Selective fluorescent sensing of chloride

Article abstract of DOI:10.1016/j.tetlet.2007.03.061

The urea functionalised phenanthroline sensor 1, which was characterised by several methods, including X-ray crystallography, gives rise to large changes in the fluorescence emission spectra upon interaction with several anions such as acetate, phosphate,

Full text of DOI:10.1016/j.tetlet.2007.03.061

Tetrahedron Letters 48 (2007) 3135–3139
Selective fluorescent sensing of chloride
*
´
Cidalia M. G. dos Santos, Thomas McCabe and Thorfinnur Gunnlaugsson
School of Chemistry, Centre for Synthesis and Chemical Biology, Trinity College Dublin, Dublin 2, Ireland
Received 20 February 2007; revised 27 February 2007; accepted 8 March 2007
Available online 13 March 2007
Abstract—The urea functionalised phenanthroline sensor 1, which was characterised by several methods, including X-ray crystal-
lography, gives rise to large changes in the fluorescence emission spectra upon interaction with several anions such as acetate, phos-
phate, fluoride and chloride in CH3CN. However, only in the presence of Clꢀ was the emission enhanced, as for the other ions
photoinduced electron transfer (PET) quenching was observed. Fitting these fluorescence changes, using non-linear regression anal-
ysis, showed that these anions bind to 1 in 1:1 (anion:sensor) stoichiometry, with the exception of Clꢀ, which was shown to give rise
to 1:1 as well as 1:2 binding, as a result of coordination of the chloride to two equivalents of 1.
Ó 2007 Elsevier Ltd. All rights reserved.
The recognition and sensing of anions has become a
very topical area of research in the field of supramole-
cular chemistry.1–3 Anions play a major function in
the environment, industry and importantly, in biology
where phosphate, carbonate and chloride are the most
commonly found. In particular, Clꢀ which has relatively
high extracellular concentrations, is essential to human
health and is transported across cell membranes by var-
ious Clꢀ proteins, often in conjunction with cation
transportation.4 Due to its spherical structure and rela-
tive large ionic radius, Clꢀ recognition is not trivial, and
often requires the use of structurally complex hosts, such
as those developed by Davis5 and Smith.6 Nature often
transports Clꢀ in the form of ion pairs and non-peptide
based natural transporters are known such as the prodi-
giosins, which can transport HCl.7 A few examples of
such transport mimics have recently been published by
Sessler et al. and by Gale and co-workers respectively.8,9
These examples demonstrate the feasibility of the use of
small and hence, structurally simple molecules for such
recognition. We are interested in the recognition and
sensing of anions3,10 using either lanthanide based coor-
dination complexes,11 or charge neutral receptors such
as ureas,12 thioureas13 and amidoureas.14 For these lat-
ter examples, the detection of ions such as AcOꢀ,
H2PO4ꢀ, pyrophosphate and Fꢀ has been demonstrated
selectively over many other anions such as Clꢀ, Brꢀ and
Iꢀ. However, in recent work, where we focused our
efforts on the development of heteroditopic receptors,
we synthesised the 1,10-phenanthroline (phen) based
urea ligand 1 (of which the X-ray crystal structure is
shown in Fig. 1),15 and investigated the effect that anion
coordination had on the photophysical properties of the
phen structure. Interestingly, we discovered that while 1
could strongly bind to a series of anions in CH3CN solu-
tion, the sensing of Clꢀ by 1 was particularly interesting
being both strong and achieved by the formation of a
2:1 self-assembly complex between 1 and Clꢀ. This is,
to the best of our knowledge, the first example of a sim-
ple charge neutral fluorescent sensor whichꢀ demon-
strates both strong and good selectivity for Cl .16
The synthesis of 1 was achieved in a few high yielding
steps as shown in Scheme 1. The first step involved
reduction of commercially available 5-nitro-1,10-phe-
nanthroline, 2, in refluxing ethanol solution, under
argon, using hydrazine monohydrate (N2H4) and 10%
Pd/C catalyst. A yellow solid was obtained after filtra-
tion and removal of the solvent under reduced pressure.
This solid was washed twice with diethyl ether to pro-
duce 3 as a pale yellow solid in 92% yield. This was then
*
Corresponding author. Tel.: +353 1 896 3459; fax: +353 1 671
2826; e-mail: gunnlaut@tcd.ie
Figure 1. The X-ray crystal structure of 1.
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.03.061

3136
C. M. G. dos Santos et al. / Tetrahedron Letters 48 (2007) 3135–3139
0.2
NH2
NO2
N
N2H4
Pd/C
EtOH
0.18
0.16
0.14
N
N
N
0.12
0.1
2
3 (92%)
NCO
0.08
0.06
0.04
0.02
0
CF3
N
N
O
CHCl3
N
N
H
H
CF3
235
255
275
295
315
335
355
375
1 (88%)
4
Wavelength [nm]
Scheme 1. The synthesis of 1.
Figure 2. The changes in the absorption spectra of 1 (4.8 lM) upon
gradual addition of Clꢀ (0–17.50 mM) in MeCN.
reacted with trifluoro-p-tolyl isocyanate, 4, in CHCl3 at
room temperature, under an inert atmosphere to yield
an off white precipitate, which was filtered and washed
with cold CHCl3. This gave an off-white solid which
was recrystallised from hot MeOH to yield the desired
tors. As seen in Figure 2, an increase was observed in
both the 266 nm and 320 nm transitions upon increasing
the concentration of Clꢀ, but no other spectral shifts, or
the formation of isosbestic points, were observed. For
both AcOꢀ and H2PO similar changes were observed,
ꢀ
4
1
receptor 1 as a crystalline solid in 88% yield.17 The H
where the absorption was enhanced by ca. 20–30%.
NMR spectrum (400 MHz, DMSO-d6) showed the pres-
ence of the two urea N–H singlets at 9.55 and 9.12 ppm,
respectively, as well as the expected set of doublets
for the phenyl aromatic protons. The 13C NMR
(100 MHz, DMSO-d6) of 1 showed all the expected 18
signals, with the urea carbonyl quaternary resonance
appearing at 152.87 ppm.
However, more structural changes were observed in
the absorption spectra in the case of Fꢀ, where the
266 nm band was shifted to 270 nm, while the 320 nm
band was shifted to 325 nm, with the formation of con-
comitant isosbestic points. These changes demonstrate
the ability of Fꢀ to (i) bind to the urea moiety, and
(ii) potentially deprotonate the urea moiety.19 In con-
trast to these results, minor changes were observed for
Brꢀ at very high anion concentrations.
The X-ray crystal structure of 1 is presented in Figure 1,
and shows that the urea moiety is coplanar with the tri-
fluoro-p-tolyl group (torsion angle of ꢀ0.26°), while
being significantly shifted out of the plane of the phen
moiety (torsion angle of ꢀ35°).15 The two urea Nꢁ ꢁ ꢁH
The fluorescence emission spectra were also monitored
upon addition of anions following excitation at both
the 265 nm and 320 nm transitions. Upon addition of
˚
AcOꢀ, H2PO and Fꢀ, the fluorescence emission was
ꢀ
bond lengths were found to be identical at 0.860 A. As
4
is clear from the crystal structure, the two urea protons
are ideally situated for directional hydrogen bonding
interactions with anions that can participate in linear
considerably quenched (98%, 94%, and 93%, respec-
tively), or ‘switched off’, as shown in Figure 3 for the
changes observed with AcOꢀ. This clearly demonstrates
the ability of 1 to function as a luminescent ‘on–off’
switch for these anions. It is worth pointing out that
no other spectral changes occurred in the fluorescence
interactions such as AcOꢀ, H2PO and Fꢀ. We were
ꢀ
4
unable to produce suitable crystals of 1 in the presence
of anions for X-ray crystal structure analysis.
The ability of 1 to sense various anions was evaluated in
CH3CN using the anions as their tetrabutylammonium
salts (TBA+). The absorption spectrum of 1, in the ab-
sence of anions, exhibited a band centred at 266 nm
(loge = 4.50), assigned to the p–p* transition of the phen
moiety and a broad shoulder centred at around 320 nm
(loge = 3.85), which was assigned to the n–p* transi-
tions. When exciting the sample at both of these wave-
lengths, a broad emission band was observed with
kmax at 422 nm. Thus both absorptions were assigned
to the phen chromophore. Significant changes were ob-
served in the absorption spectra upon titration of 1 with
120
100
80
60
40
120
100
80
20
0
60
0.0
10.0
20.0
30.0
eq. AcO-
40
20
0
anions such as AcOꢀ and H2PO and interestingly,
ꢀ
365 385 405 425 445
465 485
505 525 545 565
4
also for Clꢀ.18 These responses, clearly signify changes
Wavelength [nm]
in the ground state of the sensor upon hydrogen bond-
ing to these anions as demonstrated for Clꢀ in Figure
2. The sensing of Clꢀ is unusual as it is typically not ob-
served for such simple urea or amidourea based recep-
Figure 3. The changes in emission intensity of 1 (4.8 lM) upon gradual
addition of AcOꢀ ([AcOꢀ] = 0–1.53 mM), in MeCN upon excitation at
265 nm. Inset: The changes in the emission intensity at 422 nm as a
function of AcOꢀ equivalents.

C. M. G. dos Santos et al. / Tetrahedron Letters 48 (2007) 3135–3139
3137
emission spectra, that is, no shifts in kmax or the forma-
tion of long wavelength emitting species were observed.
Hence, we propose that upon anion recognition, the
urea moiety is twisted out of the plane of the phen fluo-
rophore which gives rise to the slight enhancement in the
p!p nature of the fluorophore (as seen in the absorp-
tion spectra). At the same time, electron transfer
quenching of the phen excited state, from the electron
rich anion receptor, is activated, causing the emission
to ‘switch off’. Hence, this can be considered as being
an anion modulated photoinduced electron transfer
(PET) quenching, even though no formal covalent
spacer separates the fluorophore from the urea recep-
tor.12,20 From these changes, binding constants of
logb11 = 5.19 ( 0.03) and logb11 = 4.35 ( 0.06) were
observed for AcOꢀÆ1 and H2PO4ꢀÆ1, respectively, using
the nonlinear least-squares fitting programme SPEC-
FIT. These values indicate strong binding of 1 for these
anions in CH3CN. Tꢀhe fact that AcOꢀ is bound more
strongly than H2PO4 reflects the ability of this anion
to bind to the receptor in a more linear ‘Y’ shape hydro-
gen bonding manner. Hence, on all occasions the best fit
for the above changes was observed for the 1:1 binding
stoichiometry. The changes in the emission intensity of 1
upon titration with Fꢀ were, however, best fitted to 2:1
binding (anion:sensor) interactions. This is in agreement
with the findings from the absorption data, where a two-
step equilibrium was observed. These can be viewed as
involving the initial interaction of the anion with 1
through hydrogen bonding to give the FꢀÆ1 complex,
followed by binding and subsequent deprotonation by
the second Fꢀ to give bifluoride HF2ꢀ, in a manner pre-
viously postulated by ourselves and Gale et al.19,21 From
these changes logb11 = 4.75 ( 0.26) and logb21 = 4.73
( 0.21) values were determined for FꢀÆ1 and Fꢀ2Æ1
(the formation of HF2ꢀ), respectively. As in the ground
state investigation above, titrations using Brꢀ did not
give rise to any significant luminescent quenching except
at high concentrations, which could be due to a heavy
atom effect rather than binding of this anion to the
receptor.
the quenching of the singlet excited state was not ob-
served as in the above cases, but a fluorescence enhance-
ment. Here, the phen emission was enhanced by ca. 45%,
with a concomitant shift towards longer wavelengths
(kmax 422 nm ! 428 nm), with the formation of an iso-
emissive point at 399 nm. This is the first time that we
have observed such luminescent behaviour for such
structurally simple receptors. Furthermore, it is clear
that these changes are of a different nature to those ob-
served for the AcOꢀ or H2PO titrations above, and
ꢀ
4
thus cannot be assigned to an enhancement in PET
quenching. We therefore propose that upon recognition
of Clꢀ, the aforementioned anion induced twisting of
the urea moiety (from the phen ligand) is minor and
the spherical anion reduces the effect of the PET quench-
ing from the trifluoro-p-tolyl group to the phen fluoro-
phore, by ‘blocking’ the pathway of the electron
transfer. Such ‘intervening media’ has been proposed
to influence energy transfer quenching in several elec-
tron-donor-acceptor systems, such as in those developed
by Shimidzu et al.22 where a cation was employed, and
in supramolecular systems designed to mimic the nature
of the electron transfer in the photosynthetic reaction
centre.23
Plotting the changes at 422 nm as a function of
ꢀlog[Clꢀ] gave rise to changes occurring over ca. 4 log-
arithmic units, indicating more than a simple 1:1 binding
process. By fitting the changes observed in Figure 4 for
1:1 type complex formation, ClꢀÆ1, a binding constant of
logb11 = 3.84 ( 0.14) was determined. While this shows
that 1 has high affinity for Clꢀ, we and others, have
demonstrated that usually such simple urea based recep-
tors do not bind to large spherical anions3 but rather
through multiple binding interactions.4,24 Consequently,
we considered an alternative binding mode for 1, where
two sensors self-assemble around the anion to give
a ClꢀÆ12 complex. Fitting the above changes to such
stoichiometry, gave a strong binding constant of
logb12 = 5.94 ( 0.16). Analysis of the speciation distri-
bution diagram, shown in Figure 5, clearly shows that
the initial addition of Clꢀ gives rise to the formation
of a self-assembly (blue line) of two molecules of 1
and Clꢀ, and that up to 27% of the species in solution
However, the most interesting results were observed for
the fluorescence titration of 1 with Clꢀ, Figure 4. Here
100
90
80
70
60
50
40
30
20
10
160
140
120
100
80
60
40
20
0
0
0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007 0.0008
[Cl-] (M)
365 385 405 425 445
465 485
505 525 545 565
Wavelength [nm]
Figure 5. The speciation distribution plot for the binding of 1 (4.8 lM)
Figure 4. Changes in the emission spectra of 1 (4.8 lM) upon titration
to Clꢀ:
= 1;
= ClꢀÆ1;
= ClꢀÆ12. Only part of the
___
___
___
with Clꢀ (0–17.50 mM) in MeCN, upon excitation at 265 nm.
concentration range is shown.

3138
C. M. G. dos Santos et al. / Tetrahedron Letters 48 (2007) 3135–3139
from [Clꢀ] = 0 ! 0.8 mM is in the form of the ClꢀÆ12
complex. However, the formation of the 1:1 complex be-
gins to dominate after 0.2 mM (green line), eventually
being the most stable species in solution.25,26 With the
aim of demonstrating the selectivity of 1 for Clꢀ, the
luminescence of 1 was recorded in the presence of one
equivalent of AcOꢀ, which quenched the fluorescence.
However, upon addition of increased concentrations of
Clꢀ, the emission was restored, giving rise to a red
shifted emission, as observed in Figure 4. These results
demonstrate that Clꢀ can be sensed selectively by 1,
through (a) the formation of a self-assembly, and (b)
by the fact that only for Clꢀ was the fluorescence of 1
increased, while being queꢀnched by other competitive
7. Ohkuma, S.; Sato, T.; Okamoto, M.; Matsuya, H.; Arai,
K.; Kataoka, T.; Nagai, K.; Wasserman, H. H. Biochem-
istry 1998, 334, 731.
8. Sessler, J. L.; Elleer, L. R.; Cho, W. S.; Nicolaou, S.;
Aguilar, A.; Lee, J. T.; Lynch, V. M.; Magda, D. J. Angew.
Chem., Int. Ed. 2005, 44, 5989.
9. Gale, P. A.; Light, M. E.; McNally, B.; Navakhun, K.;
Sliwinski, K. E.; Smith, B. D. Chem. Commun. 2005, 3773.
10. Gunnlaugsson, T.; Ali, H. D. P.; Glynn, M.; Kruger, P. E.;
Hussey, G. M.; Pfeffer, F. M.; dos Santos, C. M. G.;
Tierney, J. J. Fluoresc. 2005, 15, 287.
11. Leonard, J. P.; dos Santos, C. M. G.; Plush, S. P.;
McCabe, T.; Gunnlaugsson, T. Chem. Commun. 2007,
129; Harte, A. J.; Jensen, P.; Plush, S. E.; Kruger, P. E.;
Gunnlaugsson, T. Inorg. Chem. 2006, 45, 9465; Gunn-
laugsson, T.; Leonard, J. P. Chem. Commun. 2005, 3114;
Gunnlaugsson, T.; Leonard, J. P. J. Fluoresc. 2005, 15,
585; Harte, A. J.; Leonard, J. P.; Nieuwenhuyzen, M.
Supramol. Chem. 2003, 15, 505; Gunnlaugsson, T.; Harte,
A. J.; Leonard, J. P.; Nieuwenhuyzen, M. Chem. Commun.
2002, 2134.
12. Pfeffer, F. M.; Buschgens, A. M.; Barnett, N. W.;
Gunnlaugsson, T.; Kruger, P. E. Tetrahedron Lett. 2005,
46, 6579; Gunnlaugsson, T.; Davis, A. P.; O’Brien, J. E.;
Glynn, M. Org. Biomol. Chem. 2005, 3, 48; Pfeffer, F. M.;
Gunnlaugsson, T.; Jensen, P.; Kruger, P. E. Org. Lett.
2005, 7, 5375; Gunnlaugsson, T.; Davis, A. P.; O’Brien, J.
E.; Glynn, M. Org. Lett. 2002, 4, 2449; Gunnlaugsson, T.;
Davis, A. P.; Hussey, G. M.; Tierney, J.; Glynn, M. Org.
Biomol. Chem. 2004, 2, 1856; Gunnlaugsson, T.; Davis, A.
P.; Glynn, M. Chem. Commun. 2001, 2556.
13. dos Santos, C. M. G.; Glynn, M.; McCabe, T.; Seixas de
Melo, J. S. Burrows, H. D.; Gunnlaugsson, T. Supramol.
Chem., 2007, 19, in press.
14. Quinlan, E.; Matthews, S. E.; Gunnlaugsson, T. Tetrahe-
dron Lett. 2006, 47, 9333; Gunnlaugsson, T.; Kruger, P.
E.; Jensen, P.; Tierney, J.; Ali, H. D. P.; Hussey, G. M. J.
Org. Chem. 2005, 70, 10875.
15. The data were collected on a Bruker Smart Apex
Diffractometer*. The crystal was mounted on a 0.35 mm
quartz fibre and immediately placed on the goniometer
head in a 150 K N2 gas stream. The data were acquired
using Smart Version 5.625 software in multi-run mode and
2400 frames in total, at 0.3° per frame, were collected.
Data integration and reduction was carried out using
Bruker Saint+ Version 6.45 software and corrected for
absorption and polarization effects using Sadabs Version
2.10 software. Space group determination, structure solu-
tion and refinement were obtained using Bruker Shelxtl
Ver. 6.14 software. *SMART Software Reference Manual,
version 5.625, Bruker Analytical X-ray Systems Inc.,
Madison, WI, 2001. Sheldrick, G. M. SHELXTL, An
Integrated System for Data Collection, Processing, Struc-
ture Solution and Refinement, Bruker Analytical X-ray
Systems Inc., Madison, WI, 2001. Crystal data:
ions such as AcOꢀ, H2PO and Fꢀ.
4
In summary, we have developed 1 as a selective fluores-
cence sensor for Clꢀ. While only minor changes were
observed in the absorption spectra of 1 upon anion rec-
ognition, the fluorescence emission spectra were dramat-
ically affected. Nevertheless, only for the sensing of
Clꢀ was the fluorescence of 1 enhanced. For other com-
petitive ions the emission was either quenched or not
modulated. We are currently evaluating the anion bind-
ing of 1 in the presence of both transition and lanthanide
ions.
Acknowledgements
We would like to thank TCD and IRCSET for financial
support, Dr. John E. O’Brien for assisting with NMR
and Dr. Sally E. Plush and Dr. Susan Quinn for their
help. We particularly would like to thank Dr. Joseph
P. Leonard for his assistance at the start of this
investigation.
References and notes
1. Sessler, J. L.; Gale, P. A.; Cho, W. S., Anion Receptor
Chemistry; Royal Society of Chemistry: Cambridge, UK,
2006; Steed, J. W. Chem. Commun. 2006, 2637; Gale, P. A.
´
´
˜
Acc. Chem. Res. 2006, 39, 465; Martınez-Manez, R.;
´
Sancenon, F. Chem. Rev. 2003, 103, 4419; Suksai, C.;
Tuntulani, T. Chem. Soc. Rev. 2003, 32, 192.
2. Wu, F. Y.; Li, Z.; Guo, L.; Wang, X.; Lin, M. H.; Zhao,
Y. F.; Jiang, Y. B. Org. Biomol. Chem. 2006, 4, 624;
Ghosh, K.; Adhikari, S. Tetrahedron Lett. 2006, 47, 8165;
Evans, L. S.; Gale, P. A.; Light, M. E.; Quesada, R. Chem.
Commun. 2006, 965; Pfeffer, F. M.; Seter, M.; Lewcenko,
N.; Barnett, N. W. Tetrahedron Lett. 2006, 47, 5251; Jun,
E. J.; Swamy, K. M. K.; Bang, H.; Kim, S. J.; Yoon, J. Y.
Tetrahedron Lett. 2006, 47, 3103; Liu, B.; Tian, H. Chem.
Lett. 2005, 34, 686; Wel, L. H.; He, Y. B.; Wu, J. L.; Wu,
X. J.; Meng, L.; Yang, X. Supramol. Chem. 2004, 16, 561.
C80H52F12N16O4, Monoclinic, space group P21/c, a =
˚
13.1965(14),
b = 91.320(2)°, U = 1725.4(3) A , T = 150 K,
b = 11.8685(12),
c = 11.0189(11)(17) A,
3
˚
l (Mo-
Ka) = 0.117 mmꢀ1, Z = 4, a total of 13251 reflections
were measured for 4 < 2ꢂ < 57 and 3031 unique reflec-
tions were used in the refinement, [R(int) = 0.0288], the
final parameters were wR2 = 0.1693 and R1 = 0.0648
[I > 2r(I)]. CCDC 637076.
´
3. Gunnlaugsson, T.; Glynn, M.; Tocci (nee Hussey), G. M.;
Kruger, P. E.; Pfeffer, F. M. Coord. Chem. Rev. 2006, 250,
3094.
4. Davis, A. P.; Sheppard, D. N.; Smith, B. D. Chem. Soc.
Rev. 2007, 36, 348.
5. Davis, A. P.; Joos, J. B. Coord. Chem. Rev. 2003, 240, 143;
Boon, J. M.; Smith, B. D. Curr. Opin. Chem. Biol. 2002, 6,
749.
6. McNally, B. A.; Koulov, A. V.; Smith, B. D.; Joos, J.-B.;
Davis, A. P. Chem. Commun. 2005, 1087.
16. We have previously demonstrated the sensing of such
halides using heavy atom affect quenching: Gunnlaugsson,
T.; Bichell, B.; Nolan, C. Tetrahedron 2004, 60, 5799;
Chloride has also been elegantly detected by NMR using
catechols: Smith, D. K. Org. Biomol. Chem. 2003, 1, 3874;
and recently by using accridone fluorescence sensing:

C. M. G. dos Santos et al. / Tetrahedron Letters 48 (2007) 3135–3139
3139
´
´
´
Blazquez, M. T.; Muniz, F. M.; Saez, S.; Simon, L. M.;
20. It is possible that the anion sensing also contributes to the
formation of a twisted internal charge transfer (TICT)
excited state in 1. de Silva, A. P.; Gunaratne, H. Q. N.;
Gunnlaugsson, T. Tetrahedron Lett. 1998, 39, 5077;
Letard, J.-F.; Lapouyade, R.; Retting, W. Pure Appl.
Chem. 1993, 65, 1705.
21. Evans, L. S.; Gale, P. A.; Light, M. E.; Quesada, R. New
J. Chem. 2006, 30, 1019; Camiolo, S.; Gale, P.; Hurst-
house, M. B.; Light, M. E. Org. Biomol. Chem. 2003, 1,
741.
22. Iyoda, T.; Morimoto, M.; Kawasaki, N.; Shimidzu, T. J.
Chem. Soc., Chem. Commun. 1991, 1480.
23. de Silva, A. P.; Rice, T. E. Chem. Commun. 1999, 163;
Harriman, A.; Heitz, V.; Sauvage, S.-P. J. Phys. Chem.
1993, 97, 5940.
˜
´
´
´
Alonso, A.; Raposo, C.; Lithgow, A.; Alcazar, V.; Moran,
J. R. Heterocycles 2006, 69, 73.
17. Sensor 1 was obtained as an off-white solid in 88% yield
(1.38 g). Mp decomposes above 290 °C; Calculated for
C20H14N4OF3 [M+H] m/z = 383.1120. Found m/z =
383.1107. 1H NMR(400 MHz, DMSO-d6) dH: 9.55 (br
s, 1H, NH), 9.16 (d, 1H, PhenCH, J = 4 Hz), 9.12 (br s,
1H, NH), 9.00 (d, 1H, PhenCH, J = 4.04 Hz), 8.65 (d,
1H, PhenCH, J = 8.52 Hz), 8.43 (d, 1H, PhenCH,
J = 8.04 Hz), 8.39 (s, 1H, PhenCH), 7.89 (dd, 1H,
PhenCH, J = 8.52 Hz), 7.72 (m, 5H, PhenCH + ArCH);
13C NMR (100 MHz, DMSO-d6) dC: 152.87, 149.87,
148.74, 145.89, 143.34, 143.13, 135.61, 132.08, 130.44,
128.50, 126.25, 126.22, 123.77, 123.68, 122.95, 122.21,
118.01, 116.07; 19F NMR (376 MHz, DMSO-d6): ꢀ60.58
(CF3).
18. Chloride has recently been used as a template for the
formation of anion pseudocyrptands and directed self-
assemblies: Nabeshima, T.; Masubuchi, S.; Taguchi, N.;
Akina, S.; Saiki, T.; Sato, S. Tetrahedron Lett. 2007, 48,
1595; Goetz, S.; Kruger, P. E. Dalton Trans. 2006, 1277;
Beer, P. D.; Sambrook, M. R.; Curiel, D. Chem. Commun.
2006, 2105; Keegan, J.; Kruger, P. E.; Nieuwenhuyzen,
M.; O’Brien, J.; Martin, N. Chem. Commun. 2001, 2192.
19. Gunnlaugsson, T.; Kruger, P. E.; Lee, T. C.; Parkesh, R.;
Pfeffer, F. M.; Hussey, G. M. Tetrahedron Lett. 2003, 44,
6575; Gunnlaugsson, T.; Kruger, P. E.; Jensen, P.; Pfeffer,
F. M.; Hussey, G. M. Tetrahedron Lett. 2003, 44, 8909.
24. Davis, A. P. Coord. Chem. Rev. 2006, 250, 2939; Schaz-
mann, B.; Alhashimy, N.; Diamond, D. J. Am. Chem. Soc.
2006, 128, 8606; Bai, Y.; Zhang, B.-G.; Xu, J.; Duan, C.-
Y.; Dang, D.-B.; Liu, D.-L.; Meng, Q.-J. New J. Chem.
2005, 29, 777.
25. Without X-ray crystallographic data for the ClꢀÆ12 com-
plex it is difficult to predict its structure. However, we
propose that the two sensors hydrogen bond to the anion
in a head-to-tail fashion, where the two phen moieties
would be facing away from each other. See also Ref. 26.
26. During the course of our work, a ditopic receptor was
found to bind Clꢀ upon addition of Cu(I) in a semi-helical
fashion: Amendola, V.; Boiocchi, M.; Colasson, B.;
Fabbrizzi, L. Inorg. Chem. 2006, 45, 6138.