Strong silver-silver interactions in three silver(I) carboxylate complexes with high cytotoxicity properties

Article abstract of DOI:10.1081/SIM-200055672

Three carboxylate silver(I) complexes, [Ag(fbc)]n, (1), [Ag2(cpd)]n (2) and [Ag2(idc)]n (3), were prepared and characterized by X-ray single crystal analysis, where fbcH is 4-fluorobenzoic acid, cpdH2 is cyclopentane-1,1- dicarboxylic acid and idcH2 is iminodiacetic acid. The three coordination polymers show clear Ag-Ag bonds in their structures. The Ag-Ag bond length 2.850 ? both in 1 and 2 is much shorter than that (2.89 A) in metal silver, which is the shortest silver-silver interaction reported. The result of cytotoxicity of the three complexes indicates that they have very high crytotoxicity properties to normal cells and carcinoma cells. Copyright

Full text of DOI:10.1081/SIM-200055672

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Strong Silver‐Silver Interactions in Three Silver(I)
Carboxylate Complexes with High Cytotoxicity
Properties
Xiu‐Ying Liu a & Hai‐Liang Zhu b
a Department of Chemistry, Wuhan University of Science & Engineering, Wuhan, P.R. China
b Institute of Functional Biomolecules and State Key Laboratory of Pharmaceutical
Biotechnology, Nanjing University, Nanjing, P.R. China
Version of record first published: 16 Aug 2006.
To cite this article: Xiu‐Ying Liu & Hai‐Liang Zhu (2005): Strong Silver‐Silver Interactions in Three Silver(I) Carboxylate
Complexes with High Cytotoxicity Properties, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
35:4, 325-332
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Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:325–332, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1081/SIM-200055672
Strong Silver-Silver Interactions in Three Silver(I)
Carboxylate Complexes with High Cytotoxicity Properties
Xiu-Ying Liu
Department of Chemistry, Wuhan University of Science & Engineering, Wuhan, P.R. China
Hai-Liang Zhu
Institute of Functional Biomolecules and State Key Laboratory of Pharmaceutical Biotechnology,
Nanjing University, Nanjing, P.R. China
three silver(I) complexes with carboxylate ligands, [Ag(fbc)]n
Three carboxylate silver(I) complexes, [Ag(fbc)]n, (1), (1), [Ag2(cpd)]n (2) and [Ag2(idc)]n (3), where fbcH is
[Ag2(cpd)]n (2) and [Ag2(idc)]n (3), were prepared and character-
ized by X-ray single crystal analysis, where fbcH is 4-fluoroben-
zoic acid, cpdH2 is cyclopentane-1,1-dicarboxylic acid and
idcH2 is iminodiacetic acid. The three coordination polymers
show clear Ag–Ag bonds in their structures. The Ag–Ag bond
4-fluorobenzoic acid, cpdH2 is cyclopentane-1,1-dicarboxylic
acid and idcH2 is iminodiacetic acid. The three coordination
polymers show clear Ag-Ag bonds in their structures and
high cytotoxicity properties to normal cells and carcinoma
˚
˚
length 2.850A both in 1 and 2 is much shorter than that (2.89A) cells.
in metal silver, which is the shortest silver–silver interaction
reported. The result of cytotoxicity of the three complexes indi-
EXPERIMENTAL
cates that they have very high crytotoxicity properties to normal
cells and carcinoma cells.
Materials and Measurements
Commercially available Ag2O, 4-fluorobenzoic acid, cyclo-
pentane-1,1-dicarboxylic acid and iminodiacetic acid were
purchased from Aldrich and used without further purifica-
tion. Other solvents and reagents were used as obtained from
The Second Chemicals Factory of Shanghai, P.R. China.
C, H and N elemental analyses were performed with a
Perkin-Elmer elemental analyzer.
Keywords carcinoma cells, crystal structures, cytotoxicity, silver
complexes, silver–silver bonds
INTRODUCTION
One of the recent hot topics in the coordination chemistry of
coinage metals(I) is the d10-d10 interactions between two
closed-shell cations, many examples of which have been
reported and reviewed in silver(I) complexes (Dance, 1986;
Dance et al., 1983; Guo et al., 1999; Jansen, 1987; Jaw et al.,
1989; Leung et al., 1999; Tong et al., 1999; Wang and Mak,
2000, 2001a, 2001b; Yam and Lee, 1993; Yam and Lo,
1999; Yam et al., 1994, 1998). Silver(I) complexes with
organic ligands containing donors such as O, N, and S atoms
are also of great interest in bioinorganic chemistry (Lopez-
Garzon et al., 1990; Veen, 1983) We have been investigating
the cytotoxicity of silver(I) complexes (Chen et al., 2001a,
2001b; Zhu et al., 2003) and, as an extension of this work,
report herein the syntheses, structures and cytotoxicities of
Syntheses of the AgI Complexes [Ag(fbc)]n (1)
A solution of Ag2O (0.12 g, 0.5 mmol) in 30% aqueous
ammonia solution (5 mL) was added drop-wise with stirring
at room temperature to a solution of 4-fluorobenzoic acid
(fbcH) (0.14 g, 1 mmol) in 30% aqueous ammonia solution
(5 mL). The mixture was let to stand still in the air to
vaporize about three-quarters of the solvents and filtered.
Crystals were obtained and washed three times with water,
and then dried in a vacuum desiccator over drying CaCl2.
The yield, melting/decomposition point and the analytical
data of elemental analyses and IR determination are presented
in Table 1.
Syntheses of the AgI Complexes [Ag2(cpd)]n (2)
Received 13 July 2004; accepted 13 January 2005.
A
solution of Ag2O (0.12 g, 0.5 mmol) in 30%
aqueous ammonia solution (5 mL) was added drop-wise
with stirring at room temperature to solution of
Address correspondence to Hai-Liang Zhu, Department of
Chemistry, Wuhan University of Science & Engineering, Wuhan
430073, P.R. China. E-mail: hailiang_zhu@fync.edu.cn
a
325

326
X.-Y. LIU AND H.-L. ZHU
at room temperature to a solution of iminodiacetic acid
TABLE 1
Analytical data for complexes (1), (2) and (3)
(idcH2) (0.07 g, 0.5 mmol) in 30% aqueous ammonia solution
(5 mL). The mixture was let to stand still in the air to
vaporize about three-quarters of the solvents and filtered.
Crystals were obtained and washed three times with water,
and then dried in a vacuum desiccator over drying CaCl2.
The yields and the analytical data of elemental analyses and
IR determination are presented in Table 1.
Compound (1) Formula
FW
C7H4AgFO2
246.97
32
Yield (%)
EA
Anal. Calcd.: C, 34.04;
H, 1.63 (%) Found: C,
33.83; H, 1.70(%)
3290 w, 1603 m,
1559–1557 vs, 1425 m
1411 m, 1384 s, 1329 m,
1292 m, 1279 m,
1109 m, 1106 m,
1035 m, 966 w, 915 m,
730 m, 700 w
IR (KBr, cm21
)
Data Collection, Structural Determination and
Refinement
Diffraction intensities were collected on a CCD area
detector for compounds (1) and (3), and on a Siemens R3m
diffractometer for compound (2) using Mo-Ka radiation
(l ¼ 71.073 pm). Absorption corrections were applied
(North, A. C. T., Phillips, D. C., Mathews, F. S. Acta Crystal-
logr. Sect. A 24, 351(1968)). The structure solutions and full-
matrix least-squares refinements based on F2 were performed
with the SHELX-97 program package (Sheldrick, G. M.
SHELX-97, Program for Crystal Structure Determination,
Compound (2) Formula
FW
C7H8Ag2O4
371.87
38
Yield (%)
EA
Anal. Calcd.: C, 22.61;
H, 2.17(%) Found: C,
22.55; H, 2.25(%)
2941 m, 1529 vs, 1439 s,
1395 s, 1360 vs, 1268 m,
1203 w, 882 w, 801 m,
775 w, 711 m
¨
University of Gottingen (1997)). All the non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were generated
geometrically and allowed to ride on their parent carbon
atoms. Analytical expressions of neutral-atom scattering
factors were employed, and anomalous dispersion corrections
were incorporated. The crystallographic data for the three
compounds are summarized in Table 2. Selected bond
distances and bond angles are given in Table 3.
IR (KBr, cm21
)
Compound (3) Formula
FW
C4H5Ag2NO4
346.83
69
Yield (%)
EA
Anal. Calcd.: C, 13.85;
H, 1.45; N, 4.04(%)
Found: C, 14.01; H,
1.50; N, 3.95(%)
3290 w, 1603 m,
1559–1557 vs, 1425 m
1411 m, 1384 s, 1329 m,
1292 m, 1279 m,
1109 m, 1106 m,
1035 m, 966 w, 915 m,
730 m, 700 w
RESULTS AND DISCUSSION
Syntheses of the Complexes [Ag(fbc)]n (1), [Ag2(cpd)]n (2)
and [Ag2(idc)]n (3).
The formation of the three complexes (1)–(3) can be
expressed as the following equations:
IR (KBr, cm21
)
nAg2O þ 2nfbcH ¼ nH2O þ 2½Agð fbcÞꢀ ð1Þ
nAg O þ ncpdH ¼ nH2O þ ½Ag ðcpdÞꢀnð2Þ
nAg O þ nidcH2 ¼ nH2O þ ½Ag ðidcÞꢀ nð3Þ
2
2
2
2
2
n
The compounds were prepared by mixing the solutions of
Ag2O and bi-equimolar 4-fluorobenzoic acid (fbcH) for (1),
or equimolar cyclopentane-1,1-dicarboxylic acid (cpdH2) and
iminodiacetic acid (idcH2) for (2) and (3), respectively. 30%
aqueous ammonia solution is the most suitable solvent
for the syntheses of the complexes and crystals generated by
evaporations of the solvents of the mixtures.
cyclopentane-1,1-dicarboxylic acid (cpdH2) (0.08 g, 0.5 mmol)
in 30% aqueous ammonia solution (mL). The mixture was let
to stand still in the air to vaporize about three-quarters of the
solvents and filtered. Crystals were obtained and washed
three times with water, and then dried in a vacuum desiccator
over drying CaCl2. The yield, melting/decomposition point
and the analytical data of elemental analyses and IR determi-
nation are presented in Table 1.
Structure Description of Complex (1)
The X-ray crystallographic study reveals that compound (1)
crystallizes in the monoclinic space group P21/c, and the asym-
metric unit consists of one Ag ion and one 4-fluorobenzoate
Syntheses of the AgI Complexes [Ag2(idc)]n (3)
A solution of Ag2O (0.12 g, 0.5 mmol) in 30% aqueous anion ligand (fbc). The Ag ion in (1) has a distorted trigonal
ammonia solution (5 mL) was added drop-wise with stirring geometry, being coordinated by three oxygen atoms from

SILVER-SILVER INTERACTIONS IN THREE SILVER(I) COMPLEXES
327
TABLE 2
Crystallographic and experimental data for complexes (1), (2) and (3)
(1)
C7H4AgFO2
(2)
C7H8Ag2O4
(3)
C4H5Ag2NO4
Compound formula
FW
246.97
Long rod
0.29 ꢁ 0.13 ꢁ 0.08
Monoclinic
P21/c
371.87
Cube
346.83
Long rod
0.19 ꢁ 0.12 ꢁ 0.06
Orthorhombic
Pbca
Crystal shape
Crystal size/mm
Crystal system
Space group
0.40 ꢁ 0.40 ꢁ 0.40
Orthorhombic
Pbcn
˚
a (A)
15.619(17)
3.699(4)
11.178(12)
90
6.447(2)
10.893(3)
23.536(10)
90
6.955(4)
9.527(5)
19.384(11)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
98.951(15)
90
90
90
90
90
3
˚
U (A )
638.0(12)
4
298(2)
1652.9(10)
8
293(2)
1284.4(12)
8
298(2)
Z
T/K
m/mm21(Mo-Ka)
3.102
2.446
4.712
2.989
6.053
3.587
Dc (g cm23
Reflections
)
1311
972
1305
991
1263
1000
Independent
reflections
F(000)
448
0.7894
0.4665
1408
1.0082
0.9860
1296
0.7128
0.3926
Tmax
Tmin
Goodness of fit on F2
R1, wR [I ꢂ 2s(I)]a)
R1, wR (all data)a)
P
1.025
1.079
0.0388, 0.0879
0.0602, 0.0979
0.879
0.0211, 0.0368
0.0317, 0.0389
0.0407, 0.1029
0.0564, 0.1092
P
P
P
a)R1 ¼ jjFoj 2 jFcjj/ jFoj,
wR2 ¼ [ w(Fo2 2 Fc2)2/ w(Fo2)2]1/2
,
w ¼ [s2(Fo)2 þ (0.1(max(0, Fo2) þ
2Fc2)/3)2]21
.
three fbc ligands. Figure 1 displays the coordination environ- Structure Description of Complex (2)
ment of the silver atoms in complex (1). The Ag–O
˚
distances are in the range of 2.210(4)–2.512(4) A, which are
Compound (2) crystallizes in the orthorhombic space group
Pbcn, and the asymmetric unit is composed of two Ag ions and
one cyclopentane-1,1-dicarboxylate dianion ligands (cpd), as
shown in Figure 4. The Ag(1) ion in (2) has a distorted tetrahe-
dral geometry, being coordinated by four oxygen atoms from
three cpd ligands. The Ag(2) ion in (2) has a distorted
trigonal geometry, being coordinated by three oxygen atoms
from three cpd dianions. The Ag–O bond lengths are in the
slightly longer than common Ag–O bonds in silver(I)
complexes with similar aromatic carboxylic acids, and the
O–Ag–O angles are in the range of 90.0–157.98. The
˚
Ag–Ag distance of 2.850(3) A is significantly shorter than
˚
that (2.89 A) in silver metal, indicating a more clear Ag–Ag
bond. The fbc anion in (1) adopts a m3 coordination mode.
Adjacent Ag ions in (1), via sharing O(2) and its equivalents
˚
range of 2.213(6)–2.400(6) A, which are longer than those in
. . .
result in Ag–O chains with the sequence of Ag–O–Ag–
silver(I) complexes with aromatic carboxylic acids, but
slightly shorter than those Ag–O bonds in complex (1). The
O–Ag–O angles are in the range 74.2(2)–143.7(2)8. It
should be noted that each Ag ion in (2) has two other Ag
ions approaching it with Ag–Ag distances 2.789(2), 2.850(1)
. . .
O
, and the Ag–O chains are further linked by Ag–Ag
bonds to build up a two-dimensional layer with (6,3)
topology, as shown in Figure 2. The three-connected nodes
are provided by Ag ions and the two-connectors are provided
by oxygen bridges and Ag–Ag bonding interaction. The fbc
ligands are located on both sides of the layers, which are
stacked via aromatic rings to form hydrophobic regions
between layers (Figure 3).
˚
˚
and 2.996(2) A. The Ag–Ag distance of 2.789(2) A is among
the shortest Ag–Ag separations ever reported, indicating
clear evidence of the existence of Ag–Ag bonding interactions.
The cpd ligand in (2) adopts a m7 coordination mode (Figure 5).

328
X.-Y. LIU AND H.-L. ZHU
TABLE 3
˚
Selected bond lengths (A) and angles (8) for complexes (1), (2) and (3)
(1)
Ag(1)–O(2B)
Ag(1)–O(1A)
2.196(4)
2.210(4)
157.9(2)
99.0(2)
Ag(1)–O(1)
2.512(4)
2.850(3)
93.5(1)
. . .
Ag(1) Ag(1A)
O(1)–Ag(1)–O(1A)
O(2B)–Ag(1)–O(1A)
O(2B)–Ag(1)–O(1)
(2)
Ag(1)–O(4B)
Ag(1)–O(1)
. . .
Ag(1) Ag(1A)
2.213(6)
2.342(7)
2.789(2)
2.215(6)
2.400(6)
151.7(2)
128.0(2)
74.3(2)
Ag(1)–O(3A)
Ag(1)–O(2A)
. . .
Ag(1) Ag(2)
Ag(2)–O(1C)
2.404(6)
2.591(7)
2.850(1)
2.353(6)
2.996(2)
84.1(2)
Ag(2)–O(2)
Ag(2)–O(3B)
. . .
Ag(2) Ag(2A)
O(4B)–Ag(1)–O(1)
O(4B)–Ag(1)–O(3A)
O(1)–Ag(1)–O(3A)
O(2)–Ag(2)–O(1C)
O(2)–Ag(2)–O(3B)
O(4B)–Ag(1)–O(2A)
O(1)–Ag(1)–O(2A)
O(3A)–Ag(1)–O(2A)
O(1C)–Ag(2) –O(3B)
116.8(2)
88.4(2)
74.2(2)
140.3(3)
143.8(2)
(3)
Ag(1)–O(3A)
Ag(1)–O(1)
2.201(2)
2.213(3)
2.284(3)
2.365(3)
172.5(1)
100.3 (1)
146.2(1)
76.44(9)
97.7(1)
Ag(1)–O(4B)
. . .
Ag(1) Ag(2)
2.488(3)
2.939(1)
2.382(3)
2.489(3)
77.07(9)
116.6(1)
127.8(1)
96.82(8)
Ag(2)–N(1C)
Ag(2)–O(4A)
Ag(2)–O(1D)
Ag(2)–O(2)
O(3A)–Ag(1)–O(1)
O(3A)–Ag(1)–O(4B)
N(1C)–Ag(2)–O(1D)
O(4A)–Ag(2)–O(1D)
N(1C)–Ag(2)–O(2)
O(1)–Ag(1)–O(4B)
N(1C)–Ag(2)–O(4A)
O(4A)–Ag(2)–O(2)
O(1D)–Ag(2)–O(2)
More interestingly, adjacent Ag ions via Ag–Ag bonding ligands are located on both sides of the Ag–O layer to result
interaction generate silver chains and adjacent silver chains in a two-dimensional layer.
are further linked by sharing oxygen atoms to result in a two-
Structure Description of Complex (3)
dimensional Ag–O layer, as shown in Figure 5. The cpd
The asymmetric unit in (3) consists of two crystallographi-
cally distinct Ag ions and one iminodiacetate dianion ligand
(idc). As shown in Figure 6, the Ag(1) ion is coordinated
by three carboxylate oxygen atoms from three idc ligands
˚
with the Ag–O bond distances of 2.201(2)–2.488(3) A. The
O–Ag–O angles are 172.5(1), 77.1(1) and 100.3(1)8, which
indicate the coordination geometry of Ag(1) is closer to a
“T-shape” than a triangle “Y-shape.” The Ag(2) atom is coor-
dinated by three carboxylate oxygen atoms and one nitrogen
atom from four idc dianions. The Ag–O distances around the
˚
Ag(2) atom are in the range of 2.365(3)–2.489(3) A and the
˚
Ag–N distance is 2.284(3) A. The O–Ag–O and N–Ag–O
angles are in the range of 76.4(1)–146.2(1), indicating a
distorted tetrahedral geometry for Ag(2). The Ag(1) and
Ag(2) ions are linked by O,O’-bridges of carboxylate with
˚
Ag–Ag distance of 2.939(1) A. The Ag–Ag distance in (3),
which is comparable with those reported by Bosch, is below
˚
the sum of van der Waals radii of two Ag ions (3.44 A) and
FIG. 1. Perspective view of the coordination environments of Ag in (1).

SILVER-SILVER INTERACTIONS IN THREE SILVER(I) COMPLEXES
329
FIG. 4. Perspective view of the coordination environments of Ag in (2).
FIG. 2. Perspective view of the two-dimensional layer of (1) showing
Ag–Ag bonds. For clarity, the carbon and fluorine atoms of fbc are omitted.
The balls with diagonal lines represent the Ag atoms and the hollow balls
are the oxygen atoms.
and is an analog of that reported by Brammer (Brammer et al.,
2001). The adjacent Ag(1) and Ag(2) atoms also form a
dimeric unit via sharing of carboyxlate oxygen atoms, and
the dimeric units are further linked by Ag-Ag bonding inter-
actions to genrerate one-dimensional Ag–Ag–O chains. The
Ag–Ag–O chains are connected by idc anions to form a
˚
is close to the Ag–Ag distance in silver metal (2.89 A), indicat-
. . .
ing a strong interaction of Ag Ag in (3) (Bosch and Barnes,
2002; Schultheiss et al., 2003). The idc ligand in (3) employs
one nitrogen and four oxygen atoms to coordinate the Ag
ions and thus adopts a m7 coordination mode (Figure 7). The
compound is a dimeric motifs formed by silver(I) carboxylates
FIG. 5. Perspective view of the two-dimensional layer of (2) showing
Ag–Ag bonds. For clarity, some carbon atoms of cpd are omitted and the others
are shown with smaller hollow balls. The balls with diagonal lines represent
the Ag atoms and the bigger hollow balls are the oxygen atoms.
FIG. 3. Perspective view of the stacking array of (1).

330
X.-Y. LIU AND H.-L. ZHU
FIG. 6. Perspective view of the coordination environments of Ag in (3).
FIG. 7. The three-dimensional structure of (3). The balls with diagonal lines represent the Ag atoms and the bigger hollow balls are the oxygen atoms and the
smaller hollow balls are carbon atoms.
three-dimensional framework, as shown in Figure 7. The carcinoma), 95-D (lung carcinoma), CNE (rhinocarcinoma)
Ag–Ag bonds in (3) are shown in Figure 8.
and two normal cell lines, NIH 3T3 (mouse normal fibroblast),
and L-02 (human normal liver cell), were obtained from
Shanghai Cell Institute of the Chinese Science Academy.
These cells were subcultured in media RMPI 1640 (GIBCO
BRL product) with 10% fetal bovine serum (Hyclone
Cytotoxicity
Five human solid carcinoma cell lines, Hela (cervix adeno-
carcinoma), HepG2 (hepatocellular carcinoma), BGC (gastric
FIG. 8. The Ag–Ag bonds in (3).

SILVER-SILVER INTERACTIONS IN THREE SILVER(I) COMPLEXES
331
TABLE 4
Cytotoxicities of complexes (1), (2) and (3)
IC50 (mM)
Complex
Hela
HepG2
BGC
95-D
CNE
L-02
NIH3T3
(1)
(2)
(3)
8.1
4.2
8.7
4.2
9.3
6.3
8.7
4.2
16.2
10.8
60.1
17.4
4.2
41.6
4.2
20.6
13.4
25.4
26.8
25.8
11.7
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product), at 378C with 5% CO2. Cells were adjusted to a con-
5
centration of 10 cells mL
21
.
and were planted in 96-well
tissue culture plate, and were then exposed to the test com-
21
.
pounds ranging in concentrations from 2.5 to 100 mg mL
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and cytotoxicity evaluation of silver(I) compounds of propandioic
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for 48 hours. The cells were pigmented by MTT [3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide], and
the O.D. values were measured by an ELX800 universal micro-
plate reader (BIO-TEK Instruments, Inc.) under 490 nm wave
length. The IC50 value (concentration of drug required to
inhibit 50% growth) was calculated from linear regression of
the percent viable cells versus the log of the drug concen-
tration. The results are shown in Table 4.
Dance, I. G.; Fitzpatrick, L. J.; Rae, A. D.; Scudder, M. The
intertwined double-(-Ag-SR)-strand chain structure of crystalline
3-methylpentane-3-thiolatosilver, in relation to molecules
(AgSR)8 in solution. Inorg. Chem. 1983, 22, 3785–3788.
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The cytotoxicity properties of (1)–(3) were studied and the
concentrations required to yield 50% inhibition of the viable
cells (IC50) (Carmichael et al., 1987) are listed in Table 4.
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