Synthesis, spectroscopic and structural characterization of the high-spin Fe(II) cyanato-N and thiocyanato-N "picket fence" porphyrin complexes

Article abstract of DOI:10.1016/j.ica.2010.05.058

Two new iron(II) five-coordinated porphyrin complexes [Na(2,2,2-crypt)] [Fe^II(TpivPP)(NCO)] (1) (TpivPP = α,α,α,α- tetrakis(o-pivalamidophenyl) porphyrin known as picket fence porphyrin and 2,2,2-crypt is the cryptand-222) and [K(2,2,2-crypt)][Fe^II(TpivPP) (NCS)] (2) have been prepared and characterized. The UV-Vis and IR spectroscopic data are consistent with a cyanato-N and thiocyanato-N ferrous porphyrinates. The Mo?ssbauer data and the X-ray structural analysis indicate that the Fe(II) cation in 1 and 2 is high-spin (S = 2) and has the (dxy)2(dxz)1(dyz) 1(dz2)1(dx2-y2)1 ground state electronic configuration. For complex 1, the average equatorial iron-pyrrole N bond length (Fe-N_p = 2.120(2) ), the distance between the iron and the 24-atom mean plane of the porphyrin ring (Fe-P_C = 0.6805(7) ) and the distance between the iron and the plane made by the four pyrrole nitrogens (Fe-P_N = 0.5923(12) ) are longer than those of complex 2 and similar five-coordinated Fe(II) high-spin porphyrinates. This is probably due to the significant electronic repulsion of the dx2-y2 and d_xy orbitals by the negative charge of the pyrrole N atoms in case of 1.

Full text of DOI:10.1016/j.ica.2010.05.058

Inorganica Chimica Acta 363 (2010) 3208–3213
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Synthesis, spectroscopic and structural characterization of the high-spin Fe(II)
cyanato-N and thiocyanato-N ‘‘picket fence” porphyrin complexes
Mondher Dhifet a, Mohamed Salah Belkhiria a, Jean-Claude Daran b, Charles E. Schulz c, Habib Nasri a,
*
a Laboratoire de physico-chimie des matériaux, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019 Monastir, Tunisia
b Laboratoire de Chimie de Coordination CNRS UPR 8241, 205 Route de Norbone, 31077 Toulouse, Cedex 04, France
c Department of Physics, Knox College, Galesburg, IL 61401, USA
a r t i c l e i n f o
a b s t r a c t
Two new iron(II) five-coordinated porphyrin complexes [Na(2,2,2-crypt)] [FeII(TpivPP)(NCO)] (1) (TpivP-
Article history:
Received 2 May 2010
Received in revised form 20 May 2010
Accepted 27 May 2010
Available online 2 June 2010
P = a,a,a,a-tetrakis(o-pivalamidophenyl) porphyrin known as picket fence porphyrin and 2,2,2-crypt is
the cryptand-222) and [K(2,2,2-crypt)][FeII(TpivPP)(NCS)] (2) have been prepared and characterized.
The UV–Vis and IR spectroscopic data are consistent with a cyanato-N and thiocyanato-N ferrous porphy-
rinates. The Mössbauer data and the X-ray structural analysis indicate that the Fe(II) cation in 1 and 2 is
2
1
1
1
1
high-spin (S = 2) and has the ðdxyÞ ðdxzÞ ðdyzÞ ðdz2 Þ ðdx2ꢀy2
Þ
ground state electronic configuration.
Keywords:
For complex 1, the average equatorial iron-pyrrole N bond length (Fe–Np = 2.120(2) Å), the distance
between the iron and the 24-atom mean plane of the porphyrin ring (Fe–PC = 0.6805(7) Å) and the dis-
tance between the iron and the plane made by the four pyrrole nitrogens (Fe–PN = 0.5923(12) Å) are
longer than those of complex 2 and similar five-coordinated Fe(II) high-spin porphyrinates. This is prob-
Cyanato complex
Thiocyanato complex
Iron(II) porphyrin
Structural studies
Mössbauer spectroscopy
ably due to the significant electronic repulsion of the dx2
pyrrole N atoms in case of 1.
and dxy orbitals by the negative charge of the
ꢀy2
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
high-spin iron(II) porphyrinates presents large positive quadrupole
splitting Eq (3.50–4.36 mm/s) while high-spin iron(II) species
such as [FeII(TPP)(2-MeHIm)] (TPP = tetraphenylporphyrin) [2]
show negative
To date, there are no X-ray molecular structures of an iron(II)
cyanato or thiocyanato porphyrin species reported in the literature
and especially noteworthy is the very small number of published
structural studies on iron-cyanato complexes.
In order to gain more insight into the nature of stereochemical
and electronic structure of high-spin Fe(II) porphyrin species, the
synthesis, spectroscopic and structural properties of two new five-
coordinate Fe2+ picket fence porphyrin (TpivPP) complexes with
the cyanate and thiocyanate ions as axial ligands are reported here.
The use of picket fence porphyrin for the characterization of fer-
rous porphyrinates is directly related to the fact that small anionic
ligands, as shown by molecular structures [3], are in all cases
bound to the iron(II) by the pocket side of the protected porphyrin
which avoids the auto-oxidation of the iron(II) species to the iro-
D
Understanding how small molecules, such as NO, CO, halides or
pseudo-halides (RNC, CNꢀ, N3ꢀ, SCNꢀ, OCNꢀ, . . .) bind to the iron in
hemoproteins has been and continues to be a topic of considerable
interest [1]. In principle, single-crystal X-ray crystallographic stud-
ies of proteins should enable a determination of the local geome-
tries of metal–ligand interactions, but the relatively limited
resolution of protein crystal structure has resulted in some contro-
versies as to the actual geometries involved. Iron(II) synthetic por-
phyrin complexes have been successfully used for many decades as
models for hemoproteins.
D
Eq values in the ꢀ1.94 to ꢀ2.44 mm/s range.
It has been shown that high-spin Fe(II) porphyrins can be di-
vided into classes having two different electronic configurations
[2]. Derivatives type [FeII(Porph)(X)]ꢀ (Porph = porphyrin and X is
a monodentate anionic weak field ligand) have configuration,
2
1
1
1
1
ðdxyÞ ðdxzÞ ðdyzÞ ðdz2 Þ ðdx2ꢀy2 Þ whereas complexes of type [FeII(Por-
ph)(L)2] (L is a monodentate neutral
r-donor ligand) have the
2
1
1
1
1
ðdxyÞ ðdxzÞ ðdyzÞ ðdz2 Þ ðdx2ꢀy2 Þ ground state configuration. This divi-
sion into two groups is manifested in the molecular structures:
complexes with the former electronic configuration have signifi-
cantly larger iron displacement (ꢁ0.18 Å larger) and equatorial
Fe–Np bonds (ꢁ0.04 Å longer) than those with the second type of
electronic configuration. On the other hand, the first type of
n(III) l-oxo-porphyrin complex.
2. Experimental
2.1. General
The cryptand-222 was recrystallized from toluene, dried under
vacuum and stored under argon in the dark. Toluene and hexanes
* Corresponding author. Tel.: +216 73 500 280; fax: +216 73 500 278.
E-mail address: hnasri1@gmail.com (H. Nasri).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.05.058

M. Dhifet et al. / Inorganica Chimica Acta 363 (2010) 3208–3213
3209
were distilled from their sodium-benzophenone solution under a
2.3. Synthesis of [K(2,2,2-crypt)][FeII(TpivPP)(NCS)]ꢂC6H5Cl (2)
nitrogen atmosphere. NaOCN and KSCN salts were recrystallized
twice from hot distilled water, dried overnight at about 80 °C and
stored under argon. Chlorobenzene was purified by washing with
sulfuric acid and distilled over P2O5. All other reagents and solvents
employed were commercially available and were used as received
without further purification. All reactions and manipulations for
the preparation of the Fe(II) porphyrin derivatives were carried
out under argon using a double-manifold vacuum line, Schlenk-
ware and cannula techniques.
Complex 2 was prepared by the procedures given for 1, except
that KSCN salt used instead of NaOCN. Good quality dark purple
crystals of 2 were prepared by slow diffusion of hexanes into the
C6H5Cl solution. Anal. Calc. for 2, C89H105ClFeKN11O10S (1651.25
g/mol): C, 64.74; H, 6.41; N, 9.33. Found: C, 64.82; H, 6.39; N,
9.57%. UV–Vis [C6H5Cl: kmax in nm]: 436, 567, 612, 653. IR(KBr disk,
cmꢀ1):
m(NCS): 2070, 2054.
UV–Vis spectra were recorded on a Shimadzu UV-2401 spec-
trometer and Fourier-transformer IR data on a Shimadzu FTIR-
8400 spectrometer. Mössbauer measurements were performed
on a constant acceleration spectrometer from 25 to 100 K with
an optional small field (Knox College). Single crystal X-ray diffrac-
tion data were collected by Bruker APEXII CCD diffractometer.
2.4. X-ray crystallography
A single crystal of each compound was mounted under inert
perfluoropolyether at the tip of glass fibre and cooled in the cryo-
stream of a Bruker APEXII CCD diffractometer. Data for 1 and 2
were collected at 180 K using the monochromatic Mo Ka radiation
(k = 0.71073). The structures’ solutions were obtained by direct
method using SIR-2004-1.0 [5] and refined by full-matrix least-
squares on |F|2 using the SHELXL-97 program [6]. For complex 1 some
disorder problems were encountered during the refinement of the
structure: (i) the tert-butyl group of two pickets are disordered over
two orientations (C40A–C41A–C42A/C40B–C41B–C42B and C62A–
C63A–C64A/C62B–C63B–C64B) with refined occupancy coeffi-
cients converged to 0.674(7) and 0.326(7) (for the first tert-butyl
group) and 0.846(6) and 0.154(6) (for the second tert-butyl group),
(ii) three oxygen atoms of the TpivPP porphyrin are disordered in
two positions: O1A/O1B, O3A/O3B and O4A/O4B with major posi-
tions occupancies of 0.54(12), 0.59(1) and 0.46(1), respectively,
(iii) two oxygen atoms of one half cryptand-222 are also disordered
in two positions with occupancies with the ratio of refined occu-
2.2. Synthesis of [Na(2,2,2-crypt)][FeII(TpivPP)(NCO)](1)
[FeIII(TpivPP)(SO3CF3)(H2O)] [4] (100 mg, 0.081 mmol) and 1 mL
of zinc amalgam were stirred for 1 h under argon in 10 mL of
C6H5Cl. The deep red solution of [FeII(TpivPP)] was then filtered
into a second solution that was made by stirring for 2 h a mixture
of 120 mg (0.319 mmol) of cryptand-222 and 190 mg of NaOCN
(2.923 mmol) in 10 mL of C6H5Cl. The solution was filtered and
crystals of the complex were prepared by slow diffusion of hexanes
into the chlorobenzene solution. Anal. Calc. for 1 C83H100FeN11-
NaO11 (1506.60 g/mol): C, 66.17; H, 6.69; N, 10.23. Found: C,
66.28; H, 6.92; N, 10.35%. UV–Vis [C6H5Cl, kmax in nm]: 437, 568,
610, 650. IR(KBr disk, cmꢀ1):
m(NCO): 2206.
Table 1
Crystal data and refinement for 1 and 2a.
1
2a
Empirical formula
Formula weight, (g mol)
Temperature (K)
C83H100FeN11NaO11
1506.60
180(2)
C83H100FeKN11O10
1538.78
180(2)
S
Wavelength (Å)
Crystal system
Space group
0.71073
Monoclinic
C2
0.71073
Monoclinic
P21/n
a (Å)
b (Å)
c (Å)
b
24.0027(8)
14.7581(6)
23.6448(8)
106.078(2)
8048.2(5)
4
1.257
0.260
3236
0.36 ꢃ 0.29 ꢃ 0.27
2.60–26.37
ꢀ30 ꢄ h ꢄ 29
ꢀ18 ꢄ k ꢄ 18
ꢀ29 ꢄ l ꢄ 29
99.8
18.1846(9)
21.5680(12)
22.6229(12)
100.311(2)
8729.5(1)
4
1.171
0.304
3264
V (Å3)
Z
Dcalc (g cmꢀ1
)
l
(mmꢀ1
F(0 0 0)
)
Crystal size (mm3)
h Range for data collection
Limiting indices
0.48 ꢃ 0.30 ꢃ 0.20
2.06–26.02
ꢀ22 ꢄ h ꢄ 22
ꢀ24 ꢄ k ꢄ 26
ꢀ27 ꢄ l ꢄ 27
99.9
Completeness (%)
Absorption and minimum transmission
Reflections collected/unique
0.8931/1.0
64362/16382
0.0409/0.0447
16382/498/1080
1.024
0.8801/0.9892
127709/17182
0.0396/0.0342
17182/18/969
1.106
R
int/R(r)
Data/restraints/parameters
Goodness-of-fit on F2
Weights (w)
[
r
2(Fo2) + (0.0614P)2 + 4.7845P]ꢀ1
[r
2(Fo2) + (0.1044P)2 + 4.3502P]ꢀ1
P = [max(Fo2, 0) + 2Fc2]/3
ꢀ0.027(11)
P = [max(Fo2, 0) + 2Fc2]/3
–
x (Flack parameter)
Final R indices [I > 2
R indices (all data)
r
(I)]
R1b = 0.0448, wR2c = 0.1076
R1b = 0.0606, wR2c = 0.1166
0.422 and ꢀ0.337
R1b = 0.0562, wR2c = 0.1669
R1b = 0.0771, wR2c = 0.1803
0.799 and ꢀ0.556
Largest difference in peak and hole (e Å-3
)
a
Crystal data and refinement for 2 correspond to the complex with formula [K(2,2,2-crypt)][FeII(TpivPP)(NCS)]; the dis-
ordered chlorobenzene molecule was removed using the SQUEEZE option of the PLATON program.
b
R1
wR2 = [
=
R
||Fo| ꢀ |Fc||/
R|Fo|.
c
2
R
w(Fo ꢀ Fc2)2/
R .
w(Fo2)2]1/2

3210
M. Dhifet et al. / Inorganica Chimica Acta 363 (2010) 3208–3213
pancies being 0.65(2):0.35(2) for O9A/O9B and 0.67(9):0.33(9) for
O10A/O10B. The anisotropic displacement ellipsoids of some
atoms of the porphyrin molecules and the counterions in complex
1 were very elongated which indicates static disorder. For frag-
graphic data and structure refinement of complexes 1 and 2. Se-
lected bond distances and angles for these compounds are listed
in Table 2.
ments involving these atoms, the DFIX, DELU/SIMU and SIMU/ISOR re-
3. Results and discussion
straints [7] and the EADP constraint commands in the SHELXL-97 [6]
software were used which explains the huge number of restraints
(Table 1). The TpivPP porphyrin of 2 also presents minor disorders:
C29–C30–C31 (s.o.f. 0.863(4)/0.137(4)); C40–C41–C42 (s.o.f.
0.619(4)/0.381(4); O3 (s.o.f. 0.51(9)/0.49(9)). At the final stage of
refinement of 2, clear evidence of the presence of solvent voids
of 189 Å3 was obtained (containing approximately 46 electrons).
Thus, a correction for diffuse effects due to the inclusion of the dis-
ordered chlorobenzene solvent in the crystal was made using the
SQUEEZE subroutine in PLATON [8]. The absolute structure for 1 was
set by reference to the Flack parameter equal to ꢀ0.027(11) [9].
For both complexes 1 and 2 non-hydrogen atoms were refined
with anisotropic thermal parameters whereas H-atoms were in-
cluded at estimated positions using a riding model. Drawings were
made using ORTEP3 for windows [10]. Table 1 shows crystallo-
3.1. UV–Vis and IR
The UV–Vis spectra of complexes 1 and 2 are very similar. They
exhibit red shifted Soret bands at ꢁ436 nm which is the case for
Fe(II) five-coordinated meso-porphyrin complexes with anionic ax-
ial ligands (see Table 3). So, the electronic spectra of the pseudo-
halide NCSꢀ and NCOꢀ derivatives alone suggest the formation of
a five-coordinated iron(II) porphyrin species. As shown in Table
3, the high-spin (S = 2) Fe(II) chloro, azido and oxyanionic (ROꢀ)
species have Soret maxima around 440 nm [11]. Interestingly,
however, the Soret maxima for five-coordinated low-spin (S = 0)
iron(II) porphyrinates [FeII(TpivPP)(NO2)]ꢀ [12] and [FeII(TpivPP)
(CN)]ꢀ [13] are also in the 435–450 nm area.
Both 1 and 2 show a strong band in the IR spectra near
1102 cmꢀ1 attributed to the C–O stretching frequencies of the
cryptand-222. Complex 1 exhibits a strong absorption band at
2206 cmꢀ1 attributed to the CN stretching frequency of the OCNꢀ
axial ligand which show clearly that the cyanato group is N-bound
to the iron(II) ion [17]. The iron(III) analogue complex [FeIII
(TpivPP)(NCO)] [18], presents two absorption bands, assigned to
Table 2
Selected bond distances (Å) and angles (°) in the molecular structures of [Na(2,2,2-
crypt)][FeII(TpivPP)(NCO)] (complex 1) and [K(2,2,2-crypt)][FeII(TpivPP)(NCS)] (com-
plex 2).
Complex 1
Complex 2
Iron coordination polyhedron
Fe–N1
Fe–N2
Fe–N3
Fe–N4
2.107(2)
Fe–N1
Fe–N2
Fe–N3
Fe–N4
2.103(2)
2.106(2)
2.093(2)
2.116(2)
2.042(2)
107.06(10)
87.16(8)
153.07(8)
85.48(8)
87.38(8)
152.25(8)
87.18(8)
2.128(2)
2.111(2)
2.134(2)
2.005(3)
106.46(11)
85.10(8)
148.27(9)
85.95(8)
85.79(9)
146.84(9)
85.27(8)
Table 3
Electronic spectra dataa for selected iron(II) picket fence porphyrin complexes.
Complex
kmax (nm)
Spin S
References
Fe–N9
Fe–N9
N9–Fe–N1
N1–Fe–N2
N1–Fe–N3
N1–Fe–N4
N2–Fe–N3
N2–Fe–N4
N3–Fe–N4
N9–Fe–N1
N1–Fe–N2
N1–Fe–N3
N1–Fe–N4
N2–Fe–N3
N2–Fe–N4
N3–Fe–N4
Soret region
a, b region
[FeII(TpivPP)(NCO)]ꢀ
[FeII(TpivPP)(NCS)]ꢀ
[FeII(TpivPP)(N3)]ꢀ
[FeII(TpivPP)(Cl)]ꢀ
[FeII(TpivPP)(OMe)]ꢀ
[FeII(TpivPP)(OAc)]ꢀ
[FeII(TpivPP)(NO3)]ꢀ
[FeII(TpivPP)(NO2)]ꢀ
[FeII(TpivPP)(CN)]ꢀ
437
436
443
446
456
448
438
444
455
568
567
572
571
580
572
564
567
565
610
612
612
609
622
611
604
608
601
2
2
2
2
2
2
2
0
0
This work
This work
[14]
[15]
[11]
[11]
[16]
[12]
[13]
Cyanato-N ligand
N9–C65
C65–O5
Fe–N9–C65
N9–C65–O5
Thiocyanato-N ligand
N9–C65
C65–S
Fe–N9–C65
N9–C65–S
1.151(4)
1.197(4)
176.8(3)
179.8(6)
1.166(4)
1.639(3)
170.2(3)
178.5(3)
a
Solvent: chlorobenzene.
Sodium-cryptand-222
Na1–N10
Na1–O6
Na1–O7
Na1–O8
N10–Na1–O6
N10–Na1–O7
N10–Na1–O8
O6–Na1–O7
O6–Na1–O8
O7–Na1–O8
Na2–N11
Potassium-cryptand-222
2.701(3)
2.462(2)
2.540(3)
2.519(3)
68.86(7)
67.66(9)
69.14(9)
107.29(9)
106.73(9)
108.24(8)
2.911(4)
2.416(7)
2.676(13)
2.633(5)
2.469(10)
2.494(5)
65.1(2)
57.8(3)
62.92(15)
65.0(3)
64.98(13)
87.5(3)
113.0(4)
102.9(3)
86.0(5)
K–N10
3.058(2)
K–N11
K–O5
K–O6
K–O7
K–O8
K–O9
K–O10
N10–K–N11
O5–K–O6
O8–K–O10
O9–K–O10
N10–K–O5
N10–K–O8
N10–K–O10
N11–K–O6
N11–K–O7
N11–K–O9
3.036(3)
2.827(2)
2.808(2)
2.827(2)
2.857(2)
2.803(2)
2.864(2)
179.76(8)
60.50(7)
134.39(6)
60.04(6)
60.19(6)
59.65(6)
119.39(6)
59.68(8)
60.42(7)
120.50(7)
Na2–O9A
Na2–O9B
Na2–O10A
Na2–O10B
Na2–O11
N11–Na2–O9A
N11–Na2–O9B
N11–Na2–O10A
N11–Na2–O10B
N11–Na2–O11
O9A–Na2–O10A
O9B–Na2–O10B
O9A–Na2–O11
O9B–Na2–O11
O10A–Na2–O11
O10B–Na2–O11
115.20(15)
99.6(3)
Fig. 1. ORTEP view of the ion complex [FeII(TpivPP)(NCO]ꢀ, thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity.

M. Dhifet et al. / Inorganica Chimica Acta 363 (2010) 3208–3213
3211
the axial ligand, at lower frequencies (2200 and 2191 cmꢀ1). Com-
plex 2 shows two strong absorption bands at 2070 and 2054 cmꢀ1
attributed to the CN stretching frequencies of the thiocyanato-N li-
gand (denoted mas (NCS)) which are at higher energy than the one
of the iron(III) derivative [FeIII(TpivPP)(NCS)] [19] (2015 cmꢀ1).
3.2. Structural properties of [Na(2,2,2-crypt)][FeII(TpivPP)(NCO)]
(complex 1) and [K(2,2,2-crypt)][FeII(TpivPP)(NCS)] (complex 2)
The asymmetric unit of
1 contains one ion complex
[FeII(TpivPP)(NCO)]ꢀ and two half crystallographically indepen-
dent counterions [Na(2,2,2-crypt)]+ where each Na+ occupies a spe-
cial position on a two-fold axis. For complex 2 the asymmetric unit
is made of one ion complex [FeII(TpivPP)(NCS)]ꢀ, one [K(2,2,2-
crypt)]+ counterion and one chlorobenzene solvent molecule. For
both complexes 1 and 2, the iron(II) is coordinated to the four
nitrogens of the porphyrin ring and the nitrogen atom of the pseu-
do-halide axial ligand from the pocket side of the TpivPP porphy-
rin. Figs. 1 and 2 are ORTEP drawings of the ionic complexes
[FeII(TpivPP)(NCO)]ꢀ and [FeII(TpivPP)(NCS)]ꢀ, respectively. As a
consequence of the decreased charge, there is a small increase in
Fig. 2. ORTEP view of the ion complex [FeII(TpivPP)(NCS]ꢀ, thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity.
Table 4
Porphyrinato core parameters (Å) for selected five-coordinated iron(II) and iron(III) high-spin meso-porphyrin complexes.
a
b
c
d
Complex
Fe–Np
Fe–XL
Fe–PC
Fe–PN
References
Iron(II) high-spin porphyrins
[FeII(TpivPP)(Cl)]ꢀ
2.108(15)
2.107(2)
2.120(2)
2.104(2)
2.070(16)
2.094(3)
2.301(2)
2.034(3)
2.005(3)
2.042(2)
2.069(4)
2.078(2)
0.59
0.64
0.6805(7)
0.5923(12)
0.49
0.53
0.55
0.5922(7)
0.4965(9)
0.42
[3]
[11]
This work
This work
[16]
[FeII(TpivPP)(OAc]ꢀ
[FeII(TpivPP)(NCO)]ꢀ
[FeII(TpivPP)(NCS)]ꢀ
[FeII(TpivPP)( 1-ONO2)]ꢀ
g
[FeII(TpivPP)(N3)]ꢀ
Iron(III) high-spin porphyrins
[FeIII(TPP)(Cl)]
0.525
0.459
[14]
2.070(9)
2.066(11)
2.067(4)
2.069(5)
2.055(2)
2.211(1)
2.554(3)
1.898(4)
1.970(5)
1.956(5)
0.57
0.53
0.520(1)
0.540(1)
0.504
0.383(5)
–
0.485(1)
0.486(1)
0.462
[25]
[26]
[27]
[18]
[19]
[FeIII(TPP)(I)]
[FeIII(TTP)(OAc)]e
[FeIII(TpivPP)(NCO)]
[FeIII(TpivPP)(NCS)]
a
b
c
Average equatorial iron–nitrogen pyrrole distance.
Iron–axial ligand distance.
Distance between the iron atom and the mean plane made by the 24-atom core of the porphyrin.
Distance between the iron center and the mean plane of the four pyrrole N atoms.
TTP = tetratoluylporphyrin.
d
e
Fig. 3. ORTEP diagrams of the porphyrinato cores of the NCO derivative (left) and the NCS derivative (right). Shown are the perpendicular displacements, in units of 0.01 Å,
from the 24-atom mean plane of the porphyrinato core. Positive values of displacement are toward the pseudo-halide ligands.

3212
M. Dhifet et al. / Inorganica Chimica Acta 363 (2010) 3208–3213
the radius of Fe2+ compared to Fe3+, and this leads to increased
bond lengths in the coordination group. Thus, the axial FeII–
N(NCO) and FeII–N(NCS) bond lengths (2.005(3) Å and 2.042(2) Å,
respectively) are longer than of the correspondent distances in
the iron(III) derivatives [FeIII(TpivPP)(NCO)] [18] and [FeIII(T-
pivPP(NCS)] [19] (1.970(5) and 1.956(5) Å, respectively).
The NCO and the NCS groups are linear; the N9–C65–O5 bond
angle is 179.8(6)° and the N9–C65–S bond angle is 178.5(3)°. For
the NCO derivative N9–C65 and C65–O5 distances are 1.151(4) Å
and 1.197(4) Å, respectively while for the NCS species, N9–C65
and C65–S distances are 1.166(4) Å and 1.639(3) Å, respectively.
All these distances are in agreement with the literature values
[20,21].
The deviation from a linear coordination of the axial ligand to
the 24-atom core is more greater for the NCO ligand, i.e. Fe–N9–
C65 bond angles are 176.8(3)° for 1 and 170.2(3)° for 2. The
average equatorial Fe–Np distances for the [FeII(TpivPP)(NCO)]ꢀ
and [FeII(TpivPP)(NCS)]ꢀ ions complexes are 2.120(2) Å and
2.104(2) Å, respectively, are in the upper limit of the range
(2.072–2.115 Å) [22] found for five-coordinated high-spin iron(II)
porphyrinates. This is a stereochemical proof that complexes 1
and 2 are high-spin (S = 2). One can notice that these values are lar-
ger than those in the related Fe(III) species [FeIII(TpivPP)(NCO)]
[18] and [FeIII(TpivPP)(NCS)] [19] (2.069(5) Å and 2.055(2) Å,
respectively). In order to accommodate the high-spin iron(II) ion,
the porphyrinato cores undergo a significant radial expansion. This
is very well illustrated by the long Fe–PC = plane made by the 24-
atom core of the porphyrin) and Fe–PN (PN = plane made by the
four nitrogens of the porphyrin ring) distances shown by Fe(II)
high-spin [FeII(Porph)(X)]ꢀ complexes (X is an anionic ligand).
The values of Fe–PC distance for the iron(II) cyanato-N and thiocy-
anato-N species (0.6805(7) Å and 0.5923(12) Å, respectively) and
for other five-coordinated iron porphyrinates are summarized in
Table 4. We also notice that the Fe–PC and Fe–PN distances for 1
are the longest among all iron(II) species cited in Table 4. Illus-
trated in Fig. 3 are formal diagrams of the porphyrinato cores of
1 and 2. Given are the displacements of each atom from the mean
plane of the 24-atom porphyrin macrocycle in units of 0.01 Å.
These diagrams show (i) 1 and 2 present a large domed deforma-
tion of the C20N4 least-squares plane as indicated by the values
of the displacements of the nitrogen atoms toward the axial ligand,
(ii) a ruffling distortion is quite significant for 2 as indicated by the
displacement of the meso carbons above and below the porphyrin
mean plane, (iii) complex 1 exhibits a moderate S4 saddle distor-
tion of the 24-atom mean plane as mentioned by Scheidt and Lee
[23]. The structural decomposition method (NSD) provided by
Shelnutt and co-workers [24] indicated also a major doming defor-
mation: dom = 0.349 Å (ꢁ56%) and a moderate saddle deforma-
tion: sad = 0.154 Å (ꢁ25%) for 1, a major ruffling: ruf = 0.396 Å
(ꢁ48%) and a moderate doming: dom = 0.281 Å (ꢁ34%) for 2.
Fig. 4. Mössbauer spectra of 1 (top) and 2 (bottom) at 100 K in a weak applied
magnetic field of 500 G. The solid lines are Lorentz fits to the data.
Table 5
Mössbauer parameters for some five-coordinated high-spin (S = 2) iron(II) picket
fence porphyrin complexes.
Complex
D
Eq (mm/s)
dFe (mm/s)
T (K)
References
[FeII(TpivPP)(Cl)]ꢀ
[FeII(TpivPP)(OMe)]ꢀ
[FeII(TpivPP)(OAc)]ꢀ
[FeII(TpivPP)(NO3)]ꢀ
[FeII(TpivPP)(N3)]ꢀ
[FeII(TpivPP)(NCO]ꢀ
4.36
3,64
4.19
3.59
4.23(1)
4.040(4)
4.030(3)
4.007(3)
3.720(5)
3.739(6)
3.694(7)
1.01
1.00
1.03
0.98
1.08(1)
1.042(4)
1.043(3)
1.032(3)
1.012(5)
1.015(6)
1.014(7)
77
77
77
77
20
25
50
100
25
50
100
[3]
[11]
[11]
[16]
[14]
This work
[FeII(TpivPP)(NCS)]ꢀ
This work
3.3. Mössbauer spectrum
The Mössbauer spectra of 1 and 2 are shown in Fig. 4 and iso-
large quadrupole splitting values (
D
Eq ꢁ 3.5–4.5 mm/s). Indeed,
mer shift (dFe) and quadrupole splitting (
D
Eq) values are given in
the Eq values are 4.040(4) and 3.720(5) mm/s (at 25 K) for 1
D
Table 5 a-long with some comparative five-coordinated ferrous
high-spin (S = 2) porphyrin species. As seen in this figure, the
and 2, respectively, which is consistent with their findings. These
large quadrupole spittings values arise from a significant bond-
ing orbital contribution to the electric-field gradient from the an-
ionic axial ligand and that dxy becomes the lowest d orbital in
energy and hence, doubly occupied. We believe that the elec-
tronic repulsion of the iron(II) in-plane dxy orbital by the nega-
tive charge of the pyrrole nitrogens is thus expected to
increase the magnitude of the iron atom displacement from the
porphyrin plane with a concomitant increase in the values of
the Fe__Np, Fe__PC and Fe__PN distances as is observed for our
pseudo-halides iron(II) porphyrin derivatives.
D
Eq and dFe values of the iron(II) porphyrinate derivatives 1
and 2 did not change too much with the temperature in range
[25–100 K]. Metalloporphyrins with isomer shift values of
ꢁ1.00 mm/s are expected for high-spin iron(II) [28]. Indeed, the
isomer shift values for 1 and 2 of 1.042(4) and 1.012(5) mm/s
at 25 K, respectively strongly support a high-spin state assign-
ment for these species. It has been notice by Schulz and co-
workers [29] that five-coordinated high-spin iron(II) porphyri-
nates with anionic axial ligand (see Table 5) have distinctively

M. Dhifet et al. / Inorganica Chimica Acta 363 (2010) 3208–3213
3213
(b) C. Hu, C.D. Sulok, F. Paulat, N. Lehnert, A.I. Twigg, M.P. Hendrich, C.E. Schulz,
W.R. Scheidt, J. Am. Chem. Soc. 132 (2010) 3737.
4. Conclusion
[3] M. Schappacher, Ph.D. Thesis, Université Louis Pasteur, Strasbourg, France,
1982.
Two new five-coordinated iron(II) porphyrinates [Na(2,2,2-
crypt)] [FeII(TpivPP)(NCO)] (1) and [K(2,2,2-crypt)][FeII(TpivPP)
[4] A. Gismelseed, E.I. Bill, A.X. Trautwein, H. Winkler, H. Nasri, P. Doppelt,
D. Mandon, J. Fischer, R. Weiss, Inorg. Chem. 29 (1990) 2741.
[5] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De Caro,
C. Giacovazzo, G. Polidori, R. Spagna, J. Appl. Cryst. 38 (2005) 381.
[6] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[7] P. McArdle, J. Appl. Cryst. 28 (1995) 65.
[8] A.L. Spek, Acta Crystallogr., Sect. D 65 (2009) 148.
[9] H.D. Flack, G. Bernardinelli, J. Appl. Cryst. 33 (2000) 1143.
[10] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
[11] H. Nasri, J. Fischer, R. Weiss, J. Am. Chem. Soc. 109 (1987) 2549.
[12] H. Nasri, M.K. Ellison, C. Krebs, B.H. Huynh, W.R. Scheidt, J. Am. Chem. Soc. 122
(2000) 10795.
[13] H. Ben Abbes, H. Nasri, unpublished results.
[14] I. Hachem, M.S. Belkhiria, M. Giorgi, C.E. Schulz, H. Nasri, Polyhedron 28 (2009)
954.
(NCS)] (2) (TpivPP = a,a,a,a-tetrakis(o-pivalamidophenyl)porphy-
rin) were prepared and characterized by UV–Vis and IR spectrosco-
pies. Structural and Mössbauer results are consistent with a high-
spin (S = 2) state character of these two iron(II) pseudo-halide
2
1
1
1
1
derivatives with
a
ðdxyÞ ðdxzÞ ðdyzÞ ðdz2 Þ ðdx2ꢀy2
Þ
ground state
electronic configuration. This investigations confirm the fact that
for five-coordinated high-spin iron(II) porphyrinates type
[Fe(TpivPP)(X)]ꢀ, the large quadrupole splitting values are struc-
turally related to the large iron(II) out-of-plane displacement and
the concomitant long Fe–Np bond lengths.
[15] M. Schappacher, L. Ricard, R. Weiss, Inorg. Chem. Acta (1983) L9.
[16] H. Nasri, M.K. Ellison, B. Shaevitz, G.P. Gupta, W.R. Scheidt, Inorg. Chem. 45
(2006) 5284.
Acknowledgement
[17] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Part B, 6th ed., John Wiley and Sons, New York, 2009.
[18] M.S. Belkhiria, M. Dhifet, H. Nasri, J. Porphyrins Phthalocyanines 9 (2005) 575.
[19] H. Nasri, M. Debbabi, Polyhedron 17 (1998) 3607.
[20] A.K. Boudalis, J.-M. Clemente-Juan, F. Dahan, J.-P. Tuchagues, Inorg. Chem. 43
(2004) 1574.
The authors gratefully acknowledge financial support from the
Ministry of Higher Education and Scientific Research of Tunisia.
Appendix A. Supplementary material
[21] C.J. Siemer, F.A. Meece, W.H. Armstrong, D.M. Eichhorn, Polyhedron 20 (2001)
2637.
[22] (a) W.R. Scheidt, C.A. Reed, Chem. Rev. 81 (1981) 543;
(b) W.R. Scheidt, in: K.L. Kadish, K.M. Smith, R. Guilard (Eds.), The Porphyrin
Handbook, vol. 3, Academic Press, 2000, p. 49.
[23] W.R. Scheidt, Y. Lee, Struct. Bond. (Berlin) 64 (1987) 1.
[24] W. Jensen, J.-G. Ma, J.A. Shelnutt, J. Biophys. 74 (1998) 753.
[25] H. Nasri, Ph.D. Thesis, Universite Louis Pasteur, Strasbourg, France, 1987.
[26] K. Hatano, W.R. Scheidt, Inorg. Chem. 18 (1979) 877.
[27] H. Oumous, C. Lecomte, J. Protas, P. Cocolios, R. Guilard, Polyhedron 3 (1984)
651.
CCDC 773788 and 773789 contains the supplementary crystal-
lographic data for 1 and 2. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.05.058.
References
[28] P.G. Debrunner, in: A.B.P. Lever, H.B. Gray (Eds.), Iron Porphyrin Part 3,
Academic Press, New York, 1983 (Chapter 2).
[1] G. Simonneux, P. Le Maux, in: K.L. Kadish, K.M. Smith, R. Guilard (Eds.), The
Porphyrin Handbook, vol. 11, Academic Press, 2000, p. 133.
[2] (a) C. Hu, A. Roth, M.K. Ellison, J. An, C.M. Ellis, C.E. Schulz, W.R. Scheidt, J. Am.
Chem. Soc. 127 (2005) 5675;
[29] C. Hu, B.C. Noll, C.E. Schulz, W.R. Scheidt, J. Am. Chem. Soc. 127 (2005) 15018.