Synthetic ionophores. Part 18: Ag+ selective trithiabenzena- and dithiabenzenapyridinacyclophanes

Article abstract of DOI:10.1039/a706861a

The phase transfer catalysed nucleophilic displacement of 1,3-bis(bromomethyl)benzene, 2-methoxy-5-methyl-1,3-bis(bromomethyl)benzene (2) and 1,4-bis(bromomethyl)benzene with 2-mercaptoethanol gives the respective diols 3,4 and 12 (80-85%), which undergo

Full text of DOI:10.1039/a706861a

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Synthetic ionophores. Part 18: Ag؉ selective trithiabenzena- and
dithiabenzenapyridinacyclophanes1
Subodh Kumar,* Maninder Singh Hundal, Geeta Hundal, Palwinder Singh,
Vandana Bhalla and Harjit Singh*
Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India
The phase transfer catalysed nucleophilic displacement of 1,3-bis(bromomethyl)benzene, 2-methoxy-5-
methyl-1,3-bis(bromomethyl)benzene (2) and 1,4-bis(bromomethyl)benzene with 2-mercaptoethanol gives
the respective diols 3, 4 and 12 (80–85%), which undergo intermolecular cyclodehydrochlorination with
thiodiglycolyl dichloride and pyridine-2,6-dicarbonyl dichlorideؒHCl to provide m-phenylene (7–10)
and p-phenylene (13–14) based crownophanes. The single crystal X-ray structures of crownophanes 8
and 13 and their NMR studies show that the m-phenylene and p-phenylene rings remain in plane and
perpendicular to the macrocyclic ring both in solution and solid phases. These crownophanes offer
three soft coordinating sites (3 × S or 2 × S and 1 N) conducive to complexation with Agϩ and the steric
restrictions imposed by m- and p-phenylene rings restrict 2:1 (L:M) sandwich complexation required
for complexation with the borderline soft Pb2؉ cation. The crownophanes 7 and 9 extract Ag؉ 172 and
602 times, respectively, more than Pb2؉.
286 and 12 (85%), mp 58 ЊC, m/z 258, respectively. The slow
Introduction
addition of thiodiglycolyl dichloride to a solution of 3 contain-
ing KF (anhyd.) as base and Bu4NϩHSO4Ϫ as catalyst provided
macrocycle 7 (40%), liquid, m/z 372. Similarly, reactions of
diols 4 and 12 with thiodiglycolyl dichloride under these PTC
conditions gave crownophanes 8 (35%), mp 100 ЊC, m/z 416 and
12 (10%), mp 62 ЊC, m/z 372, respectively. The diols 3, 4 and 12
failed to react with pyridine-2,6-dicarbonyl dichlorideؒHCl
under the above PTC conditions. However, on reacting diols 3
and 12 with 6ؒHCl by using K2CO3 (anhyd.) as base, the
crownophanes 9 (35%), mp 147 ЊC, m/z 389, and 14 (25%),
mp 197 ЊC, m/z 389, respectively, could be formed. The reaction
of diol 4 with 6ؒHCl under these conditions gave 10 (35%), mp
197 ЊC, m/z 433 along with the 2:2 stoichiometric product
15 (10%), mp 180 ЊC, m/z (FAB) 867 (Mϩ ϩ 1). A 2:2
stoichiometric reaction might be triggered in the initial 1:1
stoichiometric intermediate by steric inhibition of the para-
substituents of the phenylene ring, in its cyclization.
The development of fast estimation, removal and separation
techniques for precious and toxic silver and the use of silver
complexes in photographic materials and their potential use
in cancer radioimmunotherapy has drawn the attention of
supramolecular chemists towards the design, synthesis and
evaluation of silver selective ionophores. For designing such
ionophores, the optimum requirement of 2–4 soft (S or N)
ligating sites2–7 preorganized in a three-dimensional system has
been emphasized. In the reported Agϩ selective ionophores, the
presence of ether units8–12 responsible for binding towards hard
alkali, alkaline earth and borderline Pb2ϩ cations and the possi-
bility of the formation of sandwich or polymeric complexes13–15
creating significant binding towards most soft metal ions, cause
lowering of Agϩ selectivities. We argued that in such hosts, the
absence of hard (ether) ligating sites and the presence of stereo-
chemical or structural features which could inhibit their sand-
wich or polymeric complexation requiring >1:1 stoichiometric
host–guest interaction could further enhance the Agϩ selectiv-
ity even against the similar sized Pb2ϩ cation. We envisaged that
to achieve such an inhibition, the crownophane designs 7–10,
13 and 14 could easily adopt the edge-on arrangement of m-
and p-phenylene rings with respect to the plane of the macrocy-
clic ring especially during complexation. Here, we have reported
the synthesis and evaluation of these ionophores and have
found that m-phenylene derivatives 7 and 9 show a high order
of selectivity for Agϩ.
Conformational analysis
The X-ray crystal structure of crownophane 8 (Fig. 1, Table 1)
shows that the m-phenylene ring remains in the mean plane of
the macrocyclic ring. The substituent O᎐Me seems to play a
dominant role in determining the conformation of the macro-
ring. The bond O5᎐C18 is almost perpendicular to the phenyl-
ene ring (C11᎐C16᎐O5᎐C18 being 96.7Њ). The torsion angle
S2᎐C10᎐C11᎐C16 is 86.2(3)Њ and consequently both S2᎐C10
and C18᎐O5 bonds point towards the same side with respect to
the phenylene ring (Fig. 1). To avoid steric crowding the S1᎐C1
bond points in a direction opposite to the C18᎐O5 bond, the
torsion angle C16᎐C15᎐C1᎐S1 being 97.8(3)Њ. The torsion
angle studies indicate that out of the four possible 1,4-thiaoxa
units (O᎐CH2᎐CH2᎐S), three are antiperiplanar [torsion angles
173.8(2)–177.1(2)Њ], whereas the fourth one (O4᎐C8᎐C9᎐S3) is
synclinal [59.7(3)Њ] about the C᎐C bond. The torsion angles
about the C᎐O bond are antiperiplanar and about the C᎐S
bond they are synclinal with the exception of C9᎐S2᎐C10᎐C11
which is antiperiplanar. In the segments O1᎐C4᎐O2 and
O3᎐C7᎐O4, the carbonyl oxygens O2 and O4 point towards
opposite sides of the macro-ring mean plane. The major differ-
ence in the conformation angles in the two halves of the macro-
ring is that torsion angle C2᎐S1᎐C1᎐C15 is synclinal whereas
Results and discussion
Synthesis
For the synthesis of crownophanes 7–10, 13 and 14, the two
step approach involving the reactions of appropriate dihalides
with 2-mercaptoethanol to form diols (3, 4 and 12) followed by
their intermolecular cyclodehydrochlorination with appropriate
diacid dichlorides was adopted. The phase transfer catalysed
(K2CO3–DMF–Bu4NϩHSO4Ϫ) nucleophilic displacement of
1,3-bis(bromomethyl)benzene (1) with 2-mercaptoethanol gave
diol 3 (80%), m/z 258. Similarly, reactions of 2-methoxy-5-
methyl-1,3-bis(bromomethyl)benzene (2) and 1,4-bis(bromo-
methyl)benzene (11) with 2-mercaptoethanol under these phase
transfer catalysis (PTC) conditions gave diols 4 (80%), m/z
J. Chem. Soc., Perkin Trans. 2, 1998
925

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R2
R2
O
O
X
Cl
Cl
R1
S
S
R1
X
S
S
5 X = CH2SCH2
6 X = 2,6-Py
O
O
OH
HO
3 R1 = R2 = H
4 R1 = OMe, R2 = Me
O
O
7 R1 = R2 = H, X = CH2SCH2
8 R1 = OMe, R2 = Me, X = CH2SCH2
9 R1 = R2 = H, X = 2,6-Py
10 R1 = OMe, R2 = Me, X = 2,6-Py
SH
OH
R2
Fig. 1 ORTEP view of crownophane 8. Thermal ellipsoids are drawn
with 50% probability and hydrogen atoms are drawn with arbitrary
small isotopic thermal parameters for the sake of clarity.
Br
1 R1 = R2 = H
R1
Br
2 R1 = OMe, R2 = Me
Table 1 Selected bond distances and angles for 8 and 13
O
O
O
Bond
distances/Å
Bond
angles/Њ
N
S
O
S
Crownophane 8
CH3
OCH3
CH3O
CH3
S(1)᎐C(2)
S(1)᎐C(1)
S(3)᎐C(6)
S(3)᎐C(5)
S(2)᎐C(9)
S(2)᎐C(10)
O(1)᎐C(4)
O(1)᎐C(3)
O(2)᎐C(4)
O(4)᎐C(7)
O(3)᎐C(7)
O(3)᎐C(8)
O(5)᎐C(16)
O(5)᎐C(18)
1.798(3)
1.821(3)
1.793(3)
1.796(3)
1.811(3)
1.811(3)
1.334(4)
1.455(3)
1.199(3)
1.195(3)
1.333(3)
1.453(3)
1.394(3)
1.429(4)
C(2)᎐S(1)᎐C(1)
C(6)᎐S(3)᎐C(5)
C(9)᎐S(2)᎐C(10)
C(4)᎐O(1)᎐C(3)
C(7)᎐O(3)᎐C(8)
C(3)᎐C(2)᎐S(1)
O(1)᎐C(3)᎐C(2)
O(2)᎐C(4)᎐O(1)
O(2)᎐C(4)᎐C(5)
O(1)᎐C(4)᎐C(5)
C(4)᎐C(5)᎐S(3)
C(7)᎐C(6)᎐S(3)
O(4)᎐C(7)᎐O(3)
O(4)᎐C(7)᎐C(6)
O(3)᎐C(7)᎐C(6)
O(3)᎐C(8)᎐C(9)
C(8)᎐C(9)᎐S(2)
C(11)᎐C(10)᎐S(2)
C(16)᎐O(5)᎐C(18)
C(15)᎐C(1)᎐S(1)
100.86(13)
100.96(13)
102.86(14)
117.7(2)
116.0(2)
113.1(2)
106.8(2)
124.1(3)
126.7(3)
109.2(3)
115.0(2)
115.2(2)
124.0(3)
126.7(3)
109.3(2)
109.2(2)
117.6(2)
109.5(2)
115.5(2)
113.9(2)
S
O
O
O
O
S
N
15
S
S
S
S
+
5/6
O
O
X
OH
OH
12
O
O
SH OH
13 X = CH2SCH2
14 X = 2,6-Py
Br
Br
11
Crownophane 13
C9᎐S2᎐C10᎐C11 is antiperiplanar, which may be attributed to
the steric factors. Three thioether units make a triangle with
S1᎐S2, S2᎐S3 and S3᎐S1 placed at 7.13, 6.72 and 7.72 Å.
In the p-cyclophane based macrocycle 13 (Fig. 2, Table 1),
the phenylene ring and the ᎐CH2᎐ groups attached at the para-
positions form one plane and the π-electron cloud of the
phenylene ring is almost perpendicular to the macro-ring. Both
the sulfur atoms are so oriented that the two bonds C1᎐S1 and
C10᎐S2 are on the same side of the phenylene ring, in contrast
to m-cyclophane where these bonds were on the opposite sides
of the phenylene ring mean plane due to steric crowding caused
by the OMe substituent. Out of the four 1,4-thiaoxa units,
three are antiperiplanar and one (O1᎐C4᎐C5᎐S3) is synclinal
about the C᎐C bond (Fig. 2). The two carbonyl oxygens O2
and O4 are present on opposite sides of the marco-ring mean
plane, which is also observed in the case of m-cyclophane. The
torsion angles about C᎐S are all synclinal and antiperiplanar
about C᎐O except for C4᎐O1᎐C3᎐C2 which is synclinal. This
difference in torsion angles about the C᎐O bonds gives an
extended conformation to one side of the macro-ring and
introduces a kink at the C2᎐C3 bond. The three thioether units
make a triangle with S1᎐S2, S2᎐S3 and S3᎐S1 placed at 7.15,
7.86 and 6.70 Å.
S(1)᎐C(2)
S(1)᎐C(1)
S(3)᎐C(6)
S(3)᎐C(5)
S(2)᎐C(9)
S(2)᎐C(10)
O(1)᎐C(4)
O(1)᎐C(3)
O(2)᎐C(4)
O(4)᎐C(7)
O(3)᎐C(7)
O(3)᎐C(8)
O(5)᎐C(16)
O(5)᎐C(18)
1.792(5)
1.808(6)
1.792(5)
1.803(5)
1.801(5)
1.810(5)
1.343(6)
1.437(6)
1.192(6)
1.201(6)
1.327(6)
1.451(6)
C(2)᎐S(1)᎐C(1)
C(6)᎐S(3)᎐C(5)
C(9)᎐S(2)᎐C(10)
C(4)᎐O(1)᎐C(3)
C(7)᎐O(3)᎐C(8)
C(3)᎐C(2)᎐S(1)
O(1)᎐C(3)᎐C(2)
O(2)᎐C(4)᎐O(1)
O(2)᎐C(4)᎐C(5)
O(1)᎐C(4)᎐C(5)
C(4)᎐C(5)᎐S(3)
C(7)᎐C(6)᎐S(3)
O(4)᎐C(7)᎐O(3)
O(4)᎐C(7)᎐C(6)
O(3)᎐C(7)᎐C(6)
O(3)᎐C(8)᎐C(9)
C(8)᎐C(9)᎐S(2)
C(11)᎐C(10)᎐S(2)
C(16)᎐O(5)᎐C(18)
C(15)᎐C(1)᎐S(1)
102.5(2)
101.0(3)
101.8(2)
117.0(4)
115.6(4)
113.2(3)
111.8(4)
124.2(5)
124.7(6)
111.2(6)
113.5(3)
115.4(4)
123.6(5)
125.6(6)
110.7(5)
107.6(4)
112.0(4)
114.8(3)
In 1H NMR spectra, the diols 3, 4 and 12 show benzylic CH2,
OCH2 and SCH2 signals at δ 3.70 (s), 3.63 (t) and 2.60 (t),
respectively.16 In macrocycles 7 and 8, these signals appear at
3.74, 4.20 and 2.62 respectively and SCH2CO appears at 3.36.
926
J. Chem. Soc., Perkin Trans. 2, 1998

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Table 2 Distances and angles between the three coordinating sites in crownophanes 7–10 and 13–14 as calculated from forcefield calculations
Distances/Å
Angles/Њ
Macrocycle
S1᎐S2
S2᎐S3/N
S3᎐S1/N
S1᎐S2᎐S3(N)
S2᎐S3(N)᎐S1
S3(N)᎐S1᎐S2
7
8
13
9
10
14
6.57
6.49
7.09
7.24
7.28
7.78
5.51
5.51
3.91
5.31
5.30
5.93
6.23
6.24
5.08
4.99
5.05
5.03
61.40
62.49
44.27
43.59
43.91
40.34
67.69
66.33
103.00
89.28
89.39
90.00
50.91
51.04
32.40
47.13
46.70
49.66
Fig. 2 ORTEP view of crownophane 13. Thermal ellipsoids are drawn
with 50% probability and hydrogen atoms are drawn with arbitrary
small isotopic thermal parameters for the sake of clarity.
But in the p-crownophane 13, SCH2CH2 (∆δ Ϫ0.10), SCH2CO
(∆δ Ϫ0.20) and OCH2 (∆δ Ϫ0.42) signals are shifted upfield,
benzylic CH2 is not affected and ArH appears as a sharp
4H singlet. This upfield shift of signals in 13 in comparison
with 7 and 8 clearly shows that in 13, the p-phenylene ring is
oriented perpendicular to the plane of the macrocycle, whereas
the m-phenylene rings of 7 and 8 are in the plane of the crown
ring. The planar p-phenylene ring of 12 does not show such an
effect.
Fig. 3 Energy minimized (DTMM 2.0) structures of macrocycles 7–
10, 13 and 14
The NOESY experiments on 8 show intense cross peaks
between OMe and OCH2, and between OMe and SCH2CO
with cross peak intensities of 0.37 and 0.17, respectively. These
results show the proximity of OCH2 and SCH2CO units to the
OMe unit and confirm the presence of an OMe group in the
cavity of macrocyclic ring and thus the in-plane position of the
m-phenylene and macrocyclic rings. Furthermore, NOESY
experiments on 13 show the cross peaks between OCH2 and
ArH, and between SCH2CO and ArH with cross peak inten-
sities of 0.43 and 0.15, respectively. The appearance of a singlet
for ArH and their high cross peak volumes further support the
perpendicular placement of the p-phenylene ring with respect
to the macrocyclic ring. Hence, in trithiocrownophanes 7, 8 and
13, the m-phenylene ring lies in plane and the p-phenylene ring
acquires a position perpendicular to the macrocyclic ring.
These results are further supported by molecular modelling.
The force field energy minimization17 by DTMM 2.0 (Fig. 3)
shows that in compounds 7 and 8, the m-phenylene rings remain
more or less in-plane with the mean plane of the macrocyclic
ring and three thioether units are directed towards the cavity
resulting in a triangle with three angles at 51 0.1, 62 0.5 and
67 0.6Њ and three S᎐S distances at 6.57, 5.51 and 6.23 Å for 7
and 6.49, 5.51 and 6.24 Å for 8 (Table 2). In the compound 13,
the p-phenylene ring remains perpendicular to the mean plane
of the macrocyclic ring. The S᎐S distance between two benzylic
thioethers (7.09 Å) is much larger than the other two S᎐S
distances (3.91 and 5.08 Å, Table 2).
Fig. 4 Overlap of energy minimized conformations (–––) and X-ray
crystal structure (——) for crownophanes 8 (a) and 13 (b). Graphics
drawn by SHELXTL-Plus 95.
It may be observed that the results of both X-ray and energy
minimization studies are corroborative of in-plane and per-
pendicular positions of m-phenylene in 8 and p-phenylene in 13
but some contradictions are also revealed. In crownophane 8,
the crystal structure reveals that C10᎐S2 and O5᎐C18 bonds lie
on one side and C1᎐S1 on the opposite side of the m-phenylene
ring, whereas energy minimizations put C10᎐S2 and C1᎐S1 in
one direction. This difference in the direction of C᎐S bonds
causes the rest of the ring to be less extended than is observed
in the X-ray structure [Fig. 4(a)]. Similarly, crownophane 13
exhibits a less extended conformation [Fig. 4(b)] by energy
minimization than is observed by X-ray diffraction. These dif-
ferences are not unexpected as the X-ray crystal structures are
also dependent on lattice interactions and energy minimizations
represent isolated molecules. However, both the studies, signifi-
J. Chem. Soc., Perkin Trans. 2, 1998
927

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Table 3 Cation extraction (%) profile of crownophanes 7–10, 13 and 14
Crownophane Liϩ
Naϩ
Kϩ
Mg2ϩ
Ca2ϩ
Sr2ϩ
Ba2ϩ
Tlϩ
Pb2ϩ
Agϩ
Agϩ/Pb2ϩ
Agϩ/Tlϩ
7
8
13
9
10
14
0.016
—
—
0.086
0.084
0.064
—
—
0.05
0.092
0.064
0.03
0.04
—
—
0.01
0.021
0.04
—
—
—
0.065
0.025
0.03
0.07
0.027
0.02
0.022
0.033
0.063
—
—
0.11
0.064
0.039
0.07
0.09
0.074
—
0.074
0.031
0.074
0.09
—
0.09
0.25
4.24
1.51
0.39
0.75
1.06
0.10
0.76
15.2
67.30
73.38
57.2
60.28
82.34
71.61
172.6
97.84
53.96
602.8
108.34
4.71
747.8
—
635.6
241.1
19.4
47.4
cantly, lead to similar overall conformations of the phenylene
rings with respect to the macrocyclic ring.
In crownophanes 9, 10 and 14, the appearance of OCH2,
SCH2 and ArCH2 1H NMR signals downfield of the corres-
ponding signals in trithioether derivatives by 0.2–0.4, 0.1–0.3
and 0.1–0.2 ppm, respectively, points to their relatively rigid
nature. The comparison of the 1H NMR spectrum of 1:1 stoi-
chiometric product 10 with the 2:2 stoichiometric product 15
shows ArCH2 (∆δ ϩ0.09) and SCH2 (∆δ ϩ0.20) signals down-
field in the case of 10 and indicates a relatively more rigid struc-
ture for 10 than for its dimer 15. In 14, the OCH2 signals appear
upfield (∆δ Ϫ0.16) of those in 9 and 10. So, unlike trithio-
ether based crownophanes 7, 8 and 13, the pyridine based
crownophanes 9, 10 and 14 lack orderly placement of 1H NMR
signals and hence their conformational analysis could not be
deduced from these data. However, force field energy minimiz-
ations (Fig. 3) show that in all the pyridine based macrocycles,
either pyridine or the phenylene ring lies perpendicular to the
plane of the macrocyclic ring. Again, in both 9 and 10, the m-
phenylene ring lies in the plane of the macrocyclic ring and the
pyridine ring is more or less perpendicular to this plane. In
the case of 14, the pyridine ring is in the mean plane of the
macrocyclic ring and the p-phenylene ring is perpendicular to
it. Further analysis of the distances and angles between two
thioether and one pyridine units shows that 9, 10 and 14 have
similar placement of two thioether units and pyridine N with
respect to each other.
Fig. 5 Extraction (%) of AgI and PbII by crownophanes 7–10, 13 and
14
Pb2ϩ by 8 in comparison with 7 could be attributed to the
cooperative participation of the methoxy group in complex-
ation with cations. As expected, the methoxy unit shows better
interaction with dipositive Pb2ϩ than monopositive Agϩ and
therefore Agϩ/Pb2ϩ selectivity in 8 is lowered in comparison
with 7. In 13, the p-phenylene ring places the two thioether
units relatively far apart and causes lower extraction and select-
ivity for Agϩ.
In the three-dimensional structure of the macrocycle 9 the
pyridine ring is perpendicular to the m-phenylene ring. But PyN
is placed only 5 Å units away from both the thioether ᎐S᎐ atoms
and this arrangement leads to 602 times more extraction of Agϩ
(60.28%) than Pb2ϩ (0.1%, Table 3). The conformation of
macrocycle 10 is similar to that of 9, but its cavity is filled by the
methoxy group. It seems that the methoxy group participates in
complexation and thus macrocycle 10 shows increased extrac-
tion of Agϩ, Pb2ϩ and Tlϩ by nearly 1.4, 7.6 and 16 times,
respectively, in comparison with 9, thereby lowering the Agϩ/
Pb2ϩ selectivity to 108. In the macrocycle 14, the pyridine ring is
in the plane of the macro-ring and is more available for com-
plexation than in the case of 9 and 10 and shows some increase
in extraction of Agϩ (71.61%), but extraction of Pb2ϩ is signifi-
cantly increased to 15.2% from only 0.10% in the case of 9.
As a result, 14 shows only a marginal Agϩ vs. Pb2ϩ selectivity
(Fig. 5).
Binding characteristics
Extraction18 and transport19 studies. As the process of ligand
facilitated transport of cations across a non-polar membrane
has relevance to the development of separation techniques for
cations, the extraction (complexation) and transport (com-
plexation/decomplexation) profiles of macrocycles 7–10 and
13–14 towards Agϩ, Pb2ϩ, Tlϩ, alkali metal cations (Liϩ, Naϩ,
Kϩ) and alkaline earth cations (Mg2ϩ, Ca2ϩ, Sr2ϩ, Ba2ϩ) by
using chloroform as an apolar membrane have been deter-
mined. In thioether based macrocycles, 1:1 and/or 2:2 stoi-
chiometric complexation is facilitated in the solid phase but
in the solution phase the 1:1 complexations are more pro-
nounced. So for discussion of all the extraction and transport
results 1:1 stoichiometric complexation of macrocycles with
cations has been assumed.
Amongst these designs, m-phenylene derivatives 7 and 9
show the highest degree of binding selectivity for Agϩ though
their extraction character is lower. In macrocycles 8 and 10,
the possible participation of the methoxy group increases the
extraction of all the cations but their three-dimensional arrays
include a much more pronounced increase in the extraction of
Pb2ϩ and Tlϩ, and Agϩ selectivities are lowered. Furthermore,
both p-crownophane derivatives 13 and 14 show much lower
Agϩ/Pb2ϩ selectivity than their m-phenylene counterparts 7
and 9.
The macrocycles 7, 8 and 13 (3 × ᎐S᎐) and 9, 10 and 14 (2 ×
᎐S᎐ and PyN) possess three soft ligating sites and two relatively
non-participating ester oxygens. The discussion of the iono-
phore character of these macrocycles is primarily based on
three soft ligating sites as, in their 13C NMR titrations with Agϩ,
the participation of only three soft sites is evident.
These macrocycles with the exception of 14 show significant
Agϩ/Pb2ϩ extraction selectivity (Table 3, Fig. 5). The macrocy-
cle 7 extracts 172 times more silver picrate (67.30%) than Pb2ϩ
(0.39%) and 8 shows relatively enhanced extraction of both
Agϩ (73.3%) and Pb2ϩ (0.76%) resulting in lowering of Agϩ vs.
Pb2ϩ selectivity to 98. The alkali, alkaline earth and Tlϩ cations
are extracted only marginally. p-Crownophane 3 shows lower-
ing in both extraction of Agϩ (57.2%) and Agϩ vs. Pb2ϩ select-
ivity. The m-phenylene crownophanes 7 and 8 have similar
conformations, but the higher degree of extraction of Agϩ and
The transport rates for Pb2ϩ picrate could not be determined
because of its significant leakage across chloroform.20 Since
amongst the cations studied here, after Agϩ, the most efficiently
transported cation is Tlϩ, selectivities have been presented with
respect to Tlϩ and for other cations these are fairly high (Table
4). The trithioether macrocycles 7, 8 and 13 transport Agϩ at
similar rates. But 8, in which the methoxy group can interact
with Tlϩ, shows the lowest selectivity. Amongst pyridine based
928
J. Chem. Soc., Perkin Trans. 2, 1998

View Article Online
Table 4 Transport (10Ϫ8 mol/24 h) profile of crownophanes 7–10, 13 and 14
Crownophane Liϩ
Naϩ
Kϩ
Mg2ϩ
Ca2ϩ
Sr2ϩ
Ba2ϩ
Tlϩ
88.3
128.2
44.0
43.71
297.0
227.7
Agϩ
Agϩ/Tlϩ
7
8
13
9
76.7
50.5
13.6
9.21
14.6
8.19
118.7
106.8
13.4
7.63
14.47
16.23
26.0
68.6
15.1
11.6
11.1
21.3
30.4
71.7
14.2
5.08
10.78
12.72
40.8
55.4
7.2
6.00
34.9
13.7
43.7
66.2
8.5
3.60
10.3
11.8
51.8
63.6
18.4
3.35
4.29
31.2
3266.2
3110.3
3411.1
4509.6
1279.1
1498.4
37
24
78
103
4.3
10
14
6.6
Table 5 Metal picrate induced 13C NMR coordination shifts (∆δC) of crownophanes 7, 8 and 13
Me
SCH2
SCH2
SCH2
OMe
OCH2
ArC
ArC
ArC
0.63
ArC᎐O
C᎐O
᎐
7ؒAgϩ
7ؒPb2ϩ
7ؒSr2ϩ
—
—
—
1.78
Ϫ0.01
1.80
Ϫ0.05
0
0.88
0.48
0.51
0.02
1.70
Ϫ0.54
0.07
0.05
—
—
—
Ϫ0.74
0.22
0.23
0.22
Ϫ0.99
0.03
0.05
0.04
Ϫ0.08
0.02
0.04
0.78
Ϫ0.01
0
0.08
0
Ϫ0.68
0
Ϫ0.01
0.02
—
—
—
—
Ϫ0.27
0.02
0.01
Ϫ0.01
0.40
0.02
0.05
0.03
Ϫ0.01
0.05
0.09
—
0.51
0.03
0.05
0.04
Ϫ0.05
Ϫ0.01
0.02
2.86
0.04
0.05
0.05
2.09
0.03
0.04
0.02
0.01
Ϫ0.01
Ϫ0.19
0.02
0.02
0.02
—
—
—
—
Ϫ0.05
Ϫ0.06
0.35
0.03
0.05
—
—
—
—
—
7ؒNaϩ
8ؒAgϩ
—
Ϫ0.01
2.33
0.04
0.06
0.06
0.99
0.02
0.06
Ϫ0.02
—
0
Ϫ0.10
0.02
0.03
0.05
—
—
—
0.19
0.02
Ϫ0.17
Ϫ0.77
—
—
—
0.28
0.06
0.03
0.03
0.61
0.02
0.03
0.01
8ؒPb2ϩ
8ؒSr2ϩ
8ؒNaϩ
13ؒAgϩ
13ؒPb2ϩ
13ؒSr2ϩ
13ؒNaϩ
1.17
Ϫ0.24
Ϫ0.23
Ϫ0.23
—
—
0.02
The m-phenylene crownophanes, 7 and 8, show a significant
downfield shift for three SCH2 carbon signals. This shift is more
pronounced in 8, which has been found to be a better complex-
ing agent than 7 in extraction experiments (Table 5). The par-
ticipation of OMe is also evident from the downfield shift of the
OMe NMR signal. The OCH2 signals also experience the effect
of Agϩ binding and are shifted upfield. This could be attributed
to the high electron density of Agϩ and its proximity to OCH2
units. In macrocycle 13, again SCH2 signals are shifted down-
field but OCH2 remains almost at the same position. The anal-
ysis of the DTMM based conformation of 13 shows that in
the 13–Agϩ complex, Agϩ should be placed in line with p-
phenylene thioether units and would be quite far from the
OCH2.
The addition of Agϩ picrate to a solution of crownophane 9
causes separation of a solid product and so NMR monitoring
of the complexation could not be carried out. But in the case of
10 (Table 6), as expected, SCH2 and OCH3 signals are shifted
downfield and the OCH2 signal is shifted upfield. Also, the par-
ticipation of the OMe unit is more effective in 10 than in 8.
However, due to the difficulty in differentiation of aryl and
pyridine signals, the participation of pyridine could not be
determined.
In conclusion, m-phenylene (7–10) and p-phenylene (13–14)
based crownophanes offer three soft coordinating sites (3 × S
or 2 × S and 1 N) conducive to complexation with Agϩ and the
steric restrictions imposed by m- and p-phenylene rings restrict
2:1 (L:M) sandwich complexation required for complexation
with the soft Pb2ϩ cation. These structural features induce high
Agϩ/Pb2ϩ selectivities. But in crownophanes 8 and 10, the pres-
ence of a hard ether ligating unit adversely affects the Agϩ/Pb2ϩ
selectivity.
Fig. 6 Plot of extraction (%) vs. transport of crownophanes 7–10, 13
and 14
ionophores, 9 transports Agϩ most efficiently and is the best
ionophore with the highest efficiency and selectivity amongst
all the six macrocycles discussed here. In parallel with the
extraction results, 10 and 14, which show highest extraction for
Tlϩ, also show the highest transport efficiencies and lead to only
marginal Agϩ/Tlϩ selectivities. Furthermore, amongst all these
compounds, the crownophanes 8 and 10 bearing methoxy units
show the lowest selectivities which further confirms the more
effective participation of the methoxy group in binding with
cations other than Agϩ. Also, the comparison of extraction and
transport results of Agϩ (Fig. 6) shows that with these macro-
cycles more than 60% extraction of Agϩ leads to its lower
transport rates, whereas for Tlϩ and other cations, the increased
extraction is coupled with increased transport rates. Evidently,
in the case of 10 and 14, the slower decomplexation of the
more stable macrocycle–Agϩ picrate complexes may be at least
partially responsible for lower transport rates.
Experimental
Melting points were determined in capillaries and are uncor-
rected. 1H and 13C NMR spectra were run on a Bruker AC200
MHz instrument using TMS as an internal standard. J Values
are given in Hz. Mass spectra were recorded on JEOL JMSD-
300, VG micromass 7070 F mass spectrometers, at the Central
Drug Research Institute, Lucknow, and on a Shimadzu GCMS-
QP-2000 mass spectrometer at Amritsar. IR spectra were
recorded on a PYE UNICAM SP3-300 IR spectrophotometer
by using CHCl3 or KBr (solid) as medium. UV spectra were
Complexation studies through 13C NMR spectroscopy
The comparison of 13C NMR spectra of macrocycles with
those of their 1:1 stoichiometric mixtures with metal picrates
gives significant information about the complexation character
of individual ligating sites in these macrocycles.
J. Chem. Soc., Perkin Trans. 2, 1998
929

View Article Online
Table 6 Metal picrate induced 13C NMR coordination shifts (∆δC) of crownophanes 9, 10 and 14
SCH2
SCH2
OCH3
OCH2
ArC
ArC
ArC
ArC
PyC
PyC
PyC᎐N
Ϫ0.02
Ϫ0.06
0.43
Ϫ0.02
—
0.01
0.47
Ϫ0.01
—
0.31
Ϫ0.04
—
C᎐O
᎐
9ؒPb2ϩ
9ؒTlϩ
0.05
0.17
0.05
0.06
2.35
0.01
0.37
—
—
—
—
1.44
0.00
—
—
—
—
—
1.42
0.01
Ϫ0.04
Ϫ0.03
—
—
Ϫ0.04
0.03
0.07
0.06
0.01
1.64
—
0.66
0.04
Ϫ0.20
—
Ϫ0.01
0.02
0.01
—
0.24
0.03
0.62
0.04
Ϫ0.03
0.13
—
—
—
0.22
—
—
Ϫ0.12
—
0.01
Ϫ1.90
0.03
—
—
0.01
—
Ϫ0.02
Ϫ0.08
Ϫ0.02
—
1.37
Ϫ0.01
0.36
0.01
—
0.62
0.03
—
Ϫ0.02
—
0.03
0.06
—
0.03
—
—
—
—
Ϫ0.02
—
—
—
0.03
Ϫ0.04
—
0.04
—
0.39
Ϫ0.35
—
—
—
—
—
Ϫ0.22
Ϫ0.04
Ϫ0.03
Ϫ3.12
Ϫ0.01
Ϫ0.72
Ϫ0.01
0.02
Ϫ0.06
Ϫ0.08
—
—
—
9ؒNaϩ
9ؒSr2ϩ
10ؒAgϩ
10ؒPb2ϩ
10ؒTlϩ
10ؒNaϩ
10ؒSr2ϩ
14ؒAgϩ
14ؒPb2ϩ
14ؒTlϩ
14ؒNaϩ
14ؒSr2ϩ
—
Ϫ0.02
0.66
0.03
—
—
—
—
—
—
Ϫ0.05
Ϫ0.01
Ϫ0.01
3.85
0.01
—
—
—
Ϫ0.01
0.30
Ϫ0.01
—
0.01
0.01
—
0.03
Ϫ0.01
—
—
Ϫ0.26
Ϫ0.26
Ϫ0.24
Ϫ0.03
Ϫ0.08
Ϫ0.06
Ϫ0.03
0.03
—
—
0.14
Ϫ0.04
—
0.25
0.20
—
recorded on a Shimadzu UV-240 spectrophotometer. Elem-
ental analysis of solid samples was performed at the micro-
analytical laboratory RSIC, Chandigarh.
10:1→1:1) as eluents to isolate 9. Similarly cyclocondensation
of diols 5 and 7 with thiodiglycolyl chloride gave macrocycles
10 and 11.
6,12-Dioxa-3,9,15-trithia-1(1,3)-benzenacyclohexadeca-
phane-7,11-dione (7) (40%), liquid; δH(CDCl3) 2.64 (4H, t, J
7.0, 2 × SCH2), 3.39 (4H, s, 2 × SCH2CO), 3.76 (4H, s,
2 × SCH2Ar), 4.20 (4H, t, J 7.0, 2 × OCH2), 7.23–7.35 (4H,
m, ArH); δC(CDCl3) 28.84 (t, SCH2), 34.03 (t, SCH2), 36.05
(t, SCH2), 64.42 (t, OCH2), 127.79 (d, ArCH), 129.40 (d,
Synthesis of diols 3, 4 and 12
General procedure. A solution of 1,3-bis(bromomethyl)-
benzene (1) (1.00 g, 3.7 mmol) and 2-mercaptoethanol (0.74 g,
10.11 mmol) in DMF (dry, 50 cm3) containing anhydrous
K2CO3 (2.65 g, 18.96 mmol) and tetrabutylammonium hydro-
Ϫ
gen sulfate (Bu4NϩHSO4 ) was stirred. After completion of the
ArCH), 129.69 (d, ArCH), 138.15 (s, ArC), 169.21 (s, C᎐O);
᎐
reaction (TLC, 8 h), the solid suspension was filtered and the
residue was washed with ethyl acetate (10 cm3). The combined
filtrate was distilled under vacuum. The residue was chromato-
graphed on a silica gel column using hexane–ethyl acetate
(gradient elution 10:1→1:1) as eluents to isolate diol 3. Simi-
larly, reaction of 1,3-bis(bromomethyl)-2-methoxy-5-methyl-
benzene (2) and 1,4-bis(bromomethyl)benzene (11) with 2-
mercaptoethanol gave diols 4 and 12.
1,3-Bis(2-hydroxyethylthiomethyl)benzene (3) (80%), liquid;
δH(CDCl3) 2.58 (4H, t, J 6.2, 2 × SCH2), 3.61 (4H, t, J 6.2,
2 × OCH2), 3.70 (4H, s, SCH2), 7.15–7.33 (4H, m, ArH);
δC(CDCl3) 36.43 (t, SCH2), 41.15 (t, SCH2), 61.54 (t, OCH2),
127.53 (d, ArCH), 128.70 (d, ArCH), 129.25 (d, ArCH), 138.46
(s, ArC); νmax(KBr)/cmϪ1 3400 (OH); m/z 258 (Mϩ).
1,3-Bis(2-hydroxyethylthiomethyl)-2-methoxy-5-methyl-
benzene (4) (80%), liquid; δH(CDCl3) 2.29 (3H, s, Me), 2.63
(4H, t, J 6.0, 2 × SCH2), 3.67 (4H, t, J 6.0, 2 × OCH2), 3.72 (4H,
2 × SCH2), 3.84 (3H, s, OCH3), 7.57 (2H, s, ArH); δC(CDCl3,
DEPT-135) 20.65 (ϩve, CH3), 29.61 (Ϫve, SCH2), 34.18
(Ϫve, SCH2), 60.68 (Ϫve, OCH2), 62.35 (ϩve, OCH3), 130.44
(ϩve, ArCH), 131.11 (absent, ArC), 134.01 (absent, ArC),
154.22 (absent, ArC᎐O); νmax(KBr)/cmϪ1 3400 (OH); m/z 302
(Mϩ).
νmax(CHCl3)/cmϪ1 1750, 1740 (C᎐O); m/z 372 (Mϩ).
᎐
12-Methoxy-15-methyl-6,12-dioxa-3,9,15-trithia-1(1,3)-
benzenacyclohexadecaphane-7,11-dione (8) (35%); mp 100 ЊC
(CH3CN); δH(CDCl3) 2.32 (3H, s, CH3), 2.57 (4H, deformed t, J
6.8, 2 × SCH2), 3.33 (4H, s, 2 × SCH2), 3.69 (3H, s, OCH3), 3.73
(4H, s, 2 × SCH2), 4.19 (4H, deformed t, J 6.8, 2 × OCH2), 7.13
(2H, s, ArH); δC(CDCl3) 20.89 (q, CH3), 28.23 (t, SCH2), 29.12
(t, SCH2), 33.62 (t, SCH2), 62.46 (q, OCH3), 64.56 (t, OCH2),
130.63 (d, ArCH), 130.96 (s, ArC), 134.86 (s, ArC), 154.86 (s,
ArC᎐O), 169.10 (s, C᎐O); νmax(KBr)/cmϪ1 1743 (C᎐O); m/z 416
᎐
᎐
(Mϩ, 12%) (Found: C, 52.10; H, 5.80. C18H24O5S3 requires C,
51.92; H, 5.76%).
6,12-Dioxa-3,9,15-trithia-1(1,4)-benzenacyclohexadeca-
phane-7,11-dione (13) (10%), mp 62 ЊC (CH3CN); δH(CDCl3)
2.54 (4H, deformed t, J 6.0, SCH2), 3.20 (4H, s, SCH2), 3.70
(4H, s, SCH2), 3.78 (4H, deformed t, J 6.0, OCH2), 7.33 (4H,
s, ArH); δC(CDCl3) 28.37 (t, SCH2), 34.93 (t, SCH2), 36.26 (t,
SCH2), 64.09 (t, OCH2), 129.31 (d, ArCH), 137.46 (s, ArC),
169.09 (s, C᎐O); νmax(KBr)/cmϪ1 1742 (C᎐O); m/z 372 (Mϩ)
᎐
᎐
(Found: C, 51.76; H, 5.20. C16H20O4S3 requires C, 51.61; H,
5.37%).
Synthesis of crownophanes 9, 10, 14 and 15
1,4-Bis[(2-hydroxyethylthio)methyl]benzene (12) (85%), mp
58 ЊC (CHCl3); δH(CDCl3) 2.62 (4H, t, J 6.0, 2 × SCH2), 3.63
(4H, t, J 6.0, 2 × OCH2), 3.70 (4H, s, SCH2), 7.27 (4H, s, ArH);
δC(CDCl3, DEPT-135) 34.21 (Ϫve, SCH2), 41.26 (Ϫve, SCH2),
60.32 (Ϫve, OCH2), 129.11 (ϩve, ArCH), 137.12 (absent, ArC);
νmax(KBr)/cmϪ1 3300 (OH); m/z 258 (Mϩ) (Found: C, 55.45; H,
6.87. C12H18O2S2 requires C, 55.81; H, 6.97%).
General procedure. Diol 3 (1 g, 3.9 mmol), K2CO3 (anhyd.)
and a catalytic amount of Bu4NϩHSO4Ϫ (10 mg) were dissolved
in dry dichloromethane (100 cm3) and the reaction mixture was
stirred at room temperature. Pyridine-2,6-dicarbonyl dichloride
(0.73 g, 3.9 mmol) solution in dichloromethane (dry, 50 cm3)
was added dropwise, over 0.5 h. After completion of the
reaction (TLC, 7 h), the suspension was filtered off and the
solid residue was washed with ethyl acetate (2 × 10 cm3).
The combined filtrate was distilled off. The crude reaction
product was chromatographed on a silica gel column using
hexane–ethyl acetate mixtures as eluents to isolate a white
compound 9.
6,10-Dioxa-3,13-dithia-1(1,3)-benzena-8(2,6)-pyridinacyclo-
tetradecaphane-7,9-dione (9) (35%), mp 147 ЊC (CHCl3);
δH(CDCl3) 2.67 (4H, t, J 6.0, 2 × SCH2), 3.91 (4H, s, 2 × SCH2),
4.59 (4H, t, J 6.0, 2 × OCH2), 7.25–7.34 (3H, m, ArH),
7.93 (1H, s, ArH), 8.03 (1H, t, J 7.8, PyH), 8.37 (2H, d,
J 7.8, PyH); δC(CDCl3, DEPT-135) 27.81 (Ϫve, SCH2),
36.13 (Ϫve, ArSCH2), 68.44 (Ϫve, OCH2), 127.59 (ϩve,
Synthesis of crownophanes 7, 8 and 13
General procedure. Diol 4 (1.00 g, 3.9 mmol), KF (anhyd.)
and a catalytic amount of Bu4NϩHSO4Ϫ (10 mg) were dissolved
in dry dichloromethane (100 cm3) and the reaction mixture was
stirred at room temperature. Thiodiglycolyl dichloride (0.73 g,
3.87 mmol) dissolved in dichloromethane (50 cm3) was added
dropwise, over 0.5 h. After completion of the reaction (TLC,
7 h), the solid suspended was filtered off and was washed with
ethyl acetate (2 × 10 cm3). The combined filtrate was distilled
off. The crude reaction product was chromatographed on a
silica gel column using hexane–ethyl acetate (gradient elution
930
J. Chem. Soc., Perkin Trans. 2, 1998

View Article Online
Crystal data collection and refinement parameters for
crownophanes 8 and 13
Table
7
PyCH), 128.60 (ϩve, ArCH), 129.44 (ϩve, ArCH), 132.91
(ϩve, ArCH), 137.52 (ϩve, ArCH), 138.02 (absent,
ArC), 148.54 (absent, PyC᎐N), 165.27 (absent, C᎐O);
᎐
Compounds
8
13
νmax(KBr)/cmϪ1 1715 (C᎐O); m/z 389 (Mϩ, 20%) (Found: C,
᎐
58.42; H, 4.31; N, 3.41. C19H19NO4S2 requires C, 58.61; H, 4.88;
N, 3.59%).
Empirical formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
C18H24O5S3
416.55
Monoclinic
P21/n
13.433(1)
9.941(1)
14.977(1)
103.45(10)
1945.1(3)
4
0.2 × 0.3 × 0.2
0.710 73
45
2487
2359
0.0291
2285
235
0.0356
0.384, Ϫ0.263
1.056
C16H20O4S3
372.50
Monoclinic
P21/c
16.333(1)
8.670(1)
13.005(1)
98.69(10)
1820.5(3)
4
0.3 × 0.3 × 0.2
0.710 73
35
1446
1133
0.0208
1133
208
0.0320
0.177, Ϫ0.197
1.172
12-Methoxy-15-methyl-6,10-dioxa-3,13-dithia-1(1,3)-benz-
ena-8(2,6)-pyridinacyclotetradecaphane-7,9-dione (10) (35%),
mp 128–132 ЊC (CHCl3); δH(CDCl3) 2.29 (3H, s, CH3), 2.87
(4H, t, J 6.0, 2 × SCH2), 3.72 (3H, s, OMe), 3.84 (4H, s,
2 × SCH2), 4.41 (4H, t, J 6.0, 2 × OCH2), 7.09 (2H, s, ArH),
7.94–8.01 (1H, m, PyH), 8.24 (2H, s, J 8.0, PyH); δC(CDCl3)
20.84 (q, CH3), 29.57 (t, SCH2), 30.74 (t, SCH2), 62.37 (q,
OCH3), 65.85 (t, OCH2), 127.66 (d, PyCH), 130.76 (d, ArCH),
134.40 (d, PyCH), 137.96 (s, ArC), 148.20 (s, PyC᎐N), 155.54 (s,
β/Њ
U/Å3
Z
Crystal size/mm
µ(Mo-Kα)/cmϪ1
2θmax/Њ
No. of measured reflections
No. of unique reflections
Rint
No. of observations [I > 3σ(I)]
No. of variables
Residuals: R
Max. and min. residual
Electron density/e ÅϪ3
Goodness of fit (GOOF)
ArC᎐O), 164.60 (s, C᎐O); m/z 433 (Mϩ, 13%) (Found: C, 57.74;
᎐
H, 5.30; N, 3.30. C21H23NO5S2 requires C, 58.01; H, 5.31; N,
3.23%).
6,10-Dioxa-3,13-dithia-1(1,4)-benzena-8(2,6)-pyridinacyclo-
tetradecaphane-7,9-dione (14) (25%), mp 197 ЊC (CHCl3);
δH(CDCl3) 2.62 (4H, t, J 6.6, 2 × SCH2), 3.85 (4H, s, 2 × SCH2),
4.44 (4H, t, J 6.6, 2 × OCH2), 7.30 (4H, s, ArH), 8.03 (1H, t, J
8.0, PyH), 8.32 (2H, d, J 8.0, PyH); δC(CDCl3) 28.75 (t, SCH2),
36.02 (t, SCH2), 65.91 (t, OCH2), 128.17 (d, PyCH), 129.44 (d,
ArCH), 137.16 (s, ArC), 148.25 (s, PyC᎐N), 164.60 (s, C᎐O);
᎐
m/z 389 (Mϩ) (Found: C, 58.30; H, 4.54; N, 3.30. C19H19NO4S2
requires C, 58.61; H, 4.88; H, 3.59%).
and a chloroform solution (2 cm3) of the macrocycle (0.01 mol
dmϪ3) were shaken in a cylindrical tube closed with a septum
for 5 min and kept at 27 1 ЊC for 3–4 h. An aliquot of the
chloroform layer (1 cm3) was withdrawn with a syringe and
diluted with acetonitrile to 10 cm3. The UV absorption was
measured against CHCl3–CH3CN (1:9) solution at 374 nm.
Extraction of metal picrate has been calculated as the percent-
age of metal picrate extracted in the chloroform layer and the
values reported here are the mean of three independent meas-
urements which were within 2% error (Table 2).
12,152-Dimethoxy-15,155-dimethyl-6,10,20,24-tetroxa-
3,13,17,27-tetrathia-1,15(1,3)-dibenzena-8,22(2,6)-dipyridina-
cyclooctaicosophane-7,9,21,23-tetrone (15) (10%), mp 180 ЊC
(CHCl3); δH(CDCl3) 2.24 (3H, s, CH3), 2.69 (4H, t, J 6.6,
2 × SCH2), 3.79 (3H, s, OMe), 3.87 (4H, s, 2 × SCH2), 4.44 (4H,
t, J 6.6, 2 × OCH2), 7.08 (2H, s, ArH), 7.97 (1H, t, J 8.0, PyH),
8.30 (2H, d, J 8.0, PyH); m/z (FAB) 867 (Mϩ ϩ 1).
X-Ray structure analysis of crownophanes 8 and 13
Transport measurements19
All intensity data measurements were carried out on a Sie-
mens P4 four circle diffractometer with graphite mono-
chromatic Mo-Kα radiation (λ = 0.710 69 Å). All structures
were solved and refined using the SHELXTL software20 pack-
age on a Siemens Nixdorf computer. Crystals of 8 and 13
suitable for X-ray diffraction work were obtained by recrys-
tallization from acetonitrile. The unit cell parameters were
determined from a least squares fit of setting angles of 25
reflections in the range 20 р 2θ р 25Њ. Three standard reflec-
tions were measured every 100 reflections and showed no sig-
nificant intensity variation during the data collection. The
data were corrected for Lorentz and polarization effects. No
absorption corrections were applied. The structures were
solved by the direct methods. Full matrix least squares refine-
ment was employed with anisotropic thermal parameters for
the non-hydrogen atoms. The hydrogen atoms placed at calcu-
lated positions were refined isotropically with fixed thermal
parameters and included in structure factor calculations. Crys-
tal data and parameters for data collection and refinements
are summarized in Table 7. Full crystallographic details,
excluding structure factor tables, have been deposited at the
Cambridge Crystallographic Data Centre (CCDC). For details
of the deposition scheme, see ‘Instructions for Authors’, J.
Chem. Soc., Perkin Trans. 2, available via the RSC Web page
(http://www.rsc.org/authors). Any request to the CCDC for
this material should quote the full literature citation and the
reference number 188/121.
The transport experiments were carried out at constant tem-
perature (27 1 ЊC) in a cylindrical glass cell consisting of
outer and inner jackets by using (i) metal picrate (0.01 mol
dmϪ3) in water (3 cm3) in the inner phase; (ii) water (10 cm3)
in the outer phase; (iii) ligand (10 mmol dmϪ3) in a chloro-
form layer (15 cm3) with stirring (150 5 rpm) at 27 1 ЊC.
After stirring for 6 h the picrates transported in the aqueous
receiving phase were determined from the UV absorptions at
355 nm. Each value is a mean of three experiments which are
consistent 10% (Table 3). Before determining the transport
rates, blank experiments were performed in the absence of the
carrier macrocycle in the chloroform layer to check the leak-
age of metal picrates. Under the conditions given for the
transport experiments, in the absence of crownophanes, metal
picrates (except Pb2ϩ picrate) are not transported to the receiv-
ing phase. However, Pb2ϩ picrate shows significant transport
and results for crownophane induced transport of Pb2ϩ are
not reliable and, therefore transport of Pb2ϩ was not
determined.
DTMM 2.0 programme17
The programme was used as provided by the company, without
any further modification. The programme DTMM 2.0 uses
molecular mechanistics potentials and their force fields similar
to those in ref. 21. These include bond stretching potential,
bong angle deformation potential, periodic torsional barrier
potential and non-bonding interactions for non-bonded atom
pairs. For every bond, six variables, bond length (1), bond
rotation (1) and fragment orientation (4) are minimized. All
variables are treated independently using a simple line search
algorithm with quadratic interpolation. It provides facilities for
conformational space hunting, charge calculations and hydro-
gen bonding.
Extraction measurements18
For the extraction experiments, metal picrate solutions (0.01
mol dmϪ3) were prepared in deionized distilled water. The
solutions of macrocycles (0.01 mol dmϪ3) were prepared in
chloroform (AR grade).
An aqueous solution (2 cm3) of metal picrate (0.01 mol dmϪ3)
J. Chem. Soc., Perkin Trans. 2, 1998
931

View Article Online
12 D. Siswanta, K. Nagatsuka, H. Yamada, K. Kumakura,
Acknowledgements
We thank the Department of Science and Technology, New
Delhi for a research grant (SP/SI/623/92).
H. Hisamoto, Y. Scichi, K. Toshima and K. Suzuki, Anal. Chem.,
1996, 68, 4166.
13 T. Nabeshima, K. Nishijima, N. Tsukada, H. Furusawa, T. Hosoya
and Y. Yano, J. Chem. Soc., Chem. Commun., 1992, 1092.
14 J. Casabo, T. Flor, M. N. Stuart, H. A. Jenkins, J. C. Lockhart,
S. J. Loeb, I. Romero and F. Texidor, Inorg. Chem., 1995, 34, 5410.
15 F. Texidor, M. A. Flores, L. Eschriche, G. Vinas and J. Cassabo,
J. Chem. Soc., Chem. Commun., 1994, 963.
16 Chemical shift variations for these compounds are within δ 0.02.
17 M. J. C. Crabbe and J. R. Appleyard, Desktop Molecular Modeller
2.0, Oxford Electronic Publishing, Oxford, 1991.
18 (a) S. S. Moore, T. L. Tarnowski, M. Newcomb and D. J. Cram,
J. Am. Chem. Soc., 1977, 99, 6398; (b) K. E. Koeing, G. M. Lehn,
P. Stuckler, T. Kaneda and D. J. Cram, J. Am. Chem. Soc., 1979, 101,
3553.
19 (a) K. Maruyama, H. Tsukube and T. Akai, J. Am. Chem. Soc.,
1980, 102, 3246; (b) K. Maruyama, H. Tsukube and T. Akai,
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Paper 7/06861A
Received 22nd September 1997
Accepted 8th January 1998
932
J. Chem. Soc., Perkin Trans. 2, 1998