Unique Ag-C bonds, thermal, fluorescence, structural and solution studies of two-dimensional silver(I) coordination polymer

Article abstract of DOI:10.1016/j.jorganchem.2007.05.018

A 2D polymer with unique Ag-C bonds, [Ag(μ₄-DPOAc)]_n (1) [DPOAc = diphenylacetate], has been synthesized and characterized and its structure was determined by X-ray crystallography. In addition to the coordination to the O atoms of DPOAc the Ag atoms also form strong η¹ Ag-C π bonds and exhibit weak Ag-Ag interactions, resulting in the formation of O₃ CAg ? AgO₃ C moieties. The thermal stabilities of 1 and of its thallium(I) analogue, [Tl(μ₃-DPOAc)]_n (2), were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The ligand and compounds 1-2 are luminescent in the solution state, with emission maxima at 370, 383 and 360 nm, respectively. The results of studies of the stoichiometry and formation of complexes of 1 and 2 in DMF solution were found to be in support of their solid state stoichiometry.

Full text of DOI:10.1016/j.jorganchem.2007.05.018

Journal of Organometallic Chemistry 692 (2007) 3788–3795
www.elsevier.com/locate/jorganchem
Unique Ag–C bonds, thermal, fluorescence, structural and solution
studies of two-dimensional silver(I) coordination polymer
a
a,
b
Kamran Akhbari , Ali Morsali *, Matthias Zeller
a
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14155-4838, Tehran, Islamic Republic of Iran
b
Department of Chemistry, Youngstown State University, One University Plaza, P.O. Box 44555-3663, Youngstown, OH, USA
Received 11 March 2007; received in revised form 20 April 2007; accepted 9 May 2007
Available online 23 May 2007
Abstract
A 2D polymer with unique Ag–C bonds, [Ag(l4-DPOAc)]n (1) [DPOAc = diphenylacetate], has been synthesized and characterized
and its structure was determined by X-ray crystallography. In addition to the coordination to the O atoms of DPOAc the Ag atoms also
form strong g1 Ag–C p bonds and exhibit weak Ag–Ag interactions, resulting in the formation of O3CAg Á Á Á AgO3C moieties. The ther-
mal stabilities of 1 and of its thallium(I) analogue, [Tl(l3-DPOAc)]n (2), were studied by thermal gravimetric (TG) and differential ther-
mal analyses (DTA). The ligand and compounds 1–2 are luminescent in the solution state, with emission maxima at 370, 383 and 360 nm,
respectively. The results of studies of the stoichiometry and formation of complexes of 1 and 2 in DMF solution were found to be in
support of their solid state stoichiometry.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Silver(I); Diphenyl acetic acid; AgI–C bond; Coordination polymer; Fluorescence; Thermal; Solution study
1. Introduction
organic building blocks, the number and orientation of
the coordinating sites in the organic spacers, and the sol-
vent of recrystallization, among others [2]. Silver(I) ions
are regarded as soft acids favoring coordination to soft
bases, and give rise to an interesting array of stereochemist-
ries and geometric configurations with the coordination
numbers of two to six all occurring. Previous related work
on silver(I) coordination polymers has concentrated on the
use of nitrogen-donor ligands [3] or oxygen-donor ligands
[4] or a combination with both donors [5,6], but the use
of a combination of oxygen and carbon-donor ligands
are rare [7–11]. Up to now, metalheteroatom, metal–
carbon and metal–metal interactions are three of the
most important interactions in the construction of Ag poly-
meric networks in the solid state [12–14]. A search in the
Cambridge Structural Database shows only 32 silver(I)
complexes with Ag(I)–Cphenyl bonds [15] and the most of
these silver(I) complexes are monomeric structures and
coordination polymers type are rare.
Metal-organic coordination polymers are attracting a
great deal of attention because of their potential as func-
tional materials [1]. In metal-organic crystal engineering,
one takes advantage of the coordinating ability of metal
centers and organic ligands in order to build new coordina-
tion polymers. The main goal in metal-organic crystal engi-
neering is to predict the topology of supramolecular
architectures in order to synthesize extended solid-state
materials with desired properties. However, there still
remain many problems to overcome before the synthesis
of coordination polymers with a desired topology is possi-
ble. Many parameters are involved in the formation of the
metal-organic framework (MOF), such as the metal and its
possibilities of coordination, the nature of the counter-
anion, the metal-to-ligand ratio, the flexibility of the
*
In our last work, we reported the coordination polymer
of DPOAcÀ with thallium(I) [16]. In the present study, we
Corresponding author. Tel.: +98 2188011001; fax: +98 2188011101.
E-mail address: morsali_a@yahoo.com (A. Morsali).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.05.018

K. Akhbari et al. / Journal of Organometallic Chemistry 692 (2007) 3788–3795
3789
Table 1
report on the synthesis and crystal structure determination
of a silver(I) coordination polymer with DPOAcÀ, and we
also compare thermal resistance, emission properties and
formation constants of these two coordination polymers
with each other.
Crystal data and structure refinement for compound 1
Identification code
Empirical formula
Formula weight
Temperature (K)
1
C14H11AgO2
319.10
100(2)
0.71073
Monoclinic
P21/c
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
˚
a (A)
11.9677(10)
5.6277(5)
16.6468(13)
90.00
100.2890(10)
90.00
1103.14(16)
4
1.921
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Density (calculated) (g cmÀ3
)
Absorption coefficient (mmÀ1
F(000)
)
1.810
632
Crystal size (mm3)
0.16 · 0.22 · 0.31
2.49–30.51
À15 6 h 6 15, À7 6 k 6 7,
À21 6 l 6 22
2737
2675
Multi-scan
0.749 and 0.573
h Range for data collection (ꢁ)
Index ranges
2. Experimental
Reflections collected
Independent reflections
Absorption correction
Maximum and minimum
transmission
2.1. Materials and physical techniques
All chemicals were of reagent grade and were used as
commercially obtained without further purification. IR
spectra were recorded using Perkin–Elmer 597 and Nico-
let 510P spectrophotometers. Microanalyses were carried
out using a Heraeus CHN–O– Rapid analyzer. Melting
points were measured on an Electrothermal 9100 appara-
tus and are uncorrected. The thermal behaviour was mea-
sured with a PL-STA 1500 apparatus. The luminescent
properties were investigated with a Shimadzu RF-5000
spectrofluorophotometer. All UV–Vis spectra were
recorded on a computerized double-beam Shimadzu
2550 spectrophotometer, using two matched 10-mm
quartz cells. Conductometric measurements were carried
out with a Metrohm 712 conductometer equipped with
a Julabo F12-MB circulator. Crystallographic measure-
ments were made at 100(2) K using a Bruker AXS
SMART APEX CCD diffractometer. The intensity data
were collected within the range 2.49 6 h 6 30.51ꢁ using
graphite monochromated Mo Ka radiation (k =
Refinement method
Full-matrix
Least-squares on F2
2737/0/154
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R Indices (all data)
1.232
R1 = 0.0294, wR2 = 0.0642
R1 = 0.0304, wR2 = 0.0647
0.753 and À0.440
Largest difference and peak, hole
À3
˚
(e A
)
2.2. Synthesis of [Ag(l4-DPOAc)]n (1)
In 20 ml CH3CN 0.212 g (1 mmol) 2,2-diphenylacetic
acid were mixed and stirred with a solution of 0.057 g
(1 mmol) KOH in 3 ml H2O to form a clear solution. Addi-
tion of 0.170 g (1 mmol) AgNO3 in 5 ml H2O produced a
clear solution. The resulting solution was stirred and then
allowed to stand in darkness at room temperature to evap-
orate for several days to obtain suitable crystals. The crys-
tals were washed with acetone and air dried,
m.p. = 235 ꢁC. Yield: 0.112 g (35%). IR (selected bands;
˚
0.71073 A). Accurate unit cell parameters and the orienta-
tion matrix were obtained from least-squares refinement
using the programs SMART [17] and SAINT [18], and the
data were integrated using SAINT [18]. The structure has
been solved by direct methods and refined by full-matrix
least-squares techniques on F2 using SHELXTL [19]. The
molecular structure plots were prepared using ORTEP and
Mercury [20]. Crystallographic data and details of the
data collection and structure refinements are listed in
Table 1. The observed anisotropic thermal parameters,
the calculated structure factors, and full lists of bond dis-
tances, bond angles and torsion angles are given in the
supplementary material (see Table 2).
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) for compound 1
Ag(1)–O(1)
Ag(1)–O(2)
Ag(1)–O(2)
Ag(1)–C(5)
Ag(1)–Ag(1)
O(1)–Ag(1)–O(2)
O(1)–Ag(1)–O(2)
O(2)–Ag(1)–O(2)
2.2063(17)
2.2519(17)
2.4872(18)
2.710(3)
2.8463(4)
157.11(7)
117.77(6)
74.97(7)
O(1)–Ag(1)–C(5)
O(2)–Ag(1)–C(5)
O(2)–Ag(1)–C(5)
O(1)–Ag(1)–Ag(1)
O(2)–Ag(1)–Ag(1)
O(2)–Ag(1)–Ag(1)
C(5)–Ag(1)–Ag(1)
113.18(7)
87.87(7)
75.12(7)
85.19(5)
77.25(5)
149.80(4)
115.56(6)

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K. Akhbari et al. / Journal of Organometallic Chemistry 692 (2007) 3788–3795
in cmÀ1): 554m, 637m, 691s, 723s, 752m, 1023w, 1068w,
1267w, 1328w, 1374vs, 1437w, 1479m, 1531vs and 1589m.
Anal. Calc. for C14H11AgO2: C, 52.64; H, 3.45; Ag,
33.84. Found: C, 52.50; H, 3.34; Ag, 33.60%.
3.37 A [34–39]. Thus, strong monohapto aromatic coordi-
nation of Ag atoms in the compound 1 can be considered
and appears to be yet another factor which can make vary-
ing contributions to the construction of an organic–inor-
ganic coordination polymer.
˚
2.3. Synthesis of [Tl(l3-DPOAc)]n (2)
The structure of compound 1 may also be considered as
a coordination polymer of Ag(I) consisting of one-dimen-
sional linear chains constructed of carboxylate group
bridging, running parallel to the b-axis and the individual
polymeric chains are almost parallel to each other and fur-
ther bridged by Ag–C bonds, resulting in a two-dimensional
framework as shown in Fig. 2.
Compound 2 was prepared using a reported method [16]
for evaluation of other data such as thermal stability, lumi-
nescent properties and solution study, m.p. = 157 ꢁC. IR
(selected bands): 642m, 694s, 734s, 1361s, 1484m, 1532vs,
1563s, 1587s, 2885w, 3050w. Anal. Calc. for C14H11O2Tl:
C, 40.42; H, 2.64, Tl, 49.10. Found: C, 40.82; H, 2.56; Tl,
50.10%.
The structure of compound [Tl(l3-DPOAc)]n (2) has
recently been reported [16]. The single-crystal X-ray data
of compound 2 show the coordination number in the TlI
ions to be five, the thallium atoms have an irregular coor-
dination sphere with a stereo-chemically active lone pair
and hexa–hapto (g6) interactions, thus attaining a total
hapticity of 11 in a C6O5Tl coordination environment.
A striking difference between compound 1 and 2 is that
the DPOAcÀ anion in compound 1 acts as a fourfold
donating bridging ligand, connecting four AgI ions in a
l-4,3 mode (Fig. 1b and Scheme 1a), whereas each
DPOAcÀ anion in compound 2 acts as a pentadentate
ligand, connecting three TlI ions. The carboxylate groups
of the DPOAcÀ ligand in compound 2 act as both a biden-
tate chelating and a bridging group in a l-3,2 mode
(Fig. 1b and Scheme 1a). Another difference between com-
pound 1 and 2 is that the phenyl rings in compound 1
involve in a strong g1 interaction with AgI whereas
the phenyl rings in compound 2 take part in a weak
hexa–hapto (g6) interactions with TlI.
3. Results and discussion
3.1. Structure description
The reaction between diphenylacetate (DPOAcÀ) and
Ag(NO3) provided a crystalline material of the general for-
mula [Ag(l4-DPOAc)]n (1). Determination of the structure
of 1 by X-ray crystallography showed the complex to be a
novel two-dimensional polymer (Figs. 1 and 2). The silver
atoms can be considered to be three-coordinate. The car-
boxylate groups of the DPOAcÀ ligand act as a bridging
group where each oxygen atom of the carboxylate group
coordinates to a silver(I) ion, and one of these oxygen
atoms also bridges to one other silver atom (Figs. 1 and 2).
With a low coordination number of 3 for the large sil-
ver(I) ions in 1, one tends to look for secondary interac-
tions that could possibly relieve this coordinative
unsaturation. A search was made generally for AgÁ Á ÁAg
and AgÁ Á ÁC approaches and it appears that Ag in 1 may
also be involved in both AgÁ Á ÁAg and AgÁ Á ÁC (g1) interac-
tions with the silver atoms and phenyl groups of neighbor-
ing molecules (Figs. 1 and 2).
3.2. Thermogravimetric analysis
To examine the thermal stability of the two new com-
pounds, thermal gravimetric (TG) and differential thermal
analyses (DTA) were carried out between 30 and 700 ꢁC in
a static atmosphere of air (Figs. 3 and 4). Compound 1 is sta-
ble up to 235 ꢁC. The TG curve exhibits a distinct decompo-
sition stage between 235 and 480 ꢁC with a mass loss of
63.0% (calcd. 63.6% for the formation of Ag2O). DTA curve
displays three distinct exothermic peaks at 240, 300 and
450 ꢁC and a endothermic peak at 600 ꢁC. Compound 2 is
stable up to 181 ꢁC. TG curve exhibits a distinct decomposi-
tion stage between 193 and 550 ꢁC with a mass loss of 48.5%
(calcd. 48.9% for the formation of Tl2O). The DTA curve
displays a distinct endothermic peak at 181 ꢁC and two exo-
thermic peaks at 227 and 339 ꢁC (see Figs. 3 and 4).
The Ag–Ag interactions in compound 1, Ag1–Ag1 =
˚
2.8463(4) A, (Table 2) are longer than the Ag–Ag distances
in similar dinuclear complexes (i.e., 2.704(2), 2.669(1), and
˚
2.726(1) A) [21–25] and slightly shorter than those in the
polymeric structure [26–29]. The relatively short Ag–Ag
bonds found here may thus be considered to be only
d10Á Á Ád10 noncovalent interactions [21–29].
A general search was made for Ag–C approaches in
compound 1 and it appears that the Ag atoms may unex-
pectedly be involved in an g1 interaction with the Cphenyl
atom of neighboring molecules with a Ag(1)–C(5) distance
I
˚
of 2.710(3) A, thus augmenting the Ag Ag1O3 coordina-
tion spheres and compound 1 can be considered to contain
silver atoms with fourfold coordination and
a
3.3. Luminescent properties
O3CAgÁ Á ÁAgO3C environment. In compounds with similar
˚
bonds the Ag–C distances are in the range of 2.40–2.70 A
The fluorescence spectra of compounds 1 and 2 have
been studied in DMF solution. The compounds show
broad emission bands with the maximum intensities at
383 and 360 nm upon excitation at 300 nm, respectively
(Fig. 5). These fluorescent emissions can be tentatively
[30–33], in [Ag(benzene)ClO4] for example they are 2.496
˚
and 2.634 A [24]. Some other Ag(I) polymeric complexes
with Ag–C(sp2) bonded polycyclic aromatic ligands have
been reported to have mean Ag–arene distances of 2.82–

K. Akhbari et al. / Journal of Organometallic Chemistry 692 (2007) 3788–3795
3791
Fig. 1. (a) ORTEP diagram, (b) view of the Ag environment; the phenyl groups have been omitted for clarity, (c) space-filling representations of
compound 1, close approaches of Ag to the one of carbon atoms of phenyl rings can be seen. (Ag = violet, O = red, C = gray) i: Àx, y + 1/2, Àz + 1/2; ii:
Àx, Ày, Àz; iii: x, Ày + 1/2, z + 1/2. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this
article.)
assigned to the intraligand fluorescence emission as similar
emissions at 370 nm upon the same excitation at 300 nm
(Fig. 5) can also be observed for the free ligand HDPOAc.
The strong interactions of AgI with the ligand DPOAcÀ
probably also cause this difference in the luminescent prop-
erties of the two compounds.

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K. Akhbari et al. / Journal of Organometallic Chemistry 692 (2007) 3788–3795
Fig. 2. A fragment of the two-dimensional layer in compound 1, showing the Ag–C and Ag–Ag interactions. H atoms are omitted for clarity.
Tl
H
O
O
H
O
O
Ag
Ag
Tl
Ag
Ag
Tl
Scheme 1. The coordination mode of ligand DPOAcÀ (a) in the
Fig. 4. Thermal behaviour of compound [Tl(l3-DPOAc)]n (2).
compound 1 and (b) in the compound 2.
Fig. 3. Thermal behaviour of compound [Ag(l4-DPOAc)]n (1).
3.4. Solution studies
Fig. 5. The fluorescence spectra of ligand HDPOAc and compounds 1–2
in DMF solution. Bands 1 for [Ag(l4-DPOAc)]n (2) for compound [Tl(l3-
DPOAc)]n, room temperature, kexc = 300 nm.
The formation and stoichiometry of the compounds 1
and 2 in DMF solution was investigated by both conducto-
metric and spectrophotometric methods. The conductivity
of a 5.0 · 10À5 M solution of silver(I) nitrate and thal-
lium(I) nitrate in DMF were monitored as a function of
[DPOAcÀ]/[AgI] and [DPOAcÀ]/[TlI] mole ratio, respec-
tively at 25.00 0.05 ꢁC and the resulting plot is shown
in Fig. 6. As it is seen, the initial conductivity is relatively
low, probably due to some degree of ion pairing which is
common in solvents like DMF. Addition of the ligand to
the metal salt solution then causes an increase in the solu-
tion conductivity possessing a distinct inflection point at a
molar ratio of about one, indicating the formation of 1:1

K. Akhbari et al. / Journal of Organometallic Chemistry 692 (2007) 3788–3795
3793
complexes in solution. The electronic absorption spectra of
the ligand (DPOAcÀ) in the presence of increasing concen-
tration of silver(I) and thallium(I) ion in DMF at room
temperature is shown in Figs. 7 and 8, respectively. As is
obvious, the strong absorption of the ligand at 264 nm
increases with increasing concentration of the metal ion.
The resulting absorbance against [Ag+]/[DPOAcÀ] and
[Tl+]/[DPOAcÀ] mole ratio plots, shown in the inset of
Figs. 7 and 8, respectively, revealed an indistinct inflection
point at metal-to-ligand molar ratios of about 1, emphasiz-
ing the formation of a 1:1 complex in solution.
For evaluation of the conditional formation constants,
the mole ratio data obtained by the two different physico-
chemical methods employed were fitted to the previously
Fig. 6. Conductivity vs. [HDPOAc]/[M+] mole ratio plot DMF solution
for compounds 1 and 2.
Fig. 7. (a) Electronic absorption spectra of ligand HDPOAc in DMF (1.4 · 10À4 M) in the presence of increasing concentration of silver(I) ion at room
temperature. (b) Corresponding mole ratio plot at 264 nm.
Fig. 8. (a) Electronic absorption spectra of ligand HDPOAc in DMF (1.4 · 10À4 M) in the presence of increasing concentration of thallium(I) ion at room
temperature. (b) Corresponding mole ratio plot at 264 nm.

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K. Akhbari et al. / Journal of Organometallic Chemistry 692 (2007) 3788–3795
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logK = 2.55 0.004
for
compound
1
and
logK = 0.35 0.04 and logK = 0.38 0.01 for compound
2 from the conductometric and spectrophotometric meth-
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A organosilver(I) complex with an aromatic carboxylate
ligands based coordination network was synthesized and
characterized. The aromatic carboxylate ligand in this
complex exhibits a less-common g1-coordination mode of
the phenyl rings, in addition to the normal carboxylate
coordination modes. The complex shows interesting prop-
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results of studies of the stoichiometry and formation of 1
and 2 in DMF solution were found to be in support of their
solid state stoichiometry and show that the formation con-
stant of the silver(I) compound is much larger when com-
pared with the thallium(I) one. Compounds 1–2 and
ligand HDPOAc have shown luminescent properties in
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ligands is ongoing.
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Acknowledgements
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Foundation, INSF (Project Number 84118) is gratefully
acknowledged. The Smart Apex diffractometer was funded
by NSF Grant 0087210, by Ohio Board of Regents Grant
CAP-491, and by YSU.
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