Recognition of fluoride in fluorophenyl attached tripodal amide receptors: Structural evidence of solvent capped encapsulation of anion in a C 3v-symmetric tripodal cleft

Article abstract of DOI:10.1039/c3ce42440e

A new 2,3,4,5-tetrafluorophenyl substituted tripodal amide-based receptor L1 and its pentafluorophenyl substituted analogue L2 were explored for halide binding studies in their solution and solid states. Comparative solution state binding studies of halides with L1 and L2 were carried out by ¹H-NMR titration in CDCl₃. Detailed solution state ¹H-NMR studies show that halides bind with L1 and L2 with 1:1 stoichiometry in general. Binding constants of the halides with L1 and L2 were calculated by ¹H-NMR titration studies where the fluoride shows selectivity over other halides and the fluoride binding constants (log K) with these two receptors were found to be 3.94 and 3.35, respectively. Single crystal X-ray structure analysis of the triamide receptors, L1 and L2, revealed two different conformations where L1 possesses a pre-organized C_3v symmetric tripodal cleft, whereas in the case of L2 three arms are devoid of structural pre-organization to achieve a C_3v symmetric cleft. Single crystal X-ray diffraction studies of the cases of complexes formed between L2 and fluoride/chloride, [L2(F)(CHCl₃)][N(Bu)₄] (1) and [L2(Cl)(CHCl₃)][N(Bu)₄] (2), respectively, were also carried out to elucidate the structural evidence of anion encapsulation. A detailed structural analysis of complexes 1 and 2 shows that the fluoride and chloride are engulfed in the C_3v symmetric cavity of L2 with three strong N-H...anion interactions where a CHCl₃ molecule acts as a cap that closes the open end of the C_3v symmetric cleft via C-H...anion and CHCl₃...C₆F₅ interactions.

Full text of DOI:10.1039/c3ce42440e

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Recognition of fluoride in fluorophenyl attached
tripodal amide receptors: structural evidence of
solvent capped encapsulation of anion in a
C3v-symmetric tripodal cleft†
Cite this: CrystEngComm, 2014, 16,
4796
Subrata Saha, Bidyut Akhuli, I. Ravikumar, P. S. Lakshminarayanan
*
and Pradyut Ghosh
A new 2,3,4,5-tetrafluorophenyl substituted tripodal amide-based receptor L1 and its pentafluorophenyl
substituted analogue L2 were explored for halide binding studies in their solution and solid states.
Comparative solution state binding studies of halides with L1 and L2 were carried out by 1H-NMR titration
in CDCl3. Detailed solution state 1H-NMR studies show that halides bind with L1 and L2 with 1 : 1
stoichiometry in general. Binding constants of the halides with L1 and L2 were calculated by 1H-NMR
titration studies where the fluoride shows selectivity over other halides and the fluoride binding constants
(log K) with these two receptors were found to be 3.94 and 3.35, respectively. Single crystal X-ray
structure analysis of the triamide receptors, L1 and L2, revealed two different conformations where L1
possesses a pre-organized C3v symmetric tripodal cleft, whereas in the case of L2 three arms are devoid
of structural pre-organization to achieve a C3v symmetric cleft. Single crystal X-ray diffraction studies of
the cases of complexes formed between L2 and fluoride/chloride, [L2(F)(CHCl3)][N(Bu)4] (1) and
[L2(Cl)(CHCl3)][N(Bu)4] (2), respectively, were also carried out to elucidate the structural evidence of anion
encapsulation. A detailed structural analysis of complexes 1 and 2 shows that the fluoride and chloride
are engulfed in the C3v symmetric cavity of L2 with three strong N–H⋯anion interactions where a CHCl3
molecule acts as a cap that closes the open end of the C3v symmetric cleft via C–H⋯anion and
CHCl3⋯C6F5 interactions.
Received 29th November 2013,
Accepted 6th February 2014
DOI: 10.1039/c3ce42440e
www.rsc.org/crystengcomm
cleft formed by two extended arms with a quasi-planar C2v
Introduction
symmetry.6 Later on, we and others have shown structural
Recognition of anions has a significant impact due to its
environmental and biological importance.1 Anion recognition
by synthetic hosts is mostly based on positively charged
and/or hydrogen-bonded donor containing groups.2 In gen-
eral amide based ligands have been important since anion
receptors in nature often involve amide linkages.3 In 1993,
Reinhoudt and co-workers synthesized tris-(2-aminoethyl)-
amine, tren-based tripodal ligands containing amide groups
for anion binding.4 Beer et al. have shown the extraction of
pertechnetate by tren-based tripodal tris(amido benzo-15-
crown-5) via cooperative ion-pair binding effects in solution.5
Bowman-James and co-workers demonstrated a tren based
triprotonated amine ligand for binding of bromide in the
proof of anion encapsulation with tren-based tripodal
ammonium/urea receptors that bind various spherical and
tetrahedral anions.7 Recognition of fluoride and chloride is
of special interest due to their various applications in
medical and biological fields and also in drinking water puri-
fication processes.8 Calixpyrrole systems,9 macrobicyclic cage
receptors with ammonium and amide functionalities10 and
cyanuric acid based receptors11 have shown structural
evidence of fluoride/chloride encapsulation. Previously L2
has been explored as an anion receptor in solution state
studies.12 Recently we utilized L2 as an anion receptor that
can act as a phase transfer agent in dual-host systems with
18-crown-6, for extraction of KF/KCl from water.13 Herein we
report a new tren-based amide receptor L1 decorated with
tetrafluorophenyl moieties and demonstrate its selectivity
towards fluoride. Further, we show various non-covalent
interactions that are responsible for different conformations
of L1, L2, and F−/Cl− complexes of L2 in the solid state. Inter-
estingly, L2 shows perfect encapsulation of F−/Cl− in its
C3v-symmetric cavity via three N–H⋯anion interactions
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
2A & 2B Raja S. C. Mullick Road, Kolkata 700 032, India. E-mail: icpg@iacs.res.in;
Fax: +91 33 2473 2805
† Electronic supplementary information (ESI) available: 1H-NMR, 13C-NMR,
1H-NMR titration details and packing diagrams for L1, L2, 1 and 2, ESI-MS of
L1. CCDC 973404 (L1), 701762 (L2), 701764 (1) and 710730 (2). For ESI and crys-
tallographic data in CIF or other electronic format see DOI: 10.1039/c3ce42440e
4796 | CrystEngComm, 2014, 16, 4796–4804
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where CHCl3 acts as a stopper to close the open end of the
C3v cleft via non-covalent interactions.
[L2(F)(CHCl3)][N(Bu)4] (1) and [L2(Cl)(CHCl3)][N(Bu)4] (2),
respectively. However, we were unsuccessful in obtaining
suitable crystals for anions with L1.
Results and discussion
Receptors L1 and L2
The tripodal amide-based receptor L1 is obtained by the
reaction between tris-(2-aminoethyl)amine (1 equiv.) and
2,3,4,5-tetrafluorobenzoyl chloride (3 equiv.) in the presence
of triethylamine in dry dichloromethane whereas L2 is
synthesized following a literature procedure.13 A comparative
halide binding study was performed in solution and the solid
state to evaluate the nature of anion encapsulation into the
cleft of L1 and L2 with closely related electron deficient
tripodal arms (Fig. 1).
Fig. 3 and 4 shows the single crystal structures of L1 and L2.
Both the neutral triamide receptors crystallized in a mono-
clinic P2(1)/c space group. The asymmetric unit of L1 contains
only one receptor unit without any solvent molecules. The
crystal structure of L1 revealed that all three tetrafluorophenyl
arms are projected in the same direction forming a C3v sym-
metric cleft which is evident from the corresponding N⋯N
distances of amide nitrogen centres in the tripodal arms.
Fig. 3(b) clearly shows the distances between the amide nitrogen
atoms of the proximal arms of L1 with a closer match where
N⋯N distances range from 4.461–4.542 Å. The torsion angles
involving N1apicalCCNamide are −53.93°, −55.15° and −67.71°.
The torsion angles (Cphenyl–Camide–Namide–C) involving
the carbon atoms connecting to the terminal tetrafluoro-
phenyl rings in three arms composed of the amide nitrogens
N2, N3 and N4 are almost in an extended conformation with
angles of 179.08, 179.58 and 175.82°, respectively. A strong
intramolecular hydrogen bonding N–H⋯O interaction
(N2⋯O3 = 2.943 Å, <N2–H2⋯O3 = 131°) between two
adjacent arms of L1 is observed. Further, intermolecular
hydrogen bonding interactions N–H⋯O (N4⋯O1 = 2.836 Å,
<N4–H4⋯O1 = 136°) in L1 result in a 1-D polymeric network
(Fig. 3(c)). The combined effect of intramolecular and inter-
molecular hydrogen bonding interactions are the driving
force for the formation of the C3v symmetric cleft of L1 in the
solid state.
However, the crystal structure of L2 (Fig. 4(c)) revealed
that the amide oxygen O2 of one arm acts as an acceptor and
is involved in intramolecular N–H⋯O interactions with the
donor amide hydrogen H4 (N4⋯O2 = 2.860 Å, <N4–H4⋯O2 =
167.85°). Thus, the intramolecular hydrogen bonding interac-
tions in L2 are stronger than those of L1. This particular
intramolecular hydrogen bonding assists the two arms com-
posed of the amide nitrogens N3 and N4 in being closer in
proximity, with torsion angles involving N1apicalCCNamide as
−64.25 and −69.84 whereas they are apart from the third arm
containing the N2 amide nitrogen having a N1apicalCCN2
torsion angle of 176.20°. This imposes an unsymmetrical cleft
(amide nitrogen distances between two arms are: N2⋯N3 =
5.669, N3⋯N4 = 4.243, and N2⋯N4 = 5.515 Å, Fig. 4(b)). The
torsion angles (Cphenyl–Camide–Namide–C) involving the
carbon atoms connecting to the terminal pentafluorophenyl
rings in the three arms composed of the amide nitrogens N2,
N3 and N4 are almost in an extended conformation with
angles of 166.30, 176.02 and 176.01°, respectively. The
intramolecular hydrogen bonding and unfolded orientation
of the electron deficient aromatic rings favors an open
structure of L2, which gives an unsymmetrical cleft of L2.
Further, the two intermolecular hydrogen bonding interactions
between the amide proton and carbonyl oxygen N–H⋯O
Solution state binding of halides with L1 and L2
The solution state binding properties of L1 and L2 with dif-
ferent halides as their tetrabutylammonium salts n-Bu4N+X−
1
(where X− = F−, Cl−, Br− and I−) were investigated by H-NMR
experiments in CDCl3. Substantial changes in chemical shift
were observed for the amide protons (–NH) of the receptors
with halides. Fig. 2(a) and (b) show two representative titra-
tion plots of L1 with F− and Cl− showing the participation of
–NH protons in the binding events. Fig. 2(a) and (b) show the
gradual shift of the –NH peak of L1 upon addition of various
equivalents of F− and Cl− solutions, respectively, in CDCl3.
Fig. 2(c) and (d) show the best fit for a 1 : 1 binding model
for host to guest, and the association constants are calculated
using WINEQNMR 2.0. The association constants are summa-
rized in Table 1. The stability constant data show that L1 has
a higher association toward F− compared to that of L2. The
relevant titration profiles of L1 with Br− and I− and L2 with F−
are given in the ESI† and binding constants are summarized
in Table 1.
Single-crystal X-ray structural studies
To study the structural and conformational arrangements of
the native triamide receptors we isolated crystals suitable for
single crystal X-ray diffraction studies of both the receptors
L1 and L2. Crystals were grown from CHCl3 solution upon
slow evaporation. Crystallization of L1 and L2 with n-Bu4N+F−
and n-Bu4N+Cl− were also performed in CHCl3 following a
slow evaporation process that resulted in the complexes
Fig.
1
Tris(2-aminoethyl)amine
based
tetrafluorophenyl
and
pentafluorophenyl based triamide receptors L1 and L2.
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Fig. 2 1H-NMR spectral changes of L1 upon addition of anion solutions aliquots (a & b). Change in –NH chemical shift with increasing amounts of
(c) [nBu4N+]F− and (d) [nBu4N+]Cl− in CDCl3 at 298 K.
Table 1 Association constants of F−/Cl− binding with L1 and L2 in
CDCl3 at 298 K
N3⋯N4 = 4.024 and N2⋯N4 = 4.005 Å. The torsion angles
involving N1apicalCCNamide are in a folded conformation with
angles −63.09, −68.57, and −65.63° for the three arms com-
posed of N2, N3, and N4, respectively, whereas the torsion
angles (Cphenyl–Camide–Namide–C) involving the carbon
atoms connecting the terminal pentafluorophenyl rings in
the three arms composed of the amide nitrogens N2, N3 and
N4 are in an extended conformation with angles of 173.91,
179.95, and −177.57°, respectively. Fig. 5(a) shows that in
complex 1, F− is involved in strong hydrogen bonding interac-
tions with all three amide hydrogens H2, H3 and H4 of L2
(Table 2) and one C–H⋯F− interaction from the encapsulated
chloroform molecule where the chlorine atoms of chloroform
are in short contact with the carbon atoms of the –C6F5 units.
The N–H⋯F− interactions in 1 are strong, the N⋯F− dis-
tances range from 2.70 to 2.77 Å and <N–H⋯F− range from
162 to 175°. The distance between C28⋯F16 is only 2.907 Å
which is less than the sum of the Van der Waals radii of fluo-
ride (1.33 Å) and carbon (1.70 Å).16 Therefore, the encapsu-
lated fluoride shows tetra coordination having a distorted
Binding constant (log K)
Receptors
F−
Cl−
Br−
I−
L1
L2
3.94
3.35
2.87
2.66
2.96
3.26a
1.56a
1.36a
a
Previously reported data.12
(N2⋯O3 = 2.763 Å, <N2–H2⋯O3 = 139°; N3⋯O1 = 2.829 Å,
<N3–H3⋯O1 = 170°) in L2 result in a 1-D polymeric network
(Fig. 4(c)) like L1.
Complex 1
¯
The complex 1 crystallizes in the triclinic space group P1.
Fig. 5(a) and (b) show the ditopic recognition of F− and
CHCl3 inside the C3v symmetric cleft of L2. The amide nitro-
gen distances between the two arms are: N2⋯N3 = 3.902,
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Fig. 3 MERCURY diagram showing (a) ball-stick model of L1; (b) amide N⋯N distances of tripodal arms of L1 showing C3v symmetric cleft, (c) 1-D
polymeric network of L1 with intra and intermolecular hydrogen bond distances. Non acidic hydrogen atoms are omitted for clarity. The distances
are given in Angstroms.
tetrahedral geometry (Table 3). In fact, the CHCl3 molecule is
acting as a cap for the encapsulated fluoride in the tripodal
receptor where three arms of L2 are disposed to form C3v
symmetry (Fig. 5b). Bowman-James and coworkers also
reported CHCl3 molecules as “caps” for the FHF− anion in a
cyclophane by a weak C–H⋯F− interaction (C⋯F− = 3.001 Å).14
Further, chlorine atoms of encapsulated chloroform are in
short contact with all three –C6F5 moieties of L2 with
Cl1⋯C26, Cl3⋯C8, Cl3⋯C9, Cl3⋯C16 and Cl3⋯C17 dis-
tances of 3.325, 3.411, 3.425, 3.403 and 3.332 Å, respectively,
which are less the sum of the Van der Waals radii of chlorine
(1.75 Å) and carbon (1.70 Å).15
rings in three arms composed of the amide nitrogens N2, N3
and N4 are in an extended conformation with angles of
177.56, 179.75, and 176.63°, respectively. Fig. 6(a) shows that
in complex 2, Cl− is involved in strong hydrogen bonding
interactions with all three amide hydrogens H2, H3 and H4
of L2 (Table 2) and one C–H⋯Cl− interaction from the
chloroform molecule C⋯Cl− = 3.300 Å and <C–H⋯Cl− = 174°
(which is less than the sum of the Van der Waals radii of
chloride (1.81 Å) and carbon (1.70 Å)).15 The encapsulated
chloride also shows tetra coordination with a distorted
tetrahedral geometry (Table 3). The distances between the
chloride and the centroid of the pentafluophenyl units, 3.917,
3.919 and 3.625 Å, indicate poor interaction of the encapsu-
lated halide with the electron deficient π center.
Complex 2
Fig. 6(a) and (b) show the ditopic recognition of Cl− and
CHCl3 inside the C3v symmetric cleft of L2. The amide nitrogen
distances of L2 between the two arms are: N2⋯N4 = 4.102,
N3⋯N4 = 4.158 and N2⋯N3 = 4.146 Å. The torsion angles
involving N1apicalCCNamide are in folded conformation with
angles of −69.72°, −68.36 and −64.01, for the three arms
composed of N2, N3, and N4, respectively, whereas the
torsion angles (Cphenyl–Camide–Namide–C) involving the
carbon atoms connecting the terminal pentafluorophenyl
Conclusions
In conclusion, fluorophenyl attached tripodal amide recep-
tors are selective towards binding of fluoride among the
halides. Tetrafluorophenyl attached tripodal amide is found
to be a better receptor for the recognition of fluoride com-
pared to pentafluorophenyl substituted triamide. A subtle
change in the attached moiety (tetrafluorophenyl vs.
pentafluorophenyl) shows a different conformation of the
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Fig. 4 MERCURY diagram showing (a) ball-stick model of L2; (b) amide N⋯N distances of tripodal arms of L2 showing C2v symmetric cleft, (c) 1-D
polymeric network of L2 with intra and intermolecular hydrogen bond distances. Non acidic hydrogen atoms are omitted for clarity. The distances
are given in Angstroms.
Table 2 Hydrogen bonding interactions of fluoride/chloride in 1 and 2
Table 3 Interatomic angles for the H-bonding interactions of the
encapsulated ions for 1 and 2
Interactions
H⋯A (Å)
D⋯A (Å)
<D–H⋯A (°)
Complexes
Atoms
Angle (°)
Complex 1
N(2)–H(2)⋯F(16)
N(3)–H(3)⋯F(16)
N(4)–H(4)⋯F(16)
C(28)–H(28)⋯F(16)
Complex 2
N(2)–H(2)⋯Cl(1)
N(3)–H(3)⋯Cl(1)
N(4)–H(4)⋯Cl(1)
C(28)–H(28)⋯Cl(1)
1.93
1.87
1.85
1.93
2.766(2)
2.703(2)
2.703(2)
2.907(3)
162
164
175
173
Complex 1
N(2)⋯F(16)⋯N(3)
N(3)⋯F(16)⋯N(4)
N(4)⋯F(16)⋯N(2)
N(2)⋯F(16)⋯C(28)
N(3)⋯F(16)⋯C(28)
N(4)⋯F(16)⋯C(28)
N(2)⋯Cl(1)⋯N(3)
N(3)⋯Cl(1)⋯N(4)
N(4)⋯Cl(1)⋯N(2)
N(2)⋯Cl(1)⋯C(28)
N(3)⋯Cl(1)⋯C(28)
N(4)⋯Cl(1)⋯C(28)
90.94
96.17
94.13
121.74
117.44
127.88
80.74
80.27
78.58
126.14
129.00
140.66
2.38
2.34
2.42
2.32
3.214(6)
3.187(6)
3.263(5)
3.300(7)
164
167
167
174
Complex 2
receptor. A C3v-symmetric cleft for tetrafluorophenyl and
C2v-symmetric cleft for pentafluorophenyl attached triamides
are achieved in the solid state. However, fluoride and
chloride complexes of triamide with the pentafluorophenyl
attached units clearly demonstrate the recognition of the
respective anion in the C3v symmetric cleft via different
non-bonding interactions like hydrogen bonding (N–H⋯X−,
C–H⋯X−), solvent⋯π and anion⋯π interactions, although
the native triamide does not possess such a symmetric cleft
in the solid state. Participation of a solvent molecule, CHCl3,
in the recognition process is also demonstrated in the solid
state study. Therefore a primary anion recognition element
(amide) and a suitably attached unit to the primary recogni-
tion unit and solvent interactions all have a profound effect
on controlling the overall anion recognition process. We are
currently probing new receptors with different electron
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Fig. 5 Single crystal X-ray structure of 1 showing encapsulation of F− in the cavity of L2 where chloroform is in short contact with the
pentafluorophenyl units (a); (b) spacefill model of (a). Non acidic hydrogen atoms and tetrabutylammonium cation are omitted for clarity.
Fig. 6 Single crystal X-ray structure of 2 showing encapsulation of Cl− in the cavity of L2 where chloroform is acting as a cap (a); (b) spacefill
model of (a). Non acidic hydrogen atoms and tetrabutylammonium cation are omitted for clarity.
deficient arene groups (as a secondary anion recognition
element) coupled with different primary anion recognition
elements for the selective recognition and extraction of
different anions.
and iodide were purchased from Sigma-Aldrich and were
used as received. Tetrahydrofuran (THF) was freshly distilled
over potassium and benzophenone. Triethylamine, dichloro-
methane and chloroform were distilled over calcium hydride
prior to use by the usual procedure. All solvents were
procured from Merck.
The ESI-MS experiment was carried out on a Water's QtoF
Model YA 263 mass spectrometer in positive ESI mode.
1H-NMR and 13C-NMR spectra were obtained on a 300 MHz
and 75 MHz Bruker DPX-300 MHz NMR spectrometer.
Experimental section
Materials
Tris-(2-aminoethyl)-amine, 2,3,4,5-tetrafluorobenzoyl chloride,
and tetrabutylammonium salts of fluoride, chloride, bromide
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Synthesis and characterization of N,N′,N″-tris[(2-amino-ethyl)-
2,3,4,5-tetrafluoro-benzamide] L1
room temperature for 10 minutes and warmed to 40 °C.
Then, the mixture was filtered at room temperature and
the filtrate was allowed to evaporate for crystallization at
4 °C. After 2 days, colorless single crystals of complex
[L2(Cl−)·CHCl3]·n-Bu4N+ (2) suitable for X-ray diffraction studies
were obtained in a 70% yield. 1H-NMR (300 MHz, CDCl3):
δ 0.99–1.02 (t, 3H, NCH2CH2CH2CH3, J = 7.2 Hz), 1.42–1.44
(m, 2H, NCH2CH2CH2CH3), 1.61–1.63 (m, 2H, NCH2CH2CH2CH3),
2.58 (t, 6H, NCH2CH2, J = 4.8 Hz), 3.18–3.22 (m, 2H,
NCH2CH2CH2CH3), 3.47 (t, 6H, NCH2CH2, J = 4.8 Hz), 9.71
(br, 3H, NH). Elemental analysis: calculated for C43H51ClF15N5O3:
C, 51.32; H, 5.11, N, 6.96 and experimental: C, 51.39; H, 5.06;
N, 6.88.
Tren, (1 mL, 6.7 mmol) was put in a 100 mL round bottomed
flask and dissolved in 30 mL of dry dichloromethane. About
3 mL (slight excess) of dry triethylamine was added to the
homogeneous mixture. The mixture was allowed to stir at
room temperature in a nitrogen atmosphere for 10 min.
2.92 mL (21 mmol) of 2,3,4,5-tetrafluorobenzoyl chloride was
dissolved in another 15 mL of dry dichloromethane and put
in a 50 mL pressure equalizing funnel. This solution was
added drop-wise for a period of 1 h under constant stirring at
room temperature. After the addition, the reaction mixture
was allowed to stir at room temperature in a nitrogen atmo-
sphere for another 10 h. The solution was washed with
saturated NaCl solution followed by (3 × 100) mL of distilled
water. The organic phase was separated, and dried over anhy-
drous sodium sulfate. Then the solvent was evaporated
in vacuo to yield the desired product as a pale brown solid.
The pale brown solid was re-dissolved in 100 mL of hot
CHCl3, and allowed to evaporate at room temperature to yield
the required product of L1 as a crystalline solid (3.9 g, 86%).
MS (ESI): 675.1 [M + H+].1H-NMR (300 MHz, CDCl3): δ 2.79
(s, 6H, NCH2), 3.58 (s, 6H, NCH2CH2), 7.04 (br, 3H, NH), 7.52
(m, 3H, Ar–CH). 13C-NMR (75.47 MHz, CDCl3): δ 38.2, 53.6,
112.7, 117.6, 138.9, 140.8, 142.3, 144.3, 145.6, 147.6, 148.9,
X-ray crystallography
The crystal data and details of the structural determination
refinement are summarized in Table 4. Crystals suitable for
single crystal X-ray diffraction studies were selected from the
mother liquor and immersed in paratone oil and then
mounted on the tip of a glass fiber and cemented using
epoxy resin. Intensity data for the crystals L1, L2, 1 and 2
were collected using MoKα (λ = 0.7107 Å) radiation on a
Bruker SMART APEX II diffractometer equipped with a CCD
area detector. The data integration and reduction were
processed with SAINT16a software provided with the software
package of SMART APEX II. An empirical absorption correc-
tion was applied to the collected reflections with SADABS.16b
The structures were solved by direct methods using
SHELXTL16c and were refined on F2 by the full-matrix least-
squares technique using the SHELXL-9716d program package.
Graphics were generated using PLATON16e and MERCURY
1.4.16f The non-hydrogen atoms were refined anisotropically
until convergence. In the cases of L1 and L2 and complex 2
the hydrogen atoms were geometrically fixed at idealized
positions. In the case of complex 1, all the hydrogen atoms were
located from the difference Fourier map and refined isotropically.
The routine SQUEEZE was applied to intensity data of complex 2
to take into account the disordered solvent molecules. The
number of electrons found in the solvent accessible void is
close to that expected for one CHCl3 molecule in the unit cell.
Since we could not assign a proper disorder model for the
tetrabutyl ammonium group, we isotropically refined dis-
ordered C31 and C32 atoms. The data quality of all four struc-
tures is poor, because of the small size of the crystals having
weak diffraction. However, these are the best set of data avail-
able after several attempts of data collection from the crystals
obtained from several batches. CCDC-973404 (L1), 701762 (L2),
701764 (1) and 710730 (2) contain the supplementary crystal-
lographic data for this paper.
161.0. Elemental analysis calculated for
C27H18F12N4O3:
C, 48.08; H, 2.69; N, 8.31 and experimental: C, 47.94; H, 2.65;
N, 8.25.
Crystallization of L1 and L2
Both L1 (100 mg) and L2 (100 mg) were dissolved in 40 mL
of hot CHCl3 separately and allowed to evaporate at 4 °C.
Colourless crystals suitable for X-ray diffraction studies were
obtained after 2 days.
[L2(F−)·CHCl3]·n-Bu4N+ (1)
60 mg (0.08 mmol) of L2 was dissolved in 30 ml of CHCl3
and 63 mg (0.24 mmol) of n-Bu4N+F− was added. The resulting
clear colorless solution was slightly warmed and filtered. The
filtrate was kept for crystallization at 4 °C. Colorless crystals of
complex [L2(F−)·CHCl3]·n-Bu4N+ (1) suitable for X-ray diffraction
1
studies were obtained in an 80% yield within 2 days. H-NMR
(300 MHz, CDCl3): δ 1.04 (t, 3H, NCH2CH2CH2CH3, J = 7.2 Hz),
1.44 (m, 2H, NCH2CH2CH2CH3), 1.64 (m, 2H, NCH2CH2CH2CH3),
2.57 (t, 6H, NCH2CH2, J = 4.8 Hz), 3.21 (m, 2H, NCH2CH2CH2CH3),
3.44 (t, 6H, NCH2CH2, J = 4.8 Hz), 11.87 (br, 3H, NH). Elemental
analysis: calculated for C43H51F16N5O3: C, 52.17; H, 5.19; N, 7.08
and experimental: C, 52.11; H, 5.12; N, 6.95.
1H-NMR titration studies
Complex [L2(Cl−)·CHCl3]·n-Bu4N+ (2)
All 1H-NMR titration experiments were conducted on a
Bruker 300 spectrometer at 298 K in CDCl3. The initial con-
centration of L1/L2 was ~5 mM. Aliquots of anions were
added from a stock solution of anion (~50 mM). Each
60 mg (0.08 mmol) of L2 was dissolved in 25 ml of CHCl3
and then 67 mg (0.24 mmol) of n-Bu4N+Cl− was added to the
above solution. The reaction mixture was further stirred at
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Table 4 Crystallographic data and structural refinement for compounds L1 and L2 and complexes 1 and 2
Compound reference
L1
L2
Complex 1
Complex 2
Chemical formula
Formula mass
Crystal system
a/Å
b/Å
c/Å
α/°
β/°
C27H18F12N4O3
674.45
C27H15F15N4O3
728.43
C44H52Cl3F16N5O3
1109.26
Triclinic
11.8227(9)
13.8754(10)
15.4686(11)
86.2310(10)
76.2490(10)
86.8740(10)
2457.5(3)
100(2)
¯
P1
2
21 679
7667
0.0424
0.0390
0.0866
0.0612
0.0974
1.025
701764
C44H52Cl4F15N5O3
1125.71
Monoclinic
14.4149(8)
16.8287(10)
22.6106(12)
90.00
101.373(2)
90.00
5377.3(5)
100(2)
P2(1)/c
4
40 806
7147
0.0380
0.0987
0.2871
0.1168
Monoclinic
10.8910(17)
17.196(3)
14.431(2)
90.00
103.322(4)
90.00
2629.9(7)
293(2)
P2(1)/c
4
15 142
2531
0.0667
0.0391
0.1005
0.0533
0.1123
1.012
973404
Monoclinic
16.963(3)
13.596(2)
12.654(2)
90.00
106.632(2)
90.00
2796.3(8)
100(2)
P2(1)/c
4
17 817
3013
0.0640
0.0359
0.0846
0.0599
0.0973
1.021
701762
γ/°
Unit cell volume/Å3
Temperature/K
Space group
No. of formula units per unit cell, Z
No. of reflections measured
No. of independent reflections
Rint
Final R1 values (I > 2σ(I))
Final wR(F2) values (I > 2σ(I))
Final R1 values (all data)
Final wR(F2) values (all data)
Goodness of fit on F2
CCDC
0.3073
1.009
710730
titration was performed by 13–15 measurements. The associa-
tion constants, K, were calculated by fitting the change in the
–NH chemical shift with a 1 : 1 association model with non-
linear least square analysis. WINEQNMR 2.0 was used for the
evaluation of binding constants.17 Association constants are
calculated by the following equation18
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Δδ = {([A]0 + [L]0 + 1/K)
(([A]0 + [L]0 + 1/K)2[L]0[A]0)1/2}Δδmax/2[L]0.
Acknowledgements
PG thanks the Department of Science and Technology, India
for financial support through a Swarnajayanti Fellowship.
Crystallography was performed at the DST-funded National
Single Crystal X-ray Diffraction Facility at the Department of
Inorganic Chemistry, IACS. SS and BA would like to acknowl-
edge CSIR, New Delhi, India for Fellowship.
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4804 | CrystEngComm, 2014, 16, 4796–4804
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