Octahedral iron(ii) phthalocyanine complexes: Multinuclear NMR and relevance as NO2 chemical sensors

Article abstract of DOI:10.1039/b924429h

The synthesis of new phthalocyanine iron(ii) (FePc) based coordination complexes 2-7, their structural characterization by multinuclear NMR ( ¹H, ¹³C, ¹⁵N, ³¹P, ⁵⁷Fe), and their use as improved sensit

Full text of DOI:10.1039/b924429h

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Octahedral iron(II) phthalocyanine complexes: multinuclear NMR and
relevance as NO2 chemical sensors†
Pascual On˜a-Burgos,a Mar´ıa Casimiro,a Ignacio Ferna´ndez,*a Angel Valero Navarro,b
Jorge F. Ferna´ndez Sa´nchez,*b Antonio Segura Carreterob and Alberto Ferna´ndez Gutie´rrezb
Received 20th November 2009, Accepted 5th May 2010
First published as an Advance Article on the web 3rd June 2010
DOI: 10.1039/b924429h
The synthesis of new phthalocyanine iron(II) (FePc) based coordination complexes 2–7, their structural
characterization by multinuclear NMR (1H, 13C, 15N, 31P, 57Fe), and their use as improved sensitive
and cheap optical NO2 sensors is described. d(15N) and d(57Fe) values obtained via HMQC NMR
methods show an interesting trend, the larger the chemical shift value the more the selectivity
towards NO2. Among all the sensing films prepared, the novel mixed ligand phosphite-amine
[FePc(benzylamine)(P(OEt)3] (7) immobilized into AP200/19 showed the best sensitivity, reversibility
(LOD and LOQ of 1.2 ppb and 4.0 ppb, respectively), and thermostability in the range of 4 to 25 ◦C.
as optical chemically interacting materials for the detection of a
Introduction
variety of molecules.7 The use of iron as a low cost and reduced
Chemical sensors are devices that transform chemical information
environmental impact transition metal makes exploring their use
into an analytically useful signal. This information may originate
in sensing layers a worthwhile pursuit.
from a chemical reaction or from a physical property of the
Representative varieties of optical devices and sensors have
system. The development of instrumentation, microelectronics
been developed to date, i.e. azo compounds immobilized at the
nanopores of a sol–gel structure,8 porous glass doped with sulfanil-
amides and naphthylamines,9 blue-green sol–gel acid–base indica-
tors embedded in a hydro-gel matrix,10 poly(3-octylthiophene-2,5-
diyl) systems,11 ZnO nanowires,12 or phenylenediamines immobi-
lized in polydimethylsiloxanepolycarbonate block copolymers.13
Some of us have already reported AlOOH nanostructured films
doped with phthalocyaninato-iron(II) complexes, and tested their
sensor abilities against CO and NOx.14
In this paper we present the synthesis of some new iron(II) Pc-
based coordination complexes, their structural characterization by
multinuclear NMR (1H, 13C, 15N, 31P, 57Fe), and their use as reac-
tive, sensitive and cheap optical sensors for NO2 determinations.
and computers makes possible the design of sensors using most
of the known chemical and/or physical principles. Nitrogen
dioxide (NO2) is an extremely toxic gas generated primarily from
the liberation of nitrogen contained in fuel as a byproduct of
combustion processes.1 NO2 is also a source of acid rain, damaging
buildings and polluting water sources.2 Thus, monitoring NO2
plays an important role making the environment safer and cleaner.
The implementation of optical sensors has received growing
interest since they offer potential advantages over other analytical
methods,3 i.e. sensors are easily miniaturized, they can be prepared
as disposable low-cost sensors and, when coupled to optical fibers,
pose potential non-invasive monitoring capabilities which are less
sensitive to electromagnetic interference.4
Phthalocyanines (Pc’s) and their analogues have been investi-
gated for many years, especially with regard to their properties
as dyestuffs, paints and colors.5 Together with porphyrins, both
represent a large family of functional molecular materials with
high chemical and thermal stability. The Pc molecule has a two
dimensional p-electron conjugated system (18 electrons) that can
incorporate about 70 different metals.6 Metallo-phthalocyanines
and metallo-porphyrins are attractive systems for the optical
detection of volatiles because of their open coordination sites for
axial ligation5b and intense coloration. Organic thin films based
on metals different than iron have been developed and described
Results and discussion
Synthesis of FePc complexes
Inspired by the work of Watkins and Balch in the 70’s,15 where a
number of bis adducts and mixed-ligand ferrous phthalocyanine
were isolated, we decided to extend the variety of these two families
of compounds and apply their attractive coordination properties
of the iron metal on the field of sensors. As shown in Scheme 1,
reaction of two equivalents of amine (decylamine, bencylamine,
para-methoxybencylamine, or trimethylsilylmethylenamine) with
FePc (1), in THF solution, affords complete conversion to the bis-
amine iron complexes, 2–5, respectively. Complexes 2 and 3 had
been previously characterized by us14 and they will be considered
as model compounds.
The NMR spectra of compounds 2–5 indicate that they are all
diamagnetic. Supporting the proposed composition is the elemen-
tal analysis of freshly prepared samples, which were thoroughly
consistent for all of them. These iron complexes investigated
may be ascribed into derivatives of six-coordinate bis-amine
a
´
Area de Qu´ımica Orga´nica, Universidad de Almer´ıa, Carretera de Sacra-
mento s/n, 04120, Almer´ıa, Spain. E-mail: ifernan@ual.es; Fax: +34 950
015481; Tel: +34 950 015648
bDepartment of Analytical Chemistry, University of Granada, Avenida
Fuentenueva s/n, 18071, Granada, Spain. E-mail: jffernan@ugr.es
† Electronic supplementary information (ESI) available: 1D and 2D
NMR spectra, absorption spectra, spectrophotometry calibration curve,
and stability graphs as a function of time and temperature. See DOI:
10.1039/b924429h
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Table 1 Nitrogen-15, phosphorus-31 chemical shifts (in ppm) and cou-
pling constants (in Hz) for FePc complexes 2–7a
d (15N)
d (31P)
J (15N,1H)
J (57Fe,31P)
J (31P,15N)
2
3
4
5
6
7
-34.8
-30.5
-27.6
-50.9
-1.34
+3.45
—
—
—
—
+131.8
+131.6
66.4
68.0
66.4
68.4
64.0
67.6
—
—
—
—
79.2
79.8
—
—
—
—
65.8
62.2
Scheme 1 Synthesis of bis-amine PcFe(II) complexes 2–5.
a In THF-d8 with nitrogen relative to NH3 and phosphorus relative to 85%
H3PO4.
phthalocyanine complexes with the two new nitrogen donors
occupying trans-axial positions. On the other hand, treatment of
60 mM samples of 2 or 3 with one equivalent of triethylphosphite
in THF solution at room temperature allowed, without the need
of any heat, the quantitative formation of mixed-ligand complexes
6 and 7 (Scheme 2).
Scheme 2 Synthesis of mixed ligand amine-phosphite PcFe(II) complexes
6 and 7.
Fig. 1 Section of the 1H,15N gHMQC NMR spectra (500.13 MHz,
ambient temperature in THF-d8 solution) of bis-amine complexes 2–5
Products 6 and 7 were obtained in analytical pure form (correct
elemental analysis) in good isolated yield after recrystallization
and solvent evaporation in two consecutive times. It is worth
mentioning the change in color experienced from green to bright
blue immediately after addition of the phosphite. When one or
more equivalents of triethylphosphite are added to a THF solution
of bis-amine FePc, only the replacement of one equivalent of amine
is produced, proving the high stability of the resulting mixed-
ligand complex. At 500 MHz the various signals of the aliphatic
H-atoms in complexes 2–7 are well dispersed (see ESI†).16 In all
cases it has been possible to verify the adduct stoichiometry by
comparing the integrated intensities of the adduct protons with
the intensities of the proton resonances due to the phthalocyanine
moiety.
The low frequency signals arise as a consequence of the
local anisotropic effects associated with the phthalocyaninato
structure.16,17 The specific assignment of the NH2 resonances
follows from two independent NMR experiments. In the first of
these, the 1H,13C gHMQC spectra showed no cross-peak between
the lowest frequency resonance (dH = -4 to -7 ppm) with any
carbon signal. And further, the 1H,15N gHMQC spectra, shown in
Fig. 1, correlate these low frequency NH2 signals to their respective
nitrogen-15 resonances with clear one bond couplings between
both nuclei. 15N chemical shifts and coupling constants observed
for the whole set of complexes are presented in Table 1.
and mixed amine-phosphite complexes 6–7. (2: dN = -34.8 ppm; 3: dN
=
-30.5 ppm; 4: dN = -27.6 ppm; 5: dN = -50.9 ppm; 6: dN = -1.34 ppm,
2J(31P,15N) = 65.8 Hz; 7: dN = 3.45 ppm, 2J(31P,15N) = 62.2 Hz).
observations of similar trends in dN of metal complexes and
parallels the effects induced by alkylation or protonation of
a nitrogen lone pair.19,20 As a matter of fact, the coordination
of aniline to transition metals such as ruthenium, platinum
or tungsten result in coordination chemical shifts of -62.1,
-23.5 and -19.5 ppm for [TpRu(PMe3)2(NH2Ph)][OTf] (Tp =
hydridotris(pyrazolyl)borate), [(NCN)Pt-(Me)2][BAr4] (NCN =
≡
2,6-pyrazolyl-(CH2)2C6H3), and [Tp*W(CO)(h2-Ph CMe)-
(NH2Ph)][BAr4] (Tp*
=
hydridotris(3,5-dimethylpyrazolyl)-
borate), respectively.21 The origin of these phenomena is generally
attributed to changes in the paramagnetic shielding term, where
the relatively small negative nitrogen coordination chemical shift
found (d Ncomplex < d Nligand) are attributable to the stabilization
on coordination of both frontier orbitals for the resonant atom,
so that the effective DE (see below) is not greatly changed.18b-18c,19,20
The significant down field nitrogen shift experienced by com-
plexes 6–7 compared to 2–5 is associated with the ligand-field-
strength parameter of the trans phosphite which is a better p-
acceptor. This effect has been previously shown in cyclopalladated
15
15
=
nitrosoamine complexes [(Pd(m-OAc)(O NN-(CH3)C6H4)]2 and
[PdCl{O NN-(CH3)C6H4}{P(OMe)3}], where the incorporation
=
The coordination shifts were all negative (higher shielding of
15N), and showed up in the expected region.18,19 The increase
in nitrogen shielding on metal complexation matches earlier
of the phosphite moiety produces a higher frequency shift of
23.5 ppm.22 The one-bond coupling constants 1J(15N,1H) detected
6232 | Dalton Trans., 2010, 39, 6231–6238
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on each 2D map (Table 1) appear to be smaller than might
be expected for a simple sp3 hybridized nitrogen atom which is
commonly used as diagnostic tool for complexation.18c,20,21 More
attractive, is the way of proving the formation of mixed amine-
interesting challenge to research groups fascinated on structural
features.25 In most of the cases 57Fe measurements require isotopic
enrichment of the metal, hours of NMR time, and large volumes
(10–20 mm diameter NMR tubes). Naturally, indirect detection
has become an attractive alternative method due the higher
sensitivity gain. At natural abundances of 57Fe, indirect detection
2
phophite complexes through the observation of J(31P,15N), with
values of 65.8 and 62.2 Hz for 6 and 7, respectively (Fig. 1).
These values are in accord with previous phosphorus–nitrogen
metal through (M = Pt, Rh, Au, Mo, W) values described in the
literature.23
1
via H or 31P appears to be now the most attractive alternative,
which, however, requires a sizable scalar coupling between the two
nuclei.26,27 Another alternative exploited in the last few years by
Wrackmeyer et al. is based on polarization transfer (PT) tech-
niques such as INEPT which leads to signal/noise improvements
with respect to single pulse detection.28
With respect to the chemical shift, known to date the range spans
ca. 12 000 ppm,25 what makes iron NMR an extremely powerful
and direct probe of the asymmetry of the electron distribution
around the metal. From the data currently available, the 57Fe
chemical shift range, in the case of heme axial ligand combining
phosphines and amines, from 7652 to 9275 ppm.29 As far as we are
aware there are no phthalocyanine iron chemical shifts reported
in the literature, so the ones reported herein represent the first
example of their class.
Complex 5 showed the lowest nitrogen chemical shift of the
whole set, which is related to the fact that NH2CH2TMS is
the most electron-withdrawing amine employed herein. In sharp
contrast, the para-methoxybenzylamine FePc complex 4 showed
the highest frequency chemical shift of all the bis-amine molecules
2–5. Chemical shift studies of aliphatic amines24 have already
revealed that substituent effects are rather large for a- and b-
substituents whereas the increments for g-, d- and e-groups are of
minor importance.18,19,24
1
For the silicon-containing complex 5, we performed a H,29Si
gHMQC (Fig. 2) which revealed a 29Si resonance for the Me3Si
group at dSi -2.54 ppm, that falls in the region found for tetralkyl
derivatives, but is slightly shifted to lower frequencies compared
to TMS.
In terms of structural information of FePc, apart from optical
absorption and Mossbauer data,30 spectroscopic data reported
with respect to the coordination chemistry is scarce.15,31 Only a
1
few old reports shed light on H NMR17 and none of them are
concerned about multinuclear NMR methodologies.
Our iron-57 chemical shift determination approach was based
on HMQC inverse shift correlation between the active iron isotope
1
and the phosphorus with additional H decoupling during the
whole experiment (Fig. 3).26,27
A direct triple probe head was employed using spectral ref-
erences of 85% H3PO4 and Fe(CO)5 for 31P and 57Fe, respectively.
Fig. 3 shows 31P,57Fe correlation spectra acquired in less than 3 h for
6 and 7. These 2D maps gave d(57Fe) of +6764 and +6794 ppm for 6
and 7, respectively. As usual, a second experiment changing the Fe
carrier frequency was performed confirming the same chemical
shift and therefore proving to be not folded. The detected 31P
chemical shifts of d 131.8 and 131.6 ppm fit perfectly with those
observed in the corresponding 1D NMR spectra.
The iron-57 chemical shift difference of Dd = 30 ppm between
6 and 7, suggest only minor variation in the bonding interactions.
From these data one can assume decylamine to be a more electron
donating ligand since the higher s donor at the pthalocyanine
Fig. 2 Section of the 1H,29Si gHMQC NMR spectra (500.13 MHz,
ambient temperature in THF-d8 solution) of bis(trimethyl-
silylmethyleneamine)FePc complex 5, showing three cross-peaks
between silicon and NH2, CH2, and Me3Si groups.
2
the larger the repulsion of the dz orbital, which gives rise to an
increase in DE and a decrease in the chemical shift, as arises
from the Ramsey formula.25,32 This s donor strength trend has
been previously observed in model heme complexes, such as
tetraphenylporphyrin (TPP), tetramesitylporphyrin (TMP) and
octaethylporphyrin (OEP) derivatives.29,33
Considering now the mixed-ligand complexes 6 and 7, 1H
chemical shifts for coordinated triethylphosphite are also shielded
by the ring current and appear at dH -0.18 (CH2) and +1.29
(CH3) ppm which compared to the free phosphite corresponds
to delta differences (DdH) of -2.59 and -1.53, respectively.
The 31P NMR spectra for 6 and 7 showed singlets located
at d 131.8 and 131.6 ppm, respectively with relatively small
coordination chemical shifts (compared to free phosphite) of DdP
-7.0 and -7.2 ppm, respectively.
The 57Fe-31P coupling constants, rapidly deduced from the
F2 dimension (Fig. 3), are of ca. 80 Hz (Table 1) which are
considerably larger than those found for iron coupled to nitrogen
or carbon and much larger than for iron coupled to phos-
phorus in porphyrin derivatives.34 In smaller molecules such as
4
4
Cp(dppe)FeH, (h -butadiene)2FePMe3, or (h -butadiene)2FePEt3,
1J(57Fe,31P) magnitudes are of ca. 60 Hz.26a
Fe-57 NMR
Crystals of complexes 2 and 4 obtained by slow evapora-
tion of THF solutions at room temperature clearly proved the
structure ascertained by NMR methods consisting of an iron
NMR studies of the 57Fe nucleus (I = 1/2, 2.2% natural
abundance), 7.4 ¥ 10-7 times as sensitive as the proton, present an
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Table 2 Sensing film results when membranes doped with 2–7 are exposed
to NO2, and their correlation with d(15N) and d(57Fe) values
Complex
l
max/nm
(A0 - Ax)/A0 (%)a
d (15N)b
d (57Fe)b
5
2
3
4
6
7
656
659
662
658
656
657
7.2
9.4
10.0
13.1
13.9
14.0
-50.9
-34.8
-30.5
-27.6
-1.34
+3.45
—
—
—
—
+6764
+6794
a The sensing films were exposed to 1 ppm of NO2 for 300 s at 50% RH at
a flow-rate of 200 mL min-1. b All in THF-d8 with nitrogen relative to NH3
and iron relative to Fe(CO)5.
6–7, respectively. Optical spectra of the films once incorporated
were recorded and provide clear evidence that the iron phthalocya-
nine complexes still intact after coated into the solid support (see
ESI†). Table 2 lists the experimental results for the NO2 sensing
films and the corresponding d(15N) and d(57Fe) values for each
complex.
Previous studies39 had demonstrated that the best sensor
response is obtained with a 1 : 30 (1 : NR3) molar ratio, since the
equilibrium system is influenced not only by the strength of the
bond between the amine and the metal center, but also by the con-
centration of the N-donor ligand, which needs not necessarily to
be equimolecular proportional compared to 1.39 Different molar
ratios were even though monitored and erosion on the sensor
response was in all cases experienced.
The films are characterized by measuring the relative change
in absorbance (A0 - Ax)/A0 at lmax, where Ax is the absorbance
upon exposure to 1 ppm NO2 for 300 s at 50% of relative humidity
(RH) at a flow rate of 200 mL min-1, and A0 is the absorbance of
the film in contact with synthetic air (50% RH and flow rate of
200 mL min-1). 300 s of NO2 was used as exposure time to be able
to compare the analytical features of the proposed sensing layers
with the previously published in the literature.13,14
Experimental results show that the behavior of the sensing films
containing complexes 2–7 can be predicted by just correlating
the nitrogen chemical shift versus (A0 - Ax)/A0 (Table 2). The
larger chemical shift value is in accord with the higher selectivity
towards NO2. It is known that in metallo-phthalocyanines there is
p back-donation from the metal d orbitals to the macrocycle ligand
p* orbitals.5,40 The p–p* transition, and therefore the Q-band, is
strongly influenced. The introduction of axial ligands modifies
the p back-donation on the macrocycle, and therefore the p–p*
transition. Together with these features, if one of the axial ligands is
s-donor and p–acceptor as P(OEt)3, there will be metal-to-ligand
charge transfer (MLCT) transitions reinforcing the strength of the
bond in much extent than when pure s-donors operate. Therefore,
in mixed-ligand complexes such as [FePc(NH2R)(P(OEt)3)] 6–7,
an increase of the Fe–P bond strength makes weaker the Fe–N
bond and consequently allowed the nitrogenated ligand to be more
easily removed by the NO2 gas. Based on the results highlighted
in Table 2, we choose complex 7 as the preferred sensing film
constitute.
Fig. 3 Section of the 31P,57Fe{1H} HMQC NMR spectra (500.13 MHz,
ambient temperature in THF-d8 solution) of mixed amine-phosphite
complexes 6–7.
phthalocyanine ring, two trans complexed amine ligands, and in
overall suggesting a fairly flat arrangement of the Pc system.35
There are only a few more X-ray examples of six-fold coordinated
FePc complexes containing nitrogen donors.36
Sensing performance
The sensing mechanism for NO2 recognition on nanostructured
films incorporating phthalocyanine iron(II) systems is based on
the exchange of the amine by a p-electron acceptor (NO2),
which results in a decrease in the absorbance of the Q-band
between 655 and 670 nm.14 The spectral changes indicate that
the 18-electron coordinatively saturated FePc(NH2R)2 2–5 or
FePc(NH2R)(P(OEt)3) 6–7 complexes can lose an amine ligand,
presumably via a dissociative mechanism in which the NO2
molecule occupies the vacant coordination site.
To prepare the sensing films, FePc (1) was dissolved in the
specific THF mixture (molar ratios of 1 : 30 (1 : NH2R) for 2–5,
and 1 : 30 : 15 (1 : NH2R:P(OEt)3) for 6–7), and an aliquot (0.2 mL)
of this solution was then taken and deposited onto a positively
chargednanostructured AlOOHlayer (AP200/19)byspin-coating
(at 450 rpm). AP200/19 is best described by a total pore volume
(TPV) of 20 mL m-2 and a pore diameter (PD) of 19.2 nm.37,38
AP200/1937,38 doped with [FePc(benzylamine)(P(OEt)3)] (7)
were mounted in a flow cell and fixed in a spectrophotometer.
The optical films were calibrated between 0.1 and 1 ppm NO2
(50% RH) and the regression equation y = -1.2335 + 23.444x
1
Absorption and H NMR spectra of these solutions (see ESI†)
before deposition clearly evidenced the exclusive formation of the
bis-amine complexes 2–5 or the mixed ligand amine-phosphite
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was obtained when varying partial pressures of NO2 (see ESI†).
The limit of detection (LOD) and quantification (LOQ) were
determined under IUPAC methods (LOD = 3sb/m; LOQ =
10sb/m, where sb is the standard deviation for ten blank samples
and m is the slope of the calibration curve). The NO2 LOD and
LOQ were 1.2 ppb and 4.0 ppb, respectively. Compared to sensing
layers reported in the literature, the one described herein offers
excellent sensitivity and would be located on top of all the opto-
chemical sensors assembled with an iron core as the indispensable
component. Fig. 4 shows the response recovery-curve for sensing
film-containing 7, when after each NO2 injection; flushes of fresh
air are introduced. The NO2 concentration chosen for these tests
were 1.0, 0.5, and 0.2 ppm with a gas flow rate of 200 mL min-1.
Fig. 5 (a) Stability study of complex 7 immobilized into AP200/19 at (¥)
4 ◦C, (᭹) 25 ◦C and (ꢀ) 60 ◦C; (b) thermo-stability comparison for layers
containing complexes 4, 5, 6 and 7 at 25 ◦C.
previous work and for related optical sensors. A study to unravel
the electronic structure of the NO2 adducts, together with the
implementation of these new PcFe sensing films on miniaturized
gadgets are currently undergoing in our laboratories.
Fig.
4
Room
temperature
response–recovery
curve
for
Experimental
[FePc(benzylamine)(P(OEt)3)] (7) incorporated into AP200/19 matrix,
when exposed to decreasing concentration of NO2 gas in the presence of
air.
Glassware was dried overnight in a 110 ◦C oven to remove mois-
ture. All procedures were carried out under nitrogen and solvents
were freshly distilled from potassium or sodium/benzophenone
(THF, hexane). Iron phthalocyanine 1 was purchased from Fluka,
and the rest of reagents were used as obtained from commercial
sources without further purification. Compounds 2 and 3 have
been prepared as described previously.16
One important requirement to be addressed is the stability of
the sensing films against temperature. Films containing complexes
2–7 were evaluated with 1 ppm of NO2 for 300 s at 50% RH in air
during 3 months. The stability screening was performed at 4, 25,
and 60 ◦C. Fig. 5(a) shows the stability of layers doped with 7 at
these temperatures, proving 60 ◦C to considerably affect the layer
life time. At 25 ◦C (Fig. 5(b)) the sensing layer keeps its selectivity
intact for 40 days, when starting from then is reduced down to
50% after the second month. These results significantly improve
previously reported data in which [FePc(decylamine)2] (2) films
were stable for less than one month at 25 ◦C.14
1D and 2D NMR spectra were measured on a Bruker Avance
500 spectrometer (1H, 500 MHz; 13C, 125.7 MHz; 15N, 50.7 MHz,
29Si, 99.4 MHz, 31P, 202.4 MHz and 57Fe, 16.3 MHz) equipped
with a third radiofrequency channel. A 5 mm indirect triple probe
1
1
head was used for H,15N gHMQC and H,29Si gHMQC and a
5 mm direct triple probe head was used for 31P,57Fe HMQC. The
spectral references used were TMS for 1H, 13C and 29Si, NH3
for 15N, and to external 85% H3PO4 for 31P and Fe(CO)5 for
57Fe. Unless otherwise stated, standard Bruker software routines
(TOPSPIN and XWINNMR) were used for the 1D and 2D
NMR measurements. Melting points were recorder on a Bu¨chi
B-540 capillary melting point apparatus and mass spectra were
determined by atmospheric pressure chemical ionization (APCI)
on a Hewlett-Packard 1100.
Conclusions
New octahedral iron(II) phthalocyanines complexes 2–7 have been
synthesized, structurally characterized, and tested as potential
optical sensors for NO2 determinations. d(15N) values have been
obtained by 2D NMR methods and remarkably correlated with
NO2 sensing results. 2D 31P,57Fe HMQC experiments have been
applied in phthalocyanine systems providing for the first time
phthalocyanine iron-57 chemical shifts and coupling constants.
Among the sensing films assayed, the novel mixed phosphite-
amine complex7 immobilized into AP200/19 showed the best NO2
sensitivity, reversibility (LOD and LOQ of 1.2 ppb and 4.0 ppb,
respectively), and thermo-stability in the range of 4–25 ◦C. It
constitutes a promising optical sensor providing better results than
The absorbance measurements were performed on a Spekol
1100 spectrophotometer using a specially designed flow-through
cell.14 The gases partial pressures were varied by using Bronkhorst
mass flow controllers. Relative humidity was monitored with a
Rotronic hygrometer located right after the measurement cell. A
self written LabVIEW 5.1 program which fully controls the Spekol
1100 and Bronkhorst mass flow controllers via serial interface was
employed.
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General procedure for the synthesis of complexes 4–5
[FePc(NH2(CH2)9CH3)(P(OEt)3)] (6)
The corresponding amine (para-methoxybencylamine or
trimethylsylilmethyleneamine, 0.299 mmol) was added dropwise
to a solution of 1 (85 mg, 0.150 mmol) in THF (5 mL). The
reaction mixture was stirred at ambient temperature for 15 min
after which time the dark green solution was filtered with
Millipore Millex (Nylon 0.2 mM), and then slowly concentrated
under vacuum. The resulting greenish oil was washed with cold
hexane, filtered, and dried under vacuum. This sequence was
repeated one more time. Isolated yields were 86% (108 mg) and
90% (104 mg) for 4 and 5, respectively. Alternatively, complexes 4
and 5 can be prepared in situ in an oven-dried 5 mm NMR tube,
by just mixing 0.0299 mmol (17 mg) of 1 with 0.0598 mmol of the
corresponding amine in deuterated THF (0.5 mL). After a few
minutes the solution turns deep green indicative of the desired
transformation.
Mp. 206–210 ◦C, dec. 1H NMR (500.13 MHz, THF-d8): d -5.22
(sa, 2H, NH2), -2.61 (sa, 2H, CH2), -1.18 (sa, 2H, CH2), -0.55
(sa, 2H, CH2), -0.19 (t, 9H, 3JHH 7.0 Hz, CH3), 0.06 (sa, 2H, CH2),
0.47 (sa, 2H, CH2), 0.76 (sa, 2H, CH2), 0.86 (sa, 3H, CH3), 0.95
(sa, 2H, CH2), 1.10 (sa, 2H, CH2), 1.22 (sa, 2H, CH2), 1.25 (m, 6H,
OCH2), 7.93 (m, 8H, ArH), 9.27 (m, 8H, ArH). 13C NMR d: 13.49
3
(CH3), 14.26 (d, JPC 4.3 Hz, 3CH3), 22.50 (CH2), 24.95 (CH2),
28.05 (CH2), 28.78 (CH2), 29.04 (CH2), 29.39 (CH2), 31.69 (CH2),
2
31.96 (CH2), 36.0 (NCH2), 58.15 (d, JPC 8.5 Hz, OCH2), 120.40
(8CAr), 126.92 (8CAr), 141.84 (8Cipso), 146.95 (8Cipso). 15N NMR
d: -1.34 (JNH 64 Hz), (JPN 65.8 Hz). 31P NMR d: 131.8. 57Fe NMR
d: +6764 (JFeP 79.2 Hz).
[FePc(NH2CH2Ph)(P(OEt)3)] (7)
Mp. 188–190 ◦C, dec. 1H NMR (500.13 MHz, THF-d8): d -4.82
3
(sa, 2H, NH2), -1.70 (sa, 2H, CH2), -0.32 (t, 9H, JHH 6.8 Hz,
CH3), 1.12 (m, 6H, OCH2), 4.92 (sa, 2H, ArH), 6.15 (sa, 2H,
ArH), 6.29 (sa, 1H, ArH), 7.80 (m, 8H, ArH), 9.15 (m, 8H, ArH).
13C NMR d: 12.30 (d, 3JPC 4.4 Hz, 3CH3), 38.30 (NCH2), 56.29 (d,
2JPC 9.1 Hz, OCH2), 118.51 (8CAr), 124.21 (CAr), 124.90 (2CAr),
125.05 (8CAr), 125.96 (2CAr), 139.99 (8Cipso), 140.66 (Cipso), 145.14
(8Cipso). 15N NMR d: 3.45 (JNH 67.6 Hz), (JPN 62.2 Hz). 31P NMR
d: 131.6. 57Fe NMR d: +6794 (JFeP 79.8 Hz).
[FePc(NH2CH2C6H4OMe)2] (4)
◦
1
Mp 135–140 C, dec. H NMR (500.13 MHz, THF-d8): d -6.13
(t, 4H, 3JHH 7.6 Hz, 2NH2), -1.92 (t, 4H, 3JHH 7.6 Hz, 2CH2), 3.24
(s, 6H, 2OCH3), 4.88 (d, 4H,3JHH 8.9 Hz, ArH), 5.81 (d, 4H,3JHH
8.9 Hz, ArH), 7.91 (m, 8H, ArH), 9.28 (m, 8H, ArH). 13C NMR
d: 40.89 (2CH2), 53.81 (2OCH3), 112.18 (4CAr), 120.38 (8CAr),
126.67 (8CAr), 126.76 (4CCAr), 129.07 (2Cipso), 142.56, (8Cipso),
148.26 (8Cipso), 158.02 (2Cipso). 15N NMR d: -23.75. MS (API-
ES), m/z: 843 (M+1). Analysis: Calcd. (%) for C48H38FeN10O2: C,
68.41; H, 4.54; N, 16.62. Found: C, 68.53; H, 4.59; N, 16.52.
Preparation of AP200/19 AlOOH-matrix
The preparation of the AP200/19 nanostructured matrix has been
previously described14,38,41 as follows: 50 g of the aluminium ox-
ide/hydroxide (AlOOH) DISPERSAL 100/2 (from Sasol GmbH,
Hamburg, Germany) were dispersed for 15 min with vigorous
mechanical stirring at a temperature of 20 ◦C in 948 g of doubly
distilled water. The temperature was increased to 90 ◦C and stirring
was continued for 15 min at this temperature to enable extensive
dispersion in the form of AlOOH nanocrystals. The solid was
filtered, washed three times with doubly distilled water and dried
at 110 ◦C. The resulting solid (8 g) was added to a mixture
of 63 g of doubly distilled water and 0.96 g of concentrated
acetic acid 80% (from Aldrich Chemie, Buchs, Switzerland). The
generated dispersion was exposed to ultrasounds for 3 min at
[FePc(NH2CH2SiMe3)2] (5)
Mp 128–130 ◦C, dec. 1H NMR (500.13 MHz, THF-d8): d -6.80 (t,
4H, 3JHH 7.5 Hz, 2NH2), -3.44 (t, 4H, 3JHH 7.5 Hz, 2CH2), -1.59
(s, 18H, 6CH3), 7.89 (m, 8H, ArH), 9.25 (m, 8H, ArH). 13C NMR
d: -5.93 (6CH3), 26.13 (2CH2), 120.35 (8CAr), 126.75 (8CAr),
142.54 (8Cipso), 148.04 (8Cipso). 15N NMR d: -50.79.29Si NMR d:
-2.54. MS (API-ES), m/z: 775 (M+1). Analysis: Calcd. (%) for
C46H34FeN10O2: C, 62.00; H, 5.46; N, 18.08. Found: C, 61.90; H,
5.53; N, 18.23.
◦
40 C. Afterwards, 8 g of a solution of polyvinyl alcohol (PVA),
10% by weight and with a molecular weight of 85 000 to 146 000
(from Aldrich Chemie, Buchs, Switzerland), were added and the
resulting coating solution was again exposed to ultrasounds for
3 min. Then, curtain coating was used to coat a transparent
polyester (PET) support 175 mm thick (from Dupont de Nemours)
called P72 with 28.5 g m-2 of this solution at a temperature
of 40 ◦C. The coated support was then dried for 60 min at a
temperature of 30 ◦C.
General procedure for the synthesis of complexes 6–7
Triethylphophite (0.150–0.200 mmol) was added dropwise to a
solution of 2 or 3 (0.150 mmol) in THF (5 mL). The reaction
mixture was stirred at ambient temperature for 30 min after which
time the dark green solution turned into deep blue. The resulting
solution was filtered with Millipore Millex (Nylon 0.2 mM), and
then slowly concentrated under vacuum. The blue residue was
washed with cold hexane, filtered, and dried under vacuum. This
sequence was repeated one more time. Isolated yields were 71%
(95 mg) and 68% (86 mg) for 6 and 7, respectively. Alternatively,
complexes 6 and 7 can be prepared in situ in an oven-dried
5 mm NMR tube, by just mixing equimolecular amounts of 2
or 3 (0.0170 or 0.0191 mmol) with triethylphosphite in deuterated
THF (0.5 mL). After a few minutes the solution turns deep blue
indicative of the desired transformation.
Preparation and characterization of sensing films
To prepare the sensing films, 0.2 mL of a solution which contains a
molar ratio 1 : 30 (1 : NH2R) or 1 : 30 : 15 (1 : NH2R : P(OEt)3) was
dropped by spin-coating technique on AP200/19 nanostructure
at 450 rpm.
Owing to the fact that the membrane material is made from
a suspension of nanodispersed particles (diameter smaller than
6236 | Dalton Trans., 2010, 39, 6231–6238
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half of the wavelength of the visible light), the light beam is not
scattered by the particles but passes the film. Such materials are
recognized as “transparent”.
The sensing films were characterized measuring the (A0 - Ax)/A0
signal at lmax; where A0 is the absorbance of the film in synthetic air
(50% RH and flow-rate of 200 mL min-1) and Ax is the absorbance
on exposure to NO2 (1 ppm) during 300 s at 50% RH and flow-rate
of 200 mL min-1.
Multinuclear NMR, Plenum Press: New York, 1987, pp 354, Chapt.12.
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Acknowledgements
Financial support by the Ministerio de Educacio´n y Ciencia
(project CTQ2008-117BQU), Junta de Andaluc´ıa (projects P07-
FQM-2625 and P07-FQM-2738), and the Ramo´n y Cajal program
(IF) are gratefully acknowledged. AVN thanks the Ministerio
de Educacio´n for the financial support of his grant (reference
AP2006-01147).
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