Co-conformational isomerism in a neutral ion-paired supramolecular system

Article abstract of DOI:10.1002/chem.201203483

Two different counter-ion-free host-guest complexes have been prepared and isolated. These compounds were formed from two equally and opposite doubly-charged species, the viologen guests 1 a²⁺ and 1 b ²⁺ and the anti-disulfodibenzo[24]crown-8 [DSDB24C8]^2- host, which gave rise to the 1:1 neutral complexes [1 a×DSDB24C8] and [1 b×DSDB24C8]. These species are held together by hydrogen bonding and π stacking, as well as strong electrostatic interactions. The investigation of these neutral ion-paired supramolecular systems in solution and in the solid state allowed us to establish their co-conformational preferences. Compound [1 a×DSDB24C8], with small methyl groups as substituents on the viologen unit, may adopt three different geometries, 1) an exo nonthreaded, 2) a partially threaded, and 3) a threaded arrangement, depending on the relative spatial orientation between the host and guest: The partially-threaded structure is preferred in solution and in the solid state. The presence of bulky tert-butylbenzyl groups in the viologen moiety in compound [1 b×DSDB24C8] restricts the possible geometrical arrangements to one: The exo nonthreaded arrangement. This structure was confirmed in the solid state by X-ray crystallography. The stability of the neutral complexes in solution was determined by UV/Vis spectrophotometry. The stoichiometry of the complexes was established by continuous variation experiments, and ove Copyright

Full text of DOI:10.1002/chem.201203483

FULL PAPER
DOI: 10.1002/chem.201203483
Co-Conformational Isomerism in a Neutral Ion-Paired Supramolecular
System
Ruy Cervantes, Raul I. Sꢀnchez, and Jorge Tiburcio*[a]
Abstract: Two different counter-ion-
free host–guest complexes have been
prepared and isolated. These com-
pounds were formed from two equally
and opposite doubly-charged species,
the viologen guests 1a2+ and 1b2+ and
with small methyl groups as substitu-
ents on the viologen unit, may adopt
three different geometries, 1) an exo
nonthreaded, 2) a partially threaded,
and 3) a threaded arrangement, de-
pending on the relative spatial orienta-
tion between the host and guest: The
partially-threaded structure is preferred
in solution and in the solid state. The
presence of bulky tert-butylbenzyl
groups in the viologen moiety in com-
pound [1b·DSDB24C8] restricts the
possible geometrical arrangements to
one: The exo nonthreaded arrange-
ment. This structure was confirmed in
the solid state by X-ray crystallography.
The stability of the neutral complexes
in solution was determined by UV/Vis
spectrophotometry. The stoichiometry
of the complexes was established by
continuous variation experiments, and
overall equilibrium constants and DG8
values were determined on the basis of
dilution experiments. The results ob-
served are a consequence of only the
intrinsic stability of the complexes as
there are no additional contributions
from counter ions.
the
[DSDB24C8]2ꢀ host, which gave rise to
the 1:1 neutral complexes
anti-disulfodibenzo[24]crown-8
[1a·DSDB24C8] and [1b·DSDB24C8].
These species are held together by hy-
drogen bonding and p stacking, as well
as strong electrostatic interactions. The
investigation of these neutral ion-
paired supramolecular systems in solu-
tion and in the solid state allowed us to
establish their co-conformational pref-
erences. Compound [1a·DSDB24C8],
Keywords: conformation analysis ·
counter-ion effects
·
host–guest
systems · molecular recognition ·
supramolecular chemistry
Introduction
In addition to counter-ion effects, co-conformational
isom
erism[10] can also contribute to the behavior observed in
AHCTUNGTRENNUNG
The preparation of precise structural molecular ensembles
requires the fine design of the molecular components, taking
into consideration all possible modes of interaction between
them.[1] Some of the most widely investigated supramolecu-
lar ensembles are based on viologen derivatives as cationic
guests and various kinds of hosts, such as cucurbiturils,[2] cy-
clodextrins,[3] calixarenes,[4] pillar-arenes,[5] and, in particular,
crown ethers.[6]
Because of the ionic nature of many hosts and guests, it is
necessary to consider the role played by counter ions in the
molecular recognition process and also their possible effect
on the association constants.[7] In particular, the association
between dibenzo[24]crown-8 (DB24C8) and methyl violo-
gen bis(hexafluorophosphate) in acetone has proven to be
quite complex.[8,9]
solution, affecting chemical shifts in NMR spectra and ab-
sorption bands in electronic spectroscopy. An example of
this behavior was reported by Gibson et al. for the interac-
tion between DB24C8 and benzylammonium derivatives an-
1
alyzed by NMR spectroscopy; changes in the H chemical
shifts of uncomplexed benzylammonium were observed
upon mixing the two reagents and attributed to a non-pseu-
dorotaxane exo-type complexation with the crown ether.[11]
However, a few years later, the same group provided a dif-
ferent explanation based exclusively on ion pairing.[12] Clear-
ly, a new approach must be taken to discriminate between
these two effects in solution, along with a careful selection
of the host and guest components in the supramolecular
complex.
On the other hand, we recently reported neutral [2]pseu-
dorotaxanes based on 1,2-bis(pyridinium)ethane linear
dicat
disulfo
two penACHTNUGTRNEUNG
dant sulfonate (SO3 ) functionalities.[13] An incre-
ment of two orders of magnitude in the association constant
was observed with respect to the neutral analogue of the
macrocycle, allowing the formation of stable complexes
even in highly competitive solvents such as methanol and
water. This observation was explained by significant electro-
static interactions between host and guest. Similar behavior
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ꢀ
[a] Dr. R. Cervantes, R. I. Sꢀnchez, Prof. J. Tiburcio
Departmento de Quꢁmica
Centro de Investigaciꢂn y de Estudios Avanzados
Avenida IPN 2508, Zacatenco 07360, Mꢃxico D. F. (Mꢃxico)
Fax : (+52)55-57473389
E-mail: jtiburcio@cinvestav.mx
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203483.
Chem. Eur. J. 2013, 19, 4051 – 4057
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4051

was observed by Nikitin and co-workers in a related system
based on viologens and dianionic crown ether derivatives of
bis-p-phenylene[34]crown-10.[14]
Results and Discussion
Electroneutral complexes: To eliminate any counter-ion
effect, we isolated complex [1a·DSDB24C8] as an electro-
neutral salt. This complex was synthesized by a metathesis
reaction between the bromide salt [1a][Br]2 and [NMe4]2-
In this work, we proposed separating counter-ion effects
from co-conformational issues by studying counter-ion-free
neutral complexes formed with ionic components, that is,
neutral ion-paired supramolecular systems, taking advantage
of the strong electrostatic interactions associated with this
kind of system in addition to other noncovalent interactions
such as hydrogen bonding and p stacking. Based on our pre-
vious experience, we chose a dicationic viologen derivative
and dianionic crown ether [DSDB24C8]2ꢀ as components of
the complex. A comprehensive analysis of this supramolecu-
lar system provides three possible geometrical arrangements
(Scheme 1).
AHCTUNGTREGUN[NN DSDB24C8] in water (Scheme 2). Yellow crystals of
Scheme 2. Structures of the viologen bromides [1a][Br]2 and [1b][Br]2,
and the disulfonated crown ether, anti-[NMe4]2A[DSDB24C8].
CTHUNGTRENNUNG
[1a·DSDB24C8] were obtained in good yield by slow evapo-
1
ration of the solvent and characterized by H NMR spectro-
scopy, UV/Vis spectrophotometry, HRMS (ESI-TOF), and
single-crystal X-ray diffraction analysis. Although the com-
ponents [1a][Br]2 and [NMe4]2ACTHUNGRTNEUNG[DSDB24C8] are both color-
less, the isolated complex [1a·DSDB24C8] gives a bright-
yellow color in methanol solution (lmax =380 nm), which in-
dicates the formation of a charge-transfer complex between
the viologen and crown ether.
Scheme 1. Possible co-conformational isomers of the neutral 1:1 counter-
ion-free complexes formed between viologen derivatives and DSDB24C8
in solution. Co-conformer A=partially threaded, B=exo nonthreaded,
and C=fully threaded structures.
The appearance of color is accompanied by changes in
1
the chemical shifts in the H NMR spectrum compared with
those of the parent components (Figure 1). Only a single set
of resonances is observed, which reveals fast exchange dy-
namics for the association/dissociation process on the NMR
timescale. The observed averaged aromatic signals of the
complex, compared with the nonassociated species, are shift-
ed towards lower frequencies (Ha: Dd=ꢀ0.3 ppm; Hb: Dd=
ꢀ0.9 ppm), characteristic of aromatic stacking and consis-
tent with the formation of a charge-transfer complex. In
contrast, the methyl signal is shifted to a higher frequency
(CH3: Dd= +0.1 ppm), which suggests that these protons
are involved in hydrogen bonding. Moreover, a NOESY ex-
periment (see the Supporting Information) revealed
through-space coupling between methyl protons on the viol-
ogen guest and methylene protons on the crown ether host,
indicative of the spatial proximity of the guest methyl group
Co-conformer A represents a partially threaded arrange-
ment in which one of the viologen substituents is located in
the center of the host cavity, which adopts a C-type confor-
mation. This particular arrangement results in the shielding
of one of the pyridinium rings by the two sulfonated cate-
chol rings. A similar conformation has been observed in the
crystal structure of the 2:1 complex formed between methyl
viologen and the neutral DB24C8.[9] Co-conformer B corre-
sponds to an exo nonthreaded structure in which the violo-
gen guest is rotated by 908 with respect to its analogue in
co-conformer A; this is similar to the taco complex reported
by Gibson and co-workers, although with a different crown
ether.[15] Finally, co-conformer C represents the fully thread-
ed arrangement, similar to the topologically interpenetrated
structure recently reported by Liu and co-workers in which
a methyl viologen penetrates into the cavity of a tetrasulfo-
bis-m-phenylene[26]crown-8 along the vertical direction to
form a [2]pseudorotaxane.[16]
ꢀ
and the crown ether cavity, in agreement with C H···O hy-
drogen bonding. These results support co-conformation A
as the preferred geometry of [1a·DSDB24C8] in solution.
A 1.0 mm aqueous solution of [1a·DSDB24C8] was stud-
ied by electrospray mass spectrometry. The mass spectrum
shows m/z peaks corresponding to a sodium adduct of the
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Isomerism in a Supramolecular System
FULL PAPER
rings and only one of the elec-
tron-deficient pyridinium rings
of the methyl viologen through
face-to-face p-stacking interac-
tions (av 3.7 ꢅ). The expected
torsion of the second pyridini-
um ring is observed (37.78).
The analyzed crystal belongs
¯
to the triclinic space group P1
with one crown ether, one
methyl viologen, and seven
water molecules per asymmet-
ric unit.[17] The presence of
seven water molecules was con-
firmed by the 13.6% weight
loss observed by thermogravi-
metric analysis (see the Sup-
porting Information).
Figure 1. 1H NMR spectra (300 MHz, [D4]methanol, 298 K) of [1a][Br]2 (top), [NMe4]
and [1a·DSDB24C8] (middle) at 2 mm.
2ACHTUNGRTEN[NUNG DSDB24C8] (bottom),
In fact, although the methyl
viologen guest forms
a 1:2
dicationic complex with the
AHCTUNGTRENNUNG
crown ether [H2DSDB24C8+Na]+ (exptl: m/z 631.1113;
calcd: m/z 631.1126) and the 1:1 complex [1a·DSDB24C8+
H]+ (exptl: m/z 793.2295; calcd: m/z 793.2306), which
proves that binding interactions exist between the host and
guest in the gas phase (see the Supporting Information).
Both the NMR and MS analyses support the formation of a
1:1 neutral supramolecular complex. This was also con-
firmed by single-crystal X-ray diffraction analysis.
Suitable crystals for X-ray diffraction analysis were ob-
tained by slow evaporation of a saturated aqueous solution
of [1a·DSDB24C8]. The solid-state structure confirms the
1:1 stoichiometry of the supramolecular complex in which
the only ions present are those of the host and guest, there-
by proving the electroneutral nature of the association com-
plex (Figure 2). The host–guest complex adopts a partially
threaded arrangement (co-conformer A) in which the
methyl group of the viologen guest occupies the center of
the crown ether cavity and weakly interacts with the most
basic oxygen atoms (C···O distances varies from 3.37 to
neutral crown ether dibenzo[24]crown-8 in the solid state,[9]
in the electroneutral complex [1a·DSDB24C8], only one di-
cationic guest and one dianionic host are needed to form a
stable association complex with a 1:1 stoichiometry.
So far we have established the existence of a neutral ion-
paired association complex for [1a·DSDB24C8] in the solid
state and in solution that adopts the partially threaded co-
conformation A. To determine its relative stability in solu-
1
tion, we undertook H NMR titration experiments (see the
Supporting Information). Unexpectedly, the results were not
conclusive, mainly because different association constants
were obtained depending on which proton was used for
evaluation purposes; something similar occurred when con-
1
tinuous variation experiments, also based on H NMR data,
were performed. It is widely known that the existence of
simulACTHNURGTENNtUG aACHUTNGTERNNUGneous equilibria can affect these kinds of measure-
ments.[18] Thus, we hypothesized that the NMR signal-de-
pendency of the association constants could be due to the
presence of minor amounts of other co-conformational iso-
mers of [1a·DSDB24C8] co-existing in solution with co-con-
former A, thereby affecting the observed chemical shifts
and hindering the direct determination of the association
ꢀ
3.44 ꢅ; C H···O angles varies from 132 to1658). The crown
ether adopts a C-type conformation, which favors the inter-
action between the two electron-rich sulfonated catechol
1
constant by H NMR spectroscopy.
To confirm the hypothesis that other co-conformational
isomers exist in solution, especially co-conformer B, we de-
cided to investigate another viologen derivative bearing
bulkier groups at both ends of the molecule, namely guest
1b2+ with tert-butylbenzyl substituents (Scheme 2). With the
same host, the steric hindrance at the ends of the viologen
unit would prevent the formation of the threaded (co-con-
former C) and partially threaded (co-conformer A) geome-
tries, and therefore only co-conformer B would exist.
The electroneutral complex [1b·DSDB24C8] was synthe-
sized in a similar way to [1a·DSDB24C8] and again charac-
terized by H NMR spectroscopy, UV/Vis spectrophotome-
Figure 2. Ball-and-stick and space-filling representations of the X-ray
structure of complex [1a·DSDB24C8] in the solid state. The complex
adopts a partially threaded geometry (co-conformer A). C=light gray;
S=mid gray; N=gray; O=black.
1
try, and HRMS (ESI-TOF) (see the Supporting Informa-
Chem. Eur. J. 2013, 19, 4051 – 4057
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4053

J. Tiburcio et al.
tion). The yellow color of the complex in methanol solution
(lmax =415 nm) and the changes in the chemical shifts in the
1H NMR spectrum in [D4]methanol indicate the formation
of a charge-transfer complex with fast exchange dynamics
on the NMR timescale. The aromatic signals (Ha: Dd=
ꢀ0.2 ppm; Hb: Dd=ꢀ0.4 ppm) as well as the benzyl signal
(-CH2-: Dd=ꢀ0.1 ppm) are shifted towards lower frequen-
cies, which suggests that aromatic stacking is the predomi-
nant interaction between the host and guest and is consis-
tent with the proposed spatial arrangement of co-conformer
B. Further proof of the different geometrical arrangements
of complexes [1a·DSDB24C8] and [1b·DSDB24C8] in solu-
Figure 4. Ball-and-stick and space-filling representations of the X-ray
structure of complex [1b·syn-DSDB24C8]. The complex adopts a non-
threaded geometry (co-conformer B). C=light gray; S=mid gray; N=
gray; O=black.
1
tion was obtained from H NMR titration experiments: The
shielding effect caused by aromatic stacking of the sulfonat-
ed catechol rings in the host and the pyridinium rings in
both guests is quite different. This is especially clear for
proton Hb (Figure 3). Although the initial chemical shifts of
this proton in both guests are practically the same, there is a
pronounced shift of Dd=1.7 ppm in the case of
[1a·DSDB24C8] and only Dd=0.5 ppm for [1b·DSDB24C8]
after the addition of 6 equivalents of the host.
tion by using NMR data, we turned to electronic absorption
spectroscopy. By using this technique we would be able to
obtain reliable data regardless of the co-conformers present
in solution.
As expected, the UV/Vis spectra of electroneutral com-
plexes [1a·DSDB24C8] and [1b·DSDB24C8] in methanol
show intermolecular charge-transfer bands at 380 and
415 nm, respectively, associated with the electronic interac-
tion between electron-rich catechol units in the crown ether
and electron-poor pyridinium rings in the viologen guests
1a2+ and 1b2+. To corroborate the stoichiometries of the
complexes in solution, continuous variation experiments
were performed. In both cases, a maximum molar ratio was
observed at 0.5 (Figure 5), which confirms the 1:1 stoichi
tries determined by single-crystal X-ray diffraction and
mass spectrometry.
ACHTUNGTRENNUNGom-
ACTHUNGTRENNUGeAHCTUNGTRENNNUG
So far we have demonstrated that the neutral supramolec-
ular complexes [1a·DSDB24C8] and [1b·DSDB24C8] both
exist in a 1:1 stoichiometry with the association/dissociation
equilibrium shown in Equation (1). Their dissociation guar-
antees an equimolar solution of host and guest.
½1 ꢁ DSDB24C8ꢂ Ð 12þ þ DSDB24C82ꢀ
Â
ÃÂ
Ã
12þ DSDB24C82ꢀ
ð1Þ
Kd ¼
Figure 3. 1H NMR (300 MHz, [D4]methanol, 298 K) chemical shifts for
Hb in titration experiments of guest solutions of [1a][Br]2 and [1b][Br]2
(both 2 mm) with host [NMe4]2DSDB24C8.
½1 ꢁ DSDB24C8ꢂ
Dissociation constants using equimolar solutions of host
and guest were determined by using Equation (2), which is
based on the Beer–Lambert and mass action laws, and was
adapted from a method previously reported by Ray.[20] For a
complete demonstration, see the Supporting Information.
The NMR, UV/Vis, and MS data point towards the exis-
tence of [1b·DSDB24C8] as a 1:1 complex in solution with
co-conformer B as the only possible geometry. After several
attempts, we finally managed to grow single crystals from an
aqueous solution of [1b][Br]2 and syn/anti-[NMe4]2-
ꢀ
ꢁ
1=2
co
Aobs
Kd
el
1
1
el
¼
1=2 þ
ð2Þ
ACHTUNGTRENNUNG
[DSDB24C8].[19] Although the isolated crystals were of low
Aobs
quality, they allowed us to establish that the complex has an
exo nonthreaded structure in the solid state, that is, it exists
as co-conformer B (Figure 4).
In Equation (2), Co represents the nominal concentration
the electroneutral salt [1a·DSDB24C8] or
of
[1b·DSDB24C8], Aobs is the absorbance at lmax, Kd is the
global dissociation constant for the 1:1 complex in solution,
e is the extinction coefficient of the charge-transfer band,
and l is the optical path length, which is 1 cm. The slope of a
Stability of the neutral complexes in solution: Due to the
lack of reliability of the relative stability of complexes
[1a·DSDB24C8] and [1b·DSDB24C8] determined in solu-
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Isomerism in a Supramolecular System
FULL PAPER
Figure 5. Job plots for complexes [1a·DSDB24C8] (lmax =380 nm) and [1b·DSDB24C8] (lmax =415 nm) in methanol.
1/2
plot of Co/Aobs against 1/
(Aobs
)
yields (Kd/el)1/2 and the in-
Table 1. Comparison of the extinction coefficients, association constants,
and free energies of association for the complexes formed between host
tercept is equivalent to 1/el.
We designed and performed dilution experiments for
[1a·DSDB24C8] and [1b·DSDB24C8] in methanol in the
[a]
DSDB24C82ꢀ and guests 1a2+ and 1b2+
.
[b]
[c]
e [102 mꢀ1 cmꢀ1
]
Ka [103 mꢀ1
]
DG8 [kJmolꢀ1
]
concentration ranges 2–0.2 and 3–0.3 mm, respectively.
[1a·DSDB24C8]
[1b·DSDB24C8]
6.2ꢃ0.1
2.5ꢃ0.1
9.8ꢃ1.6
8.1ꢃ1.9
ꢀ22.8ꢃ0.2
ꢀ22.3ꢃ0.2
1/2
Linear plots of Co/Aobs against 1/
(Aobs
)
are shown in
Figure 6 with correlation coefficients of 0.9960 and 0.9975,
[a] All values were determined by UV/Vis absorption spectrophotometry
at 298 K in methanol. The errors were obtained as reported by Nygaard
et al. (see ref. [21]). [b] lmax =380 and 415 nm for [1a·DSDB24C8] and
[1b·DSDB24C8], respectively. [c] DG8=ꢀnRTlnK (T=298 K).
acetonitrile.[8,9,22] This is probably due to a number of non-
AHCTUNGTREGcNNUN ovalent interactions being enhanced by electrostatic coop-
erative effects.[13] Note that the results are a consequence of
only the intrinsic stability of the complexes as there are no
additional contributions from counter ions.
Although complex [1b·DSDB24C8] can only form a non-
threaded structure, that is, co-conformer B, its DG8 value in-
dicates that it is fairly stable in solution. Unfortunately, the
association
constants
for
[1a·DSDB24C8]
and
[1b·DSDB24C8] cannot be directly compared due to the dif-
ferent nature of the guests. However, it seems reasonable to
consider that complex [1a·DSDB24C8] exists in solution
predominantly as co-conformer A with a smaller quantity of
co-conformer B. So far, no direct experimental evidence for
the presence of co-conformer C has been obtained.
1/2
Figure 6. Linear plots of Co/Aobs against 1/
(Aobs
)
for different concentra-
tions of complexes [1a·DSDB24C8] and [1b·DSDB24C8].
respectively. The dissociation constants and e values were
obtained from these plots; the association constant, Ka, is
simply the inverse of the dissociation constant, Kd. The asso-
ciation constants and extinction coefficients determined for
complexes [1a·DSDB24C8] and [1b·DSDB24C8], and their
corresponding DG8 values, are summarized in Table 1.
The association constants determined for these complexes
are several orders of magnitude higher than those reported
for related systems with neutral crown ethers in acetone or
Conclusions
We have demonstrated that it is possible to eliminate count-
AHCTUNGTREGeNNUN r-ion effects in solution and in the solid state by isolating
two neutral ion-paired supramolecular systems formed from
two equally and opposite doubly-charged species, the violo-
gen guests 1a2+ and 1b2+ and the anti-disulfodibenzo[24]-
AHCTUNGTRENNUNG
crown-8 [DSDB24C8]2ꢀ host. The components of the two
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4055

J. Tiburcio et al.
SHELXS-97-2. Least-squares refinement based on F2 was carried out by
the full-matrix method of SHELXL-97-2.[23] All non-hydrogen atoms
were refined with anisotropic thermal parameters. Hydrogen atoms were
placed in calculated positions and refined with an isotropic fixed thermal
parameter by using a riding model. Neutral atom scattering factors and
anomalous dispersion corrections were taken from International Tables
for Crystallography.[24] Molecular structure drawings were generated by
using DIAMOND for Windows.[25]
complexes are held together by hydrogen bonding and p
stacking as well as strong electrostatic interactions.
These counter-ion-free complexes stay almost completely
associated in methanol solutions (Ka ꢄ1ꢆ104 mꢀ1), which al-
lowed us to investigate their co-conformational equilibria.
With small groups as substituents in the viologen, such as
methyl, we proved the co-existence of two co-conformations,
namely partially threaded and exo nonthreaded arrange-
ments. With bulky substituents in the viologen, such as tert-
butylbenzyl groups, the number of co-conformations is re-
stricted to just one, the exo nonthreaded arrangement.
These results should allow a more specific design of supra-
molecular ensembles leading to better structural control.
The results presented herein suggest that neutral ion-
paired supramolecular complexes allow the intrinsic stability
and structural features to be determined in the absence of
interfering counter ions. Further work in this direction is in
progress.
X-ray crystallographic data for [1a·DSDB24C8]: Chemical formula:
C36H48N2O21S2, Mw =908.88, T=293(2) K, MoKa radiation (0.71073 ꢅ),
¯
triclinic, P1, a=12.006(2), b=14.099(3), c=14.310(3) ꢅ, a=77.73(3), b=
85.60(3), g=70.72(3)8, V=2234.2(8) ꢅ3, Z=2, 1calcd =1.351 g cmꢀ3, m=
0.200 mmꢀ1 (000)=956, yellow, 0.34ꢆ0.25ꢆ0.09 mm3, Enraf–Nonius
, FACHTUNTGNRUEGN
Kappa diffractometer, 27353 independent reflections, 7584 with I>2s,
min. and max. transmission: 0.9352 and 0.9823, 5 restraints, 568 parame-
ters, R1=0.0959, wR2=0.2562 [I>2s], R1=0.1241, wR2=0.2845 [all
data], GOF=1.042, largest diff. peak and hole: 0.89 and ꢀ0.76 eꢅꢀ3
.
X-ray crystallographic data for [1b·DSDB24C8]: Chemical formula:
C56H68N2O17S2, Mw =1105.24, T=293(2) K, MoKa radiation (0.71073 ꢅ),
¯
triclinic, P1, a=12.7187(6), b=13.1703(7), c=21.8508(14) ꢅ, a=
77.247(2), b=89.403(2), g=66.612(4)8, V=3264.4(3) ꢅ3, Z=2, 1calcd
1.124 g cmꢀ3, m=0.143 mmꢀ1, F(000)=1172, yellow, 0.43ꢆ0.25ꢆ0.20 mm3
=
AHCTUNGTRENNUNG
crystal, Bruker Enraf–Nonius Kappa diffractometer, 10736 independent
reflections, 8562 with I>2s, min. and max. transmission: 0.9409 and
0.9719, 0 restraints, 695 parameters, R1=0.2115, wR2=0.4974 [I>2s],
R1=0.2808, wR2=0.5280 [all data], GOF=1.865, largest diff. peak and
Experimental Section
hole: 1.08 and ꢀ0.54 eꢅꢀ3
.
General methods: Dicationic guests [1a][Br]2 and [1b][Br]2 were synthe-
sized by direct alkylation of 4,4’-bipyridine with the corresponding alkyl
or benzyl derivative. Dianionic host [NMe4]2ACTHNUTRGNEUG[N DSDB24C8] was prepared
CCDC-903399 [1a·DSDB24C8] and CCDC-903400 [1b·DSDB24C8] con-
tain the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
and isolated as its anti isomer according to a published method.[13] All re-
actions were carried out in air and solvents were used without any prior
purification. 1H NMR spectra were recorded on a Bruker DP300 spec-
trometer at 300.1 MHz, locked to the deuterated solvent. High-resolution
mass spectra were obtained on an Agilent G1969A electrospray-ioniza-
tion time-of-flight mass spectrometer. UV/Vis spectra were recorded on
an Agilent 8453A spectrophotometer. Thermogravimetric analysis was
performed with a TA Instruments Q500 Thermogravimetric Analyzer.
Acknowledgements
This work was financially supported by CONACYT (Project No.
128419). We thank Marco Leyva for his assistance in obtaining X-ray
data, Geiser Cuellar for HRMS measurements and Myriam Campos for
thermogravimetric analyses.
Synthesis of [1a·DSDB24C8]: Guest compound [1a][Br]2 (0.053 g,
0.15 mmol) was dissolved in water (15 mL) to afford a colorless solution.
Host compound [NMe4]2ACTHNUTRGNEUGN[DSDB24C8] (0.117 g, 0.15 mmol) was added to
the solution, which immediately turned yellow. This solution was heated
at 808C for 1 h with stirring. Yellow crystals were removed by filtration
after 4 days of slow evaporation of the solvent and washed with cold
water (3ꢆ2 mL) to yield [1a·DSDB24C8] as yellow crystals (0.102 g,
0.13 mmol, 87%). 1H NMR (300 MHz, [D4]methanol, 258C, TMS): d=
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8.93 (d, 2J
(s, 2H; Hf), 6.88 (d, 2J
2H; Hh), 4.58 (s, 6H; CH3), 4.01–3.89 ppm (m, 24H; CH2); HRMS (ESI-
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
+
TOF+): m/z calcd for C36H45N2O14S2
:
793.2306 [M+H]+; found:
793.2295.
Synthesis of [1b·DSDB24C8]: Guest compound [1b][Br]2 (0.10 g,
0.16 mmol) was dissolved in hot water (50 mL) to afford a colorless solu-
tion. Host compound [NMe4]2ACTHNUTRGNE[NUG DSDB24C8] (0.12 g, 0.16 mmol) was
added to the solution, which immediately turned orange. This solution
was heated at 808C for 1 h with stirring. Orange crystals were removed
by filtration after 4 days of slow evaporation of the solvent and washed
with cold water (3ꢆ2 mL) to yield [1b·DSDB24C8] as orange crystals
(0.155 g, 0.15 mmol, 94%). 1H NMR (300 MHz, [D4]methanol, 258C,
2
2
TMS): d=9.14 (d, J
Hb), 7.64 (s, 8H; Ar-H), 7.00 (d, 2J
Hf), 6.13 (d, 2J(H,H)=6 Hz, 2H; Hh), 5.85 (s, 4H; N+-CH2), 3.91–3.42
G
ACHTUNGTREN(NUNG H,H)=6 Hz, 4H;
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
(m, 24H; CH2), 1.34 ppm (s, 18H; tBu); HRMS (ESI-TOF-): m/z calcd
for C56H67N2O14S2ꢀ: 1055.4039 [M-H]ꢀ; found: 1055.4028.
Single-crystal X-ray diffraction: Single crystals were grown by slow evap-
oration of saturated aqueous solutions of the complexes. X-ray diffrac-
tion data were collected at 298 K on an Enraf–Nonius Kappa diffractom-
eter fitted with a CCD-based detector by using MoKa radiation (l=
0.71073 ꢅ). The structures were solved by direct methods using
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4056
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Chem. Eur. J. 2013, 19, 4051 – 4057

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Received: September 29, 2012
Published online: January 22, 2013
Chem. Eur. J. 2013, 19, 4051 – 4057
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4057