Ion-pair binding by mixed N,S-donor 2-ureidopyridine ligands

Article abstract of DOI:10.1039/b905555j

The synthesis of a simple ambidentate ligand 1-(3-methylsulfanyl-phenyl)-3- pyridin-2-yl-urea (L) capable of binding metal ions via a pyridyl nitrogen atom or thioether sulfur donor is reported. The pyridyl functionality is located adjacent to an anion bi

Full text of DOI:10.1039/b905555j

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www.rsc.org/dalton | Dalton Transactions
Ion-pair binding by mixed N,S-donor 2-ureidopyridine ligands†
Naseem Qureshi, Dmitry S. Yufit, Judith A. K. Howard and Jonathan W. Steed*
Received 19th March 2009, Accepted 8th May 2009
First published as an Advance Article on the web 8th June 2009
DOI: 10.1039/b905555j
The synthesis of a simple ambidentate ligand 1-(3-methylsulfanyl-phenyl)-3-pyridin-2-yl-urea (L)
capable of binding metal ions via a pyridyl nitrogen atom or thioether sulfur donor is reported. The
pyridyl functionality is located adjacent to an anion binding urea group allowing this region of the
ligand to bind contact ion-pairs by simultaneous coordination and hydrogen bonding interactions. This
intimate ion-pair binding coordination mode is demonstrated by the X-ray crystal structures of
-
-
-
[Ag(L)]X (X = CH3CO2 , 1; NO3 , 2). The non-coordinating PF6 anion is not bound as an ion-pair in
[Ag(L)](PF6) (3) and the urea NH groups exhibit short contacts to carbonyl oxygen and p-systems. The
X-ray crystal structure of [Ag(L)4]BF4 (4) is also reported, showing the ligand to be exclusively
S-bound. Anion binding by L and its silver(I) complex is also explored by solution 1H NMR
spectroscopic methods.
ion-pair binding site of the type illustrated in Fig. 1. In the
Introduction
presence of binary metal salts of univalent cations (MX) the
ligand should thus either form a N,S-bound coordination polymer
or a discrete M2X2L2 assembly, possibly templated by suitable
anions. Depending on the relative strengths of the M–N and
M–S bonds, we anticipate that the pyridylurea-bound MX ion-
pair could be stable in solution and this fragment might then
dimerise or assemble via labile metal–sulfur interactions.
Metal-based hosts for anions are receiving increasing current
interest.1–32 As well as being convenient counter-ions, metal cen-
tres, with their strong coordination geometric tendencies, also rep-
resent an excellent platform for the assembly of structurally well-
defined anion binding hosts.1 Recent work on 3-aminopyridine,
3-methylaminopyridine and 3-ureidopyridine type ligands has
resulted in a number of separated ion-pair binding compounds
in which a series of two to four ligands are organised by a metal
centre into a binding pocket for an attendant anion.8,10,11,18,19 In
these systems the anion and cation binding regions are far apart
and there is no direct interaction between the charged components.
Such a situation is potentially unstable since it involves charge
separation and contrasts to macrobicyclic systems prepared by
Smith and co-workers in which a neutral macrobicycle binds to an
alkali metal halide contact ion-pair.33–36 Earlier work by Reinhoudt
et al. has also used a metal centre as a direct anion binding site,
supported by remote hydrogen bonding interactions.37,38 We now
report the design of a simple ligand containing an intimately
connected hybrid metal–anion binding site complementary to a
contact ion-pair.
Fig. 1 (a) Structure of ligand L and (b) comparison of the proposed
ion-pair binding mode of L with analogous 3-pyridyl urea complexes.
The conformational preferences of ligand L itself were analysed
by X-ray crystallography. Remarkably L exists in at least four
polymorphic modifications and these will be reported separately.
The molecular conformation in the four different solid forms
is very similar and involves an anti conformation for the N,N¢-
disubstituted urea moiety such as to produce an S(6) intramolec-
ular hydrogen bonded ring40 from the urea g-NH to the pyridyl
nitrogen atom as is common with 2-pyridylureas.41 The remaining
urea NH and the carbonyl oxygen atom then form an R22(8)
intermolecular hydrogen bonded ring, Fig. 2.
The reaction of L with silver(I) salts yields compounds of
formula [Ag(L)]X (X = CH3CO2, 1; NO3, 2 and PF6, 3) all
of which have been characterised by X-ray crystallography. The
acetate complex 1 exists as two polymorphs (monoclinic and
triclinic forms A and B, respectively), Fig. 3, in both of which,
as anticipated, the anion is simultaneously bound to both the urea
moiety by hydrogen bonding and the metal ion by coordination
Results and discussion
Synthesis and structure
The ligand 1-(3-methylsulfanyl-phenyl)-3-pyridin-2-yl-urea (L)
was designed by analogy with the related 1-(3-methylsulfanyl-
phenyl)-3-phenyl-urea,39 to bind to metal ions such as Ag(I)
through both the thioether and pyridyl functionalities. While
the thioether is remote from the urea anion binding group, the
2-pyridyl metal binding group and the urea form a connected
Department of Chemistry, Durham University, South Road, Durham, UK
DH1 3LE. E-mail: jon.steed@durham.ac.uk
† Electronic supplementary information (ESI) available: Selected NMR
data. CCDC reference numbers 724612–724616. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b905555j
5708 | Dalton Trans., 2009, 5708–5714
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an extended coordination polymer structure in the solid state in
both polymorphs. Both structures are built out of zig-zag shaped
1D polymer strands which form corrugated layers. The two crystal
forms differ in the conformation of the polymer at the metal centre,
with form A adopting an anti-parallel arrangement of the ligands
within the 1D polymer strands, while in form B the arrangement
is parallel. Hydrogen bond distances are given in Fig. 3 and are
slightly longer in form B than form A. Form B is also less dense
than form A (1.78 g cm-3 vs. 1.81 g cm-3) and hence it may be that
form B is a kinetic form and form A is the stable polymorph.
The X-ray crystal structure of the nitrate complex 2 also exhibits
a very similar ion-pair binding motif to that found for 1, consistent
with the similar shape of the nitrate and acetate ions. Nitrate is
much less basic than acetate, however, and hence the Ag–Oanion
distances are much longer than in the acetate complex structures.
˚
The single short Ag–O2CCH3 bond of ca. 2.25 A is replaced by
˚
two much longer Ag–ONO2 contacts each ca. 2.5 A long. The fact
Fig. 2 Conformation and hydrogen bonding of ligand L derived from
that nitrate is able to coordinate on all three edges (i.e. to each
pair of oxygen atoms) also means that the extended geometry of
the structure is rather different. While it is again a coordination
polymer, the structure is based on an infinite network of dimeric
{Ag(NO3)(L)}2 units linked together by bridging nitrate anions
and Ag–S interactions, Fig. 4. The coordination geometry of the
Ag(I) centres is thus distorted tetrahedral rather than distorted
trigonal, as in 1.
X-ray crystallography.
as shown in Fig. 1(b). In both solid forms the Ag(I) ion adopts
an irregular three-coordinate geometry, binding to the pyridyl
nitrogen atom, the sulfur atom of an adjacent ligand and one
oxygen atom of the acetate counter-ion. However, in form A,
the silver ion is additionally weakly coordinated by a sulfur
˚
atom (Ag ◊ ◊ ◊ S 3.191 A) from an adjacent coordination polymeric
strand (see below), while the silver atoms in polymorph B are
-
In contrast to acetate and nitrate, the non-coordinating PF6
˚
anion in complex 3 would not be expected to interact with the
linked together by Ag ◊ ◊ ◊ Ag interactions (3.013 A). One oxygen
Ag(I) centre in these kinds of systems and indeed this proves to
atom of the acetate anion is coordinated to the silver ion in
each form, while the second oxygen atom is hydrogen bonded
in a typical R12(6) pattern20 to the urea moiety. The 1 : 1 ratio
between ligand and metal salt means that the complex adopts
˚
be the case with the shortest Ag ◊ ◊ ◊ F distances in excess of 3.4 A.
As a result the silver ions are essentially linear, two-coordinated
bound by pyridyl nitrogen and thioether groups to produce a
Fig. 3 Silver(I) acetate contact ion-pair binding motif in two polymorphs of [Ag(L)](CH3CO2) (1) (a) monoclinic form A and (b) triclinic form
˚
B (ellipsoids at 50% level). Selected bond lengths, form A: Ag(1)–N(3) 2.254(2), Ag(1)–O(2) 2.280(2), Ag(1)–S(1) 2.5905(7) A; form B Ag(1)–O(2)
˚
˚
2.2357(15), Ag(1)–N(3) 2.2383(15), Ag(1)–S(1) 2.5828(5) A. Selected hydrogen bond distances, form A: N(1)–O(3) 2.759(3), N(1)–O(3) 2.759(3) A; form
˚
B: N(1)–O(3) 2.819(2), N(2)–O(3) 2.857(2) A.
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Fig. 4 Silver(I) nitrate contact ion-pair binding motif in [Ag(L)](NO3) (2) (a) repeat unit (b) extended structure (ellipsoids at 50% level). Selected bond
˚
lengths: Ag(1)–N(3) 2.2636(16), Ag(1)–S(1) 2.4674(5), Ag(1)–O(2) 2.4957(17), Ag(1)–O(3) 2.5789(15) A. Selected hydrogen bond distances: N(1)–O(4)
˚
2.920(2), N(2)–O(3) 2.946(2) A.
1D coordination polymer chain, Fig. 5. There is also a long
Ag–O interaction from the silver ion to the urea oxygen atom.
In the absence of a strong hydrogen bond acceptor anion the urea
oxygen atom acts as a hydrogen bond acceptor for a single urea
NH ◊ ◊ ◊ O hydrogen bond, in contrast to the usual R12(6) urea tape
motif which involves the carbonyl oxygen atom as a bifurcated
acceptor.42–44 This single interaction allows the formation of the
long Ag–O bond, leaving the remaining urea NH group to form
short contacts to a single fluorine atom and to the pyridyl aromatic
ring.
Attempts were also made to prepare a 1 : 1 complex with L
and AgBF4, however, the final isolated product proved to be
an interesting 1 : 4 complex [Ag(k-S-L)4](BF4)·thf (4) which was
also characterised by X-ray crystallography (Fig. 6). The 1 : 4
ratio may arise from decomposition of some of the silver salt
leading to an excess of ligand. The Ag(I) ion is tetrahedrally
coordinated solely by the sulfur atoms of four independent ligands
˚
with Ag–S distances 2.56–2.60 A, similar to that found in 1
but rather longer than those in the two-coordinate 3. The poor
-
hydrogen bond acceptor nature of BF4 means that the urea
groups do not hydrogen bond to the anion but instead adopt
an anti conformation exhibiting a very similar combination of
intramolecular and intermolecular interactions to those observed
in the free ligand structures. The 1 : 4 ratio means that the soft Ag(I)
ion is able to satisfy its coordination requirements using only sulfur
and hence does not coordinate to the pyridyl nitrogen atoms. As a
result the pyridyl groups are free to act as hydrogen bond acceptors.
In such case, according to Etter’s rules,44 the intramolecular S(6)
motif is dominant forcing the anti conformation and hence leaving
a single NH group free to form the intermolecular R22(8) motif, as
in the free ligand structures.
Solution phase binding
Fig. 5 Silver(I) hexafluorophosphate complex [Ag(L)](PF6) (3) (ellipsoids
Given the reproducible occurrence of ion-pair binding by L in the
solid state it is of obvious interest to determine whether there is
any evidence for the persistence of these interactions in solution.
at 50% level). Selected bond lengths: Ag(1)–N(1) 2.206(2), Ag(1)–S(1)
˚
2.4316(6) A. Selected hydrogen bond distance: N(2) ◊ ◊ ◊ O(1) 2.885(3),
˚
N(1) ◊ ◊ ◊ F(4) 3.119(3) A.
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Fig. 6 The cation in the 1 : 4 silver(I) tetrafluoroborate complex [Ag(k-S-L)4](BF4)·thf (4) (ellipsoids at 50% level).
Unfortunately solution phase binding measurements on L and its
Ag(I) complexes were complicated by poor solubility. While L is
soluble in a range of solvents, H NMR spectroscopic titrations
of the urea NH groups as in Fig. 2, while in DMSO it is syn as a
result of hydrogen bonding to the solvent.
1
Titration of free L with silver(I) trifluoromethanesulfonate (as a
control using a non-coordinating anion) resulted in a small change
of Dd ca. -0.1 ppm in DMSO suggesting that Ag(I) complexation
alone does not result in a significant change in the chemical shift of
the urea NH resonances of L (see ESI†). 1H NMR spectroscopic
with metal salts had to be carried out in the highly competitive
DMSO-d6. The solvent titration of free L with NBu4 X- (X =
+
-
NO3, PF6 ) did not result in any significant chemical shift changes,
suggesting weak binding. However in both acetone-d6 and
DMSO-d6 solution addition of tetrabutylammonium acetate
resulted in the formation of a 1 : 1 complex (confirmed by Job
plot analysis, see ESI†). While the DMSO experiment resulted in a
conventional binding isotherm behaviour for both NH resonances
(NHa and NHb, Fig. 1(a)), in acetone the resonance at 8.37 ppm
(NHb) is more dramatically affected than the NHa signal at
11.53 ppm (Fig. 7). By reference to Fig. 2, we suggest that in
acetone the resonance at 11.53 ppm corresponds to the NH proton
which is intramolecularly hydrogen bonded to the pyridyl nitrogen
atom. Hence in acetone the ligand adopts an anti conformation
+
-
titrations were then undertaken of L with NBu4 MeCO2 in the
presence of 0.5, 1 and 2 equivalents of AgCF3SO3, relative to L
(Fig. 8). In the presence of 0.5 equivalents of Ag(I) (a 2 : 1 L : Ag
ratio) in contrast to the titration of the free ligand, no change
was observed in the chemical shift of NHa until 0.5 equivalents
of anion had been added. However, NHb exhibits a downfield
chemical shift change of ca. 0.4 ppm in the same range. In the
presence of one equivalent of Ag(I), a similar behaviour is observed
except that the chemical shift of NHa remains unchanged until one
equivalent of acetate is added. Interestingly the titration isotherm
in the presence of two equivalents of Ag(I) looks very similar
to the plot obtained in the presence of one equivalent of silver,
i.e. the chemical shift of NHa begins to change after addition of
one equivalent of acetate. We interpret this data by postulating
anion binding by a 1 : 1 complex of silver(I) and L. Thus in the
presence of 0.5 equivalents of Ag(I) the first 0.5 equivalents of
acetate are bound by the silver complex, affecting NHb but not
NHa. After this process is complete additional acetate is bound by
the excess free ligand (as demonstrated by Fig. 7(b)), and/or by
the “AgL+” complex in a different binding mode. In the presence
of one equivalent of Ag(I) it requires one equivalent of acetate to
bind to the “AgL+” complex. Additional acetate is then bound in a
-
different binding mode to give a “AgL·2MeCO2 ”species. There is
precedent for this binding of more than one anion by these kinds
of complexes.18 In the presence of two equivalents of silver(I) half
of the silver is in excess and makes no difference to the shape of
the isotherm. This latter experiment establishes that acetate is not
being bound by Ag(I) in the absence of L. The fact that it is NHb
and not NHa that is most affected by acetate anion binding by
“AgL+” is surprising. Examination of the crystal structure data
shown in Fig. 3 suggests that both NH resonances should be
affected. It is possible that a different binding mode occurs in
solution along the lines of that shown in Fig. 9.
Conclusions
Fig. 7 (a) 1H NMR spectroscopic titration of L with NBu4+OAc- (a) in
acetone-d6 and (b) in DMSO-d6. (ꢀ = sulfanylphenyl NH, ꢁ = pyridyl
NH, ꢀ = CH).
We have shown that the 2-ureidopyridine motif is capable of
binding anions and cations as contact ion-pairs in the solid state
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Fig. 9 Speculative acetate binding mode in a 1 : 1 Ag : L complex involving
a chemical shift change in NHb but not in NHa upon acetate binding.
SMART CCD 6000 (1A, 1B, 2, 3) and Rigaku R-AXIS Spider
IP (4) diffractometer using graphite monochromated Mo Ka
˚
radiation (l = 0.71073 A). The standard data collection temper-
ature was 120 K, maintained using an open flow N2 Cryostream
(OxfordCryosystems) device. Integration was carried out using
the Bruker SAINT and Rigaku FSProcess packages. Data sets
were corrected for Lorentz and polarisation effects, and for the
effects of absorption. Structures were solved using direct methods
and refined by full-matrix least squares on F2 for all data using
SHELXTL45 software. All non-hydrogen atoms were refined with
anisotropic displacement parameters, H-atoms were located on the
difference map and refined isotropically. Molecular graphics were
produced using the programs X-Seed46,47 and POV-Ray.48 Crystal
data for the structures studied are listed in Table 1.
Syntheses
1-(3-Methylsulfanyl-phenyl)-3-pyridin-2-yl-urea (L). 2-Amino
pyridine (2.84 g, 30.2 mmol) was reacted with 3-thiomethyl phenyl
isocyanate (4.95 g, 30.2 mmol) in 25 ml of chloroform solvent at
room temperature resulting in the formation of a white solid.
The product was isolated by filtration and washed with a small
1
amount of diethyl ether to give 7.00 g (89%) of the product. H
NMR (DMSO-d6): 10.55 (1H, bs, NH), 9.46 (1H, bs, NH), 8.29
(1H, d, J = 5.2 Hz, PyH), 7.73 (1H, dt, J = 1.6, 7.2 Hz, PyH), 7.51
(2H, m, ArH), 7.24 (2H, m, ArH), 7.01 (1H, dd, J = 4.8, 6.4 Hz,
PyH), 6.91 (1H, dt, J = 3.2, 6.0 Hz, PyH), 2.45 (3H, s, CH3). IR
◦
-1
=
(n/cm ) 1683 s (C O), 3214 br (NH). Mp 141 C. Anal. Calcd
(%) for C13H13N3OS: C, 60.21; H, 5.05, N, 16.20. Found (%) C,
Fig. 8 1H NMR spectroscopic titration of L with NBu4+MeCO2 in
the presence of (a) 0.5, (b) 1.0 and (c) 2.0 equivalents of AgCF3SO3.
-
60.17; H, 5.07; N, 16.03.
[Ag(L)](CH3CO2) 1 (form A). Ligand L (30 mg, 0.115 mmol)
in THF (2 ml) was mixed with silver acetate (19 mg, 0.115 mmol)
in methanol : H2O (1 : 1 v/v, 2 ml) and the mixture was allowed
to evaporate slowly resulting in the formation of colourless single
crystals suitable for X-ray diffraction analysis. IR (n/cm-1) 1200,
1441, 1548, 1576, 1765 s (na(CO2)), 3323 m (n(NH)). Mp 185 ◦C
(decomp.). Anal. Calcd (%) for C15H16N3O3SAg: C, 42.27; H, 3.78;
N, 9.86. Found (%) C, 42.02; H, 3.73; N, 9.66.
(ꢀ = sulfanylphenyl NH, ꢁ = pyridyl NH, ꢀ = CH).
for Ag(I) salts. Solubility problems prevent an extensive solution
phase study on a range of anions, however for the strongly bound
acetate the presence of silver(I) cations significantly perturbs the
anion binding behaviour of the free ligand and the data suggests
the formation of a 1 : 1 Ag : L complex that binds to acetate via the
formation of at least one NH ◊ ◊ ◊ anion hydrogen bond.
[Ag(L)](CH3CO2) 1 (form B). The second polymorph of 1
was obtained by dissolving L (30 mg, 0.115 mmol) in THF
(2 ml) and mixing with silver acetate (19 mg, 0.115 mmol) in
methanol : acetonitrile (1 : 1 v/v, 2 ml) and leaving the mixture
to evaporate slowly. This resulted in the formation of colourless
single crystals suitable for X-ray diffraction analysis. IR (n/cm-1)
1411, 1467, 1531, 1579, 1612, 1718 s (na(CO2)), 3199 m (n(NH)),
Experimental
X-Ray crystallography†
Suitable single crystals were grown by slow evaporation in the
dark and mounted using silicon grease on a thin glass fibre.
Crystallographic measurements were carried out on a Bruker
5712 | Dalton Trans., 2009, 5708–5714
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Table 1 Crystal data and structure refinement for compounds 1 (forms A and B), and 2–4
Compound
1-A
1-B
2
3
4
Formula
(C13H13N3OS)Ag(CH3CO2)
(C13H13N3OS)Ag (NO3) (C13H13N3OS)Ag(PF6) (C13H13N3OS)4Ag(BF4)(C4H8O)
Formula weight
Crystal system
Space group
426.24
Monoclinic
P21/c
4.3552(1)
19.5739(6)
18.4288(6)
90
95.12(2)
90
1564.75(8)
4
429.20
Triclinic
¯
P1
7.9094(2)
9.6883(3)
512.16
Orthorhombic
P212121
8.7396(2)
12.2836(2)
15.3536(3)
90
1304.08
Orthorhombic
Pca21
11.034(2)
32.057(6)
16.422(3)
90
90
90
5809(2)
4
Triclinic
P1
7.6567(4)
9.7852(4)
¯
˚
a/A
˚
b/A
˚
c/A
11.5435(5) 10.6752(3)
a/◦
b/◦
g /◦
73.77(1)
77.40(1)
75.77(1)
794.47(6)
2
1.782
1.417
428
8976
89.97(1)
69.83(1)
75.89(1)
741.53(4)
2
90
90
3
˚
V/A
1648.27(6)
4
Z
r
calc./mg m3
1.809
1.439
856
14 537
1.922
1.526
2.064
1.519
1.491
0.563
m/mm-1
F(000)
428
9809
1008
21 967
2688
36 273
Reflections
collected
Independent
reflections, Rint
No. of parameters
4130, 0.062
272
4591,
0.018
272
0.0282
0.0789
1.020
4302, 0.0182
4817,0.026
11 378, 0.116
260
243
684
Final R1 [I > 2s(I)] 0.0359
0.0278
0.0758
1.018
0.0255
0.0615
0.979
0.0941
0.2317
1.023
wR2 (all data)
0.1035
1.085
GOF on F2
3279 m (n(NH)). Mp 180 ◦C (decomp.). Anal. Calcd (%) for
C15H16N3O3SAg: C, 42.27; H, 3.78; N, 9.86. Found (%) C, 42.03;
H, 3.75; N, 9.91.
Notes and references
1 J. W. Steed, Chem. Soc. Rev., 2009, 38, 506.
2 P. D. Beer and S. R. Bayly, Top. Curr. Chem., 2005, 255, 125.
3 P. D. Beer and E. J. Hayes, Coord. Chem. Rev., 2003, 240, 167.
4 C. R. Rice, Coord. Chem. Rev., 2006, 250, 3190.
5 L. P. Harding, J. C. Jeffery, T. Riis-Johannessen, C. R. Rice and Z. T.
Zeng, Dalton Trans., 2004, 2396.
[Ag(L)](NO3) 2. Ligand L (30 mg, 0.115 mmol) was dissolved
in THF (2 ml) and added to a solution of silver nitrate (20 mg,
0.118 mmol) in H2O (2 ml). The mixture was left to slowly
evaporate for five days resulting in the formation of colourless
single crystals. IR (n/cm-1) 681, 760, 1304, 1387, 1535, 1578, 1608,
1709, 3129, 3278. Mp 180 ◦C (decomp.). Anal. Calcd (%) for
C13H13N4O4SAg: C, 36.40; H, 3.01; N, 13.10. Found (%) C, 36.30;
H, 3.07; N, 13.07.
6 J. L. Sessler, P. A. Gale and W.-S. Cho, Anion Receptor Chemistry,
Royal Society of Chemistry, Cambridge, UK, 2006.
7 P. A. Gale and R. Quesada, Coord. Chem. Rev., 2006, 250, 3219.
8 C. R. Bondy, P. A. Gale and S. J. Loeb, J. Am. Chem. Soc., 2004, 126,
5030.
9 P. A. Gale, Coord. Chem. Rev., 2003, 240, 191.
10 C. R. Bondy, P. A. Gale and S. J. Loeb, J. Supramol. Chem., 2002, 2,
93.
[Ag(L)](PF6) 3. Ligand L (30 mg, 0.115 mmol) was dissolved in
THF (2 ml) and added to a solution of silver hexafluorophosphate
(20 mg, 0.079 mmol) in H2O (2 ml). The mixture was left to slowly
11 C. R. Bondy, P. A. Gale and S. J. Loeb, Chem. Commun., 2001,
729.
12 S. Nieto, J. Pe´rez, V. Riera, D. Miguel and C. Alvarez, Chem. Commun.,
2005, 546.
evaporate for five days resulting in the formation of colourless
13 S. Nieto, J. Pe´rez, L. Riera, V. Riera and D. Miguel, Chem.–Eur. J.,
-1
=
single crystals. IR (n/cm ) 987 br (PF6), 1649 s (C O), 3308 br
2006, 12, 2244.
(NH), 3477 br (H2O). Anal. Calcd (%) for C13H12N3OSAgPF6: C,
30.42; H, 2.56; N, 8.11. Found (%) C, 30.50; H, 2.56; N, 8.22. Mass
511.16 (M + H).
14 S. Nieto, J. Pe´rez, L. Riera, V. Riera and D. Miguel, New J. Chem.,
2006, 30, 838.
15 J. Pe´rez and L. Riera, Chem. Commun., 2008, 533.
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Halcrow, New J. Chem., 2002, 26, 1634.
17 X. M. Liu, C. A. Kilner and M. A. Halcrow, Chem. Commun., 2002,
704.
18 D. R. Turner, B. Smith, E. C. Spencer, A. E. Goeta, I. R. Evans, D. A.
Tocher, J. A. K. Howard and J. W. Steed, New J. Chem., 2005, 29, 90.
19 D. R. Turner, E. C. Spencer, J. A. K. Howard, D. A. Tocher and J. W.
Steed, Chem. Commun., 2004, 1352.
20 D. R. Turner, B. Smith, A. E. Goeta, I. R. Evans, D. A. Tocher, J. A. K.
Howard and J. W. Steed, CrystEngComm, 2004, 6, 633.
21 D. R. Turner, A. Pastor, M. Alajar´ın and J. W. Steed, Struct. Bonding,
2004, 108, 97.
[Ag(L)4](BF4)·thf 4. Ligand L (30 mg, 0.115 mmol) in THF
(2 ml) was mixed with a solution of silver tetrafluoroborate
(22.5 mg, 115 mmol) in THF : H2O (1 : 1 v/v, 2 ml) and the mixture
was allowed to evaporate resulting in the formation of colourless
single crystals. IR (n/cm-1) 1037 s (BF4), 1597, 1554, 1657, 3307 m
(NH), 3368 (m, NH). Anal. Calcd (%) for C52H52N12O4S4AgBF4:
C, 52.75; H, 4.43; N, 14.20. Found (%) C, 51.50; H, 4.43; N, 14.10.
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Acknowledgements
We thank Durham University, the Higher Education Commission
of Pakistan and the Charles Wallace Trust Pakistan for partial
funding. We are grateful to Mr Ian McKeagh for assistance in
NMR titrations and valuable discussions.
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5708–5714 | 5713
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