Oxa- and azacalixarenes as ligands for uranyl ions - Evidence for two different complexation modes

Article abstract of DOI:10.1002/1099-0682(200103)2001:3<637::AID-EJIC637>3.0.CO;2-R

The first crystal structures are reported for uncomplexed parent tetrahomodioxa- and tetrahomodiazacalix[4]arene compounds and their 1:1 uranyl complexes. A 1:1 uranyl complex is also reported for a hexahomotriazacalix[3]arene. While analogous features are observed for the uncomplexed dioxa- and diazacalixarenes, completely different coordination modes are observed in their uranyl complexes. The complex of p-tert-butyltetrahomodioxacalix[4]arene is obtained in the presence of triethylamine and consists of an anionic core in which the cation is located at the centre of the lower rim, as is frequently observed. Both p-chloro-N-benzyl-hexahomotriazacalix[3]arene and p-methyl-N-benzyl-tetrahomodiazacalix[4]arene react with uranyl nitrate without adding a basic agent. The resulting 1:1 complexes are neutral, the cation being located outside the macrocycle and bound to two phenoxide groups of its zwitterionic form and to the nitrate counter-ions. The difference in coordination mode between homooxa- and homoazacalixarene complexes is attributed to the electrostatic repulsion between the uranyl ions and the ammonium groups located around the lower rim in the latter case, which prevents a close approach of the complexed cation.

Full text of DOI:10.1002/1099-0682(200103)2001:3<637::AID-EJIC637>3.0.CO;2-R

FULL PAPER
Oxa- and Azacalixarenes as Ligands for Uranyl Ions ؊ Evidence for Two
Different Complexation Modes
[a]
[a]
[b]
[c]
´
Pierre Thuery,* Martine Nierlich, Jacques Vicens, Bernardo Masci, and
Hiroyuki Takemura[d]
Keywords: Uranium / Calixarenes / Zwitterion / Crystal structure
The first crystal structures are reported for uncomplexed par-
triazacalix[3]arene and p-methyl-N-benzyl-tetrahomodiaza-
ent tetrahomodioxa- and tetrahomodiazacalix[4]arene com- calix[4]arene react with uranyl nitrate without adding a basic
pounds and their 1:1 uranyl complexes. A 1:1 uranyl complex
is also reported for a hexahomotriazacalix[3]arene. While
analogous features are observed for the uncomplexed dioxa-
and diazacalixarenes, completely different coordination
modes are observed in their uranyl complexes. The complex
agent. The resulting 1:1 complexes are neutral, the cation
being located outside the macrocycle and bound to two
phenoxide groups of its zwitterionic form and to the nitrate
counter-ions. The difference in coordination mode between
homooxa- and homoazacalixarene complexes is attributed to
of p-tert-butyltetrahomodioxacalix[4]arene is obtained in the the electrostatic repulsion between the uranyl ions and the
presence of triethylamine and consists of an anionic core in
which the cation is located at the centre of the lower rim, as
ammonium groups located around the lower rim in the latter
case, which prevents a close approach of the complexed
is frequently observed. Both p-chloro-N-benzyl-hexahomo- cation.
Introduction
oxacalix[4]arene,[2a]
p-tert-butylhexahomotrioxacalix[3]-
arene,[2i] p-tert-butylcalix[5]arene[2e]) or polynuclear with
The work of Shinkai et al., who demonstrated about ten
years ago the ‘‘uranophile’’ potential of water-soluble ca-
lixarenes, generated an interest that led to the investigation
of uranyl complexes of calixarenes.[1] Unfortunately, the
crystal structures of the complexes involved have never been
elucidated due to the difficulties encountered in growing
single crystals. However, since then a lot of structural in-
formation has been gathered about the uranyl complexes of
parent calix[n]arenes (n between 5 and 9 and n ϭ 12) and
homooxacalixarenes,[2] whereas only one crystal structure
larger,
flattened
calixarenes
(p-tert-butylcalix[8]-
p-tert-butyl-
arene,[2b,2c,2k]
p-tert-butylcalix[9]arene,[2k]
calix[12]arene[2j]). p-tert-Butylcalix[6]arene gives only ex-
ternal complexes with a 2:1,[2g] 2:2[2d] or 3:3[2k] metal:ligand
stoichiometry. Calix[7]arene is another peculiar case, being
able to engage in complexation only one of its two (trimeric
and tetrameric) subunits,[2f] or both.[2h] The complex
formed by p-tert-butylhexahomotrioxacalix[3]arene (ligand
1 in Scheme 1) is of particular interest since it constitutes
the first and, up to now, the only example of a pseudo-
trigonal equatorial coordination for the uranyl ion.[2i]
The homooxa- and homoazacalixarenes are less rigid
involving coordinating pendent arms grafted on
a
calix[4]arene has been reported.[3] Parent calixarenes and
homooxacalixarenes readily form uranyl complexes in a ba-
sic medium. These are either mononuclear with the smallest
calixarenes in cone conformation (p-tert-butyldihomo-
than calixarenes, as shown by 1H NMR spectroscopic
measurements in the case of the former.[4] Furthermore,
they possess two different kinds of potential binding sites,
and homoazacalixarenes, which were first synthesized some
years ago,[5] can bear various substituents on the amine ni-
trogen atom. The metal-ion complexes of homooxacalixar-
enes thus far reported have been obtained classically in a
basic medium.[2a,2i,6] In order to further investigate the
complexing properties of these ligands, we synthesized, in
the presence of triethylamine, the uranyl complex of an-
other oxacalixarene, p-tert-butyltetrahomodioxacalix[4]ar-
ene (2), the structure of which is reported herein as well as
that of the uncomplexed ligand. We have recently begun the
investigation of azacalixarenes as ligands and reported the
crystal structures of p-chloro-N-benzylhexahomotriazaca-
lix[3]arene (3) and of its mononuclear complex with neody-
mium nitrate.[7] This work demonstrated a peculiarity of the
homoazacalixarenes as ligands in that they are able to com-
[a]
CEA/Saclay, SCM (CNRS URA 331)
ˆ
Bat. 125, 91191 Gif-sur-Yvette, France
Fax: (internat.) ϩ33-1/6908-6640
E-mail: thuery@drecam.cea.fr
[b]
[c]
[d]
´
ECPM, Laboratoire de Chimie des Interactions Moleculaires
´
Specifiques (CNRS UMR 7512)
25 rue Becquerel, 67087 Strasbourg, France
Fax: (internat.) ϩ33-3/8813-7813
E-mail: vicens@chimie.u-strasbg.fr
Dipartimento di Chimica and Centro CNR di Studio sui
`
Meccanismi di Reazione, Universita ‘‘La Sapienza’’
Box 34, Roma 62, P.le Aldo Moro 5, 00185 Roma, Italy
Fax: (internat.) ϩ39-06/490-631
E-mail: bmasci@axrma.uniroma1.it
Department of Chemistry, Faculty of Science, Kyushu
University
Ropponmatsu 4-2-1, Chuo-ku, Fukuoka 810Ϫ8560, Japan
Fax: (internat.) ϩ81-92/726-4755
E-mail: takemura@rc.kyushu-u.ac.jp
Eur. J. Inorg. Chem. 2001, 637Ϫ643
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0303Ϫ0637 $ 17.50ϩ.50/0
637

´
P. Thuery, M. Nierlich, J. Vicens, B. Masci, H. Takemura
FULL PAPER
Scheme 1. The homooxa- and homoazacalixarenes under study
plex lanthanide ions without the addition of a basic agent
such as the commonly used triethylamine or 1,4-diazabicy-
clo[2.2.2]octane (DABCO), owing to the displacement of
the protons from oxygen to nitrogen atoms (zwitterionic or
amphiionic form) upon complexation. We report herein the
synthesis in a neutral medium as well as the crystal struc-
tures of the uranyl complexes of two azacalixarenes, 3 and
p-methyl-N-benzyltetrahomodiazacalix[4]arene (4), and the
crystal structure of the uncomplexed molecule 4. Unfortu-
nately, we have not succeeded in growing single crystals of
the complex species obtained with 3 and 4 in a basic me-
dium, for comparative purposes. To the best of our know-
ledge, the crystal structures reported herein are the first
ones for parent tetrahomodioxa- and tetrahomodiazacalix-
[4]arenes and their complexes.
Figure 1. View of p-tert-butyltetrahomodioxacalix[4]arene 2 in 5
(top) and in 6 (bottom), showing the difference in hydrogen bond-
ing patterns; hydrogen bonds in dashed lines; hydroxyl protons
represented as small spheres of arbitrary radii; other hydrogen
atoms and solvent molecules omitted for clarity; symmetry code:
Ј ϭ y, x, Ϫz
ing the four phenolic oxygen atoms, with O(3) and O(3Ј)
giving a bifurcated hydrogen bond, the O(3)···O(2) bond
being stronger than O(3)···O(1). The calixarene shape can
be characterized by the values of the dihedral angles be-
tween the phenolic rings and the mean plane defined [Ϯ
˚
0.339(4) A] by the phenolic oxygen atoms, which are 38.8(2)
and 47.2(2)° [mean value 43(6)°]. The cup shape is suffi-
ciently deep for the two acetonitrile molecules (not involved
in hydrogen bonding) to be included in the cavity: such a
situation has already been observed in the case of p-tert-
butylcalix[6]arene,[8] which confirms the similarity between
the two ligands in terms of cavity size.[9]
Results and Discussion
Uncomplexed Calixarenes
The asymmetric unit in 2·2CH3CN (5) is composed of
The asymmetric unit in 2·2.5C5H5N (6) is composed of
half a molecule, located around a binary axis perpendicular one molecule, represented in Figure 1, the overall features
to its mean plane (Figure 1). The overall shape is that of a of which are analogous to those in 5. However, the calixar-
very distorted cone, and is determined by an intramolecular ene conformation is different in the surroundings of atom
hydrogen bonding array which links both phenolic and O(5), which results in a slight enlargement of the macrocy-
ether groups (Table 1). The two ether links, which give the cle and the breaking of one of the hydrogen bonds. The
molecule its high flexibility, are positioned so as to bring interest of this structure is to show that, depending upon
the ether atom O(2) and its symmetry-related equivalent the solvent, it is possible to observe conformations of the
O(2Ј) close to the protons of the phenolic atoms O(3) and ether bridge which do not allow bifurcate hydrogen bonds.
O(3Ј). However, the macrocycle is not large enough to pre- The values of the dihedral angles between the phenolic rings
˚
vent the formation of a cyclic hydrogen bonding array link- and the mean plane defined [Ϯ 0.188(2) A] by the phenolic
638
Eur. J. Inorg. Chem. 2001, 637Ϫ643

Oxa- and Azacalixarenes as Ligands for Uranyl Ions
FULL PAPER
˚
Table 1. Selected bond lengths (A) and angles (°)
Uranium environment
8
UϪO(1)
UϪO(3)
UϪO(4)
9
2.272(4)
2.252(4)
2.269(4)
UϪO(6)
UϪO(7)
UϪO(8)
2.333(4)
1.795(4)
1.804(4)
O(1)ϪUϪO(3)
O(3)ϪUϪO(4)
O(4)ϪUϪO(6)
94.4(2)
87.5(2)
93.3(2)
O(6)ϪUϪO(1)
84.8(2)
O(7)ϪUϪO(8)
178.3(2)
UϪO(1)
UϪO(3)
UϪO(4)
10
UϪO(1)
UϪO(2)
UϪO(5)
2.284(7)
2.278(7)
1.771(8)
UϪO(5)
UϪO(6)
UϪO(7)
1.772(7)
2.576(7)
2.586(9)
UϪO(9)
2.578(7)
2.586(7)
75.1(3)
O(6)ϪUϪO(7)
O(9)ϪUϪO(10)
O(4)ϪUϪO(5)
49.2(2)
49.3(2)
175.0(3)
UϪO(10)
O(1)ϪUϪO(3)
2.234(9)
2.269(8)
1.757(8)
UϪO(6)
UϪO(7)
UϪO(8)
1.758(9)
2.530(9)
2.504(10)
UϪO(10)
O(1)ϪUϪO(2)
O(7)ϪUϪO(8)
2.398(10)
78.9(3)
50.3(4)
O(5)ϪUϪO(6)
176.4(4)
Hydrogen bonds[a]
5
O(1)···O(3Ј)
O(3)···O(1)
O(3)···O(2)
6
2.787(7)
2.915(7)
2.753(7)
O(1)ϪH
O(3)ϪH
0.94
1.09
H···O(3Ј)
H···O(1)
H···O(2)
1.91
2.08
1.89
O(1)ϪH···O(3Ј)
O(3)ϪH···O(1)
O(3)ϪH···O(2)
155
131
133
O(1)···O(2)
O(1)···O(3)
O(3)···O(4)
O(4)···O(5)
O(6)···O(1)
7
O(1)···O(4)
O(2)···O(1)
O(2)···N(1)
O(3)···O(2)
O(4)···O(3)
O(4)···N(2)
8
N(1)···O(8)
N(2)···O(6)
9
2.743(5)
2.989(5)
2.763(5)
2.657(5)
3.147(5)
O(1)ϪH
1.11
H···O(2)
H···O(3)
H···O(4)
H···O(5)
H···O(1)
1.81
2.16
1.74
1.79
2.23
O(1)ϪH···O(2)
O(1)ϪH···O(3)
O(3)ϪH···O(4)
O(4)ϪH···O(5)
O(6)ϪH···O(1)
139
129
166
133
140
O(3)ϪH
O(4)ϪH
O(6)ϪH
1.05
1.09
1.09
2.861(4)
2.903(3)
2.692(4)
2.820(3)
2.946(3)
2.713(4)
O(1)ϪH
O(2)ϪH
0.88
1.08
H···O(4)
H···O(1)
H···N(1)
H···O(2)
H···O(3)
H···N(2)
1.99
2.49
1.64
1.89
2.48
1.85
O(1)ϪH···O(4)
O(2)ϪH···O(1)
O(2)ϪH···N(1)
O(3)ϪH···O(2)
O(4)ϪH···O(3)
O(4)ϪH···N(2)
177
102
165
173
106
137
O(3)ϪH
O(4)ϪH
0.94
1.05
2.728(7)
2.715(7)
N(1)ϪH
N(2)ϪH
0.99
1.05
H···O(8)
H···O(6)
1.77
1.72
N(1)ϪH···O(8)
N(2)ϪH···O(6)
163
157
N(1)···O(1)
N(1)···O(2)
N(2)···O(2)
N(2)···O(3)
N(3)···O(1)
N(3)···O(3)
10
N(1)···O(1)
N(1)···O(2)
N(2)···O(3)
N(2)···O(4)
O(3)···O(2)
O(4)···O(1)
2.95(1)
2.64(1)
2.61(1)
2.97(1)
2.91(1)
2.84(1)
N(1)ϪH
N(2)ϪH
N(3)ϪH
0.92
1.11
1.05
H···O(1)
H···O(2)
H···O(2)
H···O(3)
H···O(1)
H···O(3)
2.44
1.91
1.74
2.20
2.37
1.92
N(1)ϪH···O(1)
N(1)ϪH···O(2)
N(2)ϪH···O(2)
N(2)ϪH···O(3)
N(3)ϪH···O(1)
N(3)ϪH···O(3)
116
136
132
124
111
145
2.88(1)
2.86(1)
2.78(1)
2.79(1)
2.62(1)
2.69(1)
N(1)ϪH
N(2)ϪH
0.99
0.97
H···O(1)
H···O(2)
H···O(3)
H···O(4)
H···O(2)
H···O(1)
2.21
2.14
2.07
1.97
1.66
1.81
N(1)ϪH···O(1)
N(1)ϪH···O(2)
N(2)ϪH···O(3)
N(2)ϪH···O(4)
O(3)ϪH···O(2)
O(4)ϪH···O(1)
124
128
128
141
145
145
O(3)ϪH
O(4)ϪH
1.09
1.03
[a]
Symmetry code: Ј ϭ y, x, Ϫz.
˚
oxygen atoms are 38.5(2), 22.7(2), 46.8 (2) and 70.6(1)°, mean plane defined [Ϯ 0.321(1) A] by the phenolic oxygen
which indicate a strong deviance with respect to a regular atoms are 41.1(1), 43.0(1), 30.0(1) and 41.1(1)°, [mean value
cone shape. Two pyridine molecules, roughly orthogonal to 39(6)°] comparable to those in 5. However, in the present
each other and not involved in hydrogen bonding, are loc- case, the cavity, which is not as deep as in 5 and 6, due to
ated in the calixarene cavity.
the replacement of tert-butyl by methyl substituents, is
The asymmetric unit in 4·CH3CN (7) comprises one mo- empty. The benzyl substituents are directed towards the ex-
lecule, without any crystallographic symmetry (Figure 2). terior of the macrocycle, on the lower rim side.
The conformation of the calixarene is strikingly similar to
If the uncomplexed oxa- and azacalixarenes present
that observed in 5, with a similar hydrogen bonding pattern. closely related features, the basic nature of the nitrogen
The hydrogen bonds linking the phenolic oxygen atoms be- atoms in the latter results in different complexing behavi-
tween them [O(1)···O(2) and O(3)···O(4)] are however much ours, exemplified hereafter in the case of uranyl ions.
weaker than their counterparts in 5: such a predominance
Uranyl Ion Complexes
of OH···N bonds over OH···O ones has already been enco-
untered in 3, but was less pronounced.[7] The values of the
The complexation of one uranyl ion by 2 in the presence
dihedral angles between the four phenolic rings and the of NEt3 to give [UO2(2 Ϫ 4H)]2Ϫ(HNEt3ϩ)2·CHCl3·
Eur. J. Inorg. Chem. 2001, 637Ϫ643
639

´
P. Thuery, M. Nierlich, J. Vicens, B. Masci, H. Takemura
FULL PAPER
the presence of a second ether link in 2 permits a more
symmetrical geometry around the cation. The ether oxygen
atoms were not coordinated in the two other uranyl com-
plexes of oxacalixarenes reported.[2a,2i] Also, in the present
case, the two ether oxygen atoms are clearly non bonding,
˚
being at distances of 3.832(4) and 3.820(4) A from the ur-
anium atom [values larger than in the previous cases:
3.534(8)[2a] and 3.1(1)[2i] A] and at distances of 1.812(6) and
˚
˚
˚
1.893(6) A from the mean plane defined [Ϯ 0.027(2) A] by
the four coordinating oxygen atoms. The disruption of the
hydrogen bonding pattern of 2 and the location of the four
phenolic oxygen atoms in a plane result in a conformation
different from those observed in 5 and 6. The values of the
dihedral angles between the four phenolic rings and the
mean plane defined by the phenolic oxygen atoms are
47.9(2), 40.0(1), 48.3(1) and 42.9(2)° [mean value 45(4)°].
The two triethylammonium counter-ions in 8 are located as
frequently observed, one of them hydrogen bonded to an
uranyl oxo atom and included in the calixarene cavity and
the other hydrogen bonded to a phenoxide group. We have
Figure 2. View of p-methyl-N-benzyltetrahomodiazacalix[4]arene 4
in 7; hydrogen bonds in dashed lines; hydroxyl protons represented
as small spheres of arbitrary radii; other hydrogen atoms and solv-
ent molecule omitted for clarity; only the main component of disor- mentioned above the similarity in size between p-tert-butyl-
dered atoms is represented
tetrahomodioxacalix[4]arene and p-tert-butylcalix[6]arene;
however, these ligands appear very different from equivalent
towards uranyl complexation, since the latter gives ‘‘ex-
ternal’’ complexes only.[2d,2g,2k]
Whereas the uranyl ion is located at the centre of the
lower rim in the three complexes of oxacalixarenes presently
reported, the coordination mode in the complex of the aza-
calixarene 3, obtained without a basic agent being added,
is completely different. The asymmetric unit in
[UO2(NO3)23]·C5H5N·CHCl3 (9) comprises one molecule
(Figure 4), which does not possess any true symmetry ele-
ment, but presents a pseudo symmetry plane containing the
atom O(2) and the uranyl ion. The cation is located outside
the lower rim array and is bound to two phenoxide ions
Figure 3. View of the ‘‘internal’’ uranyl ion complex of p-tert-butyl-
tetrahomodioxacalix[4]arene 8; hydrogen bonds in dashed lines; hy-
drogen atoms and solvent molecules omitted for clarity; only the
main component of disordered atoms is represented
CH3CN (8) is accompanied by a conformational change of
the macrocycle. As illustrated in Figure 3, the cation is loc-
ated at the centre of the lower rim, with its main axis per-
pendicular to it, and bound to the four deprotonated oxy-
˚
gen atoms [mean UϪO distance 2.28(3) A, as observed pre-
viously for phenoxide groups[2]]. The molecule presents two
orthogonal non-crystallographic symmetry planes with the
uranyl axis at their intersection and passing through either
the methylene or the ether bridges. Such a square planar
equatorial geometry is rather common in calixarene com-
plexes, having been observed in the complexes of p-tert-
butyldihomooxacalix[4]arene,[2a] p-tert-butylcalix[7]arene[2f]
and p-benzylcalix[7]arene,[2h] but it is rarely so regular
Figure 4. View of the ‘‘external’’ uranyl ion complex of p-chloro-
N-benzylhexahomotriazacalix[3]arene 9; hydrogen bonds in dashed
[mean OphenolϪUϪOphenol angle between adjacent phenolic
lines; protons of the ammonium groups represented as small
spheres of arbitrary radii; other hydrogen atoms and solvent molec-
units 90(5)°, mean OuranylϪUϪOphenol angle 90(2)°]. In par-
ticular, with respect to p-tert-butyldihomooxacalix[4]arene, ules omitted for clarity
640
Eur. J. Inorg. Chem. 2001, 637Ϫ643

Oxa- and Azacalixarenes as Ligands for Uranyl Ions
FULL PAPER
only, with its axis roughly parallel to the mean plane of ence of chlorine atoms is not necessary to promote the pro-
the molecule. The coordination sphere is completed by two tons transfer. The asymmetric unit in 10 comprises one
bidentate nitrate ions. Such a six-coordinate environment is complex molecule lacking any symmetry element (Fig-
unusual in uranyl complexes of calixarenes and is due to ure 5). The uranyl ion is bound to two phenoxide groups,
the small-bite nature of nitrate ions. The uranium atom is as in 9, and its distance from the mean plane defined
˚
˚
located at 1.556(7) A from the mean plane defined by the [Ϯ 0.030(5) A] by the four calixarene oxygen atoms is 1.543(8)
˚
three phenoxide oxygen atoms, a value comparable to that A. The two nitrate counter-ions behave differently: one is
[7]
˚
of the neodymium(III) complex of 3 [1.591(2) A] which bidentate and the other monodentate. This difference with
presents many similarities with 9 (an obvious difference be- 9 may be ascribed to an OphenolϪUϪOphenol angle slightly
ing that the neodymium ion is bound to the three phenoxide larger in 10 [78.9(3)° to be compared with 75.1(3)° in 9],
oxygen atoms). In both complexes, the three phenolic pro- which could make the available space insufficient for two
tons have been transferred to the amine groups upon com- bidentate nitrate ions. The two coordinated phenolic groups
plexation. An asymmetric array of hydrogen bonds links are deprotonated and the two amine groups are turned into
the ammonium and phenoxide groups in 9, as in the Nd3ϩ ammonium cations. Hydrogen bonds are formed between
complex. The values of the three dihedral angles between each ammonium group and its two neighbouring oxygen
the phenolic rings and the mean plane defined by the three atoms, and also between the two non-coordinated, pro-
phenolic oxygen atoms are 64.6(3), 2.23(9) and 60.2(3)°: tonated, oxygen atoms O(3) and O(4) and the two phen-
those values are different from those in both the uncom- oxide groups. The modification of the hydrogen bonding pat-
plexed molecule 3 and its Nd3ϩ complex. In the latter case, tern with respect to 7 results in a different calixarene con-
one of the rings was nearly parallel to the mean plane, as formation. The values of the dihedral angles between the
the one corresponding to the non-coordinated phenolic four phenolic rings and the mean oxygen atoms plane are
group in 9, but the two other rings are much more ‘‘ver- 61.7(3), 59.1(3), 21.0(4) and 16.1(5)°, the two uncomplexed
tical’’ in 9. Two benzyl substituents are located on the lower phenolic moieties being closer to the mean plane. Two half-
rim side and directed towards the exterior of the macrocycle cones are defined on each side of the N(1)···N(2) axis, but
whereas the third one is on the upper rim side and directed their junction does not give an overall cone conformation:
towards the cavity, in which it occupies a position nearly the usual terms defining the conformation of classical small
parallel to that of the uncomplexed phenolic ring.
The question arises as to the role of the acid-enhancing is reminiscent of larger, flattened calixarenes.
p-chlorine substituent in the auto-deprotonation process The question arises of the origins of the difference in co-
calixarenes are of no practical use in the present case, which
leading to complex 9 as well as to the Nd3ϩ complex of 3. ordination mode between the uranyl complex of p-tert-bu-
Complex 10 brings an answer as well as an interesting point tylhexahomotrioxacalix[3]arene and 8 on the one hand and
of comparison with complex 8. The complexation by ligand 9 and 10 on the other. The main reason is likely to be the
4 occurs also without a basic agent being added, giving electrostatic repulsion between the uranyl cation and the
[UO2(NO3)24]·0.5CH3OH·H2O (10) in which the complex two or three ammonium groups in the latter cases, which
molecule is neutral. This reaction indicates that the pres- prevents the cation from being located in the mean plane
Figure 5. View of the ‘‘external’’ uranyl ion complex of p-methyl-N-benzyltetrahomodiazacalix[4]arene 10; hydrogen bonds in dashed
lines; protons of the hydroxyl and ammonium groups represented as small spheres of arbitrary radii; other hydrogen atoms, benzyl groups
and solvent molecules omitted for clarity
Eur. J. Inorg. Chem. 2001, 637Ϫ643
641

´
P. Thuery, M. Nierlich, J. Vicens, B. Masci, H. Takemura
FULL PAPER
and 1 mL of NEt3; a solution of UO2(NO3)2·6H2O (0.03 g,
0.06 mmol) in 2 mL of CH3CN was then added dropwise, immedi-
ately giving an orange solution, which was allowed to slowly evap-
orate. A few orange single-crystals suitable for X-ray crystallo-
graphy deposited in three days together with a microcrystalline
powder. Microanalysis results including both crystals and powder
were unsatisfactory due to the heterogeneous nature of the latter.
defined by the lower rim. An influence of the steric hind-
rance associated with the benzyl groups occupying the cav-
ity is not likely, due to the high flexibility of these substitu-
ents and the high affinity of phenoxide groups for uranyl
ions. In spite of repeated attempts, we did not succeed in
growing single crystals of the complex species obtained with
azacalixarenes in a basic medium (NEt3 or DABCO), for
comparative purposes. It may be assumed that the depro-
tonation of the ligand by the base could lead to an anionic
complex with a coordination mode closer to that observed
with other calixarenes. It must be noted that, by contrast
with all the uranyl complexes of calixarenes reported up to
now, the azacalixarene complexes 9 and 10 are neutral and
not anionic, since the ligand itself is neutral and the metal
cation is bound to its counter-ions.
[UO2(NO3)23]·C5H5N·CHCl3 (9): Compound 3 (0.15 g, 0.19 mmol)
was dissolved in 30 mL of CH3CN/CHCl3 (1:1) and a solution of
UO2(NO3)2·6H2O (0.3 g, 0.6 mmol) in 30 mL of CH3CN was ad-
ded dropwise, immediately giving an orange solution. Orange single
crystals, unstable out of their mother solution but suitable for X-
ray crystallography, were obtained upon recrystallization from pyr-
idine. Ϫ [UO2(NO3)23]·CHCl3·H2O, UC46H45Cl6N5O12 (1310.60):
calcd. C 42.16, H 3.46; found C 42.06, H 3.35. Ϫ FAB-MS
[UO2·C45H42Cl3N3O3]: m/z ϭ calcd. 1047.26; found 1048.2.
The interest of zwitterions for the simultaneous solvent
extraction of cations and anions has recently been pointed
out and exemplified by a Schiff base bearing morpholine
groups.[10] In this case, the Schiff base with deprotonated
hydroxyl groups complexes the metal ion while the pro-
[UO2(NO3)24]·0.5CH3OH·H2O (10): Compound
4
(0.04 g,
0.055 mmol) was dissolved in 3 mL of CHCl3 and a solution of
UO2(NO3)2·6H2O (0.04 g, 0.08 mmol) in 5 mL of CH3OH was ad-
ded dropwise, immediately giving an orange solution. Orange single
crystals suitable for X-ray crystallography were obtained in a few
tonated morpholine groups complex the counter-ion. The hours. Ϫ UC48.5H54N4O13.5 (1146.99): calcd. C 50.79, H 4.75;
found C 50.28, H 4.28.
situation is somewhat different in the case of azacalixarenes
since the cationic part of the ligand is not directly involved
in complexation, but simply pushes the cation into an ‘‘ex-
ternal’’ position in which it cannot reach its usual coordina-
tion number from the calixarene and must remain bound
to its counter-ions.
Crystallography
The data were collected on a Nonius Kappa-CCD area detector
diffractometer[12] using graphite-monochromated Mo-Kα radiation
˚
(0.71073 A). The crystals were introduced in Lindemann glass ca-
pillaries with a protecting ‘‘Paratone’’ oil (Exxon Chemical Ltd.)
coating. The data were processed with DENZO-SMN.[13] The
structures were solved by direct methods with SHELXS-97[14] and
subsequent Fourier-difference synthesis and refined by full-matrix
least-squares on F2 with SHELXL-97.[15] No absorption correction
was done for 5, 6 and 7, the product µϽdϾ being lower than 0.1.
Absorption effects in 8, 9 and 10 were corrected empirically with
the program MULABS from PLATON.[16] Hydroxyl and ammo-
nium protons, as well as those of chloroform molecules, were intro-
duced as found on the Fourier difference maps whereas all other
hydrogen atoms in all compounds were introduced at calculated
positions (except in the disordered parts). All hydrogen atoms were
treated as riding atoms with a displacement parameter equal to 1.2
(OH, NH, CH, CH2) or 1.5 (CH3) times that of the parent atom.
All non-hydrogen atoms were refined anisotropically, except the
disordered ones. Special features for each compound are indicated
in the following.
Experimental Section
Synthesis
p-tert-Butyltetrahomodioxacalix[4]arene (2): This compound was
synthesized as previously reported.[11] Slow evaporation of a solu-
tion of 2 in CHCl3/CH3CN (1:1) gave colourless single crystals of
2·2CH3CN (5) suitable for X-ray crystallography, whereas slow
evaporation of a solution in pyridine gave colourless single crystals
of 2·2.5C5H5N (6) of lower quality.
p-Methyl-N-benzyl-tetrahomodiazacalix[4]arene (4): A solution of
2,2Ј-methylenebis(4-methyl-6-hydroxymethyl)phenol (8.00 g, 27.8
mmol) and benzylamine (3.4 g, 31.7 mmol) in 100 mL of xylene
was heated under reflux for 34 h. After removal of the solvent un-
der reduced pressure, the resultant oily material was subjected to
silica-gel column chromatography with CH2Cl2 as an eluent. 4 was
obtained as a colourless powder (5.81 g, yield 58.3%). The analyt-
ical sample was recrystallized from CH2Cl2/C2H5OH. M.p.
2·2CH3CN (5): The data were recorded at ambient temperature
since the crystals deteriorate at low temperature, which is seemingly
due to a phase transition phenomenon. Some soft restraints have
been applied on the badly resolved acetonitrile molecules. The ab-
solute structure could not be determined from the value of the
Flack parameter.[17]
1
146Ϫ148 °C. Ϫ H NMR (270 MHz, CDCl3): δ ϭ 2.17 (s, 12 H,
ArϪCH3), 3.43, 3.60, 4.25 (3bs, 16 H, ArϪCH2Ϫ), 6.69 (d, J ϭ
2 Hz, 4 H, ArϪH), 7.03 (d, J ϭ 2 Hz, 4 H, ArϪH), 7.34 (br. s, 10
2·2.5C5H5N (6): One tert-butyl substituent was found disordered
over two positions, which have been refined with occupation factors
constrained to sum to unity. The nitrogen atoms were not located
in the pyridine molecules (one of them disordered around a sym-
metry centre).
H, side arm ArϪH), 10.6 (br. s,
4
H, ArϪOH).
Ϫ
C48H50N2O4·0.5C2H5OH (741.93): calcd. C 79.32, H 7.20, N 3.78;
found C 79.11, H 7.35, N 3.67. Concentration of the mother liquor
also afforded 0.31 g (3.3%) of p-methyl-N-benzyldihomoazacalix-
[4]arene. Slow evaporation of a solution of 4 in CHCl3/CH3CN
(1:1) gave colourless single crystals of 4·CH3CN (7) suitable for X-
ray crystallography.
4·CH3CN (7): One of the two benzyl substituents was disordered
over two positions sharing two carbon atoms, which have been re-
fined with occupation factors constrained to sum to unity.
[UO2(2 ؊ 4H)]2؊(HNEt3ϩ)2·CHCl3·CH3CN (8): Compound
2
[UO2(2 ؊ 4H)]2؊(HNEt3ϩ)2·CHCl3·CH3CN (8): Some disorder
(0.02 g, 0.03 mmol) was dissolved in 6 mL of CH3CN/CHCl3 (1:1) was present on one tert-butyl group and one triethylammonium
642 Eur. J. Inorg. Chem. 2001, 637Ϫ643

Oxa- and Azacalixarenes as Ligands for Uranyl Ions
Table 2. Crystal data and structure refinement details
FULL PAPER
5
6
7
8
9
10
Empirical formula
M/g molϪ1
T/K
C50H66N2O6 C58.5H72.5N2.5O6 C50H53N3O4 UC61H92Cl3N3O8 UC51H48Cl6N6O11 UC48.5H54N4O13.5
791.02
293(2)
906.69
120(2)
759.95
293(2)
1339.76
100(2)
Orthorhombic
P212121
12.4313(3)
16.7223(4)
30.4446(8)
90
1371.68
100(2)
Monoclinic
Cc
1146.99
100(2)
Tetragonal
P43212
13.882(1)
13.882(1)
48.292(5)
90
Crystal system
Space group
Tetragonal Monoclinic
Triclinic
¯
P1
P41212
17.329(2)
17.329(2)
15.594(2)
90
C2/c
˚
a/A
34.380(4)
9.2515(5)
36.161(4)
90
10.943(2)
13.132(2)
16.485(2)
79.026(10)
74.077(9)
72.397(7)
2156.4(6)
2
9.3345(5)
25.283(2)
22.924(1)
90
˚
b/A
˚
c/A
α / °
β / °
γ / °
90
116.936(3)
90
90
94.634(4)
90
90
90
4683(1)
4
90
90
3
˚
V/A
10254(2)
8
6328.8(3)
4
5392.5(5)
4
9306(2)
8
Z
µ/mmϪ1
0.072
27912
4010
0.075
34044
9194
0.074
2.744
3.372
3.560
Reflections collected
Independent reflections
Observed reflections [I Ͼ 2σ(I)] 1230
Rint
R1
wR2
15878
43757
18296
9392
20655
6748
7319
11953
4252
3940
10505
8301
4812
0.124
0.083
0.169
0.184
0.101
0.206
0.064
0.088
0.068
0.121
0.080
0.042
0.050
0.060
0.201
0.090
0.122
0.111
[2c]
´
P. Thuery, N. Keller, M. Lance, J.
1995, 51, 1570Ϫ1574. Ϫ
ion, which was modelled with two positions refined with occupa-
tion factors constrained to sum to unity. The absolute structure
was determined from the value of the Flack parameter [Ϫ0.015(6)].
D. Vigner, M. Nierlich, New. J. Chem. 1995, 19, 619Ϫ625. Ϫ
[2d]
´
P. Thuery, M. Lance, M. Nierlich, Supramol. Chem. 1996,
7, 183Ϫ185. Ϫ [2e] P. Thuery, M. Nierlich, J. Inclusion Phenom.
´
[2f]
´
P. Thuery, M. Nierlich, M. I. Ogden, J.
[2g]
1997, 27, 13Ϫ20. Ϫ
[UO2(NO3)23]·C5H5N·CHCl3 (9): The absolute structure was deter-
mined from the value of the Flack parameter [Ϫ0.013(7)].
M. Harrowfield, Supramol. Chem. 1998, 9, 297Ϫ303. Ϫ
P.
C. Leverd, P. Berthault, M. Lance, M. Nierlich, Eur. J. Inorg.
Chem. 1998, 1859Ϫ1862. Ϫ [2h] P. Thuery, M. Nierlich, B. Sou-
´
ley, Z. Asfari, J. Vicens, J. Chem. Soc., Dalton Trans. 1999,
[UO2(NO3)24]·0.5CH3OH·H2O (10): The two benzyl substituents
were found disordered over two positions each. These four posi-
tions, which have been refined with occupation factors constrained
to sum to unity for each benzyl moiety, overlap between neigh-
bouring molecules and share one or two atomic positions. The oc-
cupation parameters have been chosen so as to take into account
the impossibility of a simultaneous occupation of overlapping posi-
tions. The methanol solvent molecule was also found disordered
over two sites symmetrically related, each affected with a 0.5 occu-
pation. The structure was refined as corresponding to a racemic
twin, the fractional contribution of the two components being x
and (1 Ϫ x), with x ϭ 0.504(14).
[2i]
´
P. Thuery, M. Nierlich, B. Masci, Z. Asfari,
2589Ϫ2594. Ϫ
J. Vicens, J. Chem. Soc., Dalton Trans. 1999, 3151Ϫ3152. Ϫ
[2j]
P. C. Leverd, I. Dumazet-Bonnamour, R. Lamartine, M.
[2k]
Nierlich, Chem. Commun. 2000, 493Ϫ494. Ϫ
For a review,
see: J. Harrowfield, Gazz. Chim. Ital. 1997, 127, 663Ϫ671.
P. D. Beer, M. G. B. Drew, D. Hesek, M. Kan, G. Nicholson,
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[3]
[4]
[5]
C. D. Gutsche, L. J. Bauer, J. Am. Chem. Soc. 1985, 107,
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156, 183Ϫ200.
Crystal data and structure refinement parameters are given in
Table 2. The molecular plots were drawn with SHELXTL.[18] All
calculations were performed on a Silicon Graphics R5000 workst-
ation.
[6]
C. E. Daitch, P. D. Hampton, E. N. Duesler, Inorg. Chem. 1995,
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[7]
[8]
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
no. CCDC-144187Ϫ144192 (5Ϫ10). Copies of the data can be ob-
tained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: (internat.) ϩ44-1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
´
P. Thuery, M. Nierlich, J. Vicens, H. Takemura, J. Chem. Soc.,
Dalton Trans. 2000, 279Ϫ283.
´
P. Thuery, N. Keller, M. Lance, J. D. Vigner, M. Nierlich, J.
Inclusion Phenom. 1995, 20, 373Ϫ379.
[9]
D. M. Roundhill, in Progress in Inorganic Chemistry (Ed.: K.
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[11]
[12]
[13]
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G. M. Sheldrick, SHELXTL, Version 5.1, University of
Göttingen, distributed by Bruker AXS, Madison, WI, 1999.
Received May 22, 2000
[1]
See, for example: S. Shinkai, in Calixarenes: a Versatile Class
of Macrocyclic Compounds (Eds.: J. Vicens and V. Böhmer),
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[14]
[15]
[16]
[17]
[18]
[2] [2a]
J. M. Harrowfield, M. I. Ogden, A. H. White, J. Chem.
[2b]
´
P. Thuery, N. Keller,
Soc., Dalton Trans. 1991, 979Ϫ985. Ϫ
M. Lance, J. D. Vigner, M. Nierlich, Acta Crystallogr., Sect. C
[I00212]
Eur. J. Inorg. Chem. 2001, 637Ϫ643
643