Synthesis, crystal structure and characterization of two polymeric silver(I) complexes containing imidazolate anions

Article abstract of DOI:10.1081/SIM-200035701

Two new imidazolate-containing complexes, [Ag₅(Im) ₅]_n (1) and [Ag(2-MeIm)]_n (2), were prepared and characterized by X-ray single crystal structure determination. (1) consists of 1-D chains running along three different directions, namely [2 1 1], [2 1 1] and [2 1 1]. This type of packing of chains is unusual. The chains are linked to form a three-dimensional structure through weak Ag...Ag interactions. The silver(I) atom in each chain is linearly coordinated by two nitrogen atoms from different imidazolates and the 1-D chain is somewhat helical due to the geometrical constraints imposed by the 1,3-arrangement of the nitrogen atoms in the imidazolate bridges. (2) is a linear chain in which each silver(I) atom is two-coordinated with the different bridged methylimidazolate nitrogen atoms. The two structures were refined to R₁ = 0.0315 for (1) and R₁ = 0.0495 for (2). Complexes (1) and (2) are sparingly soluble and very stable in CH₃CN containing 0.1 mol·L^-1 of n-Bu ₄NBF₄ in the range 2.0 to -2.0 V at room temperature and do not undergo any redox process. When being boiled in a solution of 30% sodium hydroxide for two hours, the large colorless prismatic crystals of (1) and (2) remain unchanged. TG/DTG analyses shows that the two complexes begin to decompose at 382°C for (1) and 357°C for (2). Copyright

Full text of DOI:10.1081/SIM-200035701

Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:155–159, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1081/SIM-200035701
Synthesis, Crystal Structure and Characterization of Two
Polymeric Silver(I) Complexes Containing Imidazolate Anions
Xiu-Ying Liu and Hai-Liang Zhu
Department of Chemistry and Environmental Engineering, Wuhan University of Science and
Engineering, Wuhan, P. R. China
chemistry of metalloprotein superoxide dismutases. The
Two new imidazolate-containing complexes, [Ag5(Im)5]n (1) imidazolate anion, obtained by deprotonation of imidazole,
and [Ag(2-MeIm)]n (2), were prepared and characterized by
X-ray single crystal structure determination. (1) consists of 1-D
is capable of acting as a bridging ligand. However, the
1,3-arrangement of the nitrogen atoms imposes geometrical
¯ ¯
chains running along three different directions, namely [2 1 1],
constraints such that only one imidazolate bridge is possible
between two metal centres. Accordingly, imidazolate-bridged
through weak Ag Ag interactions. The silver(I) atom in each transition metal complexes show high linearity (Steel, 1990).
¯ ¯ ¯
¯ ¯
[2 1 1] and [2 1 1]. This type of packing of chains is unusual.
The chains are linked to form a three-dimensional structure
...
chain is linearly coordinated by two nitrogen atoms from different
imidazolates and the 1-D chain is somewhat helical due to the
geometrical constraints imposed by the 1,3-arrangement of the
nitrogen atoms in the imidazolate bridges. (2) is a linear chain
in which each silver(I) atom is two-coordinated with the different
bridged methylimidazolate nitrogen atoms. The two structures 1972, 1986). But none of those containing silver(I) are
Indeed, many oligomeric and polymeric transition metal
complexes have been known for some time to contain imidazo-
late bridges (Ashby et al., 1978; Carlucci et al., 1994; Inoue
and Kubo, 1976; Sundberg and Martin, 1974; Trofimenko,
were refined to R1 5 0.0315 for (1) and R1 5 0.0495 for (2). Com-
plexes (1) and (2) are sparingly soluble and very stable in CH3CN
believed to be polymeric and are difficult to crystallize
(Masciocchi et al., 1994, 1995; Nomiya et al., 1998), and can
21
containing 0.1 mol L of n-Bu4NBF4 in the range 2.0 to 22.0 V
.
only be obtained as microcrystalline materials; therefore, all
structural information must be extracted from powdered
two hours, the large colorless prismatic crystals of (1) and (2) samples only (Masciocchi et al., 1995). Recently, Masciocchi
at room temperature and do not undergo any redox process.
When being boiled in a solution of 30% sodium hydroxide for
remain unchanged. TG/DTG analyses shows that the two com-
plexes begin to decompose at 382 8C for (1) and 357 8C for (2).
reported the structure of polymeric silver(I) imidazolate
[Ag(im)]n (Masciocchi et al., 1994, 1995; Nomiya et al.,
1998) by using powder X-ray diffraction data (Masciocchi
Keywords Silver(I) complexes, pyridine complexes, X-ray crystal
structure
et al., 1995), and it was found by Nomiya that this compound
has excellent antibacterial and antifungal activities (Nomiya
et al., 1997). We have reported a study on the cytotoxicity of
some silver(I) complexes recently (Chen et al., 2001a and b;
Zhu et al., 2001, 2003a, 2003b). In order to investigate the
cytotoxicity of silver(I) complexes with imidazolate-
containing ligands, we prepared silver(I) complexes contain-
ing imidazolate-bridges and determined their molecular
structures.
INTRODUCTION
Because of the importance of the involvement of histidine in
enzymic catalysis, much of the interest in imidazolate bridging
has been in a bio-inorganic context, and particularly in the
EXPERIMENTAL
Received 8 August 2003; accepted 7 July 2004..
The authors thank the Education Office of Hubei Province,
P.R. China for research grant No. 2002B29002 and the Natural
Science Foundation of Hubei Province, P.R. China for research
grant No. 2003ABB010.
Address correspondence to Hai-Liang Zhu, Department of
Chemistry and Environmental Engineering, Wuhan University of
Science and Engineering, Wuhan 430073, P. R. China. E-mail:
hlzhu@wuse.edu
Materials
Reagents were used as obtained from the Second Chemicals
Factory of Shanghai, P.R. China without further purification.
Solvents were purified by standard methods before use. The
two complexes reported in this article were prepared by
a procedure similar to that described by Masciocchi and
coworkers (Masciocchi et al., 1994); however, we obtained
155

156
X.-Y. LIU AND H.-L. ZHU
well-crystallized single crystal samples. C, H, and N elemental vacuum desiccator over silica gel; yield, 22 g (95%). Anal.
analyses were performed with a Perkin-Elmer elemental calcd. for C7H5AgO2 (FW 229.10): C, 36.72; H, 2.20; Ag,
analyser.
47.11. Found: C, 36.70; H, 2.30; Ag, 47.02%.
Electrochemical Analysis
Synthesis of [Ag5(Im)5]n (1)
The cyclic voltammograms were measured on an electro-
chemical analyzer over 2.0 to 22.0 V at room temperature
To a 1:1 (v/v) water/acetonitrile solution of [Ag2(C6H5
CO2)2] (229 mg, 1 mmol in 10 mL solution) was added a
solution of imidazole (136 mg, 2 mmol in 5 mL acetonitrile).
The pH value of the resulting solution is 7. Upon slow vaporat-
ing in air for two days, large colorless crystals of (1) suitable
for X-ray single crystal determination were deposited and
collected by filtration, washed with water, acetonitrile and
diethyl ether and dried in a vacuum desiccator over silica
gel; yield, 284 mg (81%). Anal. calcd. for C3H3N2Ag (FW
175.07): C, 20.60; H, 1.73; N, 16.01. Found: C, 20.58; H,
1.75; N, 16.92%.
21
with a sample concentration of 1.0 ꢀ 1024 mol L
in
.
MeCN solution containing n-Bu4NBF4 (0.1 mol L21) and the
.
scan rate of 100 mV s21. A platinum wire working electrode,
.
a platinum plate auxiliary electrode and a saturated calomel
electrode (SCE) reference electrode were employed. All poten-
tials were measured with respect to SCE and the experiments
were carried out at ca. 20 8C.
TG/DTG Analysis
The TG/DTG measurements were carried out by a thermo-
gravimetric analysis system (Model: DSC-822e, Mettler
Toledo Company, Switzerland) under high-purity N2. The
amounts of the samples used for TG/DTG analyses were
5.070 mg for (1) and 6.123 mg for (2), and the heating rate
Synthesis of [Ag(2-MeIm)]n (2)
Replacing imidazole with 2-methylimidazole in the same
procedure as for (1), large colorless prismatic crystals of (2)
were obtained; yield, 322 mg (85%). Anal. calcd. for
C4H5N2Ag (FW 189.10): C, 25.42; H, 2.67; N, 14.82. Found:
C, 25.44; H, 2.69; N, 14.65%.
was 10 8C min21
.
X-ray Crystallography
Crystal structure determination was carried out with a
Siemens R3m diffractometer equipped with graphite-
monochromated MoKa (l ¼ 0.71073) with Lorentz polariz-
ation and absorption corrections. Accurate cell parameters
were derived from least-squares fitting of 25 independent
RESULTS AND DISCUSSION
Preparation of (1) and (2)
The formation of the two complexes can be expressed as the
reflections in the 7–158 range. Observable reflections with following equations:
I ꢁ 2s(I) were used in the structure solution and refinements.
The structures were solved by direct methods and refined on
MeCN
5nC6H5COOAg þ 5nHim ꢂ!½Ag5ðImÞ5ꢃn ð1Þ
nAgþ þ nð2-MeImꢂÞ ꢂ!½Agð2-MeImÞꢃn
F2 by full-matrix least-squares methods using SHELX-97.
All the non-hydrogen atoms were refined anisotropically. All
the hydrogen atoms were placed in the calculated positions
and were assigned fixed isotropic thermal parameters at 1.2
times the equivalent isotropic U of the atoms to which they
are attached and allowed to ride on their respective parent
atoms. The contributions of these hydrogen atoms were
included in the structure-factors calculations. The absolute
structure for (1) has been determined with a Flack parameter
of 20.07(7).
MeCN
ð2Þ
Acetonitrile is the most suitable solvent for the syntheses of the
two complexes. When the pH ¼ 6.5 2 8, large crystals are
deposited. According to the insolubility of (1) and (2) in
common solvents, it is estimated that the values of ‘n’ in the
formulas of (1) and (2) are close to 1. Equimolar amounts of
SCN2 or SO242 anions, which form very stable compounds
with Agþ ions, do not affect the yields for the formation of
(1) and (2). When the pH value is more than 9, a lot of
powdered solid will precipitate from the clear reaction
solution in a few minutes. We failed to obtain large crystals
by recrystallization from the powder solid. When the pH
value is less than 5, there is no solid formed in a week.
Synthesis of C6H5COOAg
To a suspension solution of C6H5CO2H (12.2 g, 0.1 mol in
100 mL water) was added an aqueous solution of NaOH
(4.0 g, 0.1 mol in 10 mL water) with stirring. The resulting
solution (pH ¼ 9) was colorless. With slow stirring, to the
above solution was added a solution of AgNO3 (17 g, 0.1 mol
in 100 mL acetonitrile). Upon slow evaporation in air for
48 h, colorless prismatic crystals were deposited and were
Physical Properties
Complexes (1) and (2) are stable in CH3CN containing
21
.
collected by filtration, washed with water and dried in a 0.1 mol L
of n-Bu4NBF4 in the range 2.0 to 22.0 V at

TWO POLYMERIC SILVER(I) COMPLEXES
157
room temperature and do not undergo any redox processes,
which agrees with the very high stability of the two complexes
to strong acids and strong bases. When being boiled in a
solution of 30% sodium hydroxide (or 37% hydrochloric
acid, 10% ammonium thiocyanide, or 10% ethylenetetra-
acetate) for two hours, the large colorless prismatic crystals of
(1) and (2) remain unchanged. However, when heated to
boil the microcrystals of (1) and (2) can be easily destroyed
in the above solutions. So we expect that the large single
crystals of the two complexes (1) and (2) may be developed
into some special materials, such as high-temperature tolerable
materials.
FIG. 1. A perspective view showing the coordination environment in
complex (1).
¯ ¯ ¯ ¯ ¯ ¯ ¯
directions, namely [2 1 1], [2 1 1], and [2 1 1] (the Ag–Ag
˚
distance between the adjacent chains is 3.936 A), as shown in
Figures 1 and 2, based upon five crystallographically nonequi-
valent Ag sites, forming pentanuclear silver entities. Every
silver(I) atom in the Ag5 unit is linearly coordinated by two
nitrogen atoms from different imidazolates, as displayed in
Table 2 (the N–Ag–N angles range from 170.1 to 176.58).
Structure Description of [Ag5(Im)5]n (1)
Complex (1) crystallizes in the orthorhombic system with
the space group P212121, as summarized in Table 1.
The structure determination of (1) revealed three different
one-dimensional chains running along three different
˚
The average Ag–N bond length (2.076 A) is comparable
with those in the similar complex [fAg(im)gn] (Masciocchi
et al., 1995), but is significantly shorter than the complexes
containing silver-imine bonds (Zhu et al., 1999, 2000), indicat-
ing the much stronger Ag–N interaction in (1) or in the
complex [Ag(Im)]n (Nomiya et al., 1998).
TABLE 1
Crystal dataa for (1) and (2)
There are five different dihedral angles between the adjacent
imidazolato rings, 5.28 around Ag(1), 52.98 (around Ag(2)),
58.28 (around Ag(3)), 42.98 (around Ag(4)) and 34.58 around
Ag(5), which are greatly different from those found in the
complex [fAg(im)gn].
Compound
(1)
(2)
Formula
Fw
C30H30Ag10N20
1749.44
C4H5AgN2
188.97
...
A great deal of weak interactions (Ag Ag distances
Crystal size
Space group
0.10 ꢀ 0.15 ꢀ 0.50 0.30 ꢀ 0.35 ꢀ 0.45
˚
between 3.120 and 3.266 A) among the silver atoms in neigh-
P212121
10.798(4)
13.449(4)
14.978(6)
90
Cc
boring chains link the chains into a three-dimensional,
single-screw structure.
˚
a (A)
10.848(3)
5.9560(10)
7.875(2)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
90
90
92.51
90
3
˚
U (A )
2175.1(4)
2
0.71073
508.3(2)
4
0.71073
Z
m (mm21
(Mo-Ka)
)
T (K)
Dx (g cm23
m (MoKa)
293
2.671
4.446
293
2.469
3.815
)
(cm21
)
No. of unique
reflections
No. of observed
[I ꢁ 3s(I)]
F(000)
2587
2144
812
607
1640
0.032
0.061
P
360
R1 (I . 2s (I))a
wR2 (all data)a
P
0.049
0.068
P
P
aR1 ¼ kFoj 2 jFck/ jF j, wR ¼
w(Fo2 2 Fc2)2/ w(F2)2
,
1/2
[
]
w ¼ [s2(Fo)2 þ (0.1(max (0, Fo2) þ22Fc2)/3)2]21
.
o
o
FIG. 2. A perspective view of complex (1) showing the one-dimensional
chains running along three different directions [2 1 1], [2 1 1], and [2 1 1].
¯ ¯ ¯ ¯ ¯
¯ ¯ ¯

158
X.-Y. LIU AND H.-L. ZHU
TABLE 2
˚
Selected bond lengths (A) and angles (8) for the complexes (1) and (2)
(1)
Ag(1)–N(11)
Ag(1)–Ag(2a)
2.069(8)
3.1203(14)
2.065(7)
Ag(1)–N(42)
Ag(1)–Ag(2b)
2.063(8)
3.2261(13)
2.078(8)
3.2261(13)
2.088(7)
2.079(7)
2.075(7)
3.2656(15)
92.2(2)
Ag(2)–N(21)
Ag(1)–Ag(2c)
Ag(2)–N(52)
Ag(1)–Ag(2d)
3.1203(14)
2.072(7)
2.071(7)
Ag(3)–N(31)
Ag(4)–N(12e)
Ag(3)–N(22)
Ag(4)–N(32)
Ag(4)–Ag(5f)
Ag(5)–N(41)
3.2656(16)
2.082(7)
Ag(5)–N(51)
Ag(5)–Ag(4g)
N(42)–Ag(1)–N(11)
N(11)–Ag(1)–Ag(2a)
N(11)–Ag(1)–Ag(2b)
N(21)–Ag(2)–N(52)
N(52)–Ag(2)–Ag(1c)
N(52)–Ag(2)–Ag(1d)
N(31)–Ag(3)–N(22)
N(12)–Ag(4e)–Ag(5f)
N(51)–Ag(5)–N(41)
N(41)–Ag(5)–Ag(4g)
176.2(3)
N(42)–Ag(1)–Ag(2a)
N(42)–Ag(1)–Ag(2b)
Ag(2)–Ag(1a)–Ag(2b)
N(21)–Ag(2)–Ag(1c)
N(21)–Ag(2)–Ag(1d)
Ag(1)–Ag(2c)–Ag(1d)
N(12)–Ag(4e)–N(32)
N(32)–Ag(4)–Ag(5f)
N(51)–Ag(5)–Ag(4g)
90.4(2)
87.3(2)
171.1(4)
95.9(2)
91.3(2)
174.9(3)
80.7(2)
176.5(4)
101.8(2)
92.7(2)
136.72(3)
88.7(2)
90.6(2)
136.03(3)
170.1(3)
108.4(2)
80.2(3)
(2)
Ag(1)–N(1)
N(1)–Ag(1)–N(2a)
2.012(8)
148.5(5)
Ag(1)–N(2a)
2.110(11)
Structure Description of [Ag(2-MeIm)]n (2)
The structure of (2) displays a linear arrangement in which
each silver(I) atom is two-coordinated with different bridging
methylimidazolate nitrogen atoms. The structure is highly
symmetrical and the coordination environments of the
silvers are similar. The coordination environment of
compunds (2) and the repeated unit are shown in Figure 3.
˚
The average Ag–N bond length (2.06(1) A) is close to that in
complex (1). The N–Ag–N angle in the chain is 148.5(5)8,
which is significantly smaller than that ( . 1708) in (1),
being likely due to the effect of the repelling interaction
between the methyl groups in (2). We can see from Figure 4
FIG. 3. A perspective view showing the coordination environment in
FIG. 4. A perspective view of a part of [Ag(2-MeIm)]n (2). Hydrogen atoms
are omitted for clarity.
complex (2).

TWO POLYMERIC SILVER(I) COMPLEXES
159
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. . .
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