Anion-directed assembly of a rectangular supramolecular cage in the solid state with electron-deficient phenoxylated oxacalix[2]arene[2]triazine

Article abstract of DOI:10.1039/c2cc36465d

Chloride-π interaction along with lone-pair electrons-π interaction, hydrogen bonding and π-π stacking induced the hexameric assembly of the parent macrocycle into a rectangular supramolecular cage in the solid state.

Full text of DOI:10.1039/c2cc36465d

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COMMUNICATION
Anion-directed assembly of a rectangular supramolecular cage
in the solid state with electron-deficient phenoxylated
oxacalix[2]arene[2]triazinew
De-Xian Wang,*a Shi-Xin Fa,a Yang Liu,b Bao-Yong Houa and Mei-Xiang Wang*b
Received 5th September 2012, Accepted 8th October 2012
DOI: 10.1039/c2cc36465d
Chloride–p interaction along with lone-pair electrons–p interaction,
hydrogen bonding and p–p stacking induced the hexameric assembly
of the parent macrocycle into a rectangular supramolecular cage
in the solid state.
triazine rings.3d In other words, the anion–p interaction of
triazine toward anions was regulated by the substituents. We
have also demonstrated that anion–p interaction along with
hydrogen bonds led to interesting self-assembled structures in
the solid state.3d,4d Our interest in directing the effect of
anion–p interactions on molecular self-assembly has led us
to the current study. To fine-tune the anion–p binding ability
of triazine rings, and also to append potential p–p stacking
moieties, phenoxy and perfluorophenoxy substituents are
introduced into triazine rings of oxacalix[2]arene[2]triazine.
We were delighted to find out that chloride–p interaction along
with lone-pair electron–p interaction, hydrogen bonding and p–p
stacking induced the hexameric assembly of the parent macrocycle
into a rectangular supramolecular cage in the solid state.
Anion receptors bearing p electron-deficient arenes have attracted
increasing interest during the past decade.1 The anion–p inter-
action between charge neutral electron-deficient aromatic rings, as
predicted by theoreticians,2 has been evidenced experimentally
both by solid state and solution investigations.3–5 For example,
in the solid state, while weak s-interaction in which anions interact
with p electron-deficient arenes such as, tetracyanobenzene,3c
tetracyanopyrazine3a,b and 1,4,5,8,9,12-hexaazatriphenylene-
hexacarbonitrile,3e from the periphery of the aromatic rings
has been shown, typical anion–p interaction in which an anion
(halide) is located just over the triazine centroid of a macrocyclic
oxacalix[2]arene[2]triazine host molecule has been observed.3d
Despite the increasing number of examples of anion–p interactions
being reported in the literature, it is worth addressing that as
an emerging catalog of non-covalent bond interaction, the
directing ability of anion–p interaction to induce the molecular
assembly based on charge neutral electron deficient arenes has
rarely been studied.3a,b,d,e,4d
To synthesize the target macrocyclic molecules, we first
carried out aromatic nucleophilic substitution reaction starting
from parent dichloro-substituted oxacalix[2]arene[2]triazine 13d
with pentafluorophenol 2 and phenol. The reaction between 1
and 2 proceeded efficiently in the presence of K2CO3 in
acetonitrile at room temperature, giving 5b almost quantita-
tively. However, similar reaction using phenol as a nucleophilic
agent yielded unfortunately a trace amount of desired product
5a. A one-pot protocol with resorcinol 3 and 2,4-dichloro-6-
phenoxy-1,3,5-triazine 4 (see ESIw for synthesis of 4) as the
starting materials was then employed, which gave successfully
5a in 39% yield (Scheme 1).
As one of the typical macrocyclic molecules of heteracalix-
aromatics, a new generation of host molecules in supramolecular
chemistry,6 the 1,3-alternate conformational oxacalix[2]arene[2]-
triazines have been shown to use their electron-deficient V-shaped
cleft to interact with anions through anion–p interactions.3d,4d,7
Our previous study has demonstrated that the binding ability of
tetraoxacalix[2]arene[2]triazines towards anions was affected
remarkably by the electronic nature of the substituents on
The structures of all the synthesized compounds were established
on the basis of their spectroscopic data and microanalysis
a Beijing National Laboratory for Molecular Sciences, CAS Key
Laboratory of Molecular Recognition and Function, Institute of
Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
E-mail: dxwang@iccas.ac.cn; Fax: 008610-6279-6761;
Tel: 008610-6279-6761
b The Key Laboratory of Bioorganic Phosphorous Chemistry &
Chemical Biology (Ministry of Education), Department of
Chemistry, Tsinghua University, Beijing 100084, China
w Electronic supplementary information (ESI) available: Experimental
details, crystal structures, 1H and 13C NMR spectra of products,
spectroscopic titration data. CCDC 897876 (5a), 897874 (5b), 897875
(5aꢀ(Et4NCl)ꢀH2O). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2cc36465d
Scheme 1 Synthesis of oxacalix[2]arene[2]triazine derivatives 5a and
5b.
c
11458 Chem. Commun., 2012, 48, 11458–11460
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the benzene rings were also observed. Directed by the multiple
weak noncovalent interactions, 5a formed a unique cyclic
hexamer structure in the solid state (Fig. 1B and C and
Fig. S2, ESIw). Due to the electronic nature of the introduced
perfluorobenzenes, multiple intermolecular lone pair electrons–p
interactions were formed in the case of 5b, leading to a non-
covalently bonded dimer structure. For example, one of the
perfluorobenzene rings of one molecule located in the V-shaped
cavity formed by the two triazine rings of another molecule
forms multiple lone pair electrons–p interactions (F:–triazine)
with the distances (dF-plane) being 3.077 and 3.394 A, respectively.
Meanwhile, the perfluorobenzene ring served as a p–electron
deficient acceptor and formed intermolecular s-type lone pair
electrons–p interactions with the nitrogen of triazine and the
bridging oxygen atom, giving distances of 3.127 and 2.917 A,
respectively (Fig. S4, top, ESIw).
To investigate the host–guest chemistry between macrocycles
and anions, the single crystals of the complexes were cultivated by
slow evaporation of a mixture of dichloromethane and methanol
and the complex of 5a and tetraethylammonium chloride was
obtained. Interestingly, the cyclic hexamer self-assembly of the
host molecule 5a was disrupted in the complex, instead, two [5aꢀ
ClꢁꢀH2O] ternary complexes self-assembled into a rectangular
cage structure (Fig. 1D and Fig. S5, ESIw) through a hydrogen
bond network between two chloride and two water molecules, and
also the p–p stacking between the benzene rings on triazines. Some
details of the structure are worth addressing. As shown in Fig. 1D,
chloride was located almost above the center of one of the triazine
rings of 5a, the distance of chloride to the plane and centroid of
triazine was 3.238 (dchloride–plane) and 3.258 A (dchloride–centroid),
respectively, forming typical noncovalent chloride–p interaction.
On the other hand, a water molecule formed lone pair electrons–p
interaction with the other triazine ring of 5a, giving distances of
2.773 (doxygen–plane) and 2.830 A (doxygen–centroid), respectively.
The included chloride and water in the cavity of 5a interacted
with each other through hydrogen bonding judged from the
distance of 3.123 A between chloride and water oxygen
(dO–Cl). The two introduced benzene rings on the triazine
rings, on the other hand, changed their alignment from a
trans-form (Fig. 1A) to cis-form in the complex, in order
to form p–p stacking between the two face-to-face ternary
complexes (Fig. 1D). In addition, the host molecules interacted
with each other through CH–p interactions between the benzene
rings, which led to an infinite two dimensional cagelike self-
assembly (Fig. S5, ESIw). The formation of a supramolecular
cage is mainly attributable to multiple non-covalent interactions
of anion–p, lpe–p, hydrogen bond and p–p stacking effects
among the neutral and charged components, though the crystal
packing forces could not be excluded completely.
Fig. 1 X-ray structures of (A) 5a (side view), (B) and (C) a cyclic
hexamer of 5a through intermolecular lone pair electrons–p inter-
action and hydrogen bonding (benzene rings attached on triazines and
hydrogens are omitted for clarity) and (D) anion induced rectangular
cage structure through multiple weak noncovalent interactions. The
probability is 25%.
(see Fig. S34–S39, ESIw). To get the structural information at
the molecular level, single crystals of compounds 5a and 5b were
cultivated through slow evaporation of mixtures of dichloro-
methane and hexane, acetone and hexane, respectively.z Both
oxacalix[2]arene[2]triazine derivatives 5a and 5b adopt the
1,3-alternate conformation with the introduced benzene and
perfluorobenzene rings on the triazine rings being trans-aligned
(Fig. 1 and Fig. S3, ESIw). The introduction of benzene and
perfluorobenzene rings modified the intermolecular interaction,
which led to interesting molecular self-assemblies in the solid
state. In the case of 5a, one nitrogen of the triazine of one
molecule interacted with the triazine of another molecule
forming lone pair electrons–p (lpe–p) interaction with the
distance (dN-plane) being 3.092 A (Fig. 1B). In addition, weak
intermolecular hydrogen bonds between hydrogen bond acceptors
such as triazine nitrogen, bridging oxygen and hydrogens of
The interaction of the synthesized macrocyclic host molꢁe-
cules 5a and 5b with anions including Clꢁ, Brꢁ, N3ꢁ, NO3
,
ꢁ
ꢁ
HSO4 and H2PO4 in tetrabutylammonium salts in aceto-
nitrile was also studied by means of fluorescence titration. As
shown in Fig. S6–S13 (ESIw), the interaction of 5a with anions
caused quenching of the fluorescence emission of the host
at 354 nm except for Clꢁ, which caused the quenching of
the fluoresecence intensity at 354 nm with a concomitant
bathochromic-shift to 362 nm (Fig. S7, ESIw). The association
constants for 1 : 1 host–guest complexes (Ka(1 : 1)) were
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 11458–11460 11459

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calculated using a Hyperquad program based on the fluorescence
titration data,8 giving 7.33 ꢂ 102 Mꢁ1 for (5aꢀClꢁ), 1.67 ꢂ 102 Mꢁ1
for (5aꢀBrꢁ), 1.68 ꢂ 103 Mꢁ1 for (5aꢀN3ꢁ), 6.84 ꢂ 102 Mꢁ1 for
(5aꢀNO3ꢁ), 2.93 ꢂ 102 Mꢁ1 for (5aꢀHSO4ꢁ) and 6.04 ꢂ
103 Mꢁ1 for (5aꢀH2PO4ꢁ), respectively. Surprisingly, the
response of 5b towards anions based on the fluorescence titration
was very different from that of 5a. For example, the addition of
b = 106.571, g = 90.001, V = 2967 (10) A3, T = 173(2) K, full-matrix
least-squares refinement on F2 converged to RF = 0.1296 [I > 2s(I)],
0.1540 (all data) and Rw(F2) = 0.2943 [I > 2s(I)], 0.3110 (all data),
goodness of fit 1.386. CCDC 897874. Crystallographic data for complex
5aꢀ(Et4NCl)ꢀH2O (C38H40ClN7O7): Mr = 742.22, triclinic, space group
76.08(3)1, g = 86.191, V = 1828.6 (6) A3, T = 173(2) K, full-matrix least-
squares refinement on F2 converged to RF = 0.0508 [I > 2s(I)], 0.0610
(all data) and Rw(F2) = 0.1127 [I > 2s(I)], 0.1183(all data), goodness of
fit 1.110. CCDC 897875.
%
P1, a = 12.102 (2), b = 12.290 (3), c = 13.841 (3) A, a = 66.291, b =
anions such as, Clꢁ, Brꢁ, NO3ꢁ, HSO4 and H2PO4 did not
ꢁ
ꢁ
ꢁ
change the fluorescence of 5b at all, whereas the addition of N3
1 For reviews on anion–p interaction, see: (a) P. Gamez, T. J. Mooibroek,
S. J. Teat and J. Reedijk, Acc. Chem. Res., 2007, 40, 435;
(b) B. L. Schottel, H. T. Chifotides and K. R. Dunbar, Chem. Soc.
Rev., 2008, 37, 68; (c) B. P. Hay and V. S. Bryantsev, Chem. Commun.,
2008, 2417; (d) P. Ballester, in Recognition of Anions, ed. R. Vilar,
Springer-Verlag Berlin Heidelberg, 2008, p. 127; (e) L. M. Salonen,
M. Ellermann and F. Diederich, Angew. Chem., Int. Ed., 2011, 50, 4808;
(f) A. Robertazzi, F. Krull, E.-W. Knapp and P. Gamez, CrystEngComm,
2011, 13, 3293; (g) O. B. Berryman and D. W. Johnson, Chem. Commun.,
2009, 3143; (h) A. Frontera, P. Gamez, M. Mascal, T. J. Mooibroek and
J. Reedijk, Angew. Chem., Int. Ed., 2011, 50, 9564; (i) D.-X. Wang and
M.-X. Wang, Chimia, 2011, 65, 939; (j) D. Quinonero, P. M. Deya,
M. P. Carranza, A. M. Rodriguez, F. A. Jalon and B. R. Manzano,
Dalton Trans., 2010, 39, 794; (k) D. Quinonero, A. Frontera and
P. M. Deya, in Anion Coordination Chemistry, ed. K. Bowman-James,
led to quenching of the fluorescence inteꢁnsity at 360 nm, indicating
a selective interaction of 5b with N3 (Fig. S4B, ESIw). The
calculated association constant (Ka(1 : 1)) for the complex of 5b
with N3 was up to 1.95 ꢂ 104 Mꢁ1
.
ꢁ
We further examined the interaction between host molecules 5a,
5b and the anions by means of NMR spectroscopy. No variation
at all in the 1H NMR spectra of 5a occurred with the addition of
anions (Fig. S14–S19, ESIw). The result is consistent with our
previous observation, reflecting that anion–p interactions are
responsible for the change of fluorescence spectrum of the host
molecule.3d,4d,7 In the case of 5b (Fig. S20–S25, ESIw), whereas the
proton signals remained intact with the addition of other anions,
the addition of 0.25 to 1 equivalent of azide, however, resulted
in the observation of many signals, which most probably indicated
the conformational changes after complexation (Fig. S22, ESIw).
The formation of a complex between host 5b and azide was
further evidenced by the observation of an upfield shift of 19F
signals (Fig. S26, ESIw). The outcomes of both spectroscopic
titration and NMR experiments indicated that the interaction
between azide and 5b is most probably different from that of 5a.
Last but not least, the interaction of host molecules 5a and 5b with
anions was also evidenced by the observation of ion peaks of the
complexes in ESI mass spectra (see Fig. S27–S33, ESIw).
´
A. Bianchi and E. Carcıa-Espana, Wiley-VCH Verlag GmbH&Co.
KgaA, 2012.
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In summary, we have synthesized phenoxy- and perfluoro-
phenoxy-substituted oxacalix[2]arene[2]triazine derivatives 5a and
5b. In the solid state, 5a and 5b formed a unique cyclic hexamer and
non-covalently bonded dimer structure, respectively. In the presence
of chloride, the cyclic hexamer of 5a was turned into a rectangular
supramolecular cage structure due to the formation of chloride–p,
H2O:–p, hydrogen bonding (ClꢀꢀꢀH–O) and p–p stacking inter-
actions. On the basis of fluorescence titration, the host molecule 5a
was found to be able to interact with the examined anions
in solution, giving association constants (Ka(1 : 1)) in the range of
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Buchholz and P. Ballester, Angew. Chem., Int. Ed., 2008, 47, 4114;
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M.-X. Wang, Chem.–Eur. J., 2010, 16, 13053; (e) S. Guha and
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6 For reviews on heteracalixaromatics see: (a) M.-X. Wang, Chem.
Commun., 2008, 4541; (b) W. Maes and W. Dehaen, Chem. Soc.
Rev., 2008, 37, 2393; (c) H. Tsue, K. Ishibashi and R. Tamura, Top.
Heterocycl. Chem., 2008, 17, 73; (d) M.-X. Wang, Acc. Chem. Res.,
2012, 45, 182; (e) J. Thomas, W. V. Rossom, K. V. Hecke,
L. V. Meervelt, M. Smet, W. Maes and W. Dehaen, Chem. Commun.,
1.67 ꢂ 102 Mꢁ1 to 6.04 ꢂ 103
M
ꢁ1. Whereas 5b selectively
recognized azide with an association constant of up to 1.95 ꢂ
104
M
ꢁ1. The present study indicated that anion–p interaction
would find applications in anion-directed molecular self-assembly.
We thank the National Natural Science Foundation of
China (91127008, 21072197, 21132005, 21121004), Ministry
of Science and Technology (2011CB932501, 2013CB834504),
Chinese Academy of Sciences for financial support.
Notes and references
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¨
z Crystallographic data for 5a (C30H18N6O6): Mr = 558.50, trigonal,
%
space group R3, a = 35.328 (5), b = 35.328 (5), c = 12.311 (3) A, a =
90.001, b = 90.001, g = 120.001, V = 13307 (4) A3, T = 173 (2) K,
full-matrix least-squares refinement on F2 converged to RF = 0.0704
[I > 2s(I)], 0.0900 (all data) and Rw(F2) = 0.1557 [I > 2s(I)], 0.1669
(all data), goodness of fit 1.178. CCDC 897876. Crystallographic data
for 5b. (C30H8F10N6O6): Mr = 738.42, monoclinic, space group P2(1)/n,
a = 12.587 (3), b = 18.349 (4), c = 13.403 (3) A, a = 90.001,
7 (a) Y. Chen, D.-X. Wang, Z.-T. Huang and M.-X. Wang, Chem.
Commun., 2011, 47, 8112; (b) S. Li, S.-X. Fa, Q.-Q. Wang,
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c
11460 Chem. Commun., 2012, 48, 11458–11460
This journal is The Royal Society of Chemistry 2012