Anion-ligand interaction in binuclear cyclic dimer complex of a tribenzo-S2O2 macrocycle with silver(I) picrate

Article abstract of DOI:10.1016/j.molstruc.2006.05.032

From the reaction of tribenzo-S₂O₂ macrocyclic ligand (L¹) and silver picrate (AgPic), a unique binuclear complex [Ag₂(L¹)₂(Pic)₂] (1) has been obtained. The species 1 has been characterised by single-crystal X-ray diffraction analysis providing a definitive proof of its cyclic dimer structure as well as the anion-ligand π-π stacking interactions between L¹ and Pic^-. The result of a comparative NMR experiment suggests that the solid structure of 1 is also retained in solution.

Full text of DOI:10.1016/j.molstruc.2006.05.032

Journal of Molecular Structure 827 (2007) 201–205
www.elsevier.com/locate/molstruc
Anion–ligand interaction in binuclear cyclic dimer complex
of a tribenzo-S2O2 macrocycle with silver(I) picrate
Joobeom Seo, Mi Ryoung Song, Kaniz Fatima Sultana, Hyun Jee Kim,
*
Jineun Kim, Shim Sung Lee
Department of Chemistry (BK21) and Research Institute of Natural Science, Gyeongsang National University, Chinju 660-701, Republic of Korea
Received 6 April 2006; received in revised form 9 May 2006; accepted 13 May 2006
Available online 30 June 2006
Abstract
From the reaction of tribenzo-S2O2 macrocyclic ligand (L1) and silver picrate (AgPic), a unique binuclear complex [Ag2(L1)2(Pic)2] (1)
has been obtained. The species 1 has been characterised by single-crystal X-ray diffraction analysis providing a definitive proof of its
cyclic dimer structure as well as the anion–ligand p–p stacking interactions between L1 and Picꢀ. The result of a comparative NMR
experiment suggests that the solid structure of 1 is also retained in solution.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Tribenzo-S2O2 macrocycle; Binuclear complex; Silver picrate; Anion–ligand interaction; NMR; p–p stacking
1. Introduction
applications including recognition [10,11] and separation
[12] of soft metal ions. Recently, we have realised that
the ligand–anion interaction through the aromatic units
may contribute significantly to enhance the soft metal ion
extractability [12] as discussed elsewhere for hard metal
ion system [13]. This work has been stimulated by our
extraction results which showed efficient selectivity for sil-
ver(I) by thiaoxa-macrocycles through anion–ligand inter-
action [12]. Taking this reason into account, the complex
system of rigidity enforced tribenzo-S2O2 macrocyclic
ligand L1 with the silver(I) picrate was selected for this pur-
pose. Herein we report the synthesis and structural charac-
teristics of silver(I) picrate complex of L1 both in solid and
solution states with emphasis on the anion–ligand
interaction.
In supramolecular coordination chemistry, the addition-
al interactions such as H-bonding, p–p stacking interac-
tion, p-coordination, cooperative metal binding, or anion
assembly play a significant role not only in the stabilisation
of the resulting complexes but also in the transport proper-
ties of the related complexes such as solvent extraction and
membrane transport [1]. Since such interactions are rela-
tively weak but selective, an increasing interest has been
in the design of new ionophore system with the suitable
synergic effect in the area of separation and detection of
the target species [2–4]. The p–p stacking interactions
between aromatic units have been relatively well document-
ed that aryl groups prefer to associate in either an offset-
face-to-face or edge-to-face of an orientation [5].
Our particular interest has been the construction of
supramolecular complexes based on sulfur-containing
mixed donor macrocycles [6–9] and their use in analytical
*
Corresponding author. Tel.: +82 55 751 6021; fax: +82 55 753 7614.
E-mail address: sslee@gsnu.ac.kr (S.S. Lee).
0022-2860/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.05.032

202
J. Seo et al. / Journal of Molecular Structure 827 (2007) 201–205
Table 1
2. Experimental
Crystal data and structure refinement for 1
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C60H52Ag2N6O18S4
1489.06
173(2)
0.71073
Triclinic
2.1. Materials and instrumentation
All chemicals used in synthesis were of reagent grade
without purification. The IR spectrum was recorded as
KBr pellet on a Shimadzu FT-IR 8400S spectrometer. H
NMR spectra were obtained with a Bruker DRX-500 spec-
trometer (500 MHz). Chemical shifts for samples were
expressed in ppm and calibrated against TMS as a refer-
ence. The mass spectrum was measured with a JEOL
JMS-700 spectrometer.
˚
1
Pꢀ1
˚
a (A)
14.3642(12)
15.1665(13)
15.6077(13)
63.254(2)
˚
b (A)
˚
c (A)
a
b
c
88.7810(10)
83.168(2)
3012.9(4)
3
˚
Volume (A )
2.2. Preparation of [Ag2(L1)2(Pic)2] (1)
Z
2
Calculated density (g/cm3)
Absorption coefficient (mmꢀ1
F(000)
1.641
0.868
1512
0.4 · 0.2 · 0.05
1.43–28.32
ꢀ18 6 h 6 18
ꢀ20 6 k 6 9
ꢀ20 6 l 6 14
18,429/13,197
0.0316
h=28.32, 87.9%
Empirical SADABS
Full-matrix least squares on F2
13,196/0/821
1.106
)
L1 was synthesised by coupling reaction of 2,20-(ethylen-
edioxy)bis(benzyl chloride) and 1,3-benzenedimethanethiol
in presence of Cs2CO3 under high dilution condition. The
detailed procedure will be described elsewhere [14]. Silver
picrate (16.8 mg, 0.050 mmol) in methanol (5 mL) and L1
(20.4 mg, 0.050 mmol) in dichloromethane (5 mL) were
mixed with stirring and yellow precipitate was obtained.
The isolated solid product was dissolved in DMSO and
X-ray quality crystals of 1 were obtained by vapour diffu-
sion of diethyl ether in 65% yield. Mp 170–173 ꢁC
(decomp.). IR (KBr, cmꢀ1): 3087w, 1633s, 1566s, 1487w,
1427m, 1342vs, 1280m, 1263w, 1086w, 916w, 712w. MS
Crystal size (mm)
h range for data collection (deg)
Index range
Reflections collected/unique
R (int)
Completeness to hmax
Absorption method
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
R1 = 0.0776, wR2 = 0.1413
R1 = 0.1190, wR2 = 0.1546
1.294 and ꢀ1.170
(FAB): m/z = 1258
[
107Ag2(L1)2Pic]+. 1H NMR
ꢀ3
˚
Largest diff. peak and hole (e A
)
(500 MHz, CD3CN): 3.75 (s, 4H, H7), 3.78 (s, 4H, H6),
4.25 (s, 4H, H1), 6.90–6.92 (dd, 2H, H2), 6.94–6.97 (td, 2
H, H4), 7.06–7.07 (dd, 2 H, H9), 7.21–7.26 (m, 3H, H3,
H10), 7.36–7.38 (m, 3H, H5, H8), 8.67 (s, 2H, Picꢀ). The
proton numbers in NMR data indicate the nonequivalent
protons represented in Fig. 4.
times those of attached atoms. Crystallographic data
are summarised in Table 1.
3. Results and discussion
2.3. Crystal structure determination and refinement
The best way to prove presence of the anion–ligand
interaction is to determine the crystal structure of the cor-
responding complex and/or to find the evidence of such
interactions in solution by NMR [12,13]. Thus, the struc-
tural studies of the silver picrate complex of L1 in solid
state and in solution were undertaken.
All data were collected on a Bruker SMART diffrac-
tometer equipped with a graphite monochromated Mo
Ka (k = 0.71073 A) radiation source and a CCD detec-
˚
tor; 45 frames of two-dimensional diffraction images were
collected and processed to obtain the cell parameters and
orientation matrix [15]. The two-dimensional diffraction
images were collected, each of which was measured for
10 s at ꢀ100 ꢁC. The frame data were processed to give
structure factors using the program SAINT [15]. The
structure was solved by a direct method and refined by
full matrix least square against F2 for all data using
SHELXTL software [16]. All nonhydrogen atoms were
anisotropically refined, and in the last cycles of refine-
ment, a weighting scheme was used, where weights
3.1. Crystal structure of [Ag2(L1)2(Pic)2] (1)
Reaction of L1 with silver picrate in dichloromethane/
methanol afforded a yellow precipitate product. Vapour
diffusion of diethyl ether to the DMSO solution resulted
in single crystals. An X-ray analysis revealed that its struc-
ture is a unique binuclear cyclic dimer [Ag2(L1)2Pic2] (1)
(Fig. 1). A summary of bond lengths and angles in the
coordination sphere of each silver(I) is given in Table 2.
Since one carbon atom between O1 and O2 is disordered
occupying two positions (63:37), this may eliminate the
inversion symmetry of 1 in the crystal. While the symmetry
of the complex exists in solution, as indicated by its NMR
were
calculated
from
the
following
formula:
2
w ¼ 1=½r2ðF 02Þ þ ðaPÞ þ ðbPÞꢁ where P ¼ ðF 02 þ 2F 2cÞ=3.
The final difference Fourier map did not show any signif-
icant features except the several ghost peaks close to
heavy atoms. All hydrogen atoms were included in calcu-
lated position with isotropic thermal parameters 1.2

J. Seo et al. / Journal of Molecular Structure 827 (2007) 201–205
203
Fig. 1. Molecular structure of binuclear cyclic dimer [Ag2(L1)2(Pic)2] (1) showing p–p stacking interactions (dashed lines): (a) side and (b) top views.
Hydrogen atoms are omitted for clarity. Ellipsoids are drawn at the 50% probability level.
Table 2
Selected bond lengths (A) and angles (ꢁ) for 1
S3–Ag1–S2 150.77(7)ꢁ to S3–Ag1–O5 92.82(12)ꢁ and
S2–Ag1–O5 92.93(12)ꢁ. The distortion of the trigonal pla-
nar geometry could be attributed to the long range interac-
˚
Ag(1)–S(2)
Ag(1)–O(5)
Ag(2)–S(4)
2.452(2)
2.568(5)
2.440(2)
Ag(1)–S(3)
Ag(2)–S(1)
Ag(2)–O(12)
2.435(2)
2.440(2)
2.501(4)
˚
˚
tions of Ag1 ꢂ ꢂ ꢂ O3 3.108(6) A and Ag2 ꢂ ꢂ ꢂ O1 3.158(7) A,
forcing the silver(I) out of the trigonal S2O coordination
˚
˚
S(3)–Ag(1)–S(2)
S(2)–Ag(1)–O(5)
S(4)–Ag(2)–O(12)
150.78(6)
93.01(11)
94.00(11)
S(3)–Ag(1)–O(5)
S(4)–Ag(2)–S(1)
S(1)–Ag(2)–O(12)
92.78(11)
150.81(6)
91.81(11)
plane by 0.560 A (for Ag1) and 0.563 A (for Ag2) towards
the O-donors of the ligands.
Additionally, the p–p stacking (dashed lines in Fig. 1)
between two aromatic groups is another major interaction
in this structure. As illustrated in Fig. 3a, the coordinated
Picꢀ anions are arranged so that they form offset-face-to-
face type p–p stacking interaction with one benzo ring of
L1. The geometric parameters of the p–p interactions are
summarised in Table 3. The intercentroid distances (x)
and dihedral angles of aromatic rings between Picꢀ and
spectra (vide infra). The asymmetric unit therefore compris-
es two silver(I) centres, two ligand molecules and two pic-
rate ions. There are two crystallographically independent
Ag(I) ions, both of which show similar coordination envi-
ronments. Each silver(I) centre has a distorted trigonal pla-
nar array of two S atoms from two ligands and third site is
occupied by phenolate O atom of Picꢀ. This is an unusual
binuclear species in which two silver atoms bridge two
macrocyclic ligands forming a 2 + 2 (metal-to-ligand)
metallacycle. One similar system has been reported by
Schro¨der et al. [17].
Table 3
Geometric parameters of p–p stacking interactions for 1
˚
Interaction
Distance (A)
Dihedral
angle (ꢁ)
Centroid-to- Centroid-
˚
The Ag–S bond distances (2.435–2.451 A) are compara-
centroid (x) to-edge (y)
ble to those found in other silver(I)-thia macrocyclic com-
plexes [9,18]. The distance between two silver atoms is
6.221(1) A. The coordination sphere of each trigonal pla-
nar silver(I) is considerably distorted from the regular
one to give T-shaped geometry: the bond angles from
A(L1) ꢂ ꢂ ꢂ G(Picꢀ), face-to-face
D(L1) ꢂ ꢂ ꢂ H(Picꢀ), face-to-face
B(L1) ꢂ ꢂ ꢂ F(L1), edge-to-face
C(L1) ꢂ ꢂ ꢂ E(L1), edge-to-face
3.723
3.899
–
–
–
19.7(2)
21.2(2)
87.6(3)
83.1(3)
0
˚
4.297
4.555
–
G(Picꢀ) ꢂ ꢂ ꢂ G0(Picꢀ), face-to-face 3.450

204
J. Seo et al. / Journal of Molecular Structure 827 (2007) 201–205
Fig. 2. Packing diagram of [Ag2(L1)2(Pic)2] (1) showing intermolecular p–p stacking interactions between G and G0 rings (dashed line). The symmetry
0
operation code for is 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
1
The 500 MHz H NMR spectra of L1, [Ag2(L1)2(Pic)2]
a
b
(1) and Ag(L1)PF6 were obtained in CD3CN/CDCl3 (v/v
1:1), respectively. Figs. 4a–c show the aromatic region of
each spectrum. In complexation, the AgPF6 was also used
as a reference silver salt to exclude both silver(I)–anion and
ligand–anion interactions. The signals of seven aromatic
protons (H2–5 and H8–10) for free L1 were well resolved
and identified (Fig. 4a). Upon complexations with AgPF6
(Fig. 4b) and AgPic (Fig. 4c), the shapes and chemical
shifts for the aromatic protons of L1 change from its
uncomplexed one. These changes are caused by both
ligand–silver(I) and/or ligand–Picꢀ interactions. The max-
imum downfield shift for H8 upon complexation can be
considered due to the p-interactions [19] between silver(I)
and the aromatic ring (H8–10), which is also shown in the
solid state (see Fig. 1). Importantly, the upfield shift of
the ligand aromatic protons (H2–4 and H8,10) in 1
(Fig. 4c) compared to those of Ag(L1)PF6 complex
(Fig. 4b) supports the existence of the proposed p–p stack-
ing interactions.
O
x
NO2
Ag
y
O2N
O
O
NO2
Fig. 3. Two types of p–p stacking interactions observed in 1: (a) offset-
face-to-face interaction between L1 and Picꢀ and (b) edge-to-face
interligand interaction.
L1 [A ꢂ ꢂ ꢂ G; 3.723 A, 19.7(2)ꢁ and D ꢂ ꢂ ꢂ H; 3.899 A,
21.2(2)ꢁ] that falls in the shorter end of literature range
˚
˚
˚
(3.7–4.6 A) for the offset-face-to-face interaction type [5].
And such dihedral angles between the Picꢀ and benzo
group indicate slightly tilted orientation. In addition,
edge-to-face type (Fig. 3b) p–p interactions are also
observed between two ligands. This result indicates that
the anion–ligand interaction as well as ligand–ligand inter-
action stabilises the conformation of 1 effectively through
the p–p interactions. In packing structure, the intermolecu-
lar p–p stacking interaction (dashed line in Fig. 2) in the
In addition, three methylene peaks for the free L1 (H1;
4.222, H6; 3.708, and H7; 3.658 ppm) were well resolved
as individual singlets. Upon complexations with silver salts,
the methylene protons shifted downfield, suggesting the
complex formations. There is no significant difference in
the changes of chemical shifts between PFꢀ6 and Picꢀ ions.
The order of magnitude of the chemical shift variation is
H6, H7 (ꢃ0.08 ppm) > H1 (ꢃ0.03 ppm), indicating that
the silver(I) is strongly coordinated by S atoms, and the
O atom interacts weakly, similar to the cases in solid state.
In summary, the assembly reaction of tribenzo-S2O2
macrocycle and silver picrate has led to the preparation
of a unique binuclear cyclic dimer complex. A comparative
˚
distance of 3.450 A also stabilises the crystal lattice.
3.2. Comparative NMR study
As mentioned, the p–p interactions including anion–li-
gand interaction can contribute to the stability of the relat-
ed complexes as well as their use in separation and
detection of the species. Such interaction for the related
ion-pair complex could be conveniently estimated by
NMR [12,13]. For this purpose, the comparative NMR
experiment was undertaken.

J. Seo et al. / Journal of Molecular Structure 827 (2007) 201–205
205
Fig. 4. 500 MHz 1H NMR spectra of aromatic region for: (a) L1, (b) Ag(L1)PF6, (c) [Ag2(L1)2(Pic)2] (1) (10 mM) in CD3CN/CDCl3 (v/v 1:1). The
complex solution (b) was prepared by dissolving equimolar amount of AgPF6 in 10 mM of L1 in the solvent.
[3] Y. Kobuke, K. Kokubo, M. Munakata, J. Am. Chem. Soc. 117
NMR study suggested the formation of the p–p stacking
interaction between Picꢀ and benzo-subunit in the ligand,
(1995) 12751.
[4] B. Choi, I. Yoon, J. Kim, J. Kim, S.S. Lee, J.S. Kim, Analyst 127
which was also observed in the solid state. The structural
characteristics revealed here could be potentially useful in
(2002) 947.
[5] C.A. Hunter, J.K.M. Sanders, J. Am. Chem. Soc. 112 (1990) 5525.
the design of new receptor molecules including extractants.
[6] I. Yoon, J. Seo, J.-E. Lee, M.R. Song, S.Y. Lee, K.S. Choi, O.-S.
Jung, K.-M. Park, S.S. Lee, Dalton Trans. (2005) 2352.
[7] Y. Jin, I. Yoon, J. Seo, J.-E. Lee, S.-T. Moon, J. Kim, S.W. Han, K.-
M. Park, L.F. Lindoy, S.S. Lee, Dalton Trans. (2005) 788.
[8] K.-M. Park, I. Yoon, J. Seo, J.-E. Lee, J. Kim, K.S. Choi, O.-K.
Jung, S.S. Lee, Cryst. Growth Des. 5 (2005) 1707.
[9] J. Seo, M.R. Song, J.-E. Lee, S.Y. Lee, I. Yoon, K.-M. Park, J. Kim,
J.H. Jung, S.B. Park, S.S. Lee, Inorg. Chem. 45 (2006) 952.
[10] S.J. Lee, J.H. Jung, J. Seo, I. Yoon, K.-M. Park, L.F. Lindoy, S.S.
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Acknowledgement
This work was supported by Korea Science and Engi-
neering Foundation (Grant R01-2004-000-10321-0).
Appendix A. Supplementary material
[11] K.-M. Park, Y.H. Lee, Y.R. Jin, J. Seo, I. Yoon, S.C. Lee, S.B. Park,
M.-S. Gong, M.L. Seo, S.S. Lee, Supramol. Chem. 16 (2004) 51.
[12] M.R. Song, J.-E. Lee, S.Y. Lee, J. Seo, K.-M. Park, S.S. Lee, Inorg.
Chem. Commun. 9 (2006) 75.
[13] G.G. Talanova, N.S.A. Elkarim, V.S. Talanov, R.E. Hanes Jr., H.-S.
Hwang, R.A. Bartsch, R.D. Rogers, J. Am. Chem. Soc. 121 (1999)
11281.
Supplementary crystallographic data associated to com-
plex 1 have been deposited at the Cambridge Crystallo-
graphic Data Centre, CCDC No. 601601. Copies of the
data can be obtained free of charge on application to
CCDC, 12 Union road, Cambridge CB2 1EZ, UK (fax:
+44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk), or
electronically via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.
2006.05.032.
[14] M.R. Song, J. Seo, J.-E. Lee, S.Y. Lee, K.-M. Park, S.S. Lee
(Manuscript in preparation for submission).
[15] Bruker, SMART Ver. 5.635 and SAINT Ver. 6.22, Area detector
control and data integration and reduction software, Bruker Analyt-
ical X-ray Instruments Inc. Madison, Wisconsin, USA, 2001.
[16] G.M. Sheldrick, SHELXTL Ver. 6.10, Programs for crystal structure
analysis, University of Go¨ttingen, Go¨ttingen, Germany, 2000.
[17] L. Brammer, C.S. Rodger, A.J. Blake, N.R. Brooks, N.R. Champ-
ness, J.W. Cunningham, P. Hubberstry, S.J. Teat, C. Wilson, M.
Schro¨der, J. Chem. Soc. Dalton Trans. (2002) 4134.
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