1
Synthesis and crystal structure of uranium(IV) complexes with
calix[n]arenes (n = 4, 6 and 8): mononuclear, polynuclear and 1D
polymeric species
Lionel Salmon, Pierre Thuéry and Michel Ephritikhine
Service de Chimie Moléculaire, DSM, DRECAM, CNRS URA 331, CEA Saclay, 91191 Gifsur-Yvette,
France
Fax:
+33(0)169086640;
Tel:
+33(0)169086436;
salmon@drecam.cea.fr, thuery@drecam.cea.fr, ephri@drecam.cea.fr
E-mail:
2
Graphical Abstract
Synthesis and crystal structure of uranium(IV)
complexes with calix[n]arenes (n = 4, 6 and 8):
mononuclear, polynuclear and 1D polymeric
species
U3
U2
Lionel Salmon, Pierre Thuéry and Michel
Ephritikhine
U1
U3’
U2’
Reactions of calix[n]arenes of varying
sizes (n = 4, 6, 8) with several UX4
precursors (X = Cl, acac, OTf) in THF or
pyridine led to the crystallization of a
unique series of tetravalent uranium
compounds with macrocyclic ligands.
3
Reactions of UCl4 with calix[n]arenes (n = 4, 6) in THF gave the mononuclear
[UCl2(calix[4]arene–2H)(THF)2]·2THF (1·2THF) and the bis-dinuclear [U2Cl2(calix[6]arene–
6H)(THF)3]2·6THF (2·6THF) complexes, respectively, while the mono-, di- and trinuclear
compounds [Hpy]2[UCl3(calix[4]arene–3H)]·py (4·py), [Hpy]4[U2Cl6(calix[6]arene–6H)]·3py
(5·3py), [Hpy]3[U2Cl5(calix[6]arene–6H)(py)]·py (6·py) and [Hpy]6[U3Cl11(calix[8]arene–
7H)]·3py (3·3py) were obtained by treatment of UCl4 with calix[n]arenes (n = 4, 6, 8) in
pyridine. The sodium salt of calix[8]arene reacted with UCl4 to give the pentanuclear complex
[U{U2Cl3(calix[8]arene–7H)(py)5}2]·8py
(7·8py).
Reaction
of
U(acac)4
(acac
=
MeCOCHCOMe) with calix[4]arene in pyridine afforded the mononuclear complex
[U(acac)2(calix[4]arene–2H)]·4py (8·4py) and its treatment with the sodium salt of
calix[8]arene led to the formation of the 1D polymer [U2(acac)6(calix[8]arene–6H)(py)4Na4]n
(9). The sandwich complex [Hpy]2[U(calix[4]arene–3H)2][OTf]·4py (10·4py) was obtained
by treatment of U(OTf)4 (OTf = OSO2CF3) with calix[4]arene in pyridine. All the complexes
have been characterized by X-ray diffraction analysis.
4
Introduction
By comparison with the variety of calixarene complexes of d transition metals and 4felements,1 such compounds of the actinides are much less common, despite promising
applications
of
calixarenes
in
uranium
detection2
and
extraction3
or
lanthanide(III)/actinide(III) separation.4 Calixarenes, homooxa- and homoazacalixarenes of
various size and geometry proved to be efficient for the complexation of the uranyl UO22+
ion, affording one of the most thoroughly investigated class of compounds, from a structural
viewpoint, in this family of macrocycles.5,6 The first attempts to prepare uranium(IV)
complexes by reaction of UCl4 with p-tert-butylcalix[n]arenes (n = 4, 5, 6) resulted in the
formation of a trinuclear, 3-oxo-centered [UVI2UV] complex for n = 4, dinuclear, 2-oxocentered UV or UVI complexes for n = 5 and a mononuclear UVI homoleptic alkoxide complex
for n = 6.7 These results revealed the difficulty of isolating lower valent uranium calixarene
compounds which are extremely sensitive to adventitious traces of oxygen or water. Recently,
the trimeric uranium(IV) complex [{UCl2(Me2calix)}3] (H2Me2calix = O-dimethylated p-tertbutylcalix[4]arene) was synthesized by treatment of UCl4 with the potassium salt of the
dianionic calix[4]arene ligand in THF; the isolation of this compound was found to be
critically dependent on the method of introduction of the calixarene moiety, the nature of the
uranium precursor, the solvent and the reaction conditions.8 Here we present the synthesis and
crystal structures of a series of complexes obtained from reactions of UCl4, U(acac)4 (acac =
MeCOCHCOMe) and U(OTf)4 (OTf = OSO2CF3) with O-unsubstituted calix[n]arenes (n = 4,
6 and 8) (Scheme 1) or their deprotonated forms, in pyridine or THF.9
<Scheme 1>
5
Results and discussion
Syntheses
Reactions of UCl4 with calix[n]arenes (n = 4, 6 and 8) are summarized in Scheme 2.
Treatment of UCl4 with 1 molar equivalent of calix[4]arene in THF afforded, after heating at
80 °C for 4 d, green crystals of [UCl2(calix[4]arene–2H)(THF)2]·2THF (1·2THF) in 58%
yield. Reaction of UCl4 with 0.5 molar equivalent of calix[6]arene in THF was not so clean
and gave a mixture containing green crystals of [U2Cl2(calix[6]arene–6H)(THF)3]2·6THF
(2·6THF) as a major product, in ca 35% yield, and a pale green powder of an unidentified
compound. Reactions of UCl4 and calix[n]arenes (n = 4, 6) were carried out in pyridine at 20
°C, leading to the immediate formation of light green crystals of [Hpy] 2[UCl3(calix[4]arene–
3H)]·py (4·py) and [Hpy]4[U2Cl6(calix[6]arene–6H)]·3py (5·3py), in 80 and 72% yield,
respectively. The anionic complexes 4 and 5 can be seen as derivatives of the neutral
compounds 1 and 2 after substitution of the THF ligands and breakage of the U–Cl–U and U–
O–U bridges with chloride groups. One of the Cl ligand of 5 was replaced with a pyridine
molecule, giving yellow-green crystals of [Hpy]3[U2Cl5(calix[6]arene–6H)(py)]·py (6·py),
when the mixture of UCl4 and calix[6]arene was heated in refluxing pyridine. Calix[8]arene
being poorly soluble in THF, its reaction with 3 molar equivalents of UCl4 was performed in
refluxing pyridine and after 24 h, green crystals of [Hpy]6[U3Cl11(calix[8]arene–7H)]·3py
(3·3py) were deposited with a 34% yield. In another experiment, the calixarene was first
deprotonated with NaH in THF into the salt [Na(THF)x]7[calix[8]arene–7H] which reacted
with UCl4 in pyridine to give, after 12 h at 80 °C, orange crystals of [U{U2Cl3(calix[8]arene–
7H)(py)5}2]·8py (7·8py), together with a small quantity of green crystals of 3·3py.
<Scheme 2>
6
Replacing UCl4 with U(acac)4 in its reaction with calix[4]arene in pyridine at 20 °C
afforded light green crystals of the acetylacetonate derivative [U(acac)2(calix[4]arene–
2H)]·4py (8·4py) (Scheme 3) together with dark brown crystals of an unidentified compound.
However, reactions with the other calix[n]arenes were rather sluggish, even in refluxing
pyridine solution, and gave small quantities of untractable products. The orange powder
obtained by treatment of U(acac)4 with the sodium salt of calix[6]arene could not be
identified, whereas the green polymeric complex [U2(acac)6(calix[8]arene–6H)(py)4Na4]n (9),
which was formed together with another unknown orange compound from a 1:1:8 mixture of
U(acac)4, calix[8]arene and NaH, was crystallographically characterized.
<Scheme 3>
While reactions of UCl4 and U(acac)4 with calix[4]arene in pyridine afforded the
mono-calixarene complexes 4 and 8, which are inert in the presence of an excess of
calixarene, a solution of an equimolar mixture of U(OTf)4 and calix[4]arene in pyridine at 110
°C
deposited
a
few
dark
brown
crystals
of
the
bis-calixarene
compound
[Hpy]2[U(calix[4]arene–3H)2][OTf]·4py (10·4py) (Scheme 4). That U(OTf)4, in contrast to
UCl4 and U(acac)4, can be transformed into a bis-calixarene compound likely reflects the
lesser coordinating ability of the triflate group. These reactions are reminiscent of those of
UX4 (X = Cl, acac, OTf) with O-dimethylated p-tert-butylcalix[4]arene (H2Me2calix) which
gave respectively the mono- and bis-calixarene complexes [UCl2(Me2calix)(py)2],
[U(acac)2(Me2calix)] and [U(Me2calix)(H2calix)],10 the latter resulting from acid cleavage of
the methoxy groups of one of the two Me2calix ligands of [U(Me2calix)2]. However, the
uranium atom in 10 is in the +5 oxidation state, giving a further example of the easy
7
formation of higher valent compounds in attempts to prepare uranium(IV) complexes with
calixarene ligands.
<Scheme 4>
The syntheses of compounds 1 - 10 were reproducible and repeated at least twice.
However, most of the complexes could not be characterized by their elemental analyses and
their 1H NMR spectra because they could not be separated from other side-products and/or
were poorly soluble in organic solvents. Nevertheless, all the compounds were characterized
by their X-ray crystal structures.
Crystal structures
The crystal structures of 1·2THF, 2·6THF and 3·3py have been described in the preliminary
communication;9 selected bond lengths and angles are recalled for comparison with those
found in compounds 4–10. The structural parameters corresponding to the calix[4]-, calix[6]and calix[8]arene complexes are listed in Tables 1, 2 and 3, respectively.
The crystal structure of 4·py is shown in Fig. 1. The uranium atom is in a sevencoordinated environment which can better be seen as a distorted trigonal prism defined by the
planes [O1, O2, O3] and [Cl1, Cl2, Cl3] and capped by the O4 atom. The four donor atoms of
the calixarene define a mean O4 plane with an r.m.s. deviation of 0.246 Å and the uranium
<Fig. 1>
8
atom is located at 1.1094(15) Å from this mean plane. The macrocycle is in the distorted cone
conformation, with dihedral angles between the four aromatic rings and the O4 plane of
44.72(13), 76.07(12), 33.92(13) and 72.17(14)°. The largest angles correspond to the aromatic
rings linked to the hydrogen bonded O2 and hydroxide O4 atoms which are more distant from
the uranium atom than the phenoxide O1 and O3 atoms. The mean values of the U–Cl, U–
Ophenoxy (with no hydrogen bond) and the U–O4 bond lengths of 2.762(12), 2.135(4) and
2.605(3) Å, respectively, are slightly larger than their counterparts in 1 [mean values 2.72(1),
2.130(5) and 2.528(3) Å], likely reflecting the negative charge of the complex. As it was
already noted,11 the involvement of the phenoxide donor in an intermolecular hydrogen bond
results in a lengthening of the corresponding U–O bond; indeed, U–O2 is larger by ca. 0.14 Å
than U–O1 and U–O3. In addition to the pyridinium ion hydrogen bonded to the phenoxide
oxygen atom O2 [N1···O2 2.575(5) Å, N1–H1···O2 167°], a second pyridinium ion is
involved in a trifurcated hydrogen bond with the three chlorine atoms of the neighbouring
molecule along the a axis [N3···Cl1' 3.259(4), N3···Cl2' 3.290(4) and N3···Cl3' 3.439(4) Å, '
= 1 + x, y, z]. The hydroxide atom O4 is a hydrogen bond donor towards the pyridine
molecule [O4···N2 2.658(5) Å, O4–H4···N2 173°].
The centrosymmetric structure of 5·3py is represented in Fig. 2. In the asymmetric unit,
which exhibits a pseudo symmetry plane defined by the atoms U, N1, O2 and Cl2, U is attached
to the macrocycle via three oxygen atoms and its coordination sphere is completed with three
chlorine atoms to give a fac-O3Cl3 octahedral environment. The calix[6]arene ligand adopts the
<Fig. 2>
common 1,2,3-alternate conformation, U being located at 1.339(2) Å from the O3 plane of the
phenoxide ligands; the dihedral angles between this plane and the three aromatic rings are
9
53.48(12), 86.09(11), and 28.43(16)°. Analogous angle sequences were found in compound
2·6THF; the calixarene conformation is however slightly different in the two compounds since,
whereas the two O3 planes are parallel in 5, in which the two halves are independent from one
another with regard to uranium coordination, they define a dihedral angle of 60.4(4)° in 2, in
which the two half-complexes are connected by the chloride groups. With the exception of the
U–O2 distances corresponding to the hydrogen bonded phenoxide group which are expectedly
longer, the average U–Ophenoxy distance of 2.152(2) Å is similar to that measured in the previous
complexes. The mean U–Cl bond length of 2.68(2) Å is also close to those encountered in 1, 3
and 4. The global anionic charge is balanced by four pyridinium ions, two of which are
hydrogen bonded to the phenoxide oxygen atoms O2 and O2' [N1···O2 2.657(5) Å, N1–
H1···O2 170°], and the other two to two pyridine molecules (N3 and N3') [N2···N3 2.699(7) Å,
N2–H2···N3 168°]. The bond lengths and angles in the trianion of 6·py are close to those in the
tetraanion of 5·3py, the only difference being the replacement of one chloride group with a
pyridine molecule linked to U2 in the non-centrosymmetric complex 6·py.
The centrosymmetric pentanuclear complex 7·8py is organised around a U1 centre that is
coordinated by three adjacent phenoxide groups from each calixarene, in a partial cone
conformation (Fig. 3). The mean U1–O bond length is 2.132(15) Å and the six-coordinate
uranium environment is distorted octahedral. The five other oxygen atoms of the ligand
<Fig. 3>
emcompass two uranium atoms, U2 and U3, which are further bridged by the chlorine atom
Cl1. Charge equilibrium requires one oxygen atom to be protonated, and comparison of the U–
O bond lengths indicates that this atom must be O5. Short contacts between O5 and O4
[3.087(10) Å] or O6 [3.014(10) Å] are indicative of possible hydrogen bonds. Atom U2 is
10
bound to three adjacent phenolic/phenoxide groups and it is located at 0.607(5) Å from the
mean O3 plane they define, whereas atom U3 is bound to two phenoxide groups only. The
coordination geometry of both U2 and U3 is distorted pentagonal bipyramidal with Cl1 and O5
(Cl2 and O8) in apical position for U2 (U3). U2 (U3) is located at 0.055(4) (0.044(4)) Å from
the mean plane defined by the five atoms O4, O6, N1, N2, N3 (O7, N4, N5, Cl1, Cl3) [r.m.s.
deviation 0.21 (0.36) Å]. Complex 7 is, after [W3Cl10(p-tert-butylcalix[8]arene–8H)]12 and 3, a
new example of trinuclear compound of a calix[8]arene. The twisted conformation of the
macrocycle is analogous to that found in the tungsten complex but is different from that
revealed by the crystal structure of 3·3py, which exhibits an unprecedented geometry with three
adjacent phenyl groups lying to one side of the O8 plane and five to the other. The calixarene
conformation in 7·8py can be characterized by the eight pairs of torsion angles (, ) defined by
the methylene links [115(2), –68(2); 74(1), –104(2); –73(2), –22(2); 120(1), –69(1); 75(1), –
116(1); –107(1), 20(2); –90(1), 86(1); 94(1), 15(2)°], which gives the symbolic representation
C1[+ –, + –, – ~0, + –, + –, – ~0, – +, + ~0], evidencing two distorted partial cone sequences.13
The first corresponds to the three phenoxide groups bound to U1 [dihedral angles between the
aromatic rings and the corresponding O3 plane: 27.3(6), 89.6(3) and 45.8(5)°] and the second to
the three phenolic/phenoxide groups bound to U2 [dihedral angles between the aromatic rings
and the corresponding O3 plane: 24.8(4), 85.2(3) and 42.6(4)°].
The asymmetric unit in the neutral complex [U(acac)2(calix[4]arene–2H)]·4py (8·4py)
contains half a molecule, the other half being generated by the binary axis containing the
uranium and the N2 pyridine atoms (Fig. 4). The uranium atom is in an eight-coordinated
environment and adopts a distorted square antiprismatic configuration, one square face being
<Fig. 4>
11
defined by the four oxygen atoms of the calixarene ligand and the other by the four oxygen
atoms of the two acetylacetonate ligands. The uranium atom is located at distances of
1.210(4) and 1.320(5) Å from the calixarene and acetylacetonate mean O4 planes,
respectively, these two planes being parallel to one another. The values of the U–O bond
lengths [U–Ophenoxy 2.146(6) and U–Ohydroxy 2.522(7) Å] and the dihedral angles between the
four aromatic rings and the calixarene O4 plane [37.0(2) and 74.4(2)°] are comparable to those
in complex 4·py. The mean value of the U–Oacac bond lengths, 2.378(3) Å, is identical to the
value encountered in the corresponding O-dimethylated complex [U(acac)2(Me2calix)].10 The
hydroxy group is hydrogen bonded to a pyridine molecule [O2···N1 2.648(12) Å, O2–
H2···N1 161°].
The structure of 9 consists in polymeric chains with [Na2(acac)4] units bridging
tetranuclear [Na2U2(acac)2(calix[8]arene–6H)] assemblies (Fig. 5). The whole unit admits a
pseudo binary axis bisecting the U1–U2 and Na1–Na2 lines. Both uranium atoms are in similar
environments, being bound to three phenoxide groups and three acac ligands, in a bidentate
<Fig. 5>
fashion with two of the latter and in a monodentate fashion with the other. The resulting eightcoordination environment has the geometry of a slightly distorted square antiprism in both
cases, with the square faces defined by atoms O1, O2, O11, O12 and O3, O9, O10, O13 for U1
[r.m.s. deviations 0.10 and 0.14 Å, dihedral angle 3.8(2)°] and O5, O6, O17, O18 and O7, O15,
O16, O19 for U2 [r.m.s. deviation 0.09 Å for both, dihedral angle 2.7(2)°]. The mean U–
Ophenoxy bond lengths [2.29(4) Å for U1, 2.284(13) Å for U2] are larger than in the previous
compounds since all the phenoxide groups are also bound to sodium atoms. In the triphenoxide
subunits bound to U1 and U2, the two lateral phenoxide groups are bound to the sodium ions
12
Na1 and Na2, respectively, which are located in the calixarene cavity and which are further
bound to the phenolic atoms O4 and O8, respectively, and to two pyridine molecules (one of
them disordered, see Experimental Part). Each central phenoxide group is bound to one of the
sodium atoms located out of the cavity (Na3 and Na4). Two acac groups are bound to uranium
atoms only, with a mean U–Oacac bond length of 2.39(5) Å, close to that in compound 8·4py,
whereas the four remaining ones are bridging uranium and sodium atoms. Atoms Na1, Na2 and
Na3 are in five-coordination environments while Na4 is in a distorted octahedral configuration.
However, Na1 and Na2 are also involved in cation··· interactions with the central phenoxide
ring in each triphenoxide subunit, with Na···centroid distances of 2.79 and 2.82 Å and shortest
Na···C contacts of 2.94 and 2.93 Å, respectively. If this interaction is considered as a single
bond with the ring centroid, both Na1 and Na2 are in distorted octahedral environments. The
bridging between adjacent tetranuclear Na2U2 calixarene complex units involves Na2O2 squares,
the oxygen atoms being the acac atoms O14 and O20 and their symmetry equivalents. The
macrocycle is twisted in a propeller fashion, as in the molybdenum14 and tungsten15 complexes
[{Mo(NAr)(MeCN)}2(calix[8]arene–8H)] (Ar = C6H3Pri2) and [{WO(MeCN)}2(p-tertbutylcalix[8]arene–8H)]. The eight pairs of torsion angles (, ) defined by the methylene links
[–124(1), 68(1); –78(1), 129(1); –76(1), 98(1); –46(1), –47(1); –130(1), 72(1); –79(1), 130(1); –
77(1), 98(1); –44(1), –56(1)°] correspond to the approximate symbolic representation C2[– +, –
+, – +, – –, – +, – +, – +, – –], evidencing the partial cone arrangement of the four phenoxide
groups bearing O1, O2, O3 and O4 [dihedral angles between the aromatic rings and the mean
O4 plane (r.m.s. 0.15 Å): 26.1(3), 73.7(2), 40.5(3) and 29.3(2)°] and of the four phenoxide
groups bearing O5, O6, O7 and O8 [dihedral angles between the aromatic rings and the mean
O4 plane (r.m.s. 0.13 Å): 23.4(3), 72.2(2), 40.5(3) and 28.8(2)°]. The two (– –) pairs indicate the
twisting between the two halves, with a dihedral angle of 54.3(2)° between the two mean O4
planes. The calixarene complex thus comprises two partial cones, rotated with respect to one
13
another and each of them with a uranium atom located on its lower rim side and a sodium ion in
the cavity, with distances between these ions and the O4 plane of about 0.65 and 0.52 Å,
respectively. Such assemblies including both uranium (in the form of uranyl ions) and alkali
metal ions have previously been reported in the case of homooxacalixarenes.16
The structure of the cationic [Hpy]2[U(calix[4]arene–3H)2]·4py complex (10·4py) is
shown in Fig. 6. The asymmetric unit contains half a uranium complex, half a triflate ion, one
pyridinium ion and two pyridine solvent molecules, the other half complex being generated
by the binary axis containing the uranium atom. The O8 sandwich arrangement around the
<Fig. 6>
uranium atom defines a distorted square antiprism and the metal atom is located at 1.218(2) Å
from the mean O4 plane of each calixarene. The uranium coordination geometry in 10 is quite
identical to that in the aforementioned O-dimethylated calix[4]arene uranium(IV) congener,
[U(Me2calix)(H2calix)],10 and differs from that in [Na2(py)Ba(R2calix[4]arene)2] (R = C5H9),
the only other 1 : 2 sandwich metal complex with calix[4]arene ligands, which exhibits a
distorted cubic configuration.17 The mean value of the U–Ophenoxy bond length of 2.16(2) Å
seems slightly smaller than that of 2.190(8) Å measured in [U(Me2calix)(H2calix)], in
agreement with the variation in the radii of the UIV and UV ions.18 However, this value is
larger
than
that
of
2.093(14)
[Hpy][UCl2(homocalix[4]arene–4H)]·2.5py
Å
in
the
homocalixarene
(homocalix[4]arene
=
compound
p-tert-
butyltetrahydroxy[3.1.3.1]metacyclophane), the only other mononuclear calixarene compound
of uranium(V);19 this increase in the U–O distances can be attributed to the steric effects
generated by the sandwich arrangement of the two ligands in cone conformation. The hydroxy
group is involved in a hydrogen bond with a pyridine molecule [O2···N1 2.717(6) Å, O2–
14
H2···N1 152°], the U–O2 distance being 2.866(4) Å. The neutrality of the complex is ensured
by the presence of one triflate ion and two pyridinium ions hydrogen bonded to two pyridine
molecules [N2···N3 2.724(7) Å, N2–H···N3 174°].
Conclusion
The results demonstrate that uranium(IV) complexes with calix[n]arenes of varying sizes (n =
4, 6, 8) can be obtained from several UX4 precursors (X = Cl, acac, OTf) in different solvents
(THF, pyridine). Not surprisingly, the formation of polynuclear compounds and ionic species
is favoured by increasing the size of the macrocycle and using a more polar solvent,
respectively. With the exception of the reactions of U(acac)4 with calix[n]arenes (n = 6, 8),
the synthesis of the complexes does not require the use of the sodium salt of the macrocyclic
ligand. While the compounds are formed in a reproducible manner, providing that strictly
anhydrous and anaerobic conditions are used, the major difficulty in their synthesis is their
purification and separation from other side products.
Experimental
Syntheses
All reactions were carried out under argon (< 5 ppm oxygen or water) using standard
Schlenk-vessel and vacuum-line techniques or in a glove box. Solvents were dried by
standard methods and distilled immediately before use. [2H8]THF and [2H5]py (Eurisotop)
were dried over Na/K alloy or NaH, respectively, and stored over 3 Å molecular sieves. The
1
H NMR spectra were recorded on a Bruker DPX 200 instrument and referenced internally
using the residual protio solvent resonances relative to tetramethylsilane ( 0). Elemental
15
analyses were performed by Analytische Laboratorien at Lindlar (Germany). The
calix[n]arenes (Acros) were used without purification. UCl4,20 U(acac)4,21 and U(OTf)422 were
prepared as previously reported.
[UCl2(calix[4]arene–2H)(THF)2]·2THF (1·2THF)
A flask was charged with UCl4 (89.0 mg, 0.024 mmol) and calix[4]arene (100 mg, 0.024
mmol) in THF (15 mL). The reaction mixture was heated for 4 d at 80 °C. The green crystals
of 1·2THF were filtered off, washed with a small quantity of THF and dried under vacuum.
Yield: 120 mg, 0.014 mmol; 58%. Anal. Calcd. for C36H38O6UCl2: C 49.4, H 4.3%. Found: C
49.6, H 4.6%. 1H NMR ([2H8]THF, 23 °C:)  –8.87 and 0.45 (s, 2  4H, CH2), 6.36 and 12.96
(s, 2  2H, aromatic H), 6.96 and 14.89 (s, 2  4H, aromatic H).
[U2Cl2(calix[6]arene–6H)(THF)3]2·6THF (2·6THF)
A flask was charged with UCl4 (96.0 mg, 0.25 mmol) and calix[6]arene (80.0 mg, 0.125
mmol) in THF (15 mL). After heating for 6 d at 80 °C, a mixture containing green crystals of
2·6THF as a major product and a pale green powder of an unidentified compound was filtered
off and dried under vacuum. Yield 58 mg; ca. 35%. Complex 2 could not be obtained in an
analytically pure form. The 1H NMR spectrum of the solution before crystallization exhibits
the signals of 2 and calix[6]arene. 1H NMR ([2H8]THF, 23 °C:)  –8.01, –7.40, –6.78, 0.74,
0.92 and 2.32 (s, 6  4H, CH2), 4.22, 4.68, 4.87, 5.36, 8.55, 11.96, 13.33 and 14.09 (s, 8  4H,
aromatic 8H), 4.46 and 6.38 (s, 2  2H, aromatic H).
[Hpy]6[U3Cl11(calix[8]arene–7H)]·3py (3·3py)
A flask was charged with UCl4 (107 mg, 0.281 mmol) and calix[8]arene (80.0 mg, 0.094
mmol) in pyridine (15 mL). The brown solution was heated at 110 °C and after 24 h, the
16
green crystals of 3·3py were filtered off, washed with a small quantity of pyridine and dried
under vacuum. Yield: 83 mg, 0.096 mmol; 34%. Anal. Calcd. for C96H87N8O8U3Cl11: C 44.6,
H 3.4 %. Found: C 43.3, H 3.4%. 1H NMR ([2H5]py, 23 °C) 
–4.57 and –3.61 (s, 2  2H,
CH2), 0.38 and 1.91 (s, 2  6H, CH2), 7.71, 12.39, 13.71, 13.79, 14.91, 15.65, 16.16 (s, 7 
2H, aromatic H), 8.24 (s, 1H, aromatic H), 9.12–9.98 (m, 9H, aromatic H).
[Hpy]2[UCl3(calix[4]arene–3H)]·py (4·py)
A flask was charged with UCl4 (26.0 mg, 0.068 mmol) and calix[4]arene (30.0 mg, 0.068
mmol) in pyridine (4 mL). The light green crystals of 4·py which were immediately deposited
were filtered off, washed with a small quantity of pyridine and dried under vacuum Yield: 52
mg, 0.056 mmol; 80%. Anal. Calcd. for C38H33N2O4UCl3: C 49.3, H 3.6%. Found: C 50.0, H
3.9%. The complex could not be characterized by its NMR spectrum because of its
insolubility in organic solvents.
[Hpy]4[U2Cl6(calix[6]arene–6H)]·3py (5·3py)
A flask was charged with UCl4 (29.0 mg, 0.076 mmol) and calix[6]arene (24.0 mg, 0.038
mmol) in pyridine (4 mL). The solution was stirred at room temperature overnight and green
crystals of 5·3py were filtered off, washed with a small quantity of pyridine and dried under
vacuum. Yield: 48 mg, 0.054 mmol; 72%. Anal. Calcd. for C72H64N6O6U2Cl6: C 48.1, H 3.6,
N 4.0%. Found: C 47.9, H 3.7, N 4.4%. The complex could not be characterized by its NMR
spectrum because of its insolubility in organic solvents.
[Hpy]3[U2Cl5(calix[6]arene–6H)(py)]·py (6·py)
17
An NMR tube was charged with UCl4 (12.0 mg, 0.031 mmol) and calix[6]arene (10.0 mg,
0.015 mmol) in pyridine (0.4 mL). The reaction mixture was heated at 80 °C and a few
yellow-green crystals of 6·py were deposited from the orange solution.
[U{U2Cl3(calix[8]arene–7H)(py)5}2]·8py (7·8py)
An NMR tube was charged with calix[8]arene (16.5 mg, 0.019 mmol) and NaH (3.7 mg,
0.155 mmol) in [2H8]THF (0.4 mL); the NMR spectrum indicated that the calix[8]arene was
not completely deprotonated; the signal at  17.45 integrates for 1H, corresponding to one OH
proton per ligand molecule. The solution was evaporated to dryness and addition of UCl 4
(22.1 mg, 0.058 mmol) to the sodium salt of the ligand in pyridine (0.4 mL) led, after 12 h at
80°C, to the formation of orange crystals of 7·8py together with a small quantity of green
crystals of 3·3py.
[U(acac)2(calix[4]arene–2H)]·4py (8·4py)
An NMR tube was charged with U(acac)4 (9.0 mg, 0.014 mmol) and calix[4]arene (6.0 mg,
0.014 mmol) in pyridine (0.4 mL). The green solution was stirred at room temperature for 48
h and single crystals of 8·4py were deposited as light green platelets from the brown-green
solution together with dark brown crystals of an unidentified species. The 1H NMR spectrum
of the solution before crystallization exhibits, in addition to the signals of U(acac)4 and
calix[4]arene, the signals of 8 and acacH. 1H NMR ([2H5]py, 23 °C)  –10.99 (s, 4H, CH2), –
2.92 (s, 12H, acac), 0.20 (s, 4H, CH2), 3.77, 5.71 and 14.28 (s, 3  4H, aromatic H), 22.38 (s,
2H, acac).
18
[U2(acac)5(calix[8]arene–6H)(py)4Na4]n (9)
An NMR tube was charged with U(acac)4 (11.2 mg, 0.018 mmol) and calix[8]arene (5.0 mg,
0.006 mmol) in [2H5]py (0.4 mL). Practically no reaction was found to occur after 4 d at
110°C. NaH (1.1 mg, 0.045 mmol) was added to the solution and after 12 h at 110 °C, a
mixture containing light green crystals of 9 and orange needles of an unidentified compound
was obtained.
[Hpy]2[U(calix[4]arene–3H)2][OTf] (10·4py)
An NMR tube was charged with U(OTf)4 (13.8 mg, 0.017 mmol) and calix[4]arene (7.0 mg,
0.017 mmol) in [2H5]py (0.4 mL). Prolonged heating at 110 °C gave a few dark brown
crystals of 10·4py.
Crystallography
The data were collected at 100(2) K on a Nonius Kappa-CCD area detector diffractometer
using graphite-monochromated Mo-K radiation ( = 0.71073 Å). The crystals were
introduced in glass capillaries with a protecting “Paratone-N” oil (Hampton Research)
coating. The unit cell parameters were determined from ten frames, then refined on all data.
The data (- and -scans)23 were processed with HKL2000.24 The structures were solved by
direct methods or Patterson map interpretation with SHELXS-97 and subsequent Fourierdifference synthesis and refined by full-matrix least-squares on F2 with SHELXL-97.25
Absorption effects were corrected empirically with the program DELABS in PLATON26 or
with SCALEPACK.24 All non-hydrogen atoms were refined with anisotropic displacement
parameters. The hydrogen atoms bound to oxygen and nitrogen atoms were found on Fourierdifference maps, except for compounds 3·3py and 7·8py. All the other hydrogen atoms were
19
introduced at calculated positions (except in some disordered fragments). All 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. Special details are as follows:
1·2THF. One of the THF molecules is disordered over two positions sharing three carbon
atoms, which have been refined with occupancy parameters constrained to sum to unity.
2·6THF. Restraints on bond lengths and/or displacement parameters were applied for some
badly behaving atoms, particularly in the very badly resolved solvent molecules. Some voids
in the lattice indicate the presence of other, unresolved solvent molecules.
3·3py. One of the solvent pyridine molecules is disordered around a symmetry centre
(nitrogen atom not located) and another one has been affected with a 0.5 occupancy factor so
as to retain acceptable displacement parameters. Four pyridine molecules or pyridinium ions
were refined as idealized hexagons with restraints on displacement parameters. The
distinction of pyridinium ions from pyridine molecules was inferred from the contacts
indicative of hydrogen bonds and the nitrogen-bound hydrogen atoms were placed
accordingly.
5·3py. One pyridine molecule (containing N4) is disordered around a binary axis and was
refined as an idealized hexagon with a 0.5 occupancy factor.
7·8py. The crystals being very weakly diffracting, the rather low data quality did not permit to
get a very satisfying structure determination. The pyridine solvent molecules in particular are
very badly resolved and three of them were refined as idealized hexagons. Restraints on
displacement parameters were applied for some badly behaving atoms. Some short H···H
contacts involving the solvent molecules are likely due to their imperfect location, whereas
some voids in the lattice indicate the presence of other, unresolved solvent molecules.
8·4py. Restraints on displacement parameters were applied for some atoms of the badly
behaving pyridine solvent molecules. One of these molecules (containing N3) was refined as
20
an idealized hexagon and was affected with a 0.5 occupancy factor so as to retain acceptable
displacement parameters.
9. One pyridine molecule is disordered over two positions (corresponding to atoms N3 and
N4, bound to Na1 and Na2, respectively) which were refined as idealized hexagons, with
occupancy parameters constrained to sum to unity. Restraints on displacement parameters
were applied for some badly behaving atoms, in the acac groups and pyridine molecules.
10·4py. The triflate counter-ion is highly disordered and only the S, C and some O atoms of
two positions appeared at first. These atoms were used to locate two positions of a triflate
model, which were then refined as rigid groups with restraints on displacement parameters.
The triflate moiety was affected with an overall 0.5 occupancy parameter (refined
occupancies for each position: 0.26 and 0.24) so that the displacement parameters retain
acceptable values. This 0.5 occupancy factor is in agreement with the +5 oxidation state of
uranium. The highest residual electron density peaks are located near the disordered triflate
moiety.
Crystal data and structure refinement details are given in Table 4. The molecular plots were
drawn with SHELXTL.27 CCDC reference numbers.
21
References
1
C. D. Gutsche, Calixarenes Revisited, RSC, Cambridge, UK, 1998.
2
Q. Lu, J.H. Callahan and G.E. Collins, Chem. Commun., 2000, 1913.
3
T. Nagasaki, K. Kawano, K. Araki and S. Shinkai, J. Chem. Soc., Perkin Trans. 2
1991, 1325.
4
R. Ludwig, K. Kunogi, N. Dung and S. Tachimori, Chem. Commun., 1997, 1985.
5
P. Thuéry, M. Nierlich, J. M. Harrowfield and M. I. Ogden in Calixarenes 2001, ed. Z.
Asfari, V. Böhmer, J. M. Harrowfield and J. Vicens, Kluwer Academic Publishers,
Dordrecht, 2001, ch. 30.
6
P. Thuéry and B. Masci, Dalton Trans., 2003, 2411 and references therein; X.
Delaigue, C.D. Gutsche, J.M. Harrowfield, M.I. Ogden, B.W. Skelton, D.F. Stewart
and A.H. White, Supramol. Chem., 2004, 16, 603 and references therein.
7
P. C. Leverd and M. Nierlich, Eur. J. Inorg. Chem., 2000, 1733.
8
J. Old, A. A. Danopoulos and S. Winston, New J. Chem., 2003, 27, 672.
9
Preliminary communication: L. Salmon, P. Thuéry and M. Ephritikhine, Chem.
Commun., 2006, 856.
10
L. Salmon, P. Thuéry, Z. Asfari and M. Ephritikhine, Dalton Trans., in press.
11
L. Salmon, P. Thuéry, M. Ephritikhine, Polyhedron, 2003, 22, 2683.
12
V. C. Gibson, C. Redshaw and M. R. J. Elsegood, Chem. Commun., 2002, 1200
13
F. Ugozzoli and G. D. Andreetti, J. Incl. Phenom., 1992, 13, 337.
14
V. C. Gibson, C. Redshaw, W. Clegg and M. R. J. Elsegood, J. Chem. Soc., Chem.
Commun., 1995, 2371.
15
C. Redshaw and M. R. J. Elsegood, Eur. J. Inorg. Chem., 2003, 2071.
16
P. Thuéry and B. Masci, Dalton Trans., 2003, 2411.
17
G. Guillemot, E. Solari, C. Rizzoli and C. Floriani, Chem. Eur. J., 2002, 8, 2072.
22
18
R. D. Shannon, Acta Crystallogr. Sect. A, 1976, 32, 751.
19
L. Salmon, P. Thuéry, T. Yamato and M. Ephritikhine, Polyhedron, 2006, in press.
20
J. A. Hermann and J. F. Suttle, Inorg. Synth., 1957, 5, 143.
21
A. Vallat, E. Laviron and A. Dormond, J. Chem. Soc., Dalton Trans., 1990, 921.
22
J. C. Berthet, M. Lance, M. Nierlich and M. Ephritikhine, Eur. J. Inorg. Chem., 1999,
2005.
23
R. Hooft, COLLECT, Nonius BV, Delft, The Netherlands, 1998.
24
Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307.
25
G. M. Sheldrick, SHELXS-97 and SHELXL-97, University of Göttingen, Germany,
1997.
26
A. L. Spek, PLATON, University of Utrecht, The Netherlands, 2000.
27
G. M. Sheldrick, SHELXTL, Version 5.1, University of Göttingen, Germany,
distributed by Bruker AXS, Madison, WI, 1999.
23
Captions to Schemes and Figures
Scheme 1 Representation of the calixarene molecules.
Scheme 2 Reactions of UCl4 with calix[n]arenes (n = 4, 6, 8).
Scheme 3 Reactions of U(acac)4 with calix[n]arenes (n = 4, 8).
Scheme 4 Reaction of U(OTf)4 with calix[4]arene.
Fig. 1 View of the complex molecule 4·py. The hydrogen atoms have been omitted, except
for those involved in hydrogen bonds (dashed lines). Displacement ellipsoids are drawn at the
30% probability level. Symmetry code: ' = 1 + x, y, z.
Fig. 2 View of the complex molecule in 5·3py. The hydrogen atoms have been omitted,
except for those involved in hydrogen bonds (dashed lines). Displacement ellipsoids are
drawn at the 30% probability level. Symmetry code: ' = –x, –y, –z.
Fig. 3 View of the complex molecule in 7·8py. The hydrogen atoms have been omitted. All
atoms are represented as spheres for clarity, the carbon atoms being arbitrarily reduced.
Symmetry code: ' = –x, –y, –z.
Fig. 4 View of the complex molecule in 8·4py. The hydrogen atoms have been omitted,
except for those involved in hydrogen bonds (dashed lines). Displacement ellipsoids are
drawn at the 20% probability level. Symmetry code: ' = –x, y, 3/2 – z.
24
Fig. 5 Partial view of the polymeric chain in 9. The hydrogen atoms have been omitted,
except for those involved in hydrogen bonds (dashed lines). The carbon atoms of the pyridine
molecules have been omitted for clarity. All atoms are represented as spheres, the carbon
atoms being arbitrarily reduced. The Na– interactions are shown as dashed lines. Symmetry
codes: ' = –x – 1, 1 – y, 1 – z; " = 1 – x, –y, –z.
Fig. 6 View of the complex molecule in 10·4py. The hydrogen atoms have been omitted,
except for those involved in hydrogen bonds (dashed lines). Displacement ellipsoids are
drawn at the 30% probability level. Symmetry code: ' = –x, y, 3/2 – z.
25
Table 1. Environment of the uranium atoms in the calix[4]arene complexes 1, 4, 8 and 10:
selected bond lengths (Å) and angles (°)
1·2THF
U–O1
U–O2
U–O3
U–O4
U–O5
U–O6
U–Cl1
U–Cl2
2.135(3)
2.531(3)
2.125(3)
2.525(3)
2.579(3)
2.644(3)
2.7092(10)
2.7297(10)
U–O1–C2
U–O2–C9
U–O3–C16
U–O4–C23
176.6(3)
124.3(2)
172.0(3)
123.0(2)
4·py
U–O1
U–O2
U–O3
U–O4
U–Cl1
U–Cl2
U–Cl3
2.139(3)
2.279(3)
2.130(3)
2.605(3)
2.7772(11)
2.7629(11)
2.7470(12)
U–O1–C2
U–O2–C9
U–O3–C16
U–O4–C23
170.4(3)
125.2(3)
171.2(3)
123.7(3)
8·4py
U–O1
U–O2
U–O3
U–O4
2.146(6)
2.522(7)
2.381(8)
2.374(7)
U–O1–C2
U–O2–C9
175.0(5)
124.5(5)
10·4py
U–O1
U–O2
U–O3
U–O4
2.154(4)
2.866(4)
2.141(3)
2.185(3)
U–O1–C2
U–O2–C9
U–O3–C16
U–O4–C23
170.3(4)
120.8(3)
165.3(4)
132.0(3)
26
Table 2. Environment of the uranium atoms in the calix[6]arene complexes 2, 5 and 6:
selected bond lengths (Å) and angles (°)
2·6THF
U1–O1
U1–O2
U1–O3
U1–O7
U1–O2'
U1–Cl1
U1–Cl2
2.112(9)
2.383(7)
2.128(8)
2.506(10)
2.372(9)
2.795(4)
2.865(3)
U2–O4
2.142(9)
U2–O5
2.227(10)
U2–O6
2.123(8)
U2–O8
2.518(11)
U2–O9
2.518(10)
U2–Cl1
2.740(4)
U2–Cl2
2.888(4)
Symmetry code: ' = –x, 2 – y, –z.
5·3py
U–O1
2.154(3)
U–O2
2.238(3)
U–O3
2.149(3)
U–Cl1
2.6973(10)
U–Cl2
2.6488(12)
U–Cl3
2.6958(10)
Symmetry code: ' = –x, –y, –z.
U1–O1–C2
U1–O2–C9
U1–O3–C16
U1–O2'–C9'
U1–O2–U1'
U1–Cl1–U2
U1–Cl2–U2
150.1(9)
111.5(7)
146.5(9)
130.3(7)
117.8(4)
110.31(12)
104.30(11)
U2–O4–C23
U2–O5–C30
U2–O6–C37
165.3(8)
106.6(8)
166.6(9)
U1···U2
U1···U1'
4.5430(8)
4.0726(9)
U–O1–C2
U–O2–C9
U–O3–C16
166.4(3)
125.8(2)
163.4(3)
U···U'
7.7685(4)
6·py
U1–O1
U1–O2
U1–O3
U1–Cl1
U1–Cl2
U1–Cl3
2.123(3)
2.236(3)
2.129(3)
2.6891(12)
2.6699(11)
2.7072(12)
U1–O1–C2
U1–O2–C9
U1–O3–C16
165.0(3)
126.3(3)
162.7(3)
U2–O4
U2–O5
U2–O6
U2–Cl4
U2–Cl5
U2–N1
2.133(3)
2.203(3)
2.142(3)
2.6658(12)
2.6999(12)
2.579(4)
U2–O4–C23
U2–O5–C30
U2–O6–C37
167.0(3)
126.2(3)
166.8(3)
U1···U2
7.4012(3)
27
Table 3. Environment of the uranium atoms in the calix[8]arene complexes 3, 7 and 9:
selected bond lengths (Å) and angles (°)
3·3py
U1–O1
U1–O2
U1–O3
U1–Cl1
U1–Cl2
U1–Cl3
2.127(9)
2.244(8)
2.120(8)
2.637(4)
2.704(4)
2.702(4)
U1–O1–C2
U1–O2–C9
U1–O3–C16
167.0(8)
125.5(7)
159.5(8)
U2–O4
U2–O5
U2–Cl4
U2–Cl5
U2–Cl6
U2–Cl7
2.128(9)
2.143(8)
2.693(3)
2.649(4)
2.663(4)
2.675(4)
U2–O4–C23
U2–O5–C30
161.3(8)
144.9(7)
U3–O7
U3–O8
U3–Cl8
U3–Cl9
U3–Cl10
U3–Cl11
2.198(7)
2.107(8)
2.653(4)
2.644(5)
2.684(4)
2.650(4)
U3–O7–C44
U3–O8–C51
135.0(7)
169.8(7)
U1···U2
U1···U3
U2···U3
8.8708(9)
8.8110(9)
8.8968(11)
7·8py
U1–O1
U1–O2
U1–O3
2.111(9)
2.141(7)
2.145(7)
U1–O1–C2
U1–O2–C9
U1–O3–C16
156.9(7)
124.3(7)
166.1(7)
U2–O4
U2–O5
U2–O6
U2–Cl1
U2–N1
U2–N2
U2–N3
2.117(7)
2.231(7)
2.134(7)
2.771(3)
2.644(9)
2.625(9)
2.627(9)
U2–O4–C23
U2–O5–C30
U2–O6–C37
168.3(7)
103.5(6)
165.3(8)
U3–O7
U3–O8
U3–Cl1
U3–Cl2
U3–Cl3
U3–N4
U3–N5
2.062(8)
2.094(7)
2.993(3)
2.682(3)
2.677(5)
2.588(11)
2.611(10)
U3–O7–C44
U3–O8–C51
159.8(7)
150.1(7)
9
U1–O1
U1–O2
U1–O3
U1–O9
U1–O10
U1–O11
U1–O12
U1–O13
2.267(5)
2.264(5)
2.344(5)
2.329(5)
2.427(5)
2.344(5)
2.484(5)
2.398(5)
U1–O1–C2
U1–O2–C9
U1–O3–C16
140.9(5)
124.5(4)
143.1(4)
U2–O5
U2–O6
2.285(5)
2.267(5)
U2–O5–C30
U2–O6–C37
135.7(5)
120.5(4)
28
U2–O7
U1–O15
U1–O16
U1–O17
U1–O18
U1–O19
2.300(5)
2.446(5)
2.355(5)
2.369(5)
2.464(5)
2.400(5)
U2–O7–C44
143.9(4)
29
Table 4 Crystal data and structure refinement details
Empirical formula
M/g mol1
Crystal system
Space group
a/Å
b/Å
c/Å
/°
/°
/°
V/Å3
Z
Dcalc/g cm3
 (MoK)/mm1
F(000)
Reflections collected
Independent reflections
Observed reflections [I > 2(I)]
Rint
Parameters refined
R1
wR2
S
min/e Å3
max/e Å3
4·py
C43H38Cl3N3O4U
1005.14
monoclinic
P21/n
11.8531(2)
18.9402(4)
17.8786(5)
90
101.0440(10)
90
3939.41(15)
4
1.695
4.370
1968
76916
7390
6593
0.053
487
0.028
0.087
1.157
–1.07
1.22
5·3py
C77H69Cl6N7O6U2
1877.15
monoclinic
C2/c
26.0764(8)
12.8301(4)
24.7114(7)
90
118.024(2)
90
7298.2(4)
4
1.708
4.710
3656
58951
6923
5851
0.059
481
0.028
0.077
1.139
–1.19
0.66
6·py
C67H58Cl5N5O6U2
1682.49
monoclinic
P21/c
14.6847(5)
21.1309(7)
20.9186(4)
90
106.721(2)
90
6216.6(3)
4
1.798
5.475
3248
102896
11793
9791
0.070
766
0.030
0.080
1.062
–1.30
1.01
7·8py
C202H172Cl6N18O16U5
4510.43
monoclinic
P21/c
21.4083(15)
27.4775(13)
18.5799(14)
90
107.243(4)
90
10438.4(12)
2
1.435
4.002
4400
148163
19622
9919
0.113
1078
0.075
0.210
0.961
–0.83
1.68
8·4py
C58H56N4O8U
1175.10
monoclinic
C2/c
21.3919(5)
17.0589(5)
17.0640(5)
90
120.446(2)
90
5368.4(3)
4
1.454
3.080
2352
39725
4943
3752
0.082
339
0.071
0.186
1.082
–0.96
1.12
9
C106H104N4Na4O20U2
2321.95
triclinic
Pī
12.4838(4)
12.7588(5)
33.6497(14)
81.021(4)
79.732(4)
70.613(2)
4947.6(3)
2
1.559
3.358
2312
102502
18745
13051
0.073
1268
0.054
0.148
1.058
–1.11
1.62
10·4py
C87H74F3N6O11SU
1706.61
monoclinic
C2/c
26.448(3)
10.0747(14)
29.331(6)
90
97.737(8)
90
7744(2)
4
1.464
2.196
3444
93228
7319
6253
0.050
565
0.049
0.131
1.075
–0.93
2.29
30