Synthesis and characterization of a new series of metalloporphyrin polymers

Article abstract of DOI:10.1081/SIM-100105260

A series of bridged metalloporphyrin polymers, [M(TPP)L]_n, with pyrazine and bipyridine as the bridging ligands, L, tetraphenylporphyrin (TPP) as the macrocycle (Mac) and Fe(III), Co(II), Mn(III), Ni(II) and Cu(II) as the central metal ions M, were synthesized by a high pressure method different from traditional refluxing methods for the synthesis of one-dimensional metallomacrocycle polymers. These compounds were characterized by elemental analyses, surface photovoltage spectra and infrared spectra. The polymerization time of the polymers varied, depending on the metal ions considerably, in the order Co(II) < Fe(III) < Ni(II) < Cu(II) < Mn(III), and the ligands, bipyridine < pyrazine.

Full text of DOI:10.1081/SIM-100105260

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SYNTHESIS AND CHARACTERIZATION OF A NEW SERIES
OF METALLOPORPHYRIN POLYMERS
Xiangqing Li a , Xingqiao Wang b , Jingfu Guo a , Lianxiang Yu a & Guofa Liu a
a Department of Chemistry , Jilin University , Changchun, 130023, P. R. China
b Department of Chemistry , Jilin University , Changchun, 130023, P. R. China
Published online: 15 Feb 2007.
To cite this article: Xiangqing Li , Xingqiao Wang , Jingfu Guo , Lianxiang Yu & Guofa Liu (2001) SYNTHESIS AND
CHARACTERIZATION OF A NEW SERIES OF METALLOPORPHYRIN POLYMERS, Synthesis and Reactivity in Inorganic and Metal-
Organic Chemistry, 31:6, 1041-1051, DOI: 10.1081/SIM-100105260
To link to this article: http://dx.doi.org/10.1081/SIM-100105260
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(6), 1041±1051 (2001)
SYNTHESIS AND CHARACTERIZATION
OF A NEW SERIES OF
METALLOPORPHYRIN POLYMERS
Xiangqing Li, Xingqiao Wang,* Jingfu Guo,
Lianxiang Yu, andGuofa Liu
Department of Chemistry, Jilin University, Changchun
130023, P. R. China
ABSTRACT
Aseries of bridged metalloporphyrin polymers, [M(TPP)L] ,
n
with pyrazine and bipyridine as the bridging ligands, L, tet-
raphenylporphyrin (TPP) as the macrocycle (Mac) and
Fe(III), Co(II), Mn(III), Ni(II) and Cu(II) as the central metal
ions M, were synthesized by a high pressure method di€erent
from traditional re¯uxing methods for the synthesis of one-
dimensional metallomacrocycle polymers. These compounds
were characterized by elemental analyses, surface photo-
voltage spectra and infrared spectra. The polymerization time
of the polymers varied, depending on the metal ions con-
siderably, in the order Co(II) < Fe(III) < Ni(II) < Cu(II)
< Mn(III), and the ligands, bipyridine < pyrazine.
*Corresponding author. E-mail: anjela@sohu.com
1041
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1042
LI ET AL.
INTRODUCTION
The chemical versatility of metalloporphyrins and related macrocyclic
complexes provides an opportunity to prepare a large matrix of conductive
materials1. Porphyrin oligomers with more than three porphyrin units have
been reported as synthetic molecular devices and models of light-harvesting
systems273. Macrocyclic compounds, axially linked by 4,40-bipyridine (bpy),
pyrazine (pyz) or diisocyanobenzene (dib), lead to chain structure poly-
mers476, [MacML]n (Mac ˆ tetrabenzoporphyrin, phthalocyanine, 1,2-or
2,3-naphthalocyanine or octaethylporphyrin; M ˆ Fe(II), Re(II), Os(II); L
ˆ pyz, bpy, dib), but metallotetraphenylporphyrin complexes with similar
structures have been much less investigated7. We report here the synthesis of
sequentially ordered one-dimensional metallotetraphenylporphyrin poly-
mers, for which high complex stabilities and high conductivities were
expected. In stacked structures of this type of the macrocycle, the central
metal ions included Co(II), Mn(III), Ni(II) and Cu(II) and the bidentate-
bridging ligands included pyrazine and bipyridine (the structures of ligands
are shown in Fig. 1.). The large ¯exibility of this approach is lied in only
using di€erent bridging ligands, thereby leading to di€erent interring dis-
tances but also to an electron pathway along the central axis of the polymer.
It was found that by the traditional re¯uxing method8 which was usually
utilized to synthesize other macrocyclic compounds it is dicult to syn-
thesize metallotetraphenylporphyrin polymers, while they can be easily
prepared in a sealed stainless autoclave by higher pressure (ꢀ 2:2 Â 107 pa)
Figure 1. Structures of bridging ligands pyrazine (pyz) and bipryridine (bpy).

METALLOPORPHYRIN POLYMERS
1043
generated from the gasi®cation of solvent to accelerate the bridging ligands
to link with metalloporphyrins. So it is special to synthesize metallote-
traphenylporphyrin polymers in an autoclave. Microanalyses, surface pho-
tovoltage and infrared spectra con®rmed the formation of the target
products. It is hoped that this type of coordination polymers could be uti-
lized as ``molecular wire'' in molecular level integrated circuits.
RESULTS AND DISCUSSION
Preparation of the Metallotetraphenylporphyrin Complexes
The monomer MTPPL2 was prepared according to literature
method7,9 with some modi®cations. The polymers were synthesized by
reaction of metallotetraphenylporphyrins with bidentate ligands L in a 1:1
ratio in chloroform at high temperature and pressure. Microanalyses and
physical properties of some products are given in Table I. The reaction may
be represented by the following equation.
nMTPP ‡ nL À! ‰ MꢁTPP†LŠ
n
ꢁM ˆ FeꢁIII†; CoꢁII†; MnꢁIII†; NiꢁII† and CuꢁII†; L ˆ pyz; bpy†
Surface Photovoltage Spectroscopy
The surface photovoltage spectra of the monomer Mn(TPP)(pyz)2 and
the polymer [Mn(TPP)(pyz)]n are shown in Fig. 2. The Soret band of the
polymer (dashed line) is found at about 335 nm, representing a 65 nm blue-
shift relative to the monomer (solid line). This is consistent with previous
reports10712 that the enhanced interaction between the porphyrin macro-
cycles causes strong exciton coupling in these types of polymers. The signal
of the polymer at about 950 nm is similar to the behavior of the symmetrical
complexes [Ru(TBP)(L)]n13. It is typical of metal-to-axial ligand charge-
transfer bands.
InfraredSpectra
Infrared spectra of pyrazine and 4,40-bipyridine14 exhibit a characteristic
centrosymmetric ring-stretching mode near 1600 cmÀ1, which is infrared and
Raman-allowed for the unidentate ligand and only Raman-allowed for the
bidentate and free ligands. The infrared spectra (Fig. 3) of the monomer
Mn(TPP)(pyz)2 and the polymer [Mn(TPP)(pyz)]n illustrate this di€erence

1044
Table I. Elemental Analyses and Main Physical Constants of the Products
Found (Calcd.) %
LI ET AL.
Formula Yield Dec. p.
(ꢂC)
Complexes
C
H
N
M
weight
(%)
Co(TPP)(pyz)2
C52H36N8Co
74.59
4.03
13.01
6.62
831.9
48
163
(75.07) (4.37) (13.47) (7.09)
76.19 2.30 10.72 7.39
(76.68) (3.39) (11.18) (7.84)
[Co(TPP)(pyz)]10
7517.9
984.1
80
56
362
177
(C48H32N6Co)10
Co(TPP)(bpy)2
C64H44N8Co
77.63
(78.11) (3.90) (11.39) (5.98)
3.50
11.21
5.50
[Co(TPP)(bpy)]6
(C54H36N6Co)6
77.89 3.31 10.00 6.61
(78.34) (3.69) (10.15) (7.10)
75.02 3.72 13.25 6.11
(75.43) (3.90) (13.54) (6.60)
76.62 3.01 10.85 6.89
(77.09) (3.42) (11.24) (7.35)
77.39 3.83 11.16 5.91
(77.74) (4.01) (11.34) (6.39)
77.46 3.29 9.68 7.13
(77.90) (3.51) (10.08) (7.61)
4967.3
827.9
86
30
82
37
75
317
151
353
120
240
Mn(TPP)(pyz)2
C52H36N8Mn
[Mn(TPP)(pyz)]8
(C48H32N6Mn)8
5982.4
988.7
Cu(TPP)(bpy)2
C64H44N8Cu
[Cu(TPP)(bpy)]5
(C54H36N6Cu)5
4162.6
(the monomer and the polymer have been normalized to the same con-
centration). The characteristic absorption of the monodentate pyrazine
molecule around n ˆ 1583 cmÀ1 in the monomer just appeared as a very weak
band near 1614 cmÀ1 after polymerization, which is consistent with the pre-
sence of a high proportion of bridging pyrazine molecules (bidentate) in the
polymeric structure. So it is possible to determine the proportion of pyrazine,
bridged or terminal, in pyrazine-containing complexes this way15. From Fig. 3
it can be learned that the bands at 3112, 2773, 1461 and 1012 cmÀ1 almost
vanish upon polymerization. These bands are allowed in monomeric
Mn(TPP)(pyz)2 but not in the corresponding polymeric [Mn(TPP)(pyz)]n
compounds16. In addition, the bands of the monomer at 3378, 1621, 1415,
1330 and 1074 cmÀ1 are shifted in the polymer by 50, 37, 25, 50 and 21 cmÀ1
towards higher energy, respectively. This indicates that the symmetry of the
polymer (D2h) and the interaction between porphyrin macrocycles are
enhanced because the metalloporphyrins are linked with axial ligands16,17
Thus, the results of the infrared spectroscopy complement those of the surface
.

METALLOPORPHYRIN POLYMERS
1045
Figure 2. Surface photovoltage spectra of Mn(TPP)(pyz)2 (solid line) and [Mn
(TPP)(pyz)]n (dotted line).
Figure 3. Infrared spectra of Mn(TPP)(pyz)2 (A) and [Mn(TPP)(pyz)]n (B) (spectra
have been normalized to the same concentration).

1046
LI ET AL.
Table II. Important IR Frequenciesa (cmÀ1) of M(TPP)L2
and [M(TPP)L]n
Complexes
ꢀ(C-N), ꢀ(CˆC)
ꢀ(CˆN)
Co(TPP)(pyz)2
[Co(TPP)(pyz)]n
Co(TPP)(bpy)2
[Co(TPP)(bpy)]n
Mn(TPP)(pyz)2
[Mn(TPP)(pyz)]n
Cu(TPP)(bpy)2
[Cu(TPP)(bpy)]n
1598 vs
1589 vw
1599 vs
1606 w
1583 m
1614 w
1600 m
1606 w
1644 s
1658 m
1675 w
1653 w
1621 s
1658 vs
1649 vs
1678 w
as ˆ strong, m ˆ medium, w ˆ weak, v ˆ very.
photovoltage spectroscopy. Some of the major infrared frequencies of
metallotetraphenylporphyrin complexes are presented in Table II.
For the pyrazine-bridged polymers, the pyrazine symmetrical
``breathing'' mode at 1581 cmÀ1 is usually forbidden but can appear if the
symmetry of the molecule is lost by coordination on one nitrogen only16.
This allows the determination of the degree of polymerization (n) of
[Mn(TPP)(pyz)]n by estimation of the ratio of the absorbance of a bridging
pyrazine (in the polymer) and end group (monodentate) pyrazine (in the
monomer) after normalization of the IR spectra of Mn(TPP)(pyz)2 and
[Mn(TPP)(pyz)]n. Analysis of the spectroscopic data of Mn(TPP)(pyz)2 and
[Mn(TPP)(pyz)]n indicates
a bridging pyrazine: end group (mono-
dentate)pyrazine ratio higher than 4; the degree of polymerization n in
[Mn(TPP)(pyz)]n will therefore be estimated to be ꢃ 8. The values of n of
other metallotetraphenylporphyrin polymers [Co(TPP)(pyz)]n, [Co(TPP)
(bpy)]n and [Cu(TPP)(bpy)]n were obtained by the same method, resulting in
n ˆ 10, 6 and 5, respectively. Thus, the infrared spectra of the monomer and
polymer provide some insight into the molecular structures, including
information about their degree of polymerization.
E€ects of Temperature, Metals andLigands on the
Polymerization Time
It was found that di€erent metals and ligands had di€erent e€ects on
the formation of the polymers. For the same metal and ligand, the higher
the reaction temperature is, the shorter is the polymerization time. The e€ect
of temperature on the polymerization time is presented in Table III.

METALLOPORPHYRIN POLYMERS
1047
Table III. The E€ect of Temperature on the Polymerization Time
Polymers
Temperature (ꢂC)
Polymerization time (h)
[Co(TPP)(pyz)]n
100
120
100
120
100
120
100
120
100
120
100
120
14
10
12
9
20
16
40
30
120
45
175
49
[Co(TPP)(bpy]n
[Fe(TPP)(pyz)]n
[Ni(TPP)(pyz)]n
[Cu(TPP)(pyz)]n
[Mn(TPP)(pyz)]n
For the metals, same ligand studied and using the same concentration
and temperature, the time of polymerization was di€erent: Co(II)
<Fe(III)<Ni(II)<Cu(II)<Mn(III). This argument ignores the varying
degree of polymerization and di€erent solubility of the products. It was also
found that for the same metal ion, temperature and di€erent ligands, the
polymerization time was in the order of bpy < pyz. Perhaps, this can be
rationalized by the di€erent distance of the two nitrogen atoms in bpy and
pyz. In conclusion, the longer distance of the N,N atoms in bpy leads to
smaller electron repulsion between metalloporphyrin and bridged bipyridine
and shorter polymerization time.
Conclusions
Ahigh pressure method di€erent from traditional re¯uxing method
was adopted to synthesize a new series of one-dimensional bridged metal-
loporphyrin polymers, [M(TPP)L]n (M ˆ Fe(III), Co(II), Mn(III), Ni(II)
and Cu(II); L ˆ pyz, bpy). Arguments supporting the proposed polymeric
structures begin with the observation that a pronounced decrease in solu-
bility is found for the polymers relative to the starting materials and the
monomer. Further evidence for the structure of the polymers is found in
their IR spectra. Finally, the claiment products are con®rmed by elemental
analyses and surface photovoltage spectra. The schematic structure of
polymer is shown in Fig. 4.
Work is in progress to determine the conductivities, Ea, for the reac-
tion and polymerization rate.

1048
LI ET AL.
Figure 4. Schematic representation of the bridged metallotetraphenylporphyrin
polymer.
EXPERIMENTAL
Analyses andMeasurements
C, H and N elemental analyses were obtained with a Perkin-Elmer
2400 elemental analyzer. Metal analyses were conducted on a Perkin-Elmer
Optima 3300 inductive-coupled plasma (ICP) instrument. Decomposition
temperatures were measured with a Perkin-Elmer 7 thermogravimetric
analyzer and 1700 di€erential thermal analyzer, scanning rate 20 ꢂC=min.
Surface photovoltage spectra were measured with a home-built apparatus18.
Sample thickness was about 10 mm. The e€ect of the light source was cor-
rected by computer programming. Infrared spectra were recorded on a
Nicolet Impact 410 FTIR spectrometer in the region 40074000 cmÀ1 using
KBr pellets. UV-vis spectra were determined in a 1.00 cm matched cell with
a UV-VIS-NIR recording spectrophotometer UV-3100 (Shimadzu).
Synthesis of Monomer M(TPP)L2
According to synthetic procedures for PcFe(pyz)2 and Co(TPP)(pyz)2
adducts7,9. TPPM was reacted with excess bridged ligands as a melt in a
sealed autoclave to yield, after removal of excess ligand, the monomer
M(TPP)L2. Microanalyses and physical properties of some of these products
are shown in Table I.

METALLOPORPHYRIN POLYMERS
1049
Synthesis of Tetraphenylporphyrin Manganese(III) (MnTPPCl)
Polymer
In a 15 mL polytetra¯uoroethylene-lined stainless steel autoclave,
MnTPPCl (0.2 g, 0.296 mmole) was dissolved in 8 mL chloroform. To the
porphyrin solution was added pyrazine (0.024 g, 0.296 mmole) at room
temperature. After being stirred thoroughly, the autoclave was sealed and
placed in an oven with a constant temperature of 120 ꢂC. The reaction was
monitored by UV spectra. Every 3 h 0.1 mL solution was withdrawn from
the autoclave and its UV spectrum was determined. The reaction was
complete when the spectra of the solution in the autoclave didn't change.
The cooled reaction mixture was ®ltered and the precipitate was washed
with chloroform until the ®ltrate was colorless. The crude products were
extracted via Soxhlet apparatus ®rst with THF until the extracts became
colorless, then the residue was further extracted with DMF until the extracts
became also colorless. The ®nal residue was a product with a high degree of
polymerization (the values of the degree of polymerization are reported in
Table I). It was dried under vacuum at 80 ꢂC for 20 h and a€orded 0.18 g
(82%) of a dark green powdery product. The same procedure as described
above was used to synthesize and characterize the other metallote-
traphenylporphyrin polymers, [M(TPP)L]n (M ˆ Co(II), Fe(III), Cu(II)
and Ni(II); L ˆ bpy, bpy). Other polymers prepared with an extraction step
and their physical properties are shown in Table I.
ACKNOWLEDGMENT
We thank the National Natural Science Foundation of China (Grant
No: 20071014) for ®nancial support of this work.
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Received September 9, 2000
Accepted May 8, 2001
Referee I: C. Bruckner
È
Referee II: L. M. Mink