Synthesis, characterisation and magnetic behaviour of ionic metalloporphyrins: Metal-tetrakis(N-octyl-4-pyridinium)-porphyrins with tetrabromoferrate(III) anions

Article abstract of DOI:10.3184/174751913X13727033282329

A series of magnetic, ionic-substituted tetrapyridyl metalloporphyrins, [tetrakis(N-octyl-4-pyridinium)-metal-porphyrin][ tetrabromoferrate(III)]4 (metal=iron, cobalt, manganese, copper or zinc), have been synthesised. All compounds show weak ferromagnetic behaviour at room temperature and respond to an external neodymium magnet.

Full text of DOI:10.3184/174751913X13727033282329

JOURNAL OF CHEMICAL RESEARCH 2013
RESEARCH PAPER 445
AUGUST, 445–450
Synthesis, characterisation and magnetic behaviour of ionic
metalloporphyrins: metal–tetrakis(N-octyl-4-pyridinium)–porphyrins with
tetrabromoferrate(III) anions
Na Zhoua, Zhicheng Sunb, Qing Zhoub, Xingmei Lub and Huawu Shaoa*
aNatural Products Research Centre, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan 610041, P. R. China
bBeijing Key Laboratory of Ionic Liquids Clean Process, Key Laboratory of Green Process and Engineering, State Key Laboratory of
Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, P. R. China
A series of magnetic, ionic-substituted tetrapyridyl metalloporphyrins, [tetrakis(N-octyl-4-pyridinium)–metal–porphy-
rin][tetrabromoferrate(III)]4 (metal=iron, cobalt, manganese, copper or zinc), have been synthesised. All compounds
show weak ferromagnetic behaviour at room temperature and respond to an external neodymium magnet.
Keywords: [tetrakis(N-octyl-4-pyridinium)–metal–porphyrin][tetrabromoferrate(III)]4, magnetism, macrocycles
Metalloporphyrins, model compound of biological enzymes,
have been extensively studied because of their far-ranging
applications in separation, synthesis, catalysis, energy transfer,
coordination chemistry and novel materials.1–6 Being the
analogues of cytochrome P450, metalloporphyrins may take a
similar role in catalysing a series of oxidative reactions includ-
ing epoxidation of olefins and hydroxylation of hydrocarbons
under mild conditions without additional co-reductant.7–11
However, the realisation of efficient catalyst separation in a
reaction system is a major problem in porphyrin chemistry.
Various methods, including immobilisation of homogeneous
catalysts on inorganic supports, have been developed.12–16
Nevertheless, the resulting simple recovery was always at the
expense of decreased reactive performance due to reduction of
the active surface area of the heterogeneous catalysts.17–19
Recently, paramagnetic ionic liquids, composed mostly of
organic ions with the special properties of showing good
magnetic field response and solubility, have gained importance
in ionic liquid chemistry.20–24 These paramagnetic ionic liquids
have helped to provide fresh perspectives in separation and
catalytic chemistry applications. With the aid of a magnetic
field, they provide a completely novel tool to solve the loss of
catalysts in industrial processes. In addition, magnetic proper-
ties have, to some degree, positive catalytic impacts on certain
chemical reactions.
effectively by virtue of magnetic character under a magnetic
field. Therefore we have prepared a series of ionic metallopor-
phyrins with iron, cobalt, manganese, copper or zinc as the
central metal by means of the multi-steps synthetic method
shown in Scheme 1 and characterised them by elemental
analysis and H NMR, UV-Vis, FT-IR, ES-MS and Raman
spectroscopy.
We have investigated and compared the effect of the central
metal ions as well as anion incorporation. Furthermore, other
than the metalloporphyrin with halogenide anions, the coordi-
nation of FeBr4− improved water-solubility and magnetic
response of the obtained products, confering weak ferromag-
netic behaviour at room temperature. Interestingly, samples of
the magnetic ionic metalloporphyrins showed a strong response
to a neodymium magnet, making them attactive candidates as
“reusable compounds” in different systems.
1
Results and discussion
In this paper, we use the notation ‘TMPyPC8 + (anion)4’ to
represent the ionic salts which are composed of a tetrakis(N-
octyl-4-pyridinium)–metal–porphyrin cation and Br− or FeBr4−
anions. M, (Fe, Co, Mn, Cu, or Zn), represents the central
metal ion of the cation and C8 represents the alkyl group
(CnH2n+1) attached to the N-position of the pyridinium. TMPyP
is used to represent the neutral metalloporphyrin of tetrakis-(4-
pyridyl)–metal–porphyrin. For example, [tetrakis(N-octyl-4-
pyridinium)-iron-porphyrin][tetrabromoferrate(III)]4 is indicated
as“TFePyPC8 (FeBr4)4”andtetrakis-(4-pyridyl)-zinc-porphyrin
as “TZnPyP”.
In our work, we aimed to develop a series of novel magnetic
ionic metalloporphyrin catalysts by incorporating the para-
magnetic anion tetrabromoferrate(III) (FeBr4−) into the water
soluble metalloporphyrins (Fig. 1), which can be recycled
Synthesis
The synthetic route used for the preparation of these novel
water-soluble, magnetic, ionic metalloporphyrins is shown
in Scheme 1. The free-base tetrakis-(4-pyridyl)-porphyrin,
H2TPyP, was synthesised, as described elsewhere,25–27 from the
propionic acid-catalysed condensation of freshly distilled pyr-
role with pyridine-4-carboxaldehyde. Then by adding excess
1-bromooctane to H2TPyP at refluxing temperature, tetrakis(N-
octyl-4-pyridinium)-porphyrin bromide, H2TPyPC8Br4, was
synthesised in nearly quantitative yield.28–29 The desired prod-
ucts, [tetrakis(N-octyl-4-pyridinium)–metal–porphyrin] [tetra-
bromo-ferrate(III)]4, [TMPyPC8(FeBr4)4], were obtained by
adding a slight molar excess of FeBr3 to TMPyPC8Br4, under
refluxing temperature for 48 h.30–32 A total of five water-solu-
ble, magnetic, ionic substituted tetrapyridyl metalloporphyrins
were prepared in yields above 75%.
Fig. 1 Structures of the magnetic ionic substituted tetrapyridyl
metalloporphyrins:[tetrakis(N-octyl-4-pyridinium)–metal–
porphyrin][tetrabromoferrate(III)]4 [TMPyPC8(FeBr4)4].
Thermal properties
Thermogravimetric analysis (TGA) curves for representative
samples of TMPyPC8(FeBr4)4 under a dinitrogen atmosphere
* Correspondent. E-mail: shaohw@cib.ac.cn

446 JOURNAL OF CHEMICAL RESEARCH 2013
Scheme 1 Synthesis of ionic-substituted tetrapyridylmetalloporphyrins: TMPyPC8(FeBr4)4.
are shown in Fig. 2. The determined decomposition tempera-
tures taken from the onset of weight loss are listed in Table 1.
In general, the magnetic metalloporphyrin derivatives showed
a progressive weight loss throughout the whole temperature
scan (up to 800 °C).
More specifically, the weight losses for TMPyPC8(FeBr4)4
were all observed above 250 °C, and the weight loss in
some circumstances was followed by a second or even third
decomposition during the thermal process. For example,
TMnPyPC8(FeBr4)4 decomposed first at 330 °C, showing a
weight loss of 35%, then a second decomposition occurred at
580 °C. The higher temperature of the second decomposition
can be attributed to the increased symmetry of the metallopor-
phyrins prepared. The above-mentioned decomposition mode
suggests that the weight loss began with the paramagnetic
anions FeBr4− and then turned to the metalloporphyrin cations
TMPyPC8+, which illustrates the ionic association in the FeBr4−
salts prepared. This special phenomenon can be rationalised
on the basis of the more significant nephelauxetic effect
together with the lower molar concentration in the FeBr4−
salts. Further experiments will be performed in our laborato-
ries to gain more precise information about the process of
decomposition.
Density
Density values of the magnetic metalloporphyrins were also
obtained. Due to the greater mass of metalloporphyrin cations,
the density values of the magnetic metalloporphyrin deriva-
tives, shown in Table 1, substantially exceed that of simple
FeBr4− salts such as [1-octyl-3-methylimidazolium][FeBr4−]
(d = 1.74 g cm−3).20–23 Decreased density values were observed
in the following order: TCuPyPC8(FeBr4)4>TZnPyPC8(FeBr4)4
> TFePyPC8(FeBr4)4 >TMnPyPC8(FeBr4)4 >TCoPyPC8(FeBr4)4.
Molar concentration, estimated from the density and for-
mula weight as a function of central metal ion, is presented
in Fig. 3 and Table 1. Apparently, density values show similar
Fig. 2 TGA curves for TMPyPC8(FeBr4)4 as a function of central
metal ion.
Table 1 TGA, density and molar concentration data for the
synthesised magnetic metalloporphyrin derivatives
Entry
Compounds
Td/°C a
d b g−1 cm−3 c c/mol cm−3
1
2
3
4
5
TFePyPC8(FeBr4)4
340 (580)
2.0339
7.74×10−4
6.90×10−4
7.15×10−4
8.40×10−4
8.00×10−4
TCoPyPC8(FeBr4)4 250 (330, 590) 1.8156
TMnPyPC8(FeBr4)4 330 (580)
TCuPyPC8(FeBr4)4 340 (565)
TZnPyPC8(FeBr4)4
1.8774
2.2134
2.1093
250
a Td/TGA = decomposition temperatures, b d = density/25 °C,
Fig. 3 Dependence of the molar concentration (○) with density
(●) for TMPyPC8(FeBr4)4.
c c = molar concentration.

JOURNAL OF CHEMICAL RESEARCH 2013 447
variation trends to those of the molar concentrations. Keeping
the anion constant (FeBr4−), the molar concentration values
of the magnetic metalloporphyrin-based cations are less than
those of the salts containing smaller cations. This can be
attributed to the larger van der Waals (vdW) volumes of
metalloporphyrin-based cations.
Electronic absorption spectra
The UV-Vis spectra data for the prepared porphyrin derivatives
are given in Table 2. The neutral porphyrin {TPyP} showed a
typical electronic spectrum of a meso-substituted porphyrin in
CHCl3 with a sharp Soret band at 416 nm and four Q-bands at
512, 546, 588 and 644 nm (entry 1, Table 2). Alkylation on
pyridinium of the neutral porphyrin {TPyP}, caused the Soret
band of this precursor to red-shift by 10 nm (entry 1 and 2,
Table 2).
Interestingly, once the central metal ions were embedded
into the ionic porphyrin ligands H2TPyPC8Br4, an evident
decrease of wavelength as well as intensity for the related Q
bands and shift-changes of the Soret band are found, owing to
the improved symmetry of the metalloporphyrin molecules.
Both properties can be regarded as diagnostic for the genera-
tion of corresponding metalloporphyrins TMPyPC8Br4 (entries
8–12, Table 2). Specifically, for the cobalt, manganese or zinc
based metalloporphyrins, the Soret bands were blue-shifted.
The above mentioned shift-change on Soret bands for metal-
loporphyrins TMPyPC8Br4 can be explained by coordination
chemistry theory, namely electron flow in the σ and π bonds
generated by the coordination of the central metal ions with
the porphyrin ring. In the σ bond, flow is from the porphyrin
ring to metal ions, leading to a decreased electron density on
the porphyrin ring, whereas for the π bond, electrons flow from
the metal ions to porphyrin ring, which leads to an increased
electron density on the porphyrin ring. Thus the decreased/
increased electron density on the porphyrin ring changes the
electron energy needed to transfer to a higher/lower energy
level, leading to the corresponding shift-change of the Soret
band. Being more specific, when σ bonds have greater influ-
ences on the electron density on the porphyrin ring, the Soret
band is blue-shifted, conversely red-shifted. This phenomenon
can also be found for the neutral metalloporphyrins TMPyP
(entries 3–7, Table 2). As for the final products TMPyPC8(FeBr4)4,
the generation of FeBr4− anions equally induces certain
shift-changes of the Soret band, albeit smaller (entries 13–17,
Table 2).
Fig. 4 UV-Vis spectra for representative samples: a=TPyPC8Br4,
b=TCoPyPC8Br4, c=TCoPyPC8(FeBr4)4.
Figure 4 presents UV-Vis spectra for representative samples
(entries 2, 9 and 14, Table 2). As shown in Fig. 4, the Soret
band of TCoPyPC8(FeBr4)4 is significantly broadened, and
additionallyitsextinctioncoeffcientsareremarkablydecreased,
relative to the precursor H2TPyPC8Br4 as well as TMPyPC8Br4.
Such variations also occur for the other four compounds
prepared. In summary, the typical UV-Vis spectra absorption
bands illustrate, to some extent, the structural validity of the
porphyrin derivatives synthesised.25–27
IR spectra
Dominant IR bands for the synthesised porphyrin derivatives
are listed in Table 3. It can be concluded that C–H bands for
pyrrolyl and pyridyl of the synthesised porphyrin derivatives
appeared mainly within the 3030–3114 cm−1 range, while the
frequencies of the stretching vibrations of C=C and C=N of
the porphyrin are, respectively, within the 1593–1653 cm−1 and
1342–1387 cm−1 ranges. Peaks appearing at –793 cm−1 are
assigned to the 1,4-disubstituents of pyridyl on the porphyrin
ring.
Raman spectroscopy
In order to study the compositions of TMnPyPC8(FeBr4)4 in
more detail, Raman spectroscopy was used to illustrate the
Table 2 UV-Vis absorption data for for the synthesised porphyrin derivatives
Entry
Compound
Solvents
λmax, nm (ε×10−3, M−1 cm−1)
Soret band
Q bands
1
2
TPyP
TPyPC8Br4
CHCl3
CH3CN
416
424
413
434
476
414
422
414
456
475
417
440
422
445
480
419
429
512
546
551
640
653
610
656
602
588
644
645
517
505
548
578
538
558
569
578
581
542
564
571
558
581
542
563
590
3
TFePyP
CHCl3/CH3COOH
CHCl3/CH3COOH
CHCl3/CH3COOH
CHCl3/CH3COOH
CHCl3/CH3COOH
CH3CN
4
TCoPyP
5
TMnPyP
6
TCuPyP
7
TZnPyP
8
TFePyPC8Br4
TCoPyPC8Br4
TMnPyPC8Br4
TCuPyPC8Br4
TZnPyPC8Br4
TFePyPC8(FeBr4)4
TCoPyPC8(FeBr4)4
TMnPyPC8(FeBr4)4
TCuPyPC8(FeBr4)4
TZnPyPC8(FeBr4)4
9
CH3CN
625
680
658
10
11
12
13
14
15
16
17
CH3CN
CH3CN
575
607
CH3CN
CH3CN
CH3CN
693
679
CH3CN
CH3CN
CH3CN

448 JOURNAL OF CHEMICAL RESEARCH 2013
Table 3 Dominant infrared bands for the synthesised porphyrin derivatives
vN–Ha
vC=C–Hb
vCn–H2n+1
vC=Cd
vC=Nd
vN–H/Me
vP–Pyf
c
Entry
Compounds
1
2
TPyP
TPyPC8Br4
3325 (m)
3091 (w)
3030 (w)
3114 (w)
3114 (w)
3114 (w)
3114 (w)
3114 (w)
3054 (w)
3110 (w)
3109 (w)
3035 (w)
3082 (w)
3078 (w)
3113 (w)
3114 (w)
3059 (w)
3110 (w)
—
1593 (s)
1636 (s)
1652 (s)
1653 (s)
1647 (s)
1630 (s)
1608 (s)
1634 (s)
1653 (s)
1636 (s)
1610 (s)
1611 (s)
1632 (s)
1652 (s)
1635 (s)
1631 (s)
1630 (s)
1351 (s)
1352 (s)
1351 (s)
1351 (s)
1343 (s)
1348 (s)
1342 (s)
1358 (s)
1382 (s)
1387 (s)
1347 (s)
1342 (s)
1360 (s)
1360 (s)
1374 (s)
1359 (s)
1367 (s)
971 (s)
970 (s)
—
3330 (m)
—
2924, 2854 (m)
—
799(s)
—
3
TFePyP
993 (s)
4
TCoPyP
—
—
997 (s)
—
5
TMnPyP
—
—
1006 (s)
1001 (s)
996 (s)
—
6
TCuPyP
—
—
—
7
TZnPyP
—
—
—
8
TFePyPC8Br4
TCoPyPC8Br4
TMnPyPC8Br4
TCuPyPC8Br4
TZnPyPC8Br4
TFePyPC8(FeBr4)4
TCoPyPC8(FeBr4)4
TMnPyPC8(FeBr4)4
TCuPyPC8(FeBr4)4
TZnPyPC8(FeBr4)4
—
2924, 2853 (m)
2926, 2854 (m)
2924, 2853 (m)
2923, 2852 (m)
2926, 2855 (m)
2925, 2854 (m)
2926, 2854 (m)
2925, 2854 (m)
2924, 2854 (m)
2925, 2853 (m)
1000 (s)
1001 (s)
1011 (s)
1000 (s)
995 (s)
1001 (s)
1006 (s)
1012 (s)
1000 (s)
996 (s)
799 (s)
798 (s)
802 (s)
800 (s)
793 (s)
797 (s)
796 (s)
797 (s)
794 (s)
793 (s)
9
—
10
11
12
13
14
15
16
17
—
—
—
—
—
—
—
—
aN–H stretching vibration of pyrrolyl. bC–H stretching vibration of pyrrolyl and pyridyl. cC–H stretching vibration of alkyl chain. dC=C
and C=N stretching vibration of porphyrin. eStretching vibration of central metal ions with N on pyrrolyl. fC–H stretching vibration
of 1,4-disubstituted pyridyl derivatives.
Fig.
5
Raman spectra for representative samples: a =
TFePyPC8Br4, b = TFePyPC8(FeBr4)4, c = TCoPyPC8(FeBr4)4, d =
TMnPyPC8(FeBr4)4, e = TCuPyPC8(FeBr4)4, f = TZnPyPC8(FeBr4)4.
formation of the paramagnetic FeBr4− anions. Raman spectra
of TMnPyPC8(FeBr4)4 (M=Fe, Co, Mn, Cu and Zn), shown in
Fig. 5, all exhibit an intense band at –203 cm−1, corresponding
well with literature values for the anion FeBr4− as a solid or in
solution.33 Moreover, weak broad bands at 306 cm−1, the fea-
ture of symmetry vibrations of Fe2Br7−, were not observed,
reinforcing the specifity of FeBr4−. Additionally, the observed
Raman spectra of TMPyPC8(FeBr4)4 have a similar pattern to
those of TFePyPC8Br4, indicating the dominant existence of
the cation TMPyPC8+.
Magnetic susceptibility
Fig.
6
SQUID magnetisation of representative samples:
Magnetic properties of TMPyPC8(FeBr4)4 were examined
using the SQUID method. Small samples, (typically 10–30 mg),
were placed in gelatine capsules and the magnetic moments
were determined in a magnetic field range between –50,000
and 50,000 Oe. Figure 6 shows the obtained results of com-
pounds synthesised including TMPyPC8(FeBr4)4 (Fig. 6a) and
TMPyPC8Br4 (Fig. 6b) at 300 K.
It can be observed that TMPyPC8(FeBr4)4 show non-linear
responses to magnetic field, which is typical for ferromagnetic
materials (Fig. 6a). An increased magnetic response was
TMPyPC8 (FeBr4)4 (a) and TMPyPC8Br4 (b). Inset shows an
expansion at temperature of 300 K in the range of –3000 to
3000 Oe.
shown in the order: TCuPyPC8(FeBr4)4≤TZnPyPC8(FeBr4)4<
TMnPyPC8(FeBr4)4<TCoPyPC8(FeBr4)4<TFePyPC8(FeBr4)4,
as a function of the various central metal ions. The correspond-
ing bromides, TMPyPC8Br , are in most cases paramagnetic
materials, showing linear responses to magnetic field (Fig. 6b).
4

JOURNAL OF CHEMICAL RESEARCH 2013 449
Tetrakis(N-octyl-4-pyridinium)porphyrin bromide [H2TPyPC8Br4]
(2): In an N2 atmosphere, C8H17Br (3.86 g, 20 mmol) was added to
a solution of 1 (1.5 g, 2.5 mmol) in DMF (100 mL) at 150 °C. After
refluxing for 3 h, the reaction mixture was cooled to room temperature
and recrystallised with diethyl ether, yielding red–brown solid
H2TPyPC8Br4, 2, yield 82%. 1H NMR (CDCl3): δ = 9.6 (d, 8H, pyri-
dinium, CHN+CH), 9.2 (d, 8H, pyrrolyl, β-H), 9.0 (d, 8H, pyridinium,
CHCCH), 4.9 (t, 8H, N+CH2), 2.2 (q, 8H, N+CH2CH2), 1.6 (q, 8H,
N+CH2CH2CH2), 1.5 (q, 8H, N+CH2CH2CH2CH2), 1.4 (m, 8H,
N+CH2CH2CH2CH2CH2), 1.376–1.365 (m, 8H, N+CH2CH2CH2CH2C
H2CH2CH2), 0.9 (t, 12H, N+CH2CH2CH2CH2– CH2CH2CH2CH2), –3.1
(s, 2H, 2NH) ppm. Anal. Calcd for C72H94N8Br4: C, 62.16; H, 6.76 N,
8.06. Found: C, 63.44, H, 6.52, N, 7.75%. ESI C72H94N8Br4 (m/z+/−):
Cation 1070.04.
Tetrakis-(N-octyl-4-pyridinium)-iron-(porphyrin) bromide [TFePy
PC8Br4] (3): In an N2 atmosphere, a mixture of 2 (0.26 g, 0.19 mmol)
and FeCl2.4H2O (0.38 g, 1.9 mmol) in DMF (25 mL) was heated at
100 °C for 8 h. After removal of the solvent in vacuo, the residues
were recrystallised with methanol/diethyl ether and dark-yellow solid
TFePyPC8Br4, 3 was obtained, yield 92%. Due to the influence of the
Fe quadrupolar nucleus and the paramagnetism of 3, the signals in the
1H NMR of 3 were broadened to flatness. ESI C72H92N8FeBr4 (m/z+/−):
Cation 1125.28.
Special attention should be given to TFePyPC8Br4 and
TCuPyPC8Br4, which present performance of ferromagnetism
and diamagnetism respectively. Magnetic susceptibility, an
indicator of paramagnetic strength for magnetic materials
calculated from gradients of magnetic field dependence, is
used to explain their magnetic performance, giving magnetic
susceptibility values TMnPyPC8Br4, 32.3×106 emu g−1;
TCoPyPC8Br4, 12.8×106 emu g−1; TCuPyPC8Br4, 2.3×106 emu
g−1; ZnTPyPC8Br4, –0.8×106 emu g−1. The above greater mag-
netism diversity between TMPyPC8(FeBr4)4 and TMPyPC8Br4,
from ferromagnetism to paramagnetism, suggests the obvious
influence of the paramagnetic anions FeBr4− on the magnetic
performance.
Figure 7 show the strong magnetic response of compounds
TMPyPC8(FeBr4)4 to a neodymium magnet [TFePyPC8(FeBr4)4
is an example]. According to this special magnetism feature,
we may forecast that TMPyPC8(FeBr4)4 are potentially inter-
esting candidates for reusable catalysts or material precursors
in separation chemistry with the aid of an outside magnetic
field.
Tetrakis-(N-octyl-4-pyridinium)-cobalt-(porphyrin) bromide TCoPy
PC8Br4 (4): TCoPyPC8Br4 was synthesised according to the above
procedure from 2 and CoCl2.6H2O (0.45 g, 1.9 mmol) as a dark-green
solid in 88% yield. Due to the influence of the Co quadrupolar
nucleus and the paramagnetism of 4, the signals in its 1H NMR were
broadened to flatness. ESI C72H92N8CoBr4 (m/z+/−): Cation 1127.00.
Tetrakis-(N-octyl-4-pyridinium)-manganese-(porphyrin) bromide
[TMnPyPC8Br4] (5) : TMnPyPC8Br4 was synthesised according to the
above procedure from 2 and MnCl2 (0.24 g, 1.9 mmol) as a dark-green
in 87% yield. Due to the influence of the Mn quadrupolar nucleus and
the paramagnetism of 5, its signals in the 1H NMR were broadened to
flatness. ESI C72H92N8MnBr4 (m/z+/−): Cation 1123.00.
Experimental
Measurement and analysis
The elemental analyses were performed using a Vario EL cube micro-
analyser. Electron spray mass spectrometry was recorded on a Bruker
300 spectrophotometer in acetonitrile/water mixture (1:1 by volume).
1H NMR (600.17 MHz) spectra were recorded on a JEOL ECA-600
spectrometer and chemical shift values were referenced to SiMe4.
UV-Vis spectroscopy was recorded on a Shimadzu UV-2550 spectro-
photometer. FT-IR spectra were recorded as KBr pellets on a Nicolet
FTIR-380 spectrophotometer. Raman measurements were carried out
on a Horiba Jobin Yvon inVia Raman spectrometer at a wavelength
of 514 nm. Thermogravimetric analyses (TGA) were performed on
5–10 mg samples in platinum pans, using a TGA Q5000 thermogravi-
metric analyser under a dinitrogen atmosphere at 10 °C min−1 heating
rate. Density values were determined using an AccuPyc 1340 densim-
eter. Magnetic measurements were conducted on a SQUID Quantum
Design PPMS-9 magnetometer at 300 K and samples were loaded
into a gelatine capsule (Quantum Design). Organic solvents were
purchased as reagent grade and used as received.
Tetrakis-(N-octyl-4-pyridinium)-copper-(porphyrin) bromide [TCuPy
PC8Br4] (6): {TCuPyPC8Br4} was synthesised according to the above
procedure from 2 and Cu(CH3COO)2.H2O (0.38 g, 1.9 mmol) as a
1
dark-red solid in 92% yield. The signals in the H NMR of 6 were
broadened to flatness. ESI C72H92N8CuBr4 (m/z+/−): Cation 1133.00.
Tetrakis-(N-octyl-4-pyridinium)-zinc-(porphyrin) bromide [TZn
PyPC8Br4] (7): TZnPyPC8Br4 was synthesised according to the above
procedure from 2 and Zn(CH3COO)2.2H2O (0.42 g, 1.9 mmol) as a
dark-brown solid in 90% yield. The signals in the 1H NMR of 7 were
broadened to flatness. ESI C72H92N8ZnBr4 (m/z+/−): Cation 1133.00.
Tetrakis-(N-octyl-4-pyridinium)-iron-(porphyrin) tetrabromofer-
rate(III) [TFePyPC8(FeBr)4] (8): In an N2 atmosphere, a mixture of 3
(0.10 g, 0.07 mmol) and FeBr3 (0.09 g, 0.315 mmol) in acetonitrile
(20 mL) was heated at 85 °C for 48 h. After removal of the solvent
in vacuo, the residues were recrystallised with diethyl ether several
times until the solvent was colourless. Dark-brown, solid 8 was
obtained in 80% yield. ESI C72H92N8Fe5Br16 (m/z+/−): Cation 1125.28,
Anion 375.61.
Synthesis of [tetrakis(N-octyl-4-pyridinium)–metal–porphyrin]
[tetrabromoferrate(III)]4 [TMPyPC8(FeBr4)4]
Tetrakis-(4-pyridyl)-porphyrin] (H2TPyP) (1): In an N2 atmosphere,
propionic acid (120 mL) was added into a 250 mL three-neck round-
bottom flask equipped with stirrer, reflux exchanger and dropping
funnel. The solvent was stirred at refluxing temperature (150 °C) for
30 min. Subsequently, pyridine-4-carboxaldehyde (6.43 g, 60 mmol)
and freshly distilled pyrrole (4.07 g, 60 mmol), dissolved in 10 mL
propionic acid, were simultaneously added into the flask dropwise
over 15 min. After refluxing for another 1 h, the reaction mixture was
cooled to room temperature and then the propionic acid in the reaction
mixture was evaporated absolutely. The resultant black crude products
were poured into DMF (30 mL) and allowed to stand overnight. The
resultant purple precipitates were separated by centrifugation and
washed with DMF. The terminal product tetrakis-(4-pyridyl)-porphy-
rin [H2TPyP], 1, was purified by Al2O3 column chromatography
(CHCl3 and CH3OH as the eluents) and dried under vacuum (70 °C,
Tetrakis-(N-octyl-4-pyridinium)-cobalt-(porphyrin) tetrabromofer-
rate(III) [TCoPyPC8(FeBr4)4] (9): TCoPyPC8(FeBr4)4 was synthesised
according to the above procedure from 4 (0.10 g, 0.07 mmol) and
FeBr3 (0.09 g, 0.315 mmol). The dark-brown solid 9 was obtained in
80% yield. ESI C72H92N8CoFe4Br16 (m/z+/−): Cation 1127.00, Anion
375.61.
Tetrakis-(N-octyl-4-pyridinium)-manganese-(porphyrin) tetrabro-
moferrate(III) [TMnPyPC8(FeBr4)4] (10): TMnPyPC8(FeBr4)4 was
synthesised according to the above procedure from, 5 (0.10 g,
0.07 mmol) and FeBr3 (0.09 g, 0.315 mmol). Dark-brown solid 10
was obtained in 80% yield. ESI C72H92N8MnFe4Br16 (m/z+/−): Cation
1123.00, Anion 375.61.
1
12 h) with a yield of 21%. H NMR (CDCl3): δ 9.1 (d, 8H, pyridyl,
CHNCH), 8.9 (s, 8H, pyrrolyl, β-H), 8.2 (d, 8H, pyridyl, CHCCH),
–2.9 (s, 2H, 2NH) ppm. Anal. Calcd for C40H26N8: C, 77.67; H, 4.21;
N, 18.12. Found: C, 76.90; H, 4.29; N, 1 8.85%.
Fig. 7 Response of a block of FeTPyPC8(FeBr4)4 to a neodymium magnet.

450 JOURNAL OF CHEMICAL RESEARCH 2013
Tetrakis-(N-octyl-4-pyridinium)-copper-(porphyrin)tetrabromofer-
rate(III) [TCuPyPC8(FeBr4)4] (11): TCuPyPC8(FeBr4)4 was synthe-
sised according to the above procedure from 6 (0.10 g, 0.07 mmol)
and FeBr3 (0.09 g, 0.315 mmol). Dark-purple solid 11 was obtained in
80%yield. ESI C72H92N8CuFe4Br16 (m/z+/−): Cation 1133.00, Anion
375.61.
Received 21 March 2013; accepted 25 May 2013
Paper 1301852 doi: 10.3184/174751913X13727033282329
Published online: 9 August 2013
References
Tetrakis-(N-octyl-4-pyridinium)-zinc-(porphyrin) tetrabromofer-
rate(III) [TZnPyPC8(FeBr4)4] (12). TZnPyPC8(FeBr4)4 was synthe-
sised according to the above procedure from 7 (0.10 g, 0.07 mmol)
and FeBr3 (0.09 g, 0.315 mmol). Dark-purple, solid 12, yield 75%.
ESI C72H92N8ZnFe4Br16 (m/z+/−): Cation 1133.00, Anion 375.61.
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obtained in yield 85%.
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series of novel magnetic, ionic metalloporphyrins,
[TMPyPC8(FeBr4)4], (M = iron, cobalt, manganese, copper
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the generation of metalloporphyrins cations, while Raman
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paramagnetic anions FeBr4−. The FeBr4− paramagnetic anions
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(FeBr4)4<TFePyPC8(FeBr4)4. Interestingly, samples of the
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The work was supported by the National Natural Science
Foundation of China (grant No. 21206171 and 21276006), the
Special Funds of the National Natural Science Foundation of
China (grant No. 21127011) and the Petrochmical Joint Funds
of NSFCACNPC (grant No. U1162106).
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