Two new one-dimensional luminescent silver(I) and lead(II) coordination polymers containing the flexible ligand 2-(1H-imidazole-1-yl)acetic acid

Article abstract of DOI:10.1016/j.molstruc.2009.09.045

The free ligand, 2-(1H-imidazole-1-yl)acetate (Hima, 1), was crystallized from the mixture solution of 1. Two new coordination polymers, [Ag(Hima)(NO₃)] (2) and {[Pb(Hima)₂(NO₃)](NO₃)}_n (3), are achie

Full text of DOI:10.1016/j.molstruc.2009.09.045

Journal of Molecular Structure 938 (2009) 291–298
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Journal of Molecular Structure
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Two new one-dimensional luminescent silver(I) and lead(II) coordination
polymers containing the flexible ligand 2-(1H-imidazole-1-yl)acetic acid
*
Yong-Tao Wang , Ting-Xiao Qin, Chao Zhao, Gui-Mei Tang, Tian-Duo Li, Yue-Zhi Cui, Jun-Ying Li
Department of Chemical Engineering, Shandong Institute of Light Industry, Jinan, Shandong 250100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The free ligand, 2-(1H-imidazole-1-yl)acetate (Hima, 1), was crystallized from the mixture solution of 1.
Two new coordination polymers, [Ag(Hima)(NO3)] (2) and {[Pb(Hima)2(NO3)](NO3)}n (3), are achieved by
reaction of a flexible Hima, AgNO3 and Pb(NO3), respectively. In 2, the silver(I) atom is coordinated by
four oxygen atoms from three carboxylate groups and one nitrate ion in a distorted tetrahedral environ-
ment. The free ligand Hima acts as the tridentate coordination mode, which bridges the silver atoms into
Received 28 July 2009
Received in revised form 23 September
2009
Accepted 28 September 2009
Available online 6 October 2009
a zigzag chain featuring a rare [Ag2(carboxylato-O,O0)(carboxylato-
l1,1-O)] six-membered ring. The intra-
dimer AgꢀꢀꢀAg distance is 2.966(l) Å. In 3, Pb(II) atom exhibits an eight-coordinated dodecahedral coordi-
nation geometry, in which a unique 1-D chain structure with dicubane-like can be observed. In two poly-
mers, the ligand Hima exhibits new and unique coordination modes. Solid-state fluorescence spectra
reveal that the emission bands of complex 2 center at 462 and 510 nm (kex = 280 nm). In 3, the emission
peaks locate at 465 and 547 nm upon excitation at 280 nm. In addition, they have been characterized by
IR spectra and TG analysis.
Keywords:
Silver complex
Lead complex
2-(1H-Imidazole-1-yl)acetic acid
Dicubane-like
Fluorescence
X-ray
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
and structurally characterized in many documents owing to their
unique structures [12–14]. In addition, the coordination chemistry
During the last decades the design and syntheses of metal–or-
ganic coordination polymers have been an impetus for supramo-
lecular chemistry and property-oriented crystal engineering,
owing to their novel topologies, fascinating structures and their
potential applications in optical, electrical, magnetic, catalytic
and micro-porous materials [1–6]. The rational design and control-
lable preparation of metal–organic coordination polymers are
highly influenced by several factors, such as the coordination
geometry of the central atom, the structural nature of the bridging
ligands, the counter anion, the pH values of the reaction solution,
the reaction temperature and so on [7–9]. Among these factors,
the nature of the bridging ligands and alternation of the geometry
of the linker unit take an important role in adjusting the formation
of different frameworks with tailored properties and functions.
The ligands containing imidazole and carboxylic groups are
excellent bridging blocks for constructing novel functional materi-
als because they combine the coordination modes of imidazole and
carboxylic functional groups [10]. In particular, some transition
metal coordination polymers containing 2-(1H-imidazole-1-
yl)acetic acid (Hima) ligand have been obtained, which display fas-
cinating structures and potential applications [11]. Recently, the
complexes containing silver(I) carboxylates have been prepared
of lead(II) has been explored extensively because it possesses the
large radius, the variable stereochemical activity and the flexible
coordination environment, which provide unique opportunities
for the construction of novel structures [15–17]. Though many
complexes containing silver(I) and lead(II) have been documented,
the luminescent silver(I) and lead(II) chains with Hima have not
been reported so far. There is still great potential in exploring this
area. Meanwhile, as a program of our on-going investigation on
constructing novel metal coordination polymers with Hima, herein
we wish to report the syntheses, crystal structures and properties
of the free ligand Hima (1), the complexes [Ag(Hima)(NO3)]n (2)
and {[Pb(Hima)2(NO3)](NO3)}n (3). Additionally, the IR spectra
and TGA of these compounds have been discussed in details.
2. Experimental
2.1. Materials and general methods
All the starting materials and solvents for syntheses were ob-
tained commercially (ACROS) and used as received. Elemental
analyses were performed on a Perkin-Elmer 240 elemental ana-
lyzer. The FT-IR spectra were recorded from KBr pellets in range
400–4000 cmꢁ1 on a Bruker Tensor 27 spectrometer. Thermogravi-
metric analysis (TGA) data were collected with a Perkin-Elmer
TGS-2 analyzer in N2 at a heating rate of 10 °C minꢁ1. The
* Corresponding author. Tel./fax: +86 0531 89000551.
E-mail address: ceswyt@sohu.com (Y.-T. Wang).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.09.045

292
Y.-T. Wang et al. / Journal of Molecular Structure 938 (2009) 291–298
emission/excitation spectra were recorded on an Edinburgh
FLS920 spectrometer equipped with a continuous Xe900 Xenon
lamp and an nF900 ns flash lamp.
calculated sites and included in the final refinement in the riding
model approximation with displacement parameters derived from
the parent atoms to which they were bonded. Crystal data as well
as details of data collection and refinement for the compounds 1–3
are given in Table 1. Selected bond lengths and angles are listed in
Table 2.
2.2. Crystallization of Hima (1)
The product was recrystallized from the water–methanol mix-
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
Nos. 651848, 651849 and 695855 for 1–3, respectively. Copies of this
information may be obtained 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 http://www.ccdc.cam.ac.uk).
ture to give the bar colorless crystals 1. IR (KBr, cmꢁ1):
m 3130
(br), 3068 (w), 3013 (m), 2956 (w), 2488 (m), 1998 (m), 1618 (s),
1491 (w), 1437 (w), 1375 (s), 1326 (m), 1304 (m), 1291 (m),
1231 (w), 1190 (w), 1087 (w), 1053 (w), 1032 (w), 981 (m), 910
(m), 881 (m), 860 (m), 781 (s), 701 (w), 680 (m), 636 (m), 589
(m), 446 (m), 412 (m).
3. Results and discussion
2.3. Synthesis of [Ag(Hima)(NO3)]n (2)
3.1. Preparation of complexes 2 and 3
To a solution of Hima (126 mg, 1 mmol) in water (10 ml), a di-
lute aqueous solution of AgNO3 (199 mg, 1 mmol) was added drop-
wise. The mixture was further vigorously stirred ca. 30 min at
room temperature, and then filtered. The colorless filtrate was al-
lowed to stand at room temperature, and colorless plate single-
crystals suitable for X-ray diffraction were obtained by evaporation
of water within a week. Total yield: 78% (231 mg). Anal. calcd: for
C5H6AgN3O5: C, 20.29; H, 2.04; N, 14.20%. Found: C, 20.18; H, 2.03;
Complexes 2 and 3 were generated from aqueous solutions by
reactions of Hima with different metal salts. Compound 2 could
also be isolated when using other solvents, such as water, metha-
nol, the mixture of water and ethanol. The products were con-
firmed by X-ray diffraction, IR spectra and elemental analyses.
Similar case was also observed for complex 3, which indicates that
the final products are independent of the solvent. Furthermore, 2
and 3 have the exact 1:1 and 2:1 ligand/metal compositions,
respectively. Higher yields of the products were observed when
increasing the metal-to-ligand ratio, thus indicating that the prod-
ucts are obviously independent on the ligand-to-metal ratio.
N, 14.25%. IR (KBr, cmꢁ1):
m 3425 (br), 2362 (w), 2272 (w), 1612 (s),
1513 (m), 1431 (w), 1390 (s), 1310 (m), 1236 (m), 1108 (m), 1082
(m), 1037 (m), 976 (w), 917 (m), 831 (w), 786 (w), 753 (w), 690
(w), 664 (w), 623 (w), 584 (w), 411 (w).
2.4. Synthesis of {[Pb(Hima)2(NO3)](NO3)}n (3)
3.2. IR spectra
Hima (0.126 g, 1 mmol) was dissolved in water (10 ml) and
then a solution of Pb(NO3)2 (0.166 g, 0.5 mmol) in water (10 ml)
was added whilst stirring. The mixture was filtered and kept at
ambient temperature for several days. The plate colorless single-
crystals suitable for X-ray diffraction were obtained by slow evap-
oration of water within one week in 80% yield (233 mg). Anal.
calcd: for C10H12N6O10Pb: C, 20.59; H, 2.07; N, 14.40%. Found: C,
The IR spectrum of 2 shows characteristic bands of the carbox-
ylate group in the usual region at 1612 cmꢁ1 for the asymmetric
Table 1
Crystal and structure refinement for compounds 1–3.
1
2
3
20.48; H, 2.06; N, 14.45%. IR (KBr, cmꢁ1):
m 3149 (m), 3122 (w),
Empirical
formula
C5H6N2O2
C5H6AgN3O5
C10H12N6O10Pb
3109 (w), 3061 (w), 3010 (w), 2964 (w), 2879 (w), 2841 (w),
2767 (w), 2738 (w), 2706 (w), 2613 (w), 2571 (w), 2426 (w),
2324 (w), 2193 (w), 1592 (s), 1570 (s), 1435 (s), 1386 (s), 1313
(m), 1288 (m), 1165 (m), 1082 (m), 1026 (w), 918 (w), 881 (w),
850 (w), 781 (m), 756 (m), 688 (m), 638 (m), 624 (m), 584 (m),
520 (m), 506 (m), 430 (m), 406 (m).
Formula weight 126.12
296.00
298
0.71073
Monoclinic
P21/n
12.226(3)
4.9247(13)
14.914(4)
90
113.118(3)
90
583.46
296
0.71073
T/K
298
Wavelength/Å
Crystal system
Space group
a/Å
b/Å
c/Å
0.71073
Monoclinic
P21/n
4.6116(13)
8.571(2)
14.306(4)
90
Triclinic
ꢀ
P1
4.3852(11)
11.548(3)
16.509(4)
90.961(3)
91.721(3)
91.883(3)
835.1(4)
2
2.5. X-ray crystallography
a
/°
b/°
98.718(4)
90
558.9(3)
4
c
/°
Single crystal X-ray diffraction measurements of 1–3 were car-
ried out with a Bruker APEX II CCD diffractometer equipped with a
graphite crystal monochromator situated in the incident beam for
data collection at 298(2) K. The lattice parameters were obtained
by least-squares refinement of the diffraction data of reflections,
V/Å3
825.9(4)
4
2.442
Z
l
/mmꢁ1
0.118
10.170
Crystal size(mm) 0.20 ꢂ 0.20 ꢂ 0.50 0.08 ꢂ 0.16 ꢂ 0.35 0.20 ꢂ 0.20 ꢂ 0.40
q
/g cmꢁ3
1.499
2877
2.381
4233
2.320
7047
Reflections
collected
and data collections were performed with Mo-K
a radiation
(k = 0.71073 Å). All the measured independent reflections were
used in the structural analysis, and semi-empirical absorption cor-
rections were applied using the SADABS program. The program
SAINT [18] was used for integration of the diffraction profiles. All
the structures were solved by direct methods using the SHELXS
program of the SHELXTL package and refined with SHELXL [19].
Metal atoms were located from the E-maps and other non-hydro-
gen atoms were located in successive difference Fourier syntheses.
The final refinement was performed by full-matrix least-squares
methods with anisotropic thermal parameters for all the non-
hydrogen atoms based on F2. All the hydrogen atoms were first
found in difference electron density maps, and then placed in the
Independent
reflections
reflections
1095
980
1820
1638
3720
3573
[I > 2
F(0 0 0)
Rint
r(I)]
264
576
552
0.036
2.8/26.0
1.03
0.082
2.8/28.0
1.04
0.030
1.8/27.7
1.20
h range
Goodness of
fit on F2
Largest hole and ꢁ0.29/0.24
ꢁ0.98/1.27
ꢁ8.35/6.57
peak[e Åꢁ3
]
b
R1a/wR2
0.0461/0.1316
0.0450/0.1288
0.0803/0.2278
P
P
P
P
2
2 1=2
aR1
=
||Fo| ꢁ |Fc||/ |Fo|. bwR2 ¼ ½ ½wðFo2 ꢁ Fc2Þ ꢃ= ½wðF2oÞ ꢃꢃ
:

Y.-T. Wang et al. / Journal of Molecular Structure 938 (2009) 291–298
293
Table 2
observed that the molecule of the free ligand Hima adopts the
molecular zwitterions, partly because of being in favor of forming
the hydrogen bonds. A pair of Hima, each using the imidazole
nitrogen atom and carboxylic oxygen one, forms one kind of hydro-
gen bonds (N2–H1ꢀꢀꢀO1, Table 3) in the head–tail form [21]. Addi-
tionally, each Hima making use of imidazole carbon atom and
carboxylic oxygen one, forms another kind of hydrogen bonds
(C3–H3AꢀꢀꢀO1 Å and C4–H4Aꢀ ꢀ ꢀO2, Table 3) in the same formation.
It is interestingly observed in this 2-D array, which are three types
of hydrogen-bonded patterns A–D, notated as R24ð10Þ (Fig. 1b(A)),
R33ð13Þ (Fig. 1b(B)) and R22ð14Þ (Fig. 1b(C)), respectively. These
chains formed by N2–H1ꢀꢀꢀO1 lie parallel to each other, resulting
in a two-dimensional hydrogen-bonded layer along the bc plane
(Fig. 1b). The layers are further extended into a three-dimensional
supramolecular array through two kinds of supramolecular inter-
Selected bond lengths (Å) and angles (°) for complexes 2 and 3.
2
Ag1–O2
Ag1–O3
Ag1–Ag1a
2.281(3)
2.516(4)
2.9664(9)
Ag1–O2a
Ag1–O1b
2.575(3)
2.293(3)
O2–Ag1–O3
O2a–Ag1–O3
O2–Ag1–O2a
O1b–Ag1–O3
O1b–Ag1–O2
119.78(10)
80.43(9)
125.56(9)
85.23(11)
135.47(11)
Ag1a–Ag1–O2
Ag1b–Ag1–O2
Ag1b–Ag1–O3
Ag1a–Ag1–O3
78.68(7)
57.00(7)
149.75(7)
94.96(7)
3
Pb1–O1
Pb1–O2
Pb1–O4
Pb1–O5
2.50(2)
Pb1–O6
Pb1–O2a
Pb1–O3a
Pb1–O4b
2.72(2)
2.983(18)
2.551(14)
2.915(18)
2.567(18)
2.535(15)
2.930(15)
O1–Pb1–O2
O1–Pb1–O4
O1–Pb1–O5
O1–Pb1–O6
O1–Pb1–O2a
O1–Pb1–O3a
O1–Pb1–O4b
O2–Pb1–O4
O2–Pb1–O5
O2–Pb1–O6
O2–Pb1–O2a
O2–Pb1–O3a
O2–Pb1–O4b
O4–Pb1–O6
46.8(6)
82.1(5)
106.6(6)
98.2(7)
79.7(6)
71.3(6)
156.0(5)
73.3(5)
59.9(5)
64.1(6)
104.2(5)
114.4(5)
127.2(4)
117.4(6)
O4–Pb1–O5
O2a–Pb1–O4
O3a–Pb1–O4
O4–Pb1–O4b
O5–Pb1–O6
O2a–Pb1–O5
O3a–Pb1–O5
O4b–Pb1–O5
O3a–Pb1–O6
O2a–Pb1–O3a
O2a–Pb1–O4b
O4b–Pb1–O6
O2a–Pb1–O6
O3a–Pb1–O4b
74.6(5)
156.3(5)
80.1(5)
74.4(4)
45.0(6)
125.3(5)
154.7(5)
71.9(4)
158.9(6)
79.7(5)
121.4(5)
96.8(6)
80.4(6)
99.6(5)
actions, which are offset p–p aromatic stacking interactions with
the face-to-face distance of ca. 3.31 Å between imidazole rings,
and the weak hydrogen-bonded interactions (C2–H2Bꢀ ꢀ ꢀO2
3.386(2) Å and C5–H5Aꢀ ꢀ ꢀO23.268(2) Å) (Fig. S1 and Table 3).
3.4. Crystal structure of 2
Single X-ray analysis reveals that compound 2 has 1-D chains
structure. In 2, each Ag(I) center is coordinated by three carboxylic
oxygen atoms from three Hima ligands and one nitrate oxygen one,
as shown in Fig. 2a. The bond Ag–O lengths fall in the range of
2.281(3) and 2.575(3) Å (see Table 2), being in agreement with re-
lated Ag–O coordination bonds [12–14]. The coordination geometry
of the four-coordinated Ag(I) center is distorted (the bond angles of
O–Ag–O range from 80.43(9) to 135.47(11)°). The three metal–li-
gand bonds involving different carboxylato groups of Hima ligands
are slightly longer than those found in other silver carboxylates
[12d], and the fourth bond linked to a nitrate group is slightly smal-
ler those of axially bonded nitrate groups in the dimeric structure of
betaine silver(I) nitrate [12f]. Thus, it is observed that (carboxylato-
Symmetry codes: a3/2 ꢁ x, ꢁ1/2 + y, 1/2 ꢁ z; b3/2 ꢁ x, 1/2 + y, 1/2 ꢁ z for 2. aꢁ1 + x, y,
b
z; 1 + x, y, z; ꢁx, 1 ꢁ y, 1 ꢁ z for 3.
stretching and at 1390 cmꢁ1 for the symmetric stretching. The sep-
aration (
smaller than that in the free ligand Hima [
= 243 cmꢁ1], revealing the existence of bridging modes of the
carboxylate groups (Scheme 1a) [20]. For 3, the asymmetric and
the symmetric stretching bands are at 1592 and 1386 cmꢁ1
respectively. The
is at 206 cmꢁ1, being significantly smaller than
D) between masym(CO2) and m
sym(CO2), 222 cmꢁ1, is slightly
m
(CO2) 1618, 1375 cmꢁ1
;
D
,
O,O0)- and (carboxylato-
l1,1-O)-bridged centrosymmetric Ag2(Hi-
ma)2 dimers with the carboxylato group of Hima serving in the
D
that found in Hima, which can be assigned to the existence of both
bridging modes and chelating ones of the carboxylate groups
(Scheme 1b). The Pb–O stretching frequencies in 3 are observed
in the far-infrared region at 520 and 506 cmꢁ1, which are similar
to those found in other Pb(II) complexes [15c,16b]. The IR spectra
indicate that the Hima carboxylate groups display in different
coordination modes, being in agreement with the crystal struc-
tures of 2 and 3, respectively.
symmetric syn–syn bridging mode, resulting into forming a rare
[Ag2(carboxylato-O,O0)(carboxylato-
l1,1-O)] six-membered ring,
which is significantly distinct from those found the related silver(I)
carboxylates [12–14]. The AgꢀꢀꢀAg separation of 2.966(1) Å in the
six-membered rings is slightly larger than the average value
(2.89 Å) in metallic silver, thus indicating a weak or negligible me-
tal–metal interaction. The intra-dimer Ag–O distances and O–Ag–O
angles fall in the range of 2.281(3)–2.293(3) Å and 125.56(9)–
135.47(11)°, respectively, which are comparable to those found in
the other dimeric structures of several known silver(I) carboxylates
[12–14]. The present structure is extended into a zigzag polymeric
chain running parallel to the b axis (Fig. 2b). These chains are fur-
ther extended to a supramolecular layer along the ac plane by weak
3.3. Crystal structure of 1
Single X-ray analysis for compound 1 reveals that there exists
one molecule of Hima in asymmetric unit (Fig. 1a). It is obviously
Scheme 1. Coordination modes of Hima.

294
Y.-T. Wang et al. / Journal of Molecular Structure 938 (2009) 291–298
Fig. 1. (a) View of the structure of Hima (1). (b) 2-D supramolecular network extended by hydrogen bonds along the bc plane in 1. The red dashed-lines stand for hydrogen
bonds. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this paper.)
hydrogen-bonding
interactions
(C4–H4Aꢀ ꢀ ꢀO3a
3.242(6) Å,
Table 3
Hydrogen bond geometries in the crystal structure of 1–3.
a = ꢁ1 + x, y, z) (Fig. S2) [21]. A 3-D supramolecular framework is
constructed by interlayer weak hydrogen-bonding interactions
(N2–H2ꢀ ꢀ ꢀO5b, C2–H2Aꢀ ꢀ ꢀO1c and N2–H2ꢀ ꢀ ꢀO5a 2.854(6), 3.270(5)
and 3.117(6) Å, respectively. a = ꢁ1 + x, y, z; b = 1 ꢁ x, ꢁ1 ꢁ y, ꢁz;
c = x, 1 + y, z) (Fig. S2 and Table 3).
It is worthy of note that in complex 2, the Hima ligand is a neu-
tral molecule and adopts the zwitterionic formation, be signifi-
cantly different from those found previously in related
complexes containing Hima [11]. Compared to the previously re-
ported coordination modes of Hima (Scheme 1a and b) [11], it is
observed that there exists new type of coordination mode for the
free ligand Hima in 2 (Scheme 1c).
Compounds
1
D–Hꢀ ꢀ ꢀA
Hꢀ ꢀ ꢀA [Å]
Dꢀ ꢀ ꢀA [Å]
D–Hꢀ ꢀ ꢀA [°]
N2–H1ꢀ ꢀ ꢀO1a
C2–H2Bꢀ ꢀ ꢀO2b
C3–H3Aꢀ ꢀ ꢀO1b
C4–H4Aꢀ ꢀ ꢀO2c
C5–H5Aꢀ ꢀ ꢀO2d
N2–H2ꢀ ꢀ ꢀO5a
N2–H2ꢀ ꢀ ꢀO5b
C2–H2Aꢀ ꢀ ꢀO1c
C4–H4Aꢀ ꢀ ꢀO3a
N2–H2ꢀ ꢀ ꢀO8a
N2–H2ꢀ ꢀ ꢀO9a
N4–H4ꢀ ꢀ ꢀO8b
N4–H4ꢀ ꢀ ꢀO10b
C2–H2Aꢀ ꢀ ꢀO6c
C2–H2Bꢀ ꢀ ꢀO1b
C3–H3Aꢀ ꢀ ꢀO7c
C4–H4Aꢀ ꢀ ꢀO9d
C7–H7Bꢀ ꢀ ꢀO3e
C9–H9Aꢀ ꢀ ꢀO10d
C10–H10Aꢀ ꢀ ꢀO7f
1.72(2)
2.4900
2.2200
2.4400
2.4600
2.647(2)
3.386(2)
3.143(2)
3.321(2)
3.268(2)
173(2)
153.00
174.00
158.00
145.00
2
3
2.58(9)
1.91(7)
2.3600
2.3500
3.117(6)
2.854(6)
3.270(5)
3.242(6)
114(6)
157(6)
156.00
162.00
2.4800
2.0500
2.4700
1.9300
2.3900
2.5400
2.5600
2.4800
2.3700
2.5100
2.2200
3.05(4)
2.87(3)
3.02(4)
2.78(3)
3.31(3)
3.25(3)
3.45(4)
3.32(4)
3.22(3)
3.28(4)
3.10(3)
124.00
159.00
122.00
172.00
159.00
130.00
161.00
151.00
146.00
141.00
158.00
3.5. Crystal structure of 3
X-ray single-crystal structure determination reveals that 3 crys-
tallizes in the triclinic system space group P1. Complex 3 possesses
ꢀ
one-dimensional (1-D) chain constructed by Pb(II) centers, Hima
ligands and nitrate ions. Pb1 is coordinated by two oxygen atoms
(O5 and O6) from one nitrate ion, and six carboxylate oxygen
atoms (O1, O2, O2A, O3A, O4 and O4B) from four different Hima
molecules, forming an eight-coordinated dodecahedral coordina-
tion geometry (Fig. 3a). The distances between Pb and O atoms
Symmetry codes: aꢁ1/2 + x, 1/2 ꢁ y, ꢁ1/2 + z; bꢁ1/2 ꢁ x, ꢁ1/2 + y, 1/2 ꢁ z; cꢁx, 1 ꢁ y,
ꢁz; d1 + x, y, z for 1. aꢁ1 + x, y, z; b1 ꢁ x, ꢁ1 ꢁ y, ꢁz; cx, 1 + y, z for 2. ax, 1 + y, z; b1 + x,
c
e
f
y, z; ꢁx, 2 ꢁ y, 1 ꢁ z; d1 ꢁ x, 1 ꢁ y, ꢁz; ꢁ1 + x, y, z; 1 ꢁ x, 1 ꢁ y, 1 ꢁ z for 3.

Y.-T. Wang et al. / Journal of Molecular Structure 938 (2009) 291–298
295
Fig. 2. (a) View of coordination environments of the metal atom in 2 (hydrogen atoms are omitted for clarity). The pale-green dashed-lines denote the silver–silver
interactions. (b) View of 1-D chain along the c axis in 2. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this
paper.)
(ranging from 2.50(2) to 2.98(2) Å) fall in the range of Pb–O cova-
lent bonds (ranging from 2.46 to 2.96 Å) (Fig. 3b) [15,17]. Longer
distance is observed between Pb and one oxygen atoms (O2) from
Hima molecule (2.98(2) Å), being shorter than Pb–O bonds (3.11 Å)
[17]. All Hima ligands act as two- and three-connectors to link four
lead centers through bis- and tridentate carboxylate oxygen atoms
(Scheme 1d and e). A holodirected geometry in 3 is observed due to
the absence of clear gap in the coordination sphere of the Pb(II) ion
[22]. As shown in Fig. 3c, in 3 structure, two kinds of separations of
PbꢀꢀꢀPb can be found, for example, Pb1 and Pb1A are bridged by a
carboxyl O atom with a PbꢀꢀꢀPb distance of 4.385(2) Å. The distance
between Pb1 and Pb1C separated by two O atoms of carboxyl
groups is 4.970(1) Å. Pb1 and Pb1B are also bridged by another car-
boxyl O atom, forming a Pb2O2 unit with a PbꢀꢀꢀPb distance of
4.372(1) Å, which is too long to include metal–metal interaction
[22b,23]. Interestingly, along the c axis, four Pb(II) atoms are lo-
cated at the four corners of a defective double cubane (two cubanes
sharing one face and each missing one vertex) and bridged by
to 3.05(4) Å, Fig. S2 and Table 3). The thickness of 2-D layer is
1.3 nm and the distance of PbꢀꢀꢀPb in two neighboring chains is
7.618(2) Å (Fig. S4). For 3, neighboring 2-D layers stack in AAA
way (Fig. S5). The interlayer distance is 16.509(2) Å (PbꢀꢀꢀPb sepa-
ration in two neighboring layers). These 2-D layers are further ex-
tended to
a
3-D supramolecular structure by weak C–HꢀꢀꢀO
supramolecular interactions (DꢀꢀꢀA distances fall in the range of
3.10(3) to 3.45(4) Å) (Fig. S5 and Table 3).
Being similar to complex 2, the ligand Hima is also a neutral
molecule in 3. It is interestingly observed that there exist other
two kinds of coordination modes for Hima in 3 (Scheme 1d and
e), being significantly distinct from that in both complex 2 and
those found in the previous documents [11].
3.6. Thermogravimetric analysis (TGA)
TGA measurements were conducted to determine the thermal
stability of 2 and 3. The TGA curve reveals that compound 2 re-
mains intact until one consecutive weight loss occurs from 280
to 350 °C, being ascribed to the loss of ligands (found: 60.49%;
calcd: 60.86%). The remaining product weight is 39.51% when fur-
ther heating at the range of 350–700 °C, which can be ascribed to
Ag2O residue (calcd: 39.14%). TGA of complex 3 indicates that
the weight is unchanged until the temperature increases to
310 °C, indicating that the thermal stability of 3 is higher than 2.
The first weight loss of 61.08% (calcd: 61.75%) occurs at the range
of 310–390 °C, corresponding to the release of the ligands. The final
decomposed product hardly loses any weight (38.92%) upon fur-
means of two carboxylic O atoms and two l2-O atoms. It is noted
that only a limited number of dicubane-like structures constructed
through Pb–O bond and bridging O atoms of carboxylate group
were observed [24]. By sharing the Pb2O2 planes, the kind of dicub-
ane was further extended to a 1-D dicubane-like chain along the c
axis (Fig. 3c). The diagram of simplified 1-D chain structure is illus-
trated in Fig. S3.
The structure of compound 3 is expanded into a two-dimen-
sional layer structure along the crystallographic bc plane through
N–HꢀꢀꢀO hydrogen bonds interactions from uncoordinated nitrate
anions and imidazole groups (DꢀꢀꢀA distances range from 2.78(3)

296
Y.-T. Wang et al. / Journal of Molecular Structure 938 (2009) 291–298
Fig. 3. (a) Perspective view showing the coordination environment around the metal atom in 3 (hydrogen atoms and nitrate ion are omitted for clarity). (b) The 1-D chain of
3. Partial of nitrate anions are omitted for clarity. (c) The 1-D incomplete-cubane chain of 3. Partial of carbon and hydrogen atoms are omitted for clarity. Symmetry codes: (a)
ꢁ1 + x, y, z; (b) ꢁx, 1 ꢁ y, 1 ꢁ z; (c) ꢁ1 ꢁ x, 1 ꢁ y, 1 ꢁ z.
ther heating from 390 to 700 °C, which can be ascribed to PbO res-
idue (calcd: 38.25%).
upon an excitation maximum at 280 nm. The solid-state photolu-
minescence spectrum of 3 at room temperature is observed with
the main emission at 465 and 547 nm (kex = 280 nm). To further
study the relative luminescence of between the free ligand and
its complexes, the photoluminescent spectrum of free ligand Hima
was also investigated in solid state at room temperature (Fig. 4).
The free ligand Hima shows the fluorescent emission centers on
3.7. Luminescent properties
As illustrated Fig. 4, the solid-state room temperature photolu-
minescence of 2 exhibits the emission peak at 462 and 510 nm

Y.-T. Wang et al. / Journal of Molecular Structure 938 (2009) 291–298
297
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2
3
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300
400
500
600
700
800
Wavelength/nm
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356 and 682 nm with an excitation maximum at 280 nm. In
comparison to the free ligand Hima, the main emission peaks of
2 and 3 are red-shifted about 106 and 109 nm, respectively. Appar-
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Using a flexible ligand Hima we isolated two new silver and
lead coordination polymers possessing the unique 1-D chains,
which were characterized by single crystal X-ray diffraction, IR
spectra, elemental analysis, photoluminescence as well as thermal
analysis. The present study shows that Hima displays three new
kinds of coordination modes and can be used as an excellent bridg-
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to further investigate other coordination polymers based on this
kind of flexible organic ligands are in progress in our laboratory.
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This work was financially supported by the Project of Shandong
Province Higher Educational Science and Technology Program
(J09LB03), and the Starting Funding of Shandong Institute of Light
Industry (to Dr. Yong-Tao Wang). We are indebted to Prof. Xiao-
Ming Chen at Sun Yat-Sen University for helpful discussion.
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.09.045.
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