Encapsulation of [X2(H2O)4]2- (X = F/Cl) clusters by pyridyl terminated tripodal amide receptor in aqueous medium: Single crystal X-ray structural evidence

Article abstract of DOI:10.1039/c3dt52694a

A new tris-amide receptor L based on 1,3,5-methyl substituted benzene platform and pyridyl as an attached unit is synthesized and explored towards anion recognition in aqueous environment. The presence of pyridyl terminal in L facilitates its aqueous solubility. The binding of halides and oxyanions towards L are examined by ¹H-NMR technique in solution and by single crystal X-ray crystallography in solid state studies. Crystallization of fluoride and chloride with L is carried out in acetone-water (1 : 1, v/v) binary solvent mixture that yields crystals for respective host-guest complexes, [L] ₂·[F₂(H₂O)₄]·[TBA] ₂ (1) and [L]₂·[Cl₂(H₂O) ₄]·[TBA]₂ (2) suitable for single crystal X-ray diffraction studies. On the other hand, complexation of L with fluoride in dioxane-acetone (1 : 1, v/v) solvent mixture, results the formation of SiF ₆^2- encapsulated complex, [L]₂·[SiF ₆(H₂O)₂]·[TBA]₂ (3). Crystallographic result shows the formation of [F₂(H ₂O)₄]^2- and [Cl₂(H ₂O)₄]^2- zipped 1D-polymeric tweezer-like assemblies of L in acetone-water (1 : 1, v/v) binary solvent mixture in complexes 1 and 2 respectively. Solution state ¹H-NMR studies in D₂O-acetone-d₆ (1 : 19, v/v) support 1 : 4 (host-guest) binding stoichiometry of F^-, Cl^-, Br^-, NO ₃^-, HSO₄^- and H₂PO ₄^- with L. Binding constants of these investigated anions with L by 1 : 1 binding model are calculated which show the following binding order: NO₃^- ≈ HSO₄^- > F ^- ≈ Cl^- ≈ Br^- > H₂PO ₄^-. Further, solution state ¹⁹F-NMR studies are also carried out to establish the F^- binding with L in DMSO-d ₆.

Full text of DOI:10.1039/c3dt52694a

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Encapsulation of [X2(H2O)4]2− (X = F/Cl) clusters by
pyridyl terminated tripodal amide receptor in
aqueous medium: single crystal X-ray structural
evidence†
Cite this: Dalton Trans., 2014, 43,
2061
Sourav Chakraborty, Ranjan Dutta, M. Arunachalam‡ and Pradyut Ghosh*
A new tris-amide receptor L based on 1,3,5-methyl substituted benzene platform and pyridyl as an
attached unit is synthesized and explored towards anion recognition in aqueous environment. The pres-
ence of pyridyl terminal in L facilitates its aqueous solubility. The binding of halides and oxyanions
towards L are examined by 1H-NMR technique in solution and by single crystal X-ray crystallography in
solid state studies. Crystallization of fluoride and chloride with L is carried out in acetone–water (1 : 1, v/v)
binary solvent mixture that yields crystals for respective host–guest complexes, [L]2·[F2(H2O)4]·[TBA]2 (1)
and [L]2·[Cl2(H2O)4]·[TBA]2 (2) suitable for single crystal X-ray diffraction studies. On the other hand, com-
2−
plexation of L with fluoride in dioxane–acetone (1 : 1, v/v) solvent mixture, results the formation of SiF6
encapsulated complex, [L]2·[SiF6(H2O)2]·[TBA]2 (3). Crystallographic result shows the formation of
[F2(H2O)4]2− and [Cl2(H2O)4]2− zipped 1D-polymeric tweezer-like assemblies of L in acetone–water (1 : 1,
v/v) binary solvent mixture in complexes 1 and 2 respectively. Solution state 1H-NMR studies in D2O–
acetone-d6 (1 : 19, v/v) support 1 : 4 (host–guest) binding stoichiometry of F−, Cl−, Br−, NO3−, HSO4 and
−
Received 27th September 2013,
Accepted 21st October 2013
H2PO4− with L. Binding constants of these investigated anions with L by 1 : 1 binding model are calculated
which show the following binding order: NO3 ≈ HSO4 > F− ≈ Cl− ≈ Br− > H2PO4−. Further, solution
−
−
DOI: 10.1039/c3dt52694a
www.rsc.org/dalton
state 19F-NMR studies are also carried out to establish the F− binding with L in DMSO-d6.
becomes much more less feasible compared to that of other
anions.3 The presence of fluoride in drinking water exerts a
Introduction
Anions are present in their hydrated form in nature. Thus rec- strong impact by causing dental and skeletal fluorosis.4 Over
ognition of anions in their hydrated form is of immense 100 million people are drinking fluoride containing water of
importance.1 Particularly, recognition of fluoride is of vast sig- geogenic origin above the limit suggested by World Health
nificance due to its high hydration energy among the mono Organisation.5 Studies have shown presence of fluoride in
negative species (ΔGh = −465 kJ mol−1, ΔH° = 100–110 kcal human body beyond its toxic level can cause osteosarcoma
mol−1).2 As a chemical entity fluoride has the highest electro- and various health related problems.6–9 Thus recognition of
negativity, a high solvation enthalpy, the highest charge hydrated anions has attracted a great deal of attention in
density and a relatively smaller ionic radius (1.47 Å). In order recent years for real world applications. Development of recep-
to hydrate fluoride, water molecules form a highly structured tor that can encapsulate fluoride in an aqueous medium is an
first solvation sphere for which binding of hydrated fluoride important target in anion recognition chemistry. Even fluoride
water cluster plays an important role in stabilising heme pro-
teins like ferric sperm whale myoglobin.10 Polyammonium
Department of Inorganic Chemistry Indian Association for the Cultivation of Science,
macrobicycles and macrocycles have shown encapsulation of
2A & 2B Raja S. C. Mullick Road, Kolkata 700032, India. E-mail: icpg@iacs.res.in;
hydrated fluoride in aqueous medium.11 On the other hand,
Fax: (+91) 33-2473-2805
†Electronic supplementary information (ESI) available: 1H and 13C spectra of L,
complexes 1 and 2, 1H and 13C spectra of 3, H-bonding tables, Partial 1H NMR
and 19F spectra, Job’s plot of all NMR titrations, FIT plots of NMR titrations,
X-ray crystal structure of 3, H-bonding distances and angles of clusters. CCDC
933028 (1), 933029 (2) and 933030 (3). For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c3dt52694a
we and others have demonstrated the formation of capsular
dimeric assemblies templated by hydrated anion clusters by
neutral receptors.12–14 However, these neutral receptors are
generally insoluble in water/aqueous medium because of the
ligand functionality and their attached units. Thus encapsula-
tion of hydrated anions in these cases is achieved in purely
organic solvents where source of water is either moisture in
‡Present address: Department of Inorganic Chemistry, VirginiaTech,
Blacksburg, VA-24060, USA.
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the solvent or water of hydration of the salt used. For practical
application it is indeed important to design a receptor that
can recognize hydrated anions in an aqueous medium. In this
direction, we have designed a tripodal amide receptor on an
arene platform having pyridyl as an attached moiety for anion
recognition study in aqueous medium. Herein, we structurally
demonstrate the isolation of tweezer-like assemblies of
[F2(H2O)4]2− and [Cl2(H2O)4]2− clusters zipped 1D-polymeric
complexes of L from acetone–water (1 : 1, v/v) binary solvent
mixture. Moreover, the dimeric assembly of L can also encap-
2−
sulate SiF6 anion in dioxane–acetone (1 : 1 v/v). Further solu-
tion state binding of halides and oxyanions with L are also
carried out by 1H NMR titration and 19F NMR studies.
Results and discussion
Receptor L is constructed on 1,3,5-methyl substituted benzene
platform and decorated with pyridyl substituted amide func-
tionality. Here 4-pyridyl substitution is chosen to introduce
hydrophilic moiety to the receptor. L is synthesized by the reaction
of 1,3,5-tris-(aminomethyl)-2,4,6-trimethyl benzene with three
equivalents of isonicotinoyl chloride hydrochloride in the pres-
ence of excess triethylamine in tetrahydrofuran (THF) at 0 °C
(Scheme 1). After the reaction the solvent is evaporated under
vacuum and the residual mass is washed with water in order
to remove triethylammonium chloride salt. L is found to be
soluble even upto 1 : 3 (v/v) acetone–water, binary solvent
mixture. Here L is treated with excess tetrabutylammonium
(TBA) salts of F− and Cl− in acetone–water (1 : 1, v/v) solvent
mixture to synthesize the respective host–guest complexes
[L]2·[F2(H2O)4]·[TBA]2 (1) and [L]2·[Cl2(H2O)4]·[TBA]2 (2). On the
other hand, complexation of L with fluoride in dioxane–
acetone (1 : 1, v/v) solvent mixture resulted in the formation of
Fig. 1 (a) 1D-Polymeric arrangement of tweezer-like assembly of
complex 1. (b) Perspective view of encapsulation of [F2(H2O)4]2− cluster
inside the cavity of the dimeric capsular assembly of L.§
interaction between pyridyl N of L and H2O. The pyridyl nitro-
gen atoms N2, N4 and N6 are connected with the water mole-
cules O6, O3 and O2 respectively. The water molecule
represented by O2 is a part of [F2(H2O)4]2− cluster which is
composed of a cyclic [F2(H2O)2]2− unit, hydrogen bonded to
two other water molecules (O2 and O2′) (Fig. 1b). The geometry
of cyclic [F2(H2O)2]2− unit is more like a parallelogram where
an alternate fluoride (F1/F1*) and water (O5/O5″) reside in
each corners (Fig. 2). Bond distances (F⋯O) and angles in
[F2(H2O)2]2− cluster are as follows: F1⋯H5A–O5 = 2.702 Å and
F1⋯H5B–O5″ = 2.618 Å; ∠O5–F1–O5″ = 83.79°, ∠F1–O5–F1* =
96.21° (Fig. 2). The average H-bonding distance in [F2(H2O)4]2−
is found to be 2.798 Å which ranges from 2.651 Å to 2.945 Å
(Table 1S, ESI†). The cluster is stabilized mainly by two
N–H⋯F, six O–H⋯F and four N–H⋯O interactions (Fig. 1b). In
each L, three aryl C–H (Hb) protons of the pyridyl moiety also
participate in weak hydrogen bonding interaction with both F−
and H2O molecules via one C–H⋯F and two C–H⋯O inter-
actions which play an important role to stabilise the overall
hydrated cluster. The geometry around the encapsulated
penta-coordinated fluoride (F1) in complex 1 is distorted trigo-
nal bipyramidal (TBP) (Fig. 1S, ESI†). In such distorted TBP
arrangement F1 sits 1.047 Å above the plane containing
2−
SiF6 encapsulated complex, [L]2·[SiF6(H2O)2]·[TBA]2 (3). The
2−
SiF6 anion is generated upon reaction of TBAF with glass
vials in dioxane–acetone (1 : 1 v/v) during crystallization.
Single crystal X-ray structural description of
[L]2·[F2(H2O)4]·[TBA]2 (1)
In complex 1, the asymmetric unit contains one receptor L,
one F−, one TBA counter cation and five H2O. Fig. 1a shows
the formation of 1D-polymeric chain of dimeric assembly of L
zipped by a fluoride–water cluster, [F2(H2O)4]2−. Dimeric
assembly is further propagated to 1D-polymer via the
§Color codes: yellow: carbon, cyan: nitrogen, gray: hydrogen, red: oxygen, light
Scheme 1 Synthesis of L.
green: fluoride, dark green: chloride.
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Fig. 2 H-bonding distances and angles of the [(F)2(H2O)4]2− cluster in
complex 1.
O5–N3–O5″ and distance of F1 from the centroid of plane con-
taining O5–N3–O5″ is 1.166 Å. The plane containing O2–F1–
C17 and O5–N3–O5″ dissects each other with an angle of
78.81° which means these planes are distorted by −11.19°
compared to perfect TBP arrangement.
Fig. 3 (a) 1D-polymeric arrangement of tweezer-like assembly of
complex 2. (b) Perspective view of encapsulation of [Cl2(H2O)4]2− cluster
inside the cavity of the dimeric capsular assembly of L.§
Single crystal X-ray structural description of
[L]2·[Cl2(H2O)4]·[TBA]2 (2)
In 2 the asymmetric unit is consisting of one L, three H2O, one
Cl− and one TBA counter cation. Various H-bonding inter-
actions lead to the formation of [Cl2(H2O)4]2− cluster encapsu-
lated in the dimeric capsular assembly of 1D polymeric
network as observed in 1. However, in 2 the cluster is stabil-
ized via four N–H⋯Cl, six O–H⋯Cl and two N–H⋯O inter-
actions. Each chloride ion is hydrogen bonded to two amide
groups namely N2–H2 and N3–H3 (Fig. 3). In complex 2, aryl
C–H of one pyridyl subunit does not participate in bonding
where as other two aryl C–H protons involve in H-bonding
interaction either with Cl− or H2O molecule. Here one aryl
proton Ha participates in H-bonding via C29–H29⋯O6 and
another aryl proton Hb of another arm participates in
H-bonding via C21–H21⋯Cl1 interaction. The average
H-bonding distance in [Cl2(H2O)4]2− is found to be 3.081 Å
which ranges from 2.732 Å to 3.421 Å (Table 2S, ESI†). In this
cluster O6 sits almost in the same plane of the parallelogram
having an angle ∠O6–Cl1–O4 = 161.71° (Fig. 4) whereas in
complex 1, the corresponding water molecule O2 sits above the
plane of the parallelogram with an angle ∠O2–F1–O5 = 116.44°
(Fig. 2). Bond distances (Cl⋯O) and angles in [Cl2(H2O)2]2−
cluster are as follows: Cl1⋯H4A–O4 = 3.375 Å and Cl1⋯H4B–
O4″ = 3.317 Å.
Fig. 4 H-bonding distances and angles of the [(Cl)2(H2O)4]2− cluster in
complex 2.
(O4″–Cl1–N3) and equatorial planes (O4–N2–O6–C21) in
complex 2 is 88.67°, slightly distorted by −1.33°. The distance
between the centroids of the two epical benzene caps is found
to be 9.412 Å in complex 1 which is slightly lower than that of
complex 2 (9.618 Å) which could be due to relatively larger size
of Cl− than F−.
Single crystal X-ray structural description of
[L]2·[SiF6(H2O)2]·[TBA]2 (3)
In complex 2 the coordination geometry around hexa-co-
ordinated chloride (Cl1) is distorted octahedral (Fig. 1S, ESI†). In 3 the asymmetric unit is consisting of one L, three H2O, one
2−
Here Cl1 sits just 0.326 Å above the centroid of plane contain- SiF6 and one TBA counter cation. A number of H-bonding
2−
ing O4–N2–O6–C21. In perfect octahedral arrangement the interactions lead to the formation of SiF6
encapsulated
angle between axial atoms has to be 180° but in complex 2, dimeric capsular assembly of 1D polymeric network as
∠O4″–Cl1–N3 = 139.22° which means the structure is more observed in 1 and 2 (Fig. 5). The encapsulated SiF62− is mainly
axially distorted by −40.78°. The angle between axial stabilized by four C–H⋯F and four N–H⋯F interactions. The
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Fig. 6 Comparative partial 1H NMR (300 MHz) spectra of L (∼4 mM) in
D2O–acetone-d6 (1 : 19, v/v) after addition of an excess amount
(∼3 equivalent) of TBA salts of different anions.
spectrum of L, a doublet at 8.64–8.63 ppm can be assigned to
Ha protons whereas doublet at 7.77–7.76 ppm can be attribu-
ted to Hb protons. In each case the Hb proton is downfield
shifted upon addition of an excess amount (3 equivalents) of
TBA salts of respective anions.
2−
Fig. 5 Labelled structure of complex 3, SiF6 encapsulated dimeric
capsule.
aryl C–H (Hb) protons of two pyridyl subunits take part in
H-bonding with fluoride atoms. Here aryl protons Hb participates
in H-bonding via C22–H22⋯F2 and C28–H28⋯F3 interactions
(Fig. 5). The average hydrogen bonding distance in the case of
3 is 3.12 Å which ranges from 2.844 Å to 3.449 Å (Table 3S,
ESI†). Amide protons also participate in weak bonding
through N4–H4⋯F2 and N6–H6⋯F1. The water molecules
present in the asymmetric unit are stabilized by C9–H9B⋯O1
and N5–H5⋯O5 interactions. Details of hydrogen bonding
interactions are mentioned in Table 3S, ESI.† We have
obtained the crystals of 3 from dioxane–acetone binary solvent
Hb proton is found to be shifted upto 7.90–8.00 ppm for all
the studied anions (except iodide). In a typical NMR titration
experiment, an aliquot of the guest in acetone-d6 is added
gradually to a stock solution of the host in D2O–acetone-d6
(1 : 19, v/v) solvent system. The Job’s plot analysis shows an
overall 1 : 4 (host–guest) binding pattern of L with halides
(Fig. 7) and oxyanions (Fig. 13S–23S, 26S–29S, ESI†). Chemical
shift change vs. anion equivalents plots of 1H NMR titration of
L with F− and Cl− are presented in Fig. 8. In case of F− titration
with L in D2O–acetone-d6 (1 : 19, v/v), a doublet for Hb proton
is found to be at 7.76 ppm. This proton is shifted to 7.83 ppm
upon addition of around 1 equivalent of F− (Fig. 13S, ESI†).
Further addition of F− beyond 1 equivalent (upto 6.5 equiva-
lents of F−) shows a downfield shift of Hb proton upto
7.93 ppm (Fig. 14S, ESI†). In the case of chloride binding in
D2O–acetone-d6 (1 : 19, v/v), the doublet for Hb around 7.76 is
found to be shifted to 7.85 ppm upon addition of 1 equivalent
of chloride (Fig. 13S, ESI†). The chemical shift of Hb proton in
2−
mixture in the presence of excess TBAF. SiF6 is generated in
the system due to the reaction of TBAF with glass vials.
Solution state anion binding studies
An appreciable shift of the aryl C–H protons is observed in the
qualitative 1H NMR experiments of L with different anions (F−,
Cl−, Br−, NO3−, H2PO4−, HSO4−) as their TBA salts in D2O–
1
acetone-d6 (1 : 19, v/v) solvent system (Fig. 6). In the H NMR
Fig. 7 Job’s plot analysis of L in D2O–acetone-d6 (1 : 19, v/v) after adding TBAF. (b) Job’s plot for binding L in D2O–acetone-d6 (1 : 19, v/v) after
adding TBACl.
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Fig. 8 Change in chemical shift vs. anion equivalents plots of 1H NMR titrations of L with (a) TBAF and (b) TBACl in D2O–acetone-d6 (1 : 19, v/v).
Table 1 Binding constants of the anions for 1 : 1 stoichiometry with L
Solvent system
Anions
log K
ΔG (kcal mol−1
)
D2O–acetone-d6
D2O–acetone-d6
D2O–acetone-d6
D2O–acetone-d6
D2O–acetone-d6
D2O–acetone-d6
F−
1.59
1.58
1.56
2.02
1.96
0.87
−2.168
−2.154
−2.127
−2.754
−2.673
−1.186
Cl−
Br−
NO3
HSO4
H2PO4
−
−
−
Details of FIT plot, anion equivalent plots and WINEQNMR output
files are mentioned in the ESI.
this case is found to be larger compared to that of fluoride.
Detailed FIT plots and residual plots for all the studied anions
are depicted in Fig. 30S–35S in ESI.† Job’s and FIT plots for all
the other anions (Br−, NO3−, HSO4−, H2PO4−) are presented in
the ESI† (Fig. 30S–35S). We have calculated the binding con-
stant and ΔG values for anion binding to L in 1 : 1 fitting
pattern at 298 K in D2O–acetone-d6 (1 : 19, v/v) (Table 1). For
each calculation, we have taken the chemical shift values upto
its saturation and fitted these values in WINEQNMR soft-
ware.15 The details of the binding constants are tabulated in
Table 1. From binding constant data it is found that L shows
Fig. 9 Comparative 19F NMR spectra (500 MHz) of (a) TBAF (5 mM). (b)
TBAF (∼1 equivalent) + L (5 mM). (c) Complex 3 (5 mM). (d) Complex 1.
−94.68 ppm, this indicates a similar trend of chemical shift as
observed in 1.
Experimental section
Materials and methods
1H and 13C NMR spectra of L, 1–3 were recorded using a
300 MHz FT-NMR spectrometer in DMSO-d6 solvent. HRMS
measurements were carried out in a QTof-Micro YA 263 instru-
ment. Tetrabutyl ammonium salts were directly purchased
from Sigma-Aldrich. 1,3,5-tris(aminomethyl)-2,4,6-trimethyl-
−
comparable binding constant with the halides, whereas NO3
and HSO4− show slightly higher binding constants.
19F NMR studies
19F NMR spectroscopy is also employed to verify the binding of benzene was synthesised as per the modified literature
F− with L in solution (Fig. 9). When L (5 mM) is added to procedure,16 where 1,3,5-tris(bromomethyl)-2,4,6-trimethyl-
TBAF (3 equivalent) in DMSO-d6, the fluorine peak is shifted benzene was used instead of 1,3,5-tris(bromomethyl)-2,4,6-
to −106.82 ppm from the fluoride signal of free TBAF (5 mM, triethylbenzene. Tetrahydrofuran was dried over metallic
−108.34 ppm). Here 3 equivalents of F− is added to L as 1H sodium before preparing L.
NMR titration experiment of L with F− shows 1 : 3 (host–guest)
Synthesis of L. 1,3,5-tris(aminomethyl)-2,4,6-trimethylben-
stoichiometry in DMSO-d6 (Fig. 21S, ESI†). However, in the 19F zene (0.450 g, 2.17 mmol) and triethylamine (1.50 ml,
spectrum of 1 (5 mM), we obtain a peak around −99.53 ppm, 10.85 mmol) were dissolved in dry tetrahydrofuran and stirred
2−
whereas in complex 3 (5 mM), a peak for SiF6 is found to be in 0 °C in a round bottom flask for 2 hours. Isonicotinoyl
at −126.99 ppm. This indicates that the F− in 1 is not naked F− chloride hydrochloride (1.20 g, 6.727 mmol) was added
or bound SiF62−. When 1 equivalent of TBAF is added to L directly to the round bottom flask and the solution was stirred
(5 mM) in DMSO-d6, the fluoride signal is shifted to for 12 hours. Then the solution was evaporated to dryness.
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The dried mass was thoroughly washed with excess of water in (75 MHz, DMSO-d6): δ (ppm) 13.7, 16.3, 19.4, 23.3, 57.8, 121.8,
order to remove triethylamine hydrochloride salts and 132.4, 137.4, 141.7, 150.3, 165.3. Elemental analysis calculated
unreacted isonicotinoyl chloride hydrochloride salt. Then the for C62H108F6N8O6Si is: C, 61.87; H, 9.04; N, 9.31. Found: C,
white residue was washed with diethyl ether and was dried in 61.72; H, 9.02; N, 9.23.
air in order to obtain a white solid mass. Yield obtained for L
is 70%. 1H NMR (300 MHz, DMSO-d6): δ (ppm) 2.42 (s, Ph-
Single crystal X-ray crystallographic details
Me), 4.56–4.58 (d, PhCH2), 7.72–7.74 (d, Pyridine-Hb),
The crystallographic details of complexes 1, 2, and 3 are given
in Table 2. In each case, a crystal of suitable size was collected
from the mother liquor and was dipped in paratone oil. Then
8.69–8.70 (d, Pyridine-Ha), 8.71 (b, Amide N-H). 13C NMR
(75 MHz, DMSO-d6): δ (ppm) 16.1, 121.5, 132.3, 137.1, 141.3,
150.0, 164.7. One 13C peak corresponding to methylene carbon
it was mounted on the tip of a glass fibre and cemented using
(PhCH2) falls in the range of DMSO-d6 carbons. HRMS (ESI):
epoxy resin. Intensity data for all crystals are collected using
MoKα (λ = 0.7107 Å) radiation on a Bruker SMART APEX diffr-
m/z 523.45 [L +H]+. Elemental analysis calculated for
C30H30N6O3 is: C, 68.95; H, 5.79; N, 16.08. Found: C, 68.89; H,
actometer equipped with a CCD area detector at 120 K. The
5.82; N, 16.06.
data integration and reduction are processed with SAINT17a
software. An empirical absorption correction was applied to
Synthesis of complex 1. [L]2·[F2(H2O)4]·[TBA]2 was obtained
in a glass beaker by adding 3 equivalents of tetrabutyl-
the collected reflections with SADABS.17b The structures were
ammonium fluoride salt in 10 ml acetone–water (1 : 1, v/v)
solved by direct methods using SHELXTL18 and were refined
binary solvent mixture containing L (40 mg). The beaker was
on F2 by the full-matrix least-squares technique using the
kept in a refrigerator to maintain a slow evaporation of the sol-
SHELXL-9719 program package. Graphics were generated using
vents. Colorless crystals were obtained after around three
PLATON-9720 and MERCURY 3.1.21 In all cases non-hydrogen
weeks. Yield 40%. 1H NMR (300 MHz, DMSO-d6): δ (ppm)
atoms were refined anisotropically except for the disordered
carbon atoms, C46, C46A and oxygen atom O3 in complex 1.
0.92–0.95 (t, 12H, –NCH2CH2CH2CH3), 1.28–1.33 (m, 8H,
–NCH2CH2CH2CH3), 1.55–1.58 (m, 8H, –NCH2CH2CH2CH3),
All the amide nitrogen atoms in 1, 2, and 3 are geometrically
2.37 (s, Ph-Me) 3.14–3.18 (t, 8H, –NCH2CH2CH2CH3),
fixed and hydrogen atoms associated with water molecules
were located in the Fourier map and were isotropically refined.
DFIX restrain was used in 1 on O2-H2A, O2-H2B and O4-H4B.
4.53–4.54 (d, PhCH2), 7.86–7.87 (d, Pyridine-Hb), 8.62–8.63 (d,
Pyridine-Ha). 13C NMR (75 MHz, DMSO-d6): δ (ppm) 13.5, 16.0,
19.2, 23.0, 57.5, 57.6, 121.7, 132.2, 136.8, 141.7, 149.9, 164.6.
Elemental analysis calculated for C46H76FN7O8 is: C, 63.20; H,
Table 2 Crystallographic data of complexes 1, 2 and 3
8.76; N, 11.22. Found: C, 63.17; H, 8.76; N, 11.19.
Synthesis of complex 2. [L]2·[Cl2(H2O)4]·[TBA]2 was obtained
in a glass beaker by adding 3 equivalents of tetrabutyl-
Compound
reference
Complex 1
Complex 2
Complex 3
ammonium chloride salt in 10 ml acetone–water (1 : 1, v/v) Chemical
C46H69FN7O8 C46H72ClN7O6 C92H132F6N14O12Si
formula
binary solvent mixture containing L (40 mg). The beaker was
kept in a refrigerator to maintain slow evaporation of the sol-
Formula mass
Crystal system
867.08
854.56
Triclinic
1768.21
Triclinic
12.254(3)
12.594(3)
17.033(4)
110.208(5)
95.567(6)
98.637(5)
2407.3(9)
Triclinic
12.483(2)
12.508(3)
16.245(3)
104.033(4)
91.958(5)
101.757(5)
2399.6(8)
vents. Colorless crystals were obtained after around three a/Å
12.2430(17)
12.9014(18)
15.817(2)
71.150(3)
87.662(4)
88.303(4)
2362.0(6)
weeks. Yield 55%. 1H NMR (300 MHz, DMSO-d6): δ (ppm)
b/Å
c/Å
α/°
0.91–0.96 (t, 12H, –NCH2CH2CH2CH3), 1.27–1.34 (m, 8H,
–NCH2CH2CH2CH3), 1.57 (m, 8H, –NCH2CH2CH2CH3), 2.41 (s, β/°
γ/°
Ph-Me), 3.14–3.19 (t, 8H, –NCH2CH2CH2CH3), 4.57 (d, PhCH2),
7.73–7.75 (d, Pyridine-Hb), 8.67–8.68 (d, Pyridine-Ha) 8.72 (b,
Unit cell
volume/Å3
Amide N-H). 13C NMR (75 MHz, DMSO-d6): δ (ppm) 13.5, 16.1, Temperature/K
120(2)
P1
120(2)
P1
150(2)
P1
ˉ
ˉ
ˉ
Space group
No. of formula
units per unit
19.2, 23.0, 57.5, 121.5, 132.2, 137.1, 141.3, 150.0, 164.7.
Elemental analysis calculated for C46H72ClN7O6 is: C, 64.65; H,
2
2
1
8.49; N, 11.47. Found: C, 64.48; H, 8.52; N, 11.45.
Synthesis of complex 3. [L]2·[SiF6(H2O)2]·[TBA]2 was
obtained in a glass beaker by adding 3 equivalents of tetra-
cell, Z
No. of reflections 15 145
measured
No. of
25 649
9722
23 389
8704
5151
butylammonium fluoride salt in 10 ml acetone–dioxane (1 : 1, independent
reflections
Rint
Final R1 values
v/v) binary solvent mixture containing L (40 mg). The solution
was warmed and filtered. The beaker was kept in a refrigerator
0.0472
0.0861
0.0410
0.0529
0.0435
0.0666
to maintain slow evaporation of the solvents. Colorless crystals (I > 2σ(I))
Final wR(F2)
0.2835
0.1005
0.3015
1.093
0.1284
0.1017
0.1538
1.008
0.1919
0.0955
0.2119
1.212
were obtained after around 10 days. Yield 40%. 1H NMR
values (I > 2σ(I))
(300 MHz, DMSO-d6):
δ
(ppm) 0.92–0.95 (t, 12H,
Final R1 values
–NCH2CH2CH2CH3), 1.28–1.33 (m, 8H, –NCH2CH2CH2CH3), (all data)
Final wR (F2)
1.52–1.57 (m, 8H, –NCH2CH2CH2CH3), 2.38 (s, Ph-Me),
3.14–3.18 (t, 8H, –NCH2CH2CH2CH3), 4.53 (d, PhCH2),
values (all data)
Goodness of fit
7.83–7.82 (d, Pyridine-Hb), 8.62–8.63 (d, Pyridine-Ha). 13C NMR on F2
2066 | Dalton Trans., 2014, 43, 2061–2068
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In the case of 1, good crystals were diffracted at 120 K but did
not show diffraction beyond the respective theta max obtained
even after several attempts. DFIX restrain was also used in 2 on
O6-H6A and O5-H5B.
(n) M. Arunachalam and P. Ghosh, Chem. Commun., 2011,
47, 8477–8492.
2 (a) F. Hofmeister, Arch. Exp. Pathol. Pharmakol., 1888, 24,
247–260; (b) Y. J. Marcus, J. Chem. Soc., Faraday Trans.,
1991, 87, 2995–2999.
3 S. Merchant and D. Asthagiri, J. Chem. Phys., 2009, 130,
195102–195111.
4 S. Ayoob and A. K. Gupta, Crit. Rev. Environ. Sci. Technol.,
2006, 36, 433–487.
5 R. P. Schwarzenbach, B. I. Escher, K. Fenner,
T. B. Hofstetter, C. A. Johnson, U. von Gunten and
B. Wehrli, Science, 2006, 313, 1072–1077.
6 (a) E. B. Bassin, D. Wypij and R. B. Davis, Cancer, Causes
Control, 2006, 17, 421–428; (b) S.-X. Wang, Z.-H. Wang,
X.-T. Cheng, J. Li, Z.-P. Sang, X.-D. Zhang, L.-L. Han,
X. Y. Qiao, Z.-M. Wu and Z.-Q. Wang, Environ. Health
Perspect., 2007, 115, 643–647.
7 (a) P. Connet, Fluoride, 2007, 40, 155–158; (b) R. G. Foulkes,
Fluoride, 2007, 40, 229–237; (c) R. J. Carton, Fluoride, 39,
163–172; (d) L. W. Ripa, J. Publ. Health Dent., 1993, 53,
17–44; (e) M. S. McDonagh, P. F. Whiting, P. M. Wilson,
A. J. Sutton, I. Chestnutt, J. Cooper, K. Misso, M. Bradley,
E. Treasure and J. Kleijnen, Br. Med. J., 2000, 321, 855–859.
8 A systematic review of the efficacy and safety of fluori-
dation, 2007, National Health and Medical Research
Council, Australian Government, available at http://www.
nhmrc.gov.au/
Conclusions
In conclusion, we have structurally demonstrated the encapsu-
lation of [X2(H2O)4]2− (X = F/Cl) by a 1D-polymeric assembly of
arene capped pyridyl functionalized tripodal receptor that is
obtained from aqueous media. In both cases [X2(H2O)4]2−
zipped dimeric capsular assembly of L is observed where both
the hydrated anion–water clusters are of similar empirical
1
formula with different structural arrangement. H NMR titra-
tion study shows binding of halides and oxyanions with
reasonable binding constants for halides and oxyanions in a
semi-aqueous solvent system.
Acknowledgements
P. G. gratefully acknowledges the Department of Science and
Technology (DST), New Delhi, India for financial support
through Swarnajayanti Fellowship. S. C. and R. D. would like
to acknowledge IACS, Kolkata, India for fellowship. X-Ray crys-
tallographic studies were performed at the DST-funded
National Single-Crystal X-ray Diffraction Facility at the Depart-
ment of Inorganic Chemistry, IACS.
9 (a) M. Zhang, A. G. Wang, T. Xia and P. He, Toxicol. Lett.,
2008, 179, 1–5; (b) T. Wurtz, S. Houari, N. Mauro,
M. MacDougall, H. Peters and A. Berdal, Toxicology, 2008,
249, 26–34.
10 S. Aime, M. Fasano, S. Paoletti, F. Cutruzzola, A. Desideri,
M. Bolognesi, M. Rizzi and P. Ascenzi, Biophys. J., 1996, 70,
482–488.
Notes and references
1 (a) Supramolecular Chemistry of Anions, ed. A. Bianchi,
K. Bowman-James and E. Garcia-España, Wiley-VCH, 11 (a) S. Mason, J. M. Llinares, M. Morton, T. Clifford and
New York, 1997; (b) J. L. Sessler, P. A. Gale and W.-S. Cho,
Anion Receptor Chemistry: Monographs in Supramolecular
Chemistry, RSC Publishing, Cambridge, UK, 2006;
(c) Supramolecular chemistry of anionic species themed
Issue: Chem. Soc. Rev., 2010, 39, 3581–4008; (d) B. Dietrich,
J.-M. Lehn, J. Guilhem and C. Pascard, Tetrahedron Lett.,
K. Bowman-James, J. Am. Chem. Soc., 2000, 122, 1814–1815;
(b) M. A. Hossain, J. M. Llinares, S. Mason, P. Morehouse,
D. Powell and K. Bowman-James, Angew. Chem., Int. Ed.,
2002, 41, 2335–2338; (c) E. Garcia-España, P. Díaz,
J. M. Llinares and A. Bianchi, Coord. Chem. Rev., 2006, 250,
2952–2986.
1989, 30, 4125–4128; (e) C. J. Woods, S. Camiolo, 12 (a) J. L. Atwood and A. Szumna, Chem. Commun., 2003,
M. E. Light, S. J. Coles, M. B. Hursthouse, M. A. King,
P. A. Galenand and J. W. Essex, J. Am. Chem. Soc., 2002,
124, 8644–8652; (f) C. A. Ilioudis, D. A. Tocher and
J. W. Steed, J. Am. Chem. Soc., 2004, 126, 12395–12402;
(g) G. W. Bates, P. A. Gale and M. E. Light, Chem. Commun.,
2007, 2121–2123; (h) Anion Coordination Chemistry, ed.
K. Bowman-James, A. Bianchi and E. Garcia-España, Wiley-
VCH, New York, 2012; (i) M. Cametti and K. Rissanen,
Chem. Soc. Rev., 2013, 42, 2016–2038; ( j) C. Caltagirone and
P. A. Gale, Chem. Soc. Rev., 2009, 38, 520–563; (k) S. Kubik,
Chem. Soc. Rev., 2009, 38, 585–605; (l) P. A. Gale,
940–941; (b) G. V. Zyryanov, M. A. Palacios and
P. Anzenbacher, Angew. Chem., Int. Ed., 2007, 46, 7849–
7852; (c) Y. Li, K. M. Mullen, T. D. W. Claridge, P. J. Costa,
V. Felix and P. D. Beer, Chem. Commun., 2009, 7134–7136;
(d) M. Arunachalam and P. Ghosh, Chem. Commun., 2009,
5389–5391; (e) M. Arunachalama and P. Ghosh, Inorg.
Chem., 2010, 49, 943–951; (f) P. Ballester, Chem. Soc. Rev.,
2010, 39, 3810–3830; (g) A. L. Cresswell, M. M. Piepenbrock
and J. W. Steed, Chem. Commun., 2010, 46, 2787–2789;
(h) M. Arunachalam and P. Ghosh, Chem. Commun., 2011,
47, 6269–6271.
S. E. García-Garrido and J. Garric, Chem. Soc. Rev., 2008, 37, 13 (a) M. Cametti and K. Rissanen, Chem. Commun., 2009,
151–190; (m) S. O. Kang, R. A. Begum and K. Bowman-
James, Angew. Chem., Int. Ed., 2006, 45, 7882–7894;
2809–2829; (b) Q. Q. Wang, V. W. Day and K. Bowman-
James, Angew. Chem., Int. Ed., 2012, 51, 2119–2123;
This journal is © The Royal Society of Chemistry 2014
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View Article Online
Paper
Dalton Transactions
(c) M. A. Hossain, M. A. Saeed, A. Pramanik, B. M. Wong, 15 M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311–312.
S. A. Haque and D. R. Powell, J. Am. Chem. Soc., 2012, 134, 16 C. Nativi, M. Cacciarini, O. Francesconi, A. Vacca,
11892–11895; (d) A. Pramanik, D. R. Powell, B. M. Wong
and M. A. Hossain, Inorg. Chem., 2012, 51, 4274–4284;
G. Moneti, A. Lenco and S. Roelens, J. Am. Chem. Soc.,
2007, 129, 4377–4385.
(e) Q. Q. Wang, V. W. Day and K. Bowman-James, J. Am. 17 (a) G. M. Sheldrick, SAINT and XPREP, 5.1 edn, Siemens
Chem. Soc., 2013, 135, 392–399.
14 (a) R. Custelcean and M. G. Gorbunova, J. Am. Chem. Soc.,
2005, 127, 16362–16363; (b) J. R. Butchard, O. J. Curnow,
Industrial Automation Inc., Madison, WI, 1995;
(b) SADABS, empirical absorption Correction Program, Univer-
sity of Göttingen, Göttingen, Germany, 1997.
D. J. Garett and R. G. A. R. Maclagan, Angew. Chem., Int. 18 G. M. Sheldrick, SHELXTL Reference Manual: Version 5.1,
Ed., 2006, 45, 7550–7553; (c) M. Mascal, L. Infantes and Bruker AXS, Madison, WI, 1997.
J. Chisholm, Angew. Chem., Int. Ed., 2006, 45, 32–36; 19 G. M. Sheldrick, SHELXL-97: Program for Crystal Structure
(d) M. C. Das, S. K. Ghosh, S. Sen and P. K. Bharadwaj,
CrystEngComm, 2010, 12, 2967–2974; (e) R. Saha, S. Biswas,
Refinement, University of Göttingen, Göttingen, Germany,
1997.
I. M. Steele, K. Dey and G. Mostafa, Dalton Trans., 2011, 40, 20 A. L. Spek, PLATON-97, University of Utrecht, Utrecht, The
3166–3175; (f) M. N. Hoque, A. Basu and G. Das, Cryst. Netherlands, 1997.
Growth Des., 2012, 12, 2153–2157; (g) A. Basu and G. Das, 21 Mercury 3.1 Supplied with Cambridge Structural Database;
Chem. Commun., 2013, 49, 3997–3999. CCDC: Cambridge, U.K., 2001–2012.
2068 | Dalton Trans., 2014, 43, 2061–2068
This journal is © The Royal Society of Chemistry 2014