Lanthanide complexes of new polyaminocarboxylate complexes with two chromophores derived from bispyrazolylpyridine and aceto or benzophenone: Synthesis, characterization and photophysical properties

Article abstract of DOI:10.1016/j.tet.2005.05.009

New ionophores derived from 2,6-bis(N-pyrazolyl)pyridine and aceto/benzophenone have been synthesized and fully characterized. The lanthanide complexes of these new ligands were studied from their UV-vis and fluorescence data. Eu³⁺ and Tb³⁺ complexes were easily formed and their photophysical properties measured. In all cases, lanthanide emission lifetimes were in the range of ms albeit quantum yields were relatively low. Possible flaws in the energy-transfer mechanisms are discussed.

Full text of DOI:10.1016/j.tet.2005.05.009

Tetrahedron 61 (2005) 6757–6763
Lanthanide complexes of new polyaminocarboxylate complexes
with two chromophores derived from bispyrazolylpyridine and
aceto or benzophenone: synthesis, characterization and
photophysical properties
*
´
Ernesto Brunet, Olga Juanes, Rosa Sedano and Juan Carlos Rodrıguez-Ubis
*
´ ´ ´
Departamento de Quımica, Organica, C-1, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid, Spain
Received 17 February 2005; revised 8 April 2005; accepted 2 May 2005
Abstract—New ionophores derived from 2,6-bis(N-pyrazolyl)pyridine and aceto/benzophenone have been synthesized and fully
characterized. The lanthanide complexes of these new ligands were studied from their UV–vis and fluorescence data. Eu3C and Tb3C
complexes were easily formed and their photophysical properties measured. In all cases, lanthanide emission lifetimes were in the range of
ms albeit quantum yields were relatively low. Possible flaws in the energy-transfer mechanisms are discussed.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Lanthanide trivalent cations have excellent photolumi-
nescent properties usable in a high range of different
applications. But the ions’ poor ability to absorb light makes
it necessary to dress them up with an organic skin in the
form of a complex. The design of the organic part of such
complexes is thus paramount in achieving the required
circumstances for the complex to be efficiently luminescent.
The usual conditions to be fulfilled are good yields for
intersystem crossing and reasonable matching between the
Figure 1. 2,6-Bis(N-pyrazolyl)pyridine and acetophenone derivatives used
as reference in this work.
quantum yields for triplet sensitization of lanthanide
chromophore first triplet state and the resonance level of the
luminescence.4 Also Beeby and Williams have described
metal. The organic ligand must also provide good isolation
recently the photosensitization of lanthanides by means of
of the metal from water vibronic O–H deactivators. The
acetophenone and benzophenone in polyazamacrocyclic
achievement of all these requirements is not an easy task
and research in this area is very active.1
Suitable building blocks for designing photoactive probes
are heteroaromatic rings like pyridine, pyrazine or pyrazole.
We have already prepared a number of useful complexes
based on these motifs.2 From all chromophores synthesized,
2,6-bis(N-pyrazolyl)pyridine (1; Fig. 1) was the most
successful and its Eu3C and Tb3C complexes displayed
excellent luminescent properties.3 More recently, we have
also shown that complexes based on the relatively simple
acetophenone chromophore (2; Fig. 1) possessed excellent
Keywords: Lanthanides; Luminescence.
*
Corresponding author. Tel.: C341 497 4150; fax: C341 497 3966;
e-mail: jcrubis@uam.es
Figure 2. Ligands prepared in this work.
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.05.009

6758
E. Brunet et al. / Tetrahedron 61 (2005) 6757–6763
structures.5 Both the outstanding properties of these two
chromophores and our previous studies on photoactive
macrocycles,6 cryptates7 and polyaminocarboxylates8 led us
to design two new ligands based on a combination of these
chromophores. Therefore, this paper deals with the
synthesis and photophysical study of Eu3C and Tb3C
complexes of ligands 3 (Fig. 2), based on 2,6-bis(N-
pyrazolyl)pyridine and aceto/benzophenone subunits.
All compounds were studied from their UV–vis and
emission data.
hydroxybenzophenone (4b), obtained respectively from
acetylation or benzoylation of hydroxyl groups of pyro-
catechol, followed by Fries rearrangement, as previously
reported.9 Reaction of 4a,b with an excess of dibromo-
derivative of 2,6-bis(N-pyrazolyl)pyridine, in the presence
of potassium carbonate in acetone, afforded compounds
5a,b. The introduction of the aminocarboxylate moieties
was performed by treatment of the dibromo derivative with
di-tert-butyliminodiacetate. The resulting tert-butyl esters
6a,b were cleaved to the acids 3a,b with trifluoroacetic acid
in dichloromethane with good yields.
2. Results and discussion
2.2. Lanthanide complexes
The Eu3C and Tb3C complexes of ligands 3a,b were
prepared by the addition of the stoichiometric amount of the
corresponding lanthanide chloride (aqueous solution) to the
ligand in water. The 1:1 stoichiometry was confirmed in
2.1. Synthesis of the ligands
Compounds 3a,b were synthesized as depicted in Scheme 1,
starting from 3,4-dihydroxyacetophenone (4a) and 3,4-di-
Scheme 1. Compounds synthesized in this work.
Table 1. Wavelength maxima and molar absorption coefficients of Eu3C and Tb3C complexes of compounds 1,2, and 3a,b (buffer pH 8.6; rt)
Ligand Complex
Eu3C
Tb3C
1
l abs (nm)
245
17.6
300
12.2
270
12.3
313
8.1
270
11.2
313
7.8
3 (103 MK1 cmK1
)
)
)
)
2
l abs (nm)
272
10.7
301
8.0
260
12.2
287
5.0
260
11.8
287
5.0
3 (103 MK1 cmK1
3a
l abs (nm)
3 (103 MK1 cmK1
246
45.5
303
33.0
245
40.1
306
28.0
245
38.4
306
26.6
3b
l abs (nm)
3 (103 MK1 cmK1
249
43.5
309
30.5
250
39.2
310
27.6
250
35.4
310
25.4

E. Brunet et al. / Tetrahedron 61 (2005) 6757–6763
6759
Figure 3. Absorption and excitation spectra of Eu3C complex of 3a and 3b respectively.
both ligands by titration experiments performed in the
emission spectra. The photophysical study was performed in
borate buffer (pH 8.6) at a concentration 10K5 M for
absorption and 10K7 M for emission spectroscopy. No
changes in absorption and luminescence spectra were
observed in aerated water after several days at room
temperature, indicating that these complexes are kinetically
inert in water solution.
lanthanide. In contrast, ligands 3a,b displayed much smaller
changes, if any, suggesting that the conformational changes,
which undoubtedly should take place upon complexation,
might not involve such alterations in the electronic states of
the chromophore.
2.4. Luminescence studies
The emission spectra of the Eu3C and Tb3C complexes,
excited into the lowest energy (ligand-centered) absorption
band, showed the well-known, structured luminescence of
the lanthanide ions, with the highest intensity band at
615 nm for Eu3C(5D0–7F2 transition) and 545 nm for
Tb3C(5D4–7F5 transition).
2.3. Electronic spectra
The UV–vis spectra of the ligands showed the characteristic
bands for the bis-pyrazolylpyridine chromophore, (245 and
300 nm), with minor variations (Table 1). The bands of
aceto/benzophenone chromophore (270 and 290 nm) should
be obscured under the first, owing to the higher molar
absorption coefficients of the double bispyrazolylpyridine
system.
The global accordance between absorption and excitation
spectra (Fig. 3) clearly shows that in the two complexes
lanthanide ions are efficiently excited by ligand-to-metal
intersystem energy transfer from sensitized bis-(N-pyrazo-
lyl)pyridine and aceto or benzophenone chromophores. It is
noteworthy that the excitation spectra of 3a,b showed
important maxima at ca. 270 nm, very similar to that
displayed by compound 2 (depicted in Fig. 1). This is a
qualitative proof of the higher importance of the phenone
chromophore in transferring energy to the metal, despite its
apparent long distance to the iminodiacetate groups where
the metal is assumed to be coordinated. Unfortunately, we
were unable to obtain good crystals of the complexes to
carry out x ray studies. However, simple conformational
analysis of the complexes suggested that the phenone
moiety may lay in reasonable proximity to the metal. In this
situation lanthanide ion could be surrounded by up to nine
oxygen atoms saturating the first lanthanide coordinating
sphere, see below. Nitrogen heterocyclic atoms are not
directly involved in this coordination. Figure 4 displays the
calculated energy minimum.
The first feature that should be remarked is that compounds
1 and 2 showed substantial changes in wavelength maxima
upon complexation (ca. 13 and K12 nm, respectively). Due
to the excellent quantum yields measured for these ligands
(vide infra), these sizable variations were attributed to con-
formational rearrangements leading to enhanced coopera-
tivity between the different coordinating atoms with the
The cascade of photophysical processes that occurs in these
lanthanide complexes is well known. Light is absorbed into
the first excited singlet state (1E00) of the ligand that is
followed by intersystem crossing (ISC) to its triplet state
(3E00) which finally populates the lanthanide emissive
Figure 4. Calculated energy minimum (AM1/MMC) for complex 3a/
.
Eu3C
3
Table 2. Triplet state energy of gadolinium complexes and differences
between this state and others indicated in cmK1
levels. Table 2 shows the energy values of E00 levels
measured in the gadolinium complexes for the compounds
3a,b studied in this work and 1 and 2 (depicted in Fig. 1) as a
reference.
Compound
3E00
1E00K3E00
3E00K5D0
(Eu)
3E00K5D4
(Tb)
1
2
3a
3b
25150
24000
24572
24572
6798
10843
8107
7686
7900
6750
7322
7322
4650
3500
4072
4072
It may be seen that 3a,b 3E00 levels are comprised between
the 3E00 levels of 1 and 2 complexes, suggesting that ligands
3a,b may be, a priori, as good lanthanide sensitizers as 1 and

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E. Brunet et al. / Tetrahedron 61 (2005) 6757–6763
Table 3. Lifetime data in H2O and D2O at rt and 77 K (ms), quantum yields, (f) of the metal-centered emission of the complexes with ligands 1, 2 and 3a,b and
number of water molecules estimated with the Horrocks method
fb
qH2O
c
a
a
a
77 K
300 K
H2O
300 K
D2O
t
t
t
D2O
1 Eu3C
Tb3C
1.3
2.8
0.6
1.6
2.5
3.3
1.9
2.7
2.2
1.9
2.2
2.0
3.4
3.1
3.1
3.0
3.0
2.9
2.7
3.0
0.1
0.6
0.2
0.9
0.002
0.03
0.001
0.02
0.4
0.3
1.1
1.0
0.3
0.6
0.3
0.2
2$Eu3C
Tb3C
3a$Eu3C
Tb3C
0.3–1.7d
1.5
1.5
3b Eu3C
Tb3C
1.8
a Estimated standard error !10%.
b Measured in borate buffer pHZ8.6. Estimated standard error of 30%.
c Uncertainty G0.5 water molecules.
d Bi-exponential decay.
2, and in fact, they are. However Table 3 shows that
complexes 3a,b displayed much lower emission quantum
yields (f) than those obtained with ligands 1 and 2
containing each chromophore separately†.2 Therefore,
there should be some flaws in the energy transfer
mechanism of complexes 3a,b that are absent with ligands
1 and 2.
metal excited states thought the O–H vibration occurs, even
with a low number of water molecules in the first
coordination sphere. The higher values of the lifetime at
77 K, may be indicative of other deactivation pathways,
caused by excited states which can be thermally populated
from the emitting state, or the existence of potencial LMCT
states for the case of Eu3C
.
The lanthanide quantum yield of luminescence (f) is a
balance between the ligand-to-metal energy transfer effi-
ciency and the radiative and non-radiative rate constants of
the luminescent Ln(III) levels. An important non-radiative,
deactivation mechanism of sensitized lanthanides comprises
their coupling with O–H oscillators that effectively
quenches metal luminescence. In Table 3 it can be seen
that the number of water molecules in the first coordination
sphere of complexes 3a,b is very low (0.3–0.6) and similar
to 1 and inferior to 2, as calculated by Horrocks equation,10
and other different methods.11,12 This result confirmed the
disposition of the lanthanide discussed from the calculated
structure.
In relation with other factors involved in the lanthanide
energy-transfer process, (LET), it is imperative a good
3
match between E00 and Di levels, as Mukkala and co-
5
3
workers have stated.13 Had the E00–5Di energy gap been
too small, non-radiative deactivation by metal-to-ligand
back-energy transfer is a serious competing process to metal
luminescence. On the contrary, if the gap is too large,
ligand-to-metal energy transfer is produced to high vibronic
levels of the metal which partially relaxes by thermal,
non-radiative pathways, thus reducing energy-transfer
3
5
efficiency. The best match between E00 and Di levels is
achieved when their differences are above 6500 cmK1 for
Eu3C complexes and 3500 cmK1, for Tb3C. Compounds
3a,b ample fulfil this condition, see their increments in
Table 2. Concerning ISC efficiency, it is known14 that
the energy gap between the singlet and triplet states of the
ligand (1E00K3E00) should be at least 5000 cmK1. It can be
seen in Table 2 that complexes 3a,b also satisfy this
condition.
It is thus clear that the lanthanides in complexes of 3a,b are
as well protected from surrounding water molecules as they
are within ligand 1 or even better than in 2 and therefore,
the low quantum yields cannot be explained only by the
quenching due to coupling with first coordination sphere
water molecules.
Therefore, the low quantum yields with Eu3C complexes
and in minor extent with Tb3C, cannot be explained only
with the concourse of the points mentioned above, specially
when all the photophysical parameters fulfil the optimal
values, estimated by comparison with complexes with the
close related ligands 1 and 2 which showed excellent
quantum yields.
The lifetimes gathered in Table 3, were calculated from the
decay curves of the excited states of the Eu3C and Tb3C
complexes, excited in the lowest energy ligand-centred
absorption band. In each case, monoexponential decay
curves were observed, except in the case of complex 3a
Eu3C. In H2O solution and at room temperature, the
luminescence lifetimes were in the 1.5–1.8 ms range, with
3b Tb3C complex having the longest lifetime and 3a Eu3C
the shortest. The lifetime values are higher in D2O than in
H2O (1.4 and 1.1 factors for Eu3C and Tb3C respectively)
It is widely known that the distance chromophore lanthanide
plays an important role in the energy transfer process, and
two mechanisms have been proposed in the literature.15 The
so-called Dexter mechanism implies two simultaneous,
concerted electron transfers which requires good orbital
overlapping. The batho- or hypsochromic shifts upon
complexation not exhibited by ligands 3a,b (vide supra)
suggests that their heteroatoms do not modify their positions
as a result of the required orbital overlapping. The
5
5
indicating that nonradiative deactivation of the D0 or D4
† The quantum yield were measured only by excitation at the lowest energy
band (306 nm for 3a and 310 nm for 3b). In fact, although the 245 nm
band is characteristic from the bispyrazolyl moiety whereas that of
270 nm comes from the phenone, measurements by excitation on these
bands are ambiguous as the maximum at 245 nm shifts to 270 nm and that
of 270 nm to 260 nm by complexation.
¨
alternative Forster mechanism does not entail electron

E. Brunet et al. / Tetrahedron 61 (2005) 6757–6763
6761
transfer but coulombic coupling of the appropriate orbitals.
This interaction is strongly dependent upon orientation and
distance (ka r-6). The low experimental f values indicate
that a good coulombic coupling cannot be attained either in
ligands 3a,b. Although molecular modelling suggests that
the phenone chromophore may lay much closer to the metal
than anticipated, the only explanation to the low quantum
yields measured for 3a,b is that the probable, preferential
chelation of the metal with the iminodiacetates unfortu-
nately makes its relative arrangement to the chromophores
to be inappropriate for efficient energy transfer.
(quinine sulfate and 9,10-diphenylanthracene) and two
phosphorescent (Ru(bipy)3Cl2 and Tb Terbipy complex)
delivered by Wallac Oy. Despite this, the expected errors of
this measurement are within 30%. Triplet state energy levels
were measured from the highest energy band in the 77 K
phosphorescence spectrum of the gadolinium complexes.
4.2.1. 3,4-Bis-{[6-(3-bromomethyl-1-pyrazolyl)-pyridin-
2-yl]-1H-pyrazol-3-yl-methoxy} acetophenone (5a) and
3,4-bis-{[6-(3-bromomethyl-1-pyrazolyl)-pyridin-2-yl]-
1H-pyrazol-3-yl-methoxy}benzophenone (5b). To a sus-
pension of 2,6-bis-(3-bromomethyl-1-pyrazolyl)pyridine
(1.6 g, 4.03 mmol) and potassium carbonate (2.7 g,
20.15 mmol) in refluxed acetone, was added slowly an
acetone solution of 3,4-dihydroxyacetophenone or benzo-
phenone (0.39 mmol in 10 mL). The mixture was refluxed
and stirred for 7 h. The salts were filtered off and the filtrate
was evaporated to dryness. The solid residue was flash
chromatographed. The first elution with dichloromethane
yields the unreacted dibromo derivative. Further elution
with dichloromethane/methanol 97:3 yields the derivatives
5a (168 mg, 55%) or 5b (220 mg 62%).
3. Conclusion
Two new ionophores derived from 2,6-bis(N-pyrazol-1-
yl)pyridine motif attached to aceto/benzophenone and
iminodiacetic subunits have been synthesized. Eu3C and
Tb3C complexes were prepared and their luminescence
properties were studied in borate buffer. Lanthanide
emission lifetimes were long enough (well in the range of
ms) to make these complexes highly valuable for appli-
cations in time-resolved luminescence measurements.
However, quantum yields were much lower than those
observed for simpler complexes prepared by us in the recent
past. Probably, the arrangement of the chelating imino-
diacetate subunits relative to the chromophores hampers an
efficient path for energy transfer.
Compound 5a data. Mp: 206–208 8C. MS:(L-SIMSC):783
(MC, 9), 785 ((MC2)CHC, 19), 787 ((MC4)CHC, 9). 1H
NMR: (CDCl3) d (ppm) (500 MHz): 8.46 (2H, d, JZ2.5 Hz,
Pz(H5)); 8.44 (2H, 2d, JZ2.6 Hz, Pz(H5)); 7.91 (2H, t, JZ
8.0 Hz Py (H4)); 7.81–7.74 (5H, m, Py (H3,5) and Ar(H2));
7.55 (1H, dd, JZ2.1, 8.3 Hz, Ar(H6)); 7.08 (1H, d, JZ
8.4 Hz, Ar(H5)); 6.59 (1H, d, JZ2.6 Hz, Pz(H4)); 6.57 (1H,
d, JZ2.6 Hz, Pz(H4)); 6.52 (2H, t, JZ2.4 Hz, Pz(H4)); 5.31
(2H, s, p-OCH2Pz); 5.29 (2H, s, m-OCH2Pz); 4.53 (4H, s,
PzCH2Br); 2.51 (3H, s, CH3CO). 13C NMR: (CDCl3) d
(ppm) (75 MHz):197.5 (CO); 153.2 (Ar4); 152.1;152.0
(Pz3); 150.4 (Py 2–6); 148.5 (Ar3); 141.7 (Py4); 130.9
(Ar1); 128.7;128.4 (Pz5); 124.0 (Ar6); 114.4 (Ar2); 113.2
(Ar5); 109.9; 109.7 (Py 3,5); 108.4; 108.1 (Pz4); 65.5
(m-OCH2Pz); 65.3 (p-OCH2Pz); 26.5 (CH3CO); 24.9
(PzCH2Br).
4. Experimental
4.1. General
1H NMR and 13C NMR: Bruker AC-200 (200 and 50 MHz),
´
AMX-300 (300 and 75 MHz), (Departamento de Quımica
Organica, DQO) and DRX-500 (500 and 125 MHz),
´
´
(Servicio Interdepartamental de Invesigacion, SIdI). M.S.:
VG Autospec spectrometer (SIdI) in FAB mode (L-SIMSC)
or EIC. Absorption spectra: Lambda 6 Perkin-Elmer
spectrophotometer (DQO). Excitation and emission spectra:
LS50 Perkin-Elmer spectrofluorometer (DQO). The exci-
tation spectra were automatically corrected and the emission
spectra were corrected according to the instrument guide-
book. Elemental analyses of compounds (Perkin-Elmer
CHN 2400 automatic analyzers, SIdI) were correct within
experimental error. All solvents were purified prior to their
use. Lanthanide chlorides were purchased from Aldrich and
used as received. Structure of Figure 4 was calculated using
the HyperChem 7.0 package.
Compound 5b data. Mp: 110–111 8C. MS:(L-SIMSC):845
(MCHC, 22), 847 ((MC2)CHC, 44,), 849 ((MC4)CHC,
24). H NMR: (CDCl3) d (ppm) (300 MHz):8.42 (4H, m,
1
Pz(H5)); 7.81–7.28 (13H, m, Py(H) and Ar(H)); 7.09 (1H, d,
JZ8.4 Hz, Ar(H5)); 6.53 (2H, m, Pz(H4)); 6.47 (2H, d, JZ
2,6 Hz, Pz(H4)); 5.28 (2H, s, p-OCH2Pz); 5.23 (2H, s,
m-OCH2Pz); 4.48 (4H, s, PzCH2Br).13C NMR: (CDCl3) d
(ppm) (75 MHz): 195.3 (CO); 152.5; 151.9; 151.5; 151.3;
149.7; 148.0; 141.4; 138.0; 131.8; 130.6; 129.6; 128.3;
128.1; 125.6; 115.9; 112.8; 109.4; 108.1; 107.7; 107.4
(ArC); 65.3 (m-OCH2Pz); 65.1 (p-OCH2Pz); 24.7
(PzCH2Br).
4.2. General methods
Synthesis of lanthanide complexes. Absorption and emis-
sion measurements. The complexes were formed by
addition of equimolecular amounts of the corresponding
lanthanide chloride to the ligand solutions in borate buffer
pHZ8.6. (Europium complexes: 10K5 M for absorption and
emission. Terbium complexes: 10K5 M for absorption and
10K7 M for emission). The resulting solutions were kept
closed at rt for 18 h. The emission quantum yields were
measured complying with reported procedures by Rhys-
Williams16 and referenced to four standards, two fluorescent
4.2.2. N,N,N0,N0-3,4-Bis-{[6-(3-aminomethyl-1-pyrazo-
lyl)-pyridin-2-yl]-1H-pyrazol-3-yl-methoxy} aceto-
phenone tetra(tert-butil acetate) (6a) and N,N,N0,N0-3,4-
bis-{[6-(3-aminomethyl-1-pyrazolyl)-pyridin-2-yl]-1H-
pyrazol-3-yl-methoxy}benzophen-one tetra(tert-butyl
acetate) (6b). A mixture of the dibromo derivative (5a or
5b) (0.1 mmol), tert-butyl iminodiacetate (0.2 mmol) and
sodium carbonate (0.5 mmol) in 90 mL of acetonitrile were
stirred at rt for 24 h. The solvent was then removed and the
resulting residue was washed with water and extracted with

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E. Brunet et al. / Tetrahedron 61 (2005) 6757–6763
dichloromethane. The tetra ester was obtained as a yellow
oil and used without further purification. Yield 70–75%.
Py(H3,5) and Ar(H)); 6.74 (1H, d, JZ2.6 Hz, Pz(H4));
6.66 (1H, d, JZ2,1 Hz, Pz(H4)); 6.54 (2H, m, Pz(H4)); 5.32
(2H, s, p-OCH2Pz); 5.26 (2H, s, m-OCH2Pz); 3.93 (4H, s,
PzCH2N); 3.46 (8H, s, NCH2CO2H). 13C NMR: (DMSO-d6)
d (ppm) (75 MHz): 194.8 (CO); 172.5 (CO2H); 152.1;
150.5; 148.7; 138.3; 131.2; 130.0; 128.2; 125.1; 114.5;
108.0 (ArC); 65.0 (OCH2Pz); 54.1 (NCH2CO2H); 50.5
(PzCH2N).
Compound 6a data. MS: (L-SIMSC):1135 (MCNaC, 70).
1H NMR: (CDCl3) d (ppm) (300 MHz):8.51 (4H, m,
Pz(H5)); 8.10–7.53 (6H, m, Py(H) and Ar(H)); 7.44 (2H,
t, JZ7.6 Hz, Py(H4)); 7.11 (1H, d, JZ8.7 Hz, Ar(H5));
6.55 (4H, m, Pz(H4)); 5.36 (2H, s, p-OCH2Pz); 5.32 (2H, s,
m-OCH2Pz); 4.03 (4H, s, PzCH2N); 3.50 (8H, s, NCH2-
CO2t Bu); 2.53 (3H, s, CH3CO); 1.47 (36H, s, COt2Bu). 13C
NMR: (CDCl3) d (ppm) (75 MHz): 196.6 (CO); 170.4
(COt2Bu); 153.5; 152.9; 151.4; 151.2; 150.0; 149.8; 148.3;
141.4; 141.2; 133.1; 130.9; 129.7; 128.3; 128.2; 128.0;
127.7; 123.5; 114.1; 113.0; 109.4; 108.9; 108.8; 108.4;
108.1; 107.7; 107.5 (ArC); 80.9 (C(CH3)3); 65.4 (OCH2Pz);
65.2 (OCH2Pz); 55.3 (NCH2CO); 51.1(NCH2Pz); 28.1
(C(CH3)3).
Acknowledgements
´
Financial support from Comision Interministerial de
Ciencia and Tecnologıa of Spain and indirect funding
´
from FYSE-ERCROS S.A. are gratefully acknowledged.
Compound 6b data. 1H NMR: (CDCl3) d (ppm) (200 MHz):
8.50 (4H, m, Pz(H5)); 7.97–7.36 (13H, m, Py(H) and
Ar(H)); 7.15 (1H, d, JZ8.3 Hz, Ar(H5)); 6.60 (4H, m,
Pz(H4)); 5.40 (2H, s, p-OCH2Pz); 5.35 (2H, s, m-OCH2Pz);
4.05 (4H, s, PzCH2N); 3.51 (8H, s, NCH2COt2Bu); 1.48
(36H, s, COt2Bu). 13C NMR (CDCl3) d (ppm) (75 MHz):
195.3 (CO); 170.3 (CO2H); 153.3; 152.5; 151.4; 151.2;
149.9; 149.6; 148.0; 141.3; 141.2; 138.0; 131.8; 130.6;
129.6; 128.0; 127.9; 128.5; 116.1; 112.9; 109.4; 109.3;
107.6; 107.5 (ArC); 80.9 (C(CH3)3); 65.4 (OCH2Pz); 65.2
(OCH2Pz); 59.9; 55.3 (NCH2CO); 55.1 (NCH2Pz); 28.1
(C(CH3)3.
References and notes
1. For very recent examples see: Bassett, A. P.; Magennis, S. W.;
Glover, P. B.; Lewis, D. J.; Spencer, N.; Parsons, S.; Williams,
R. M.; De Cola, L.; Pikramenou, Z. Highly Luminescent,
triple- and quadruple-stranded, dinuclear Eu, Nd, and Sm(III)
lanthanide complexes based on bis-diketonate ligands.
J. Am. Chem. Soc. 2004, 126, 9413–9424. Ramirez, F. M.;
Charbonniere, L.; Muller, G.; Bunzli, C. G. Tuning the
stoichiometry of lanthanide complexes with calixarenes:
Bimetallic complexes with a calix[6]arene bearing ether-
amide pendant arms. Eur. J. Inorg. Chem. 2004, 11,
2348–2355. Eliseeva, S. V.; Mirzov, O. V.; Troyanov, S. I.;
Vitukhnovsky, A. G.; Kuzmina, N. P. Synthesis, characteriz-
ation and luminescence properties of europium(III) and
terbium(III) complexes with 2-pyrazinecarboxylic acid. Crys-
tal structure of [Eu(pyca)3(H2O)2]$6H2O. J. Alloys Comp.
2004, 374, 293–297. Atkinson, P.; Bretonniere, Y.; Parker, D.
Chemoselective signalling of selected phospho-anions using
lanthanide luminescence. Chem. Commun. 2004, 438–439.
Quici, S.; Marzanni, G.; Forni, A.; Accorsi, G.; Barigelletti, F.
New lanthanide complexes for sensitized visible and near-IR
light emission synthesis, 1H NMR, and X-ray structural
investigation and photophysical properties. Inorg. Chem.
2004, 43, 1294–1301. Teotonio, E. E. S.; Felinto,
M. C. F. C.; Brito, H. F.; Malta, O. L.; Trindade, A. C.;
Najjar, R.; Strek, W. Synthesis, crystalline structure and
photoluminescence investigations of the new trivalent rare
earth complexes (Sm3C, Eu3C and Tb3C) containing
2-thiophenecarboxylate as sensitizer. Inorg. Chim. Acta
2004, 357, 451–460.
4.2.3. N,N,N0,N0-3,4-Bis-{[6-(3-aminomethyl-1-pyrazo-
lyl)-pyridin-2-yl]-1H-pyrazol-3-yl-methoxy} acetophe-
none tetracetic acid (3a) and N,N,N0,N0-3,4-bis-{[6-(3-
aminomethyl-1-pyrazolyl)-pyridin-2-yl]-1H-pyrazol-3-
yl-methoxy}benzophenone tetracetic acid (3b). A solu-
tion of tetraester (6a or 6b), (0.07 mmol), trifluoroacetic
acid (TFA) (1 mL) in dichloromethane (2 mL) was stirred at
rt for 18 h. The solvent is then removed in vacuo and the
residue was crushed in diethyl ether. The resulting white
solid 3a or 3b was filtered. Yield 65–70%.
Compound 3a data. Mp: 190–192 8C. MS: (L-SIMSC): 889
(MCHC, 79), 911 (MCNaC, 100). Anal. calc. for:
C13H13N5O.22CF3CO2H Calc(%): C 49.47; H 3.79; N
1
15.05. Found(%): C 49.16; H 3.83; N 15.73. H NMR:
(DMSO-d6) d (ppm) (300 MHz): 8.89 (2H, m, Pz(H5)); 8.84
(2H, m, Pz(H5)); 8.09 (2H, t, JZ7.8 Hz, Py(H4)); 7.76–7.63
(6H, m, Py(H3,5) and Ar(H2,6)); 7.30 (1H, d, JZ8.5 Hz,
Ar(H5)); 6.70 (1H, m, Pz(H4)); 6.67 (1H, m, Pz(H4)); 6.53
(2H, m, Pz(H4)); 5.30 (2H, s, p-OCH2Pz); 5.26 (2H, s,
m-OCH2Pz); 3.92 (4H, s, PzCH2N); 3.45 (8H, s, NCH2-
CO2H); 2.51 (3H, s, CH3CO). 13C NMR: (DMSO-d6) d
(ppm) (75 MHz): 196.5 (CO); 172.5 (CO2H); 152.5; 151.5;
151.2; 149.6; 149.4; 147.8; 142.8; 130.5; 129.4; 129.1;
123.7; 113.6; 113.2; 109.2; 108.8; 108.6 (ArC); 64.6
(OCH2Pz); 64.4 (OCH2Pz); 55.7 (NCH2CO2H); 51.9
(PzCH2N); 26.6 (CH3).
´
2. Rodrıguez-Ubis, J. C.; Sedano, R.; Barroso, G.; Juanes, O.;
Brunet, E. Lanthanide complexes of polyacid ligands derived
from 2,6-bis(pyrazol-1-yl)pyridine,-pyrazine, and 6,60-bis-
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´
´
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3. Remuin˜an, M. J.; Roman, H.; Alonso, M. T.; Rodrıguez-Ubis,
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Compound 3b data. Mp: 184–185 8C. MS: (L-SIMSC): 951
1
(MCHC, 13); 973 (MCNaC, 7). H NMR: (DMSO-d6) d
´
4. Rodrıguez-Ubis, J. C.; Alonso, M. T.; Juanes, O.; Sedano, R.;
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Pz(H5)); 8.10 (2H, m, Py(H4)); 7.78–7.36 (12H, m,

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