Conformational supramolecular isomerism in one-dimensional silver(i) coordination polymer of a flexible bis(bidentate) N,N-donor ligand with p-xylyl spacer

Article abstract of DOI:10.1039/c0dt01429j

The isolation and structural characterisation of three isomeric silver(i) complexes, 1a, 1b and 2 with the general formula {[AgL¹]ClO ₄}_n (where L¹ is a bis(bidentate) N,N-donor ligand derived from the Schiff-ba

Full text of DOI:10.1039/c0dt01429j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2011, 40, 3647
www.rsc.org/dalton
PAPER
Conformational supramolecular isomerism in one-dimensional silver(I)
coordination polymer of a flexible bis(bidentate) N,N-donor ligand with
p-xylyl spacer†
Biswarup Chakraborty, Partha Halder and Tapan Kanti Paine*
Received 20th October 2010, Accepted 3rd February 2011
DOI: 10.1039/c0dt01429j
The isolation and structural characterisation of three isomeric silver(I) complexes, 1a, 1b and 2 with the
general formula {[AgL1]ClO4}n (where L1 is a bis(bidentate) N,N-donor ligand derived from the
Schiff-base condensation of a,a¢-diamino-p-xylene and pyridine-2-carboxaldehyde) are discussed.
Single-crystal X-ray structures reveal the polymeric nature for the complexes where all the silver ions
are in pseudotetrahedral geometry with the AgN4 coordination environment. Isomers 1a (Pc space
group) and 1b (Cc space group) were crystallised from acetonitrile whereas 2 (C2/c space group) was
crystallised during the synthesis from a solvent mixture of dicholormethane and methanol. The flexible
ligand (L1) adopts only an anti conformation in 1b and the presence of two different anti conformations
in the repeating unit results in the formation of a trapezoidal wave polymeric chain. However, both
gauche and anti conformations of the ligand are found to be present in the polymeric chains of 1a. In
the polymeric chain of 2, only one anti isomer of the ligand is present in the repeating unit resulting in a
triangular wave chain. The structure of isomer 1a is solvent induced and solvent plays a major role in
the crystal packing of this isomer. One-dimensional coordination polymers 1a, 1b and 2 are related to
each other as conformational supramolecular isomers. Additionally, two independent polymeric chains
parallel to each other: one triangular wave consisting of only an anti conformation and a trapezoidal
wave chain consisting of alternate gauche and anti conformations of the ligand are observed in 1a. This
is a rare example of two supramolecular isomers present in the same crystal. Six different conformers of
the flexible ligand are observed in the crystals of coordination polymers.
polymeric architecture. Apart from the difficulty in predicting
the polymeric structures, conformationally flexible ligands give
rise to supramolecular isomers.10,13–15 Zaworotko et al. have first
Introduction
The polymeric assemblies of transition metal complexes are of par-
ticular interest in the field of coordination polymer chemistry.1–4
reported the example of supramolecular isomerism in cobalt(II)
Several factors, such as coordination geometry, metal–ligand
complexes with the conformationally flexible ligand 1,2-bis(4-
pyridyl)ethane.16 The coordination polymers of copper(II) derived
from flexible 1,2-bis(4-pyridinecarboxamido)ethane give rise to 1-
D chains and 2-D network structures.17,18 Coordination polymers
of flexible ligands based on aromatic spacers linked to thioether-
pyridine arms form a diverse supramolecular structure.19–22 This
type of isomerism has also been considered as a factor to design
ligands for various supramolecular structures.23–32
Dicompartmental Schiff-base ligands derived from diamines
and pyridine-2-aldehyde have been used for the synthesis of
coordination polymers with versatile structures and topologies.33,34
We have recently reported that Schiff-base bis(bidentate) N,N-
donor ligands bind with silver(I) to form coordination polymers
of different topologies.35 It is expected that the self-assembly of
silver(I) and ligands having a conformationally flexible spacer
between the two binding domains prefers to stabilise different
polymeric architectures.5,7,9,19,20,22,36 As an obvious and natural
interaction, ligand conformation, non-covalent interactions, sol-
vents, effect of counterions etc. are involved in the formation of
different topologies in polymeric networks.5–9 The design of a
polymeric network with predictable structures and properties is
a challenging task and therefore warrants more examples with
systematic studies to obtain useful information for structural
control. The assembly of metal complexes supported by con-
formationally flexible ligands is even more challenging.10–12
A
subtle change in flexibility of ligands dramatically changes the
Department of Inorganic Chemistry, Indian Association for the Cultivation
of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata, 700032,
India. E-mail: ictkp@iacs.res.in; Fax: +91-33-2473-2805; Tel: +91-33-
2473-4971
† Electronic supplementary information (ESI) available: Crystallographic
data for 1a, 1b and 2 in CIF file format and TGA curves. CCDC reference
numbers 794247–794249. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01429j
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3647–3654 | 3647
©

View Article Online
silver(I) complex {[AgL1]ClO4}n (1) in good yield. An isomeric
complex 2 was obtained during the reaction of silver(I) per-
chlorate with ligand in a solvent mixture of dichloromethane
and methanol. The silver(I) complexes are soluble only in ace-
tonitrile. The ligand and silver(I) complexes were characterised
by different spectroscopic and analytical techniques like IR,
1HNMR, ESI-MS and elemental analysis. The spectral patterns
are very similar both in powder form and in solution indicat-
ing a very similar chemical composition for all three silver(I)
complexes.
progression of our earlier work, we have synthesised
a
bis(bidentate) N,N-donor ligand (L1)37,38 derived from the Schiff-
base condensation of a,a¢-diamino-p-xylene and pyridine-2-
carboxaldehyde (Chart 1). The synthesis and solid state struc-
ture of 1,4-bis(2-pyridylmethyleneaminomethyl)benzene (L1) have
been reported recently where only the anti conformation of the
flexible ligand was observed in the crystal lattice.39 However,
both anti- and gauche conformers are expected to be present
in solution. In the present work we describe the isolation and
crystal structures of three different coordination polymers, 1a, 1b
and 2 that result from the combination of the ligand (L1) and
silver perchlorate. While both gauche and anti conformations of
L1 are found to be present in the polymeric chains within the
same crystal of 1a, only the anti conformation of the ligand is
observed in the polymeric chains of 1b and 2. The conformational
supramolecular isomers 1a and 1b (and 2) differ in orientation
of the p-xylyl spacer in the one-dimensional chain and also
by the presence of solvent. The role of ligand conformation,
non-covalent interaction, and solvent on the supramolecular
isomerism and architectures of silver(I) coordination polymers are
discussed.
The dicompartmental ligand contains a flexible p-xylyl spacer
between the two binding sites. The flexibility of the spacer would
affect the solid state packing and structure of metal complexes
because of the two possible conformations (gauche and anti)
for this kind of ligand (Chart 1). Both the conformers exist
in equilibrium due to a low energy barrier for conformational
change. Interestingly, two different crystalline forms (1a and 1b)
were obtained during the crystallisation of bulk complex (1)
from acetonitrile (Fig. 1). Initially, prism-shaped crystals (1a)
were isolated followed by the isolation of rhombic-shaped crystals
(1b) from the filtrate. Additionally, rectangular crystals of 2 were
isolated during the reaction of metal ion and ligand from a solvent
mixture of dichloromethane and methanol. When the reaction
was carried out in a solvent mixture of methanol and acetonitrile,
crystals of 1b were separated. Solvent, therefore, plays a crucial
role in the crystallisation process and is clear from the solid state
packing of the crystals. Isomer 1a crystallises in monoclinic space
group Pc with solvent molecules inside the void space (Fig. 6)
whereas 1b crystallises in monoclinic space group Cc without
any solvent molecule (Fig. 8). This isomerism can be termed as
supramolecular isomerism.10,13 It is important to mention here
that when a solution of 1b dissolved in acetonitrile is allowed
to recrystallise, the crystals of 1a are isolated initially followed
by the crystals of 1b. Similarly, when an acetonitrile solution
of 2 is kept for crystallisation, 1a is separated first from the
solution and then the crystals of 1b are obtained from the filtrate.
This clearly suggests the existence of rapid equilibria between
different conformers of ligand and metal complexes of varying
nuclearities. The conformers of L1 give rise to different isomeric
complexes depending upon the stability and packing of the
solids crystallised from different solvents. The inclusion of solvent
molecules helps the complex to crystallise in different isomeric
forms.
Chart 1 Different conformers of the ligand (L1).
Results and discussion
The ligand (L1)39 was prepared by Schiff-base condensation of
one equivalent of a,a¢-diamino-p-xylene and two equivalents of
pyridine-2-carboxaldehyde in dry ethanol at room temperature.
The ligand is soluble in most of the organic solvents. The reaction
of silver(I) perchlorate with L1 in dry methanol afforded the
Fig. 1 Three isomeric (1a, 1b and 2) silver(I) coordination polymers.
3648 | Dalton Trans., 2011, 40, 3647–3654
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
The thermal behaviour of silver(I) complexes are found to be
similar, as established by thermogravimetric analysis (TGA) (see
ESI†). The complexes are stable up to 180 ◦C and no appreciable
solvent loss was observed for the complexes. This suggests that the
polycrystalline samples, contrary to the case of the crystals, do not
contain any solvent molecules.
Structural description
Conformational supramolecular isomer 1a
The single-crystal X-ray structure of 1a reveals the presence of
two isomeric and parallel 1-D polymeric chains (A and B) in the
same crystal. In addition to two polymeric chains, perchlorate
anions, solvent acetonitrile and water molecules are present in
the asymmetric unit. In both the chains, each silver ion is
coordinated by two pyridylimine units from two ligands giving
rise to pseudotetrahedral coordination geometry (Fig. 3).
The purity of bulk crystalline compounds was checked by
comparing the experimental XRPD pattern with that of simulated
pattern obtained from the single-crystal data (Fig. 2). The peaks
for 1a and 1b match well with the corresponding simulated
patterns, suggesting the purity of bulk crystalline compounds. The
experimental XRPD data of 2 do not match well with the simulated
patterns. On the other hand the experimental data for 2 match with
the simulated one of 1b. This is due to the fact that the crystals of
isomer 2 lose solvent molecules from the crystal lattice resulting in
the formation of polycrystalline form with a very similar structural
motif as in 1b (see the structures of 1b and 2). The absence of
solvent molecules in the polycrystalline form is observed in the
thermogravimetric analysis of 1b. The presence of solvent in the
lattice forces the ligand to adopt a slightly different conformation
in the crystals and is reflected in the simulated XRPD patterns of
2.
Chain A consists of the repeating [AgL1](ClO4) unit with Ag–
Npy distances of 2.39(1) and 2.44(1) A and Ag–Nimine distances
˚
˚
of 2.28(1) and 2.31(1) A (Table 2). In chain B, the repeating
unit is [Ag2L1 ](ClO4)2 with Ag(1)–Npy bond distances of 2.27(1)
2
˚
and 2.24(1) A and Ag(2)–Npy distances of 2.34(1) and 2.46(1)
˚
˚
A. The Ag(1)–Nimine distances of 2.44(1) and 2.32(1) A are closly
comparable with the Ag(2)–Nimine distances of 2.26(1) and 2.37(1)
˚
A. The metal–nitrogen distances are in good agreement with other
reported silver(I) complexes of Schiff-base ligands.35,40,41
The polymeric chains, parallel to each other, are elongated
along the crystallographic c axis (Fig. 4). In chain A, the
ligand is folded in an anti conformation (torsion angle N(12)–
C(60) ◊ ◊ ◊ C(47)–N(10) = 176.5◦) such that the pyridylimine planes
are perpendicular to the plane of spacer phenyl ring. The donor
sites are positioned in a trans configuration with respect to each
other. Chain B contains both gauche and anti conformers of the
ligand in an alternate arrangement. The gauche conformer with
the torsion angle across the phenyl spacer N(6)–C(27) ◊ ◊ ◊ C(34)–
N(8) = 60.6◦ is folded in such a way that the pyridylimine donor
site are positioned trans to each other. The anti conformation in
this chain is folded in a similar fashion as in chain B but differ in
torsion angle along the phenyl spacer (N(3)–C(14) ◊ ◊ ◊ C(7)–N(2)
= 175.9◦). Two chains are packed to exhibit a weak inter-chain
p ◊ ◊ ◊ p interaction between the two pyridine rings from an anti
conformer of the ligand in two different chains with a centroid-
0
˚
to-centroid distance of 3.82 A and a dihedral angle of 5.4 . In
Fig. 2 Experimental and simulated XRPD pattern for 1a, 1b and 2.
Fig. 3 Ball and stick representation of the cationic repeating unit of 1a. The hydrogens are omitted for clarity. Symmetry codes: (¢) x, -y, 1/2 + z; (¢¢) x,
1 - y, -1/2 + z.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3647–3654 | 3649
©

View Article Online
Table 1 Crystallographic data of 1a, 1b and 2
Parameters
1a·2CH3CN·H2O
1b
2
Empirical formula
Formula weight
Crystal system
Space group
C64H62Ag3Cl3N14O13
1665.24
Monoclinic
Pc
13.8187(8)
19.7414(12)
13.2414(7)
90.00
109.4690(10)
90.00
3405.7(3)
2
1.624
1.044
1680
1.03–19.93
19520
6146
0.0671
4941
868
1.027
0.0435
0.0987
0.458, -0.359
C40H36Ag2Cl2N8O8
1043.41
Monoclinic
Cc
18.3455(11)
11.7661(7)
19.1766(13)
90.00
99.0270(10)
90.00
4088.1(4)
4
1.695
1.152
2096
2.06–23.13
16119
5637
0.0449
5115
542
1.015
0.0340
0.0740
0.582, -0.309
C20H18AgClN4O4
521.70
Monoclinic
C2/c
17.7975(10)
13.0420(7)
12.8957(13)
90.00
126.4250(10)
90.00
2408.5(3)
4
1.439
0.978
1048
2.11–25.00
13879
2132
0.0246
2055
142
1.243
0.0636
0.1897
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
Volume/A
Z
D
calc/Mg m-3
mMo-Ka/mm-1
F(000)
q range data collection/◦
Reflections collected
Reflections unique
Rint
Data (I > 2s(I)
Parameters refined
Goodness-of-fit on F2
R1 [I > 2s(I)]
wR2
-3
˚
Residuals e A
1.312, -1.065
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 1a
Ag(1)–N(8)
Ag(1)–N(2)
Ag(2)–N(6)
Ag(2)–N(3)
Ag(3)–N(12)
Ag(3)–N(9)
N(8)–Ag(1)–N(1)
N(1)–Ag(1)–N(2)
N(1)–Ag(1)–N(7)
N(6)–Ag(2)–N(4)
N(4)–Ag(2)–N(3)
N(4)–Ag(2)–N(5)
N(12)–Ag(3)–N(10)
N(10)–Ag(3)–N(9)
N(10)–Ag(3)–N(11)
2.237(12)
2.316(11)
2.262(12)
2.368(11)
2.284(11)
2.393(12)
144.2(4)
72.8(4)
128.4(4)
147.6(4)
71.6(5)
127.7(4)
138.0(4)
72.5(5)
Ag(1)–N(1)
Ag(1)–N(7)
Ag(2)–N(4)
Ag(2)–N(5)
Ag(3)–N(10)
Ag(3)–N(11)
N(8)–Ag(1)–N(2)
N(8)–Ag(1)–N(7)
N(2)–Ag(1)–N(7)
N(6)–Ag(2)–N(3)
N(6)–Ag(2)–N(5)
N(3)–Ag(2)–N(5)
N(12)–Ag(3)–N(9)
N(12)–Ag(3)–N(11)
N(9)–Ag(3)–N(11)
2.267(12)
2.436(12)
2.341(12)
2.456(11)
2.308(12)
2.435(11)
130.5(4)
72.6(4)
113.3(4)
128.6(4)
72.7(4)
112.2(4)
141.3(5)
70.9(4)
Fig. 4 (a) Propagation of one-dimensional parallel chains in 1a along the
crystallographic c axis. (b) View of the chains along the c axis.
122.2(4)
117.8(4)
˚
8.62 A. The silver ions positioned along two different vectors are
addition, an inter-chain CH ◊ ◊ ◊ p interaction is present between
the pyridine ring of chain A and the spacer phenyl ring of a gauche
conformer of the ligand in chain B with the distance of 3.41 A.
In chain B, the dihedral angle of 10.60 and the distance of 3.71
connected by an anti conformer of the ligand with the Ag ◊ ◊ ◊ Ag
˚
distance of 8.81 A. A relatively shorter distance (Ag ◊ ◊ ◊ Ag distance
˚
˚
of 4.63 A) is observed between two silver ions not directly
connected by a ligand along the vectors. This arrangement of
ligand and silver ions generates an isosceles trapezoidal wave in
the polymeric chain (Fig. 5).
˚
A between the two pyridine rings N(4) and N(7) (one from a
gauche conformer and another from an anti conformer) cause a
weak intra-chain p ◊ ◊ ◊ p interaction. Again the two conformers
are arranged for a weak p ◊ ◊ ◊ p interaction occurring between the
phenyl spacer of an anti conformer and the pyridine rings (N(5)
and N(7)) of symmetry related cis conformers within the polymeric
˚
chain with the centroid-to-centroid distances of 3.93 A and 3.96
˚
A, respectively.
The metal ions are aligned along two parallel vectors in chain
A and the distance between the two adjacent silver ions connected
◦
˚
by ligand is 7.12 A with the Ag–Ag–Ag angle of 136.7 . This
arrangement gives rise to a triangular wave-like zigzag polymeric
chain. In chain B, the metal ions are aligned along two parallel
vectors where two silver ions are connected along the vector by
a gauche conformer of the ligand with the Ag ◊ ◊ ◊ Ag distance of
Fig. 5 Triangular wave (chain A) and trapezoidal wave (chain B)
polymeric chain in 1a.
3650 | Dalton Trans., 2011, 40, 3647–3654
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for 1b
In 1a, two polymeric chains are packed to create some void
space for solvent molecules and counterions (Fig. 6). The confor-
mational variation of the ligand makes the void space in chain B
to accommodate acetonitrile solvent. This, in turn, helps in crystal
packing to form the polymeric network structure. Two polymeric
chains in 1a are separated by a layer of water-perchlorate chain
where each water molecule is placed in between the two perchlorate
anions by a strong hydrogen bonding interaction with the O ◊ ◊ ◊ O
Ag(1)–N(7)
Ag(1)–N(8)
2.317(5)
2.371(5)
Ag(1)–N(2)
Ag(1)–N(1)
Ag(2)–N(4)
Ag(2)–N(6)
N(7)–Ag(1)–N(8)
N(7)–Ag(1)–N(1)
N(2)–Ag(1)–N(1)
N(5)–Ag(2)–N(4)
N(5)–Ag(2)–N(6)
N(4)–Ag(2)–N(6)
2.313(6)
2.404(5)
2.358(5)
2.364(5)
71.70(19)
157.66(17)
71.14(18)
156.49(16)
71.72(19)
117.86(18)
Ag(2)–N(5)
Ag(2)–N(3)
2.342(5)
2.361(6)
N(2)–Ag(1)–N(7)
N(2)–Ag(1)–N(8)
N(8)–Ag(1)–N(1)
N(5)–Ag(2)–N(3)
N(4)–Ag(2)–N(3)
N(3)–Ag(2)–N(6)
128.17(19)
127.27(19)
107.00(19)
120.09(18)
71.35(17)
131.32(18)
˚
distances of 2.81 and 2.86 A, respectively.
Fig. 8 (a) One-dimensional polymeric chain of isomer 1b along the
crystallographic c axis. (b) View of the chain along the c axis.
Fig. 6 1-D parallel chains of 1a with perchlorate counter anions and
solvent (acetonitrile) molecules in the void space.
angles across the phenyl spacers being N(8)–C(39) ◊ ◊ ◊ C(27)–
N(6) = 162.77◦ and N(3)–C(14) ◊ ◊ ◊ C(7)–N(2) = 177.86◦. The
central phenyl ring of the spacer is almost perpendicular to the
pyridylimine planes and the donor sites are positioned trans to
each other. In fact the dihedral angles (3.47◦ and 3.06◦) among
the phenyl ring and pyridine rings (N(7) and N(5)) allow a weak
p ◊ ◊ ◊ p interaction occurring between the phenyl ring of a spacer
and the pyridine rings of symmetry related ligands with centroid-
Conformational supramolecular isomer 1b
The X-ray structural analysis of 1b shows a one-dimensional
polymeric chain with two bis(bidentate) ligands and two silver(I)
ion as the repeating unit (Fig. 7). Each silver ion is in pseu-
dotetrahedral geometry coordinated by pyridylimine nitrogens
from two separate ligands (Table 3). The bond parameters are in
good agreement with that in isomer 1a and other related silver(I)
complexes.35
˚
to-centroid distances of 3.792 and 3.760 A, respectively.
In the polymeric chain of 1b, the metal ions are aligned along
four parallel vectors with an alternate arrangement of silver ions
on each vector (Fig. 9). The distances between the adjacent silver
ions connected by anti conformers of the ligand◦are 7.891(2) and
8.282(2) A with Ag–Ag–Ag angles of 91.90(2) and 98.47(2)◦,
˚
respectively. This results in a trapezoidal wave along the polymeric
chain.
Fig. 9 Trapezoidal wave polymeric chain in isomer 1b.
Conformational supramolecular isomer 2
The single crystal X-ray data of isomer 2 reveals a similar bond
parameters and polymeric motif as observed in Chain A of isomer
1a (Fig. 10, Table 4). With the repeating [AgL1](ClO4) unit, the
one-dimensional chain is elongated along the diagonal axis of the
ac plane (Fig. 11).
The ligand in the repeating unit adopts an anti conformation
with the torsion angle across the phenyl ring being 180◦. The
solid-state structure of the ligand shows the presence of the ◦stable
anti isomer in the crystal lattice with the torsion angle of 180 .39 In
spite of the similarity in ligand conformation and one-dimensional
polymeric motif, a slight change in the torsion angle makes the
Fig. 7 Molecular structure of the repeating unit in 1b. The perchlorate
anions and hydrogen atoms are omitted for clarity. Symmetry codes: (¢) x,
1 - y, -1/2 + z.
The 1-D polymer chain of 1b is elongated in the direction
of the crystallographic c-axis (Fig. 8) where the ligand assumes
only an anti conformation. In the repeating units, two different
anti conformations of the ligand are present with the torsion
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3647–3654 | 3651
©

View Article Online
◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for 2
Ag(1)–N(1)
N(1)–Ag(1)–N(1¢)
N(2)–Ag(1)–N(1¢)
2.318(6)
139.6(3)
127.9(2)
Ag(1)–N(2)
N(2)–Ag(1)–N(2¢)
N(2)–Ag(1)–N(1)
2.298(6)
125.6(3)
72.7(2)
Fig. 12 Different conformations of L1 with their torsion angles across
the phenyl ring (N–C ◊ ◊ ◊ C–N) in the solid-state structure of coordination
polymers 1a, 1b and 2.
Fig. 10 Crystal structure of the repeating cationic unit in 2. The
perchlorate anions and hydrogen atoms are omitted for clarity. Symmetry
codes: (¢) 1/2 - x, 1/2 - y, -z.
The presence of isomeric polymer chains in the same crystal is
not very common. There are a few examples where supramolecular
isomers have been shown to be present in the same crystal.7,22,23,43–53
However, supramolecular isomers present in the same crystal due
to the different conformations of a flexible ligand are rare.22,23
Two independent polymeric chains differing in network structures
in the crystals of 1a represent an example of conformational
supramolecular isomers present in one crystal.
Fig. 11 (a) One-dimensional polymeric chain of isomer 2 along the
diagonal axis of the ac plane. (b) View of the chain along the diagonal
of the ac plane.
Conclusions
chain in 2 different from that in chain A of 1a. As a result, the
distance between the two adjacent silver ions aligned along two
The synthesis and characterisation of three isomeric one-
dimensional silver(I) coordination polymers of bis(bidentate)
N,N-donor ligand containing a flexible p-xylyl spacer were
studied. The solid state structures of the coordination polymers
supported by the ligand were discussed. The presence of different
conformers (gauche and anti) of ligand affect the solid-state
packing in polymeric chains made of similar building blocks. In
one of the isomers, both the gauche and anti conformers are present
in the polymeric chain. Additionally two independent polymeric
chains, related to each other as conformational supramolecular
isomer, are present in the same crystal. A rare example of six
different conformers of one flexible ligand has been shown to
be present in the crystals of the coordination polymers and
highlights the importance of this ligand in directing the topology of
coordination polymeric structures. Solvent has been shown to play
an important role in the solid state packing of the coordination
polymers. The results described herein show the effect of ligand
flexibility, non-covalent interactions, and solvent on the structural
diversity of coordination polymers in the solid state.
˚
vectors increases to 7.790 A with concomitant increase in the Ag–
Ag–Ag angle to 137.26◦ (Fig. 11).
Three coordination polymers described here are made of same
molecular building blocks but differ in network structures because
of different conformations adopted by the flexible ligand. A slight
change in the torsion angle may affect the network architecture
dramatically. The anti conformation of the ligand is present in
2, 1b and chain A of 1a, however different network structures
are obtained. While one anti conformation of the ligand results
in a triangular wave polymeric chain (chain A in 1a and in
2), another set of anti conformers stabilise a trapezoidal wave
chain (1b). Additionally, the 1-D polymers in 1b and chain B
of 1a are both made of a compositionally similar repeating unit
and show a trapezoidal wave but their network structures differ.
A careful analysis of the structures revealed that two different
anti conformers are present in the repeating unit in 1b whereas
one gauche conformer and one anti conformer is present in the
repeating unit of chain B in 1a. Moreover, the anti conformers
of the ligand present in chain A of 1a and in 2 have different
torsion angles. This amounts to six different conformers of flexible
ligand present in the crystals of silver(I) coordination polymers
(Fig. 12). A pure anti conformer forms a polymeric chain with
a triangular wave as seen in chain A of 1a and in 2. It is also
expected that a pure gauche conformer would lead to a triangular
wave polymeric chain. Also, a combination of one gauche and one
anti or two different anti conformers would form a trapezoidal
wave. Different types of polymeric arrays like linear, double-
stranded, triple-stranded, helical, and ladder chains are observed
in coordination polymers.1 The trapezoidal waveforms observed
in 1a and 1b are rare examples of coordination polymeric chains.42
Experimental
All chemicals were purchased from commercial sources. Solvents
used for synthesis and crystallisation were distilled and dried
before use. Although no problems were encountered during the
synthesis of the complex, perchlorate salts are potentially explosive
and should be handled with care!54 The silver(I) complexes were
synthesised and stored in the absence of light.
Fourier transform infrared spectroscopy on KBr pellets was
performed on a Shimadzu FT-IR 8400S instrument. Elemental
analyses were performed on a Perkin-Elmer 2400 series II CHN
3652 | Dalton Trans., 2011, 40, 3647–3654
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
series. Electro-spray ionization mass spectra were recorded with
a Waters QTOF Micro YA263. 1H NMR spectra were measured
at room temperature using Bruker DPX-300 spectrometer. Con-
ductivity measurements were carried out in acetonitrile solution
at room temperature on a Systronics Conductivity Meter 306.
Powder XRD measurements were carried out on a Bruker D8
perchlorate (0.010 g, 0.05 mmol) and an acetonitrile solution (5
mL) of ligand (0.016 g, 0.05 mmol). Yield: 73% (0.019 g). Anal.
calcd for C40H36Ag2Cl2N8O8 (1043.4 g mol-1): C, 46.04; H, 3.48; N,
10.74. Found: C, 46.2; H, 3.5; N, 10.5%. IR (KBr, cm-1): 3565(br),
3084(w), 3068, 1651(m), 1591(m), 1473, 1444(m), 1443(s), 1381,
1302, 1090(vs), 839, 783(m), 623(m).
˚
Advance Powder (Cu Ka1 radiation, l = 1.5406 A) instrument.
[Ag(L1)](ClO4) (2). Light yellow single crystals of isomer
2 were isolated after 5 d by layer diffusion of a methanolic
solution (5 mL) of silver perchlorate (0.010 g, 0.05 mmol) and
a dichlormethane solution (5 mL) of ligand (0.016 g, 0.05 mmol).
Yield: 69% (0.018 g). Anal. calcd for C20H18AgClN4O4: C, 46.04;
H, 3.48; N, 10.74. Found: C, 46.1; H, 3.4; N, 10.7%. IR (KBr,
cm-1): 3559(br), 3082(w), 3066, 1651(s), 1591(s), 1474, 1441(s),
1381, 1300, 1090(vs), 843, 783(m), 623(m).
Synthesis of ligand L1
To a solution of pyridine-2-carboxaldehyde (2.14 g, 20 mmol)
in dry ethanol (25 mL), was added p-xylylenediamine (1.36 g,
10 mmol) slowly with constant stirring. The resulting yellow
solution was stirred for 24 h at room temperature. The solution
was concentrated and kept in a refrigerator for 2 d. The solid
ligand was isolated by filtration, washed with ice-cold ethanol–
pentane (1 : 1) solvent mixture and dried under vacuum. Light
yellow solid. Yield: 82% (2.57 g). Anal. calcd for C20H18N4 (314.38
g mol-1): C, 76.41; H, 5.77; N, 17.82. Found: C, 76.3; H, 5.8;
N, 17.6%. IR (KBr, cm-1): 3433(br), 3047(m), 3005(m), 2901(m),
2849(m), 1639(s), 1585(m), 1564(m), 1468(m), 1431(m), 1014(m),
987(m), 848(s), 777(s), 569, 507, 405. ESI-MS (positive ion mode,
MeCN): m/z = 315.00 (100%, [L1 + H]+), 336.97 (45%, [L1+Na]+).
1H NMR (300 MHz, CDCl3): d, ppm: 8.65 (d, 2H, J = 4.2 Hz),
8.49 (s, 2H), 8.07 (d, 2H, J = 7.9 Hz), 7.49 (t, 2H, J = 7.7 Hz), 7.32
(m, 6H), 4.88 (s, 4H).
X-ray crystallographic data collection and refinement of the
structures. Crystallographic data for 1a, 1b and 2 are given
in Table 1. Diffraction data were collected at 120(2) K on a
˚
Bruker Smart APEX II (Mo-Ka radiation, l = 0.71073 A). Cell
refinement, indexing and scaling of the data set were carried out
using the Apex2 v2.1-0 software.55 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.56 In all the complexes the hydrogen atoms
were fixed. Oxygen atoms of one of the perchlorates in 1a were
found disordered over two positions. The hydrogen atoms of water
molecule (O13) in 1a were not assigned. Isomer 1a diffract at low
angles as a distinctive feature of crystals. Crystal quality of isomer
1a is not the best but sufficient attempts were made to collect the
best possible data set. All the non hydrogen atoms were refined
anisotropically except the disordered perchlorate anion of 1a. In
isomer 2, Cl, O(2) and O(3) atoms of the perchlorate anion were
found disordered over two positions whereas O(1) and O(4) of the
perchlorate anion were found disordered over four positions. The
positions of the chlorine and oxygen atoms are fixed accordingly.
Attempts were made to assign diffused electron density for solvent
molecules in the unit cell. The routine SQUEEZE was applied to
intensities data of isomer 2 to take into account the disordered
solvent molecules.57 The number of electrons found in the solvent
accessible void is close to that expected for two dichloromethane
molecules in the unit cell. CCDC 794247–794249 contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif
or by emailing data_request@ccdc.cam.ac.uk, or by contacting
The Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Synthesis of silver(I) complex
{[AgL1]ClO4}n (1). To the solution of ligand (0.628 g, 2 mmol)
in dry MeOH (~15 mL) was added a methanolic (2–3 mL) solution
of anhydrous silver perchlorate (0.414 g, 2 mmol). The light-
yellow solution was stirred overnight at room temperature to
precipitate off-white solid. The solid was isolated by filtration
and recrystallised from acetonitrile. Yield: 88% (0.92 g). Anal.
calcd for C20H18AgClN4O4 (521.70 g mol-1): C, 46.04; H, 3.48; N,
10.74. Found: C, 45.8; H, 3.4; N, 10.6%. IR (KBr, cm-1): 3460(br),
3082(w), 2906(w), 1649(m), 1591(m), 1473, 1441(m), 1381, 1302,
1092(vs), 840, 783(m), 623(m). K (mho cm2 mol-1 in MeCN): 155.
ESI-MS (positive ion mode, MeCN): m/z = 331.92 (60%, [{L1–
C6H3N}+Ag]+), 420.91 (20%, [L1+Ag]+), 555.76 (100%, [{L1–
C6H3N}2Ag]+). H NMR (300 MHz, DMSO-d6): d, ppm: 8.76
1
(s, 2H), 8.53 (t, 2H), 8.12 (t, 2H, J = 7.9 Hz), 7.90 (d, 2H, J = 7.2
Hz), 7.68 (s, 2H), 6.96 (s, 4H), 4.73 (s, 4H).
[Ag3(L1)3](ClO4)3·2CH3CN·H2O (1a). Complex 1 (0.052 g, 0.1
mmol) was dissolved in 10 mL acetonitrile in a sample vial. The
light yellow solution was kept in the dark for slow evaporation
of solvent. Light yellow prismatic single crystals suitable for X-
ray diffraction were obtained after 5 d. Yield: 23% (0.012 g).
Anal. calcd for C60H54Ag3Cl3N12O12 (1565.1 g mol-1): C, 46.04;
H, 3.48; N, 10.74. Found: C, 46.2; H, 3.6; N, 10.6%. IR (KBr,
cm-1): 3464(br), 3084(w), 3067, 1651(m), 1591(m), 1473, 1443(m),
1381, 1302, 1090(vs), 839, 783(m), 623(m).
Acknowledgements
We gratefully acknowledge the Department of Science and
Technology, Government of India for financial support. Single
crystal data for complexes were collected at the DST-funded
National Single Crystal Diffractometer Facility at the Department
of Inorganic Chemistry, IACS. The authors acknowledge Dr
Deepak Chopra, M. Arunachalam and N. N. Adarsh for their help
with crystal structure determination. B. C. and P. H. acknowledge
the Council of Scientific and Industrial Research (CSIR), India
for research fellowships.
[Ag2(L1)2](ClO4)2 (1b). The mother liquor, after the isolation
of single crystals of 1a, was kept in dark for further evaporation
of solvent. Rhombic shaped light-yellow single crystals suitable
for single crystal X-ray diffraction were isolated after 10–12 d.
Yield: 44% (0.023 g). Crystals of 1b were isolated with a better
yield by layer diffusion of a methanolic solution (5 mL) of silver
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3647–3654 | 3653
©

View Article Online
29 C. V. K. Sharma, R. J. Diaz, A. J. Hessheimer and A. Clearfield, Cryst.
Eng., 2000, 3, 201–208.
30 X.-C. Huang, J.-P. Zhang, Y.-Y. Lina and X.-M. Chen, Chem.
Commun., 2005, 2232–2234.
31 X.-J. Li, R. Cao, Z.-G. Guo, Y.-F. Li and X.-D. Zhu, Polyhedron, 2007,
26, 3911–3919.
32 I. Boldog, J. Sieler and K. V. Domasevitch, Inorg. Chem. Commun.,
2003, 6, 769–772.
References
1 A. N. Khlobystov, A. J. Blake, N. R. Champness, D. A. Lemenovskii,
A. G. Majouga, N. V. Zyk and M. Schro¨der, Coord. Chem. Rev., 2001,
222, 155–192.
2 G. F. Swiegers and T. J. Malefetse, Chem. Rev., 2000, 100, 3483–3537.
3 R. Robson, J. Chem. Soc., Dalton Trans., 2000, 3735–3744.
4 C. Janiak, Dalton Trans., 2003, 2781–2804.
5 M. Hong, W. Su, R. Cao, M. Fujita and J. Lu, Chem.–Eur. J., 2000, 6,
427–431.
33 J. Keegan, P. E. Kruger, M. Nieuwenhuyzen and N. Martin, Cryst.
Growth Des., 2002, 2, 329–332.
6 M. J. Plater, M. R. S. J. Foreman, T. Gelbrich, S. J. Coles and M. B.
Hursthouse, J. Chem. Soc., Dalton Trans., 2000, 3065–3073.
7 L. Carlucci, G. Ciani, D. M. Proserpio and S. Rizzato, CrystEngComm,
2002, 4, 121–129.
8 X.-H. Bu, W. Chen, W.-F. Hou, M. Du, R.-H. Zhang and F. Brisse,
Inorg. Chem., 2002, 41, 3477–3482.
34 M. Barboiu, E. Petit, A. van der Lee and G. Vaughan, Inorg. Chem.,
2006, 45, 484–486.
35 P. Halder, E. Zangrando and T. K. Paine, Dalton Trans., 2009, 5386–
5394.
36 J. Zhou, X. Liu, Y. Zhang, B. Li and Y. Zhang, Inorg. Chem. Commun.,
2006, 9, 216–219.
9 M. O. Awaleh, A. Badia and F. Brisse, Cryst. Growth Des., 2005, 5,
1897–1906.
10 B. Moulton and M. J. Zaworotko, Chem. Rev., 2001, 101, 1629–1658.
11 B. Moulton and M. J. Zaworotko, Adv. Supramol. Chem., 2000, 7, 235–
283.
37 M.-a. Haga and K. Koizumi, Inorg. Chim. Acta, 1985, 104, 47–50.
38 S. Chakraborty, P. Munshi and G. K. Lahiri, Polyhedron, 1999, 18,
1437–1444.
39 C. Li, F.-A. Sun, M.-Y. He, H. Xu and Q. Chen, Acta Crystallogr., Sect.
E: Struct. Rep. Online, 2009, E65, o286.
12 X. Yang, J. D. Ranford and J. J. Vittal, Cryst. Growth Des., 2004, 4,
40 H.-C. Wu, P. Thanasekaran, C.-H. Tsai, J.-Y. Wu, S.-M. Huang, Y.-S.
Wen and K.-L. Lu, Inorg. Chem., 2006, 45, 295–303.
41 F. Tuna, J. Hamblin, G. Clarkson, W. Errington, N. W. Alcock and M.
J. Hannon, Chem.–Eur. J., 2002, 8, 4957–4964.
42 C.-L. Chen, C.-Y. Su, Y.-P. Cai, H.-X. Zhang, A.-W. Xu, B.-S. Kang
and H.-C. z. Loye, Inorg. Chem., 2003, 42, 3738–3750.
43 P. L. Caradoc-Davies, L. R. Hanton and W. Henderson, J. Chem. Soc.,
Dalton Trans., 2001, 2749–2755.
781–788.
13 J.-P. Zhang, X.-C. Huang and X.-M. Chen, Chem. Soc. Rev., 2009, 38,
2385–2396.
14 S. A. Bourne, J. Lu, B. Moulton and M. J. Zaworotko, Chem. Commun.,
2001, 861–862.
15 M. J. Zaworotko, Chem. Commun., 2001, 1–9.
16 T. L. Hennigar, D. C. MacQuarrie, P. Losier, R. D. Rogers and M. J.
Zaworotko, Angew. Chem., Int. Ed. Engl., 1997, 36, 972–973.
17 M. Sarkar and K. Biradha, Cryst. Growth Des., 2007, 7, 1318–1331.
18 Q. Chen, S.-C. Chen, B. Xiao, Z.-H. Zhang, M.-Y. He, F.-H. Yin and
M. Du, Inorg. Chem. Commun., 2008, 11, 1371–1374.
19 L. R. Hanton and K. Lee, J. Chem. Soc., Dalton Trans., 2000, 1161–
1166.
44 L. Carlucci, G. Ciani and D. M. Proserpio, Chem. Commun., 2004,
380–381.
45 D. M. Shin, I. S. Lee, Y. K. Chung and M. S. Lah, Chem. Commun.,
2003, 1036–1037.
46 N. Masciocchi, G. A. Ardizzoia, G. LaMonica, A. Maspero and A.
Sironi, Angew. Chem., Int. Ed., 1998, 37, 3366–3369.
47 O. R. Evans and W. Lin, Chem. Mater., 2001, 13, 3009–3017.
48 J. Y. Lu and A. M. Babb, Chem. Commun., 2001, 821–822.
49 D. M. Shin, I. S. Lee, Y. K. Chung and M. S. Lah, Inorg. Chem., 2003,
42, 5459–5461.
20 P. L. Caradoc-Davies and L. R. Hanton, Chem. Commun., 2001, 1098–
1099.
21 P. L. Caradoc-Davies, D. H. Gregory, L. R. Hanton and J. M. Turnbull,
J. Chem. Soc., Dalton Trans., 2002, 1574–1580.
22 D. B. Cordes, A. S. Bailey, P. L. Caradoc-Davies, D. H. Gregory, L. R.
Hanton, K. Lee and M. D. Spicer, Inorg. Chem., 2005, 44, 2544–2552.
23 L. Carlucci, G. Ciani, D. M. Proserpio and L. Spadacini, CrystEng-
Comm, 2004, 6, 96–101.
24 S. A. Barnett, A. J. Blake, N. R. Champness and C. Wilson, Chem.
Commun., 2002, 1640–1641.
50 L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, Inorg. Chem.,
1998, 37, 5941–5943.
51 Y.-C. Jiang, Y.-C. Lai, S.-L. Wang and K.-H. Lii, Inorg. Chem., 2001,
40, 5320–5321.
52 C.-Y. Su, A. M. Goforth, M. D. Smith and H.-C. zur Loye, Inorg.
Chem., 2003, 42, 5685–5692.
ˇ
25 S. Muthu, J. H. K. Yip and J. J. Vittal, J. Chem. Soc., Dalton Trans.,
2001, 3577–3584.
53 G. Yang, R. G. Raptis and P. Safa´r, Cryst. Growth Des., 2008, 8, 981–
985.
26 L. Carlucci, G. Ciani, M. Moret, D. M. Proserpio and S. Rizzato,
Angew. Chem., Int. Ed., 2000, 39, 1506–1510.
27 Y.-B. Dong, R. C. Layland, N. G. Pschirer, M. D. Smith, U. H. F. Bunz
and H.-C. zur Loye, Chem. Mater., 1999, 11, 1413–1415.
28 D. K. Kumar, A. Das and P. Dastidar, Cryst. Growth Des., 2007, 7,
2096–2105.
54 W. C. Wolsey, J. Chem. Educ., 1973, 50, A335–A337.
55 APEX 2v2.1-0, Bruker AXS, Madison, WI, 2006.
56 G. M. Sheldrick, SHELX97 Programs for Crystal Structure Analysis,
1998, University of Go¨ttingen, Germany.
57 P. van der Sluis and A. L. Spek, Acta Crystallogr., Sect. A: Found.
Crystallogr., 1990, A46, 194–201.
3654 | Dalton Trans., 2011, 40, 3647–3654
This journal is
The Royal Society of Chemistry 2011
©