Influence of anion on the network structure of one dimensional silver(I) coordination polymers of dicompartmental N,N-donor ligands

Article abstract of DOI:10.1016/j.poly.2012.10.038

Three one-dimensional silver(I) coordination polymers {[AgL ¹]NO₃}_n (1), {[AgL²]ClO ₄}_n (2) and {[AgL²]NO₃}_n (2a), where L¹ (pyridin-2-ylmethylene-(4-{[(pyridin-2-ylmethylene)- amino]-methyl}-benzyl)-amine) is a dicompartmental iminopyridine ligand derived from the Schiff-base condensation of α,α′-diamino-p-xylene and pyridine-2-carboxaldehyde and L² (N-(4-((methyl(pyridin-2-ylmethyl) amino)methyl)benzyl)-N-methyl(pyridin-2-yl)methanamine) is the reduced N-methyl derivative of L¹, have been isolated from the reaction of ligands with various silver salts. Six different conformations of L¹ are known that give rise to different network structures for {[AgL ¹]ClO₄}_n. X-ray single crystal structure of polymer 1·5H₂O reveals that the asymmetric unit contains five water molecules that form a two-dimensional hydrogen bonding network with nitrate counter anion. A new conformer of L¹ is observed in the polymeric structure of 1·5H₂O. Coordination polymers 2 and 2a, both made of [AgL²]⁺ repeating unit, contains different conformers of L². As a result, different polymeric structures are obtained for 2 and 2a. The effect of counterion on the ligand conformation and subsequently on the polymeric structure is reported.

Full text of DOI:10.1016/j.poly.2012.10.038

Polyhedron 52 (2013) 122–127
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Influence of anion on the network structure of one dimensional silver(I)
coordination polymers of dicompartmental N,N-donor ligands
⇑
Biswarup Chakraborty, Subhadip Maiti, Tapan Kanti Paine
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S.C. Mullick Road, Jadavpur, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Three one-dimensional silver(I) coordination polymers {[AgL1]NO3}n (1), {[AgL2]ClO4}n (2) and
{[AgL2]NO3}n (2a), where L1 (pyridin-2-ylmethylene-(4-{[(pyridin-2-ylmethylene)-amino]-methyl}-
benzyl)-amine) is a dicompartmental iminopyridine ligand derived from the Schiff-base condensation
Article history:
Available online 5 November 2012
Dedicated to Professor Alfred Werner on the
100th Anniversary of his Nobel Prize in
Chemistry in 1913.
of
a,
a0-diamino-p-xylene and pyridine-2-carboxaldehyde and L2 (N-(4-((methyl(pyridin-2-ylmethyl)
amino)methyl)benzyl)-N-methyl(pyridin-2-yl)methanamine) is the reduced N-methyl derivative of L1,
have been isolated from the reaction of ligands with various silver salts. Six different conformations of
L1 are known that give rise to different network structures for {[AgL1]ClO4}n. X-ray single crystal structure
of polymer 1ꢀ5H2O reveals that the asymmetric unit contains five water molecules that form a two-
dimensional hydrogen bonding network with nitrate counter anion. A new conformer of L1 is observed
in the polymeric structure of 1ꢀ5H2O. Coordination polymers 2 and 2a, both made of [AgL2]+ repeating
unit, contains different conformers of L2. As a result, different polymeric structures are obtained for 2
and 2a. The effect of counterion on the ligand conformation and subsequently on the polymeric structure
is reported.
Keywords:
Silver
Coordination polymer
Nitrogen-donor ligand
Solid-state structure
Ligand conformer
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
solvent of crystallization affect the conformation of such flexible
ligand by various supramolecular interactions. Supramolecular
Since the development of Werner’s Coordination theory, transi-
tion metal coordination complexes have found immense applica-
tions in chemistry, biology, material science and technology. The
polymeric assemblies of transition metal ions and organic ligands
have attracted considerable interests in coordination polymer
chemistry [1–4]. The polymeric materials have potential applica-
tions in magnetic, electrical, optical, photophysical, host-guest
chemistry and catalysis [2,5–10]. Versatile coordination geome-
tries of transition metal ions give rise to a variety of polymeric
architectures [1]. The formation of structurally diverse polymeric
structures also depends on the geometry of ligands, solvents, coun-
terions and reaction/crystallization conditions [11–17]. In addition,
weak non-covalent interactions stabilize the polymeric network
structure [18]. To achieve the desired properties of polymeric
materials, it is necessary to have control on these parameters in or-
der to isolate polymers with predictable structures and dimen-
sions. This is a challenging job which needs an in-depth and
systematic study. Moreover, coordination polymers derived from
a flexible ligand exhibit supramolecular isomerism due to the pres-
ence of different conformations of the ligand during the self-
assembly process [19–23]. The nature of the counter-anion and
isomerism with flexible ligands, 1,2-bis(4-pyridyl)ethane and
1,2-bis(4-pyridinecarboxamido)ethane has been well documented
in the literature [24,25]. Furthermore flexible ligands based on
aromatic spacers linked to thioetherpyridine unit results in
multiple supramolecular structures [26–29].
We have recently reported the synthesis and characterization of
structurally diverse silver(I) coordination polymers (general
formula: {[AgL1]ClO4}n) derived from a conformationally flexible
dicompartmental Schiff base ligand L1 (Scheme 1) containing
p-xylyl spacer between the two binding domains [30]. Two confor-
mational supramolecular isomers have been isolated that differ in
orientation of the flexible spacer in the coordination polymeric
structures. Both gauche and anti conformations of the ligand were
observed and six different conformers of the flexible ligand have
been shown to stabilize in the solid-state structures of three
coordination polymers [30]. The nature of the solvent has been
shown to affect the topology of coordination polymeric structures.
As a continuation of our ongoing research on the coordination
polymers of conformationally flexible ligands, we have isolated a
family of silver(I) coordination polymers from different silver(I)
salts. It is expected that the interaction between solvent and differ-
ent counterions would lead to different conformations of the
ligand. We have earlier shown that the reduction and subsequent
N-methylation of iminopyridine groups in Schiff-base ligands
⇑
Corresponding author. Tel.: +91 33 2473 4971; fax: +91 33 2473 2805.
E-mail address: ictkp@iacs.res.in (T.K. Paine).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.038

B. Chakraborty et al. / Polyhedron 52 (2013) 122–127
123
3460(br), 2924(m), 2852(m), 1645(s), 1589(s), 1437(m), 1383(m),
1365(s), 1296(m), 845(s), 779(s). ESI-MS (positive ion mode,
CH3CN): m/z = 421.15 (100%, [L1 + Ag]+). 1H NMR (500 MHz,
DMSO-d6): d, ppm: 8.78 (s, 2H), 8.53 (d, 2H, J = 4.5 Hz), 8.14 (m,
2H), 7.93 (d, 2H, J = 7.5 Hz), 7.69 (m, 2H), 6.98 (s, 4H), 4.75 (s, 4H).
2.2.3. {[AgL2]ClO4}n (2)
To the solution of L2 (0.35 g, 1 mmol) in dry MeOH (ꢂ15 mL)
was added anhydrous silver(I) perchlorate (0.20 g, 1 mmol). The
light yellow solid was isolated by filtration after 12 h stirring at
room temperature. Single crystals suitable for X-ray diffraction
were obtained after 5 days from acetonitrile solution of the com-
plex. Yield: 68% (0.55 g). Anal. Calc. for
C22H26AgClN4O4
(553.79 g/mol): C, 47.71; H, 4.73; N, 10.12. Found: C, 47.3; H,
4.7; N, 10.2%. IR (KBr, cmꢁ1): 3470(br), 2924(m), 2848(m),
1743(m), 1593(s), 1437(m), 1365(m), 1144, 1117, 1088(s),
874(m), 769(s). ESI-MS (positive ion mode, CH3CN): m/z = 346.85
(60%, [L2 + H]+), 453.63 (100%, [L2 + Ag]+). 1H NMR (500 MHz,
DMSO-d6): d, ppm: 8.59 (d, 2H, J = 4.5), 7.90 (t, 2H, J = 7.5 Hz),
7.49 (d, 2H, J = 7.5 Hz), 7.41 (t, 2H, J = 6.0 Hz), 7.13 (S, 4H), 3.84
(s, 4H), 3.67 (s, 4H), 2.05(s, 6H).
Scheme 1. Synthesis of silver(I) complexes.
resulted in a greater flexibility of the dinucleating ligands [31]. We
have also tested the effect of N-methylation of L1 on the structure
of coordination polymers.
We report herein the syntheses and characterization of silver(I)
coordination polymers {[AgL1]X}n (X = NO3, 1) and {[AgL2]X}n
(X = ClO4, 2; X = NO3, 2a). We also report the solid-state structures
of three coordination polymers 1ꢀ5H2O, 2 and 2a. The effects of the
counter-anion and of N-methylation of L1 on the topologies of sil-
ver(I) coordination polymers are discussed.
2.2.4. {[AgL2]NO3}n (2a)
Complex 2a was synthesized using ligand L2 (1 mmol) accord-
ing to the procedure described for 1. Single crystals of 2a were
grown from a solvent mixture of acetonitrile and methanol. Yield:
52% (0.29 g). Anal. Calc. for C22H26AgN5O3 (516.34 g/mol): C, 51.17;
H, 5.08; N, 13.56. Found: C, 51.1; H, 5.3; N, 13.5%. IR (KBr, cmꢁ1):
3441(br), 3053(m), 2845(m), 1741(m), 1599(s), 1570(m), 1443(s),
1381(s), 1364(s), 1333(s), 1306(m), 1244(s), 1130(m), 1102(m),
833(s), 772(s). ESI-MS (positive ion mode, CH3CN): m/z = 455.06
(100%, [L2 + Ag]+).
2. Experimental
2.1. Chemicals
2.3. Physical methods
Chemicals purchased from commercial sources were used for the
synthesis of ligands and complexes. Solvents were distilled and
dried prior to use. Although no problem was encountered during the
synthesis of the complexes, perchlorate salts are potentially explosive
and should be handled with care! [32]. Ligand L1 (pyridin-2-ylmethyl-
ene-(4-{[(pyridin-2-ylmethylene)-amino]-methyl}-benzyl)-amine)
was synthesized according to the reported procedure [30]. The
silver(I) complexes were synthesized and stored under dark.
Fourier transform infrared spectroscopy on KBr pellets was per-
formed on a Shimadzu FT-IR 8400S instrument. Elemental analyses
Table 1
Crystallographic data for 1ꢀ5H2O, 2 and 2a.
Parameters
1ꢀ5H2O
2
2a
2.2. Syntheses
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C
40H36Ag2N10O11 C22H26AgClN4O4 C22H26AgN5O3
1048.53
orthorhombic
Fddd
553.79
tetragonal
I-42d
516.35
orthorhombic
Pbca
2.2.1. Synthesis of N-(4-((methyl(pyridin-2-ylmethyl)amino)methyl)-
benzyl)-N-methyl(pyridin-2-yl)methanamine (L2)
L2 was prepared by reductive amination followed by N-methyl-
ation of ligand L1 (1.58 g, 5 mmol) according to reported procedure
[31]. The compound was isolated as a yellow liquid. Yield: 80%
(1.4 g). IR (KBr, cmꢁ1): 3304(br), 3167(br), 2920(m), 1697(m),
1589(m), 1470(m), 1433(m), 1281(m), 1234(s), 1090(s), 1036(m),
932(s). ESI-MS (positive ion mode, CH3CN): m/z = 347.08 (100%,
[L1 + H]+). 1H NMR (500 MHz, CDCl3): d, ppm: 8.50 (d, 2H,
J = 4.5 Hz), 7.65 (t, 2H, J = 7.5 Hz), 7.51 (d, 1 H), 7.33 (s, 4H) 7.27
(s, 1 H), 7.14 (t, 2H), 3.69 (s, 2H), 3.58 (s, 2H), 2.24 (s, 6H).
17.263(3)
22.510(4)
45.316(8)
90.00
90.00
90.00
17609(5)
16
1.582
0.959
8448
14.3358(7)
14.3358(7)
27.646(3)
90.00
12.526(5)
15.388(6)
23.192(9)
90.00
b (Å)
c (Å)
a
(°)
b (°)
(°)
90.00
90.00
c
90.00
90.00
Volume (Å3)
Z
5681.6(7)
8
4470(3)
8
Dcalc (Mg/m3)
1.295
1.534
l
(mm–1
)
0.833
0.935
F(000)
2256
2112
h Range data
collection (°)
Reflections collected
Reflections unique
Rint
1.55–21.99
1.60–23.47
1.76–21.78
2.2.2. {[AgL1]NO3}n (1)
To the solution of L1 (0.32 g, 1 mmol) in dry MeOH (ꢂ15 mL)
was added an acetonitrile (2–3 mL) solution of anhydrous silver(I)
nitrate (0.18 g, 1 mmol). The light yellow solid was separated
slowly upon stirring for 12 h at room temperature. The solid was
isolated by filtration and dried in air. Single crystals were grown
from the solvent mixture of acetonitrile and methanol. Yield: 62%
(0.26 g). Anal. Calc. for C20H18AgN5O3 (484.26 g/mol): C, 49.60; H,
3.75; N, 14.46. Found: C, 49.5; H, 3.7; N, 14.6%. IR (KBr, cmꢁ1):
30401
2701
0.0420
1927
287
22242
2098
0.0614
1637
144
1.138
0.0588
0.1771
ꢁ0.894, 0.376
28898
2657
0.0830
2002
282
0.845
0.0338
0.1013
ꢁ0.450, 0.436
Data (I > 2r(I)
Parameters refined
Goodness-of-fit on F2 0.972
R1 [I>2
r(I)]
0.0339
0.1141
ꢁ0.448, 0.221
wR2
Residuals (e Å–3
)

124
B. Chakraborty et al. / Polyhedron 52 (2013) 122–127
were performed on a Perkin Elmer 2400 series II CHN analyzer.
Electro-spray ionization mass spectra were recorded with a Waters
QTOF Micro YA263. 1H NMR spectra were measured at room tem-
perature using Bruker DPX-500 spectrometer.
analytical techniques. IR spectra of the complexes display the char-
acteristic bands due to the counterions in addition to the bands ex-
pected from the coordinated ligands. 1H NMR spectral data of the
complexes exhibit proton resonances slightly different from that
of the free ligands, indicating the presence of equilibrium between
the ligand and silver salt in solution. ESI-MS and elemental analysis
of the complexes suggest the 1:1 metal–ligand composition with
respective counterions.
2.3.1. X-ray crystallographic data collection and refinement of the
structures
Crystallographic data for 1ꢀ5H2O, 2 and 2a are given in Table 1.
Diffraction data were collected at 120(2) K on a Bruker Smart APEX
3.2. X-ray structures
II (Mo Ka radiation, k = 0.71073 Å). Cell refinement, indexing and
scaling of the data set were carried out using the Apex2 v2.1-0
software [33]. The structures were solved by direct methods and
subsequent Fourier analyses and refined by the full-matrix least-
squares method based on F2 with all observed reflections [34]. In
all the complexes the hydrogen atoms were fixed. The hydrogen
atoms of water molecules in 1ꢀ5H2O were not assigned. Oxygen
atoms of the perchlorate anion in 2 were found to be disordered.
All the non hydrogen atoms were refined anisotropically except
the disordered perchlorate anion of 2. The routine SQUEEZE was
applied to intensities data of isomer 2 to take into account the dis-
ordered solvent molecules [35].
To understand the structure of the complexes in solid-state, ef-
forts were made to grow the single-crystals of the complexes.
Single-crystals of 1ꢀ5H2O, 2 and 2a were isolated for X-ray diffrac-
tion. The silver ions in all the complexes exhibit four-coordinate
distorted tetrahedral coordination geometry with two nitrogens
either from amine or imine moiety and two pyridine nitrogen do-
nors from the ligands.
3.2.1. Crystal structure of 1ꢀ5H2O
Single crystals of 1ꢀ5H2O suitable for X-ray diffraction were iso-
lated from a solvent mixture of acetonitrile and methanol and the
complex crystallized in an orthorhombic Fddd space group. X-ray
structure of 1ꢀ5H2O reveals the presence of two silver ions, two
Schiff-base ligands (L1), two nitrates and five water molecules in
the asymmetric unit. The cationic part consisting of the [AgL1]+
unit is repeated to form a one-dimensional coordination polymer
(Fig. 1). In each of the repeating unit, the average Ag–Nimine and
Ag–Npyridine distances (Table 2) are found to be 2.340(4) Å and
2.319(4) Å, respectively, which are in good agreement with the
previously reported silver(I) complexes of L1 with perchlorate
counterion.[30]
3. Results and discussion
3.1. Syntheses and characterization
The silver(I) complexes were synthesized by mixing equimolar
amounts of ligands and silver(I) salts in methanol (Scheme 1). All
the complexes were characterized by several spectroscopic and
The polymeric chain in 1 elongates along the crystallographic ab
plane (Fig. 2) where the ligand in the repeating unit adopts an anti
conformations with the torsion angles across the phenyl spacer
N2–C7ꢀꢀꢀC14–N3 being 140.68°. Although the ligand adopts an anti
conformation as observed in different supramolecular isomers of
{[AgL1]ClO4}n [30], a new anti conformation of L1 makes the poly-
meric structure of 1 different from the perchlorate complex. Due
to this particular conformation of the ligand, the silver ions are dis-
posed along two parallel vectors resulting in the formation of a tri-
angular wave polymeric chain with the distance between the two
adjacent silver ions of 7.315 Å and the Ag–Ag–Ag angle of 151.6°
Fig. 1. The cationic repeating unit in the polymeric chain of 1. The counterions are
omitted for clarity. Symmetry code: (0) 1/4 ꢁ x, 5/4 ꢁ y, z.
(Fig. 2). Weak
pꢀꢀꢀp interactions are observed in the polymeric
chains between the phenyl ring of p-xylyl spacer and pyridine rings
with the distances of 4.54 and 4.53 Å (Fig. 2a).
Table 2
Each of the asymmetric units of 1 consists of five water mole-
cules and two counter-anions along with two repeating units.
Water molecules and nitrate ions are assembled through hydrogen
bonding in the solid-state and forms two-dimensional network
(Fig. 3a) resulting in a planar hexameric water cluster (Fig. 3b).
In this particular network each water cluster is surrounded by four
nitrate anions. The OꢀꢀꢀO distances between the water molecules in
the cluster are in a range of 2.47–2.73 Å whereas other OꢀꢀꢀO
Selected bond lengths (Å) and angles (°) for 1ꢀ5H2O.
Ag(1)–N(1)
2.353(4)
Ag(1)–N(2)
2.302(4)
2.336(4)
129.44(13)
124.58(18)
72.47(15)
137.7(2)
Ag(2)–N(3)
2.327(4)
Ag(2)–N(4)
N(1)–Ag(1)–N(1)
N(2)–Ag(1)–N(1)
N(3)–Ag(2)–N(3)
N(3)–Ag(2)–N(4)
136.83(17)
72.95(14)
124.01(19)
129.78(13)
N(2)–Ag(1)–N(1)
N(2)–Ag(1)–N(2)
N(3)–Ag(2)–N(4)
N(4)–Ag(2)–N(4)
Fig. 2. (a) One-dimensional polymeric chain of 1 and (b) view along the crystallographic plane ab.

B. Chakraborty et al. / Polyhedron 52 (2013) 122–127
125
Fig. 3. (a) Two-dimensional hydrogen-bonded network and (b) hexameric water cluster consisting of water molecules and nitrate anions.
Fig. 5. Conformations of L1 observed in the solid-state structures of silver(I)
coordination polymers {[AgL1]ClO4}n [30] and {[AgL1]NO3}n. The torsion angles
across the phenyl ring (N–CꢀꢀꢀC–N) for each conformation is provided at the bottom.
Fig. 4. Propagation of the coordination polymer 1ꢀ5H2O through the channels
formed by hydrogen-bonded network involving nitrate counterions and water
molecules.
distances are quite longer and in a range of 3.01–3.03 Å. The hex-
americ water cluster is proposed to be the smallest unit in bulk
water [36]. Hexameric water clusters with different conformations
including planar water hexamer in the lattice of coordination com-
pounds have been reported in literature [37–49].
A two-dimensional hydrogen-bonded network between the sol-
vent molecules and anions creates void channels through which
the polymeric chains are propagated (Fig. 4).
Fig. 6. Repeating unit of the polymeric chain in 2. The counter-anions are omitted
for clarity. Symmetry codes: (0) 1 ꢁ x, 1 ꢁ y, z; (00) 1 ꢁ x, ꢁ1/2 + y, 1/4 ꢁ z.
It is important to mention that six different conformations of
the flexible ligand L1 have been found in the solid-state structure
of the silver(I) complex {[AgL1]ClO4}n depending upon the crystal-
lization technique and the solvent of crystallization [30]. The solid-
state packing of 1ꢀ5H2O leads to a new conformer of L1 with the
torsion angle of 140.68° (Fig. 5). This is an outcome of the effect
of interaction between the counter-anion (nitrate) and water mol-
ecules present in the solvent used for crystallization. Including this
conformation, a total number of seven conformations are now
known for the flexible Schiff-base ligand.
Table 3
Selected bond lengths (Å) and angles (°) for 2.
Ag(1)–N(1)
N(1)–Ag(1)–N(10)
N(10)–Ag(1)–N(2)
2.299(6)
117.5(3)
140.0(2)
Ag(1)–N(2)
N(2)–Ag(1)–N(1)
N(2)–Ag(1)–N(20)
2.391(5)
73.7(2)
124.2(3)
Symmetry code: (0) 1 ꢁ x, 1 ꢁ y, z.
3.2.2. Crystal structure of 2
The single-crystal X-ray structure of 2 (Fig. 6) displays a one-
dimensional polymeric chain with one ligand (L2), one silver(I)
ion and a perchlorate anion as the repeating unit. The Ag–N dis-
tances and N–Ag–N angles (Table 3) are comparable with 1 and
with other reported silver(I) complexes [30,31,50,51].
Complex {[AgL2]ClO4}n (2) was isolated to see the effect of the
reduction of imine moiety and subsequent N-methylation on L1.
Single-crystals of 2 were isolated from an acetonitrile solution of
the complex and were crystallized in tetragonal I-42d space group.

126
B. Chakraborty et al. / Polyhedron 52 (2013) 122–127
Fig. 7. Propagation of one-dimensional polymeric chain in 2 along crystallographic b axis.
Fig. 8. Repeating unit of the polymeric chain of 2a. The counterions are omitted for
clarity. Symmetry code: (0) ꢁx, 2 – y, –z; (00) –x, 1 – y, –z.
Table 4
Selected bond lengths (Å) and angles (°) for 2a.
Ag(1)–N(1)
2.313(4)
Ag(1)–N(2)
2.436(4)
Ag(1)–N(3)
2.549(4)
Ag(1)–N(4)
2.260(5)
N(4)–Ag(1)–N(1)
N(1)–Ag(1)–N(2)
N(1)–Ag(1)–N(3)
144.84(13)
71.89(14)
106.15(13)
N(4)–Ag(1)–N(2)
N(4)–Ag(1)–N(3)
N(2)–Ag(1)–N(3)
142.36(13)
71.52(13)
113.56(13)
The [AgL2]+ unit in 2 is repeated along the crystallographic axis
b (Fig. 7) in a zigzag fashion. The metal ions in the polymeric chain
are positioned along two parallel vectors forming a triangular wave
where two adjacent silver atoms are separated by 7.233 Å with the
Ag–Ag–Ag angle of 164.58°. Ligand L2 in the polymer chain adopts
an anti conformation with the torsion angle across the phenyl
spacer N2–C8ꢀꢀꢀC80–N20 of 146.44°. The coordination of tertiary
amine nitrogen to the metal center makes the amine nitrogen chi-
ral. All the amine nitrogens have R configuration and similar con-
figuration of all the silver centers results in the formation of a
chiral, isotactic polymer. In this particular arrangement of the
Fig. 10. Two different conformations of L2 along with their torsion angles across p-
xylyl spacer observed in the solid-state structures of 2 and 2a.
and pyridine ring are observed with the centroid-to-centroid dis-
tance of 5.43 Å.
3.2.3. Crystal structure of 2a
Single crystals of {[AgL2]NO3}n (2a) were grown from a solvent
mixture of acetonitrile and methanol. The complex crystallized in
orthorhombic Pbca space group. X-ray structural analysis of 2a
polymer, weak
pꢀꢀꢀp interactions among the spacer phenyl ring
Fig. 9. Propagation of one-dimensional polymeric chain in 2a. (b) View along crystallographic b axis.

B. Chakraborty et al. / Polyhedron 52 (2013) 122–127
127
(Fig. 8) establishes the complex to be a coordination polymer con-
References
sisting of [AgL2]+ repeating unit and perchlorate counterion. In this
molecule, the average Ag–Namine distance is significantly longer
than the average Ag–Npyridine distance (Table 4). An anti conforma-
tion of the ligand is present in the polymeric chain with the torsion
angle across the phenyl spacer being 180.00°. The effect of nitrate
on the polymeric structure is evident in this complex compared to
that in the perchlorate complex 2.
The polymeric chain of 2a is propagated along crystallographic
b axis (Fig. 9) in a zigzag fashion where the metal ions are aligned
along two parallel vectors forming an asymmetrical triangular
wave. The distances between two adjacent silver ions connected
by L2 are 8.33 and 12.74 Å, respectively. In spite of the presence
of a single anti isomer, the asymmetry in distance between the sil-
ver centers arises due to a trans arrangement between the two
binding sites of the flexible dicompartmental ligand. It is important
to note that the tertiary amine nitrogens of the ligand exhibit RSSR
type configuration along the polymer chain.
It is clear from the above discussion that in spite of the presence
of repeating units having same metal-ligand compositions, the
polymeric structure of 2 and 2a are different. Two different poly-
meric networks result from the different conformations adopted
by the flexible ligand (Fig. 10). Moreover, different configuration
of amine nitrogens in L2 upon binding with silver in two complexes
gives rise to different polymeric architectures.
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Acknowledgments
Financial support from the Department of Science and
Technology, Government of India is gratefully acknowledged.
Single-crystal diffraction data were collected at the DST-funded
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graphic data for this paper. These data can be obtained free of
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