Dinuclear silver(I) complexes of N,N′-dibenzyl-4,13-diaza-18-crown-6- ether and dibenzo-24-crown-8-ether

Article abstract of DOI:10.1016/j.poly.2004.03.026

Three silver(I) coordination complexes of diaza- and dibenzo-crown ethers, [Ag(DDAC)](CF₃SO₃) (1) [Ag₂(DDAC)(CF ₃SO₃)₂] (2) and [Ag₂(DB24C8)(CF ₃SO₃)₂] (3) have been synthesized by using different molar ratios of ligand to silver triflate salt, and characterized structurally. A large excess of DDAC ligand leads to mononuclear complex 1, and a large excess of silver triflate gives rise to dinuclear complex 2, based on metal-heteroatom and metal-oxygen interactions. Ligand DB24C8 coordinates two silver(I) ions to afford dinuclear complex 3.

Full text of DOI:10.1016/j.poly.2004.03.026

Polyhedron 23 (2004) 2117–2123
www.elsevier.com/locate/poly
Dinuclear silver(I) complexes of
N; N0-dibenzyl-4,13-diaza-18-crown-6-ether and
dibenzo-24-crown-8-ether
a,d,
b
b
b
Ming Wen
*, Megumu Munakata , Yusaku Suenaga , Takayoshi Kuroda-Sowa ,
c
Masahiko Maekawa , Iwade Kodai
b
a
Department of Chemistry, Tongji University, 1239# Siping Road, Shanghai 200092, China
Department of Chemistry, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
Research Institute for Science and Technology, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
b
c
d
State Key Laboratory of Coordination Chemistry, Nanjing University, 210093, China
Received 5 February 2004; accepted 23 March 2004
Available online 28 July 2004
Abstract
Three silver(I) coordination complexes of diaza- and dibenzo-crown ethers, [Ag(DDAC)](CF3SO3) (1), [Ag2(DDAC)(CF3SO3)2]
(2) and [Ag2(DB24C8)(CF3SO3)2] (3) have been synthesized by using different molar ratios of ligand to silver triflate salt, and
characterized structurally. A large excess of DDAC ligand leads to mononuclear complex 1, and a large excess of silver triflate gives
rise to dinuclear complex 2, based on metal–heteroatom and metal–oxygen interactions. Ligand DB24C8 coordinates two silver(I)
ions to afford dinuclear complex 3.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Silver(I) complexes; Dinuclear complex; Mononuclear complex
1. Introduction
silver(I) ions [14,15], because these silver(I) complexes
used usually involve the oxygen base cavities and
p-donor phenyl groups. Same as the reported example
[16], two different coordination complexes can be
constructed by using different molar ratios of crown
ether ligand to silver(I) ion in this work. The macro-
cyclic crown ether and cryptand ligands were incor-
porated into the dimers.
In this work, two cryptand type ligands of
crown ethers, N; N0-dibenzyl-4,13-diaza-18-crown-6-ether
(DDAC) and dibenzo-24-crown-8-ether (DB24C8), as a
continuation ofour previous work [15], havebeenselected
as ligands to synthesize three silver(I) coordination
complexes, [Ag(DDAC)](CF3SO3) (1), [Ag2-(DDAC)-
(CF3SO3)2] (2) and [Ag2(DB24C8)(CF3SO3)2] (3). The
cryptand crown ether hosts, diaza-crown ether and dib-
enzo-crown ether, using different coordination modes
bind the guest silver(I) ions and build up distinctive
molecular architectures.
Macrocyclic ligands have long been employed for
studies involving transition metal ion recognition [1,2].
There has been tremendous development with respect
to cyclic type ligands like crown ethers [3] which are
able to perform specific functions. When the macro-
cyclic ligands are bound to polymeric supporting ma-
terials, the resulting materials can serve as ion sensors,
exchange resins, metal ion extractors, phase transfer
catalysts, mimics of enzyme systems and photore-
sponsive chromophores [4–6].
Cryptand type ligands, crown ether systems are
suitable to be used in the design of complexation
agents for metal ions [7–13]. We have been continu-
ously studying dibenzo-crown ether complexes with
* Corresponding author. Fax: +86-21-6598-2287.
E-mail address: m_wen@mail.tongji.edu.cn (M. Wen).
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.03.026

2118
M. Wen et al. / Polyhedron 23 (2004) 2117–2123
2.2.2. [Ag2(DDAC)(CF3SO3)2] (2)
O
O
O
A solution of DDAC (12.8 mg, 0.03 mmol) in toluene
(10 ml) was treated with Ag(CF3SO3) (38.8 mg, 0.30
mmol). The above procedure was repeated to yield
colorless platelet single crystals of 2 (13.4 mg, yields
26%). Anal. Calc. for Ag2S2F6O10N2C28H38: C, 34.42;
H, 4.09; N, 2.81. Found: C, 35.16; H, 4.00; N, 2.93%.
Main IR bands (KBr, m/cmꢀ1): 2887(m), 2370(w),
1458(w), 1285(s), 1267(s), 1148(s), 1106(s), 1036(s),
736(m), 708(m), 638(m).
H2C
N
N
CH2
O
N,N'-Dibenzyl-4,3-diaza-18-crown-6-ether
(DDAC)
O
O
O
O
O
O
O
O
2.2.3. [Ag2(DB24C8)(CF3SO3)2] (3)
Dibenzo-24-crown-8-ether
(DB[24]C8)
Similar to the previous complexes, DB[24]C8 (44.8
mg, 0.10 mmol) was added to a solution of AgCF3SO3
(51.4 mg, 0.20 mmol) in toluene, and yielded colorless
platelet single crystals of 3 (26.9 mg, yield 28%). Anal.
Calc. for Ag2S2F6O14C26H32: C, 32.42; H, 6.88. Found:
C, 32.05; H, 6.56%. Main IR bands (KBr, m/cmꢀ1):
3547(m), 2910(s), 1597(s), 1504(s), 1456(s), 1352(s),
1278(s), 1224(s), 1160(s), 1116(s), 1083(s), 1047(s),
1033(s), 951(s), 938(s), 905(m), 746(m), 634(s).
2. Experimental
2.1. General procedures
All reactions and manipulations were performed
under an argon atmosphere by using Schlenk tech-
niques. All chemicals were reagent grade and used as
supplied without further purification. Solvents were
dried and distilled by using standards methods before
use. Reagent grade DDAC was purchased from Tokyo
Chemical Industry Co. Ltd., whereas silver perchlorate
and all other chemicals were purchased from Wako
Pure Chemical, Inc. and used as received. The IR
spectra were measured as KBr disks on a JASCO FT/
IR-8000 spectrometer at room temperature. All crys-
tallizations of the silver complexes were performed in
the dark.
2.3. Crystallography
Single crystal X-ray data for all complexes were
measured on a Rigaku/MSC Mercury CCD diffrac-
tometer with graphite monochromated Mo Ka radia-
ꢀ
tion ðk ¼ 0:71073 A) at )123 ꢁ 1 °C for 1 and 2, and
26.0 ꢁ 1 °C for 3. Details are summarized in Table 1.
Selected bond lengths and angles for the three complexes
are given in Table 2.
3. Results
2.2. Syntheses
3.1. Syntheses and infrared spectroscopy
2.2.1. [Ag(DDAC)](CF3SO3) (1)
3.1.1. Syntheses
To a toluene solution (8 ml) containing Ag-
(CF3SO3) (12.6 mg, 0.048 mmol), DDAC (106.2 mg,
0.24 mmol) was added. The mixture was stirred at
room temperature for 20 min and filtered. A portion
of the filtrate (2 ml) was introduced into a 7 mm glass
tube and layered with n-hexane as a diffusion solvent.
After the glass tube was sealed under argon and left
standing at room temperature for one week, colorless
block crystals of 1 suitable for X-ray determination
were isolated. The theoretical value of elemental
analysis and the isolated yield (21.4 mg, 18%) are
based on the formula without THF molecules. Anal.
Calc. for AgSF3O7N2C27H38: C, 46.36; H, 5.48; N,
4.00. Found: C, 46.35; H, 5.06; N, 3.96%. Main IR
bands (KBr, m/cmꢀ1): 2858(m), 1494(w), 1452(m),
1266(s), 1145(s), 1106(s), 1030(s), 749(m), 709(m),
638(s).
It is noted that in the preparations described above
different metal:ligand ratios were used. Generally, co-
ordination of an aromatic ligand to silver ions can be
achieved via a stoichiometric reaction [17,18], but
sometimes an excess of ligand or metal ion has to be
used to obtain coordinated complexes [19–23]. In this
work, the complexes presented here are prepared via
reactions of excess ligand or metal ion. In the experi-
ments, when the molar ratios of M:L were 5:1, 1:10 and
1:2 for 1, 2 and 3, respectively, crystallized solids were
isolated at room temperature, and the different molar
ratios led to different crystal structures. Reasons for the
use of silver salt excesses in 3 are as follows: (i) The
solvent toluene may form metal complexes in solution
with silver ions [24] which partially consumes the metal
salt. Thus, the preparation of silver(I) complexes in
toluene sometimes requires an excess of the silver salt

M. Wen et al. / Polyhedron 23 (2004) 2117–2123
2119
Table 1
Crystallographic data for complexes 1–3
Complex
1
2
3
Formula
AgSF3O7N2C27H38
699.53
Ag2S2F6O10N2C28H38
1912.92
triclinic
AgSF3O7C13H16
481.19
Formula weight
Crystal system
Space group
monoclinic
P21=n (#14)
11.261(3)
monoclinic
P21=c (#14)
10.0449(3)
21.051(3)
ꢁ
P1 (#2)
ꢀ
a (A)
12.603(6)
15.094(7)
10.252(6)
98.76(2)
100.34(2)
109.46(1)
1760(1)
2
ꢀ
b (A)
13.523(4)
20.222(6)
ꢀ
c (A)
8.6860(5)
a (°)
b (°)
c (°)
V (A )
Z
109.870(3)
110.4894(6)
3
ꢀ
2896(1)
4
1720.5(2)
4
F(0 0 0)
T (°C)
q (g/cm3)
k, A (Mo Ka)
l (cm)
Number of reflections measured
1440.00
)123.0
1.604
960.00
)123.0
1.804
960.00
26.0
1.858
ꢀ
0.71069
8.33
0.71069
13.15
0.71069
13.53
9062 (total)
6594 (unique)
6049
19 999 (total)
7949 (unique)
5651
20 973 (total)
2018 (unique)
3912
Number of observed reflections [I > 2rðIÞ]
Number of variable parameters
Residuals: R; Rw
370
0.026; 0.053
1.07
452
0.066; 0.128
1.07
274
0.055; 0.108
1.44
Goodness-of-fit
P
P
P
P
2
2 1=2
R ¼ jjFoj ꢀ jFcjj= jFoj. Rw ¼ ½ wðFo2 ꢀ Fc2Þ = wðFo2Þ ꢂ
.
[25]. (ii) When a compound (complex) in solution is
‘‘incongruently saturating’’, its crystal cannot be ob-
tained via a stoichiometric reaction [26]. We examined
the effect of a different molar ratio on the nature of the
final product. The reactivity of AgCF3SO3 with
DB24C8 was systematically studied in toluene with
Table 2
ꢀ
Selected bond lengths (A) and bond angles (°) for complexes 1–3
Complex 1
Bond lengths
Ag(1)–O(3)
Ag(1)–N(2)
2.598(1)
2.316(2)
Ag(1)–O(4)
2.686(2)
Ag(1)–N(1)
2.305(2)
Bond angles
O(3)–Ag(1)–O(4)
O45)–Ag(1)–N(1)
Ag(1)–O(3)–C(21)
Ag(1)–O(4)–C(24)
Ag(1)–N(1)–C(25)
Ag(1)–N(2)–C(26)
63.6(4)
O(3)–Ag(1)–N(1)
O(4)–Ag(1)–N(2)
Ag(1)–O(3)–C(23)
Ag(1)–N(1)–C(19)
Ag(1)–N(2)–C(16)
71.7(4)
73.6(4)
O(3)–Ag(1)–N(2)
N(1)–Ag(1)–N(2)
Ag(1)–O(4)–C(17)
Ag(1)–N(1)–C(22)
Ag(1)–N(2)–C(18)
121.9(4)
166.1(4)
102.5(9)
108.4(1)
111.8(9)
113.8(4)
110.7(8)
103.9(1)
108.4(1)
107.0(1)
117.5(1)
113.9(1)
111.5(1)
Complex 2
Bond lengths
Ag(1)–O(1)
Ag(1)–N(1)
Ag(2)–O(8)
2.511(4)
2.287(4)
2.252(3)
Ag(1)–O(2)
Ag(2)–O(6)
Ag(2)–N(2)
2.589(4)
2.592(4)
2.325(4)
Ag(1)–O(3)
Ag(2)–O(7)
2.203(4)
2.506(5)
Bond angles
O(1)–Ag(1)–O(2)
O(2)–Ag(1)–O(3)
O(6)–Ag(2)–O(7)
O(7)–Ag(2)–O(8)
115.5(1)
105.2(1)
121.5(1)
113.4(1)
O(1)–Ag(1)–O(3)
O(2)–Ag(1)–N(1)
O(6)–Ag(2)–O(8)
O(7)–Ag(2)–N(2)
121.4(2)
73.7(1)
113.0(1)
74.5(1)
O(1)–Ag(1)–N(1)
O(3)–Ag(1)–N(1)
O(6)–Ag(2)–N(2)
O(8)–Ag(2)–N(2)
78.8(2)
161.5(2)
71.0(1)
163.5(2)
Complex 3
Bond lengths
Ag(1)–O(1)
2.450(4)
112.3(3)
Ag(1)–O(5)
2.538(5)
113.6(4)
Ag(1)–O(6)
2.634(6)
Bond angles
Ag(1)–O(1)–C(1)
Ag(1)–O(1)–C(2)

2120
M. Wen et al. / Polyhedron 23 (2004) 2117–2123
ꢀ
different M:L ratios. Reactions similar to that described
in the experimental section but performed with M:L
ratios of 1:1 led to no evidence for formation of an
isolable complex. In order to obtain polymeric com-
plexes by connecting silver(I) ions and the phenyl group
of DDAC besides silver(I) locating in the cavities, a
large excess of silver triflate was used with L:M ¼ 1:10
which led to dinuclear complex 2. The effect of a dif-
ferent molar ratio was studied by employing a large li-
gand excess with L:M ¼ 5:1. The result was the
mononuclear complex 1.
2.315(2) A. The O–Ag–O and N–Ag–N angles are
63.6(4)° and 166.13(4)°, respectively. The remaining two
ligand oxygen atoms are not involved in coordination,
and the triflate ion only plays a charge-balance and
space-filling role.
3.2.2. Dinuclear complex [Ag2(DDAC)(CF3SO3)2] (2)
An ORTEP drawing of complex 2 with the atom
numbering scheme is shown in Fig. 2. The symmetric
unit contains two independent dinuclear molecules each
located at an inversion center. The coordination envi-
ronment of each metal atom is almost tetrahedral,
comprising of three oxygen atoms of which two are from
DDAC and one from a triflate group, plus a nitrogen
atom. The DDAC ligand thus contains two silver(I)
centers in its heterocyclic hard donor cavity with Ag–O
3.1.2. Infrared spectroscopy
In the IR spectra of 1–3, a broad strong absorption
occurs in the region 638–1254 cmꢀ1, and their peaks are
shifted to slightly different frequencies compared with
the normal absorption of AgCF3SO3 at 1256, 1179,
1037, and 629 cmꢀ1. This suggests that the triflate
groups in these complexes are present not as ionic spe-
cies, but as coordinated ones [27]. The coordination of
silver(I) ions to oxygen or nitrogen atoms of diaza-
crown ether and dibenzo-crown ether can also be seen
by comparing the spectra of 1–3 with those of the two
ꢀ
bond lengths ranging from 2.203(4) to 2.592(4) A and
ꢀ
Ag–N bond lengths of 2.287(4) and 2.325(4) A. The
present Ag–O bond lengths are well within the normal
ꢀ
range 2.17–2.61 A observed in silver(I)–crown ether
complexes [15] and the Ag–N bond lengths are normal
free ligands (DDAC at 1453, 1123, 1056, 749, 701 cmꢀ1
DB24C8 at 1594, 1507, 1357, 1225, 960, 740 cmꢀ1).
,
3.2. Description of the structures
3.2.1. Mononuclear complex [Ag(DDAC)](CF3SO3)
(1)
Molecules of triflate anion exist independently of the
complex in lattice interstices. The molecular structure of
complex 1 together with the numbering scheme is shown
in Fig. 1. The silver(I) ion is in a distorted tetrahedral
environment, being coordinated by two nitrogen atoms
and two oxygen atoms on the same side of the N–Ag–N
system, in which Ag–O bond lengths are 2.598(1) and
ꢀ
2.686(2) A and Ag–N bond lengths are 2.305(2) and
Fig. 1. ORTEP view of the molecular structure of 1.
Fig. 2. Molecular structure of the dinuclear unit of 2.

M. Wen et al. / Polyhedron 23 (2004) 2117–2123
2121
Fig. 3. Molecular structure of the dinuclear unit of 3.
compared with those in previously reported crystate–
silver(I) complexes [10].
The average Ag–O bond lengths of 2.642, 2.442 and
ꢀ
2.540 A observed for 1, 2 and 3, respectively, are within
the normal range observed in silver(I)–crown ether
complexes [10]. The average Ag–N bond lengths of
3.2.3. Dinuclear complex [Ag2(DB24C8)(CF3SO3)2]
(3)
ꢀ
ꢀ
2.310 A in 1 and 2.306 A in 2 are virtually the same and
a little longer than that in the silver(I) complex of
1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, but slight
shorter than that in the silver(I) complex of N-methy-
lated (L2) and N-benzylated 1,4,10,13-tetraoxa-7,
16-diazacyclooctadecane (L3) [10]. In the present com-
plexes, each silver(I) ion is not coordinated to all oxygen
and nitrogen atoms as in [Ag(L3)]PF6 [10]. In addition,
triflate oxygen atoms are not coordinated to silver(I)
ions in 1, but are coordinated to silver(I) ions in 2, and
the Ag–O bond length of silver(I) with triflate is shorter
than that of silver(I) with the ligand oxygen atoms.
Furthermore, the crown ether hosts in this work
are not involved in coordination of the phenyl group
to silver(I) via a p interaction, as our previous work in
DB18C6–Ag(I) complexes [15a] (Fig. 4). Two sym-
metry-related silver(I) ions can be located in the ox-
ygen base cavity of DB24C8 without silver(I)–p
interaction and p–p interaction (Fig. 4(c)). On the
other hand, even though DDAC has the same size,
six-membered hard donor cavity as that of DB18C6,
the silver(I) guest number and coordination fashion
differ distinctly. The coordination unit of DB18C6-
Ag(I) complexes can involve both r bonding at an
oxygen group and silver–p as well as p–p interaction
between two parallel phenyl groups (Fig. 4(a)). DDAC
only contains two symmetry-related silver(I) ions in its
Fig. 3 depicts a perspective view with the atom
numbering of centrosymmetric complex 3, in which each
silver(I) ion is octahedrally coordinated by two triflate
ꢀ
oxygens with an average Ag–O length of 2.586 A and
five oxygens of the ligand with an average Ag–O bond
ꢀ
length of 2.450 A. Each DB24C8 host molecule contains
two silver(I) ions as guests with a Agꢃ ꢃ ꢃAg distance of
ꢀ
3.95 A. Unlike dinuclear silver(I) coordination com-
plexes of the dibenzo-crown ether family in our previous
works, [Ag(DB[18]C6)(ClO4)](THF) [15a], the silver(I)
ions are not coordinated to phenyl groups.
4. Discussion
In this work, the diaza- and dibenzo-crown ether
hosts accommodate silver(I) ions as guests in their cyclic
hard donor base cavities. The structures of these three
silver(I) complexes display different characteristics with
the cation being encapsulated in a macrocyclic envi-
ronment with different L:M stoichiometries. A large
excess of DDAC ligand leads to mononuclear complex
1, and a large excess of silver triflate gives rise to
dinuclear complex 2 based on metal–heteroatom and
metal–oxygen interactions. DB24C8 coordinates to two
silver(I) ions to afford dinuclear complex 3.

2122
M. Wen et al. / Polyhedron 23 (2004) 2117–2123
-
CF3SO3
O
O
O
O
O
O
3.50Å
O
O
Ag
O
O
O
O
-O3SF3C
(a)
-
CF3SO3
CH2
O3SF3C
O
N
Ag
3.76Å
Ag
O
O
O
O
O
O
Ag
O
N
O
Ag
CH2
-
O
O
O
CF3SO3
CF3SO3
(b)
(c)
Fig. 4. Schematic view of dinuclear Ag(I) complexes with dibenzo- and diaza-crown ethers. [Ag(DB18C6)(CF3SO3)]2(acetone)2 (a),
[Ag2(DDAC)(CF3SO3)2] (b), [Ag2(DB24C8)(CF3SO3)2] (c).
six-membered heterocyclic hard donor cavity without
silver–p and p–p interaction (Fig. 4(b)). This case is
the same as the formation of the Ag(I)–DB24C8
complex with a eight-membered hard donor cavity.
This indicates that the structure construction process
in the crown ether–silver(I) complex system is strongly
dependent on the ligand: cavity size and the existence
of heteroatoms as well as flexibility of the phenyl
group.
In conclusion, with the cryptand type ligands, two
distinct coordination complexes 1 and 2, have been
synthesized with different L:M stoichiometry. With re-
gard to silver(I) complexes with diaza- and dibenzo-
crown ethers (Fig. 4), there are two kinds of substantial
dinuclear complexes. The ligand DB18C6 is based on
the silver(I)–p interaction, in which the coordination
unit involves both r bonding at oxygen donor sites and
p–p interaction between two phenyl groups. The other
kind comprise dinuclear complex 2 and 3 in this work, in
which two silver(I) ions occupy the cyclic or heterocyclic
base cavity to coordinate to oxygen atoms without
Ag(I)–p interaction or p–p interaction. It is believed that
self-assembly of macrocyclic cryptand or dibenzo-crown
ether compounds with transition metal ions can be
constructed using stereospecific diaza- and dibenzo-
crown ethers ligands (cavity size, the existence of het-
eroatoms as well as the flexibility of phenyl groups) and
the molar ratio effect [10].
5. Supplementary material
Crystallographic data for the structures reported here
have been deposited with the Cambridge Crystallo-
graphic Data Center as Supplementary Publication Nos.
CCDC-220695, 220694 and 220693 for complex 1, 2 and
3, respectively. Copies of this information may be ob-
tained free of charge from: The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk or www:http//
www.ccdc.cam.ac.uk).
Acknowledgements
This work was partially supported by Grants-in-Aid
for Science Research [Nos. 10440201, 11874092,
12440189, 10016743 (priority area: metal-assembled
complexes)] from the Ministry of Education, Science,
Culture, Sports of Japan, and the Project-sponsored by
SRF for ROCS from the SEM [No. 1380241005], the

M. Wen et al. / Polyhedron 23 (2004) 2117–2123
2123
[14] T.B. Lu, X.M. Gan, M.Y. Tan, K.B. Yu, Polyhedron 12 (1993)
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Science Fund [No. 1380219042] from Tongji University
of China.
[15] (a) M. Wen, M. Munakata, Y. Suenaga, T. Kuroda-Sowa, M.
Maekawa, Inorg. Chim. Acta 322 (2002) 18;
(b) M. Wen, M. Munakata, Y. Suenaga, T. Kuroda-Sowa, M.
Maekawa, Inorg. Chim. Acta 338 (2002) 111.
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