Two new silver(I) ammine complexes by displacement reaction between [Ag(NH3)2]+ ions and different pyridine-4,5-Imidazoledicarboxylic Acids

Article abstract of DOI:10.1002/zaac.201000269

[Ag(NH₃)₂]⁺ ions are chosen as an initial reaction precursor because of its simple displacement reaction and intrinsic arrangement as well as specific coordination directionality. Two new silver(I) ammine complexes, Ag₂(NH₃)HL² (2) and Ag ₂(NH₃)₂HL³ (3), were obtained by a simple substitution reaction between [Ag(NH₃)₂] ⁺ ions and pyridine-4,5-imidazoledicarboxylic acid [H ₃L² = 2-(3′-pyridyl) 4,5-imidazoledicarboxylic acid and H₃L³ = 2-(4′-pyridyl) 4,5-imidazoledicarboxylic acid]. Silver dimers are connected into a 2D layer and 1D chain in complexes 2 and 3, respectively. In complex 2 two kinds of displacement reactions (mono-substituting and bis-substituting) occurred between the ammine molecules in [Ag(NH₃)₂]⁺ ions and H₃L ², however, only the mono-substituting reaction occurs in complex 3.

Full text of DOI:10.1002/zaac.201000269

ARTICLE
DOI: 10.1002/zaac.201000269
Two New Silver(i) Ammine Complexes by Displacement Reaction Between
+
[
Ag(NH ) ] Ions and Different Pyridine-4,5-Imidazoledicarboxylic Acids
3
2
[a]
[a,b]
[a]
[a]
Rui-Sha Zhou, Jiang-Feng Song,*
Yan-Bin Li, Chun-Yan Xu, and
[a]
Xiao-Feng Yang
Keywords: Ammine ligands; Pyridine-4,5-imidazoledicarboxylic acid; Silver; Substitution reaction; X-ray diffraction
3 2 3
Abstract. [Ag(NH )
]+ ions are chosen as an initial reaction precursor idazoledicarboxylic acid and H L3 = 2-(4'-pyridyl) 4,5-imidazoledicar-
because of its simple displacement reaction and intrinsic arrangement boxylic acid]. Silver dimers are connected into a 2D layer and 1D
as well as specific coordination directionality. Two new silver(I) am- chain in complexes 2 and 3, respectively. In complex 2 two kinds of
2
3
mine complexes, Ag
2
(NH
3
)HL (2) and Ag
2
(NH
3
)
2
HL (3), were ob- displacement reactions (mono-substituting and bis-substituting) oc-
+
+
2
tained by a simple substitution reaction between [Ag(NH
pyridine-4,5-imidazoledicarboxylic acid [H
3
)
2
] ions and curred between the ammine molecules in [Ag(NH
3
)
2
] ions and H
3
L ,
2
3
L = 2-(3'-pyridyl) 4,5-im- however, only the mono-substituting reaction occurs in complex 3.
Introduction
of silver coordination complexes under aqueous conditions of-
ten results in the formation of very insoluble “silver salts”,
however, the use of ammoniacal conditions can enhance the
The research interest in coordination polymers is rapidly in-
creasing because of their intriguing structures and wide poten-
solubility of the silver connectors and organic linkers. (2)
tial applications as functional materials.[
1–9]
Promising results
+
[
Ag(NH ) ] with an intrinsic geometry as well as specific co-
3
2
were achieved and startling applications are being developed,
however, the rational design and synthesis of coordination pol-
ymers with unique structure and function still remain a long-
term challenge. The self-assembly process of coordination pol-
ymers is frequently influenced by various factors such as me-
dium, pH value of solution, temperature, the nature of metal
ions, coordination arrangement, stereochemistry, and number
ordination directionality can guarantee subsequent substitution
processes that occur between the connectors and the organic
ligands.
Pyridine-4,5-imidazoledicarboxylic acids as selected organic
ligands are introduced based on following considerations: (1)
Similar to 4,5-imidazoledicarboxylic acid, the pyridine-4,5-im-
idazoledicarboxylic acids, which can be partly or fully depro-
tonated dependent on the pH level, are especially good linkers
not only because of their various coordination modes to metal
ions, but also because of their abilities to act as hydrogen-
bond acceptors and donors to assemble various supramolecular
[10–16]
of coordination donors provided by organic ligands.
In-
sight into the self-assembly process can be obtained by carry-
ing out systematic studies under completely similar reaction
conditions, while imposing subtle alterations such as changing
the anions, the crystallization solvent, pH value of solution,
or substituent groups of organic ligands, etc. These strategies
undoubtedly help to shed light on the prediction, design, and
synthesis of the target complexes.
[21, 22]
structures.
(2) The different coordination activity between
imidazole groups and carboxylate groups with metal ions re-
sults in selective substitution reactions. (3) The two nitrogen
atoms in the imidazole ring can gear the coordination orienta-
tion, which is similar to Si–O–Si bond angles in zeolites or
M–IM–M bond angles in zeolitic imidazolate frame-
Silver is a particularly versatile transition metal in its coordi-
[
17–19]
nation number and arrangement,
but the silver coordina-
+
[20]
tion geometry in [Ag(NH ) ] ion always keeps linear.
3
2
[
23, 24]
+
+
works (ZIF).
(4) The study on coordination chemistry
Compared with the Ag ion, [Ag(NH ) ] as the selected con-
3
2
of pyridine-4,5-imidazoledicarboxylic acids is relatively
nector features two special characteristics: (1) The preparation
[21, 22]
rare.
Recently, a new silver(I) ammine complex based on 4,5-im-
*
Dr. J. F. Song
E-Mail: jfsong0129@gmail.com
idazoledicarboxylic acid, namely, [Ag (C H N O )(NH ) ] (1),
2
5
2
2
4
3 2
[
a] Department of Chemistry, College of Science
North University of China
has been reported by our group, in which only one NH molec-
3
+
[25]
Taiyuan, 030051, P. R. China
ular in one [Ag(NH
3
)
2
] ion was displaced.
The relative
[
b] Shanxi Research Center of Engineering Technology for
Engineering Plastics
+
studies were carried out through reactions of [Ag(NH ) ] ion
3
2
and derivatives of 4,5-imidazoledicarboxylic acid to investi-
gate the influence of different organic linkers with 4,5-imida-
zoledicarboxylic acid on the construction of silver(I) ammine
frameworks. Two new silver(I) ammine complexes based on
North University of China
Taiyuan, 030051, P. R. China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201000269 or from the
author.
Z. Anorg. Allg. Chem. 2011, 637, 251–256
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
251

J.-F. Song et al.
ARTICLE
different
pyridine-4,5-dicarboxylic
acids,
namely, dried in air. C10
H
11Ag
2
N
5
O
4
(480.98): calcd.: C 24.95; H 2.29; N
2
3
1
3
2.47 %; found: C 24.91; H 2.36; N 12.37 %. IR (KBr): ν˜ = 3300 w,
Ag (NH )HL (2) and Ag (NH ) HL (3) were synthesized at
2
3
2
3 2
–1
142 m, 1668 m, 1607 s, 1347 s, 1065 m, 783 s, 668 m cm .
room temperature. By comparison, different pyridine-4,5-imid-
azoledicarboxylic acids, which adopt various coordination
modes, and steric hindrance are crucial factors for the forma-
tion of the different silver(I) ammine frameworks.
Crystal Structure Determination: The crystal structures were deter-
mined by single-crystal X-ray diffraction. The reflection data were col-
α
lected with a Bruker P4 CCD area-detector diffractometer (Mo-K ra-
diation, graphite monochromator) at room temperature with ω-scan
mode. Empirical adsorption correction was applied to all data using
the SADABS program. The structure was solved by direct methods
Experimental Section
2
and refined by full-matrix least-squares on F using SHELXTL 97
Materials and Methods: All chemicals purchased were of reagent
grade and used without further purification. Elemental analysis (C, H,
N) was performed with a Perkin–Elmer 240C elemental analyzer. The
IR spectrum was measured with a Perkin–Elmer Spectrum One FT-IR
spectrometer using KBr pellets. Thermogravimetric analysis (TGA)
was performed with a Perkin–Elmer TGA-7000 thermogravimetric an-
alyzer under flowing air at a temperature ramp rate of 10 °C·min .
The luminescence properties were measured with a Perkin–Elmer
LS55 spectrometer.
software.[ Non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were located from difference maps and refined with
isotropic temperature factors in complexes 2 and 3. All calculations
were carried out using SHELXTL 97 and PLATON 99.[ The crystal-
lographic data and pertinent information are summarized in Table 1.
Selected bond lengths and angles are listed in Table 2. Hydrogen bonds
are listed in Table 3.
26]
27]
–
1
CCDC-742091 and CCDC-742092 for complexes 2 and 3, respec-
tively, contain the supplementary crystallographic data. These data
can be obtained free of charge from CCDC The Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK
2
3
Syntheses of H L and H L
3
3
2
L3 was
(
Fax: +44-1223336033; or E-Mail: deposit@ccdc.cam.ac.uk or http://
The preparation of H
3
L was presented as an example, and H
3
2
www.ccdc.cam.ac.uk/data_request/cif).
obtained by essentially the same procedure as H
3
L .
Synthesis of 2-(3'-Pyridyl)-benzimidazole: A mixture of o-phenyl-
enediamine (2.16 g, 20 mmol), nicotinic acid (2.46 g, 20 mmol), and Supporting Information (see footnote on the first page of this article):
polyphosphoric acid (PPA, 50 g) was stirred at 180 °C for 4 h under Coordination environments of the silver atoms in complexes 2 and 3.
nitrogen. Afterwards, the mixture was cooled to 100 °C and poured TGA curves of complexes 2 and 3.
into water (400 mL). After the PPA was dissolved, the resulting solu-
tion was cooled and the pH was adjusted to 7 by the addition of NaOH.
The precipitated solid was filtered off. The crude product was recrys- Results and Discussion
tallized from alcohol and water, the yields obtained 50 %.
Synthesis
2
Synthesis of H
3
L : 2-(3'-pyridyl)-benzimidazole (1.8 g, 9.3 mmol)
Crystals of silver carboxylate complexes in good quality
could be obtained from the mixture of Ag[(NH ) ]NO , aque-
powdered potassium dichromate (12 g). After 20 minutes the mixture ous ammonia, and derivatives of 4,5-imidazoledicarboxylic
was quenched with ice-cold water and cooled to 0 °C. Crystallization acid, however, reactions of derivatives of 4,5-imidazoledicar-
was induced by scratching the sides of the vessel. The precipitated boxylic acid with silver(I) ions in presence of a base like
was added to a mixture of concentrated sulfuric acid (15 mL) and
water (19 mL) at 90 °C. This was followed by the careful addition of
3 2
3
acid was filtered and washed with water, alcohol, and finally with
diethyl ether.
NaOH usually result in insoluble colorless solids, which ob-
struct further structural studies by X-ray single crystal diffrac-
tion. The derivatives of 4,5-imidazoledicarboxylic acid con-
taining triethylamine are easier to solve in water than those
containing ammonia or NaOH. Ammonia here may serve as:
Syntheses of Complexes 2 and 3
2 3 3
Synthesis of Ag (NH
)HL2 (2): A solution of H L2 (10 mg, (a) a ligand competing with carboxylate oxygen that keeps the
0
.05 mmol) in water (2 mL) containing triethylamine (14 μL, 1 mmol) coordination arrangement of silver linear; (b) a ligand to form
was directly mixed with a solution of AgNO
3
in aqueous ammonia
+
+
[
Ag(NH ) ] , which may slower the reaction rate between Ag
3
2
(
2 mL, 25 %) and the resulted yellow solution was allowed to crystal-
and the organic linker and can facilitate the growth of single
crystals.
lize slowly at room temperature in the dark. After one week, brown
single crystals suitable for X-ray diffraction in 35 % yield (based on
2
H
3
L ) were collected by filtration, washed with small amounts of water
and dried in air. C10
H
8
Ag
2 4 4
N O (463.94): calcd.: C 25.86; H 1.72; N
Crystal Structure of Complex 2
10.35 %; found: C 25.91; H 1.66; N 10.37 %. IR (KBr): ν˜ = 3415 w,
3132 m, 1602 s, 1358 s, 1068 m, 739 s, 628 m cm (w = weak, m =
–
1
The crystal structure analysis reveals that complex 2 crystal-
medium, s = strong).
lizes in monoclinic system with space group P2 /n. The asym-
1
3
metric unit consists of two crystallographically independent
Synthesis of Ag (NH
2
3
)
2
HL (3): Complex 3 was prepared in the same
+
3
Ag ions, one partly deprotonated 2-(3'-pyridyl) 4,5-imidazole-
way with complex 2 except that H
3
L (10 mg, 0.05 mmol) was used
2
2
dicarboxylic acid (HL ) ligand and one ammonia molecule.
instead of H
3
L (10 mg, 0.05 mmol). After one week, brown single
3
crystals suitable for X-ray diffraction in 51 % yield (based on H
were collected by filtration, washed with small amounts of water and nitrogen atoms from an ammonia molecule (N1) and from the
3
L ) The Ag1 atom adopts a linear arrangement constructed by two
2
52 www.zaac.wiley-vch.de
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 251–256

Silver(I) Ammine Complexes by Displacement Reaction
Table 1. Crystal data and structure refinement for 2 and 3.
Complex
2
3
Empirical formula
C
10
463.94
H
8
Ag
2
N
4
O
4
C
10 2 5 4
H11Ag N O
Formula weight
480.98
Crystal system
monoclinic
P2 /n
monoclinic
P2 /n
Space group
a /Å
1
1
11.3560(7)
7.0833(5)
15.1125(10
90
10.2073(4)
9.9453(4)
13.4594(6)
90
b /Å
c /Å
α /°
β /°
101.3750(10)
111.8280(10)
γ /°
90
90
3
Volume /Å
1191.74(14)
4
1268.37(9)
4
Z
–
3
ρ
calc /g·cm
2.586
3.306
2.519
3.113
–
1
Absorption coef. /mm
Crystal size /mm
θ range /°
0.21 × 0.24 × 0.29
2.06 –26.10
6387
0.24 × 0.15 × 0.08
2.62–26.09
6857
Reflections collected
Unique reflections (Rint)
2366 [R(int) = 0.0265]
99.7 %
2517 [R(int) = 0.0218]
99.7 %
Completeness to theta
2
Goodness-of-fit on F
1.051
1.084
a)
R indexes [I > 2σ(I)]
R
R
1
= 0.0241, wR
= 0.0312, wR
2
2
= 0.0530
= 0.0558
R
R
1
= 0.0246, wR
= 0.0264, wR
2
2
= 0.0609
= 0.0617
a)
R (all data)
1
1
1 o c o o c 2 o
a) R = Σ||F |–|F ||/Σ|F |; wR = [Σw(F /Σw(F
2–F 2) 2)2]1/2.
2
imidazole unit (N2) of HL ligand, respectively. Ag2 adopts a
coordination arrangement similar to the one of Ag1, but the
two nitrogen atoms stem from the imidazole unit (N3) and the
Table 2. Bond lengths /Å and angles /° for complexes 2 and 3.
2
2
pyridyl group (N4) of two different HL ligands, as shown in
Ag(1)–N(1)
Ag(1)–N(2)
Ag(1)–Ag(2)
Ag(2)–N(3)
2.119(4)
2.129(3)
3.106(5)
2.174(3)
Ag(2)–N(4)
N(1)–Ag(1)–N(2)
N(3)–Ag(2)–N(4)
2.178(3)
168.51(13)
177.31(11)
Figure S1a (Supporting information). The Ag–N distances
range from 2.119(4) to 2.178(3) Å, and the N–Ag–N bond an-
gles range from 168.51(13) to 177.31(11)°. The bond lengths
and bond angles of silver in complex 2 are similar with the
3
[28]
reported complex, Ag(im), (Him = imidazole), and the cor-
responding bond lengths and angles around the silver ions are
given in Table 2. It is worth to note that the bond lengths of
Ag–O [d(Ag1···O3) = 2.7631 Å, d(Ag2···O1) = 2.6975 Å] are
much longer than those observed in the reported silver carbox-
N(1)–Ag(1)#1
Ag(1)–N(4)
Ag(1)–Ag(2)
Ag(2)–N(5)
2.151(3)
2.142(3)
3.136(4)
2.136(3)
N(4)–Ag(1)–N(1)#2 174.41(13)
Ag(2)–N(2)
2.153(3)
N(5)–Ag(2)–N(2)
178.73(13)
Symmetry transformations used to generate equivalent atoms: #1: –
x+3/2, y+1/2, –z+3/2; #2: –x+3/2, y–1/2, –z+3/2.
[29]
ylate complexes, which indicate weak interactions between
the silver atoms and the carboxylate oxygen atoms. It is as-
sumed that the silver atom adopts linear coordination arrange-
Table 3. Hydrogen bonds for complexes 2 and 3.
D–H···A
d(D–H)
d(H···A)
d(D···A)
<DHA
2
N1–H1···O4#1
N1–H2···O2#2
N1–H3···O1#3
O2–H8···O4#4
3
0.704
0.845
0.861
1.082
2.393
2.152
2.228
1.348
3.088
2.982
3.088
2.427
169.66
167.48
175.51
174.00
N4–H10···O3#5
N5–H7···O2#6
N4–H11···O2
N5–H6···O4#7
N5–H8···O4#8
N4–H9···O1#9
0.900
0.823
0.882
0.935
0.815
0.803
2.218
2.395
2.566
2.085
2.535
2.133
3.095
3.171
3.395
3.014
3.156
2.935
164.72
157.49
156.92
171.95
133.93
176.48
Symmetry codes: #1: –x+3/2, y–1/2, –z+3/2; #2: –x+5/2, y–1/2, –z+3/2; #3: x, y–1, z; #4: –x+2, –y+1, –z+2; #5: –x+1, –y+2, –z+1; #6: –x+1/2,
y–1/2, –z+3/2; #7: x, y–1, z; #8: –x+1, –y+2, –z+2; #9: –x+1/2, y–1/2, –z+3/2.
Z. Anorg. Allg. Chem. 2011, 251–256
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
253

J.-F. Song et al.
ARTICLE
ment. The weak interactions between silver atoms and the car- structed by two nitrogen atoms from an ammonia molecule
3
boxylate oxygen atoms result in a Ag–IM–Ag angle (149.93°) and from the imidazole unit of HL ligand, respectively (Figure
that deviates from Si–O–Si (145°).
S2a). The Ag–N distances range from 2.136(3) to 2.153(3) Å,
In complex 2, Ag1 and Ag2 are joined into a Ag1···Ag2 and the N–Ag–N bond angles range from 174.41(13) to
dimer through short Ag···Ag interactions [d(Ag1···Ag2) = 178.73(13)°. The corresponding N–Ag–N bond angles listed
3
.1065(5) Å]. Two Ag dimers were assembled into a in Table 2 further illustrate that linear coordination environ-
2
Ag (HL ) Ag building block through two imidazole groups ments with minor geometric variation exist for complex 3. The
2
2
2
2
from two different HL ligands (Figure 1). Strong π···π interac- bond lengths of Ag–O [d(Ag1···O3)
=
2.5598 Å,
2
tions between HL ligands (face-to-face distance of 3.3655 Å d(Ag2···O2) = 2.5751 Å] are slightly shorter than those ob-
2
and offset angle 7.07°) enforce the Ag (HL ) Ag building served in complexes 1 and 2, which indicate that the weak
2
2
2
2
I
block. The Ag (HL ) Ag building blocks are linked into a 2D interactions between Ag and the carboxylate oxygen atom in
2
2
2
layer through the interaction between Ag2 and pyridyl group complex 3 are stronger than those in complexes 1 and 2, how-
of 2-(3'-pyridyl) 4,5-imidazoledicarboxylic acid along the bc2 ever, this is not able to change the coordination orientation of
3
plane (Figure 1). Interestingly, Ag2 ions are linked by HL
the imidazole ring in HL ligand.
ligand in a μ mode (Figure S1b) into a left-hand and a right-
In complex 3, the atoms Ag1 and Ag2 are assembled into a
3
hand 2 helix with helical pitch of 7.833 Å along b axis in Ag1···Ag2 dimer through short Ag···Ag interactions
1
the 2D layer, respectively (Figure 2). Left-hand and right-hand [d(Ag1···Ag2) = 3.1361(4) Å]. Due to larger steric hindrance
3
chains are joined together through short Ag1···Ag2 contacts. of 4,5-imidazoledicarboxylic acid, the HL ligands in the silver
Hydrogen bonds within layers further enforce the 2D structure dimer are perpendicular to one another, the corresponding tor-
stability (N1–H1···O4, N1–H3···O1 and O2–H8···O4).
sion angle amounts 92.299°. Larger steric hindrance of the or-
ganic linkers prevents formation of silver tetramers as complex
1
. Each silver dimer is linked into a 1D chain by two HL3
ligands (Figure S2b). Compared with complex 2, the pyridyl
3
group of HL is not coordinated to the silver atom, so a 2D
layer like that of complex 2 is not formed. Hydrogen bonds
within the chain further enforce the 1D structure stability (N5–
H6···O4, N4–H11···O2). The 1D chain is linked into a 3D su-
pramolecular network through hydrogen bonds among chains
(
Figure 3), and the corresponding hydrogen bonds are listed in
Table 3.
2 2 2
Figure 1. 2D layer constructed by Ag Ag units in complex 2.
(HL2)
Figure 3. 3D supramolecular network in complex 3.
Figure 2. Alternative left-hand and right-hand helical chains in 2D
layer of complex 2.
TG Curves of Complexes 2 and 3
The thermal behavior of complex 2 was studied from 25 °C
to 700 °C under air. The thermogravimetric analysis (Figure
S3) revealed that complex 2 decomposes through two major
processes. The first loss amounts approximately 28.05 % in
Crystal Structure of Complex 3
The crystal structure analysis reveals that complex 3 crystal- the range of 200–345 °C, corresponding to the weight loss of
2
lize in monoclinic system with space group P2 /n. The asym- NH and part of the HL ligand. The second weight loss occurs
1
3
metric unit consists of two crystallographically independent between 345 and 434 °C and is characteristic of the combus-
+
2
Ag ions, one partly deprotonated 2-(4'-pyridyl) 4,5-imidazole- tion of the remaining part of the HL ligand moiety. The total
3
dicarboxylic acid (H L ) ligand and two ammonia molecules. weight loss of complex 2 amounts to 54.06 % (calcd.
3
The atoms Ag1 and Ag2 both adopt a linear arrangement con- 53.44 %).
2
54
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 251–256

Silver(I) Ammine Complexes by Displacement Reaction
The thermogravimetric analysis of complex 3 (Figure S4) that allows modeling and the study of phenomena, which are
revealed that complex 3 also decomposes through two major superimposed upon a more complicated, multi-component sys-
processes. The first loss amounts approximately 25.67 % in tem, is helpful to establish general principles. After careful
+
the range of 200–340 °C, corresponding to the weight loss of consideration, [Ag(NH ) ] ions are chosen as an initial reac-
3
2
NH3 and part of the HL3 ligand. The second weight loss tion precursor because of its simple displacement reaction and
(
26.44 %) occurs between 340 and 400 °C and is assigned to intrinsic arrangement as well as specific coordination direc-
3
the combustion of the remaining part of the HL ligand moiety. tionality. We obtained three silver(I) ammine complexes when
+
The total weight loss of complex 3 amounts to 52.11 % (calcd. [Ag(NH ) ] ions react with the organic linkers containing 4,5-
5
3
2
5.09 %).
imidazoledicarboxylic acid. X-ray single crystal diffraction re-
I
veals that the coordinations of Ag in complexes 1–3 are basi-
cally linear within minor differences. The mono-substituting
Luminescence Properties
+
reaction of [Ag(NH ) ] ions occurred in complexes 1 and 3,
3
2
however, both mono- and bis-substituting reactions occurred
in complex 2. The possible reasons of the formation of this
kind of silver(I) ammine complexes are as follows: (1) coordi-
The photoluminescence spectra of complexes 2 and 3 as well
2
3
as those of the ligands H L and H L are shown in Figure 4.
3
3
2
3
The ligands H L and H L both exhibit blue photolumines-
3
3
1
3
nation selectivity and orientation of the ligands H L –H L
cence with emission maxima at 440 and 468 nm upon excita-
tion at 380 nm, respectively. Similarly, complexes 2 and 3 also
exhibit blue photoluminescence with emission maxima at 441
3
3
play an important role in the formation of silver(I) ammine
complexes, (2) the strong negative induction effect of carbox-
ylate decreases the coordination ability of the imidazole group
of the organic linkers containing 4,5-imidazoledicarboxylic
acid, (3) compared with nitrogen donors, such as imidazole,
and 422 nm upon excitation at 365 nm, respectively. Com-
2
pared with the photoluminescence spectra of H L and com-
3
plex 2, we find that the maximum emission wavelength of
2
4
,4'-bipyridine, and pyrazine etc., larger steric hindrance of the
complex 2 is similar to that of H L ligand. Although the maxi-
3
organic linkers containing 4,5-imidazoledicarboxylic acid pre-
mum emission wavelengths of complex 3 undergo a very slight
+
vents further displacement reactions of the [Ag(NH ) ] ions.
blueshift, the emission bands for complexes 3 are very similar
3 2
3
In complexes 1–3, 4,5-imidazoledicarboxylic acid results in
the formation of silver tetramer in complex 1, however, the
larger steric hindrance of pyridine-4,5- imidazoledicarboxylic
acid prevents the silver dimers to form silver tetramers in com-
plexes 2 and 3 through short Ag···Ag contacts. The organic
linkers containing 4,5-imidazoledicarboxylic acid play an im-
portant role in the formation of silver(I) ammine complexes:
they (1) act as bridging bis-monodentate nitrogen donors, (2)
to those found for the free H L ligand in terms of position
3
and band shape. Therefore, the emission bands of complexes
2
and 3 are mainly due to an intraligand emission state similar
1
0
with the reported d metal complexes with N-donor carboxyl-
ate ligands.[
30, 31]
The intensity increase of the luminescence
for these complexes than their corresponding ligands may be
attributed to the chelation of the ligand to the metal atom,
2
3
which increases the rigidity of HL or HL and reduces the
nonradiative relaxation process.
prevent the further formation of displacement reaction of
+
[
Ag(NH ) ] ions due to steric hindrance, (3) act as a good
3
2
acceptor of hydrogen bonds.
Conclusions
+
[
Ag(NH ) ] ions are chosen as initial reaction precursor be-
3
2
cause of their simple displacement reaction and intrinsic ar-
rangement as well as specific coordination directionality. Two
new silver(I) ammine complexes were obtained by a simple
+
substitution reaction between [Ag(NH ) ] ions and different
3
2
pyridine-4,5-imidazoledicarboxylic acids. The results revealed
that the organic linkers containing 4,5-imidazoledicarboxylic
acid play an important role in the formation of silver(I) am-
mine complexes: they (1) act as bridging bis-monodentate ni-
trogen donors, (2) prevent the further formation of displace-
+
ment reaction of [Ag(NH ) ] ions due to steric hindrance, (3)
3
2
Figure 4. Solid-state emission spectra for complexes 2 and 3 as well
act as a good acceptor of hydrogen bonding. Although we are
so far unable to control the formation of target silver ammine
complexes, the unusual bonding configuration of silver(I) am-
2
3
as ligands H
3
L and H
3
L at room temperature.
+
mine complexes resulting from [Ag(NH ) ] ion and the deriv-
3
2
atives of 4,5-imidazoledicarboxylic acid may be useful for de-
signing new silver-based materials. Study on the porous metal-
Discussion
Although the rational design and synthesis of target com- organic frameworks constructed by the organic linkers contain-
plexes is still a great challenge, exploiting a simple system ing 4,5-imidazoledicarboxylic acid will be reported.
Z. Anorg. Allg. Chem. 2011, 251–256
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
255

J.-F. Song et al.
ARTICLE
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Acknowledgement
This work was supported by the Natural Science Young Scholars Foun-
dation of North University of China and the Scientific Research Start-
up Foundation of North University of China.
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Received: July 6, 2010
Published Online: September 29, 2010
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 251–256