Cation-π interaction: A case for macrocycle-cation π-interaction by its ureidoarene counteranion

Article abstract of DOI:10.1039/b509240j

We report the solid state structures of homocomplex [1·K] ⁺[I]^- and of heterocomplexes [1·K] ⁺[3·I]^- and [1·K]⁺[4·I]. In the [1·K]⁺[I]^- complex the apical position of the K⁺ in the macrocycle is occupied by a -CH₂- moiety of a neighboring 18-crown-6, consistent with a close contact and corresponding to 'agostic' interactions between K⁺ and -CH₂- moieties. In the [1·K]⁺[3·I]^- complex the second apical site of the cation is coordinated by a bridging water molecule which is simultaneously H-bonded to both the phenol hydroxyl and the iodide anion. In the [1·K]⁺[4·I]^- complex the second apical site of the cation is occupied by the indole moiety. Moreover, the new heterocomplex system [1·K]⁺[4·I]^- presented here, despite the multiple possibilities of K⁺-π contacts with the sterically available phenyl, phenyl-indole and pyrrole-indole rings of 4, shows that the pyrrolo C2=C3 double bond is a versatile π-donor. ¹H NMR results led us to conclude that the complexes adopt similar conformations in solution to those observed in the solid state. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.

Full text of DOI:10.1039/b509240j

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P A P E R
Cation–p interaction: a case for macrocycle–cation p-interaction
by its ureidoarene counteranion
Carole Arnal-Herault, Mihail Barboiu,* Eddy Petit, Mathieu Michau and Arie van der Lee
´
`
Institut Europeen des Membranes - UMR-CNRS 5635, Place Eugene Bataillon, CC 047,
F-34095 Montpellier Cedex 5, France. E-mail: mihai.barboiu@iemm.univ-montp2.fr;
Fax: þ33 467 149 119; Tel: þ33 467 149 195
Received (in St Louis, MO, USA) 30th June 2005, Accepted 10th October 2005
First published as an Advance Article on the web 28th October 2005
We report the solid state structures of homocomplex [1 ꢀ K]1[I]ꢁ and of heterocomplexes [1 ꢀ K]1[3 ꢀ I]ꢁ and
[1 ꢀ K]1[4 ꢀ I]. In the [1 ꢀ K]1[I]ꢁ complex the apical position of the K1 in the macrocycle is occupied by a
–CH2– moiety of a neighboring 18-crown-6, consistent with a close contact and corresponding to ‘agostic’
interactions between K1 and –CH2– moieties. In the [1 ꢀ K]1[3 ꢀ I]ꢁ complex the second apical site of the
cation is coordinated by a bridging water molecule which is simultaneously H-bonded to both the phenol
hydroxyl and the iodide anion. In the [1 ꢀ K]1[4 ꢀ I]ꢁ complex the second apical site of the cation is occupied
by the indole moiety. Moreover, the new heterocomplex system [1 ꢀ K]1[4 ꢀ I]ꢁ presented here, despite the
multiple possibilities of K1–p contacts with the sterically available phenyl, phenyl-indole and pyrrole-indole
1
rings of 4, shows that the pyrrolo C2 C3 double bond is a versatile p-donor. H NMR results led us to
Q
conclude that the complexes adopt similar conformations in solution to those observed in the solid state.
potassium salts from water to an organic phase and we have
Introduction
observed anomalous p-interactions in solution between the
resulting cationic [1 ꢀ K]1 and the anionic-arene [2–4 ꢀ I]ꢁ in-
dividual species. In many known K1–crown complexes, the
cation is bound equatorially by the 18-crown-6 macroring and
the counteranion, solvent (water) and aromatic moieties occu-
py the cation’s apical positions.2,4 Although the membrane
transport chemistry remains under investigation, the exciting
implication that the crown–K1 cation and the non-covalently
bound p-donor residues of the discrete benzoureidoarene anion
receptors 2–4 could present cation–p contacts, despite the
entropically unfavourable conditions (Scheme 1b), led us to
study these systems in solution and in the solid state.
Intermolecular interactions involving aromatic rings are key
processes in both chemical and biological recognition. Among
these interactions, cation–p interactions between positively
charged species (alkali, ammonium and metal ions) and aro-
matic systems with delocalized p-electrons are now recognized
as important non-covalent binding forces of increasing rele-
vance.1 The importance of interactions between alkali cations
and the side chains of aromatic amino acids has been known for
many years and they are of particular biological significance.1,2
Structural evidence for alkali cation–aromatic interactions
may be found in the literature and it was best revealed by
computational, solution (ES-MS, NMR) and solid state studies
of different ion–molecule complexes.2–12 Most of the first
pioneering examples include aromatics, organic anions or
solvent molecules.2b The development of different homo- and
heteroditopic receptors like calixarenes,3a salophens,3b or me-
tallic complexes3c showed cation–p interactions based on ion-
pairing interactions in solution and in solid state.8 Gokel and
co-workers made crucial advances during the last decade and
provided useful insights in this field.4 Their studies were
confined to macrocyclic equatorially-bound alkali-cations.4–9
Different crown-ethers were chosen as well known Na1 and
K1 complexants and were decorated with one or two identical
covalently-attached arene sidearms of four essential aromatic
amino acids.5 They were connected by flexible sidearms, long
enough to permit the arene to occupy the vacant apical
coordination sites (Scheme 1a). The direct bonding of the
aromatic moieties in a specific position with respect to the
crown molecule imposes a spatially limited, but optimized
position of the arene. Particular success has been encountered
using only 2-carbon linker arms and no conclusive or negative
results have been obtained for other linker lengths.4b,c
Results and discussions
Three phenylureidoarene anion receptors 2–4 were prepared
for studies described here. We restricted our studies to benzene
2, phenol 3, and indole 4 as the arene (Ar) termini of phenyl-
alanine, tyrosine and tryptophan, three aromatic essential
amino acids (Scheme 2). The imidazole derivative could not
be employed for this study due to its low solubility. The phenyl
isocyanate was treated with the corresponding aromatic amine
(CH3CN, D, 5 h) to afford, after crystallization, 2–4 as white
powders (90%). The heteroditopic systems were obtained by
dissolving 1 : KI (1 : 1, mol : mol) and 1 : 2/3/4 : KI (1 : 1 : 1,
mol : mol : mol), respectively, in acetone-d6. Layering these
solutions with isopropyl ether resulted in the formation of
colorless single crystals of homocomplex [1 ꢀ K]1[I]ꢁ and of
heterocomplexes [1 ꢀ K]1[3 ꢀ I]ꢁ and [1 ꢀ K]1[4 ꢀ I]ꢁ. Attempts to
crystallize the heterocomplex [1 ꢀ K]1[2 ꢀ I]ꢁ failed until now
and only tiny single crystals, too small for X-ray analysis, could
be obtained from different solution-diffusion experiments.
In the solid state structures of [1 ꢀ K]1[I]ꢁ (Fig. 1), [1ꢀ K]1
[3 ꢀ I]ꢁ (Fig. 2a) and [1 ꢀ K]1[4 ꢀ I]ꢁ (Fig. 2b) the 18-crown-6 ring is
nearly planar and in the D3d conformation. The distances
between the oxygen donors and the bound K1 are as expected
(average dKꢀꢀꢀO of 2.80 A). Generally, one apical position of K1 is
Our strategy was to use 18-crown-6, 1 and phenylureidoar-
ene (PhNHCONHAr) 2–4 compounds (Scheme 2) as well-
recognized macrocyclic- and urea-receptors of K1 and of Iꢁ,
respectively.10 We have examined these systems as synergetic
individual cation and anion receptors for the co-extraction of
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 5 3 5 – 1 5 3 9
1535

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Scheme 1
occupied by the Iꢁ anion (dKꢀꢀꢀI of 3.40 A). In the heterocomplex
structures [1 ꢀ K]1[3 ꢀ I]ꢁ and [1 ꢀ K]1[4ꢀ I]ꢁ the Iꢁ anion is hydro-
gen-bonded to the urea N–H residues (average dHꢀ ꢀꢀI 2.75 A).
We have found in the Cambridge Structural Database (April
2005)11a only the poly-iodide structures of [1 ꢀ K]1[I3]ꢁ 11b and
[1 ꢀ K]1[I5]ꢁ,11c but surprisingly, not the crystal structure of
[1 ꢀ K]1[I]ꢁ, which is very different from the previous ones. In
the solid state structure of [1 ꢀ K]1[I]ꢁ two Iꢁ anions are H-
bonded by a bridging water molecule (average dOꢀ ꢀ ꢀI of 3.75 A)
leading to a layered water–iodide network (Fig. 1a). These layers
are stratified with adjacent macrocyclic layers of [1 ꢀ K]1 and are
in close contact by K1 ꢀ Iꢁ apical ionic interactions. The second
apical position of the K1 in the macrocyclic layer is occupied by
a –CH2– moiety of a neighboring 18-crown-6 (Fig. 1b). The
ionic radius of K1 is 1.4–1.5 A11d and the half-thickness of a
–CH2– moiety is about 2.00 A; adding these values, the contact
values are in the range of 3.4–3.5 A. In [1 ꢀ K]1[I]ꢁ the distance
Fig. 1 Crystal structure (stick representation) of (a) [1 ꢀ K]1[I]ꢁ. (b)
Apical ‘‘agostic’’ K1ꢀ ꢀ ꢀH–C-interactions. K1 magenta, water mole-
cules red and Iꢁ violet spheres.
dKꢀ ꢀ ꢀC is 3.50 A, consistent with a close contact and correspond-
ing to ‘‘agostic’’ interactions12 between K1 and –CH2– moieties.
To our knowledge, the present system is the first example of a
macrocyclic complex where the K1ꢀ ꢀ ꢀH–C- ‘‘agostic’’ interac-
tions and an apical contact might in principle be associated.
In the [1 ꢀ K]1[3 ꢀ I]ꢁ complex the second apical site of the
5
6
structures of K1 and Ca21 lariat-ether complexes, the
second apical position is coordinated by a bridging water
molecule which is simultaneously H-bonded to both the phenol
hydroxyl (dOꢀ ꢀ ꢀO of 2.83 A) and the iodide anion (dOꢀ ꢀ ꢀI of
3.56 A). Moreover the phenol hydroxyl is H-bonded to the
urea oxygen (dOꢀ ꢀ ꢀO of 2.66 A) of the neighboring receptor 3.
In [1 ꢀ K]1[4 ꢀ I]ꢁ the second apical site of the cation is
occupied by the indole moiety. As in most of the previously
reported structures we observed a close p-contact between
indole and the bound K1 cation at the pyrrolo-subunit.7–9
Selected distances and the relative orientation of the K1 with
respect to the indole are shown in Table 1 and Fig. 3,
respectively. The NH indole moiety is H-bonded with the urea
oxygen (dNꢀ ꢀ ꢀO of 2.80 A) of a vicinal phenylureidoindole 4
molecule. This influences the relative interaction between the
indole-ring and the bound K1, inducing a lateral contact
cation is coordinated by one water molecule (dOꢀ ꢀ ꢀ
of
K1
2.71 A) which plays a critical role in organizing the partners
in the network. In contrast with previously reported solid state
between the C2 C3 double bond and the cation (Fig. 3).
Q
Scheme 2 Structure of K1 (1) and Iꢁ (2–4) cation and anion,
respectively, receptors.
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Table 1 Geometry of the K1–indole p-interaction. A comparison
between Gokel’s lariat complex7,8 [5 ꢀ K]1[I]ꢁ and the [1 ꢀ K]1[4 ꢀ I]ꢁ
heterocomplex
K1–R distance (A)
R
5
[1 ꢀ K]1[4 ꢀ I]ꢁ
K1–Nindole
3.51
3.32
3.57
3.89
3.91
3.50
4.77
4.43
3.34
3.27
4.40
4.97
3.96
5.63
K1–C2indole
K1–C3indole
K1–C8indole
K1–C9indole
K1–pyrrolocentroid
K1–benzocentroid
The urea NH protons and the adjacent aromatic protons
(H3, H4, H5) showed typical downfield shifts of 1.01 to 1.25
ppm and 0.15 ppm, respectively, which is indicative of strong
H-bonding with the Iꢁ anion. The other hydrogen atoms H1,
H5, H7 and H8, non-adjacent to the urea moiety, were upfield
shifted (Dd ¼ ꢁ0.07 to ꢁ0.15 ppm) and suggesting their close
proximity with the bound cation. Similar effects have been
reported for alkali metal cation–indole p complexation in
solution and in all cases the arene residue is predicted to
coordinate the cation.7,8 Hydrogens of the indole NH and
the phenol OH exhibited modest shifts and seem practically
unaffected by complexation: Dd ¼ ꢁ0.02 and ꢁ0.1 ppm,
respectively. The expected deshielding, consistent with the
H-bonding observed in the solid state structures, is probably
accompanied by a shielding phenomenon due to the close
proximity of the cation. We therefore conclude that the com-
plexes adopt similar conformations in solution to those ob-
served in the solid state. This could be argued by strong ion-
pairing interactions and favorable hydrogen bonding in a
solvent like acetone.
Conclusion
In summary, we present here solid state and solution study
evidence that demonstrates alkali metal cation–p and K1ꢀ ꢀ ꢀ
H–C- ‘‘agostic’’ interactions for a family of macrocyclic het-
erocomplexes. We have emphasized the macrocycle–cation
p-interaction by its ureidoarene counteranion in solution and
in the solid state. Other similar systems include inorganic
anions, such as tetraphenylborate, or solvent molecules, such
as toluene or benzene, forming the cation–p complexes with
alkali cations.3b In our case, two distinct entities, the aromatic
residue of the anion receptor and the crown–cation, could
interact apically as constituents of geometrically discrete ion-
pair receptors. Theoretical treatments and most solid state
Fig. 2 Crystal structure (stick representation) of (a) [1 ꢀ K]1[3 ꢀ I]ꢁ and
(b) [1 ꢀ K]1[4 ꢀ I]ꢁ. K1 magenta and Iꢁ violet spheres.
In [1 ꢀ K]1[4 ꢀ I]ꢁ the distance between K1 and the C2 C3
Q
centroid is 3.24 A, indicating rather strong K1–p contacts.
This new interaction is geometrically different from most of the
cation–p interactions observed in the solid state structure of the
lariat-crown complex [5 ꢀ K]1[I]ꢁ reported by Gokel et al.
(Table 1, Fig. 3), where the cation is centered to the pyrrole
ring and is closely situated to the C2 atom.7,8
In nature either aromatic subunit of the indole ring, the
arene terminus of tryptophan, may be available for cation
complexation. Moreover, the new heterocomplex system
[1 ꢀ K]1[4 ꢀ I]ꢁ presented here, despite the multiple possibilities
of K1–p contacts with the sterically available phenyl, phenyl-
indole and pyrrole-indole rings of 4 (the ligand could turn/
translate around/with the Iꢁ anion), shows that the pyrrolo
C2 C3 double bond is a versatile p-donor.
Q
1H NMR experiments were performed on solutions of
phenylureidoarene anion receptors 2–4 and of heterocomplexes
[1 ꢀ K]1[2 ꢀ I]ꢁ, [1 ꢀ K]1[3 ꢀ I]ꢁ and [1 ꢀ K]1[4 ꢀ I]ꢁ in acetone-d6 at
25 1C (Fig. 4).
1H NMR dilution experiments on solutions of 0.04 to 0.16
mol Lꢁ1 of [1 ꢀ K]1[2 ꢀ I]ꢁ, [1 ꢀ K]1[3 ꢀ I]ꢁ and [1 ꢀ K]1[4 ꢀ I]
showed an invariant shift of all 1H NMR signals upon increas-
ing concentration, which is indicative of a strong self-associa-
tion through the anion hydrogen bonding, cation
complexation and ion-pairing of resulted species in solution.
Fig. 3 Top and side-view CPK representation of K1–indole cation–p
and (c), (d)
7,8
interactions for the complexes (a), (b) [5 ꢀ K]1[I]ꢁ
[1 ꢀ K]1[4 ꢀ I]ꢁ. K1 represented as magenta scaled spheres.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 5 3 5 – 1 5 3 9
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Experimental
Methods and materials
All reagents were obtained from commercial suppliers and
used without further purification. All organic solutions were
1
routinely dried by using sodium sulfate (Na2SO4). H NMR
spectra were recorded on an ARX 300 MHz Bruker spectro-
meter in acetone-d6, with the use of the residual solvent peak as
reference. Mass spectrometric studies were performed in the
negative and the positive ion mode using a quadrupole mass
spectrometer (Micromass, Platform 2þ). Samples were dis-
solved in acetonitrile and were continuously introduced into
the mass spectrometer at a flow rate of 10 mL minꢁ1 through a
Waters 616HPLC pump. The temperature (60 1C) and the
extraction cone voltage (Vc ¼ 5–10 V) were usually set to avoid
fragmentations.
General procedure for the synthesis of compꢁounds 2–4 and
.
1
ꢁ
1
1
heterocomplexes [1 K] [2 I] , [1 K] [3 I] and [1 K] [4 I]
.
.
.
.
.
2–4 were prepared by adding phenyl isocyanate to the corre-
sponding amino derivative in acetonitrile and the reaction was
refluxed under argon for 5 h. After removal of the solvent, the
residue was subjected to recrystallization from acetonitrile to
afford 2–4.
1
The numerations used for the assignments of the H NMR
signals (according to the corresponding COSY spectra) are
shown in Fig. 4.
1,3-Diphenylurea, 2. 1H NMR (300 MHz, acetone-d6):
d(ppm) 8.13 (s, 2H, NH); 7.59 (dd, 4H, H3, J ¼ 7.91 Hz);
7.32 (t, 4H, H2, J ¼ 8.44 Hz); 7.03 (t, 2H, H1, J ¼ 7.42 Hz).
[1 ꢀ K]1[2 ꢀ I]ꢁ. 1H NMR (300 MHz, acetone-d6): d(ppm) 9.22
(s, 2H, NH); 7.63 (dd, 4H, H3, J ¼ 8.58 Hz); 7.18 (t, 4H, H2,
J ¼ 8.32 Hz); 6.87 (t, 2H, H1, J ¼ 7.68 Hz); 3.55 (m, 24H,
CH2–O). ESI-MS (CH3CN) m/z: 339.2 [2 ꢀ I]ꢁ; 551.7
[(2)2I ꢁ H]ꢁ; 763.70 [(2)3I ꢁ H]ꢁ.
1-(4-Hydroxyphenyl)-3-phenylurea. 3 1H NMR (300 MHz,
acetone-d6): d(ppm) 8.09 (s, 1H, OH); 8.03 (s, 1H, NHu2); 7.87
(s, 1H, NHu1); 7.56 (dd, 2H, H3, J ¼ 3.07 Hz); 7.37 (dd, 2H,
H4, J ¼ 4.61 Hz); 7.30 (t, 2H, H2, J ¼ 16 Hz); 7.00 (t, 1H, H1,
J ¼ 7.3 Hz); 6.82 (dd, 2H, H5, J ¼ 4.48 Hz).
[1 ꢀ K]1[3 ꢀ I]ꢁ. 1H NMR (300 MHz, acetone-d6): d(ppm)
9.14 (s, 1H, NHu2); 9.98 (s, 1H, NHu1); 8.00 (b, 1H, OH);
7.71 (dd, 4H, H3, J ¼ 6.66 Hz); 7.52 (dd, 2H, H4, J ¼ 8.96 Hz);
7.27 (t, 2H, H2, J ¼ 8.33 Hz); 6.95 (t, 1H, H1, J ¼ 7.3 Hz);
6.81 (dd, 2H, H5, J ¼ 8.96 Hz); 3.60 (m, 24H, CH2–O). ESI-MS
(CH3CN) m/z: 355.5 [3 ꢀ I]ꢁ; 582.8 [(3)2I ꢁ H]ꢁ; 811.27
[(3)3I ꢁ H]ꢁ; ESIþMS (CH3CN) m/z: 267.7 [3 ꢀ K]1; 495.7
[(3)2K þ H]1; 723.7 [(3)3K þ H]1; 952.2 [(3)4K þ H]1; 1180.5
[(3)5K þ H]1; 1408.1 [(3)6K þ H]1.
Fig. 4 1H NMR spectra of phenylureidoarene anion receptors (a,
bottom) 2, (b, bottom) 3, (c, bottom) 4 and of heterocomplexes (a, top)
[1 ꢀ K]1[2 ꢀ I]ꢁ, (b, top) [1 ꢀ K]1[3 ꢀ I]ꢁ and (c, top) [1 ꢀ K]1[4 ꢀ I]ꢁ in
acetone-d6 at 25 1C.
1-(1H-Indol-5-yl)-3-phenylurea. 4 1H NMR (300 MHz, acet-
one-d6): d(ppm) 10.17 (s, 1H, NH); 8.04 (s, 1H, Hu2); 7.92
(s, 1H, Hu1); 7.83 (s, 1H, H4); 7.60 (dd, 2H, H3, J ¼ 9 Hz);
7.21–7.40 (m, 5H, H2, H5, H6, H7); 7.00 (t, 1H, H1, J ¼ 7.29
Hz); 6.45–6.47 (t, 1H, H8, J ¼ 4.23 Hz).
structures predict that indole should bind to an alkali metal
with the benzocentroid.2 In terms of dynamic diversity the
heteroduplex complex [1 ꢀ K]1[4 ꢀ I]ꢁ represents an attractive
illustration of the self-selection, based on specific cation–
pyrrole p-interactions in competition with two other benzene
rings, of a unique solid state component. Once again, and
without any constraining steric impediment in the [1 ꢀ K]1[4 ꢀ
1
[1K]1[4I]ꢁ. H NMR (300 MHz, acetone-d6): d(ppm) 10.16
I]ꢁ complex, the pyrrolo subunit of the indole (i.e. the C2 C3
(s, 1H, NH); 9.18 (s, 1H, Hu2); 8.99 (s, 1H, Hu1); 7.97 (s, 1H,
H4); 7.73 (dd, 2H, H3, J ¼ 7.56 Hz); 7.32–7.36 (m, 2H, H5, H7);
7.21–7.27 (m, 3H, H2, H6); 6.91 (t, 1H, H1, J ¼ 8.45 Hz); 6.40
(d, 1H, H8, J ¼ 4.48 Hz); 3.68 (m, 24H, CH2–O). ESIþMS
(CH3CN) m/z: 290.4 [4 ꢀ K]1; 541.5 [(4)2K þ H]1. ESI-MS
Q
bond) is a strong p-donor group.
These systems may be used in principle for comparative
membrane transport experiments, leading to more subtle ana-
lyses of these interactions, and such studies are under way.
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(CH3CN) m/z: 378.7 [3I]ꢁ; 629.9 [(4)2I
[(4)3I ꢁ H]ꢁ.
ꢁ
H]ꢁ; 881.2
et de la Technologie’’ (ACI Jeunes Chercheurs 2002) and by the
CNRS. G. Vaughan is kindly thanked for assistance during the
measurements at the ID11, ESRF, Grenoble. R. Astier is
kindly thanked for the X-ray data collection in Montpellier.
Crystallographic details
[1 ꢀ K]1[I]ꢁ ꢀ H2O, C12H26IKO7, orthorhombic, space group
P212121, a ¼ 8.230(3) A, b ¼ 12.890(7) A, c ¼ 7.337(7) A, V
¼ 839.2(14) A3, Z ¼ 4, Dc ¼ 1.619 g cmꢁ3, R1 ¼ 0.0746, wR2 ¼
0.0769 for 4541 [I 4 2s(I)] data, 199 parameters refined.
[1 ꢀ K]1[3 ꢀ I]ꢁ ꢀ H2O, C25H38IKN2O9, orthorhombic, space
group P212121, a ¼ 8.2770(11) A, b ¼ 10.5760(13) A, c ¼
34.165(5) A, V ¼ 2990.7(7) A3, Z ¼ 4, Dc ¼ 1.503 g cmꢁ3, R1 ¼
0.0243, wR2 ¼ 0.0219 for 7772 [I 4 2s(I)] data, 344 parameters
refined.
References
1
(a) R. MacKinnon, Angew. Chem., Int. Ed., 2004, 43, 4265–4277;
(b) A. M. Meyer, R. K. Castellano and F. Diederich, Angew.
Chem., Int. Ed., 2003, 42, 1210–1250; (c) J. C. Ma and D. A.
Dougherty, Chem. Rev., 1997, 97, 1303–1324.
2
3
(a) E. S. Meadows, S. L. De Wall and G. W. Gokel, Eur. J. Org.
Chem., 2000, 2967–2978, and references therein; (b) see ref. 49–56
in ref. 6.
(a) P. Lhotak and S. Shinkai, J. Phys. Org. Chem., 1997, 10, 273–
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references therein; (c) S. D. Zaric, Eur. J. Inorg. Chem., 2003,
2197–2209.
[1 ꢀ K]1[4 ꢀ I]ꢁ, C27H37IKN3O7, orthorhombic, space group
P212121, a ¼ 8.7154(9) A, b ¼ 10.7550(10) A, c ¼ 32.742(3) A,
V ¼ 3069.0(5) A3, Z ¼ 4, Dc ¼ 1.475 g cmꢁ3, R1 ¼ 0.0317, wR2
¼ 0.0299 for 4266 [I 4 2s(I)] data, 353 parameters refined.
The diffraction intensities for [1 ꢀ K]1[I]ꢁ and [1 ꢀ K]1[3 ꢀ I]ꢁ
were collected at the ID11 beamline of the European Synchro-
tron Radiation Facility in Grenoble, France, using a Bruker
Smart CCD Camera at 120 K. The diffraction intensities for
[1 ꢀ K]1[4 ꢀ I]ꢁ were collected at the X-ray Scattering Service of
4
(a) G. W. Gokel, L. A. Barbour, S. L. De Wall and E. S.
Meadows, Coord. Chem. Rev., 2001, 222, 127–154; (b) G. W.
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the Institut Europe
´
en des Membranes and the Institut Charles
de Montpellier II, France, at 175 K
Gerhardt of the Universite
´
5
6
7
8
9
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using an Oxford Diffraction Xcalibur I diffractometer. All
three structure were solved by direct methods using
SIR200213 and refined by least-squares methods on F using
CRYSTALS.14 [I]ꢁ in [1 ꢀ K]1[I]ꢁ was found to be disordered
over three different sites with site occupancy factors (s.o.f.)
0.15, 0.8, and 0.05, respectively. This disorder could not be
satisfactorily modelled using anisotropic ADP’s; the s.o.f.’s
were determined – and fixed – as to have approximately equal
and reasonable isotropic ADP’s for the three atoms. A largest
electron density hole of ꢁ5.83 A3 was found at about 1 A from
the [I]ꢁ ion in the space between crown ether moieties; it can be
probably be considered as a spurious hole due to a – still –
inadequate modelling of the electron density distribution of the
[I]ꢁ ion. CCDC reference numbers 284056–284058. For crys-
tallographic data in CIF or other electronic format and
detailed information about the crystal structure refinements
see DOI: 10.1039/b509240j
J. Hu, L. J. Barbour and G. W. Gokel, J. Am. Chem. Soc., 2002,
124, 10940–10941.
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Acknowledgements
This research was supported by the European Science Founda-
tion (EURYI Award 2004), by the ‘‘Ministere de la Recherche
14 P. W. Betteridge, J. R. Carruthers, R. I. Cooper, K. Prout and D.
J. Watkin, J. Appl. Crystallogr., 2003, 36, 1487.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 5 3 5 – 1 5 3 9
1539