Calix[6]arene-picolinamide extractants for radioactive waste treatment: Effect of additional carboxy binding Sites in the pyridine 6-positions on complexation, extraction efficiency and An/Ln separation

Article abstract of DOI:10.1002/ejoc.200901479

The effect of the presence of an additional ester or amide carboxy group in the 6-position of the pyridine nuclei of calixarene-based picolinamide ligands on the extraction and complexation properties of lanthanide(III) and actinide(III) metal ions was studied. For this purpose, six new ligands 1-6 were synthesized; their conformational properties were studied both in solution and in the solid state, and their binding properties towards lanthanide (Ln ^III) and actinide (An^III) metal ions were determined under extracting conditions simulating those present in radioactive waste. In the presence of BrCosan as synergizer, a rather high efficiency in the extraction of trivalent metal ions by these ligands was observed even at [HNO₃] > 2-3 M. Complexation of Ln^III metal ions was also studied under homogeneous conditions (methanol solution), both in chloride and nitrate media, by using spectrophotometry and calorimetry. A comparison with the data obtained with ligands L1-L3, lacking the additional binding sites in the 6-position of the pyridine nuclei, is reported and the effects of the structure of the ligands on the stoichiometry of the complexes, coordination of the metal ions, basicity of the pyridine binding groups and efficiency and selectivity in the extractions are also discussed.

Full text of DOI:10.1002/ejoc.200901479

FULL PAPER
DOI: 10.1002/ejoc.200901479
Calix[6]arene-Picolinamide Extractants for Radioactive Waste Treatment:
Effect of Additional Carboxy Binding Sites in the Pyridine 6-Positions on
Complexation, Extraction Efficiency and An/Ln Separation
Elena Macerata,[a] Francesco Sansone,[b] Laura Baldini,[b] Franco Ugozzoli,[c]
Frederic Brisach,[d,e] Jaouad Haddaoui,[d,e] Véronique Hubscher-Bruder,[d,e]
Françoise Arnaud-Neu,[d,e] Mario Mariani,*[a] Rocco Ungaro,[b] and Alessandro Casnati*[b]
Dedicated to Professor Saverio Florio on the occasion of his 70th birthday
Keywords: Calixarenes / Actinides / Lanthanides / Waste treatment / N ligands
The effect of the presence of an additional ester or amide
carboxy group in the 6-position of the pyridine nuclei of ca-
lixarene-based picolinamide ligands on the extraction and
complexation properties of lanthanide(III) and actinide(III)
metal ions was studied. For this purpose, six new ligands 1–
6 were synthesized; their conformational properties were
studied both in solution and in the solid state, and their bind-
ing properties towards lanthanide (LnIII) and actinide (AnIII)
metal ions were determined under extracting conditions sim-
ulating those present in radioactive waste. In the presence of
BrCosan as synergizer, a rather high efficiency in the extrac-
tion of trivalent metal ions by these ligands was observed
even at [HNO3] Ͼ 2–3
. Complexation of LnIII metal ions
M
was also studied under homogeneous conditions (methanol
solution), both in chloride and nitrate media, by using spec-
trophotometry and calorimetry. A comparison with the data
obtained with ligands L1–L3, lacking the additional binding
sites in the 6-position of the pyridine nuclei, is reported and
the effects of the structure of the ligands on the stoichiometry
of the complexes, coordination of the metal ions, basicity of
the pyridine binding groups and efficiency and selectivity in
the extractions are also discussed.
fact, would allow the long-lived minor actinides (Np, Am,
Cm) to be transmutated in fast nuclear reactors or dedi-
cated devices, which would therefore minimize radiotoxicity
in the ultimate waste, making nuclear power plants more
efficient and sustainable.[2–5] A rather selective solvent ex-
traction process based on heterocyclic polynitrogen li-
gands[6] has been proposed and tested for AnIII/LnIII sepa-
ration from 1  nitric acid solutions,[7] but new ligands are
still needed that could work at even higher nitric acid con-
centrations.
It was demonstrated that the preorganisation of binding
groups on macrocycles[8] such as calixarenes,[9–15] resorcar-
enes[16] or tripodal scaffolds[17,18] strongly enhances the effi-
ciency in extraction. We previously found that calixarene-
based picolinamide ligands (e.g., L1–L3) are rather efficient
Introduction
Since the last decade, the chemistry of the nuclear fuel
cycle[1] has focussed on the difficult and ambitious goal of
separating actinides from lanthanides in solutions derived
from nuclear fuel reprocessing plants. This separation, in
[a] Dip.to di Energia – Sezione Ingegneria Nucleare Ce.SNEF, Po-
litecnico di Milano,
Via Ponzio 34/3, 20133 Milano, Italy
Fax: +39-02-23996309
E-mail: mario.mariani@polimi.it
[b] Dip.to di Chimica Organica e Industriale, Università di Parma,
Viale G.P. Usberti 17/A, 43124 Parma, Italy
Fax: +39-0521-905472
E-mail: casnati@unipr.it
[c] Dip.to di Chimica Generale ed Inorganica, Chimica Analitica,
Chimica Fisica, Università di Parma,
Viale G.P. Usberti 17/A, 43124 Parma, Italy
Fax: +39-0521-905557
and selective (separation factors SFAm/Eu
D
=
DAm/
Eu Յ11.4), at least up to [HNO3] = 10–2/10–3 .[9] More
recently, we also showed that calixarene-based picolinamide
ligands having electron-withdrawing groups in the para po-
sition of the pyridine nuclei are able to extract trivalent
metal ions into the organic phase even at higher nitric acid
concentrations.[19] Although it is well known that the intro-
duction of additional binding sites such as carboxylic acid,
ester or amide groups in the ortho position to the heterocy-
E-mail: ugoz@unipr.it
[d] Université de Strasbourg, IPHC,
25 rue Becquerel, 67087 Strasbourg, France
Fax: +33-3-68852747
E-mail: farnaud@chimie.u-strasbg.fr
[e] CNRS, UMR7178,
67037 Strasbourg, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200901479.
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M. Mariani, A. Casnati et al.
FULL PAPER
clic N atom of pyridine,[20,21] bipyridine[22] and phenan- 16 with active esters 11–14 at 90 °C in toluene for 24 h
throline[23] strongly increases their coordination ability to- (Scheme 3) afforded final ligands 1–4 in 76–88% yield. Fi-
ward highly charged lanthanide and actinide metal ions, nally, secondary butyl amide derivative 5 was obtained
nothing is known, to the best of our knowledge, on their (66%) by heating methyl ester 1 at reflux in neat butylamine
effect on An/Ln selectivity. We have therefore synthesised a for 5 d, whereas hexaacid 6 was easily isolated (88%) by
series of novel calixarene-based picolinamide ligands 1–6 hydrogenolysis of benzyl ester 2. Hexaacid 6 is completely
bearing additional carboxylic ester, amide and acid moieties insoluble in both polar and apolar organic solvents, and it
in the 6-position of the pyridine nuclei and studied how shows moderate solubility only in acetone/alcohol mixtures.
1
these substituents affect An/Ln selectivity and the efficiency The peaks in the H NMR spectra of compounds 1–5 in
of extraction at low pH values.
CDCl3 at room temperature are very broad because of ex-
tensive H-bonding between the picolinamide groups at the
lower rim of the calixarenes. At room temperature in [D6]-
DMSO, the resonances in the 1H NMR spectra become
slightly sharper as a result of H-bond breaking. Sharp sing-
lets and multiplets could be found only when the spectra
were recorded at high temperatures in this solvent. The
presence of singlets for the methylene bridge (ArCH2Ar)
protons around 3.9 ppm clearly indicates fast interconver-
sion between different conformations for these compounds.
Low-temperature 1H NMR spectra in CDCl3 were also reg-
istered for compound 5, which showed that the calixarene
was blocked in a single conformation at –10 °C. Two dou-
blets (δ = 4.48 and 3.42 ppm, 4 H each) and a singlet (δ =
3.90 ppm, 4 H) are present for the methylene bridge (Ar-
CH2Ar) protons, which together with all the other signals
are indicative of a centre of symmetry in the molecule (Fig-
ures S1–S5, Supporting Information), thus suggesting a
1,2,3-alternate structure for 5 in solution. The 13C NMR
spectra, on the other hand, are usually sharp in [D6]DMSO
at room temperature (see Supporting Information). A single
crystal, suitable for X-ray diffraction studies, was obtained
for compound 2. In Figure 1, the molecular structure of
complex 2·2H2O is illustrated, showing the macrocycle to
be in a conformation quite similar to that determined for
ligand 5 in solution. This confirms, once again, that the
1,2,3-alternate structure is rather common and highly pre-
ferred for hexasubstituted calix[6]arene macrocycles.[9,19]
Complex 2·2H2O is centrosymmetric and the conformation
of the calix[6]arene basket is unequivocally defined by the
conformational parameters[26,27] φ and χ and by the dihe-
dral angles[28] δ reported in Table 1. As a result of the inver-
sion centre, the opposite phenolic rings are antiparallel in
pairs (A is antiparallel to AЈ and so on).
Results and Discussion
Synthesis and Conformations of the Ligands
We previously demonstrated[9] that lower-rim picolinam-
ide calix[n]arenes (e.g., L1–L3) can be efficiently synthesised
through reaction with the pentafluorophenyl esters of pico-
linic acids. Following a similar strategy, we prepared penta-
fluorophenyl esters 11–14 (Scheme 1) by treating picolinic
acids (7–10) modified in the 6-position with methyl ester,
benzyl ester, diethylacetamido or acetylamino groups,
respectively, with dicyclohexylcarbodiimide (DCC) and
pentafluorophenol (68–99% yield).
Scheme 1.
Compounds 7,[24] [25] and 10[24] were prepared according
8
to literature procedures, whereas monoamido derivative 9
of dipicolinic acid was synthesised according to Scheme 2.
The monomethyl ester of dipicolinic acid 7 was transformed
Scheme 2.
The orientation of the amide chains at the calixarene
into the acyl chloride and subsequently into the mono- subunits A and B, extended far from the calix[6]arene bas-
amido-monomethyl ester derivative 15, which was hydro- ket, is determined by the two intramolecular N1A–H···N2A
lysed to compound 9 with KOH in aqueous methanol (76% and N1B–H···N2B hydrogen bonds (see Table 2 for geomet-
overall yield). Reaction of 3-aminopropyloxycalix[6]arene rical parameters of hydrogen bonds), whereas the amide
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Calix[6]arene-Picolinamide Extractants for Radioactive Waste Treatment
Scheme 3.
chain at the calixarene subunit C is folded close to the calix-
[6]arene basket due to the intramolecular hydrogen bond
N1C–H···O1C.
Table 2. Geometrical parameters for hydrogen-bonding interactions
found in the structure of 2·2H2O.
Donor–H···Acceptor
H···A (Å)
D···A (Å)
D–H···A (°)
N1B–H···O1W
N1C–H···O1C
N1A–H···N2A
N1B–H···N2B
N1C–H···N2C
2.133(9)
2.206(2)
2.212(3)
2.310(3)
2.314(3)
3.038(9)
2.839(4)
2.660(3)
2.668(4)
2.738(4)
156.6(3)
122.4(2)
107.3(2)
101.2(2)
106.0(2)
Two water molecules, O1W and the centrosymmetric one
O1WЈ, are linked to the host by the strong intermolecular
hydrogen bonds N1B–H···O1W and N1BЈ–H···O1WЈ. The
role of the water molecules is pivotal in the crystal packing.
In fact, as shown in Figure 2, in the symmetry-extended
structure, each water molecule acts as a hydrogen-bond ac-
ceptor from the N1B–H group of one complex, and con-
temporarily it acts as a hydrogen-bond donor towards the
oxygen atom O2B of the first neighbouring complex. Then,
because of the centre of symmetry, the complexes are self-
assembled in 1D polymeric chains in which pairs of nearest
Figure 1. Perspective view of the molecular structure of complex
2·2H2O (primed atoms are related to the unprimed ones by the
centre of symmetry). Only hydrogen bonds (dotted lines) with water
molecules (black spheres) have been evidenced. Atoms are as fol-
lows: C, light grey; N, grey; O, black, H, white. For a coloured
picture see Figure S6 in the Supporting Information.
Table 1. Conformational parameters φ and χ (the symbolic repre-
sentation of the molecular conformation is Ci +–, ++, –+), and
dihedral angles δ [°] between the reference plane R (the weighted
least-squares plane through the CH2 bridging groups) and the
planes of the aromatic rings (A,B,C,AЈ,BЈ,CЈ) in the molecular
structure of 2·2H2O.
Conformational parameters
Dihedral angles
φ (°)
χ (°)
δ (°)
C–B
B–A
95.1(6)
87.2(4)
–23.4(5)
73.6(6)
A–R
B–R
302.8(1)
69.8(1)
Figure 2. Perspective view of the polymeric self-assembly of 2·2H2O
in the crystal lattice. Only hydrogen bonds (dotted lines) with water
molecules (black spheres) have been evidenced. Atoms are as fol-
lows: C, light grey; N, grey; O, black, H, white. For a coloured
picture see Figure S7 in the Supporting Information.
A–CЈ
CЈ–BЈ
BЈ–AЈ
AЈ–C
–19.4(5)
–23.4(5)
–87.2(4)
19.4(5)
104.1(5)
95.1(6)
–73.6(6)
–104.1(5)
C–R
AЈ–R
BЈ–R
CЈ–R
138.5(1)
360-δA–R
360-δB–R
360-δC–R
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M. Mariani, A. Casnati et al.
FULL PAPER
neighbouring complexes along each polymeric chain are Table 3. Solubility and third-phase formation issues of the extract-
ants in the different diluents.
held together by four hydrogen bonds with two water mole-
cules.
Diluent
Solubility
Third-phase
formation
Soluble
Insoluble
NPHE
Methyl hexyl ketone
1-Octanol
NPHE/ACP, 70:30
NPHE/ACP, 50:50
NPHE/ACP, 20:80
1–5
6
1–6
3, 5
6
2,[a] 3, 4, 5[a]
Extraction Properties
1, 2, 6
1–5
1–5
1–5
6[a]
3,[b] 4,[b] 5[b]
4[b]
Novel calix[6]arene-based picolinamide derivatives 1–6
were studied in the extraction of americium and europium
from acidic solutions, with or without a synergistic agent.
In the present work, a large lipophilic cobalt bisdicarbollide
anion (BrCosan, Figure 3) was used as a synergizer. The
data were collected according to the procedure described in
the Experimental Section.
6
6
4[b]
[a] It was impossible to reach complete phase separation. [b] The
formation of a negligible third phase was observed.
extracting properties was observed. Table 4 reports the
distribution coefficients (DM) and the separation factor
(SFAm/Eu) for all the ligands as a function of the percentage
of NPHE in the diluent mixture. In general, the DAm and
DEu values strongly increase by increasing the percentage of
NPHE, as expected by the increase in the polarity of the
medium passing from ACP (17.9 D) to NPHE (25.7 D). In
particular, the greatest improvements in the DM values were
observed for ligands 1, 3 and 5. Moreover, for ligands 3 and
4, the extraction of AmIII and EuIII is similarly influenced
and the selectivity remains constant, whereas for ligands 1,
2 and 5 the variation in the mixture composition affects
much more the extraction of AmIII, leading to higher sepa-
ration factors.
The effect of the concentration of the synergizer on the
extracting properties of the new ligands was considered by
testing the molecules at increasing concentrations of the li-
pophilic anion. All the ligands are poorer extractants in the
Figure 3. Molecular structure of the BrCosan anion (for a coloured
picture see Figure S8 in the Supporting Information).
First, we tested the compounds in o-nitrophenyl hexyl absence of the synergizer. Other studies in the literature
ether (NPHE), a diluent already considered in previous showed that calixarenes in combination with lipophilic
studies for industrial process applications. The preliminary anions exhibit a synergistic effect in the extraction of tri-
tests outlined solubility problems in this solvent for some valent metal ions.[9,29] Figures 4, 5 and 6 show the effect of
of the ligands and difficulties in the extraction tests due the BrCosan concentration on the extraction capability of
to the formation of a third phase. For these reasons, we ligands 1, 2 and 5, respectively, in a mixture of NPHE/ACP
considered different diluents, such as alcohols, ketones or (70:30). The results underline that the ligand/synergizer ra-
ethers, and their mixtures, to select a diluent in which all tio strongly affects the extraction efficiency with a compar-
the ligands were soluble (Table 3).
able effect for AmIII and EuIII. An increase of two orders
The addition of different amounts of acetophenone of magnitude in DM was observed when [BrCosan] passed
(methyl phenyl ketone/ACP) to NPHE enabled most of from 1 to 6 m. Similar experiments, carried out in the ab-
these difficulties to be overcome. Anyway, it was not pos- sence of any calixarene ligand and with the only BrCosan
sible to find a proper solvent mixture for hexaacid 6. There- in the organic phase, clearly showed that the synergizer
fore, extraction tests with ligand 6 were not continued. alone does not significantly extract AnIII or LnIII ions
Then, different NPHE/ACP mixtures were considered and (Table S1, Supporting Information). On the contrary, the
a strong influence of the diluent composition on the separation factors are influenced to a lesser extent.
Table 4. DAm, DEu and SFAm/Eu as a function of the percentage of NPHE in the mixture. Experimental conditions: [ligand] = 1 m,
[BrCosan] = 1.5 m, diluent = NPHE/ACP and [H+] = 0.1 .
20% NPHE
50% NPHE
70% NPHE
100% NPHE
DAm
DEu
SFAm/Eu
DAm
DEu
SFAm/Eu
DAm
DEu
SFAm/Eu
DAm
DEu
SFAm/Eu
1
2
3
4
5
0.0035
0.057
0.126
0.0082
0.058
0.0015
0.028
0.093
0.0117
0.043
2.31
2.01
1.35
0.70
1.35
0.191
0.214
41.99
0.081
4.99
0.063
0.096
31.87
0.122
2.69
3.05
2.22
1.32
0.66
1.86
9.61
8.95
4552
0.84
212.91
2.85 3.37
2.51 3.57
1058
–
322.02
–
3.28
[a]
[a]
[a]
–
3706
1.23
1.29 0.65
92.89 2.29
ϾϾ5000 ϾϾ5000
1.61 2.53
–
0.64
[a]
[a]
[a]
–
–
–
[a] Data not available due to incomplete phase separation.
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Calix[6]arene-Picolinamide Extractants for Radioactive Waste Treatment
Figure 4. Extraction of AmIII and EuIII from nitric acid (0.1 ) at
25 °C by ligand 1 as a function of the concentration of BrCosan.
Figure 6. Extraction of AmIII and EuIII from nitric acid (0.1 ) at
25 °C by ligand 5 as a function of the concentration of BrCosan.
decrease in the values of DM upon increasing the concentra-
tion of HNO3 as a result of the protonation of the pyridine
nitrogen atoms of the picolinamide binding groups. How-
ever, some general important considerations can be drawn
from all these results. Ligand 3, functionalised with a terti-
ary amide, shows the highest extraction efficiency among
all the ligands. This behaviour is expected and explained by
the fact that the amide C=O oxygen atom is much more
basic and therefore coordinating. At the same time, this li-
gand is among the less selective. Similar behaviour was ob-
served for ligand 5, functionalised with a secondary amide.
It shows high distribution coefficients at [H+] = 0.1 , even
if lower than those of ligand 3, but a slightly higher selectiv-
ity.
Ligands 1 and 2, functionalised with methyl and benzyl
esters, respectively, show rather similar behaviour, both hav-
ing a markedly high selectivity and a decrease in the values
of DM by nearly two orders of magnitude on passing from
Figure 5. Extraction of AmIII and EuIII from nitric acid (0.1 ) at
25 °C by ligand 2 as a function of the concentration of BrCosan.
Finally, it was observed that the synergism between the [H+] = 0.01 to 0.1 . Picolindiamide ligands 3 and 5 display
ligand and the dicarbollide anion is affected by the diluent. higher chelating ability towards trivalent LnIII and AnIII
As shown in Table 5, in particular for ligand 2, the distribu- metal ions compared to monoester-monoamide derivatives
tion coefficients for Am and Eu increase by a factor 2 in 1 and 2. This is due to the higher basicity of both the pyr-
the mixture NPHE/ACP, 20:80, and by a factor 8 in the idine N atom and the additional amide carbonyl group. The
mixture 70:30, when the synergizer concentration was much higher coordination ability of picolindiamide ligands
doubled.
3 and 5 strongly reduces the competition with the proton
To assess the influence of the acidity of the aqueous (even if the latter is at least six orders of magnitude more
phase on the extracting properties of the new picolinamide concentrated than the cations) and allows these ligands to
extractants, we performed a series of liquid–liquid extrac- be rather efficient extracting agents even at [H+]Ն1 
tion tests in NPHE/ACP (70:30) by varying [H+] between (Tables 6 and 7). Ligand 4 also possesses two amide groups
0.01 and 1  (Table 6). All the ligands showed a remarkable per pyridine nuclei, but the CH3C=O group does not give
Table 5. Comparison of the extracting properties in two different diluent mixtures (NPHE/ACP, 20:80 and 70:30) with increasing concen-
tration of BrCosan. Experimental conditions: [ligand] = 1 m and [H+] = 0.1 .
1
2
5
[BrCosan]
NPHE/ACP, 20:80 NPHE/ACP, 70:30 NPHE/ACP, 20:80 NPHE/ACP, 70:30 NPHE/ACP, 20:80
NPHE/ACP, 70:30
DAm
DEu
DAm
DEu
2.85
16.17
DAm
0.057
0.107
DEu
0.028
0.051
DAm
DEu
2.51
21.2
DAm
0.058
0.956
DEu
0.043
0.637
DAm
DEu
0.0015 
0.003 
0.0035
0.0178
0.0015
0.0074
9.61
56.61
8.95
68.64
212.91
3151
92.89
1625
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M. Mariani, A. Casnati et al.
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Table 6. Distribution coefficients and separation factors of the li- at very low [H+] but strongly decreases with a slight increase
in the acidity of the aqueous phase (see data for L1 at [H+]
= 0.005 and 0.1 ), the separation factors of ligands 1 and
3 around 3 and 1, respectively, seem to be constant even at
high concentrations of nitric acid.
gands studied as a function of the acidity of the aqueous phase.
[ligand] = 1 m, [BrCosan] = 1.5 m, diluent = NPHE/ACP, 70:30.
[H+]
0.01
1
2
3
4
5
DAm
952.45 933.31 ϾϾ5000 893.63 ϾϾ5000
0.05
0.1
0.5
1
–
9.61
–
37.58
8.95
–
–
4552
–
–
0.84
–
–
212.91
12.03
2.52
Complexation Properties in Methanol
0.004
0.024
1.55 0.0011
The complexation properties of the best extracting li-
gands 3 and 5 with La3+, Eu3+ and Yb3+ chlorides were
studied in methanol by using UV/absorption spectropho-
tometry. For comparison purpose, the properties of L1–L3
were also investigated. In all cases the spectrophotometric
titrations led to significant spectral changes, especially with
the hexamers. The complexation of LaCl3 by ligand 5 is
illustrated in Figure 7 as an example. The stability constants
and stoichiometry of the complexes were calculated from
the absorbance variations by the Specfit software. The re-
sults, corresponding in each case to at least three indepen-
dent experiments, are given in Table 8.
DEu
0.01
0.05
0.1
0.5
1
396.27 534.48 ϾϾ5000 1337
ϾϾ5000
–
–
2.85
–
12.41
2.51
–
–
3706
–
–
1.29
–
92.89
3.36
1.77
0.0014
0.009
1.29 0.0017
SFAm/Eu 0.01
2.40
–
3.37
–
1.75
3.03
3.57
–
–
–
0.67
–
–
–
2.29
3.60
1.43
0.05
0.1
0.5
1
1.23 0.65
–
–
2.86
2.75
1.20 0.65
rise to such an efficient chelating effect with the heterocyclic
N atom. Selectivity for ligand 4 is also inverted compared
to that of the other ligands, as it extracts LnIII better than
AnIII
.
Table 7. Comparison among ligands L1–L3 and newly synthesised
1 and 3 in NPHE. The concentrations of the ligand and the synerg-
izer were changed due to solubility problems.
[H+]
L1[a]
L2[b]
L3[b]
1[a]
3[c]
DAm
0.001
0.005
0.1
2
2.5
3
–
16.3
173
–
–
–
–
277.95
0.0317
–
–
–
–
–
–
–
–
–
–
–
–
–
ϾϾ1000 ϾϾ1000
42.22
–
–
88.32
–
8.94
DEu
0.001
0.005
0.1
2
2.5
3
–
1.43
–
–
–
–
19.6
–
–
–
–
–
–
–
–
35.15
0.00878
ϾϾ1000 ϾϾ1000
13.39
–
Figure 7. Spectrophotometric titration of ligand 5 ([ligand] =
2.17ϫ10–5 ), lower spectrum, by a solution of LaCl3 in methanol
(0 Յ [La]/[ligand] Յ 8.5).
–
84.06
–
–
–
–
3.02
SFAm/Eu 0.001
–
11.4
8.8
–
–
–
–
–
–
–
3.16
–
–
–
–
–
1.05
–
Table 8. Overall stability constants (logβxy Ϯ σ) of lanthanide com-
plexes with ligands 3, 5 and L1–L3 in methanol ([Et4NCl] ϫ 10–2 ,
25 °C).
0.005
0.1
2
2.5
3
7.91
3.73
–
–
–
–
–
–
–
–
Ligand Complex
La3+
Eu3+
Yb3+
–
2.89
3
1:1
2:1
1:1
2:1
1:1
6.4Ϯ0.2
10.9Ϯ0.2
5.6Ϯ0.4
10.5Ϯ0.4
5.3Ϯ0.1
5.3Ϯ0.2
10.5Ϯ0.2
4.6Ϯ0.2
10.3Ϯ0.2
5.9Ϯ0.2
6.00Ϯ0.05
11.7Ϯ0.1
5.0Ϯ0.3
11.3Ϯ0.2
5.9Ϯ0.2
[a] [1] = [L1] = 1 m and [BrCosan] = 3 m. [b] [L] = 10 m and
[BrCosan] = 3 m. [c] [3] = 1 m and [BrCosan] = 1.8 m.
5
Moreover, the electron-donating ability of the
CH3CONH nitrogen atom certainly strongly increases the
basicity of the pyridine N atom, which is probably already
protonated at [H+]Ն0.1 . This behaviour resembles that
of previously studied ligands L1–L3 in NPHE under the
same experimental conditions (Table 7).[9,30] Ligands L1–L3
showed interesting extracting properties, both in efficiency
and selectivity, but only at very low concentrations of the
acid ([H+]Յ0.005 ). On the contrary, in the case of newly
synthesised ligands 1 and 3, the distribution coefficients are
L1
(2.72Ϯ0.05)[a] (3.03Ϯ0.03)[a]
1:2
1:1
1:2
1:1
1:2
9.4Ϯ0.4
5.1Ϯ0.2
9.6Ϯ0.3
5.2Ϯ0.1
8.8Ϯ0.1
11.1Ϯ0.7
5.3Ϯ0.5
9.9Ϯ0.2
5.4Ϯ0.1
9.0Ϯ0.2
11.0Ϯ0.5
5.7Ϯ0.5
10.0Ϯ0.5
5.6Ϯ0.2
9.5Ϯ0.2
L2
L3
[a] 1:1 complexes in nitrate medium (nitrate salts and Et4NNO3 as
supporting electrolyte).
In all cases two complexes have been found in agreement
still well above unity at [H+] = 2.5 .[31] Moreover, whereas with the number of absorbing species found by the factor
the selectivity of ligands L1–L3 ranges between 7.9 and 11.4 analysis routine included in the program: four absorbing
2680
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2675–2686

Calix[6]arene-Picolinamide Extractants for Radioactive Waste Treatment
species were observed with Eu3+ corresponding to the li- Ͼ Eu3+ Ͼ La3+). However, the logarithms of the stepwise
gand, the metal and two complexes, whereas only three spe- stability constants of the 2:1 complexes increase in the
cies with La3+ and Yb3+ as these ions do not absorb in the series, from 4.5 (La3+) to 5.2 (Eu3+) and 5.7 (Yb3+) with 3
investigated region. The results show that the stoichiometry and from 4.9 (La3+) to 5.7 (Eu3+) and 6.3 (Yb3+) with 5. A
of the complexes differs from one ligand to another: 1:1 positive cooperative effect is found for the formation of the
and 2:1 (Ln/L) complexes are formed with 3 and 5, whereas 2:1 complexes only for 5 with Eu3+ and Yb3+. It is interest-
1:1 and 1:2 complexes are formed with hexamer L1 and ing to note that, despite the very small spectral changes
tetramers L2 and L3. The distribution curves correspond- observed during the spectrophotometric titrations of La3+
ing to the La3+–5 system are given in Figure 8. They show and Eu3+ nitrates with L1 in the presence of Et4NNO3, the
the coexistence of the two 1:1 and 2:1 complexes in a wide stability constants of the 1:1 complexes could be deter-
concentration range. Tetramers L2 and L3 form complexes mined. These values are much lower than those obtained
of similar stability (within experimental error), indicating in chloride medium (Table 8), showing a competition effect
that neither the upper rim substituent nor the linker length between the ligand and the nitrate anion.
between the calixarene and the picolinamide binding group
Calorimetric titrations have been performed with 3 and
play an important role in the binding efficiency. The com- 5 and europium chloride. The results are given in Table 9
plexes of hexamer L1 are slightly more stable. The stepwise and globally show a good agreement with the data obtained
stability constants for the 1:2 complexes of L1–L3 (logK2 = by spectrophotometry in terms of both stoichiometry and
logβ12 – logβ11 = 3.6–5.2) are lower than the logβ11 values stability of the complexes. With the two ligands, the forma-
(ranging between 5.1 and 5.9) for the 1:1 complexes.
tion of the 1:1 complex is characterised by strongly positive
T∆S11 values and very small –∆H11 values, which is consis-
tent with important desolvation effects upon complexation.
On the contrary, the formation of the 2:1 complex is en-
thalpy driven, as shown by highly favourable values of the
stepwise enthalpy changes (e.g., ∆H2 = ∆H21 – ∆H11
=
–58.7 kJmol–1 with 3), whereas the corresponding entropy
values are negative and unfavourable (e.g., T∆S2 = T∆S21
–
T∆S11 = –34 kJmol–1 with 3). This may indicate strong in-
teractions with the binding groups and/or strong rearrange-
ment of the ligand upon binding of the second cation.
Table 9. Stability constants (logβxy) and overall complexation
thermodynamic parameters (kJmol–1) of europium chloride by li-
gands 3 and 5.
Figure 8. Speciation curves (LnLH species) corresponding to the
Complexes
(Eu/L)
Thermodynamic
parameter
3
5
system La3+–5 ([ligand] = 2.17ϫ10–5 ).
1:1
logβ11
–∆G11
–∆H11
T∆S11
logβ21
–∆G21
–∆H21
T∆S21
5.4Ϯ0.2 (5.3)[a] 5.7Ϯ0.5 (4.6)[a]
These ligands do not display any remarkable selectivity
among lanthanides, although the trend is a slight increase
in stability from La3+ to Yb3+, which is consistent with the
increase in the charge density on the cations and in agree-
ment with the “classical” behaviour of lanthanide chelates.
The presence of an additional amide function on the picolin-
amide ring as in 3 and 5 does not significantly modify
the stability of the 1:1 complexes: La3+ forms more stable
complexes with 3 and 5 (logβ = 6.4 and 5.6, respectively)
than with L1 (logβ = 5.3), whereas the opposite trend is
found with Eu3+, which forms less stable complexes with 3
and 5 (logβ = 5.3 and 4.6) than with L1 (logβ = 5.9). How-
ever, completely different are the types of complexes formed
besides the 1:1 species: ligands 3 and 5, having three donor
atoms per picolinamide chain, form only 2:1 (Ln/L) com-
plexes, whereas ligands L1–L3 possessing only an oxygen
and a nitrogen donor atom give 1:2 species. The higher
number of binding sites (3ϫ6 = 18) present on picolindia-
mides 3 and 5 compared to L1 (2ϫ6 = 12) or L2 and L3
(2ϫ4 = 8) clearly allows the binding of two high coordina-
tion number lanthanide cations. With ligands 3 and 5 the
31Ϯ1
2.29Ϯ0.05
28Ϯ1
32Ϯ3
2.2Ϯ0.6
30Ϯ3
2:1
9.7Ϯ0.3 (10.5)[a] 10.8Ϯ0.3 (10.3)[a]
55Ϯ2
61Ϯ4
–6Ϯ5
62Ϯ2
40Ϯ6
22Ϯ8
[a] Spectrophotometric results.
The fact that the ∆H21 value is more negative
(–61 kJmol–1) for 3 bearing tertiary amides than for 5
bearing secondary amides (–40 kJmol–1) supports the as-
sumption that also the amide functions in the 6-position
of the pyridine ring are involved in cation binding. Such a
difference in the enthalpy contribution has already been
shown for alkali and alkaline earth metal ion complexes
with calix[4]arene derivatives substituted with both second-
ary and tertiary amides.[32,33]
Conclusions
stability order of the 1:1 complexes is La3+ Ͼ Yb3+ Ͼ Eu3+
,
Calixarene-based picolinamide ligands proved to be
in contrast with the sequence observed with L1–L3 (Yb3+ quite efficient complexing agents for trivalent lanthanide
Eur. J. Org. Chem. 2010, 2675–2686
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2681

M. Mariani, A. Casnati et al.
FULL PAPER
and actinide ions. In homogeneous solution (methanol), it calix[6]arenes 3 and 5 form 1:1 complexes in methanol of
was found that the stoichiometry of the complexes is similar stabilities (logβ = 4.6–6.4 vs. logβ = 5.0–6.4[34]) and
strongly dependent on the size of the macrocycle or the sub- have comparable values of SFAm/Eu in extraction,[35]
stitution of the pyridine nuclei. For unsubstituted picolin- whereas calix[4]arenes L2 and L3 form slightly less stable
amide binding groups (no substituents in the pyridine 6- complexes in methanol (logβ = 5.1–5.7) but are consider-
position, X6 = H), 1:1 and 1:2 (Ln/L) complexes are formed ably more selective in extraction (SFAm/Eu up to 11.4).
with calix[6]arene (L1) and calix[4]arenes (L2 and L3). It is
likely that the reduced number of donor atoms induces the
participation of the two macrocycles to complete the coor-
Experimental Section
dination sphere of the LnIII metal ion. On the other hand,
General Remarks: Melting points were determined with an Electro-
when picolinamide nuclei of calix[6]arenes are substituted
thermal apparatus in sealed capillaries under an atmosphere of ni-
in the 6-position with an additional binding group [X6 =
trogen. 1H and 13C NMR spectra were recorded with Bruker spec-
-CO(N)R1R2, in ligands 3 or 5], in addition to the 1:1 spe-
trometers AC300 (1H: 300 MHz, 13C: 75 MHz) with residual sig-
cies 2:1, (Ln/L) complexes also form. In this case, three do-
nals of partially deuterated solvents as internal standard. Mass
nor atoms are present for each picolindiamide chelating
spectra were obtained in the ESI mode with a Micromass 4LCZ or
unit allowing two metal ions with a high coordination
number such as LnIII to be bound. The calorimetric data
are in nice agreement with the spectrophotometric results
both in terms of stoichiometry and stability of the com-
plexes. In extraction experiments, the newly synthesised ca-
lix[6]arene ligands 1–5, bearing additional carboxy groups
in the 6-positions of the picolinamide nuclei, showed re-
markable efficiency in the extraction of both Eu3+ and
Am3+ ions, even at the very high concentrations of nitric
acid that are used for the treatment of nuclear waste. Com-
pared to ligands L1–L3 lacking the 6-substituents and
which are effective only at [HNO3]Յ0.05 , ligands 1–5
proved to be much more efficient: for instance, at [H+] =
0.1 , the value of DM for 3 is six orders of magnitude
higher than that of L1. This is due, on one side, to the better
chelation offered by the tridentate picolindiamide moiety
compared to the bidentate picolinamide one and, on the
in the CI (CH4) mode with Finnigan Mat SSQ710 spectrometers.
TLC was performed on precoated silica gel Merck 60 F254. All
solvents were purified by standard procedures; dry solvents were
obtained by literature methods and stored over molecular sieves.
All reactions were carried out under an atmosphere of nitrogen.
Dipicolinic acid monomethyl ester (7),[24] dipicolinic acid monob-
enzyl ester (8),[25] 6-acetylamino picolinic acid (10)[24,36] and hexa-
kis(3-aminopropoxy)calix[6]arene (16)[9] were prepared according
to the procedure reported in the literature.
2-(Methoxycarbonyl)-6-[(N,N-diethylamino)carbonyl]pyridine (15):
To a sample of monomethyl dipicolinate (7; 1.5 g, 8.28 mmol) in a
round-bottomed flask cooled with an ice bath was slowly added
thionyl chloride (20 mL) and a drop of DMF. The suspension was
stirred at 60 °C until all the solid dissolved (1 h). Thionyl chloride
was removed under reduced pressure and then dry DCM (30 mL)
was added. This solution was cooled with an ice bath and then
diethylamine (4.3 mL, 41.6 mmol) was added. The solution was
stirred at 40 °C for 2 h and then quenched with a solution of
other side, to the decrease in the basicity of the pyridine N NH4Cl. The organic layer was separated and washed with water
(2ϫ30 mL). DCM was then removed under reduced pressure to
atom due to the presence of an additional electron-with-
drawing group in the ortho position, which disfavours H+
binding and favours Ln3+ binding. The inversion of atom
attachment of the amide group from the carboxy group [X6
= -C(O)N] of ligand 3 or 5 to the N atom [X6 = -NC(O)]
changes the electronic effects on the pyridine N atom and
increases its basicity, so that compound 4 is at least 300
times less efficient already at pH 1. Finally, amide deriva-
tives 3 and 5 are by far more efficient than ester compounds
give a light brown oil. Yield: 1.91 g (98%). 1H NMR (300 MHz,
3
3
CDCl3, 298 K): δ = 8.11 (d, J = 7.6 Hz, 1 H, Py-H3), 7.90 (t, J
= 7.6 Hz, 1 H, Py-H4), 7.79 (d, J = 7.6 Hz, 1 H, Py-H5), 3.95 (s,
3 H, OCH3), 3.53 and 3.37 (2q, 3J = 6.9 Hz, 2 H each, NCH2),
1.24 and 1.21 (2t, 3J = 6.9 Hz, 3 H each, NCH2CH3) ppm. 13C{1H}
NMR (75 MHz, CDCl3): δ = 167.3 (COO), 165.2 (CON), 154.9
(Py-C2), 146.3 (Py-C6), 137.8 (Py-C4), 126.7 (Py-C5), 125.4 (Py-
C3), 52.7 (OCH3), 43.5 and 40.6 (NCH2), 14.1 and 12.7
(NCH2CH3) ppm. MS (ESI+): m/z
= 259.4 [M +
Na]+.
1 and 2. An opposite effect is found on the selectivity be- C12H16N2O3 (236.27).
tween An and Ln: diamides 3 and 5 are less selective than
monoamide-monoesters 1 and 2. In conclusion, as a general
trend, the introduction of additional carboxy substituents
in the 6-position of the picolinamide ligands supported on
2-(Hydroxycarbonyl)-6-[(N,N-diethylamino)carbonyl]pyridine (9):[37,38]
A suspension of compound 15 (1.91 g, 8.08 mmol) in a mixture of
MeOH/H2O (1:1, 80 mL) was cooled to 0 °C and then KOH
(0.91 g, 16.16 mmol) was added. After 2 h stirring, the reaction
a calixarene scaffold strongly increases the efficiency of ex- mixture was quenched with 0.2  aqueous HCl to pH 4. The aque-
ous phase was extracted with EtOAc (3ϫ50 mL). The solvent was
removed from the combined organic extract under reduced pres-
sure, and product 9 was obtained by precipitation with Et2O. Yield:
traction even at very high concentrations of HNO3 in the
water layer but, simultaneously, also lowers the separation
factors SFAm/Eu compared to previously synthesised picol-
inamide-based calixarene extractants (e.g., L1–L3). Owing
to the particular extraction conditions used (solvents, syner-
gizer and acidity) and to the stoichiometry of the complexes
formed by these multicoordinate ligands[8] in homogeneous
solution, a direct comparison with acyclic ligands is not
feasible. However, compared with lower-rim calix[4]arene
1
3
1.40 g (78%). H NMR (300 MHz, CDCl3, 298 K): δ = 8.25 (d, J
3
= 7.8 Hz, 1 H, Py-H3), 8.04 (t, J = 7.8 Hz, 1 H, Py-H4), 7.82 (d,
J = 7.8 Hz, 1 H, Py-H5), 3.58 and 3.30 (2q, 3J = 6.9 Hz, 2 H each,
NCH2), 1.28 and 1.19 (2t, 3J = 6.9 Hz, 3 H each, NCH2CH3) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 167.4 (COO), 165.1 (CON),
153.8 (Py-C2), 144.9 (Py-C6), 139.3 (Py-C4), 127.1 (Py-C5), 124.3
(Py-C3), 43.1 and 40.2 (NCH2), 14.3 and 12.7 (NCH2CH3) ppm.
tetracarbamoylmethyldiphenylphosphane oxide derivatives, MS (ESI+): m/z = 245.4 [M + Na]+. C11H14N2O3 (222.24).
2682 Eur. J. Org. Chem. 2010, 2675–2686
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Calix[6]arene-Picolinamide Extractants for Radioactive Waste Treatment
General Procedure for the Synthesis of Pentafluorophenyl Esters 11–
14: To a suspension of acid 7–10 (3.00 mmol) in dry DCM (20 mL)
was added dicyclohexylcarbodiimmide (DCC; 0.68 g, 3.30 mmol)
and pentafluorophenol (0.61 g, 3.30 mmol). After 3–8 h, the re-
sulting white solid of dicyclohexylurea (DCU) was filtered off and
washed carefully with DCM. The solvent was removed from the
combined filtrates under reduced pressure, and the product was
purified from this crude as reported below for the single com-
pounds.
then removed under reduced pressure, and the residue was purified
as reported below for the single products.
37,38,39,40,41,42-Hexakis{3-[(pyridine-6-methoxycarbonyl-2-carb-
oxy)amino]propoxy}calix[6]arene (1): The product was recrystallised
from hexane. Yield: 1.640 g (82 %); m.p. 184–185 °C. 1H NMR
(300 MHz, CDCl3, 298 K): δ = 8.40 (br. s, 12 H, NH and PyH),
2
2
8.18 (d, J = 7.5 Hz, 6 H, PyH), 7.96 (t, J = 7.5 Hz, 6 H, PyH),
7.30–6.90 (br. s, 18 H, ArH), 3.95–3.55 (br. s, 42 H, ArCH2Ar,
OCH3, OCH2), 3.10–2.90 (br. s, 12 H, NCH2), 2.05 (br. s, 12 H,
1
2-(2,3,4,5,6-Pentafluorophenoxycarbonyl)-6-(methoxycarbonyl)pyr-
OCH2CH2) ppm. H NMR (300 MHz, [D6]DMSO): δ = 8.51 (s, 6
idine (11): Reaction time, 3 h. Pure compound was obtained by
H, NH), 8.21–8.08 (m, 18 H, PyH), 7.2–6.7 (br. s, 18 H, ArH), 3.73
(s, 42 H, ArCH2Ar, OCH3, OCH2), 3.35 (br. s, 12 H, NCH2), 1.80
(br. s, 12 H, OCH2CH2) ppm. 13C{1H} NMR ([D6]DMSO,
75 MHz): δ = 164.4 (COO), 162.7 (CON), 154.3 (Aripso), 149.9 (Py-
C2), 146.2 (Py-C6), 139.1 (Py-C4), 134.1 (Arortho), 126.8 (Armeta),
124.9 (Py-C3, Py-C5), 123.3 (Arpara), 70.8 (OCH2CH2CH2), 52.3
(OCH3), 36.7 (OCH2CH2CH2), 29.7 and 29.5 (OCH2CH2CH2 and
ArCH2Ar) ppm. MS (ESI+): m/z = 1980.1 [M + Na]+, 1001.8 [M
+ 2Na]2+. C108H108N12O24·2H2O (1994.11): calcd. C 65.05, H 5.66,
N 8.43; found C 64.89, H 5.54, N 8.52.
1
crystallisation from hexane/DCM (9:1). Yield: 1.65 g (83%). H
NMR (300 MHz, CDCl3, 298 K): δ = 8.45 and 8.43 (2d, 3J =
7.8 Hz, 1 H each, Py-H5 and Py-H3), 8.13 (t, 3J = 7.8 Hz, 1 H, Py-
H4), 4.05 (s, 3 H, OCH3) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ
= 164.6 (COOMe), 160.5 (COO), 148.9 (Py-C6), 145.3 (Py-C2),
141.06 (dd, J = 250, 9 Hz, C2-C6F5), 140.3 (dt, J = 140, 12 Hz, C4-
C6F5), 138.3 (Py-C4), 136.9 (dt, J = 140, 9 Hz, C3-C6F5), 129.1
(Py-C3 and Py-C5), 125.0 (t, J = 8 Hz, C1-C6F5), 53.2 (OCH3)
ppm. MS (ESI+): m/z = 686.5 [M + Na]+.C34H38F5N3O5 (663.67).
2-(2,3,4,5,6-Pentafluorophenoxycarbonyl)-6-(benzyloxycarbonyl)pyr-
idine (12): Reaction time, 8 h. Pure compound was obtained by
crystallisation from Et2O. Yield: 1.55 g (70 %). 1H NMR
37,38,39,40,41,42-Hexakis{3-[(pyridine-6-benzyloxycarbonyl-2-carb-
oxy)amino]propoxy}calix[6]arene (2): The product was purified by
crystallisation from hexane/AcOEt (3:1). Yield: 1.185 g (86%); m.p.
3
(300 MHz, CDCl3, 298 K): δ = 8.43 and 8.38 (2d, J = 7.6 Hz, 1
1
125–126 °C. H NMR (300 MHz, CDCl3, 298 K): δ = 8.39 (br. s,
H each, Py-H5 and Py-H3), 8.09 (t, 3J = 7.6 Hz, 1 H, Py-H4), 7.49
(d, 3J = 7.6 Hz, BnH), 7.39 (m, 3 H, BnH), 5.49 (s, 2 H, OCH2)
ppm. MS (ESI+): m/z = 762.6 [M + Na]+. C40H42F5N3O5 (739.77).
12 H, Py-H3 and NH), 8.16 (br. s, 6 H, Py-H5), 7.92 (t, 3J = 7.5 Hz,
6 H, Py-H4), 7.32–7.28 (s, 30 H, PhH), 7.30–6.85 (br. s, 18 H,
ArH), 5.34 (br. s, 12 H, CH2Ph), 3.90–3.15 (br. s, 42 H, ArCH2Ar,
OCH2, CH2N), 2.00 (br. s, 12 H, OCH2CH2) ppm. 1H NMR
(300 MHz, [D6]DMSO, 373 K): δ = 8.21–8.18 (m, 12 H, Py-H3 and
NH), 8.13–8.03 (m, 12 H, Py-H4, Py-H5), 7.40–7.27 (m, 30 H,
2-(2,3,4,5,6-Pentafluorophenoxycarbonyl)-6-[(N,N-diethylamino)carb-
onyl]pyridine (13): Reaction time, 3 h. After a first trituration in
DCM, the resulting solid was purified by flash chromatography
(SiO2; hexane/EtOAc, 1:1 to 1:2). Yield: 2.09 g (99%). 1H NMR
(300 MHz, CDCl3, 298 K): δ = 8.31 (dd, J = 7.2, 2.1 Hz, 1 H, Py-
3
3
PhH), 6.88 (d, J = 7.5 Hz, 12 H, ArHmeta), 6.79 (t, J = 7.5 Hz, 6
H, ArHpara), 5.32 (s, 12 H, OCH2Ph), 3.91 (s, 12 H, ArCH2Ar),
3
3
3
H5), 8.1–8.0 (m, 2 H, Py-H4 and Py-H3), 3.59 and 3.46 (2q, J =
3.43 (t, J = 5.7 Hz, 12 H, OCH2CH2CH2), 3.33 (q, J = 6.6 Hz,
12 H, OCH2CH2CH2), 1.57 (quint., 3J = 6.6 Hz, 12 H, OCH2CH2)
ppm. 13C{1H} NMR (75 MHz, [D6]DMSO, 298 K): δ = 163.6
(COO), 162.7 (CON), 154.2 (Aripso), 150.1 (Py-C2), 146.1 (Py-C6),
139.1 (Py-C4), 135.6 (Ph-C1), 134.0 (Arortho), 128.2, 127.9 and
127.7 (Ph-C2, Ph-C6), 127.0 (Armeta), 125.0 (Py-C3, Py-C5), 123.3
(Arp a r a ), 70.6 (OCH2 CH2 CH2 ) , 6 6. 5 ( OC H2 Ph), 36.7
(OCH2CH2CH2), 29.6 (OCH2CH2CH2 and ArCH2Ar) ppm. MS
(ESI+): m/z = 2437.4 [M + Na]+. C144H132N12O24 (2414.65): calcd.
C 71.63, H 5.51, N 6.96; found C 71.42, H 5.64, N 7.02.
7.2 Hz, 2 H each, NCH2CH3), 1.32 (m, 6 H, NCH2CH3) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 166.6 (COO), 160.8 (CON),
155.3 (Py-C6), 143.3 (Py-C2), 141.3 (dd, J = 235, 9 Hz, C2-C6F5),
139.5 (dt, J = 130, 12 Hz, C4-C6F5), 138.3 (Py-C4), 137.9 (dt, J =
135, 9 Hz, C3-C6F5), 128.3 (Py-C3), 125.6 (Py-C5), 124.8 (t, J =
8 Hz, C1-C6F5), 43.8 and 40.9 (NCH2CH3), 14.1 and 12.6
(NCH2 CH3 ) ppm. MS (ESI+): m/z = 727.8 [M + Na]+ .
C37H45F5N4O4 (704.77).
2-(2,3,4,5,6-Pentafluorophenoxycarbonyl)-6-(acetylamino)pyridine
(14): Reaction time, 4 h. Pure compound was obtained by flash
chromatography (SiO2; DCM/EtOAc, 20:1 to 4:1). Yield: 1.36 g
(68 %). 1H NMR (300 MHz, CDCl3, 298 K): δ = 8.54 (d, 3J =
37,38,39,40,41,42-Hexakis{3-[(pyridine-6-N,N-diethylaminocarb-
onyl-2-carboxy)amino]propoxy}calix[6]arene (3): The product was
purified by precipitation with Et2O and column chromatography
(SiO2; 100% AcOEt to 50% AcOEt/MeOH). Yield: 1.21 g (76%);
m.p. 169–170 °C. 1H NMR (300 MHz, [D6]DMSO, 298 K): δ =
8.54 (br. s, 6 H, NH), 8.01 (m, 12 H, Py-H3, Py-H4), 7.65 (m, 6
H, Py-H5), 7.20 (br. s, 12 H, ArHmeta), 6.78 (br. s, 6 H, ArHpara),
3.74 (br. s, 12 H, ArCH2Ar), 3.45–3.00 (br. s, 48 H, OCH2CH2CH2
and NCH2CH3), 1.85 (br. s, 12 H, OCH2CH2), 1.04 and 0.94 (s, 18
H each, NCH2CH3) ppm. 1H NMR (300 MHz, [D6]DMSO,
345 K): δ = 8.24 (t, 3J = 5.7 Hz, 6 H, NH), 8.06–7.98 (m, 12 H,
3
7.8 Hz, 1 H, Py-H5), 8.32 (s, 1 H, NH), 8.01 (d, J = 7.8 Hz, 1 H,
Py-H3), 7.94 (t, 3J = 7.8 Hz, 1 H, Py-H4), 2.23 (s, 3 H, CH3) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 169.0 (CON), 160.8 (COO),
151.7 (Py-C6), 142.9 (Py-C2), 141.9 (dd, J = 230, 9 Hz, C2-C6F5),
140.2 (dt, J = 135, 12 Hz, C4-C6F5), 139.7 (Py-C4), 137.0 (dt, J =
130, 9 Hz, C3-C6F5), 125.1 (t, J = 8 Hz, C1-C6F5), 122.5 (Py-C3),
119.1 (Py-C5), 24.5 (CH3CO) ppm. MS (+): m/z = 685.4 [M +
Na]+. C34H39F5N4O4 (662.69).
3
4
General Procedure for the Synthesis of Ligands 1–4: To a solution
of hexaaminocalix[6]arene 16 (1.00 g, 1.02 mmol) in dry toluene
(75 mL) was added the proper pentafluorophenyl ester 11–14
(6.73 mmol) and triethylamine (0.4 mL, 3.1 mmol). This mixture
was heated at 90 °C in a sealed tube under an atmosphere of nitro-
gen for 24 h. The solvent was then removed under reduced pressure,
and the reaction was quenched with 2  NaHCO3 (50 mL). The
product was extracted in DCM (2ϫ30 mL), and the combined or-
ganic layer was washed with water (2ϫ50 mL). The solvent was
Py-H3,H4), 7.62 (dd, J = 6.6 Hz, J = 1.5 Hz, 6 H, Py-H5), 6.92
(d, 3J = 7.2 Hz, 12 H, ArHmeta), 6.80 (t, 3J = 7.2 Hz, 6 H, ArHpara),
3.89 (s, 12 H, ArCH2Ar), 3.40–3.10 (br. s, 48 H, OCH2CH2CH2
and NCH2CH3), 1.48 (br. s, 12 H, OCH2CH2), 1.04 (br. s, 36 H,
NCH2CH3) ppm. 13C{1H} NMR (75 MHz, [D6]DMSO, 298 K): δ
= 166.9 (CONEt2), 162.9 (CONH), 154.1 (Aripso), 153.7 (Py-C6),
148.6 (Py-C2), 138.7 (Py-C4), 134.1 (Arortho), 127.0 (Armeta), 124.6
(Py-C5), 123.2 (Arpara), 121.9 (Py-C3), 70.6 (OCH2CH2CH2), 42.3
(NCH2), 36.6 (OCH2CH2CH2), 29.5 (OCH2CH2CH2 and Ar-
Eur. J. Org. Chem. 2010, 2675–2686
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2683

M. Mariani, A. Casnati et al.
FULL PAPER
CH2Ar), 13.7 and 12.5 (NCH2CH3) ppm. MS (ESI+): m/z = 2226.4 = 164.9 (COOH), 162.8 (CONH), 154.4 (Aripso), 149.4 (Py-C2),
[M + Na]+. C126H150N18O18 (2204.65): calcd. C 68.64, H 6.86, N
11.44; found C 68.73, H 6.95, N 11.51.
146.4 (Py-C6), 139.5 (Py-C4), 134.1 (Arortho), 128.7 (Armeta), 126.4
(Py-C5), 125.0 (Py-C3), 123.4 (Arpara), 70.7 (OCH2CH2CH2), 36.5
(NCH2), 29.8 (OCH2CH2CH2 and ArCH2Ar) ppm. MS (ESI+):
m/z = 1895.9 [M + Na]+. C102H96N12O24 (1873.92): calcd. C 65.38,
H 5.16, N 8.97; found C 65.26, H 5.25, N 9.01.
37,38,39,40,41,42-Hexakis{3-[(pyridine-6-acetylamino-2-carboxy)-
amino]propoxy}calix[6]arene (4): The product was purified by pre-
cipitation with Et2O/DCM (8:1). Yield: 0.615 g (88%); m.p. 218–
1
220 °C. H NMR (300 MHz, CDCl3, 298 K): δ = 8.50–8.40 (m, 18
Extraction Experiments: The organic solutions were prepared by
dissolving the ligands and the synergizer in the considered diluents.
The ligand concentration was set to 1 m. The synergizer concen-
3
3
H, NH and Py-H5), 7.82 (d, J = 6.9 Hz, 6 H, Py-H3), 7.74 (t, J
= 6.9 Hz, Py-H4), 6.85 (br. s, 18 H, ArH), 3.9–3.3 (br. s, 36 H,
ArCH2Ar, OCH2CH2CH2), 2.08 (s, 18 H, CH3CO), 1.73 (br. s, 12 tration was varied between 1 and 6 m. The aqueous solutions
H, OCH2CH2) ppm. 13C{1H} NMR (75 MHz, CDCl3, 298 K): δ = were prepared by spiking aqueous nitric acid with a stock solution
169.2 (CH3CO), 164.0 (CON), 154.4 (Aripso), 150.2 (Py-C2), 147.8
(Py-C6), 139.7 (Py-C4), 134.0 (Arortho), 129.1 (Armeta), 124.0 (Ar-
of 241Am and 152Eu. The specific activity of Am and Eu in the
aqueous solutions was about 4000 kBq/L, whereas the acidity
para), 117.5 (Py-C5), 116.5 (Py-C3), 71.2 (OCH2CH2CH2), 37.2 ranged between 0.01 and 1 . Liquid–liquid extraction experiments
(OCH2CH2CH2), 29.9 (OCH2CH2CH2 and ArCH2Ar), 24.4
were performed by contacting the same volume (500 µL) of each
phase in a single-use microtest tube. The samples were shaken for
1 h at room temperature. Complete separation of the phases was
ensured by letting the samples settle for 5 min and then by spinning
the tubes in a centrifuge for 10 min. After centrifugation, an ali-
quot of 200 µL of each phase was taken and analysed by γ-spec-
trometry by using a NaI(Tl) detector. The measurement times were
set to obtain a relative standard deviation of the counting statistics,
which is less than 1%. The efficiency of the extractant systems is
described by the distribution coefficients, DM, calculated as the ra-
tio between the cation γ activity in the organic and aqueous phase,
whereas the selectivity for AmIII over EuIII is expressed by the sepa-
ration factor, SFAm/Eu, defined as the ratio of distribution coeffi-
( CH3 CO) ppm. MS (ESI+): m/z = 19 74 . 3 [M + N a]+
.
C108H114N18O18 (1952.17): calcd. C 66.45, H 5.89, N 12.91; found
C 66.31, H 5.97, N 13.03.
37,38,39,40,41,42-Hexakis{3-[(pyridine-6-N-butylaminocarbonyl-2-
carboxy)amino]propoxy}calix[6]arene (5): A suspension of the hexa-
methyl ester 1 (0.150 g, 0.077 mmol) in neat butylamine (10 mL)
was stirred in a closed tube at 90 °C for 5 d. Then, the solvent was
removed under reduced pressure, and the residue was purified by
flash chromatography (SiO2; acetone) and then crystallised from
Et2O. Yield: 0.075 g (66%); m.p. 165–166 °C. 1H NMR (300 MHz,
[D6]DMSO, 373 K): δ = 8.86 and 8.66 (br. s, 6 H each, NH), 8.14
(d, 3J = 7.8 Hz, 12 H, Py-H3, Py-H5), 8.03 (t, 3J = 7.8 Hz, 6 H,
cients DAm/DEu
.
3
3
Py-H4), 6.83 (d, J = 7.5 Hz, 12 H, ArHmeta), 6.72 (t, J = 7.5 Hz,
6 H, ArHpara), 3.92 (s, 12 H, ArCH2Ar), 3.57 (t, 3J = 6.6 Hz, 12 Complexation Experiments: The overall stability constants βxy de-
H, OCH2CH2CH2), 3.39 and 3.24 (q, 3J = 6.9 Hz, 12 H each, fined as concentration ratios and corresponding to the complex-
3
3x+
NCH2CH3), 2.92 (br. s, 12 H, OCH2CH2CH2), 1.72 (quint., J =
7.1 Hz, 12 H, OCH2CH2), 1.47 and 1.29 (quint. and sext., 3J = nide cation and L the ligand) were determined in methanol by UV
7.2 Hz, 12 H each, NCH2CH2CH2), 0.84 (t, 3J = 7.2 Hz, 18 H each,
absorption spectrophotometry at 25 °C and constant ionic strength
NCH2CH2CH2CH3) ppm. 13C{1H} NMR (75 MHz, [D6]DMSO, provided by 0.01  Et4NCl in all cases and by 0.01  Et4NNO3 in
ation equilibria xLn3+ + yL ↔ LnxLy
(where Ln is the lantha-
298 K): δ = 163.1 and 162.8 (CONH), 154.2 (Aripso), 148.7 and
148.6 (Py-C6 and Py-C2), 139.3 (Py-C4), 134.0 (Arortho), 128.6 (Ar-
m e t a ), 1 24 . 0 (P y -C 5 a n d P y - C 3 ) , 12 3. 6 ( Arp a r a ), 71.0
the case of lanthanum and europium nitrates with L1. The ligand
concentrations were in the range 2.0–5.0ϫ10–5  and the spectra,
recorded with a Shimadzu UV-2101 PC spectrophotometer, were
(OCH2CH2CH2), 38.5 and 36.4 (NCH2), 31.4 (NCH2CH2), 30.0 treated by the program Specfit, which also allowed the distribution
and 29.5 (OCH2CH2CH2 and ArCH2Ar), 19.6 (CH2CH3), 13.6 curves to be established.[39] Lanthanides were provided as chloride
(CH2 CH3 ) ppm. MS (ESI+): m/z = 2226.4 [M + Na]+
C126H150N18O18 (2204.65): calcd. C 68.64, H 6.86, N 11.44; found
C 68.51, H 6.99, N 11.65.
.
or nitrate salts (Alfa Aesar), which were dried for 24 h before use.
Microcalorimetric titrations were performed at 25 °C by using a
2277 Thermal Activity Monitor Microcalorimeter (Thermometric)
according to the procedure already reported.[40] Heats of complex-
37,38,39,40,41,42-Hexakis{3-[(pyridine-6-hydroxycarbonyl-2-carb-
oxy)amino]propoxy}calix[6]arene (6): To a suspension of hexabenzyl
ester 2 (0.70 g, 0.290 mmol) in acetone/EtOH (1:1, 100 mL) was
added a catalytic amount of Pd/C, and the mixture was stirred in
a Parr apparatus under 3 bar H2 pressure for 1 week. Then the
catalyst was removed by filtration, and the solvents were removed
from the filtrate. The residue was crystallised from DCM/Et2O
(1:4), and the product collected as a white powder. Yield: 0.48 g
(88%); m.p. 225 °C (decomp.). 1H NMR (300 MHz, [D6]acetone/
ation were recorded after addition of 15ϫ15 µL aliquots of 10–2

europium chloride in methanol on 2.7 mL of 1.0–1.5ϫ10–4  li-
gand solutions in the same solvent. The enthalpy of complexation
(∆Hxy) and the stability constants were refined simultaneously from
these data after correction for the dilution by using the ligand bind-
ing analysis program DIGITAM version 4.1.[41] The corresponding
values of the entropy contribution (T∆Sxy) were then calculated
from the equation ∆Gxy = ∆Hxy – T∆Sxy, knowing ∆G = –RTln
βxy.
3
CD3OD = 1:1, 298 K): δ = 8.27 (d, J = 7.5 Hz, 6 H, Py-H3), 8.19
(d, 3J = 7.5 Hz, 6 H, Py-H5), 8.09 (t, 3J = 7.5 Hz, 6 H, Py-H4), X-ray Crystallographic Study: Data were collected with a Siemens
6.91 (br. s, 12 H, ArHmeta), 6.80 (br. s, 6 H, ArHpara), 3.91 (s, 12
AED diffractometer equipped with graphite monochromated Cu-
H, ArCH2Ar), 3.47 (br. s, 24 H, OCH2CH2CH2), 1.67 (br. s, 12 H,
Kα radiation source (λ = 1.54178 Å). Intensity data were collected
OCH2CH2) ppm. 1H NMR (300 MHz, [D6]DMSO, 373 K): δ = at 293 K and corrected for Lorentz and polarisation effects and for
8.67 (t, 3J = 7.8, 5.4 Hz, 6 H each, NH), 8.20 (d, 3J = 7.2 Hz, 6 H,
absorption effects. The crystal data and the most relevant experi-
mental parameters used in the X-ray measurements and in the crys-
tal structure analyses are reported in Table 10. The structure was
3
Py-H3), 8.16–8.06 (m, 12 H, Py-H4, Py-H5), 6.85 (d, J = 7.5 Hz,
3
12 H, ArHmeta), 6.73 (t, J = 7.5 Hz, 6 H, ArHpara), 3.94 (s, 12 H,
3
ArCH2Ar), 3.54 (t, J = 6.5 Hz, 12 H, OCH2CH2CH2), 3.50–3.35 solved by direct methods by using SIR2004[42] and refined by full-
(m, 24 H, OCH2CH2CH2), 1.68 (quint., 3J = 6.9 Hz, 12 H, matrix least-squares methods on F2 by using the SHELXL-97 pro-
OCH2CH2) ppm. 13C{1H} NMR (75 MHz, [D6]DMSO, 298 K): δ
2684
gram.[43] The complex lies on a crystallographic centre of sym-
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2675–2686

Calix[6]arene-Picolinamide Extractants for Radioactive Waste Treatment
Rapport Final, Technical Report CEA-R-6066, Commissariat
à lЈénergie atomique, 2004.
F. Arnaud-Neu, V. Böhmer, B. Casensky, A. Casnati, J. F.
Desreux, B. Gruner, C. Grüttner, J. de Mendoza, G. Pina, P.
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of Minor Actinides from High Activity Liquid Waste by Orga-
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C. Hill, F. Arnaud-Neu, A. Glez-Espartero, J. F. Desreux, G.
Modolo, S. Bourg, R. Malmbeck, C. Caravaca, M. Harrison,
G. De Angelis, J. Uhlir, N. Ouvrier, C. Madic, EUROPART
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metry. All the non-hydrogen atoms were treated with anisotropic
atomic displacements except the atoms of the terminal amido
groups at the calixarene subunits B and C and the guest water
molecule, which were all treated with isotropic atomic displace-
ments. The hydrogen atoms were placed at their calculated posi-
tions with geometrical constraint C–H 0.96 Å and refined “riding”
[3]
on their corresponding parent atoms. The hydrogen atoms of the
[4]
guest water molecule were not located in final Fourier ∆F map and
were not included in the refinement. CCDC-757083 contains the
supplementary crystallographic data for this paper. These data can
[5]
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be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Table 10. Crystal data and structure refinement for 2·2H2O.
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Empirical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C144H132N12O24·2H2O
1225.36
triclinic
[8]
[9]
¯
P1
17.652(2)
19.060(2)
10.408(2)
95.110(9)
100.21(1)
108.059(6)
3237.5(8)
1
α (°)
β (°)
[10]
[11]
[12]
γ (°)
V (Å3)
Z
Dcalcd. (g/cm3)
F(000)
1.257
1292
Temperature (K)
θ Range (°)
Index ranges
293
8.0, 140.0
–21 Յ h Յ 17
–23 Յ k 23
–4 Յ l Յ 12
13022
12252 (Rint = 0.0569)
3962
12252/18/756
R1 = 0.0571
wR2 = 0.1896
0.758
[13]
[14]
Refl. measured
Indep. refl.
Obs. refl. [F0 Ͼ 4σ(F0)]
Data/restr./param.
Final R indices[a]
(Obs. data)
[15]
[16]
Goodness of fit S[b]
Min. and max. residual ρ [e/Å3] 0.36, –0.33
[17]
[18]
[19]
[20]
[21]
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2007, 31, 1620–1632.
M. W. Peters, E. J. Werner, M. J. Scott, Inorg. Chem. 2002, 41,
1707–1716.
2
2 2
4 1/2
[a] R1 = Σ ||Fo| – |Fc|| / Σ|Fo|, wR2 = [Σw(Fo – Fc ) / ΣwFo
] .
2
2 2
[b] Goodness of fit S = [Σw(Fo – Fc ) / (n – p)]1/2, where n is the
number of reflections and p the number of parameters.
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Supporting Information (see footnote on the first page of this arti-
cle): VT-, COSY and HSQC NMR experiments for ligand 5; per-
spective views (in colour) of the molecular structure and polymeric
self-assembly of ligand 2; coloured molecular structure of the Br-
Cosan anion; table with the extracting properties of BrCosan at
different concentrations in the absence of the ligand.
[22]
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Eur. J. Org. Chem. 2010, 2675–2686
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2685

M. Mariani, A. Casnati et al.
FULL PAPER
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Received: December 18, 2009
Published Online: March 23, 2010
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