Supramolecular assemblages from uranyl ion complexes of
calixarenes and potassium complexes of 18-crown-6 or dibenzo18-crown-6
Pierre Thuéry a, Bernardo Masci b, Masashi Takimoto c, Takehiko Yamato c
a
CEA/Saclay, DSM/DRECAM/SCM (CNRS URA 331), Bât. 125, 91191 Gif-sur-Yvette, France.
E-mail: pierre.thuery@cea.fr
b
Dipartimento di Chimica, Università “La Sapienza”, Box 34, Roma 62, P.le Aldo Moro 5, 00185
Roma, Italy. E-mail: bernardo.masci@uniroma1.it
c
Department of Applied Chemistry, Faculty of Science and Engineering, Saga University, Saga 8408502, Japan. E-mail: yamatot@cc.saga-u.ac.jp
Abstract
Reaction of uranyl nitrate with p-tert-butyl[3.1.3.1]homocalixarene (L1H4) or p-tertbutylcalix[8]arene (L2H8) has been carried out in the presence of KOH and 18-crown-6 (18C6) or
dibenzo-18-crown-6
(db18C6),
giving
[K(db18C6)(H2O)2]3[{UO2(L1)}2K(H2O)5]
(1)
the
and
supramolecular
assemblages
[K(18C6)(OH)2][{(UO2)2(L2H5)(OH)}-
{K(18C6)}] (2). Compound 1 comprises a sandwich, “complex-within-complex” assemblage in
which two uranyl/calixarene complexes encompass a potassium/crown ether guest. A direct bond
between uranyl and K(18C6) is present in 2, in which a columnar arrangement of alternate
dimetallic calixarene complexes and potassium/crown ether species is formed.
Keywords: Uranyl ion; Calixarenes; Homocalixarenes; Crown ethers, Supramolecular
assemblage
1
The assembling properties of the uranyl ion UO22+, due to both its geometrical
requirements of planar coordination environments and the Lewis basicity of its oxo groups
and their subsequent involvement in coordination or hydrogen bonds, have been investigated
in the past years [1]. We have shown in particular that the cationcation U=OM bonds, in
which M is an alkali metal ion, can be used to assemble uranyl/homooxacalixarene complexes
to form various assemblages, among which columnar architectures are noticeable [1c].
Further work was devoted to assemblages comprising the cone-shaped uranyl complex with
p-tert-butyl[3.1.3.1]homooxacalixarene
[2]
as
host
and
the
quasi-spherical
{M[2.2.2](H2O)2}2+ cations (M = Sr, Ba and [2.2.2] = [2.2.2]cryptand) as guests, which are
novel examples of “complex-within-complex” species [1a]. The variety of assemblages
obtained with uranyl/homooxacalixarene complexes and different guests prompted us to
extend this work to other building units. We report herein the synthesis and crystal structure
of the first complexes in this family including the simple potassium complexes of 18-crown-6
(18C6) or dibenzo-18-crown-6 (db18C6), obtained with two calixarenes of very different size
and conformation, p-tert-butyl[3.1.3.1]homocalixarene (L1H4) and p-tert-butylcalix[8]arene
(L2H8) (Scheme 1).
As often with such products which are difficult to obtain in crystalline form,
complexes
[K(db18C6)(H2O)2]3[{UO2(L1)}2K(H2O)5]
(1)
and
[K(18C6)(OH)2][{(UO2)2(L2H5)(OH)}{K(18C6)}] (2) were obtained in very low yields [3],
but their crystal structures could be determined [4]. The dianionic uranyl complex moiety
[UO2(L1)]2 in compound 1 is analogous to that previously determined with this macrocycle
in the presence of triethylamine [5]. The uranyl ion is located at the centre of the calixarene in
the cone conformation and is bound to the four phenoxide groups with an average UO bond
length of 2.274(5) Å (tetragonal bipyramidal or distorted octahedral uranium environment).
The four phenoxide oxygen atoms define a mean plane with an r.m.s. deviation of 0.015 Å,
2
with the uranium atom displaced by 0.069(2) Å, and making dihedral angles of 44.84(11),
31.81(13), 46.52(14) and 41.31(13)° with the four aromatic rings. Two such complex dianions
are assembled around a sandwiched [K(db18C6)(H2O)2]+ moiety, giving a centrosymmetric
trianionic “complex-within-complex” species in which the guest is held by two H2O···O(oxo)
hydrogen bonds [O16···O6 2.919(6) Å] (Fig. 1). Other weak interactions may be present,
such as van der Waals, cationanion, cation and CH interactions. Among the latter, two
are notable, one involving a proton of the central carbon atom of a (CH2)3 bridge of the
calixarene and the aromatic ring of the crown ether (H···centroid distance 2.96 Å,
CH···centroid angle 158°) and the other between a proton of a CH2 group of the crown and
the aromatic ring bearing O1 (H···centroid distance 2.81 Å, CH···centroid angle 139°). The
two water molecules bound to K1 are in trans positions and the crown ether assumes a rather
flat, centrosymmetric shape.
In contrast, in the [K(db18C6)(H2O)2]+ moiety containing atom K2, the crown ether is
strongly curved [dihedral angle between the two aromatic rings 79.8(2)°] and the two water
molecules are in cis position with respect to one another, both on the convex side of the crown
ether. The two uranyl and three potassium complexes give an overall 1 charge, which is
compensated by a potassium ion highly disordered over four positions (K3A, K3B and their
symmetry equivalents [4]; the U/K 1 : 2 ratio was confirmed by atomic absorption
spectroscopy [3]). This potassium ion is not bound to a crown ether molecule, but instead to
two uranyl oxo atoms located out of the calixarene cavity (O5 and one of its symmetry
equivalents), to one phenoxide group and to four water molecules (K3A) or to two oxo groups
and six water molecules (K3B) (hence the average of five water molecules per potassium ion).
The average KO(oxo) bond length, 2.67(13) Å, is in the lower part of the range
2.658(6)3.230(6) Å previously observed [1c]. Several hydrogen bonds link these water
molecules to those bound to K2 and to phenoxide oxygen atoms. The [K(db18C6)(H2O)2]+
3
complex containing K2 interacts loosely with the uranyl calixarene complex, through
hydrogen bonds [O17···O3 2.795(5), O17···O5 3.183(6) Å] and several CH interactions
involving four different calixarene units (H···centroid distances in the range 2.712.98 Å,
CH···centroid angles in the range 116172°). Moreover, these [K(db18C6)(H2O)2]+
complexes self-assemble to form dimers with crown ethers facing one another through their
concave face and offset so that K interactions may be present (Fig. 2). However, the
shortest K2···C contact of 3.534(6) Å and the K2···centroid distance of 4.43 Å are large
values compared with other instances of K interactions (for example the K···centroid
distances of 3.503.65 Å and the shortest K···C contacts of 3.183.26 Å in the calixarene
complex cited above [1c]). The main interaction between the two crowns may thus be
essentially a parallel-displaced -stacking one between the two aromatic rings
(centroid···centroid distance 3.84 Å, centroid offset 1.46 Å). A similar case, but with more
clearcut metal interactions, has been reported for a rubidium complex of db18C6 [6]. In the
crystal packing of 1, the calixarene/crown ether sandwiches are held in columns parallel to the
c axis by the hydrated potassium ions K3A/K3B, these columns being then interlinked by the
hydrogen bonded {[K(db18C6)(H2O)2]2}2+ dimers.
Compound 2, [K(18C6)(OH)2][{(UO2)2(L2H5)(OH)}{K(18C6)}], comprises one of
the largest calixarenes used up to now in this family of supramolecular assemblages (the
rubidium-containing capsule [(UO2)4Rb4(LH4)2(OH)4(H2O)4], involving the even larger ptert-butyloctahomotetraoxacalix[8]arene or p-tert-butyl[3.1.3.1.3.1.3.1]homooxacalixarene
LH8 has been reported previously [7]). The uranyl/calixarene complex core in 2 is the
hydroxo-centered bimetallic species described earlier in the presence of triethylammonium
counter ions [8], in which each uranyl ion is bound to four phenolic/phenoxide and one
hydroxide oxygen atoms (pentagonal bipyramidal uranium environment), the calixarene being
in a saddle-shaped conformation (Fig. 3). The bond lengths and angles around the uranium
4
atoms are identical to those in the previous case, with however a difference in the
deprotonation degree of the calixarene. Whereas four phenolic groups are deprotonated in the
previous complexes (corresponding to O2, O3, O6 and O7 with the present numbering), the
bond lengths in 2 show unambiguously that the calixarene is deprotonated only at the three
sites O2, O3 and O7, the phenolic oxygen atom O6 being further involved as a donor in a
hydrogen bond (see below). The uranyl/calixarene complex in 2 is thus a neutral species.
Two [K(18C6)]+ moieties are present in the asymmetric unit. In one of them, the
potassium atom K1 is bound to two extra oxygen atoms located on the same side of the crown
ether mean plane (O20, O21), which, for charge balance, have been considered as being
hydroxide ions. Through the latter, this moiety is hydrogen bonded to the phenoxide atoms
O2 and O3 [O2···O20 2.765(17) and O3···O21 2.746(19) Å]. Another hydrogen bond is
formed between the ether atom O18 and the phenolic group HO6 on a neighbouring unit
[O6'···O18 2.759(18); symmetry code: ' = –x, –y, –z]. The other [K(18C6)]+ moiety is more
tightly bound to the uranyl complex, through a K2O10(oxo) bond, with a bond length of
2.705(14) Å which is well in the range 2.658(6)3.230(6) Å previously observed for such
bonds [1c] and a U1O10K2 angle of 168.1(7)°. The crown ether is also involved in a
hydrogen bond with the bridging hydroxide group [O13···O26 2.851(19) Å], hence its
position nearly parallel to the mean plane of the half-calixarene containing U1.
The packing in 2 comprises columns of uranyl/calixarene complexes directed along
the c axis, with successive units related by inversion centers and separated either by two
hydrogen bonded K1 complexes or by two oxo- and hydrogen bonded K2 complexes (Fig. 4).
Curiously, apart from a possible CH interaction linking a proton of the crown ether bound
to K2 and an aromatic ring of the neighbouring calixarene along the c axis (H···centroid
distance 2.98 Å, CH···centroid angle 131°), there is no significant -stacking or other CH
5
interactions present. The packing thus seems to depend mainly on hydrogen bonding and van
der Waals interactions.
The two compounds 1 and 2 are novel examples of the assemblages uniting different
metal complexes which can be obtained in the uranyl/calixarene family. In both cases, the
uranyl/calixarene complex geometry remains essentially the same, whatever the associated
species or counter ions, as it is also the case with p-R-[3.1.3.1]- and p-R[3.3.3]homooxacalixarenes [1a,c]. The first compound, involving a homocalixarene in the
cone conformation and of suitable size for the potassium/crown ether guest, is a “complexwithin-complex” sandwich species, in which the situation is however complicated, with
respect to previous examples of such architectures [1a], by the presence of a second
potassium/crown ether moiety located out of the cavity and a highly disordered, oxo-bound
potassium ion. Compound 2 includes the much larger p-tert-butylcalix[8]arene, which is
suitable for complexation of two, hydroxo-bridged, uranyl ions. No cavity is defined in this
case, the uranyl/calixarene moiety being much flatter than in 1. Cation-cation interactions
between uranyl and potassium are also present in compound 2, thus uniting the two metal
complexes. The packing in 2 comprises a columnar arrangement of alternate uranyl/calixarene
and potassium/crown ether complexes.
6
References
[1] (a) B. Masci, P. Thuéry, CrystEngComm 8 (2006) 764;
(b) P. Thuéry, C. Villiers, J. Jaud, M. Ephritikhine, B. Masci, J. Am. Chem. Soc. 126
(2004) 6838;
(c) P. Thuéry, B. Masci, Dalton Trans. (2003) 2411;
(d) P. Thuéry, B. Masci, Supramol. Chem. 15 (2003) 95;
(e) P. Thuéry, M. Nierlich, J. Vicens, B. Masci, J. Chem. Soc., Dalton Trans. (2001) 3410.
(f) P. Thuéry, M. Nierlich, B. Souley, Z. Asfari, J. Vicens, J. Chem. Soc., Dalton Trans.
(1999) 2589.
[2] The names [3.1.3.1]homooxacalixarene and [3.1.3.1]homocalixarene replace the current
but ambiguous names tetrahomodioxacalix[4]arene and tetrahomocalix[4]arene. See: (a)
B. Masci, in Calixarenes 2001, eds. Z. Asfari, V. Böhmer, J. Harrowfield, J. Vicens,
Kluwer Academic Publishers, Dordrecht, 2001, ch. 12; (b) B. Masci, S. Levi Mortera, D.
Persiani, P. Thuéry, J. Org. Chem. 71 (2006) 504.
[3] L1H4 was synthesized as previously reported [9]. L2H8 was purchased from Acros and the
crown ethers from Merck; all were used without further purification.
Synthesis of 1. A solution of UO2(NO3)2·6H2O (15 mg, 0.030 mmol) and dibenzo-18crown-6 (43 mg, 0.120 mmol) in MeOH/CHCl3 1 : 1 (20 mL) was added to a solution of
L1H4 (21 mg, 0.030 mmol) and KOH (7 mg, 0.125 mmol) in MeOH (40 mL). The
resulting orange solution was refluxed for 10 min and left to evaporate slowly, yielding
orange crystals within some days. The reaction yield was too low for a chemical analysis
to be performed. The U/K ratio could however be confirmed by atomic absorption
spectroscopy (ratio U/K = 2.92; calculated for the 1 : 2 stoichiometry: 3.04).
7
Synthesis of 2. A solution of UO2(NO3)2·6H2O (43 mg, 0.086 mmol) and 18-crown-6 (92
mg, 0.348 mmol) in MeOH (10 mL) was added to a solution of L2H8 (56 mg, 0.043
mmol) and KOH (20 mg, 0.357 mmol) in MeOH (30 mL). The resulting dark orange
solution was refluxed for 10 min and left to evaporate slowly, yielding orange crystals in
low yield within some days.
[4] Crystal data for 1: C156H214K4O41U2, M = 3377.73, triclinic, space group Pī, a =
12.4980(11), b = 16.3604(13), c = 20.8724(11) Å,  = 84.095(5),  = 82.685(5),  =
72.784(4)°, V = 4033.9(5) Å3, Z = 1, T = 100(2) K. Refinement of 965 parameters on
15232 independent reflections out of 82283 measured reflections (Rint = 0.086) led to R1 =
0.051, wR2 = 0.122, S = 1.039, min = –1.18, max = 1.74 e Å–3.
Crystal data for 2: C112H160K2O27U2, M = 2492.66, triclinic, space group Pī, a =
18.2306(17), b = 18.4573(15), c = 21.1925(12) Å,  = 104.778(4),  = 103.085(5),  =
107.386(3)°, V = 6216.2(8) Å3, Z = 2, T = 100(2) K. Refinement of 1311 parameters on
21861 independent reflections out of 75054 measured reflections (Rint = 0.083) led to R1 =
0.118, wR2 = 0.338, S = 1.027, min = –1.25, max = 1.70 e Å–3.
Data were collected on a Nonius Kappa-CCD area-detector diffractometer and processed
with HKL2000 [10]. The structures were solved by Patterson map interpretation (1) or by
direct methods (2) and refined by full-matrix least-squares on F2 with SHELXTL [11].
Absorption effects were corrected empirically with DELABS [12]. All non-hydrogen
atoms were refined with anisotropic displacement parameters. In 1, one of the potassium
atoms (K3) is highly disordered and two positions (A and B) have been refined with
occupancy parameters constrained to sum to 0.5, in order to account for the impossibility
of symmetry-related positions to be simultaneously occupied (being too close to one
another). The associated water molecules are disordered as well. The U/K ratio was
confirmed by atomic absorption spectroscopy [3]. Some voids in the packing of 2 likely
8
indicate the presence of unresolved solvent molecules. CCDC- (1) and (2) contain the
supplementary crystallographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk.
[5] P. Thuéry, J.T. Gil, T. Yamato, Supramol. Chem. 15 (2003) 359.
[6] P. Lin, W. Clegg, R.W. Harrington, R.A. Henderson, Dalton Trans. (2005) 2349.
[7] P. Thuéry, B. Masci, Supramol. Chem. 16 (2004) 81.
[8] (a) P. Thuéry, N. Keller, M. Lance, J.D. Vigner, M. Nierlich, Acta Crystallogr., Section C
51 (1995) 1570;
(b) P. Thuéry, N. Keller, M. Lance, J.D. Vigner, M. Nierlich, New J. Chem. 19 (1995)
619.
[9] T. Yamato, Y. Saruwatari, S. Nagayama, K. Maeda, M. Tashiro, J. Chem. Soc., Chem.
Commun. (1992) 861.
[10] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307.
[11] G.M. Sheldrick, SHELXTL, Version 5.1, Bruker AXS Inc., Madison, WI, USA, 1999.
[12] A.L. Spek, PLATON, University of Utrecht, The Netherlands, 2000.
9
Figures captions
Scheme 1. The calixarenes under study.
Fig. 1. View of compound 1. Only one position of the disordered atom K3 is represented.
Hydrogen atoms have been omitted. Hydrogen bonds are shown as dashed lines. Symmetry
codes: ' = 1 – x, 2 – y, 2 – z; " = 1 – x, 2 – y, 1 – z. Selected bond lengths (Å) and angles (°):
U–O1 2.279(4), U–O2 2.278(3), U–O3 2.266(4), U–O4 2.273(4), U–O5 1.798(4), U–O6
1.799(3); O1–U–O2 86.68(13), O2–U–O3 92.53(13), O3–U–O4 87.70(13), O4–U–O1
92.90(13), O5–U–O6 179.05(18).
Fig. 2. View showing the intermolecular association of [K(db18C6)(H2O)2]+ moieties in 1 by
-stacking interactions (dashed line). Symmetry code: ' = 2 – x, 1 – y, 1 – z.
Fig. 3. View of compound 2. Hydrogen atoms have been omitted. Hydrogen bonds are shown
as dashed lines. Symmetry code: ' = –x, –y, –z. Selected bond lengths (Å) and angles (°): U1–
O1 2.554(12), U1–O2 2.235(10), U1–O3 2.250(11), U1–O4 2.622(12), U1–O9 1.719(10),
U1–O10 1.728(11), U1–O13 2.347(9), U2–O5 2.430(11), U2–O6 2.515(10), U2–O7
2.294(10), U2–O8 2.418(11), U2–O11 1.685(11), U2–O12 1.674(8), U2–O13 2.305(10), K2–
O10 2.705(14); O1–U1–O2 75.8(4), O2–U1–O3 79.5(4), O3–U1–O4 72.9(4), O4–U1–O13
65.6(4), O13–U1–O1 67.4(4), O9–U1–O10 178.6(5), O5–U2–O6 72.0(3), O6–U2–O7
71.7(4), O7–U2–O8 77.1(4), O8–U2–O13 69.1(4), O13–U2–O5 71.5(4), O11–U2–O12
177.3(5), U1–O13–U2 141.4(5), U1–O10–K2 168.1(7).
10
Fig. 4. View of the columnar assemblage along the c axis in compound 2. Hydrogen bonds are
shown as dashed lines. Symmetry codes: ' = –x, –y, –z; " = –x, –y, 1 – z.
11
Scheme 1
12
Figure 1
Figure 2
13
Figure 3
Figure 4
14
Graphical Abstract
Two assemblages comprising uranyl/calixarene and potassium/crown ether complexes are
described. A sandwich architecture is obtained with the smaller, cone-shaped p-tertbutyl[3.1.3.1]homocalixarene, whereas a columnar stacking is obtained with the larger and
flatter p-tert-butylcalix[8]arene.
U
K
U
15