Synthesis and characterization of monomer and dimer complexes of porphyrin iron(III) with bridging phenylcyanamide ligands

Article abstract of DOI:10.1016/j.ica.2008.12.023

Several new mono and dinuclear complexes of [(P)Fe^III(L)], in which P is the dianion of tetraphenylporphyrin(TPP) and tetramesitylporphyrin(TMP) and L is the monoanion of 4-azo(phenylcyanamido)benzene (apc) (1) and (2) or dianion 1,4-di cyanami

Full text of DOI:10.1016/j.ica.2008.12.023

Inorganica Chimica Acta 362 (2009) 2782–2787
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Synthesis and characterization of monomer and dimer complexes of porphyrin
iron(III) with bridging phenylcyanamide ligands
*
Jafar MohammadNezhad, Nasser Safari
Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Several new mono and dinuclear complexes of [(P)FeIII(L)], in which P is the dianion of tetraphenyl-
porphyrin(TPP) and tetramesitylporphyrin(TMP) and L is the monoanion of 4-azo(phenylcyanami-
do)benzene (apc) (1) and (2) or dianion 1,4-di cyanamidobenzene (dicyd) (3), (4), (7), (8) and
4,40-azo-diphenylcyanamide (adpc) (5), (6), (9), (10) have been prepared by the reaction of [(P)FeIIICl]
with appropriate thallium salts of phenylcyanamide derivatives. Each of the complexes has been charac-
terized by FT-IR, UV–Vis, 1H NMR, MALDI-TOF and EPR spectroscopic data. In non-coordinating solvents
(such as toluene or chloroform) these complexes exhibit 1H NMR spectra that are characteristic of high-
spin (S = 5/2) species. The cyanamide group (NCN) of the bridging ligand is coordinated to Fe(III) ions
through the nitrile-nitrogen. The iron(III) phenylcyanamide complexes are not reactive toward dioxygen,
they convert into [TPPFeIIICl] when treated with HCl. EPR and NMR have shown that in dinuclear com-
plexes weak magnetic interactions take place between two iron(III) paramagnetic centers.
Ó 2009 Elsevier B.V. All rights reserved.
Article history:
Received 10 September 2008
Received in revised form 16 December 2008
Accepted 16 December 2008
Available online 25 December 2008
Keywords:
Tetraphenylporphyrin
Tetramesitylporphyrin
Phenylcyanamide derivatives
Dinuclear complexes
1. Introduction
gands as analogue of DCNQIs) in both neutral and anionic forms
with MnII and other metals.
Expansion of the
p-electronic system of component molecules
1,4-Dicayanamidobenzene (dicyd) and 4,40-azo-diphenylcyana-
mide (adpc) ligands are well-suited for intramolecular electro- and
is one of the most important and promising approaches, not only
to achieve high conductivity, but also for attracting strong effective
magnetic coupling [1–3]. Furthermore, molecular materials with
special properties, such as one or two dimensional electronics
magneto- communications via
a
hole-transfer mechanism
[23,25,26]. Work on dinuclear systems derived from cyanamide
or dicyanamide anions acting as bridging ligands is a fast-growing
research field due to the large variety of topologies, dimensionali-
ties, and magnetic properties that can be obtained [27].
based on planar p-conjugated molecules, are a very active field to-
day, due to their potential applications in a new generation of elec-
tronic, magnetic, and/or photonic devices [4–9]. Porphyrin arrays
have attracted considerable interest as synthetic targets due to
the potential for exploitation as photochemical devices. These por-
phyrins become self-assembled together due to the axial ligand or
periphery. These compounds have electronic, magnetic and pho-
tonic properties and application in semiconductors, transistors, so-
lar cells and electroluminescents [10–14].
Therefore, due to large p-conjugated systems in porphyrins and
phenylcyanamides and magnetic properties of Fe(III), which is usu-
ally high-spin in porphyrin complexes [28–30], we have previously
reported porphyrin iron(III) with phenylcyanamide derivatives as
the axial ligand. So, here we wish to report the synthesis and char-
acterization of 10 porphyrin iron(III) with extended azodiphenylc-
yanamide and phenyldicyanamides in monomer or dimer forms.
These complexes are thoroughly characterized and magnetic inter-
action in dimers is discussed.
The discovery of the N,N0-dicyanodiimines derived from benzo-
quinones (DCNQIs), naphthoquinones (DCNNIs), and anthraqui-
nones (DCNAIs) family of strong electron acceptor molecules by
Hünig and Aumüller in 1984 [15] has led to the development of
a large variety of highly conducting materials [16]. In this regard,
[TPPMn][tetracyanoethylene] ꢀ 2PhMe has shown to act as a mole-
cule-based magnet [17–21] and (2,5-dimethyl-N,N0-dicyanoqui-
none diimine)2Cu (DCNQI) has shown to exhibit extremely high
conductivity of 500000 S cmꢁ1 at 3.5 K [22]. Crutchley et al.
[23,24] have largely investigated DCNQI and phenylcyanamide (li-
2. Experimental
2.1. Reagents and materials
Dichloromethane, N,N-dimethylformamide, methanol, p-
chloranil, toluene, I2, n-hexane, benzophenone, Na and iron (III)
chloride were reagent grade and purchased from Merck and pyr-
role, benzaldehyde and 2,4,6-trimethylbenzaldehyde were from
Fluka. Prior to use, dichloromethane and methanol were pre-dried
and distilled over P2O5 and Mg + I2, respectively. Toluene was
* Corresponding author. Tel.: +98 21 22413885; fax: +98 21 22431661.
E-mail address: n-safari@cc.sbu.ac.ir (N. Safari).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.12.023

J. MohammadNezhad, N. Safari / Inorganica Chimica Acta 362 (2009) 2782–2787
2783
Scheme 1. Metathesis reaction and abbreviation for synthesis of iron Porphyrin phenylcyanamide derivatives.
pre-dried and distilled over Na and benzophenone. All manipula-
tions involving phenylcyanamide coordination to iron(III)porphy-
rin were carried out under nitrogen using standard Schlenk
technique. Tetraphenylporphyrin (TPPH2) and tetramesithylporph-
yrin(TMPH2) were synthesized by Lindsey’s [31] and Hoffmann’s
methods [32], respectively and TPPFeCl and TMPFeCl by Adler’s
After 30 min of vacuum and then under nitrogen atmosphere
(Schlenk technique), 50 ml dry toluene was transferred to the
reaction flask and stirred for 24 h. The mixture was filtered and
the volume of filtrate was reduced to 10 ml and then 50 ml of dried
n-hexane was added in portion while the solution was stirring. Pre-
cipitate was removed by filtration and dried in air. Compound 2
was prepared by the same procedure except that TPP was replaced
by TMP. FT-IR, UV–Vis data and yields of products are summarized
in Table 1. Anal. Calc. for C57H37FeN8 (891.847) (1): C, 76.7; H, 4.2;
N, 12.6. Found: C, 75.9; H, 3.9; N, 12.2%. Anal. Calc. for C69H61FeN8
(1060.171) (2): C, 78.1; H, 5.8; N, 10.6. Found: C, 77.9; H, 5.7; N,
10.2%.
method [33]. Extra care to exclude any trace of impurity of l-oxo
dimer and pre-treatment of TPPFeCl with HCl was necessary. Prep-
aration of the thallium salts of phenylcyanamide derivatives li-
gands has been previously reported [34].
Caution: Thallium is toxic.
2.2. Physical measurements
2.3.2. Preparation of monomers PFeNCN-C6H4-NCN-Tl (3) and (4)–(6)
Eighty milligrams (0.142 mmol) of thallium salt of dicydTl2 was
placed in a two-neck round-bottom flask, and 50 ml dry methanol
was transferred to the flask. After 20 min under vacuum, the flask
was placed under N2 atmosphere (Schlenk technique). Then
100 mg (0.142 mmol) of TPPFeCl dissolved in 50 ml dried and dis-
tilled toluene was added to the reaction flask by dropping funnel
during 4 h. The mixture reaction stirred for 30 h under dried nitro-
gen atmosphere at room temperature. After 30 h, the mixture reac-
tion was filtered and the volume of the filtrate was reduced to
approximately 10 ml and then 50 ml of dried n-hexane was added
in portion while the solution was stirring. Precipitate was removed
by filtration and dried in air. Compound 4 was prepared by the
2.2.1. Spectroscopy
UV–Vis spectra were recorded on a Shimadzu 2100 spectrome-
ter using a 1 cm path length cell in toluene at room temperature.
The FT-IR spectra (4000–400 cmꢁ1) of solid samples were recorded
on a Bomem MB-series spectrophotometer, in the solid state (KBr).
1H NMR spectra for paramagnetic complexes were acquired on a
Bruker AC-300 MHz spectrometer at ambient temperature in
C6D6. The 1Hnmr spectra were collected over a 50-kHz bandwidth
with 16 K data points and a 5-ls 45° pulse. For a typical spectrum,
between 1000 and 5000 transients were accumulated with a 50-ms
delay time. The signal-to-noise ratio was improved by apodization
of the free inducting decay. For MALDI-TOF-MS measurement the
reaction products were collected in a capillary Pyrex tube, which
was immersed in liquid nitrogen. Elemental analysis was per-
formed using a Heraeus CHN-O rapid analyzer. The collected prod-
ucts were analyzed using Kratos Kompakt MALDI-TOF-MS in
reflectron mode. Dithranol and lithium bromide were used as ma-
trix and cationization agent, respectively. The matrix has resonance
absorption at laser energy (k = 337 nm) and thus absorbs the laser
energy, causing rapid heating of the matrix. This rapid heating re-
sults in expulsion and soft ionization of the sample molecules with-
out fragmentation [35]. X-band electron paramagnetic resonance
were recorded on toluene at liquid nitrogen temperatures on a Joel
RE2x electron spin resonance spectrometer by using DPPH
(g = 2.0036) as a standard. All abbreviations for complexes 1–10
and for phenycyanamide derivatives are presented in scheme 1.
Table 1
UV–Vis electron absorptiona and FT-IR datab for P–Fe–L complexes 1–10 and thallium
salts of phenylcyanamide.
Complex
UV–Visc
t
(NCN)d,e
Yield
(%)
Soret
band
Q bands
Thallium
salt
Complex
TPPFe(apc) (1)
TMPFe(apc) (2)
418
417.5
418
417
418
417.5
419
419.5
419
505, 570
507, 571
504, 572
510, 571
506, 571
507, 573
505, 574
512, 578
511, 579
508, 577
2059
2059
2045
2045
2040
2040
2045
2045
2040
2040
2069
2085
78
81
64
66
77
79
61
69
68
76
TPPFe(dicyd)Tl (3)
TMPFe(dicyd)Tl (4)
TPPFe(adpc)Tl (5)
TMPFe(adpc)Tl (6)
TPPFe(dicyd)FeTPP (7)
TMPFe(dicyd)FeTMP (8)
TPPFe(adpc)FeTPP (9)
TMPFe(adpc)FeTMP (10)
2073, 2122
2030, 2066
2042, 2084
2050, 2102
2120
2110
2085
2110
2.3. Preparation of complexes 1–10
419
a
In nm.
2.3.1. Preparation of monomer PFe-NCN-C6H4-NN- Ph (1) and (2)
Fifty milligrams of tetraphenylporphyrin iron chloride, TPPFeCl
powder (0.071 mmol) and 100 mg (0.235 mmol) of thallium salt of
apcꢁTl+ were placed together in a two-neck round-bottom flask.
b
In cmꢁ1
.
c
d
e
In toluene.
KBr disk.
Strong.

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same procedure except that TPP was replaced by TMP and the
compound 5 was prepared by the same procedure except that dic-
ydTl2 was replaced by adpcTl2. Compound 6 was also prepared by
the same procedure except that TPP and dicydTl2 were replaced by
TMP and adpcTl2. FT-IR, UV–Vis data and yields of products are
summarized in Table 1.
was prepared by the same procedure except that dicydTl2 was re-
placed by apcdTl2. Compound 10 was prepared by the same proce-
dure except that TPP and dicydTl2 were replaced by TMP and
apcdTl2. FT-IR, UV–Vis data and yields of products are summarized
in Table 1. Anal. Calc. for C96H60Fe2N12 (1493.22) (7): C, 77.2; H,
4.0; N, 11.2. Found: C, 76.5; H, 3.9; N, 11.4%. Anal. Calc. for
C120H108Fe2N12 (1829.84) (8): C, 78.7; H, 5.9; N, 9.2. Found: C,
76.6; H, 5.7; N, 8.8%.
2.3.3. Preparation of dimers PFeNCN-C6H4-NCN-FeP (7) and (8)–(10)
Seventy-three milligrams (0.071 mmol) of complex
3 was
placed in a two-neck round-bottom flask, and 50 ml of dry metha-
nol was transferred to the flask. After 20 min under vacuum, the
flask was placed under N2 atmosphere (Schlenk technique). Then
50 mg (0.071 mmol) of TPPFeCl dissolved in 50 ml of dried and dis-
tilled toluene was added to reaction flask by dropping funnel dur-
ing 4 h. The mixture reaction stirred for 24 h at room temperature.
After 24 h, it was filtered and the volume of the filtrate was re-
duced to approximately 10 ml. precipitate was removed by filtra-
tion and dried in air. Compound 8 was prepared by the same
procedure except that TPP was replaced by TMP and compound 9
3. Results and discussion
The most studied synthetic iron porphyrins are those with
anionic axial ligands [36]. To the best of our knowledge, no studies
of dimer complexes of bridging ligands for example, phenylcyana-
mide derivatives to iron were reported in the literature until the
present work, where we describe the first synthesis and spectro-
scopic of dimer iron (III) porphyrin with dicyd and adpc axial
ligands. The FeIIIporphyrin complexes of 1,4-dicyanamido-
benzene(dicyd) and 4,40-azo-diphenyl cyanamide(adpc) were
Fig. 1. (a) MALDI-TOF mass spectra of a TPPFe(dicyd) FeTPP (7) and (b) MALDI-TOF mass spectra of a TMPFe(dipcyd)FeTMP (8).

J. MohammadNezhad, N. Safari / Inorganica Chimica Acta 362 (2009) 2782–2787
2785
synthesized in generally good yields to the following metathesis
reaction in refluxing dry toluene. Scheme 1 shows the reaction
equation and abbreviation used.
During preparation period, this reaction is very sensitive to
moisture and to a less extent to O2. The presence of water results
in the formation of
l-oxo dimer, PFe–O–FeP. The l-oxo dimer
impurity is hard to remove, since chromatography on silica gel or
aluminum oxide may lead to its additional formation. The reaction
yields for compounds 1–10 were quantitative, although during the
process of precipitation and isolation 20–30% of the products were
lost, isolated yields are reported in Table 1. These products are less
sensitive to moisture or oxygen after formation. So, no effort was
made to exclude air or moisture for spectroscopic studies. All com-
pounds are fairly soluble in non-coordinating solvent except for
saturated hydrocarbons. Phenylcyanamide derivative complexes
readily react with HCl and result in the formation of starting PFeCl.
Attempt to make suitable crystals for the dimer complexes were
failed. However, MALDI-TOF of compound 7 shows the mother
peak at 1492.84 (expected for C96H60Fe2N12 at 1493.22) and for
Fig. 2. UV–Vis spectra of TPPFeCl (__), TPPFe-dicyd-Tl (---) (3) and TPPFe-dicyd-
FeTPP (...) (7), 10ꢁ6 M in toluene.
compound
C120H108Fe2N12 at 1829.84), Fig. 1.
8
the mother peak at 1829.84 (expected for
parison with thallium salts and iron dimers in 7–10 clearly
demonstrate that lower frequency is for coordination to thallium
and higher frequency for coordination to iron. The presence of only
one sharp and intense absorption band at around 2070–2095 cmꢁ1
for the cyanamide stretching frequency in the dinuclear complexes
7–10, provides evidence that both cyanamide moieties on the
phenyl ring of the bridging ligands, dicyd and adpc, are equivalent
in the solid state. When the cyanamide moieties are inequivalent
4. Spectroscopic characterization
4.1. IR and UV–Vis studies
Cyanamide group is a three atom p-system, which is a poorer p-
acceptor but better donor analogous of nitrile ligands [37]. The IR
(3–6), multiple
m(N@C@N) bands are observed [24]. However, in
these complexes,
m
(N@C@N) consistently frequency shifted around
spectra of the neutral ligands (dicydH2 and adpcH2) show a strong
10–80 cmꢁ1 higher in contrast with the thallium salts. The same
trend was observed for monomer complexes of tetraphenylpor-
phyrin manganase(III) and tetraphenylporphyrin iron(III) of phe-
band around 2225–2250 cmꢁ1 that is assigned to
m(C@N) of the
cyanamide groups [23] and coordinated nitrile in FeIII–CN com-
plexes was reported at 2129 cmꢁ1 [38]. The IR spectrum of the
thallium salt of the anion ligands of dicydTl2, adpcTl2 and apcTl
nylcyanamides [42,43]. The
m(N@C@N) frequencies for thallium
shows a very strong band at 2045, 2040 cmꢁ1 and 2059 cmꢁ1
,
salts and compounds 1–10 are listed in Table 1.
Fig. 2 shows UV–Vis spectra of compounds 3 and 7 in toluene in
comparison with TPPFeCl. These spectra and the results for other
compounds in Table 1 indicate the similarity of the electronic spec-
tra of prepared compounds.
The UV–Vis spectra of iron(III) porphyrin are sensitive to oxida-
tion and spin state of iron(III). Differentiation of the nature of axial
ligands of iron(III) porphyrin when accompanied by spin change, is
often possible by UV–Vis spectra [44].
The kmax values of the phenylcyanaꢁmide-ligated species are in
the same range to those of the Clꢁ, N3 and NCSꢁ iron porphyrin
species in the soret region. This confirms the existence of high-spin
iron(III) oxidation states. Fig. 2 also indicates higher absorption
respectively for m(N@C@N) stretch.
Coordination of neutral and anionic dicyanamidobenzene
ligands to metal cations can occur via amine or nitrile nitrogens
and there are examples in the literature of both types of
coordination [23]. Transition metal complexes appear to prefer
coordination to the nitrile nitrogen. This may be due to the
p-
back-bonding and donor properties of the nitrile groups and the
steric hindrance that would be experienced upon coordination to
the amine of N-alkyl- or N-phenyl-substituted cyanamides. The
neutral cyanamide ligands have
to the delocalization of the amine electron lone pair into a nitrile
-bond of the correct symmetry [23,39,40]. The anionic cyanamide
ligand is expected to be a strong -donor ligand because two lone
pairs can delocalize into the nitrile system. It is suggested that
p-donor properties that are due
p
coefficient of 7 and 3 due to the coordination of a longer p-conju-
gated axial ligand.
p
p
the resonance structure B (scheme 2) will dominate when the an-
ion ligand is coordinated to Fe (III) [41].
4.2. 1H NMR studies
The IR spectra of the monomer complexes (1 and 2) exhibit
1H NMR spectroscopy has been shown to be a uniquely defini-
tive method for detecting and characterizing iron porphyrins. The
hyperfine shift patterns are sensitive to the iron oxidation, spin
and ligation state. Pyrrole protons in particular provide a direct
probe of the porphyrins macrocycle [37]. Magneto chemical series
proposed by Reed et al. are based on the position of the ptrrole pro-
tons in TPPFe-X ranging from ꢁ62 ppm to +80 ppm for different X-
ligands [45,46].
strong absorption bands for m ,
(N@C@N) at 2069 and 2085 cmꢁ1
respectively. The IR spectra of the complexes 3–6 shows two strong
absorption bands at arounds 2030–2070 cmꢁ1 due to coordination
of NCN to thallium and 2075–2125 cmꢁ1 due to coordination of
cyanamide to the iron. Two cyanamides are inequivalent in com-
pounds 3–6 due to their coordination to iron and thallium. Com-
The 1H NMR spectra of mono and dinuclear phenylcyanamide
complexes are shown in Figs. 3 and 4, respectively, and full assign-
ment of signals for compounds 1–10 are presented in Table 2. Res-
onance assignments have been made on the basis of relative
intensity, line width, previous assignments of P–Fe–L moiety in
high-spin Fe(III)complexes [43,44] and direct comparison of sig-
nals in compounds 1–10.
Scheme 2. Three modes of coordination of dicyanamides ligands.

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J. MohammadNezhad, N. Safari / Inorganica Chimica Acta 362 (2009) 2782–2787
Fig. 3. 1H NMR spectra of iron(III)porphyrin complexes: TPPFedicyd-Tl (3), TPPFe(dicyd) FeTPP (7) and TMPFe(dicyd)FeTMP (8) in C6D6 at 300 K. *impurity of TPPFeCl and
compound (7).
Fig. 4. 1H NMR spectra of iron(III)porphyrin complexes with azo-phenylcyanamides: TPPFe(apc) (1) and TPPFe(adpc)FeTPP (9) in C6D6 at 300 K.
Table 2
phenyl ring appear in ꢁ61.5 ppm and protons in 3,5 position on
1H NMR spectral data of P–Fe–L complexes.a
phenyl ring have chemical shift of +36 ppm [43]. However, interac-
tion of two iron atoms in dimers 7 and 8 cause spin transfer of both
iron atoms on the protons of the phenyl ring and result in changing
of chemical shift of protons in 2,6 position from ꢁ61.5 ppm in
monomer to ꢁ35 ppm in dimer complexes. This 26.5 ppm chemi-
cal shift on protons of the phenyl on bridging phenylcyanamide
shows that both irons have transferred spin to the bridging ligand.
However, pyrrole protons in 1 and 2 are at 79.0 and 77.6 ppm,
respectively. In dimers 7 and 8 pyrrole resonances are around
75 ppm. The pyrrole signal position is very sensitive to the magne-
tization state of the iron and antiferromagnetic coupling changes
the pyrrole position dramatically [28]. There for little change of
3–4 ppm in pyrrole position of the dimmers, relative to the mono-
mers indicates that there is a very weak antiferromagnetic cou-
pling between two iron centers in these dimers.
Complex
pyrr-H m-H
H2
H3
H5
H6
TPPFe(apc) (1)
TMPFe(apc) (2)
79.0
77.6
78.1
75.5
78.8
77.9
75.3
75.4
79.1
12.3, 11.3 ꢁ61.5
44.0
44.0
41.6
34.4
ꢁ61.5
15.5, 13.9 ꢁ58.8b 41.6
12.5, 11.5 ꢁ35.2b 34.4
ꢁ58.8b
ꢁ35.2b
TPPFe(dicyd)Tl (3)
TMPFe(dicyd)Tl (4)
TPPFe(adpc)Tl (5)
TMPFe(adpc)Tl (6)
TPPFe(dicyd)FeTPP (7)
TMPFe(dicyd)FeTMP (8)
TPPFe(adpc)FeTPP (9)
14.0, 12.6 ꢁ40.5
36.4b 36.4b ꢁ40.5
12.2, 11.2 ꢁ61.1b 44.3
44.3
35.0
ꢁ61.1b
ꢁ40.1
ꢁ35.4
ꢁ40.3
14.5, 13.1 ꢁ40.1
11.8, 11.1 ꢁ35.4
13.9, 12.6 ꢁ40.3
35.0
12.2, 11.2 ꢁ62.1b 37.1
37.1
35.1
ꢁ62.1b
c
c
TMPFe(adpc)FeTMP (10) 78.1
14.5, 13.2
35.1
a
In C6D6, data in ppm vs. TMS reference at 0.00 ppm at 300 K.
Very broad.
Not observed.
b
c
The effect of temperature on the 1H NMR spectrum of hydro-
gens of phenylcyanamide for 8 in chloroform solution is shown
in Fig. 5, where the chemical shifts for the pyrrole proton and
2,6-H are plotted versus 1/T (Kꢁ1). This plot shows Curie law
behavior and confirms weak interaction between metal centers,
since the plot is almost linear.
Trace of compound 1 in Fig. 4 with monoanion apc axial ligand
shows two signals at ꢁ61.5 and 44.0 ppm which arises from two
kinds of hydrogen, ortho and meta position with ratio of 1:1. When
mononuclear complex 1 is replaced by dinuclear complex 9 of adpc
For example, traces of 7 and 8 in Fig. 3 show only a signal at
ꢁ35.4 and ꢁ40.3 ppm, respectively, so, the presence of only one
signal for the hydrogen phenylcyanamides in the dinuclear com-
plexes, provides evidence that hydrogens present in both position
of ortho and meta cyanamide moieties on the phenyl ring are
equivalent. Trace of 3 in Fig. 3 has shown a new signal low field re-
gion at 34.4 ppm with similar intensities of signal in ꢁ35.2 ppm.
This signal in 34.4 ppm has been assigned to 3,5-H for compound
3. In compound 1, signals related to protons in 2,6 position in

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Fig. 5. Plot of the chemical shift versus 1/T (K) for the pyrrole (a), 2,6-H (b)
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ligand, as expected, the same 1H NMR pattern is seen, trace 9 of
Fig. 4. It seems that in the case of azophenylcyanamide dimer com-
plexes 9 and 10 larger distance between paramagnetic centers re-
sult in almost zero coupling between two iron centers, which are
negligible. Their pyrrole positions are around 79 ppm similar to
monomer complexes. Signals of phenyl of tetraphenylporphyrins
in compounds 1–10 have been seen in almost the same place for
TPPFeCl, Table 2.
The EPR of compound 1 in toluene at liquid nitrogen tempera-
ture has shown signals at g = 5.82 and 2.035. The signals for com-
pound 8 are at g = 5.84 and 2.029, which is in the similar position
to the monomer signals and these are indicative of iron(III) high-
spin species with S = 5/2 for monomers and dimers and confirm
that the magnetic coupling for the iron centers in the dimeric com-
plexes is weak or non-existent.
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We wish to thank the Ministry of Science, Research and Tech-
nology of Islamic Republic of Iran for Nanotechnology Committee
Grant No. 31-959. We would also like to thank the following: Dr.
Raofie for providing us MS analysis, Prof. Amani for providing us
EPR analysis and Dr. Hadadzadeh for providing some phenylcyana-
mide derivatives.
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