z (assignment,
relative intensity): 842 ([Zn(N-p-NCOC6H4NO2-tpp)]ϩ, 18.00),
840([Zn(N-p-NCOC6H4NO2-tpp) Ϫ 2H]ϩ, 18.55), 692 ([Zn-
(tpp) ϩ N]ϩ, 15.57), 678 ([Zn(tpp)]ϩ, 75.96), 676 ([Zn(tpp)-
EPR spectroscopy
EPR spectra were measured on an X-band Bruker EMX-10
spectrometer equipped with an Oxford Instruments liquid
helium cryostat. Magnetic field values were measured with an
NMR gaussmeter and the frequency calibrated with a digital
counter.
2H]ϩ, 100.00). UV/visible spectrum, λ/nm (ε × 10Ϫ3/MϪ1 cmϪ1
)
in MeOH: 435 (429.4), 566 (15.9), 606 (8.0).
Preparation of Fe(N-p-NCOC6H4NO2-tpp)Cl (5)
Crystallography
A mixture of N-p-HNCOC6H4NO2-Htpp (100 mg, 0.0136
mmol) in CHCl3 (100 cm3) and FeCl3ؒ6H2O (100 mg,
0.37 mmol) in MeOH (20 cm3) was refluxed for 1 h. After con-
centrating, the residue was dissolved in CHCl3 and filtered
through a Celite pad. The filtrate was concentrated and the
residue was recrystallized from CHCl3–MeOH [1 : 1 (v/v)] yield-
ing a dark blue solid of 5 (7.32 mg, 8.43 × 10Ϫ3 mmol, 62%).
Compound 5 was dissolved in CHCl3 and layered with MeOH
to get the single-crystal for X-ray analysis. MS, m/z (assign-
ment, relative intensity): 868 ([Fe(N-p-NCOC6H4NO2-tpp)Cl]ϩ,
3.48), 704 ([Fe(tpp)Cl]ϩ, 8.18), 703 ([Fe(tpp)Cl Ϫ H]ϩ, 15.02),
669 ([Fe(tpp)]ϩ, 25.97), 668 ([Fe(tpp) Ϫ H]ϩ, 42.74). UV/visible
spectrum, λ/nm (ε × 10Ϫ3/MϪ1 cmϪ1) in CHCl3: 358 (72), 422
(162), 521 (243), 696 (6.4).
Table 1 presents the crystal data for 4(MeOH)ؒMeOH and
5ؒCHCl3. Measurements were taken on a Siemens SMART
CCD diffractometer using monochromated Mo-Kα radiation
(λ = 0.71073 Å). The empirical absorption corrections were
made for both complexes. The structures were solved by direct
methods (SHELXTL PLUS)32 and refined by the full-matrix
least-squares method. All non-hydrogen atoms were refined
with anisotropic thermal parameters, whereas all hydrogen
atom positions were calculated using a riding model and were
included in the structure factor calculation. Table 2 lists selected
bond distances and angles for both 4(MeOH)ؒMeOH and 5.
CCDC reference numbers 182281 and 182282.
See http://www.rsc.org/suppdata/dt/b2/b202842p/ for crystal-
lographic data in CIF or other electronic format.
NMR spectroscopy
1H and 13C NMR spectra were recorded at 599.95 and 150.87
MHz respectively on Varian Unity Inova-600 spectrometers
locked on deuteriated solvent, and referenced to the solvent
Results and discussion
Molecular structures of 4(MeOH)ؒMeOH (S ؍ 0) and
5 (S ؍ 5/2)
1
peak. H NMR is relative to CD2Cl2 or CDCl3 at δ = 5.30
or 7.24 and 13C NMR to the center line of CD2Cl2 or CDCl3
at δ = 53.6 or 77.0. HMQC (heteronuclear multiple quan-
tum coherence) was used to correlate protons and carbon
The molecular framework is depicted in Fig. 1a for complex
4(MeOH)ؒMeOH and in Fig. 1b for 5ؒCHCl3. Both the five-
coordinate structures have metal atoms bonding with three
3002
J. Chem. Soc., Dalton Trans., 2002, 3001–3006

View Article Online
Table 2 Selected bond distances (Å) and angles (Њ) for compounds
4(MeOH)ؒMeOH and 5ؒCHCl3
p-nitrobenzoylimido (NNB) moiety is inserted into the Zn–N
bond of (meso-tetraphenylporphyrinato)zinc(), Zn(tpp),9,10
and the Fe–N bond of chloro(meso-tetraphenylporphyrin-
ato)iron(), Fe(tpp)(Cl).11 The unusual metal–ligand bond dis-
tances, i.e., from the Zn() and Fe() atoms to the ligand and
the angles are summarized in Table 2.
4(MeOH)ؒMeOH
Zn(1)–N(1)
Zn(1)–N(2)
Zn(1)–N(3)
2.061(3)
1.951(3)
2.069(3)
Zn(1)–N(5)
Zn(1)–O(4)
Zn(1) ؒ ؒ ؒ N(4)
2.035(3)
2.106(3)
2.564(3)
Bond distances (Å) are Zn(1)–O(4) = 2.106(3) and the mean
Zn(1)–N(p) = 2.029(3) for 4(MeOH)ؒMeOH; for 5 the values
are Fe(1)–Cl(1) = 2.238(1) and the mean Fe(1)–N(p) = 2.048(3).
The average Fe–N(p) distance of 2.048(3) Å in 5 is similar to
that observed for the iron–pyrrole nitrogen bond of the high-
spin (S = 5/2) iron() porphyrin complex Fe(N-NTs-tpp)Cl
[Fe–N(p) = 2.036 Å], but it is substantially longer than the
1.990 Å value of intermediate-spin (S = 3/2) complexes.4 The
Zn(1)–O(4)(MeOH) distance of 2.106(3) Å is slightly longer
than the sum of the covalent radii of Zn and O (1.93 Å) but is
significantly shorter than the sum of the van der Waals radii of
Zn and O (2.90 Å).12 This Zn(1)–O(4) contact may be described
as a weak covalent bond. The pyrrole nitrogen N(4) is no longer
bonded to the zinc and iron as indicated by their longer inter-
nuclear distances, 2.564(3) Å for Zn(1) ؒ ؒ ؒ N(4) and 2.434(3) Å
for Fe(1) ؒ ؒ ؒ N(4).
Zn(1)–O(4)–C(52)
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(3)
N(1)–Zn(1)–O(4)
131.9(4)
94.6(1)
169.7(1)
94.2(1)
N(2)–Zn(1)–N(3)
N(2)–Zn(1)–O(4)
N(3)–Zn(1)–O(4)
94.3(1)
111.4(2)
87.4(1)
5ؒCHCl3
Fe(1)–N(1)
Fe(1)–N(2)
Fe(1)–N(3)
2.086(3)
1.979(3)
2.078(3)
Fe(1)–N(5)
Fe(1)–Cl(1)
Fe(1) ؒ ؒ ؒ N(4)
2.008(3)
2.238(1)
2.434(3)
Cl(1)–Fe(1)–N(1)
Cl(1)–Fe(1)–N(2)
Cl(1)–Fe(1)–N(3)
Cl(1)–Fe(1)–N(5)
N(1)–Fe(1)–N(2)
96.71(9)
112.5(1)
96.7(1)
125.53(9)
91.0(1)
N(1)–Fe(1)–N(3)
N(1)–Fe(1)–N(5)
N(2)–Fe(1)–N(3)
N(2)–Fe(1)–N(5)
N(3)–Fe(1)–N(5)
164.6(1)
83.5(1)
90.9(1)
122.0(1)
82.6(1)
The distortion in these five-coordinate complexes can be
quantified by the “degree of trigonality” which is defined as
τ = (β Ϫ α)/60, where β is the largest and α the second largest of
the Lbasal–M–Lbasal angles.13,14 The limiting values are τ = 0 for
an ideal tetragonal geometry and τ = 1 for an ideal trigonal-
bipyramid. In the present case, we find β = 164.6(1)Њ [N(3)–
Fe(1)–N(1)] and α = 125.33(9)Њ [N(5)–Fe(1)–Cl(1)] for 5, and
β = 169.7(1)Њ [N(3)–Zn–N(1)] and α = 130.5(1)Њ [N(2)–Zn–O(5)]
for 4(MeOH)ؒMeOH. Thus the value τ = 0.65 is obtained for
both 4(MeOH)ؒMeOH and 5. Hence the geometries around
Zn() in 4(MeOH)ؒMeOH and Fe() in 5 are best described as
a distorted trigonal bipyramid (or a square-based pyramidally
distorted trigonal bipyramid, SBPDTBP)15 with N(2), N(5),
and O(4) [or N(2), N(5), and Cl(1)] lying in the equatorial plane
for 4(MeOH)ؒMeOH (or 5). The τ values calculated for
Fe(N-NTs-tpp)Cl4 and Ga(N-NTs-tpp)(OAc)6 by the same
method are 0.72 and 0.68, respectively, and the coordination
geometry for these two compounds is also distorted trigonal
bipyramidal (or SBPDTBP). We adopt the plane of three
strongly bound pyrrole nitrogen atoms [i.e., N(1), N(2) and
N(3)] as a reference plane, 3N.
Fig. 2 shows the actual porphyrin skeleton of 4(MeOH)ؒ
MeOH and 5. Because of the larger size of Fe3ϩ, Fe(1) lies
0.27 Å below the 3N plane toward the chlorine atom in 5, com-
pared to 0.09 Å for Zn(1) in 4(MeOH)ؒMeOH [cf. 0.17 Å for
Ni() in 1, 1.15 Å for Tl() in 3, and 0.21 Å for Fe() in Fe-
(N-NTs-tpp)Cl] (Fig. 2). The porphyrin macrocycle is indeed
distorted because of the presence of the NB group (Fig. 2).
Thus, the N(4) pyrrole rings bearing the NB group would
mostly deviate from the 3N plane and orient separately in a
dihedral angle of 30.0Њ for 4(MeOH)ؒMeOH and 27.8Њ for 5,
whereas small angles of 17.7Њ, 9.3Њ and 13.0Њ occur with N(1),
N(2), and N(3) pyrroles for 4(MeOH)ؒMeOH and the corre-
sponding angles are 6.3Њ, 2.1Њ, and 10.2Њ for 5. In the dia-
magnetic compound 4(MeOH)ؒMeOH, such a large deviation
from planarity for the pyrrole N(4) is also reflected by observ-
ing a 13–15 ppm upfield shift in the 13C NMR spectrum of the
Cβ (C19, C20) at 118.8 ppm compared to 134.1 ppm for Cβ (C5,
C14), 132.6 ppm for Cβ (C9, C10), and 132.0 ppm for Cβ (C4,
C15). Similar upfield shifts were also observed for the dia-
magnetic complexes of Cβ resonances due to the non-planarity
of porphyrin with a magnitude of 12–19 ppm for Ni(N-p-
NCOC6H4NO2-tpp) and 17–21 ppm for Tl(N-p-NCOC6H4-
NO2-tpp)(OAc).7
Fig. 1 Molecular configuration and atom-labeling scheme for (a)
4(MeOH)ؒMeOH and (b) 5ؒCHCl3, with atomic displacement
ellipsoids drawn at 30% probability. Hydrogen atoms for both
compounds and the free solvent C(52)H(52A)Cl(2)Cl(3)Cl(4) for 5ؒ
CHCl3 are omitted for clarity. O(1) and O(1Ј) of 4(MeOH)ؒMeOH are
disordered with an occupancy factor of 0.7 for O(1) and 0.3 for O(1Ј).
nitrogen atoms of the porphyrins and one extra nitrogen atom
of the nitrene fragment in common, but they are different with
an axial MeOH ligand for 4(MeOH)ؒMeOH and a ClϪ ligand
in the axial site for 5ؒCHCl3. In both 4 and 5, it appears that the
The pyrrole ring nitrogen N(4) is in fact inclined towards the
Zn and Fe atoms in 4(MeOH)ؒMeOH and 5, respectively. These
distortions make the distances between opposite pyrrole nitro-
gen atoms unusual. The normal diameter of the “hole” in an
J. Chem. Soc., Dalton Trans., 2002, 3001–3006
3003

View Article Online
Fig.
3
Temperature dependence of the molar paramagnetic
susceptibility, χM, and the magnetic moment, µeff, for a microcrystalline
sample of 5 in the range 5–300 K. Points are the experimental data;
solid lines represent the least-squares fit of the data to eqn. (3).
Fig. 2 Diagram of the porphyrinato core (C20N4, M, NB, ClϪ, and
OMe) of (a) compound 4(MeOH)ؒMeOH and (b) compound 5. The
values represent the displacements (in Å) of the atoms from the mean
3N plane [i.e., N(1), N(2) and N(3) for 4(MeOH)ؒMeOH and 5].
undistorted metalloporphyrin complex has been estimated to
be 4.02 Å.16 The N(2) ؒ ؒ ؒ N(4) distances of 4.468 Å in
4(MeOH)ؒMeOH and of 4.328 Å in 5 are unusually long, which
is caused by the large deviation of the N(4) pyrrole in
4(MeOH)ؒMeOH and 5 from the 3N plane. Because of this
distortion, the N(1) ؒ ؒ ؒ N(3) distance is 4.113 Å in 4(MeOH)ؒ
MeOH and 4.126 Å in 5. Hence, in 4(MeOH)ؒMeOH(or 5), the
zinc() [or iron()] atom is bound in an expanded porphyrinato
(4N) core. The plane (P) defined by Zn(1), N(5), N(4), and
C(45) in 4(MeOH)ؒMeOH, or by Fe(1), N(5), N(4), and C(45)
in 5 is almost perpendicular to the 3N plane with an angle of
94.1Њ in 4(MeOH)ؒMeOH and 79.9Њ in 5. The p-nitrobenzoyl
group (NB) [i.e., the plane for NB is C(46)–C(51)] is bonded to
N(5) in 4(MeOH)ؒMeOH and 5 so that it lies above the macro-
cycle, orienting in a dihedral angle of 47.9Њ and 61.3Њ with the
3N plane in 4(MeOH)ؒMeOH and 5, respectively. The dihedral
angles between the mean plane of the skeleton (3N) and the
planes of the phenyl groups are 46.1Њ [C(24)], 49.3Њ [C(30)],
58.0Њ [C(36)], and 46.5Њ [C(42)] for 4(MeOH)ؒMeOH and the
corresponding angles are 44.0Њ, 78.7Њ, 87.4Њ, and 42.2Њ for 5.
Fig. 4 1H NMR spectrum of 5 at 599.95 MHz in CDCl3 at 20 ЊC.
1H NMR spectroscopy of 5 in solution
The 1H NMR spetrum of 5 in CDCl3 at 20 ЊC is shown in Fig. 4.
The signals at 92.22, 88.11, 86.22, and Ϫ31.34 ppm have been
assigned to the pyrrole protons (Hβ). These four signals for Hβ
indicate that complex 5 has effective Cs symmetry in solution
with a mirror plane running through the Cl(1)–Fe(1)–N(2)–
N(5)–N(4) unit. The signals at 13.21, 11.89, 11.39, and
10.40 ppm are due to the meta protons of the phenyl group
(m-H). The signals at 6.69, and 3.45 ppm are assigned to the
para protons of the phenyl rings (p-H). The two broad signals
at 5.35 and 4.35 ppm have been assigned to the ortho protons of
the phenyl group (o-H), which are closer to the paramagnetic
center compared to the meta protons. Thus, the NMR spectra
show clear evidence of spin density delocalization onto the
Magnetic properties of complex 5
The temperature dependence of the molar magnetic suscepti-
bility, χM, and magnetic moment, µeff, of the crystalline complex
5 is shown in Fig. 3. As can be seen in Fig. 3, the value of µeff
varies from 5.87 µB at 300 K to 4.28 µB at 5 K. The magnetic
moment clearly shows a plateau equal to 5.87 µB at high
temperatures (300–50 K), which is close to the expected value
of 5.92 µB for a sextuplet high-spin state (S = 5/2). Below 20 K,
the magnetic moment drops rapidly, reflecting the large zero-
field splitting of the ground state which is usual in high-spin
iron() porphyrins.17,18
3004
J. Chem. Soc., Dalton Trans., 2002, 3001–3006

View Article Online
ligand for the Fe() complex, giving the so-called contact shifts
for the 1H spectra.19,20 Since signal assignment of the 13C NMR
data is not simple for compound 5, it is difficult to see whether
this spin delocalization effect is present in the 13C spectra or
not.
A reasonable estimate of the principal g values associated
with the middle doublet may be obtained by using the min-
imum, maximum, and inflection points of the g = 4.2 EPR
absorption derivative as limits for the g values.27 The g value for
the maximum (g = 4.6), minimum (g = 3.9), and inflection point
(g = 4.2) of the main signal at g = 4.2 were close to the calc-
ulated values of g2z = 4.53, g2y = 4.03, and g2x = 4.24 derived
from the transitions in the middle Kramers doublet (Fig. 6). As
EPR spectra of 5
The spin Hamiltonian (Hs, S = 5/2) used to interpret the EPR
data is21–23
Hs = Hz ϩ HCF
(1)
where
Hz = gµBHS
HCF = D [Sz2 Ϫ S(S ϩ 1)/3] ϩ E(Sx2 Ϫ Sy2)
The first term Hz in the spin Hamiltonian (Hs) is the electronic
Zeeman term, which describes the interaction of the electronic
spin S, with the external magnetic field H. HCF is the crystalline
electric field, µB is the Bohr magneton, g is the electronic
g-tensor, and D and E are the axial and rhombic zero-field
splitting (ZFS) parameters.
The rhombicity parameter, λ (= E/D), is a measure of the
departure of the electronic environment of the iron center from
axial symmetry. In an appropriate axis system, axial symmetry
correponds to λ = 0 while a maximally rhombic symmetry
corresponds to λ = 1/3.24,25 For D ӷ hν (the energy of the
microwave, ∼0.32 cmϪ1 at X-band), the three Kramers doublets
of a S = 5/2 system act approximately like independent “S =
1/2” systems with effective g-values that are dependent only on λ.
The high degree of rhombicity of the iron center in 5 is
demonstrated by the presence of the intense signal at g = 4.2 in
a powdered solid, as shown in Fig. 5. In the solid-state spectra,
Fig. 6 Schematic representation of the energy levels for 5 with an S =
5/2 system for E/D = 0.29 and the spin Hamiltonian (1), where Ei
represents the energy of the three Kramers doublets with i = 1, 2, 3 for
the ground (the lowest), middle, and uppermost doublets, respectively.
shown in Figs. 5 and 6, the g values with g1x = 1.12 and g1y = 9.55
calculated for the lowest Kramers doublet indeed agree semi-
quantitatively with observed g1x = 1.1 and g1y = 9.5 0.4. The
eigenfunctions and energies of eqn. (1) with λ = 0.29 in zero
field (for D > 0) are
(2)
and they are shown schematically in Fig. 6.31
The paramagnetic susceptibility, χM, and effective magnetic
moment, µeff, data shown in Fig. 3 for 5 were least-squares
which fit to eqn. (3) to give the fitting parameters D = 0.79 cmϪ1
and g = 2.39.
(3)
In eqn. (3), X = D/kT, g is the average g value, and the other
symbols have their usual meanings. Eqn. (3) is the simple theor-
etical susceptibility equation resulting from the axial and
rhombic zero-field splitting (ZFS) for S = 5/2 as governed by the
spin Hamiltonian Hs in eqn. (1). Importantly, the energy split-
ting diagram for 5 with λ = 0.29 shown in Fig. 6 and the eigen-
functions shown in eqn. (2) are used in the derivation of eqn.
(3). The solid lines in Fig. 3 represent this fit. This value of D
means that the relative energies of the three Kramer doublets at
Fig. 5 Solid-state X-band EPR spectrum of a finely powdered sample
of 5 at 4 K. EPR conditions: microwave frequency 9.466 GHz;
modulation amplitude 1.60 G; modulation frequency 100.00 kHz;
microwave power 1.997 mW.
a shoulder was observed on the large (g = 4.2) signal at
zero magnetic field are 0, 2.55, and 5.40 cmϪ1
.
approximately g = 9.5
0.4. A weak transition was also
On consideration of all the experimental data combined, i.e.,
the magnetic moment µ = 5.92 µB at 300–50 K, the EPR signals
observed in the region near g = 1.1. From plots of the effective
g values versus λ, we conclude that λ = E/D = 0.29 for complex 5
which is 87% towards complete rhombicity.21,26–29 According to
this analysis, the prominent signal at g = 4.2 arises from the
middle Kramers doublet with “Ms = 3/2”, while the weaker
signal at g = 9.5 0.4 results from the lowest Kramers doublet
with “Ms = 1/2”. The resonance at g = 1.1 corresponds to
transitions in the lowest (or ground) Kramers doublet with
“Ms = 1/2”. Moreover the “rhombicity” of the iron d orbitals
had not been reported for complex Fe(N-NTs-tpp)Cl.4,30
at g = 9.5
0.4, 4.2, and 1.1 at 4 K, the Fe–N(p) distance
2.048(1) Å at 22 ЊC, and NMR shifts of the pyrrole protons
(Hβ) (δ = 92.22, 88.11, 86.22, Ϫ31.34) at 20 ЊC firmly establish a
high-spin (S = 5/2) state for complex 5. Although the character-
istics of complex 5 are similar to those previously reported for
the high-spin pentacoordinate iron() porphyrin complex
Fe(N-NTs-tpp)Cl,4 the fine structure of the EPR signals and
paramagnetic susceptibility data allow us unambiguously to
evaluate the parameters λ = 0.29 and D = 0.79 cmϪ1 for 5. This is
J. Chem. Soc., Dalton Trans., 2002, 3001–3006
3005

View Article Online
12 J. E. Huheey, E. A. Keiter and R. L. Keiter, Inorganic Chemistry,
Harper Collins College Publishers, New York, 4th edn., 1993,
p. 114.
13 A. W. Addison, T. N. Rao, J. Reedijk, J. V. Rijn and G. C. Verschoor,
J. Chem. Soc., Dalton Trans., 1984, 1349.
14 R. G. Garvey, R. O. Koob and M. L. Morris, Acta Crystallogr., Sect.
C, 1987, 43, 2056.
15 G. Murphy, P. Nogle, B. Murphy and B. Hathaway, J. Chem. Soc.,
Dalton Trans., 1997, 2645.
the first report applying the rhombicity evaluation by EPR
methods to bridged metalloporphyrins with a Fe–NNB–N
likage.
In conclusion, we have investigated two pentacoordinate
[one diamagnetic, 4(MeOH)ؒMeOH, and one paramagnetic,
5], mononuclear, and bridged metal complexes of N-p-
nitrobenzoylamido-meso-tetraphenylporphyrin having a M–
NNB–N [M = Zn(), Fe()] linkage, and established their
X-ray structures. X-Band EPR spectroscopy and solid-state
magnetic susceptibility data can be used to assess the zero-field
splitting, D, and the rhombicity parameter, λ (= E/D), for 5.
16 D. M. Collins and J. L. Hoard, J. Am. Chem. Soc., 1970, 92,
3761.
17 S. Mitra, in Iron Porphyrins part II, eds. A. B. P. Lever and H. Gray,
Addison-Wesley, Reading, MA, 1983, p. 1.
18 M. Mazzanti, J. C. Marchon, J. Wojaczyski, S. Wolowiec, L.
Lotos-Grazynski, M. Shang and W. R. Scheidt, Inorg. Chem., 1998,
37, 2476.
Acknowledgements
19 F. H. Kohler, in Magnetism: Molecules to Materials, Models and
Experiments, eds. J. S. Miller and M. Drillon, Wiley–VCH,
Weinheim, 2001, p. 379.
20 R. S. Drago, Physical Methods for Chemists, Saunders College
Publishing, New York, 2nd edn., 1992, pp. 507–542.
21 (a) H. H. Eickman, M. P. Klein and D. A. Shirley, J. Chem. Phys.,
1965, 42, 2113; (b) W. R. Hagen, Adv. Inorg. Chem., 1992, 38,
165.
Financial support from the National Science Council of
the R.O.C. under Grant NSC 90-2113-M-005-014 is grate-
fully acknowledged. The NMR instrument (Varian Unity
Inova-600) was funded in part by the National Science Council
and by the Chung-Cheng Agriculture Science & Social Welfare
Foundation.
22 B. J. Graffney and H. J. Silverstone, in Biological Magnetic
Resonance in EMR of Paramagnetic Molecules, eds. J. Berliner and
J. Reuben, Plenum Press, New York, 1993, vol. 13, pp. 1–57.
23 K. Spartalian, W. T. Oosterhuis and J. B. Neilands, J. Chem. Phys.,
1975, 62, 3538.
24 W. E. Blumberg, in Magnetic Resonance in Biological Systems, eds.
A. Ehrenberg, B. G. Malmstrom and T. Vanngard, Pergamon Press,
Oxford, 1967, pp. 119–133.
References
1 J. C. Setsune, Y. Kishimoto, Y. Ishimaru, K. Fukuhara and T. Kiato,
Organometallics, 1991, 10, 1099.
2 Y. I. Li, C. S. Chang, J. Y. Tung, C. H. Tsai, J. H. Chen, F. L. Liao
and S. L. Wang, Polyhedron, 2000, 19, 413.
3 H. J. Callot, B. Chevrier and R. Weiss, J. Am. Chem. Soc., 1978, 100,
4733.
4 J. P. Mahy, P. Battioni, G. Bedi, D. Mansuy, J. Fishcher, R. Weiss and
I. Morgenstern-Badarau, Inorg. Chem., 1988, 27, 353.
5 H. J. Callot, B. Chevrier and R. Weiss, J. Am. Chem. Soc., 1979, 101,
7729.
25 P. L. Hall, B. R. Angle and J. P. E. Jones, J. Magn. Reson., 1974, 15,
64.
26 A. J. Simaan, F. Banse, P. Mialane, A. Boussac, S. Un, T.
Kargar-Grisel, G. Bouchoux and J. J. Girerd, Eur. J. Inorg. Chem.,
1999, 993.
6 J. Y. Tung, J. I. Jang, C. C. Lin, J. H. Chen and L. P. Hwang, Inorg.
Chem., 2000, 39, 1106.
7 C. S. Chang, C. H. Chen, Y. I. Li, B. C. Liau, B. T. Ko, S. Elango,
J. H. Chen and L. P. Hwang, Inorg. Chem., 2001, 40, 2905.
8 P. J. Kellett, M. J. Powlik, L. F. Taylor, R. G. Thompson, M. A.
Lerstik, O. P. Anderson and S. H. Strauss, Inorg. Chem., 1989, 28,
440.
9 R. J. Abraham, G. R. Bedford, G. R. McNeillie and B. Wright, Org.
Magn. Reson., 1980, 14, 418.
10 D. F. Marsh and L. M. Mink, J. Chem. Educ., 1996, 73, 1188.
11 H. J. Callot, B. Chevrier and R. Weiss, J. Am. Chem. Soc., 1978, 100,
4733.
27 J. N. Burstyn, J. A. Roe, A. R. Miksztal, B. A. Shuevitz, G. Lang and
J. S. Valentine, J. Am. Chem. Soc., 1988, 110, 1382.
28 Y. Deligiannakis, A. Boussac, H. Bottin, V. Perrier, O. Barzu and
A. M. Gilles, Biochemistry, 1997, 36, 9446.
29 J. Peisach, W. E. Blumberg, E. T. Lode and M. J. Coon, J. Biol.
Chem., 1971, 246, 5877.
30 E. I. Solomon, J. Zhou, F. Neese and E. G. Pavel, Chem. Biol., 1997,
4, 495.
31 A. X. Trautwein, E. Bill, E. L. Bominaar and H. Winkler, Struct.
Bonding (Berlin), 1991, 78, 1.
32 G. M. Sheldrick, SHELXTL PLUS, Bruker Analytical X-Ray
Instruments, Madison, WI, 1990.
3006
J. Chem. Soc., Dalton Trans., 2002, 3001–3006