Coordination networks of Ag(I) and N,N′ - Bis(3-pyridinecarboxainide)-1,6-hexane: Structures and anion exchange

Article abstract of DOI:10.1039/b206680g

A bidentate ligand N,N′ - bis(3-pyridinecarboxamide)-1,6-hexane (L) and its silver complexes have been synthesized and characterized by single crystal X-ray diffraction. Reaction of AgClO₄ and L in H₂O/EtOH gives rise to a coordination polymer [Ag₂L₃OH][ClO₄]·2.5H₂O. The X-ray crystal structure of the compound shows honeycomb-like networks in which four-coordinated Ag ions are linked to three-coordinated Ag ions via three ligands L. The coordination of the long ligands L to the Ag ions creates tube-like structures and the tubes of adjacent honeycomb layers are interlocked, leading to an interpenetrating network. The compound [AgL][ClO₄], synthesized from CH₃OH, is composed of twisted zigzag coordination polymers in which ligands L are linked by Ag ions. Ligand L displays two different conformations A and B within a single strain of polymer. The two conformers differ in the orientation of the two pyridyl-groups which are arranged periodically in the polymer in the sequence ABBABBA. The polymer chains assemble into 2-D undulating sheets via amide hydrogen bonds. Reaction between AgNO₃/AgCF₃SO₃ and L leads to polymeric compounds [AgL][NO₃] and [AgL][CF₃SO₃]. The compounds are composed of coordination polymers in zigzag conformation and the polymer chains assemble into undulating sheets via inter-chain hydrogen bonds. The inter-sheet Ag-Ag distances of the compounds are in the order [AgL][CF₃SO₃] > [AgL][ClO₄] > [AgL][NO₃]. The anion exchange properties of the compounds are monitored by using X-ray powder diffraction, infrared spectroscopy and elemental analysis. Our results show that the anions in [AgL][NO₃] and [AgL][CF₃SO₃] can be totally replaced with ClO₄^-. However, the exchange is not reversible. In additional, interconversion between [AgL][NO₃] and [AgL][CF₃SO₃] by anion exchange is shown to be unfeasible. Anion selectivity could be due to the different hydration energy of the anions and the structural reorganization involved in the conversion.

Full text of DOI:10.1039/b206680g

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Coordination networks of Ag(I) and N,NЈ- bis(3-pyridine-
carboxamide)-1,6-hexane: structures and anion exchange
Sebastian Muthu, John H. K. Yip* and Jagadese J. Vittal
Department of Chemistry, The National University of Singapore, 10 Kent Ridge Crescent,
1
19269, Singapore
Received 9th July 2002, Accepted 3rd October 2002
First published as an Advance Article on the web 6th November 2002
A bidentate ligand N,NЈ- bis(3-pyridinecarboxamide)-1,6-hexane (L) and its silver complexes have been synthesized
and characterized by single crystal X-ray diffraction. Reaction of AgClO and L in H O/EtOH gives rise to a
4
2
coordination polymer [Ag L OH][ClO ]ؒ2.5H O. The X-ray crystal structure of the compound shows honeycomb-
2
3
4
2
like networks in which four-coordinated Ag ions are linked to three-coordinated Ag ions via three ligands L. The
coordination of the long ligands L to the Ag ions creates tube-like structures and the tubes of adjacent honeycomb
layers are interlocked, leading to an interpenetrating network. The compound [AgL][ClO ], synthesized from
4
CH OH, is composed of twisted zigzag coordination polymers in which ligands L are linked by Ag ions. Ligand
3
L displays two different conformations A and B within a single strain of polymer. The two conformers differ in the
orientation of the two pyridyl-groups which are arranged periodically in the polymer in the sequence ABBABBA.
The polymer chains assemble into 2-D undulating sheets via amide hydrogen bonds. Reaction between AgNO3/
AgCF SO and L leads to polymeric compounds [AgL][NO ] and [AgL][CF SO ]. The compounds are composed
3
3
3
3
3
of coordination polymers in zigzag conformation and the polymer chains assemble into undulating sheets via
inter-chain hydrogen bonds. The inter-sheet Ag–Ag distances of the compounds are in the order [AgL][CF SO ] >
3
3
[
AgL][ClO ] > [AgL][NO ]. The anion exchange properties of the compounds are monitored by using X-ray powder
4
3
diffraction, infrared spectroscopy and elemental analysis. Our results show that the anions in [AgL][NO ] and
3
Ϫ
[
AgL][CF SO ] can be totally replaced with ClO . However, the exchange is not reversible. In additional, inter-
3
3
4
conversion between [AgL][NO ] and [AgL][CF SO ] by anion exchange is shown to be unfeasible. Anion selectivity
3
3
3
could be due to the different hydration energy of the anions and the structural reorganization involved in the
conversion.
Introduction
The synthesis of coordination polymers is a rapidly expanding
1
field of research. Given the high directionality of metal–ligand
bonds and the regular geometry of metal complexes, it is
possible to control the 3-D structures of coordination polymers
by judicial choice of metal ion and design of ligand and based
on this synthetic strategy, numerous intriguing 2-D and 3-D
Scheme 1
1–4
polymeric structures have been created. Aside from their
interesting structures, coordination polymers are attractive
because of their modular nature which makes incorporation of
functional groups into a 3-D network synthetically straight-
forward. This allows a bottom-up approach to functional
were characterized by single crystal X-ray diffraction. Recently,
the anion exchange behavior of some coordination polymers
has been examined and the results highlighted the potential
applications of the polymers to anion sequestering and
sensing. To explore the properties of the coordination
polymers, the anion exchange reactions of the three [AgL][X]
compounds were investigated by using X-ray powder diffrac-
tion, infrared absorption spectroscopy and elemental analysis.
6
7
5
materials. There are examples showing that coordination
6
polymer networks can be applied to anion exchange, chemical
7
8
9
sensing and gas storage. Our recent study showed that the
compound N,NЈ- bis(3-pyridinecarboxamide)-1,2-ethane, sim-
ilar to many other bipyridines, is capable of forming coord-
1
0
I
II
II
ination polymers with d Ag , Zn and Cd ions. A special
feature of the Ag() polymers is that the polymer chains can zip
up into 2-D undulating sheets via inter-chain amide hydrogen
bonds. The possibility that increasing the length of the bridg-
ing ligand would form flexible coordination frameworks
of high porosity or coordination polymers with interesting
Experimental
General methods
All chemicals were purchased from Aldrich and used without
further purification. H-NMR and IR spectra (KBr pellet)
1
spectra were recorded on a Bruker ACF 300 spectrometer and
a Bio-Rad FTIR spectrometer, respectively. Electrospray mass
spectra (ES-MS) were measured on a Finnigan-MAT 731
spectrometer with HPLC-grade MeOH as mobile phase.
Elemental analyses were carried out in the microanlytical
laboratory in the Department of Chemistry, The National
University of Singapore.
10
interpenetration have led us to study the ligand N,NЈ-bis-
3-pyridinecarboxamide)-1,6-hexane (L) (Scheme 1). Unlike
(
N,NЈ-bis(3-pyridinecarboxamide)-1,2-ethane, the ligand L is
found to form 3-D hexagonal nets with Ag() ions. In addition,
we also showed that Ag and L form zigzag coordination poly-
Ϫ
Ϫ
Ϫ
mers [AgL][X] (X = ClO4 , NO3 or CF SO3 ) whose structures
3
DOI: 10.1039/b206680g
J. Chem. Soc., Dalton Trans., 2002, 4561–4568
This journal is © The Royal Society of Chemistry 2002
4561

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Synthesis
N,NЈ-Bis(3-pyridinecarboxamide)-1,6-hexane
Hexanediamine (1 g, 17 mmol) was slowly added to a pyridine
solution (50 ml) of 3-pyridnecarboxylic acid (4.23 g,34 mmol).
The mixture was stirred for 15 min and triphenyl phosphite
solution containing a different anion (LiClO , LiCF SO or
4
3
3
NaNO ). The mixture was kept dark and stirred at room
3
(L).
1,6-
temperature for 12 h before filtration. Prolonged immersion
(
2 weeks) and higher salt concentrations (0.1 M) were used for
Ϫ Ϫ
the exchange reactions [AgL][ClO ] ϩ NO /CF SO and
4
3
3
3
Ϫ
Ϫ
[AgL][NO ] ϩ CF SO ↔ [AgL][CF SO ] ϩ NO . The solids
3 3 3 3 3 3
(
9 ml, 34 mmol) was added slowly through a dropping funnel
collected by filtration were washed extensively with water
before being characterized by infrared spectroscopy, ESI mass
spectrometry (negative mode), elemental analyses and X-ray
powder diffraction.
over the period of 15 min. The mixture was refluxed for 6 h and
then the volume was reduced to 10 ml by vacuum evaporation.
A white precipitate was obtained from the solution after
standing at room temperature for 24 h. The solid was filtered
off and washed with cold water. Recrystallization from ethanol
1
X-Ray powder diffraction
gave colorless crystals. Yield 70%. H NMR (CDCl , δ) 9.03
3
(
(
2H, s, H2-py), 8.7 (2H, d, H4-py), 8.14 (2H, d, H6-py), 7.35
2H, t, 5H-py), 6.7 (2H, s, NH), 3.46 (4H, t, N–CH ), 1.64 (4H,
X-Ray powder diffraction (XRPD) data were collected on a
D5005 Bruker AXS X-ray diffractometer at 25 ЊC at 50 kV and
100 mA for Cu-α at a scan rate of 5Њ min . The 2θ was
increased at intervals of 0.02Њ. All the XRPD analyses were
performed using a V12 sample holder.
2
Ϫ1
p, N–CH –CH ), 1.44 (4H, p, N–CH –CH –CH ), mp: 169–172
ЊC. Anal Calcd(%) for C H N O : C, 66.26; H, 6.74; N, 17.18.
Found(%): C, 66.02; H, 6.41; N, 16.83. ES-MS: M , 326;
2
2
2
2
2
18
22
4
2
ϩ
ϩ
[M ϩ H] , 327.
X-Ray crystallography
[
Ag L OH][ClO ]ؒ2.5H O. An ethanol solution of L (0.33 g,
2
3
4
2
The X-ray diffraction experiments were carried out on a Bruker
SMART CCD diffractometer with a Mo-Kα sealed tube at
1
mmol) was layered on top of an aqueous solution of AgClO4
(
0.21 g, 1 mmol). After three weeks, large cubic crystals of
2
23(2) K. The wavelength of the radiation was 0.71073 Å. The
the compound were found at the interface. Yield 20%. Anal
Calcd(%) for C H N O ClAg : C, 47.81; H, 5.31; N, 12.39.
Found(%): C, 47.15; H, 5.26; N, 12.41. IR (cm ), ν(ClO ),
11
program SMART was used for collecting frames of data,
SAINT for integration of the intensity of reflections and
scaling, SADABS for absorption correction and SHELXTL
54
72 12 13.5
2
11
Ϫ1
4
12
13
1
145 (s).
for space group and structure determination and least-square
2
refinements on F . Anisotropic thermal parameters were
[
AgL][ClO ]. L (0.33 g, 1 mmol) was dissolved in 20 ml of
4
refined for the non-hydrogen atoms. The hydrogen atoms were
placed in ideal positions. The relevant crystallographic data and
refinement details are shown in Table 1. The oxygen atoms
methanol and AgClO (0.20 g, 1 mmol) was added and stirred
for 1 h. The white precipitate obtained was filtered off and
washed with an excess of methanol. Needle like crystals were
obtained by slow diffusion of diethyl ether into a CH CN
solution of the compound.. Yield 70%. H NMR (CD CN, δ)
8
7
4
of the perchlorate ion in [AgL][ClO ] are disordered and are
4
3
1
modeled with an occupancy of 0.5. Oxygen atoms O , O , O ,
3
4
3A
3
Ϫ
O4A of NO3 in [AgL][NO ] are disordered and modeled with
.91 (2H, s, H2-py), 8.63 (2H, d, H4-py), 8.11 (2H, d, H6-py),
3
occupancies of 0.4 and 0.1. N and O are disordered with an
.44 (2H, t, 5H-py), 7.12 (2H, s, NH), 3.33 (4H, t, N–CH ), 1.58
3
3
2
occupancy of 0.5. Common isotropic thermal parameters were
(
4H, p, N–CH –CH ), 1.42 (4H, p, N–CH –CH –CH ). Anal
2 2 2 2 2
refined for the model. Soft constraints were applied for N–O,
Calcd(%) for C H N O ClAg: C, 40.49; H, 6.74; N, 10.50.
Found(%): C, 40.63; H, 4.14; N, 10.61. IR (cm ), ν(ClO ), 1145
18
22
4
6
13
Ϫ1
O–O distances using SADI.
4
ϩ
ϩ
CCDC reference numbers 189551–189555.
See http://www.rsc.org/suppdata/dt/b2/b206680g/ for crystal-
lographic data in CIF or other electronic format.
(
s). ES-MS: M , 433.4; [M ϩ 2] , 435.4.
[
AgL][NO ]. 0.17 g of AgNO (1 mmol) was added to a
3
3
methanol solution of L (0.33 g, 1 mmol). A white precipitate
appeared immediately and the mixture was stirred for 1 h at
room temperature. The white solid collected after filtration was
washed with an excess of methanol. Colorless crystals were
Results and discussion
N,NЈ-Bis(3-pyridinecarboxamide)-1,6-hexane (L)
obtained by slow evaporation of a CH CN solution of the
3
1
The compound was synthesized by a condensation reaction
between 3-pyridinecarboxylic acid and 0.5 mol of 1,6-
hexanediamine. The compound is highly soluble in protic
solvents such as water but insoluble in most of the organic
solvents except dimethyl sulfoxide. The poor solubility is a sign
of the presence of intermolecular hydrogen bonds. Indeed the
X-ray crystal structure of the compound shows that molecules
of L are aligned in parallel with the amide carbonyl of one
chain directed toward the amide nitrogen of its two adjacent
compound. Yield 65%. H NMR (CD CN, δ) 8.93 (2H, s,
3
H2-py), 8.65 (2H, d, H4-py), 8.07 (2H, d, H6-py), 7.4 (2H, t,
5
H-py), 7.14 (2H, s, NH), 3.35 (4H, t, N–CH ), 1.58 (4H, p,
2
N–CH –CH ), 1.42 (4H, p, N–CH –CH –CH ). Anal Calcd(%)
2
2
2
2
2
for C H N O Ag: C, 43.56; H, 4.44; N, 14.11. Found(%): C,
1
8
22
5
5
Ϫ1
4
3.44; H, 4.62; N, 13.91. IR (cm ), ν(NO ), 1384 (s). ES-MS:
3
ϩ ϩ
M , 433.4; [M ϩ 2] , 435.
[
AgL][CF SO ]. The compound was synthesized by layering
3
3
molecules (Fig. 1 and Table 2) and the N(H) ؒ ؒ ؒ O᎐C distance
an ethanol solution of L (0.33 g, 1 mmol) over an aqueous
᎐
of 2.990(2) Å compares favorably with the ones observed in
solution of AgCF SO (0.25 g, 1 mmol). Slow diffusion of the
3
3
14
1
amide hydrogen bonds. Clearly the polymer aggregation is
solutions led to the formation of cubic crystals. Yield 45%. H
sustained by intermolecular amide N–H ؒ ؒ ؒ O᎐C hydrogen
NMR (CD CN, δ) 8.92 (2H, s, H2-py), 8.64 (2H, d, H4-py),
᎐
3
bonds. The two pyridyl-groups show an anti-orientation and
they are related by inversion at the centre of the molecule.
As the six carbon atoms in the backbone are all in anti-
conformation, the ligand extends its full length and the two
pyridine nitrogen atoms are widely separated by 18.375(2) Å.
8
3
.08 (2H, d, H6-py), 7.43 (2H, t, 5H-py), 7.16 (2H, s, NH),
.35 (4H, t, N–CH ), 1.50 (4H, p, N–CH –CH ), 1.40 (4H, p,
2
2
2
N–CH –CH –CH ). Anal Calcd(%) for C H F N O SAg: C,
2
2
2
19 22
3
4
5
3
9.11; H, 3.77; N, 9.61. Found(%): C, 39.21; H, 3.56; N, 9.55.
Ϫ
1
ϩ
ϩ
IR (cm ), ν(CF SO ), 1261 (s). ES-MS: M , 433.4; [M ϩ 2] ,
3
3
4
35.4.
[
Ag L OH][ClO ]
2 3 4
Anion exchange
In a typical anion exchange experiment, crystals of [AgL][X]
Slow diffusion of an aqueous solution of AgClO into 1 mol of
L in ethanol produced crystals of [Ag L OH][ClO ]ؒ2.5H O. As
shown by its X-ray crystal structure, the compound is
4
2
3
4
2
Ϫ2
(
X = NO , ClO , CF SO ) were suspended in a 10 M aqueous
3
4
3
3
4
562
J. Chem. Soc., Dalton Trans., 2002, 4561–4568

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Table 1 Crystal data for the compounds
Compound
L
[Ag L OH][ClO ]ؒ2.5H O
[AgL][ClO4]
[AgL][NO3]
[AgL][CF SO ]
3 3
2
3
4
2
Formula
Formula weight
C H N O
326.40
C H Ag ClN O
1355.42
C H AgClN O S
533.72
C H AgN O
496.28
C H AgF N O S
19 22 3 4 5
582.33
1
8
22
4
2
54 72
2
12 13.5
18 22
4
6
18 22
5
5
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
Monoclinic
P2(1)/c
5.2078(8)
5.0943(8)
30.930(5
90
94.829(3)
90
817.7(2)
2
Trigonal
P3(2)
15.1300(2)
15.1300(2)
22.1343(5)
90
90
120
4388.08(1)
3
0.789
R1 = 0.0608,
wR 2= 0.1359
0.0212
1.393, Ϫ0.998
1.041
Monoclinic
C2/c
26.502(2)
5.1431(4)
44.366(3)
90
94.348(2)
90
6029.7(8)
12
Triclinic
P1
Triclinic
P1
¯
¯
5.0952(1)
6.9931(2)
13.6355(4)
93.510(2)Њ
98.761(2)
95.219(2)
476.80(2)
1
9.1289(1)
10.0509(2)
13.0946(2)
108.608(1)Њ
107.677(1)
93.597(1)
1067.82(3)
2
β/Њ
γ/Њ
V/Å
3
Z
µ/mm
Ϫ1
)
0.089
1.181
1.099
1.109
a
Final R indices
R1 = 0.0567,
wR2 = 0.1113
0.0429
0.207, Ϫ0.320
0.915
R1 = 0.0481,
wR2 = 0.1134
0.0326
1.133, Ϫ0.850
1.003
R1 = 0.0371,
wR2 = 0.0868
0.0206
0.560, Ϫ0.592
1.078
R1 = 0.0339,
wR2 = 0.0792
0.0166
0.502, Ϫ0.623
1.135
Rint
Ϫ3
Final diff ρ (e Å
)
max
b
GOF
a
2
2
4
1/2
b
2
2
c
2
1/2
R1 = (|F | Ϫ |F |)/(|F |); wR2 = [w(F Ϫ F )/w(F )]
.
Goodness of fit = [(w(Fo Ϫ F ) /(n Ϫ p)] . For all structures determined, the scan type is ω
o
c
o
o
c
o
and the Mo-Kα wavelength is 0.71073 Å.
Table 2 Selected bond lengths (Å) and angles (Њ) in L
C(4)–O(1)
C(4)–N(1)
1.240(1)
1.341(2)
O(1)–C(4)–N(1)
C(5)–C(4)–N(1)
122.08(1)
116.99(1)
Table 3 Selected bond lengths (Å) and angles (Њ) in [Ag L OH][ClO ]ؒ
2
3
4
2
.5H O
2
Ag(1)–N(8)
Ag(1)–N(1)
Ag(1)–N(5)
Ag(1)–O(7)
Ag(2)–N(10)
Ag(2)–N(11)
Ag(2)–N(4)
Ag(2)–O(11)
Ag(2)–O(1S)
C(6)–O(1)
2.260(6)
2.286(5)
2.289(7)
2.514(7)
2.277(7)
2.292(6)
2.292(5)
2.926(5)
2.698(5)
1.219(8)
1.329(9)
N(8)–Ag(1)–N(1)
N(8)–Ag(1)–N(5)
N(1)–Ag(1)–N(5)
N(8)–Ag(1)–O(7)
N(1)–Ag(1)–O(7)
N(5)–Ag(1)–O(7)
N(10)–Ag(2)–N(11)
N(10)–Ag(2)–N(4)
N(11)–Ag(2)–N(4)
C(4)–C(6)–N(2)
110.9(2)
121.9(2)
119.9(2)
101.8(2)
104.5(2)
91.3(3)
118.9(2)
116.6(2)
122.5(2)
117.1(6)
124.5(7)
2
1
Fig. 1 ORTEP plot of L (thermal ellipsoid 50%).
C(6)–N(2)
O(1)–C(6)–N(2)
composed of interpenetrated hexagonal networks of Ag ions
and ligands L extending along the ab-plane (Fig. 2a). Viewed
along the c-axis, the network resembles a honeycomb, showing
an infinite array of interconnected hexagons. Unlike most of
the reported honeycomb networks, in which the hexagonal
nectivity, both Ag(1) and Ag(2) are the same and it would be
appropriate to classify the present system as a (6,3)-net. The
coordination of the long ligands L to the Ag ions gives rise to a
tube-like structure surrounding the silver ions. Perchlorate ions
are located in the cavity of the tubes. One of its oxygen atoms is
15
units are either planar, or puckered (in either chair or boat
2
.926(5) Å away from the Ag(2) ion and the other three O atoms
16
conformation), the net of [Ag L OH][ClO ]ؒ2.5H O resembles
2
3
4
2
are hydrogen bonded to amide N–H groups of the surrounding
an egg tray as the Ag ions occupying alternate nodal positions
of the net are located in two different planes (Fig. 2a). These
two sets of Ag ions, labeled as Ag(1) and Ag(2), are crystal-
lographically independent. The Ag(1) ion is four-coordinate
and in a distorted tetrahedral coordination including nitrogen
atoms of three pyridyl groups and a hydroxide (Fig. 2b). The
distance between the metal and oxygen, 2.514(7) Å, falls into
ligands L. There are 2.5 H O molecules per Ag ion in the crystal
2
and they are possibly involved in hydrogen bonding interactions
with the ligands L and the coordinated hydroxide ions (Fig. 2c
and Table 4).
Like many other hexagonal nets,
1f,15,16
the rugged nets in
[
Ag L OH][ClO ]ؒ2.5H O show interpenetration. The large
2 3 4 2
cavities in the tubes in one layer are partially filled with the
tubes from its adjacent layers. Fig. 2b shows a pair of inter-
locked or catenated tubes. Interestingly, the interlocking only
occurs between Ag(2)-containing and Ag(1)-containing tubes.
Consequently, the Ag(1)- and Ag(2)-containing tubes within
a layer are linked respectively with the Ag(2)- and Ag(1)-
containing tubes of its two adjacent layers, as schematically
represented in Fig. 2c.
17
the typical range of Ag–O bonds (≈2.3–2.6 Å) (Table 3).
Apparently the hydroxide ions came from the solvent water
whose deprotonation could be facilitated by the Lewis acidic
Ag ions. On the other hand, the Ag(2) ion is coordinated to
three nitrogen atoms of the ligands L, showing a distorted
trigonal planar geometry. The nodal silver ions in the two
planes are connected by three ligands L, and accordingly the
adjacent Ag(1) and Ag(2) are widely separated by 18.719(4) Å.
The shortest distance between two Ag(1) ions (or two Ag(2)
ions) is 15.130(4) Å. Each repeating [Ag L OH ][ClO ] hexa-
[
AgL][ClO4]
6
6
3
4 3
gon comprises three Ag(1) and three Ag(2) ions and possesses a
X-Ray crystallographic analysis shows that the compound
crystallographic C -symmetry axis passing through its center
[AgL][ClO ] is a coordination polymer composed of ligands L
3
4
and the equivalent Ag(1) or Ag(2) ions are related by C3-
rotation. Even though Ag(1) is four-coordinate, the hydroxide
ion does not link to another Ag ion; hence in terms of con-
and Ag() ions (Fig. 3a, for selected bond lengths and angles, see
Table 5). Examining the bond parameters shows that there are
two independent silver atoms which are slightly different in
J. Chem. Soc., Dalton Trans., 2002, 4561–4568
4563

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Fig. 2 (a) (i) Viewed along the c-axis, the X-ray crystal structure of a layer of [Ag L OH][ClO ]ؒ2.5H O shows a honeycomb-like structure. (ii) A
2
3
4
2
cross section of a layer of [Ag L OH][ClO ]ؒ2.5H O along the c-axis showing the tube-like structures. (b) Diagram showing two interlocking
2
3
4
2
molecular tubes and the position of the perchlorate ion and water molecules and possible hydrogen bonds. (c) (i) Schematic diagram showing the
overlay of three adjacent layers in [Ag L OH][ClO ]ؒ2.5H O. The overlapped circles represent positions where two tubes are interlocked. (ii) Diagram
2
3
4
2
showing the interpenetration of the 2-D networks and interlocking of molecular tubes.
Table 4 Bond lengths and angles of hydrogen bonds in the compounds
Compound
D–H ؒ ؒ ؒ A
D ؒ ؒ ؒ A/Å
H ؒ ؒ ؒ A/Å
D–H ؒ ؒ ؒ A/Њ
Symmetry operator
L
N(1)–H(1) ؒ ؒ ؒ O(1)
2.990
2.516
2.900
2.956
2.973
3.119
3.040
2.918
2.770
3.287
3.132
3.052
3.002
3.000
2.116
1.736
2.099
2.180
2.149
2.488
2.216
2.527
2.310
2.628
2.365
2.229
2.150
2.177
169.12
158.20
154.73
149.94
160.14
130.75
160.31
111.93
110.77
130.88
140.86
157.56
166.47
157.54
x, y ϩ 1, z
[Ag L OH][ClO ]ؒ2.5H O
O(7)–H(7A) ؒ ؒ ؒ O(3S)
N(2)–H(2A) ؒ ؒ ؒ O(10)
N(3)–H(3B) ؒ ؒ ؒ O(8)
N(6)–H(6a) ؒ ؒ ؒ O(8)
N(7)–H(7B) ؒ ؒ ؒ O(9)
N(9)–H(9A) ؒ ؒ ؒ O(9)
O(1S)–H(1SA) ؒ ؒ ؒ O(2)
O(1S)–H(1SB) ؒ ؒ ؒ O(6)
O(2S)–H(2SB) ؒ ؒ ؒ O(5)
O(3S)–H(3SA) ؒ ؒ ؒ O(2S)
N(2)–H(2A) ؒ ؒ ؒ O(1)
N(3)–H(3A) ؒ ؒ ؒ O(2)
N(6)–H(6A) ؒ ؒ ؒ O(3)
2
3
4
2
x ϩ y ϩ 3, Ϫx ϩ 2, z ϩ 1/3
x ϩ y ϩ 2, Ϫx ϩ 2, z ϩ 1/3
x ϩ y ϩ 3, Ϫx ϩ 2, z ϩ 1/3
x ϩ y ϩ 4, Ϫx ϩ 2, z ϩ 1/3
y ϩ 3, x Ϫ y, z ϩ 2/3
x, y, z Ϫ 1
x, y Ϫ 1, z
x, y ϩ 1, z
[AgL][ClO4]
x, y ϩ 1, z
[
[
AgL][NO3]
N(2)–H(2A) ؒ ؒ ؒ O(1)
2.970
2.166
155.58
x Ϫ 1, y, z
AgL][CF SO ]
N(2)–H(2) ؒ ؒ ؒ O(2)
N(4)–H(4) ؒ ؒ ؒ O(1)
2.989
3.013
2.328
2.264
172.26
172.45
Ϫx ϩ 1, Ϫy ϩ 1, Ϫz ϩ1
Ϫx ϩ 1, Ϫy, Ϫz ϩ 1
3
3
4
564
J. Chem. Soc., Dalton Trans., 2002, 4561–4568

View Article Online
Table 5 Selected bond lengths (Å) and angles (Њ) in [AgL][ClO4]
Table 6 Selected bond lengths (Å) and angles (Њ) in [AgL][NO3]
Ag(1)–N(1)
Ag(2)–N(4)
Ag(2)–N(5)
C(6)–O(1)
C(6)–N(2)
2.173(4)
2.191(4)
2.194(4)
1.225(5)
1.336(5)
N(1A)–Ag(1)–N(1)
N(4)–Ag(2)–N(5)
N(2)–C(6)–O(1)
N(2)–C(6)–C(4)
N(3)–C(13)–O(2)
180.0(3)
173.15(1)
123.0(4)
116.6(4)
121.6(4)
Ag(1)–N(1)
Ag(1)–O(2)
C(6)–O(1)
C(6)–N(2)
2.185(3)
2.554(8)
1.235(4)
1.330(4)
N(1A)–Ag(1)–N(1)
N(1A)–Ag(1)–O(2)
N(1)–Ag(1)–O(2)
N(2)–C(6)–O(1)
180.00(1)
96.51(2)
83.49(2)
122.3(3)
Fig. 3 (a) X-Ray crystal structure of [AgL][ClO ]. (b) (i) The
4
A-conformation of L in [AgL][ClO ]. (ii) The B-conformation. (c)
4
Diagram showing the 2-D rugged sheets arising from the self-assembly
of the [AgL][ClO ] coordination polymers.
4
their coordination geometry. One of the silver atoms, labeled as
Ag(1), is coordinated to two nitrogen atoms of pyridyl groups
in an ideal linear geometry, showing a N–Ag–N angle of
1
80.0(3)Њ. The metal ion lies on a centre of inversion. Whereas
the other silver ions, labeled as Ag(2), show a slightly bent
coordination geometry with a N(4)–Ag(2)–N(5) angle of
1
73.15(1)Њ. The Ag(1)–N bond length is slightly shorter than
the one between N(4) and Ag(2). The Ag–N bond lengths lie
within the normal range of 2.120–2.60 Å. The two pyridyl-rings
that are connected by Ag(1) are coplanar while the two rings
coordinated to Ag(2) show a small dihedral angle of 12Њ.
In addition to these small differences in local coordination
geometry, the ligands L coordinated to Ag(1) and Ag(2) adopt
two different conformations A and B (Fig. 3b). The two con-
formations differ in the dihedral angle of the two pyridyl-rings:
in the A-conformation, the two rings are nearly coplanar while
in the B-conformation, the two rings show a dihedral angle of
Fig. 4 (a) X-Ray crystal structures of (i) [AgL][NO
] and (ii)
3
[
AgL][CF SO ]. (b) Diagrams showing the solid-state stacking of the
3 3
2
-D sheets of (i) [AgL][NO ] and (ii) [AgL][CF SO ].
3 3 3
8
3.3Њ. The two conformers are arranged periodically in a single
atom and the nearest Cl atom is 3.581(2) Å. The Ag–O distance
is uncertain as the anion is disordered.
strand of polymer in the sequence ABBABBA. The presence
of B-conformation ligands gives the polymer a twisted con-
formation (Fig. 3c) which is different from the planar zigzag
conformation of [AgL][NO ] and [AgL][CF SO ] (see later).
[
AgL][NO ] and [AgL][CF SO ]
3 3 3
3
3
3
The coordination polymers are linked together via com-
Crystals of [AgL][NO ] were obtained by slow evaporation
3
plementary N–H ؒ ؒ ؒ O᎐C hydrogen bonds between the
of an acetonitrile of the compound. However, crystals of
[Agl][CF SO ] could not be obtained by this method. We
resorted to growing crystals of the compound by slow diffusion
᎐
adjacent chains, leading to 2-D undulating sheets (Fig. 3c).
The parameters of the hydrogen bonds are given in Table 4. The
shortest Ag–Ag distance between the two adjacent chains in a
3
3
of a solution of the ligand into another solution of AgCF SO .
3
3
sheet is 5.143(2) Å. The stacking of sheets in [AgL][ClO ] is
Different combinations of solvents (i.e. H O/methanol,
4
2
staggered, forming a crisscross pattern as shown in Fig. 3c. The
CH CN/H O) were tried and it was found that the solvent pair
3
2
inter-sheet distance, defined as the shortest Ag–Ag distance
H O/MeOH gave the best result in terms of yield and quality of
2
between the two adjacent sheets, is 7.456(3) Å. The counter
crystals. The X-ray crystal structures of [AgL][NO ] and
3
Ϫ
ions, ClO , are sandwiched between the adjacent sheets and
[AgL][CF SO ] are highly similar as both compounds are com-
4
3
3
associated with the silver atoms. The distance between the silver
posed of zigzag chains of AgL polymers (Fig. 4a and Tables 6
J. Chem. Soc., Dalton Trans., 2002, 4561–4568 4565

View Article Online
Table 7 Selected bond lengths (Å) and angles (Њ) in [AgL][CF SO ]
3
3
Ag(1)–N(1)
Ag(1)–N(3)
Ag(1)–O(3)
C(6)–O(1)
C(6)–N(2)
2.167(2)
2.171(2)
2.584(2)
1.235(3)
1.330(3)
N(1)–Ag(1)–N(3)
N(1)–Ag(1)–O(3)
N(3)–Ag(1)–O(3)
N(2)–C(6)–O(1)
N(4)–C(15)–O(2)
172.64(9)
98.16(9)
89.15(8)
123.5(2)
123.4(2)
and 7). The Ag ions in both compounds show similar linear
geometry and metal–ligand bond lengths ([AgL][NO ]: N–Ag–
3
N = 180.00(1)Њ, Ag–N = 2.185(3) Å; [AgL][CF SO ]: N–Ag–N =
3
3
1
72.64(9)Њ, Ag–N
= 2.167(2) and 2.171(2) Å). Unlike
[
AgL][ClO ], the ligands L in the present compounds are all in
4
the A-conformation, giving the polymer chains a flat zigzag
Ϫ
Ϫ
conformation. The NO3 and CF SO3 ions in the compounds
3
are closely associated with the Ag ion, showing Ag–O distances
of 2.554(8) Å and 2.584(2) Å, respectively. The polymer chains
of the compounds aggregate into 2-D corrugated sheets via
complementary amide hydrogen bonds (Fig. 4b and Table 4).
[
AgL][NO ] (5.095(3) Å) and [AgL][CF SO ] (5.089(3) Å) show
3
3
3
inter-chain Ag–Ag separations similar to the one observed in
AgL][ClO ] (5.143(2) Å). This suggests that the inter-chain
[
4
separation in all of these compounds is governed mainly by the
amide hydrogen bonds. The major difference between the two
compounds is the inter-sheet distance. As shown in Fig. 4b, the
corrugated sheets of [AgL][NO ] and [AgL][CF SO ] stack
3
3
3
Ϫ
Ϫ
along the b axis and the NO3 and CF SO3 ions are located
3
between the slabs. In contrast to [AgL][ClO ], the stacking sheets
4
of the compounds are in complete overlap. The inter-sheet
Ag–Ag separations observed in the three silver compounds
follow the order [AgL][CF SO ] (9.129(3) Å) > [AgL][ClO ]
3
3
4
(
7.456(3) Å) > [AgL][NO ] (6.993(3) Å). Reasonably, the trend
3
Ϫ Ϫ Ϫ
parallels the size of the anions (CF SO > ClO > NO )
Fig. 5 (a) IR (KBr pellet) spectra of (A) [AgL][NO ] as prepared, (B)
3
3
4
3
3
which occupy the space between the sheets.
after exchange with LiClO , (C) [AgL][ClO ] as prepared. (b) IR (KBr
4
4
pellet) spectra of (A) [AgL][CF SO ] as prepared, (B) after exchange
3
3
with LiClO , (C) [AgL][ClO ] as prepared.
4
4
Anion exchange
The anion exchange properties of the three coordination
could not be achieved despite high salt concentration (0.1 M)
and prolonged immersion (two weeks).
Ϫ
Ϫ
Ϫ
polymers [AgL][X] (X = ClO , NO and CF SO ) were
4
3
3
3
investigated using X-ray powder diffraction (XRPD), elemental
analysis and infrared (IR) absorption spectroscopy. Our results
The anion exchange among the three coordination polymers
is highly selective: only the conversion from [AgL][NO3]/
[CF SO ] to [AgL][ClO ] is possible. Selectivity of anion
show that immersion of the crystals of [AgL][NO ] in an
3
3
3
4
6,7
aqueous solution of LiClO for 12 h leads to complete replace-
exchange has been observed in several coordination polymers
4
Ϫ
Ϫ
ment of NO3 with ClO . The IR spectrum of [AgL][NO ]
but its mechanism is not well understood. In some cases, anion
4
3
Ϫ
3
Ϫ1
6
shows an intense NO absorption band at 1384 cm (Fig.
a). However, the absorption band does not appear in the IR
exchange is accompanied by bond formation or dissociation
18
19
5
and a recent study showed that the irreversibility of the
spectrum of the solids obtained after the anion exchange.
exchange of [Ag(bpp)][ClO ] (bpp = 1,3-bis(4-pyridyl)propane)
with PF6 is attributed to the formation of Ag–Ag interactions
4
Ϫ
Ϫ
Instead, new and intense ClO bands show up at 1145–1089
4
Ϫ1 18
cm .
Other peaks of the spectrum remain virtually
in [Ag(bpp)][PF ]. However, it is unlikely to be the reason for
6
unchanged, suggesting the skeletal structure of the compound
remains intact after the exchange process. The peaks of the
XRPD pattern of the exchanged compound are slightly broad-
ened, most probably due to the loss of crystallinity after the
exchange. Nonetheless, the diffraction pattern closely resembles
the experimental or simulated XRPD patterns of [AgL][ClO4]
the selective exchange observed in the present compounds as
they show no obvious difference in bonding. Selectivity of
20
anion exchange has been widely observed in anion resins and
was shown to be governed by the hydration energy (∆G ) of
h
the anion, which is a function of its radius and charge. ∆G of
h
the anions could play an important role in determining the
selectivity. In addition, since the three compounds have differ-
ent crystal structures and packing, inter-conversion of the
compounds must require energy for the structural reorganiza-
(
Fig. 6a). Elemental analysis of the exchanged sample (Table 8)
matches that of [AgL][ClO ]. Analogous to [AgL][NO ],
4
3
Ϫ
Ϫ
CF SO3 ions in [AgL][CF SO ] can be replaced with ClO
4
3
3
3
Ϫ
after suspending crystals of the compound in an aqueous
tion. The exchange of [AgL][NO ] with ClO is favored as ∆G
3
4
h
Ϫ
Ϫ1
Ϫ
solution LiClO for 12 h. The IR spectrum shows the complete
of NO3 (Ϫ300 kJ mol ) is higher than that of ClO (Ϫ205 kJ
4
Ϫ1 Ϫ
4
Ϫ
Ϫ1
disappearance of the CF SO3 band at 1261 cm and the
appearance of intense ClO4 bands at 1145–1089 cm
mol ). Although ∆G of CF SO3 ion is not known, it is
h 3
Ϫ Ϫ
3
Ϫ
Ϫ1
expected to be smaller than those of ClO4 and NO . The
3
Ϫ Ϫ
(
(
Fig. 5b). The XRPD pattern is identical to that of [AgL][ClO4]
Fig. 6b). Elemental analysis (Table 8) also supports complete
difference in ∆G between NO3 and CF SO3 may explain the
h 3
Ϫ
fact that the exchange of [AgL][CF SO ] with NO is not
3
3
3
anion exchange.
While the exchange of [AgL][NO ]/[CF SO ] with ClO is
feasible. Considering the hydration energy of the ions, it
Ϫ
4
Ϫ
Ϫ
is anomalous that CF SO3 cannot replace the anions in
3
3
3
3
Ϫ
facile, the reverse process, [AgL][ClO ] ϩ NO /CF SO
[AgL][ClO ] and [AgL][NO ]. This suggests that there are
4
3
3
3
4
3
Ϫ
[
AgL][NO ]/[CF SO ] ϩ ClO , was not observed even when
factors other than ∆Gh in determining the anion exchange
selectivity. The X-ray crystal structures of the compounds show
that the inter-sheet distance in [AgL][CF SO ] (9.129(3) Å) is
3
3
3
4
crystals of [AgL][ClO ] were immersed in a concentrated
4
solution (0.1 M) of NaNO3 or LiCF SO3 for two weeks.
3
3
3
Similarly the inter-conversion [AgL][NO ] ↔ [AgL][CF SO ]
much longer than the ones in [AgL][ClO ] (7.456(3) Å) and
3
3
3
4
4
566
J. Chem. Soc., Dalton Trans., 2002, 4561–4568

View Article Online
Table 8 Elemental analysis (EA) of [AgL][ClO ] and the products obtained from the anion exchange
4
EA for the product of
the exchange reaction
EA for the product of
the exchange reaction
EA calculated
for [AgL][ClO4]
EA for a sample
of [AgL][ClO4]
Elements
[AgL][NO ] ϩ LiClO (aq)
[AgL][CF SO ] ϩ LiClO (aq)
3
4
3 3 4
C
40.46
4.12
10.57
6.64
40.57
4.09
10.63
6.60
40.37
4.14
10.57
6.52
40.60
4.05
10.48
6.40
H
N
Cl
unusual co-existence of two ligand conformers in the same
coordination polymer chain. In addition, the AgL polymers are
able to zip up via inter-chain amide hydrogen bonds into 2-D
undulating sheets. The anion exchange of the coordination
Ϫ
4
Ϫ
3
Ϫ
3
polymer [AgL][X] (X = ClO , NO and CF SO ) was shown
3
to be selective and the anion exchange selectivity could be
governed by the hydration energy of the anions and the energy
required for structural reorganization.
Acknowledgements
J. H. K. Y. thanks the National University of Singapore
for financial support. We are grateful to Ms Tan Geok Kheng
for her assistance with the X-ray crystal structure
determinations.
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3
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6
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3
3
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h
explanation is that the close packed structure of [AgL][ClO ] is
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4
3
3
2
001, 40, 4422.
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2
6
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