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Synthesis and crystal structure of sodium and caesium ion complexes of unsubstituted calix[4]arene.
Polyhedron 21 (2002) 2497 /2503 www.elsevier.com/locate/poly
Synthesis and crystal structure of sodium and caesium ion complexes of unsubstituted calix[4]arene. New polymeric chain arrangements Pierre Thue´ry a,*, Zouhair Asfari b, Jacques Vicens b, Ve´ronique Lamare c, Jean-Franc¸ois Dozol c b
a CEA/Saclay, DSM/DRECAM/SCM (CNRS URA 331), Baˆt. 125, 91191 Gif-sur-Yvette, France ECPM, Laboratoire de Chimie des Interactions Mole´culaires Spe´cifiques (CNRS UMR 7512), 25 rue Becquerel, 67087 Strasbourg, France c CEA/Cadarache, DED/SEP/LCD, 13108 Saint-Paul-lez-Durance, France
Received 20 June 2002; accepted 22 August 2002
Abstract Calix[4]arene, devoid of p -alkyl substituents, has been used to complex sodium and caesium ions in a basic medium. The crystal structures of one sodium and two caesium complexes are reported and compared to previous structures with related p -tert butylcalixarenes. The sodium complex is dimeric, two cations being sandwiched between two mono-anionic calixarenes through Ocoordination, and bound also to three acetone molecules (one bridging) in the median plane. Both caesium complexes are polymeric, with a stacking of alternate cations and mono-anionic calixarenes, with both polyhapto bonding and O-coordination. This novel arrangement is attributed to the lack of bulky p -substituents in the ligand, which enables the cation included in the cavity of one calixarene to be closely approached by the oxygen donors of a second one on the other side. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Alkali metal ions; Sodium ion; Caesium ion; Calix[4]arene; Crystal structures
1. Introduction The affinity of parent or functionalized calixarenes towards alkali metal ions is a much investigated phenomenon. ‘Template’ effects during the base-induced synthesis of calixarenes, which depend on the alkali metal hydroxide used as a catalyst, have been suggested early [1], while p-tert -butylcalix[4,6,8]arenes proved to be efficient transporters of alkali metal ions through liquid membranes with a selectivity for caesium ions [2]. Some work has been devoted to the structural characterization of the complexes formed with lithium, sodium and potassium ions by simple calixarenes, particularly p -tert -butylcalix[4]arene and its O-alkylated derivatives [3 /8], also potassium with p -tert -butylca-
* Corresponding author. Tel.: /33-1-6908-6329; fax: /33-1-69086640 E-mail address: [email protected] (P. Thue´ry).
lix[8]arene [9], and with the largest caesium ions, by ptert -butylcalix[4]arene [10] and p-tert -butyldihomooxacalix[4]arene [11]. Recently, the complexation of the whole Li /Cs series by p -tert-butyltetrathiacalix[4]arene has been investigated [12]. Partial calix[n]arenes (polyaryloxide ligands) have also been considered in this respect [13]. Broadly speaking, two extreme coordination modes are observed with these calixarenes: an exo one, in which the cation is bound to the ‘hard’ phenolic/ phenoxide oxygen atoms, and an endo one which corresponds to p-bonding by the ‘soft’ aromatic rings defining the calixarene cavity. Mixed situations evidencing this ambivalent character of calixarenes as ligands are however commonly observed [6,7,11], while sulfur atoms compete with aromatic rings as ‘soft’ sites in tetrathiacalix[4]arenes [12]. p-Bonding was further exploited in the design of selective extractants for caesium cations which are needed in the context of nuclear fuel reprocessing, using calixcrowns and calix bis (crowns) in the 1,3-alternate conformation [14],
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 2 2 9 - 9
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which are also used to build selective sensors [15]. In addition, many examples of alkali metal ion complexation by calix[4]arenes bearing complexing arms on the lower rim (particularly carbonyl derivatives) are known [16] as well as complexes uniting transition metal and alkali metal ions [17] and complexes with p -sulfonato derivatives of calix[4,5]arenes [18] and calix[6]arenes [19]. Considering the relative scarcity of simple calix[4]arenes (unsubstituted on the lower rim) used for the structural characterization of such complexes, these being reduced to p -tert -butylcalix[4]arene, p -tert-butyldihomooxacalix[4]arene and p -tert-butyltetrathiacalix[4]arene, we decided to investigate the complexes formed by the simplest member of this family, calix[4]arene, denoted LH4 hereafter, in its anionic state and we report herein the synthesis and crystal structures of one sodium and two caesium ion complexes obtained in the course of this work. In the case of caesium, novel arrangements result from the absence of para substituents in the ligand.
2. Experimental
1 h at r.t., then filtered. The solution was evaporated to dryness and recrystallized from CH3CN, giving colourless single crystals suitable for X-ray crystallography on slow evaporation. 2.2. Crystallography The data were collected on a Nonius Kappa-CCD area detector diffractometer [21] using graphite-mono˚ ). The crystals chromated Mo Ka radiation (0.71073 A were introduced in Lindemann glass capillaries with a protecting ‘Paratone’ oil (Exxon Chemical Ltd.) coating. The unit cell parameters were determined from the reflections collected on 10 frames and were then refined on all data. The data were processed with DENZO-SMN [22]. The structures were solved by direct methods with SHELXS-97 [23] and subsequent Fourier-difference synthesis and refined by full-matrix (compounds 2 and 3) or blocked full-matrix (compound 1) least-squares on F2 with SHELXL-97 [24]. Absorption effects were empirically corrected with the program DELABS from PLATON [25]. All non-hydrogen atoms were refined with anisotropic displacement parameters. Special details for each compound are as follows.
2.1. Synthesis Calix[4]arene was synthesized as previously published [20]. 2.1.1. {Na2(LH3)2[(CH3)2CO]3} ×/2CHCl3 ×/2H2O (1) Calix[4]arene (500 mg, 1.18 mmol) was dissolved in a mixture of CHCl3 (120 ml) and aq. NaOH 6 M (120 ml). After stirring for half an hour at room temperature (r.t.) a sevenfold excess of NaNO3 (700 mg, 8.24 mmol) was added and the resulting mixture stirred for 2 h. The organic phase was then separated, evaporated to dryness and the product recrystallized from hot acetone, resulting in colourless crystals suitable for X-ray crystallography. 2.1.2. [Cs(LH3)(py)] (2) Calix[4]arene (100 mg, 0.24 mmol) was dissolved in CH3CN (100 ml) in the presence of a large excess of NaOH (1.5 g). The solution became light pink on refluxing. Cs2CO3 in excess (200 mg, 0.61 mmol) was then added and the resulting pink solution was further stirred for 1 h at r.t., then filtered. The solution was evaporated to dryness and recrystallized from pyridine, giving colourless single crystals suitable for X-ray crystallography on slow evaporation. 2.1.3. [Cs2(LH3)2(H2O)] ×/CH3CN (3) Calix[4]arene (110 mg, 0.26 mmol) was dissolved in CHCl3 (50 ml) with a large excess of NEt3 (4 ml). Cs2CO3 in excess (330 mg, 1.01 mmol) was then added and the resulting cloudy whitish solution was stirred for
2.2.1. Compound 1 Some constraints have been applied, particularly on the badly resolved chloroform molecules. Phenolic and water protons were not found, nor introduced. All other protons were introduced at calculated positions as riding atoms, with an isotropic displacement parameter equal to 1.2 (CH, CH2) or 1.5 (CH3) times that of the parent atom. 2.2.2. Compound 2 Constraints on displacement parameters have been applied for some atoms behaving badly on refinement. The phenolic protons were not found, nor introduced. All other protons were introduced at calculated positions as riding atoms, with an isotropic displacement parameter equal to 1.2 times that of the parent atom. 2.2.3. Compound 3 The protons bound to the phenolic oxygen atoms have been found on the Fourier-difference map and introduced as riding atoms with an isotropic displacement parameter equal to 1.2 times that of the parent atom. All other protons (except those of the water molecule) were introduced at calculated positions as riding atoms, with an isotropic displacement parameter equal to 1.2 (CH, CH2) or 1.5 (CH3) times that of the parent atom. Crystal data and refinement details are reported in Table 1. The molecular plots were drawn with SHELXTL [26]. All calculations were performed on a Silicon Graphics R5000 workstation.
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3. Discussion
Table 1 Crystal data and structure refinement details 1 Empirical formula M (g mol 1) Temperature (K) Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) V (A Z m (mm 1) Reflections collected Observed reflections [I 2s (I )] Independent reflections Rint Parameters refined R1 wR2
2
2499
3
C67H70Cl6Na2O13 C33H28CsNO4 C58H51Cs2NO9 1341.91 100(2) triclinic ¯/ /P1 17.2328(17) 19.5644(13) 21.1940(18) 105.926(5) 99.702(4) 101.258(5) 6550(1) 4 0.338 43 164
635.47 100(2) orthorhombic P 212121 7.1288(10) 18.5462(17) 20.032(2) 90 90 90 2648.5(5) 4 1.439 14 461
1171.82 100(2) monoclinic Cc 26.3258(18) 11.1154(8) 17.7265(9) 90 111.824(4) 90 4815.4(5) 4 1.576 16 213
8718
1721
6746
22 079
4599
8109
0.088 1643
0.052 353
0.058 632
0.102 0.234
0.083 0.153
0.045 0.090
Fig. 1. View of one of the dimers in complex 1. Hydrogen atoms and solvent molecules have been omitted for clarity. Thermal ellipsoids are drawn at the 30% probability level.
The asymmetric unit in {Na2(LH3)2[(CH3)2CO]3} ×/ 2CHCl3 ×/2H2O (1) corresponds to two independent and nearly identical dimeric complexes, with calixarene molecules denoted A /B and C /D in the two dimers, respectively. As represented in Fig. 1 in the case of the A /B dimer, two mono-anionic calixarenes in cone conformation are bridged by two sodium ions, the coordination sphere of the latter being completed by three acetone molecules located in the median plane, two of them monodentate and one bridging. Each calixarene acts as a bidentate ligand towards one sodium ion and monodentate towards the other, the situation respective to each cation being reversed in the two calixarenes. In each molecule, the phenolic atom O3 is not bound to the cation, which results in the two calixarenes not being parallel to each other. The plane defined by the four oxygen atoms being taken as a reference plane the dihedral angles between these two planes in each dimer are 50.1(2) and 48.9(2)8, respectively, the distance between the two planes being the largest where they are separated by the bridging acetone molecule. The protons were not located in this rather large structure due to the limited data quality and it cannot be ascertained where the phenoxides are located. The Na /Ocalixarene distances, reported in Table 2, do not provide any clear-cut clue in this respect, being in the ˚ , in range 2.280(5) /2.518(6) [mean value 2.34(7)] A agreement with published values. The O O separations between adjacent phenolic groups are in the range ˚ , with however a difference between 2.472(8) /2.905(8) A the O O separations relative to the oxygen atoms coordinated to the same cation (O1 and O2 in molecules A and C, O1 and O4 in B and D) and all the other distances. The former are significantly larger, with a ˚ and a mean value of 2.87(3) range 2.849(8) /2.905(8) A ˚ A, than the latter, which are in the range 2.472(8) / ˚ . When taking in 2.684(8) [mean value 2.56(6)] A consideration the corresponding distances in complex 3, in which the protons were located (vide infra), it can be concluded that the two atoms corresponding to the largest separation are both protonated and involved in strong hydrogen bonds with their other two neighbours, the phenoxide atom among the latter being probably the coordinated one. The dihedral angles between the reference O4 planes and the mean planes defined by the aromatic rings are in the range 43.1(2) /72.4(2)8. The largest values, associated to the more ‘vertical’ aromatic rings, correspond in the four calixarenes to coordinated groups, and particularly to those bound to the same cation, while the lowest values, in all but one case, correspond to the uncoordinated group. It may be that the latter adopts a more ‘horizontal’ position due to the vicinity of the bridging acetone molecule. The three acetone molecules are located so that the three donating
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Table 2 ˚ ) and angles (8) in complexes 1 /3 Selected distances (A 1 Na1 O1A Na1 O2A Na1 O2B Na1 O1 Na1 O3 Na1 Na2 O1A O2A O2A O3A O3A O4A O4A O1A
2.284(5) 2.327(5) 2.337(5) 2.206(6) 2.394(5) 3.857(3) 2.876(8) 2.602(8) 2.481(8) 2.523(7)
Na2 O4A Na2 O1B Na2 O4B Na2 O2 Na2 O3
2.339(5) 2.320(5) 2.391(5) 2.234(5) 2.368(5)
O1B O2B O2B O3B O3B O4B O4B O1B
2 Cs O1? a O1 O2
3.169(12) 2.56(2)
3 Cs1 O1B? b Cs1 O4B? b O3A O4A O1A O2A O3A O2A O4A O1A O1B O2B O3B O2B O4B O3B
3.065(5) 3.079(5) 2.91(1) 2.491(9) 2.507(9) 2.819(10) 2.585(7) 2.457(6) 2.627(7)
a b
2.533(8) 2.472(8) 2.590(8) 2.905(8)
Na3 O1C Na3 O2C Na3 O2D Na3 O4 Na3 O6 Na3 Na4 O1C O2C O2C O3C O3C O4C O4C O1C
2.280(5) 2.518(6) 2.298(5) 2.300(5) 2.357(5) 4.001(4) 2.849(9) 2.684(8) 2.520(9) 2.541(8)
Cs O3 O2 O3
3.704(16) 2.56(2)
Cs N O3 O4
3.098(16) 2.77(2)
Cs1 O1 Cs2 O1A O1B O4B O1A H1A O3A H3A O4A H4A O1B H1B O3B H3B O4B H4B
2.97(3) 3.396(6) 2.994(7) 1.05 0.76 1.29 1.06 1.16 0.89
Cs2 O2A Cs2 O3A O1? b O3B H1A O2A H3A O2A H4A O1A H1B O2B H3B O2B H4B O3B
3.361(6) 3.233(7) 2.71(1) 1.49 1.76 1.60 1.54 1.41 1.75
Na4 O4C Na4 O1D Na4 O4D Na4 O5 Na4 O6
2.309(5) 2.308(5) 2.375(5) 2.334(5) 2.457(5)
O1D O2D O2D O3D O3D O4D O4D O1D
2.559(8) 2.519(8) 2.645(8) 2.849(8)
O4 O1
2.86(2)
Cs2 O4A Cs2 O2B
3.283(8) 3.673(5)
O1A H1A O2A O3A H3A O2A O4A H4A O1A O1B H1B O2B O3B H3B O2B O4B H4B O3B
158.2 170.9 153.5 169.5 145.8 169.2
Symmetry code: x1, y , z . Symmetry code: x0.5, 2.5y , z0.5.
oxygen atoms are roughly located in a plane bisecting the two calixarene mean planes, with Na /O distances ˚] larger for the bridging species [mean value 2.39(4) A ˚ than for the other ones [mean value 2.27(6) A]. The coordination geometry of the cation can be described as distorted trigonal bipyramidal, with, in the case of Na1 for instance, O1, O3 and O1A defining the equatorial plane and O2A and O2B the axial positions, with an O2A /Na1 /O2B angle of 169.3(2)8 (Fig. 1). The location of the solvent molecules is unremarkable, the water molecules being hydrogen bonded to each other, but not to the calixarene phenol/phenoxide oxygen atoms. It is worth comparing this structure to those of sodium complexes of simple, parent calix[4]arenes and tetrathiacalix[4]arenes previously reported. In the presence of sodium hydride [4] or triethylamine [12] as deprotonating agent, mono-deprotonation of these ligands is always observed in the case of sodium complexation (the dianion has however been reported in the case of the 1,3-dimethyl ether derivative of p-tert butylcalix[4]arene in the presence of sodium hydride [6]). All other conditions being equal, LiH leads to twofold deprotonation of p -tert -butylcalix[4]arene and NaH to mono-deprotonation [4]. This observation has been discussed on the basis of structural arguments [4] (see also Ref. [12]). The present result, with concentrated NaOH as a deprotonating agent, does not differ from the previous cases in this respect. It is however possible
to generate higher deprotonation degrees, up to three and fourfold ones, in the presence of lithium amide [5] and butyl-lithium [7,8], respectively. The sodium cation/ calixarene system appears to give very different complexes depending on the calixarene and conditions used. Central coordination by all four oxygen atoms is observed with the tetramethyl ether derivative of ptert -butylcalix[4]arene [3] and exo coordination to two oxygen atoms with the parent p -tert -butylcalix[4]arene [4] and p-tert -butyltetrathiacalix[4]arene [12], with additional loose coordination to sulfur in the latter. Complex 1 is closer to the sodium-fused calixarene systems obtained with the 1,3-dimethyl ether derivative of ptert -butylcalix[4]arene [6] or some mixed transition metal ion/sodium ion complexes of p -tert -butylcalix[4]arene [17]. The closest relative to 1 is however to be found in the potassium ion complex of p -tert butyltetrathiacalix[4]arene [12], which is also a M2(LH3)2 binuclear ‘sandwich’, with one singly coordinating, two chelating and one uncomplexed oxygen atoms in each calixarene and two coordinated diethylether and one bridging water molecules near the bisecting plane. Similar arrangements are thus obtained with either the smallest or the largest cation/calixarene pair (tetrathiacalix[4]arene being significantly more spacious than its methylene-linked counterpart), with however the difference of a higher coordination number in the case of K ensured by bonding to sulfur.
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The isolation of the complex [Cs(LH3)(py)] 2 from a solution highly concentrated in sodium ions evidences a selectivity for caesium which has been demonstrated in the related case of p -tert -butylcalix[4]arene [2]. Compound 2 crystallizes with only one complex molecule in the asymmetric unit, but it appears to be a polymeric compound, as represented in Fig. 2. As in complex 1, the calixarene in 2 is a mono-anion. As a common feature with the caesium complex of p -tert-butylcalix[4]arene, in which caesium p-bonding by a calixarene was structurally evidenced for the first time and in which the calixarene is also mono-anionic [10], the cation in 2 is complexed in an endo fashion, with likely p-bonding to the aromatic rings, but the absence of bulky para substituents results in novel features and overall arrangement. Whereas Cs was located on the fourfold symmetry axis of p-tert -butylcalix[4]arene, it is located off-centre in 2, the interactions with the four aromatic rings being quite dissymetric, with mean Cs C dis˚ and tances of 4.3(4), 3.6(1), 4.0(4) and 3.6(1) A ˚ Cs centroid distances of 4.14, 3.30, 3.79 and 3.35 A for the four rings, respectively. The shortest Cs C contacts for each ring are 3.78(2), 3.42(2), 3.55(2) and ˚ , respectively, and they involve the carbon 3.45(2) A atoms bound to oxygen in rings 1 and 3 and either ortho or meta carbon atoms in rings 2 and 4. On the basis of these distances, the interactions with rings 2 and 4 at
Fig. 2. Partial view of the columnar arrangement in complex 2, a axis vertical. p-Bonding is indicated by dashed lines joining the cation and the aromatic ring centroids. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at the 10% probability level. Symmetry codes: ?/x /1, y , z ; ƒ/x /2, y , z .
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least can be considered as strong p-bonds (in the possible range of interactions from h1 to h6, these are closer to the latter). For comparison, the Cs C ˚ distances were 3.545(3) /4.121(4) and 3.53(1) /4.17(1) A ˚ and the Cs centroid distances 3.57 and 3.61 A in the complexes of p -tert-butylcalix[4]arene and p-tert -butyldihomooxacalix[4]arene, respectively (two aromatic rings only being involved in the latter). The cation in 2 is also bound to one phenolic (or phenoxide) oxygen atom of the calixarene in which it is included, with a Cs / ˚ , larger than that observed for O3 distance of 3.704(16) A bonding to two oxygen atoms in the p -tert -butyldiho˚ ], which may be mooxacalix[4]arene complex [3.422(7) A due to the smaller cavity size and less shallow conformation of calix[4]arene preventing the cation from going deeper in the cavity, i.e. closer to the coordinated oxygen atom. However, a peculiar feature of complex 2 is that the cation is bound to one phenolic (or phenoxide) oxygen atom of the neighbouring molecule along the a axis, with a shorter Cs /O1? distance of ˚ . The cation coordination sphere is com3.169(12) A pleted by a pyridine molecule located between the calixarene moieties. By contrast with the observation that solvents with high cation solvating ability, such as acetone or acetonitrile, are likely to withdraw Cs from the calixarene cavity [11], acetonitrile has been used as the reaction solvent in the present case and pyridine, used for recrystallization, completes the coordination sphere, which suggests that 2 is a highly stable species. The resulting structure consists of polymeric chains directed along the a axis, the calixarenes being tilted with respect to this axis. The O O separations, as in complex 1, seem to indicate that O1 and O4 are both protonated, the phenoxide group corresponding either to O2 or O3, both involved in strong hydrogen bonds with all their neighbours. The dihedral angles between the four mean planes defined by the aromatic rings and the reference O4 plane are 46.5(5), 58.4(5), 42.3(7) and 76.2(5)8, the two rings more strongly involved in pbonding being more ‘vertical’ than the other ones. These dihedral angles are 57.4(1)8 in the p-tert -butylcalix[4]arene complex and 25.4(3) (O-coordinated rings) and 68.7(3)8 (polyhapto-coordinated rings) in the p -tert butyldihomooxacalix[4]arene one. Comparison of complex 2 with the two other caesium complexes of simple and small calixarenes, p-tert butylcalix[4]arene and p -tert -butyldihomooxacalix[4]arene, evidences some interesting features (p-tert -butyltetrathiacalix[4]arene does not provide a relevant comparison since it complexes Cs in an exo fashion, the soft sulfur donors being prefered to p-electrons). The distance between the cation and the O4 reference plane can be taken as a measure of the depth of cation inclusion. This value is virtually identical in calix[4]arene ˚, and its p -tert -butyl derivative (3.56 and 3.57 A respectively) and it is significantly shorter in the homo-
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˚ ), allowing for a stronger intraoxacalixarene (3.06 A molecular O-coordination in the latter. Slight differences in conformation probably account for Ocoordination by calix[4]arene and its absence in the p tert -butyl derivative. O-coordination to a neighbouring calixarene in 2, which can be seen as ‘intermolecular’ Ocoordination for the sake of clarity, notwithstanding the ambiguity of this term in the present case, is very likely related to the absence of p-tert -butyl substituents, which enables a closer approach of the second anion. In the p tert -butyl derivative, an acetonitrile molecule is located on the main axis of the calixarene, near its upper rim, and is coordinated to Cs. The distance between the cation and the mean plane defining (approximately) the border of the upper rim (aromatic carbon atoms in para position in 2, terminal tert -butyl carbon atoms in the other complexes) is a parameter which gives some information on the accessibility of the cation towards ‘intermolecular’ coordination. This parameter amounts ˚ in 2, to be compared to 2.29 and 1.83 A ˚ in the to 0.23 A other two compounds. The cation is thus far more accessible in the former case, with approximately a free half-coordination sphere.
Fig. 3. Partial view of the columnar arrangement parallel to the (101) direction in complex 3. p-Bonding is indicated by dashed lines joining the cation and the aromatic ring centroids. Hydrogen bonds are represented as dashed lines and phenolic protons as small spheres of arbitrary radii. Other hydrogen atoms and solvent molecules are omitted for clarity. Thermal ellipsoids are drawn at the 10% probability level. Symmetry code: ?/x /0.5, 2.5 /y , z /0.5.
A similar situation arises in [Cs2(LH3)2(H2O)] ×/ CH3CN (3). This complex, obtained with triethylamine as a deprotonating agent, crystallizes with two independent caesium ions and two calixarene mono-anions, denoted A and B, in the repeat unit (it may be noted that in its triethylammonium ion complexes, calix[4]arene is also mono-deprotonated [27]). As shown in Fig. 3, the overall shape, with formation of polymeric chains parallel to the (101) direction from units related by the glide plane perpendicular to the b axis, is roughly analogous to that of complex 2, but the details are quite different. The two caesium ions are not equivalent in what concerns their environment. Both of them are located in the cavity of a calixarene moiety and are involved in polyhapto bonding. The mean Cs C ˚ in the distances are 3.9(3), 4.0(3), 3.9(2) and 3.7(4) A case of Cs1 and the four aromatic rings of calixarene A, with the corresponding shortest contacts of 3.530(7), ˚ and Cs centroid 3.540(7), 3.652(7) and 3.637(8) A ˚ . In the case of distances of 3.61, 3.73, 3.69 and 3.41 A Cs2 and the four aromatic rings of calixarene B, the ˚, mean distances are 3.74(9), 4.1(4), 4.0(3) and 3.71(8) A the shortest contacts 3.639(7), 3.518(7), 3.558(6) and ˚ and the Cs centroid distances 3.47, 3.89, 3.596(7) A ˚ . p-Bonding is obvious in both cases, the 3.71 and 3.44 A four rings being differently involved, as in compound 2. Cs1 is further bound to two phenolic oxygen atoms of a neighbouring calixarene, with a mean Cs /O distance of ˚ , slightly shorter than its counterpart in 3.07(1) A complex 2 and it is also bound to a water molecule (O1) located in a similar manner as the pyridine molecule in 2. No bond between Cs1 and the oxygen atoms of the calixarene in which it is included is observed, at variance with the previous complex. By contrast, Cs2 is bound to one such oxygen atom, with a ˚ comparable to its equivalent bond length of 3.673(5) A in 2, and it is also bound to the four oxygen atoms of the neighbouring calixarene, with a much larger mean Cs /O ˚ . The distances between caesium bond length of 3.9(3) A ions and the mean planes defining the borders of the lower and upper rims (O4 in the first case) are 3.559(3) ˚ for Cs1 and calixarene A and 3.520(3) and 0.144(5) A ˚ for Cs2 and calixarene B, i.e. in both and 0.145(4) A cases the cation is even closer to the upper rim than in complex 2. The dihedral angles between the aromatic rings and the reference O4 plane are 52.9(2), 44.3(3), 58.8(3) and 73.7(2)8 in calixarene A and 68.2(2), 37.4(3), 48.1(2) and 70.8(2)8 in calixarene B, both sets of values indicating a distorsion of the cone conformation analogous to that in complex 2. The dihedral angle between the two reference O4 planes is 13.0(4)8, indicating a slight deviation of the calixarene units with respect to parallelism. By contrast with the structures of complexes 1 and 2, the phenolic protons can be located in that of 3. In both molecules A and B, the phenoxide oxygen atom is O2, which is involved in strong hydrogen bonds with
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its two neighbours (Table 2). A possible hydrogen bond links the water molecule and O3B of the neighbouring calixarene. Apart from the differences between complexes 2 and 3 with regards to O-coordination, the same polymeric structure is found, with a stacking of alternate cations and anions, the latter all pointing towards the same direction. To the best of our knowledge, this peculiar arrangement has never been observed in alkali metal ion complexes of p-R -calix[4]arene and its derivatives. The lack of p-alkyl substituents in the present cases enables the cation enclosed in the calixarene cavity to be easily complexed through the upper rim aperture by a bulky species such as a second calixarene moiety. Although stacking of uncomplexed calixarenes in columns held by feeble interactions is known, the present results show that novel tightly linked polymeric chain assemblages can be obtained from alkali-metal ions and one of the simplest calixarenes.
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 187709/187711 for compounds 1, 2 and 3, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: /441223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
References [1] C.D. Gutsche, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001 (Chapter 1), Kluwer Academic Publishers, Dordrecht, 2001, pp. 1 /25. [2] R.M. Izatt, J.D. Lamb, R.T. Hawkins, P.R. Brown, S.R. Izatt, J.J. Christensen, J. Am. Chem. Soc. 105 (1983) 1782. [3] S.G. Bott, A.W. Coleman, J.L. Atwood, J. Am. Chem. Soc. 108 (1986) 1709. [4] F. Hamada, K.D. Robinson, G.W. Orr, J.L. Atwood, Supra. Chem. 2 (1993) 19. [5] H. Bock, A. John, C. Na¨ther, Z. Havlas, J. Am. Chem. Soc. 117 (1995) 9367.
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[6] S.R. Dubberley, A.J. Blake, P. Mountford, Chem. Commun. (1997) 1603. [7] M.G. Davidson, J.A.K. Howard, S. Lamb, C.W. Lehmann, Chem. Commun. (1997) 1607. [8] G. Guillemot, E. Solari, C. Rizzoli, C. Floriani, Chem. Eur. J. 8 (2002) 2072. [9] N.P. Clague, W. Clegg, S.J. Coles, J.D. Crane, D.J. Moreton, E. Sinn, S.J. Teat, N.A. Young, Chem. Commun. (1999) 379. [10] J.M. Harrowfield, M.I. Ogden, W.R. Richmond, A.H. White, J. Chem. Soc., Chem. Commun. (1991) 1159. [11] R. Assmus, V. Bo¨hmer, J.M. Harrowfield, M.I. Ogden, W.R. Richmond, B.W. Skelton, A.H. White, J. Chem. Soc., Dalton Trans. (1993) 2427. [12] A. Bilyk, A.K. Hall, J.M. Harrowfield, M.W. Hosseini, B.W. Skelton, A.H. White, Inorg. Chem. 40 (2001) 672. [13] B.W.F. Gordon, M.J. Scott, Inorg. Chim. Acta 297 (2000) 206. [14] For reviews on this topic, see: (a) P. Thue´ry, M. Nierlich, V. Lamare, J.F. Dozol, Z. Asfari, J. Vicens, J. Incl. Phenom. 36 (2000) 375; (b) A. Casnati, R. Ungaro, Z. Asfari, J. Vicens, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001, Kluwer Academic Publishers, Dordrecht, 2001 (Chapter 20), pp. 365 /384; (c) F. Arnaud-Neu, M.J. Schwing-Weill, J.F. Dozol, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001, Kluwer Academic Publishers, Dordrecht, 2001 (Chapter 35), pp. 642 /662. [15] H.F. Ji, R. Dabestani, G.M. Brown, R.L. Hettich, J. Chem. Soc., Perkin Trans. 2 (2001) 585 (and references therein). [16] F. Arnaud-Neu, M.A. McKervey, M.J. Schwing-Weill, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001 (Chapter 21, and references therein), Kluwer Academic Publishers, Dordrecht, 2001, pp. 385 /406. [17] C. Floriani, R. Floriani-Moro, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001 (Chapter 29, and references therein), Kluwer Academic Publishers, Dordrecht, 2001, pp. 536 /560. [18] J.L. Atwood, L.J. Barbour, M.J. Hardie, C.L. Raston, Coord. Chem. Rev. 222 (2001) 3 (and references therein). [19] Z. Asfari, J. Harrowfield, P. Thue´ry, J. Vicens, Supra. Chem., in the press. [20] R. Ungaro, A. Pochini, J. Chem. Soc., Perkin Trans. 2 (1984) 1979. [21] Kappa-CCD Software, Nonius B.V., Delft, 1998. [22] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307. [23] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467. [24] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures, University of Go¨ttingen, 1997. [25] A.L. Spek, PLATON, University of Utrecht, 2000. [26] G.M. Sheldrick, SHELXTL, Version 5.1, University of Go¨ttingen, distributed by Bruker AXS Inc., Madison, WI, 1999. [27] P. Thue´ry, Z. Asfari, M. Nierlich, J. Vicens, Acta Crystallogr., Sect. C 58 (2002) o223.
Synthesis and crystal structure of sodium and caesium ion complexes of unsubstituted calix[4]arene. New polymeric chain arrangements Pierre Thue´ry a,*, Zouhair Asfari b, Jacques Vicens b, Ve´ronique Lamare c, Jean-Franc¸ois Dozol c b
a CEA/Saclay, DSM/DRECAM/SCM (CNRS URA 331), Baˆt. 125, 91191 Gif-sur-Yvette, France ECPM, Laboratoire de Chimie des Interactions Mole´culaires Spe´cifiques (CNRS UMR 7512), 25 rue Becquerel, 67087 Strasbourg, France c CEA/Cadarache, DED/SEP/LCD, 13108 Saint-Paul-lez-Durance, France
Received 20 June 2002; accepted 22 August 2002
Abstract Calix[4]arene, devoid of p -alkyl substituents, has been used to complex sodium and caesium ions in a basic medium. The crystal structures of one sodium and two caesium complexes are reported and compared to previous structures with related p -tert butylcalixarenes. The sodium complex is dimeric, two cations being sandwiched between two mono-anionic calixarenes through Ocoordination, and bound also to three acetone molecules (one bridging) in the median plane. Both caesium complexes are polymeric, with a stacking of alternate cations and mono-anionic calixarenes, with both polyhapto bonding and O-coordination. This novel arrangement is attributed to the lack of bulky p -substituents in the ligand, which enables the cation included in the cavity of one calixarene to be closely approached by the oxygen donors of a second one on the other side. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Alkali metal ions; Sodium ion; Caesium ion; Calix[4]arene; Crystal structures
1. Introduction The affinity of parent or functionalized calixarenes towards alkali metal ions is a much investigated phenomenon. ‘Template’ effects during the base-induced synthesis of calixarenes, which depend on the alkali metal hydroxide used as a catalyst, have been suggested early [1], while p-tert -butylcalix[4,6,8]arenes proved to be efficient transporters of alkali metal ions through liquid membranes with a selectivity for caesium ions [2]. Some work has been devoted to the structural characterization of the complexes formed with lithium, sodium and potassium ions by simple calixarenes, particularly p -tert -butylcalix[4]arene and its O-alkylated derivatives [3 /8], also potassium with p -tert -butylca-
* Corresponding author. Tel.: /33-1-6908-6329; fax: /33-1-69086640 E-mail address: [email protected] (P. Thue´ry).
lix[8]arene [9], and with the largest caesium ions, by ptert -butylcalix[4]arene [10] and p-tert -butyldihomooxacalix[4]arene [11]. Recently, the complexation of the whole Li /Cs series by p -tert-butyltetrathiacalix[4]arene has been investigated [12]. Partial calix[n]arenes (polyaryloxide ligands) have also been considered in this respect [13]. Broadly speaking, two extreme coordination modes are observed with these calixarenes: an exo one, in which the cation is bound to the ‘hard’ phenolic/ phenoxide oxygen atoms, and an endo one which corresponds to p-bonding by the ‘soft’ aromatic rings defining the calixarene cavity. Mixed situations evidencing this ambivalent character of calixarenes as ligands are however commonly observed [6,7,11], while sulfur atoms compete with aromatic rings as ‘soft’ sites in tetrathiacalix[4]arenes [12]. p-Bonding was further exploited in the design of selective extractants for caesium cations which are needed in the context of nuclear fuel reprocessing, using calixcrowns and calix bis (crowns) in the 1,3-alternate conformation [14],
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 2 2 9 - 9
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which are also used to build selective sensors [15]. In addition, many examples of alkali metal ion complexation by calix[4]arenes bearing complexing arms on the lower rim (particularly carbonyl derivatives) are known [16] as well as complexes uniting transition metal and alkali metal ions [17] and complexes with p -sulfonato derivatives of calix[4,5]arenes [18] and calix[6]arenes [19]. Considering the relative scarcity of simple calix[4]arenes (unsubstituted on the lower rim) used for the structural characterization of such complexes, these being reduced to p -tert -butylcalix[4]arene, p -tert-butyldihomooxacalix[4]arene and p -tert-butyltetrathiacalix[4]arene, we decided to investigate the complexes formed by the simplest member of this family, calix[4]arene, denoted LH4 hereafter, in its anionic state and we report herein the synthesis and crystal structures of one sodium and two caesium ion complexes obtained in the course of this work. In the case of caesium, novel arrangements result from the absence of para substituents in the ligand.
2. Experimental
1 h at r.t., then filtered. The solution was evaporated to dryness and recrystallized from CH3CN, giving colourless single crystals suitable for X-ray crystallography on slow evaporation. 2.2. Crystallography The data were collected on a Nonius Kappa-CCD area detector diffractometer [21] using graphite-mono˚ ). The crystals chromated Mo Ka radiation (0.71073 A were introduced in Lindemann glass capillaries with a protecting ‘Paratone’ oil (Exxon Chemical Ltd.) coating. The unit cell parameters were determined from the reflections collected on 10 frames and were then refined on all data. The data were processed with DENZO-SMN [22]. The structures were solved by direct methods with SHELXS-97 [23] and subsequent Fourier-difference synthesis and refined by full-matrix (compounds 2 and 3) or blocked full-matrix (compound 1) least-squares on F2 with SHELXL-97 [24]. Absorption effects were empirically corrected with the program DELABS from PLATON [25]. All non-hydrogen atoms were refined with anisotropic displacement parameters. Special details for each compound are as follows.
2.1. Synthesis Calix[4]arene was synthesized as previously published [20]. 2.1.1. {Na2(LH3)2[(CH3)2CO]3} ×/2CHCl3 ×/2H2O (1) Calix[4]arene (500 mg, 1.18 mmol) was dissolved in a mixture of CHCl3 (120 ml) and aq. NaOH 6 M (120 ml). After stirring for half an hour at room temperature (r.t.) a sevenfold excess of NaNO3 (700 mg, 8.24 mmol) was added and the resulting mixture stirred for 2 h. The organic phase was then separated, evaporated to dryness and the product recrystallized from hot acetone, resulting in colourless crystals suitable for X-ray crystallography. 2.1.2. [Cs(LH3)(py)] (2) Calix[4]arene (100 mg, 0.24 mmol) was dissolved in CH3CN (100 ml) in the presence of a large excess of NaOH (1.5 g). The solution became light pink on refluxing. Cs2CO3 in excess (200 mg, 0.61 mmol) was then added and the resulting pink solution was further stirred for 1 h at r.t., then filtered. The solution was evaporated to dryness and recrystallized from pyridine, giving colourless single crystals suitable for X-ray crystallography on slow evaporation. 2.1.3. [Cs2(LH3)2(H2O)] ×/CH3CN (3) Calix[4]arene (110 mg, 0.26 mmol) was dissolved in CHCl3 (50 ml) with a large excess of NEt3 (4 ml). Cs2CO3 in excess (330 mg, 1.01 mmol) was then added and the resulting cloudy whitish solution was stirred for
2.2.1. Compound 1 Some constraints have been applied, particularly on the badly resolved chloroform molecules. Phenolic and water protons were not found, nor introduced. All other protons were introduced at calculated positions as riding atoms, with an isotropic displacement parameter equal to 1.2 (CH, CH2) or 1.5 (CH3) times that of the parent atom. 2.2.2. Compound 2 Constraints on displacement parameters have been applied for some atoms behaving badly on refinement. The phenolic protons were not found, nor introduced. All other protons were introduced at calculated positions as riding atoms, with an isotropic displacement parameter equal to 1.2 times that of the parent atom. 2.2.3. Compound 3 The protons bound to the phenolic oxygen atoms have been found on the Fourier-difference map and introduced as riding atoms with an isotropic displacement parameter equal to 1.2 times that of the parent atom. All other protons (except those of the water molecule) were introduced at calculated positions as riding atoms, with an isotropic displacement parameter equal to 1.2 (CH, CH2) or 1.5 (CH3) times that of the parent atom. Crystal data and refinement details are reported in Table 1. The molecular plots were drawn with SHELXTL [26]. All calculations were performed on a Silicon Graphics R5000 workstation.
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3. Discussion
Table 1 Crystal data and structure refinement details 1 Empirical formula M (g mol 1) Temperature (K) Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) V (A Z m (mm 1) Reflections collected Observed reflections [I 2s (I )] Independent reflections Rint Parameters refined R1 wR2
2
2499
3
C67H70Cl6Na2O13 C33H28CsNO4 C58H51Cs2NO9 1341.91 100(2) triclinic ¯/ /P1 17.2328(17) 19.5644(13) 21.1940(18) 105.926(5) 99.702(4) 101.258(5) 6550(1) 4 0.338 43 164
635.47 100(2) orthorhombic P 212121 7.1288(10) 18.5462(17) 20.032(2) 90 90 90 2648.5(5) 4 1.439 14 461
1171.82 100(2) monoclinic Cc 26.3258(18) 11.1154(8) 17.7265(9) 90 111.824(4) 90 4815.4(5) 4 1.576 16 213
8718
1721
6746
22 079
4599
8109
0.088 1643
0.052 353
0.058 632
0.102 0.234
0.083 0.153
0.045 0.090
Fig. 1. View of one of the dimers in complex 1. Hydrogen atoms and solvent molecules have been omitted for clarity. Thermal ellipsoids are drawn at the 30% probability level.
The asymmetric unit in {Na2(LH3)2[(CH3)2CO]3} ×/ 2CHCl3 ×/2H2O (1) corresponds to two independent and nearly identical dimeric complexes, with calixarene molecules denoted A /B and C /D in the two dimers, respectively. As represented in Fig. 1 in the case of the A /B dimer, two mono-anionic calixarenes in cone conformation are bridged by two sodium ions, the coordination sphere of the latter being completed by three acetone molecules located in the median plane, two of them monodentate and one bridging. Each calixarene acts as a bidentate ligand towards one sodium ion and monodentate towards the other, the situation respective to each cation being reversed in the two calixarenes. In each molecule, the phenolic atom O3 is not bound to the cation, which results in the two calixarenes not being parallel to each other. The plane defined by the four oxygen atoms being taken as a reference plane the dihedral angles between these two planes in each dimer are 50.1(2) and 48.9(2)8, respectively, the distance between the two planes being the largest where they are separated by the bridging acetone molecule. The protons were not located in this rather large structure due to the limited data quality and it cannot be ascertained where the phenoxides are located. The Na /Ocalixarene distances, reported in Table 2, do not provide any clear-cut clue in this respect, being in the ˚ , in range 2.280(5) /2.518(6) [mean value 2.34(7)] A agreement with published values. The O O separations between adjacent phenolic groups are in the range ˚ , with however a difference between 2.472(8) /2.905(8) A the O O separations relative to the oxygen atoms coordinated to the same cation (O1 and O2 in molecules A and C, O1 and O4 in B and D) and all the other distances. The former are significantly larger, with a ˚ and a mean value of 2.87(3) range 2.849(8) /2.905(8) A ˚ A, than the latter, which are in the range 2.472(8) / ˚ . When taking in 2.684(8) [mean value 2.56(6)] A consideration the corresponding distances in complex 3, in which the protons were located (vide infra), it can be concluded that the two atoms corresponding to the largest separation are both protonated and involved in strong hydrogen bonds with their other two neighbours, the phenoxide atom among the latter being probably the coordinated one. The dihedral angles between the reference O4 planes and the mean planes defined by the aromatic rings are in the range 43.1(2) /72.4(2)8. The largest values, associated to the more ‘vertical’ aromatic rings, correspond in the four calixarenes to coordinated groups, and particularly to those bound to the same cation, while the lowest values, in all but one case, correspond to the uncoordinated group. It may be that the latter adopts a more ‘horizontal’ position due to the vicinity of the bridging acetone molecule. The three acetone molecules are located so that the three donating
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2500
Table 2 ˚ ) and angles (8) in complexes 1 /3 Selected distances (A 1 Na1 O1A Na1 O2A Na1 O2B Na1 O1 Na1 O3 Na1 Na2 O1A O2A O2A O3A O3A O4A O4A O1A
2.284(5) 2.327(5) 2.337(5) 2.206(6) 2.394(5) 3.857(3) 2.876(8) 2.602(8) 2.481(8) 2.523(7)
Na2 O4A Na2 O1B Na2 O4B Na2 O2 Na2 O3
2.339(5) 2.320(5) 2.391(5) 2.234(5) 2.368(5)
O1B O2B O2B O3B O3B O4B O4B O1B
2 Cs O1? a O1 O2
3.169(12) 2.56(2)
3 Cs1 O1B? b Cs1 O4B? b O3A O4A O1A O2A O3A O2A O4A O1A O1B O2B O3B O2B O4B O3B
3.065(5) 3.079(5) 2.91(1) 2.491(9) 2.507(9) 2.819(10) 2.585(7) 2.457(6) 2.627(7)
a b
2.533(8) 2.472(8) 2.590(8) 2.905(8)
Na3 O1C Na3 O2C Na3 O2D Na3 O4 Na3 O6 Na3 Na4 O1C O2C O2C O3C O3C O4C O4C O1C
2.280(5) 2.518(6) 2.298(5) 2.300(5) 2.357(5) 4.001(4) 2.849(9) 2.684(8) 2.520(9) 2.541(8)
Cs O3 O2 O3
3.704(16) 2.56(2)
Cs N O3 O4
3.098(16) 2.77(2)
Cs1 O1 Cs2 O1A O1B O4B O1A H1A O3A H3A O4A H4A O1B H1B O3B H3B O4B H4B
2.97(3) 3.396(6) 2.994(7) 1.05 0.76 1.29 1.06 1.16 0.89
Cs2 O2A Cs2 O3A O1? b O3B H1A O2A H3A O2A H4A O1A H1B O2B H3B O2B H4B O3B
3.361(6) 3.233(7) 2.71(1) 1.49 1.76 1.60 1.54 1.41 1.75
Na4 O4C Na4 O1D Na4 O4D Na4 O5 Na4 O6
2.309(5) 2.308(5) 2.375(5) 2.334(5) 2.457(5)
O1D O2D O2D O3D O3D O4D O4D O1D
2.559(8) 2.519(8) 2.645(8) 2.849(8)
O4 O1
2.86(2)
Cs2 O4A Cs2 O2B
3.283(8) 3.673(5)
O1A H1A O2A O3A H3A O2A O4A H4A O1A O1B H1B O2B O3B H3B O2B O4B H4B O3B
158.2 170.9 153.5 169.5 145.8 169.2
Symmetry code: x1, y , z . Symmetry code: x0.5, 2.5y , z0.5.
oxygen atoms are roughly located in a plane bisecting the two calixarene mean planes, with Na /O distances ˚] larger for the bridging species [mean value 2.39(4) A ˚ than for the other ones [mean value 2.27(6) A]. The coordination geometry of the cation can be described as distorted trigonal bipyramidal, with, in the case of Na1 for instance, O1, O3 and O1A defining the equatorial plane and O2A and O2B the axial positions, with an O2A /Na1 /O2B angle of 169.3(2)8 (Fig. 1). The location of the solvent molecules is unremarkable, the water molecules being hydrogen bonded to each other, but not to the calixarene phenol/phenoxide oxygen atoms. It is worth comparing this structure to those of sodium complexes of simple, parent calix[4]arenes and tetrathiacalix[4]arenes previously reported. In the presence of sodium hydride [4] or triethylamine [12] as deprotonating agent, mono-deprotonation of these ligands is always observed in the case of sodium complexation (the dianion has however been reported in the case of the 1,3-dimethyl ether derivative of p-tert butylcalix[4]arene in the presence of sodium hydride [6]). All other conditions being equal, LiH leads to twofold deprotonation of p -tert -butylcalix[4]arene and NaH to mono-deprotonation [4]. This observation has been discussed on the basis of structural arguments [4] (see also Ref. [12]). The present result, with concentrated NaOH as a deprotonating agent, does not differ from the previous cases in this respect. It is however possible
to generate higher deprotonation degrees, up to three and fourfold ones, in the presence of lithium amide [5] and butyl-lithium [7,8], respectively. The sodium cation/ calixarene system appears to give very different complexes depending on the calixarene and conditions used. Central coordination by all four oxygen atoms is observed with the tetramethyl ether derivative of ptert -butylcalix[4]arene [3] and exo coordination to two oxygen atoms with the parent p -tert -butylcalix[4]arene [4] and p-tert -butyltetrathiacalix[4]arene [12], with additional loose coordination to sulfur in the latter. Complex 1 is closer to the sodium-fused calixarene systems obtained with the 1,3-dimethyl ether derivative of ptert -butylcalix[4]arene [6] or some mixed transition metal ion/sodium ion complexes of p -tert -butylcalix[4]arene [17]. The closest relative to 1 is however to be found in the potassium ion complex of p -tert butyltetrathiacalix[4]arene [12], which is also a M2(LH3)2 binuclear ‘sandwich’, with one singly coordinating, two chelating and one uncomplexed oxygen atoms in each calixarene and two coordinated diethylether and one bridging water molecules near the bisecting plane. Similar arrangements are thus obtained with either the smallest or the largest cation/calixarene pair (tetrathiacalix[4]arene being significantly more spacious than its methylene-linked counterpart), with however the difference of a higher coordination number in the case of K ensured by bonding to sulfur.
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The isolation of the complex [Cs(LH3)(py)] 2 from a solution highly concentrated in sodium ions evidences a selectivity for caesium which has been demonstrated in the related case of p -tert -butylcalix[4]arene [2]. Compound 2 crystallizes with only one complex molecule in the asymmetric unit, but it appears to be a polymeric compound, as represented in Fig. 2. As in complex 1, the calixarene in 2 is a mono-anion. As a common feature with the caesium complex of p -tert-butylcalix[4]arene, in which caesium p-bonding by a calixarene was structurally evidenced for the first time and in which the calixarene is also mono-anionic [10], the cation in 2 is complexed in an endo fashion, with likely p-bonding to the aromatic rings, but the absence of bulky para substituents results in novel features and overall arrangement. Whereas Cs was located on the fourfold symmetry axis of p-tert -butylcalix[4]arene, it is located off-centre in 2, the interactions with the four aromatic rings being quite dissymetric, with mean Cs C dis˚ and tances of 4.3(4), 3.6(1), 4.0(4) and 3.6(1) A ˚ Cs centroid distances of 4.14, 3.30, 3.79 and 3.35 A for the four rings, respectively. The shortest Cs C contacts for each ring are 3.78(2), 3.42(2), 3.55(2) and ˚ , respectively, and they involve the carbon 3.45(2) A atoms bound to oxygen in rings 1 and 3 and either ortho or meta carbon atoms in rings 2 and 4. On the basis of these distances, the interactions with rings 2 and 4 at
Fig. 2. Partial view of the columnar arrangement in complex 2, a axis vertical. p-Bonding is indicated by dashed lines joining the cation and the aromatic ring centroids. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at the 10% probability level. Symmetry codes: ?/x /1, y , z ; ƒ/x /2, y , z .
2501
least can be considered as strong p-bonds (in the possible range of interactions from h1 to h6, these are closer to the latter). For comparison, the Cs C ˚ distances were 3.545(3) /4.121(4) and 3.53(1) /4.17(1) A ˚ and the Cs centroid distances 3.57 and 3.61 A in the complexes of p -tert-butylcalix[4]arene and p-tert -butyldihomooxacalix[4]arene, respectively (two aromatic rings only being involved in the latter). The cation in 2 is also bound to one phenolic (or phenoxide) oxygen atom of the calixarene in which it is included, with a Cs / ˚ , larger than that observed for O3 distance of 3.704(16) A bonding to two oxygen atoms in the p -tert -butyldiho˚ ], which may be mooxacalix[4]arene complex [3.422(7) A due to the smaller cavity size and less shallow conformation of calix[4]arene preventing the cation from going deeper in the cavity, i.e. closer to the coordinated oxygen atom. However, a peculiar feature of complex 2 is that the cation is bound to one phenolic (or phenoxide) oxygen atom of the neighbouring molecule along the a axis, with a shorter Cs /O1? distance of ˚ . The cation coordination sphere is com3.169(12) A pleted by a pyridine molecule located between the calixarene moieties. By contrast with the observation that solvents with high cation solvating ability, such as acetone or acetonitrile, are likely to withdraw Cs from the calixarene cavity [11], acetonitrile has been used as the reaction solvent in the present case and pyridine, used for recrystallization, completes the coordination sphere, which suggests that 2 is a highly stable species. The resulting structure consists of polymeric chains directed along the a axis, the calixarenes being tilted with respect to this axis. The O O separations, as in complex 1, seem to indicate that O1 and O4 are both protonated, the phenoxide group corresponding either to O2 or O3, both involved in strong hydrogen bonds with all their neighbours. The dihedral angles between the four mean planes defined by the aromatic rings and the reference O4 plane are 46.5(5), 58.4(5), 42.3(7) and 76.2(5)8, the two rings more strongly involved in pbonding being more ‘vertical’ than the other ones. These dihedral angles are 57.4(1)8 in the p-tert -butylcalix[4]arene complex and 25.4(3) (O-coordinated rings) and 68.7(3)8 (polyhapto-coordinated rings) in the p -tert butyldihomooxacalix[4]arene one. Comparison of complex 2 with the two other caesium complexes of simple and small calixarenes, p-tert butylcalix[4]arene and p -tert -butyldihomooxacalix[4]arene, evidences some interesting features (p-tert -butyltetrathiacalix[4]arene does not provide a relevant comparison since it complexes Cs in an exo fashion, the soft sulfur donors being prefered to p-electrons). The distance between the cation and the O4 reference plane can be taken as a measure of the depth of cation inclusion. This value is virtually identical in calix[4]arene ˚, and its p -tert -butyl derivative (3.56 and 3.57 A respectively) and it is significantly shorter in the homo-
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˚ ), allowing for a stronger intraoxacalixarene (3.06 A molecular O-coordination in the latter. Slight differences in conformation probably account for Ocoordination by calix[4]arene and its absence in the p tert -butyl derivative. O-coordination to a neighbouring calixarene in 2, which can be seen as ‘intermolecular’ Ocoordination for the sake of clarity, notwithstanding the ambiguity of this term in the present case, is very likely related to the absence of p-tert -butyl substituents, which enables a closer approach of the second anion. In the p tert -butyl derivative, an acetonitrile molecule is located on the main axis of the calixarene, near its upper rim, and is coordinated to Cs. The distance between the cation and the mean plane defining (approximately) the border of the upper rim (aromatic carbon atoms in para position in 2, terminal tert -butyl carbon atoms in the other complexes) is a parameter which gives some information on the accessibility of the cation towards ‘intermolecular’ coordination. This parameter amounts ˚ in 2, to be compared to 2.29 and 1.83 A ˚ in the to 0.23 A other two compounds. The cation is thus far more accessible in the former case, with approximately a free half-coordination sphere.
Fig. 3. Partial view of the columnar arrangement parallel to the (101) direction in complex 3. p-Bonding is indicated by dashed lines joining the cation and the aromatic ring centroids. Hydrogen bonds are represented as dashed lines and phenolic protons as small spheres of arbitrary radii. Other hydrogen atoms and solvent molecules are omitted for clarity. Thermal ellipsoids are drawn at the 10% probability level. Symmetry code: ?/x /0.5, 2.5 /y , z /0.5.
A similar situation arises in [Cs2(LH3)2(H2O)] ×/ CH3CN (3). This complex, obtained with triethylamine as a deprotonating agent, crystallizes with two independent caesium ions and two calixarene mono-anions, denoted A and B, in the repeat unit (it may be noted that in its triethylammonium ion complexes, calix[4]arene is also mono-deprotonated [27]). As shown in Fig. 3, the overall shape, with formation of polymeric chains parallel to the (101) direction from units related by the glide plane perpendicular to the b axis, is roughly analogous to that of complex 2, but the details are quite different. The two caesium ions are not equivalent in what concerns their environment. Both of them are located in the cavity of a calixarene moiety and are involved in polyhapto bonding. The mean Cs C ˚ in the distances are 3.9(3), 4.0(3), 3.9(2) and 3.7(4) A case of Cs1 and the four aromatic rings of calixarene A, with the corresponding shortest contacts of 3.530(7), ˚ and Cs centroid 3.540(7), 3.652(7) and 3.637(8) A ˚ . In the case of distances of 3.61, 3.73, 3.69 and 3.41 A Cs2 and the four aromatic rings of calixarene B, the ˚, mean distances are 3.74(9), 4.1(4), 4.0(3) and 3.71(8) A the shortest contacts 3.639(7), 3.518(7), 3.558(6) and ˚ and the Cs centroid distances 3.47, 3.89, 3.596(7) A ˚ . p-Bonding is obvious in both cases, the 3.71 and 3.44 A four rings being differently involved, as in compound 2. Cs1 is further bound to two phenolic oxygen atoms of a neighbouring calixarene, with a mean Cs /O distance of ˚ , slightly shorter than its counterpart in 3.07(1) A complex 2 and it is also bound to a water molecule (O1) located in a similar manner as the pyridine molecule in 2. No bond between Cs1 and the oxygen atoms of the calixarene in which it is included is observed, at variance with the previous complex. By contrast, Cs2 is bound to one such oxygen atom, with a ˚ comparable to its equivalent bond length of 3.673(5) A in 2, and it is also bound to the four oxygen atoms of the neighbouring calixarene, with a much larger mean Cs /O ˚ . The distances between caesium bond length of 3.9(3) A ions and the mean planes defining the borders of the lower and upper rims (O4 in the first case) are 3.559(3) ˚ for Cs1 and calixarene A and 3.520(3) and 0.144(5) A ˚ for Cs2 and calixarene B, i.e. in both and 0.145(4) A cases the cation is even closer to the upper rim than in complex 2. The dihedral angles between the aromatic rings and the reference O4 plane are 52.9(2), 44.3(3), 58.8(3) and 73.7(2)8 in calixarene A and 68.2(2), 37.4(3), 48.1(2) and 70.8(2)8 in calixarene B, both sets of values indicating a distorsion of the cone conformation analogous to that in complex 2. The dihedral angle between the two reference O4 planes is 13.0(4)8, indicating a slight deviation of the calixarene units with respect to parallelism. By contrast with the structures of complexes 1 and 2, the phenolic protons can be located in that of 3. In both molecules A and B, the phenoxide oxygen atom is O2, which is involved in strong hydrogen bonds with
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its two neighbours (Table 2). A possible hydrogen bond links the water molecule and O3B of the neighbouring calixarene. Apart from the differences between complexes 2 and 3 with regards to O-coordination, the same polymeric structure is found, with a stacking of alternate cations and anions, the latter all pointing towards the same direction. To the best of our knowledge, this peculiar arrangement has never been observed in alkali metal ion complexes of p-R -calix[4]arene and its derivatives. The lack of p-alkyl substituents in the present cases enables the cation enclosed in the calixarene cavity to be easily complexed through the upper rim aperture by a bulky species such as a second calixarene moiety. Although stacking of uncomplexed calixarenes in columns held by feeble interactions is known, the present results show that novel tightly linked polymeric chain assemblages can be obtained from alkali-metal ions and one of the simplest calixarenes.
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 187709/187711 for compounds 1, 2 and 3, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: /441223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
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[6] S.R. Dubberley, A.J. Blake, P. Mountford, Chem. Commun. (1997) 1603. [7] M.G. Davidson, J.A.K. Howard, S. Lamb, C.W. Lehmann, Chem. Commun. (1997) 1607. [8] G. Guillemot, E. Solari, C. Rizzoli, C. Floriani, Chem. Eur. J. 8 (2002) 2072. [9] N.P. Clague, W. Clegg, S.J. Coles, J.D. Crane, D.J. Moreton, E. Sinn, S.J. Teat, N.A. Young, Chem. Commun. (1999) 379. [10] J.M. Harrowfield, M.I. Ogden, W.R. Richmond, A.H. White, J. Chem. Soc., Chem. Commun. (1991) 1159. [11] R. Assmus, V. Bo¨hmer, J.M. Harrowfield, M.I. Ogden, W.R. Richmond, B.W. Skelton, A.H. White, J. Chem. Soc., Dalton Trans. (1993) 2427. [12] A. Bilyk, A.K. Hall, J.M. Harrowfield, M.W. Hosseini, B.W. Skelton, A.H. White, Inorg. Chem. 40 (2001) 672. [13] B.W.F. Gordon, M.J. Scott, Inorg. Chim. Acta 297 (2000) 206. [14] For reviews on this topic, see: (a) P. Thue´ry, M. Nierlich, V. Lamare, J.F. Dozol, Z. Asfari, J. Vicens, J. Incl. Phenom. 36 (2000) 375; (b) A. Casnati, R. Ungaro, Z. Asfari, J. Vicens, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001, Kluwer Academic Publishers, Dordrecht, 2001 (Chapter 20), pp. 365 /384; (c) F. Arnaud-Neu, M.J. Schwing-Weill, J.F. Dozol, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001, Kluwer Academic Publishers, Dordrecht, 2001 (Chapter 35), pp. 642 /662. [15] H.F. Ji, R. Dabestani, G.M. Brown, R.L. Hettich, J. Chem. Soc., Perkin Trans. 2 (2001) 585 (and references therein). [16] F. Arnaud-Neu, M.A. McKervey, M.J. Schwing-Weill, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001 (Chapter 21, and references therein), Kluwer Academic Publishers, Dordrecht, 2001, pp. 385 /406. [17] C. Floriani, R. Floriani-Moro, in: Z. Asfari, V. Bo¨hmer, J. Harrowfield, J. Vicens (Eds.), Calixarenes 2001 (Chapter 29, and references therein), Kluwer Academic Publishers, Dordrecht, 2001, pp. 536 /560. [18] J.L. Atwood, L.J. Barbour, M.J. Hardie, C.L. Raston, Coord. Chem. Rev. 222 (2001) 3 (and references therein). [19] Z. Asfari, J. Harrowfield, P. Thue´ry, J. Vicens, Supra. Chem., in the press. [20] R. Ungaro, A. Pochini, J. Chem. Soc., Perkin Trans. 2 (1984) 1979. [21] Kappa-CCD Software, Nonius B.V., Delft, 1998. [22] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307. [23] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467. [24] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures, University of Go¨ttingen, 1997. [25] A.L. Spek, PLATON, University of Utrecht, 2000. [26] G.M. Sheldrick, SHELXTL, Version 5.1, University of Go¨ttingen, distributed by Bruker AXS Inc., Madison, WI, 1999. [27] P. Thue´ry, Z. Asfari, M. Nierlich, J. Vicens, Acta Crystallogr., Sect. C 58 (2002) o223.