Self-assembly of three cationic silver(I) coordination networks with flexible bis(pyrazolyl)-based linkers

Article abstract of DOI:10.1016/j.poly.2017.03.048

Three new cationic silver(I) coordination polymers, {[Ag(μ-bpmb)](SO₃CF₃)}_n (1), {[Ag(μ-bdb)_1.5](SO₃CF₃)}_n (2) and {[Ag(μ-bpb)₂](NO₃)}_n (3), with

Full text of DOI:10.1016/j.poly.2017.03.048

Accepted Manuscript
Self-assembly of three cationic silver(I) coordination networks with flexible
bis(pyrazoly)-based linkers
Sara Azizzadeh, Valiollah Nobakht, Lucia Carlucci, Davide M. Proserpio
PII:
S0277-5387(17)30246-2
DOI:
http://dx.doi.org/10.1016/j.poly.2017.03.048
POLY 12563
Reference:
Polyhedron
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Revised Date:
Accepted Date:
16 February 2017
17 March 2017
19 March 2017
Please cite this article as: S. Azizzadeh, V. Nobakht, L. Carlucci, D.M. Proserpio, Self-assembly of three cationic
silver(I) coordination networks with flexible bis(pyrazoly)-based linkers, Polyhedron (2017), doi: http://dx.doi.org/
10.1016/j.poly.2017.03.048
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Self-assembly of three cationic silver(I) coordination networks with flexible
bis(pyrazoly)-based linkers
Sara Azizzadeh,[a] Valiollah Nobakht,*[a] Lucia Carlucci,[b] Davide M. Proserpio [b],[c]
[a] Department of Chemistry, Faculty of Sciences, Shahid Chamran University of Ahvaz, Ahvaz,
Iran. Fax: +98 613 3331042; E-mail: v.nobakht@scu.ac.ir
[b] Dipartimento di Chimica, Università degli Studi di Milano, Via C. Golgi 19, 20133, Milano,
Italy.
[c] Samara Center for Theoretical Materials Science (SCTMS), Samara University, Samara 443011,
Russia.
Abstract
Three new cationic silver(I) coordination polymers, {[Ag(µ-bpmb)](SO3CF3)}n (1), {[Ag(µ-
bdb)1.5](SO3CF3)}n (2)
and
{[Ag(µ-bpb)2](NO3)}n (3), with flexible
1,4-
bis[(pyrazolyl)methyl]benzene
(bpmb), 1,4-bis[(3,5-dimethylpyrazolyl)methyl]benzene
(bdb), and 1,4-bis(pyrazolyl)butane (bpb) have been prepared at room temperature by the
solvent layering method. The three compounds were characterized by FT-IR spectroscopy,
PXRD, elemental analyses and single-crystal X-ray diffraction. Compound 1 is a highly
undulated polymeric 1D chain in which the silver ions adopt a linear geometry, coordinating
two bpmb linkers. Compounds 2 and 3 are both 2D coordination polymers with their silver
atoms being three and four coordinated, and resulting in 63-hcb and 44-sql underlying net
topologies, respectively. The flexible bispyrazolyl ligands display various conformations in
the solid state, causing the formation of different Ag…Ag separations in the polymeric
structures.
Keywords: Silver(I), coordination polymer, flexible ligand, pyrazolyl ligand.
1

1. Introduction
The construction of coordination polymers (CPs) by the self-assembly of metal ions or metal
clusters and organic linkers is an active research area. Such interest is not only due to the
creation of a great variety of fascinating structures, from one-dimensional chains to two-
dimensional sheets and three-dimensional networks, [1] but also to the wide range of
applications of CPs, including gas storage (particularly hydrogen storage) and separation [2],
catalysis [3], explosives [4], biomedicine, optical and electronic devices [5]. When rigid
bridging ligands are involved in the self-assembly process, it is easier to design predictable
networks with desired structures and appropriate properties, while using flexible ligands
makes it difficult to design favored supramolecular architectures. However, the flexibility of
the linkers usually generates greater structural diversity with possible unusual entanglements
[6]. The self-assembly process in the presence of flexible linkers is influenced by a number of
factors, including the nature of the solvent and counter ion, mole ratio of the reagents,
coordination preference of the metal ion and geometry of the linker ligands [3f,7]. Non-
covalent weak interactions, such as C-H hydrogen bonds, π···π stacking and C-H···π
interactions, may also be expected to play a role in the assembly and dimensionality of the
resulting structures [8].
Among variety of polymeric structures reported up until now, Ag(I) and Cu(I) ions are
particularly well-suited cations for study, because they display a variety of coordination
numbers and coordination geometries without crystal field stabilization energy preferences
[9]. These CPs also exhibit outstanding luminescent properties and the silver(I) species
exhibit well-known antibacterial activity [10]. In the structure of Ag(I) CPs, the silver(I) ion
can associate in Ag···Ag interactions that can play a significant role in directing the assembly
2

of the coordination networks. On the basis of our experiences on the design and synthesis of
copper(I) and silver(I) coordination polymers [7d,e, 11], in this current work we explore the
type of coordination polymers that can be formed by combining flexible bispyrazolyl ligands
(scheme 1) with Ag(I) centers in the presence of triflate and nitrate ions. We report herein the
synthesis and structural characterization of three new silver(I) coordination polymers and
investigate the effect of the ligand geometry and weak non-covalent interactions on their
structures and dimensionality. We hope that this work will assist in identifying factors that
govern the structure of coordination polymers and thus provide a basis for the rational design
of coordination polymers constructed from flexible bridging ligands.
N
N
N
N
N
N
N
N
N
N
N
N
bpmb
bpb
bdb
Scheme 1. Structure of the bispyrazolyl linker ligands
2. Experimental
2.1. Materials and physical measurements
All experiments were carried out in air. The starting materials were purchased from
commercial sources and used without further purification. The infrared spectra (4000-400
cm−1) were recorded as KBr discs with a BOMEN MB102 FT-IR spectrometer. The
elemental analyses for C, H and N were performed on a Costech-ECS 4010 CHNSO
3

analyzer. X-ray powder diffraction patterns were recorded on a Philips X’Pert Pro
diffractometer (Cu Kα radiation, λ = 1.54184 Å) in the 2θ range 5-50°. The simulated XRD
powder patterns, based on single crystal data, were obtained using Mercury software [12].
2.2. Synthetic procedures
2.2.1. Preparation of the bpmb, bdb and bpb ligands: The ligands were prepared
according to the published methods [13]. Typically, a mixture of pyrazole (1.36 g, 20 mmol)
or 3,5-dimethyl-pyrazole (1.92 g, 20 mmol) and finely powdered potassium hydroxide (2.24
g, 40 mmol) in DMSO (12 mL) were vigorously stirred at 80 ºC for 2 h. Then, the
corresponding dihalide, 1,4-bis(chloromethyl)benzene (1.64 g, 10 mmol) or 1,4-
dichlorobutane (1.11 mL, 10 mmol), in DMSO (5 mL) was added dropwise to the slurry
mixture. The mixture was stirred at 80 ºC until completion of the reaction (checked by TLC).
The mixture was then cooled to room temperature and the vessel was moved to an ice bath.
250 mL of cooled water was poured into the reaction mixture and a precipitate formed
immediately, which was collected by filtration, washed with water and dried under vacuum.
In the case of bpb, as the product is a liquid, the reaction mixture was poured into water (250
mL) and extracted with chloroform (3 × 20 mL). The extract was washed with water (2 × 20
mL) and dried over calcium chloride. After evaporation of chloroform under vacuum, the
product was isolated as a yellow oil.
2.2.2. Synthesis of {[Ag(µ-bpmb)](SO3CF3)}n (1)
A solution of bpmb (15 mg, 0.06 mmol) in 3 mL of acetone was gently layered on the top of
a clear solution of AgSO3CF3 (10 mg, 0.04 mmol) in 3 mL of water in a test tube. The vessel
was covered by aluminum foil and kept in a dark place. Colorless needle-shaped single
crystals of 1 suitable for X-ray crystallography were obtained after 2 days. They were
4

collected and dried in air. (0.015 g, 76% yield based on Ag). Anal. Calcd for
C15H14AgF3N4O3S: C 36.38, H 2.85, N 11.31; Found: C 36.51, H 2.90, N 11.12%.
2.2.3. Synthesis of {[Ag(µ-bdb)1.5](SO3CF3)}n (2)
A solution of bdb (30 mg, 0.12 mmol) in 4 mL of acetone was gently layered on the top of a
clear solution of AgSO3CF3 (15 mg, 0.06 mmol) in 4 mL of water in a test tube. The vessel
was covered by aluminum foil and kept in a dark place. Colorless needle-shaped single
crystals of 2 suitable for X-ray crystallography were obtained after a week. They were
collected and dried in air. (41 mg, 81% yield based on Ag). Anal. Calcd for
C28H33AgF3N6O3S: C 48.15, H 4.76, N 12.03; Found: C 47.72, H 4.50, N 11.85%.
2.2.4. Synthesis of {[Ag(µ-bpb)2](NO3)}n (3)
A solution of bpb (0.11 g, 0.57 mmol) in 4 mL of EtOH was gently layered on the top of a
clear solution of AgNO3 (0.05 g, 0.29 mmol) in 4 mL of water in a test tube. The vessel was
covered by aluminum foil and kept in a dark place. Colorless cubic single crystals of 3
suitable for X-ray crystallography were obtained after two weeks. They were collected and
dried in air. (55 mg, 34% yield based on Ag). Anal. Calcd for C20H28AgN9O3: C 43.65, H
5.12, N 22.91; Found: C 43.60, H 5.12, N 23.43%.
2.3. Single crystal X-ray crystallographic studies:
X-ray data were collected on a Bruker Apex II diffractometer using MoKα radiation. The
structures were solved using direct methods and refined using a full-matrix least squares
procedure based on F2 using all data [14]. Hydrogen atoms were placed at geometrically
estimated positions. The high R value for compound 3 is intrinsically related to the high
flexibility of the ligand. Different collection data were obtained from several crystals at room
and low temperature without improving the final refinement beyond the one reported. Details
5

relating to the crystals and the structural refinements are presented in Table 1. Full details of
the crystal data and the structure refinements, in CIF format, are available as Supporting
Information.
Table 1. Crystallographic data and structure refinement details for 1-3.
Compound
1
2
3
Formula
C15H14AgF3N4O3S
495.23
C28H33Ag F3N6O3S
698.53
C20H28AgN9O3
550.38
Molecular weight
T (K)
293
293
293
Triclinic
monoclinic
P21/c
monoclinic
P2/c
Cryst syst
space group
a (Å)
P-1
9.2496(16)
10.1206(17)
11.698(2)
68.602(2)
74.582(3)
65.432(2)
15.623(5)
15.226(5)
13.409(5)
90
17.4440(3)
8.4164(12)
33.155(5)
90
b (Å)
c (Å)
α (°)
101.587(5)
90
104.594(2)
90
β (°)
γ (°)
V (Å3)
Z
Dcalcd (g cm-3)
918.8(3)
2
1.790
20332
3124.7(18)
4
1.485
4709.5(13)
8
1.553
92315
731650
Data collected
5293 (0.048)
5293/0/244
10079 (0.037)
10079/0/379
13192 (0.055)
13192/172/597
Unique data (Rint
)
data/restraints/params
0.0420
0.0960
0.0505
0.1479
0.1003
0.2365
R1[I> 2σ(I)]
wR2 (all data)
3. Results and discussion
3.1. Synthesis of complexes 1-3.
The silver(I) coordination polymers were prepared at room temperature by the solvent
layering method, reacting silver(I) triflate or nitrate salts with the bis(pyrazolyl) ligands. The
solvent layering method is a simple and efficient strategy to obtain high quality single
crystals of Ag(I) CPs. The complexes are almost stable towards air and moisture; they were
characterized by elemental analyses, FT-IR spectroscopy, PXRD and single-crystal X-ray
diffraction.
3.2. Description of the crystal structures
6

3.2.1. Crystal structure of {[Ag(µ-bpmb)](SO3CF3)}n (1)
Compound 1 crystallizes in the triclinic space group P-1 with Z = 2 (Table 1). The structure
consists of square-wave-like cationic 1D polymeric chains and the uncoordinated triflate
counteranion, SO3CF3- (Figure 1b). The asymmetric unit contain one silver atom, one triflate
anion and two halves of two centro-symmetric ligands (Figure 1a). The Ag(I) centers are
bound to the N atoms of two pyrazolyl groups from separate ligands, forming an almost
linear AgN2 geometry [Ag−N= 2.136(2) and 2.138(2) Å; N-Ag-N=175.37(13)°]. The bridging
ligands are crystallographically independent and hence exhibit different (Ag)N…N(Ag)
distances (7.79 and 7.96 Å for the green and red color linkers, respectively) and two different
Ag∙∙∙Ag separations of 7.25 and 6.61 Å along the chain. Usually, the metal•••metaal separration
should be longer than the linker length, however the anti conformation of the bpmb ligands
are such as to bring the two coordination sides of the ligand into close proximity of each
other and provide a shorter Ag∙∙∙Ag distance. All the ligands are centrosymmetric, with
centers of inversion located at the center of phenyl spacer rings. It follows that the mean
planes of the pyrazolyl rings are parallel. The phenyl rings of both independent ligands are
almost perpendicular to the corresponding pyrazolyl mean planes, 83.9° (N3N4) and 81.2°
(N1N2). All the chains within the crystal are parallel and extend along the crystallographic a
axis. The structure is arranged in a manner that the phenyl spacers are stacked along the a
axis (Figure 1c).
7

(a)
(b)
(c)
8

Figure 1. The structure of {[Ag(µ-bpmb)](SO3CF3)}n (1). (a) Part of the infinite chain with the
numbering scheme; centers of inversion are located at the centre of the phenyl spacer rings (b) Ball
and stick representation of the extended polymeric chain, showing two different conformations for the
bpmb linkers (c) Packing of the chains along the a axis; the triflate anions are located between the
chains without any interaction with the silver(I) ions.
The triflate anions are located between the cationic [Ag(µ-bpmb)]+n chains (Figure 1c) and
show only weak C−H∙∙∙O hydrogen bonds between its oxygen atoms and the neighboring
hydrogen atoms of pyrazolyl or methylene groups. Details of the hydrogen bonding geometry
are given in Figure S1 and Table S2 [Supporting information]. The main non-covalent
interactions present in 1 are two types of inter-chain π···π stacking involving
crystallographically equivalent pyrazolyl rings of adjacent chains. These are characterized by
centroid···centroid distances of 3.567(3) and 3.870(2) Å for the perfectly parallel N3N4 and
N1N2 pyrazolyl groups, respectively [15]. Taking into account such π···π weak interactions,
the 1D coordination motifs extend to a 3D supramolecular architecture.
Curiously, looking in the literature we found a crystal structure that shows similarities with
compound 1 which is worth commenting on. {[Ag(µ-L)](ClO4)}n L= 1,4-bis(imidazol-1-
ylmethyl)naphthalene with CSD refcode HEXLUS [16], is a silver 1D chain very similar to
1. Despite the differences in the nature of the ligands and counteranions, the two structures
show very similar crystallographic parameters and structural features. Both compounds show
square wave-like chains that are connected to each other through π···π interactions. However,
in HEXLUS there are naphthalene instead of phenyl spacers, which are oriented almost
perpendicular to the running direction of the [0 1 -1] chains, that are involved in inter-chain
π···π stacking, while in 1 the terminal five membered rings are involved in the inter-chains
π···π interactions.
9

3.2.2. Crystal structure of {[Ag(µ-bdb)1.5](SO3CF3)}n (2)
Compound 2 is a two-dimensional structure that crystallizes in the monoclinic space group
P21/c with Z= 4 (Table 1). The asymmetric unit consists of one silver(I) ion, one and a half
bdb ligands and an uncoordinated triflate ion as a counter anion (Figure 2). The silver(I) ions
are coordinated by three N atoms of µ-bdb linkers in a distorted trigonal planar, TP, geometry
with angles between 101.00(8) and 142.44(9)˚ (Table S1). Deviation from the ideal TP
geometry is probably due to the large steric hindrance induced by the 3,5-dimethylpyrazole
rings of the µ-bdb ligands. The Ag-N distances are in the range 2.215(2)-2.362(2) Å. Due to
the coordination of the bdb linkers to the silver centres, 66-membered cationic [Ag6(µ-
bdb)6]6+ metallacyclic rings are formed; the extended connection of the [Ag6(µ-bdb)6]6+ units
generate highly undulating cationic 2D sheets with a 63-hcb network (Figure 2a,b). The 2D
sheets extend in the bc plane and are packed along the a axis in an AAA manner. The triflate
ions remain uncoordinated between the highly wavy sheets. Because of the wavy character of
the layers, the thickness of each sheet is of about 20 Å. Although the triflate ions remained
uncoordinated, they contribute to weak intermolecular C−H∙∙∙O interactions between the
oxygen atoms of the triflate ions and the H atoms of methylene groups or pyrazolyl rings
(Figure 2b and Table S2). The 2-D honeycomb structure of 2 is composed of µ-bbd ligands
with two different types of conformation; they are shown in different colors in Figure 2b. The
green color ligand is centrosymmetric, with an (Ag)N…N(Ag) distance of 8.81 Å and
parallel pyrazolyl rings; the red color ligands are shorter than the green in length, with an
N…N distance of 8.20 Å, and exhibit a dihedral angle between the planes of the two
pyrazolyl rings of 10.2˚. The different conformations of the ligands cause two different
Ag···Ag separations (10.04 and 7.28 Å).
10

(a)
(b)
(c)
Figure 2. The structure of {[Ag(µ-bdb)1.5](SO3CF3)}n (2). (a) Asymmetric unit with the numbering
scheme for the non-H and -C atoms (b) Ball and stick representation of the cationic 66-membered
[Ag6(µ-bdb)6]6+ metallacyclic ring, showing two different conformations for the bdb linkers and non-
classic C−H···O interactions between the triflate ions and the H atoms of the ligand (c) Schematic
11

representation of the wavy honeycomb sheets along the c (left) and a (right) axes together with the
-
position of the SO3CF3 ions.
3.2.3. Crystal structure of {[Ag(µ-bpb)2](NO3)}n (3)
Compound 3 crystallizes in the monoclinic space group P2/c with Z= 8 (Table 1). The
structure consists of cationic two-dimensional polymeric sheets and an uncoordinated nitrate
counteranions, NO3- (Figure 3). The cationic 2-D sheets are composed of four coordinated
silver(I) ions and µ-bpb as linker ligands. A closer inspection of the crystal structure shows
that the unit cell is composed of five crystallographically independent bpb ligands, three
silver(I) ions and two different nitrate counterions (Figure 3a, b). All the silver ions are
coordinated by four pyrazolyl nitrogen atoms from µ-bpb ligands in a distorted tetrahedral
ZnN4 coordination geometry. Deviations from an ideal tetrahedral geometry can be specified
by the τ4 value [17]. The values of τ4 for perfect tetrahedral and trigonal pyramidal geometries
are 1.00 and 0.85, respectively. The calculated τ4 values of 0.83, 0.82 and 0.82 for the Ag1,
Ag2 and Ag3 ions, respectively, show a geometry closer to trigonal pyramidal (Figure 3c).
(a)
12

(b)
(c)
(d)
Figure 3. The structure of {[Ag(µ-bpb)2](NO3)}n (3). (a) Asymmetric unit with the numbering scheme
for the non-H and -C atoms (b) Ball and stick representation of a 2D square layer, showing the five
different conformations for the bpb linkers and the resulting five different Ag•••Ag disstancess ((square
window edges) (c) Coordination environments of the three independent silver(I) ions. (d) Schematic
representation of the 44-sql structure of 3 along the b (left) and a (right) axes together with the
position of the nitrate ions.
13

The geometries of the five bpb linkers are summarized in Table 2. Four of the bpb ligands
show the same anti-anti-anti (aaa) conformation, whilst one, the yellow colored one in
Figure 3, which exhibits a gauche-anti-gauche (gag) conformation. For this reason, the
length of the yellow bpb (6.96 Å) is almost 1 Å shorter than the lengths of the other bpb
linkers (7.64-7.85 Å). From a topological point of view, each Ag(I) ion can be considered as
a four-connected node. The connection of the silver(I) ions by the bpb linkers form a two-
dimensional sheet structure with a 44-sql net. The different lengths of the linkers cause
different Ag•••Ag ddistannces (8..41-8.86 Å) in the 2D net structure of 3 (Figure 3b).
Table 2. Conformation, torsion (˚), dihedral angles (˚), N-to-N and Ag•••Ag separations (Å) for the bpb linker
ligands in the structure of 3.
Ligand
Yellow
Green
Blue
Red
Orange
Conformation
NCCC
gagb
51.18
176.91
-53.30
aaa
177.42
180
aaa
aaa
aaa
178.69
180
179.48
178.50
-178.34
179.14
178.82
-176.83
CCCC
CCCN
-177.42
-178.69
Dihedral anglea
N-to-N
2.31
6.96
8.41
0
2.40
7.639
8.522
4.80
7.792
8.841
0
7.848
8.862
7.739
8.798
Ag···Ag
a
Dihedral angle between the mean planes of pyrazolyl rings belonging to the same bpb ligand.
b
gauche refers to torsion angles comprised between 30°/90° and -30°/-90°; anti to torsion angles
comprised between +/- 90° and 180°.
The 2D square layers extend in the crystallographic ac plane and pack along the b axis with
an AAA sequence, forming 1D channels across the 2D sheets (Figure 3d). The nitrate ions are
located along the channels at the center of the square windows and between adjacent 2D
-
sheets. There is no significant interaction between the NO3 anions and the Ag(I) centers.
However, a closer inspection shows that there are weak C-H···O hydrogen bonds, with C-
H···O distances of 2.32-2.40 Å, between two oxygen atoms of the nitrate anions and H atoms
of the pyrazolyl rings or butyl spacers (Figure S2). Details of the hydrogen bonding
14

geometries are given in Table S2. No remarkable short contacts or π···π interactions are found
between adjacent sheets. Analysis of the structures by the Platon software [18] confirms no
accessible void for guest molecules.
3.3. Spectroscopic characterization
The FT-IR spectra of coordination polymers 1-3 are shown in Figure S3. The stretching
vibration of C=N bonds typical of the pyrazolyl rings of the linkers is present at 1517 (bpmb
in 1), 1550 (bdb in 2) and 1512 (bpb in 3) cm-1. The location of the peaks depends on the type
of substituents of the pyrazolyl rings. Therefore, the C=N stretching vibrations of the bdb
linker, with two methyl substituents on the pyrazolyl rings, are present at higher
wavenumbers compared to the bpb and bpmb ligands without Me substituents on the rings.
The other peaks at 3120 (bpmb in 1), 3128 (bdb in 2) and 3107 and 3128 cm-1 (bpb in 3) are
assigned to the stretching vibration of aromatic C-H bonds of the coordinated ligands.
Symmetric and asymmetric stretching vibrations of the methylene (–CH2–) and methyl (-
CH3) groups of the linkers are observed in the region 2867-2950 cm-1. In addition, the
infrared spectra of the compounds show the characteristic bands of the counter anions. The
sharp bands at 1262 (in 1) and 1257 and 1275 (in 2) cm-1 are attributed to the asymmetric
−
νas(SO3) stretching modes of the CF3SO3 anions [19]. The symmetric νs(SO3) stretching
bands of the triflate anions appear at 1030 cm-1 (for 1 and 2), while the asymmetric νs(CF3)
and symmetric νas(CF3) stretching bands appear at 1224 and 1160 (for 1) and 1224 and 1153
(for 2) cm-1, respectively [19]. The results confirm the non-coordinating character of the
triflate anions in the structures of 1 and 2. The band at 1379 cm-1 in the infrared spectrum of 3
-
is assigned to the stretching vibrational mode of the uncoordinated NO3 anions.
In order to confirm the phase purity of the bulk materials, powder X-ray diffraction (PXRD)
experiments were carried out for compounds 1-3. The PXRD patterns are consistent with
15

their simulated patterns (Figure 4). The results also show a higher crystallinity of the product
3.
(a)
(b)
16

(c)
Figure 4. PXRD patterns for 1-3. Calculated (from the single-crystal structure) and observed PXRD
patterns for the bulk samples.
4. Conclusions
The self–assembly of silver(I) ions with flexible bidentate pyrazolyl-based linkers affords
three new cationic silver(I) coordination polymers with different coordination environment of
the metal ions, dimensionality and network topology of the structures. Interestingly, the
results show that the steric hindrance of the donating groups of the ligands is not the only
factor governing the geometries in these coordination compounds. However, an evaluation of
the effects of anions and ligand conformation on the three structures is not straightforward,
the three ligands being different. Nonetheless a comparison between compounds 1 and 2, that
have the same triflate anion and quite similar ligands, highlights the bulky effect of the
methyl groups on the pyrazolyl ring of the bdb vs. bpmb ligands (see Scheme 1). this may be
responsible for the different conformations of the ligands, resulting in a 2-coordination mode
for silver atoms in 1 (shorter Ag-N...N-Ag distance for bpmb) compared to the 3-coordination
mode in 2. On the other hand, the more flexible bis(pyrazolyl) ligand and smaller nitrate
17

anion in compound 3 may be responsible for the increase in the Ag coordination number to
four, resulting in a sql topology compared to the hcb topology of compound 2 which shows a
3-coordination for the Ag atoms. Non-covalent weak interactions, such as hydrogen bonds
and π···π stacking, also seem to be important structure-directing factors in the self-assembly
of these silver(I) coordination polymers.
Appendix A. Supplementary data
CCDC 1532273-1532275 contain the supplementary crystallographic data for compounds 1-
3,
respectively.
These
data
can
be
obtained
or from
free
the
of
charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html,
Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk
Acknowledgements
The authors thank Shahid Chamran University (Grant No.: 31400) and the Università degli
Studi di Milano for financial support. DMP acknowledges the Ministry of Education and
Science of Russia (Grant 14.B25.31.0005).
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Three new cationic bis(pyrazolyl)-based silver(I) coordination polymers showing different
metal coordination environments, dimensionalities and network topologies have been
obtained and characterized.
22