Pre-organisation or a hydrogen bonding mismatch: Silver(I) diamide ligand coordination polymers versus discrete metallo-macrocyclic assemblies

Article abstract of DOI:10.1080/10610278.2012.699052

The investigation of novel motifs to selectively complex anions is an area of considerable importance due to the significant environmental, biological and medicinal roles of anions. The synthesis of discrete metallo-macrocyclic compounds or coordination polymers displaying anion-binding pockets can generate specific anion receptors from relatively simple components. Here, we examine the self-assembly of a series of flexible diamide compounds L1-L5 with silver(I) metal salts. A new diamide ligand, 2,6-[N,N-bis(di-(pyridin-2-yl)methyl) pyridine]-2,6-dicarboxamide (L5), with two chelating di-2-pyridylmethyl donor groups, was also prepared. Compounds L1-L3, lacking the pre-organising effect of a central 2,6-pyridine dicarboxamide core, form 1D coordination polymers {[Ag(L1)(CH₃CN)](PF₆)} n (6), {[Ag(L2)](NO ₃)·(H₂O)]} n (7) and {[AgNO₃(L3)] ·(CH₃OH)]} n (9) which in turn form 2D and 3D hydrogen-bonded networks through orthogonal hydrogen bonding. In one instance, L2 gives rise to a dinuclear metallo-macrocycle in the solid state, [Ag₂(CF ₃CO₂)₂(L2)₂][Ag₂(μ ₂-CF₃CO₂)₂(L2)₂] (8). Both diamide ligands L4 and L5 form dinuclear metallo-macrocycles, [Ag ₂(NO₂)₂(L4)₂] (10) and [Ag ₂(L5)₂](NO₃)₂·2CH ₃OH·2H₂O (11), in solution and in the solid state. Where possible, all compounds were investigated in solution and their solid-state structures were determined using X-ray crystallography. This enabled the effect of competing supramolecular synthons, covalent M-L bonding and hydrogen bonding, to be examined by comparing the solution and solid-state behaviour of each metal-ligand combination.

Full text of DOI:10.1080/10610278.2012.699052

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Pre-organisation or a hydrogen bonding mismatch:
silver(I) diamide ligand coordination polymers versus
discrete metallo-macrocyclic assemblies
Maisara Abdul-Kadir a , Philip R. Clements a , Lyall R. Hanton b , Courtney A. Hollis a
Christopher J. Sumby a
&
a School of Chemistry and Physics, The University of Adelaide , Adelaide , Australia
b Department of Chemistry , University of Otago , Dunedin , New Zealand
Published online: 04 Jul 2012.
To cite this article: Maisara Abdul-Kadir , Philip R. Clements , Lyall R. Hanton , Courtney A. Hollis & Christopher J. Sumby
(2012) Pre-organisation or a hydrogen bonding mismatch: silver(I) diamide ligand coordination polymers versus discrete
metallo-macrocyclic assemblies, Supramolecular Chemistry, 24:8, 627-640, DOI: 10.1080/10610278.2012.699052
To link to this article: http://dx.doi.org/10.1080/10610278.2012.699052
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Supramolecular Chemistry
Vol. 24, No. 8, August 2012, 627–640
Pre-organisation or a hydrogen bonding mismatch: silver(I) diamide ligand coordination
polymers versus discrete metallo-macrocyclic assemblies
Maisara Abdul-Kadira1, Philip R. Clementsa, Lyall R. Hantonb, Courtney A. Hollisa and Christopher J. Sumbya*
b
aSchool of Chemistry and Physics, The University of Adelaide, Adelaide, Australia; Department of Chemistry, University of Otago,
Dunedin, New Zealand
(Received 11 April 2012; final version received 10 May 2012)
The investigation of novel motifs to selectively complex anions is an area of considerable importance due to the significant
environmental, biological and medicinal roles of anions. The synthesis of discrete metallo-macrocyclic compounds or
coordination polymers displaying anion-binding pockets can generate specific anion receptors from relatively simple
components. Here, we examine the self-assembly of a series of flexible diamide compounds L1–L5 with silver(I) metal salts.
A new diamide ligand, 2,6-[N,N0-bis(di-(pyridin-2-yl)methyl)pyridine]-2,6-dicarboxamide (L5), with two chelating di-2-
pyridylmethyl donor groups, was also prepared. Compounds L1–L3, lacking the pre-organising effect of a central 2,6-pyridine
dicarboxamide core, form 1D coordination polymers {[Ag(L1)(CH3CN)](PF6)}n (6), {[Ag(L2)](NO3)·(H2O)]}n (7) and
{[AgNO3(L3)]·(CH3OH)]}n (9) which in turn form 2D and 3D hydrogen-bonded networks through orthogonal hydrogen
bonding. In one instance, L2 gives rise to a dinuclear metallo-macrocycle in the solid state, [Ag2(CF3CO2)2(L2)2][Ag2(m2-
CF3CO2)2(L2)2] (8). Both diamide ligands L4 and L5 form dinuclear metallo-macrocycles, [Ag2(NO2)2(L4)2] (10) and
[Ag2(L5)2](NO3)2·2CH3OH·2H2O (11), in solution and in the solid state. Where possible, all compounds were investigated in
solution and their solid-state structures were determined using X-ray crystallography. This enabled the effect of competing
supramolecular synthons, covalent MZL bonding and hydrogen bonding, to be examined by comparing the solution and
solid-state behaviour of each metal–ligand combination.
Keywords: metallo-supramolecular chemistry; coordination polymers; orthogonal interactions
1. Introduction
species to bind anions can provide a number of advantages
over neutral organic receptors (5, 20–22). Firstly, the anion
binding and encapsulating aspects of a self-assembled
system can be readily explored by combining a number of
relatively simple organic ligands, which display moieties
capable of interacting with anions, with different metal ions;
the structural complexity required to bind an anion of
interest is controlled by the choice of metal ion (26)
(Figure 1(a)). Altering the affinity for a particular anion
could be achieved by substituting in a different, but
structurally similar, ligand (Figure 1(b)) or by changing the
metal ion (26). Furthermore, labile transition metal centres
might allow such receptors to respond to external stimuli,
while the correct choice of metal centre could facilitate
detection as a consequence of optical or electrochemical
responses to binding (5).
The development of novel metallo-supramolecular species
with useful inclusion behaviour for neutral, cationic and
anionic guests has been a focus of much research effort
(1–6). These materials have been studied, for example,
from the perspective of exploring the self-assembly of such
compounds (2), to develop receptors (3, 5), to stabilise
reactive intermediates or products, and for investigating
catalysis within the closed environment of polyhedral
assemblies (3, 4, 6). A related field of the study of anion
binding has undergone a similar, rapid development
(7–12). This birth of anion coordination chemistry (13)
stems from the significant impact that anions have on
environmental, biological and medicinal settings. Strat-
egies to selectively complex anions require the synthesis of
hosts utilising one or more of a toolbox of interactions (11),
including hydrogen bond donor groups (10, 12), p-acidic
heteroarene scaffolds (14–17), cationic groups for electro-
static interactions (11, 18) and Lewis acidic moieties (11).
The investigation of metallo-supramolecular assemblies
(5, 19–22) and coordination polymers (23–25) as anion
receptors and for anion separation or sequestration has also
received attention. In the context of developing such systems
for anion inclusion, the use of a metallo-supramolecular
The incorporation into metallo-supramolecular species
and coordination polymers of ligands containing hydrogen
bond donor groups has been explored (5, 27–31).
In particular, transition metal complexes with pendant
hydrogen bond donor groups have been investigated (5, 32,
33), and metallo-supramolecular assemblies with internal
hydrogen bonding domains have also been reported (20, 21,
26, 34–38). Such self-assembled metallo-supramolecular
*Corresponding author. Email: christopher.sumby@adelaide.edu.au
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2012 Taylor & Francis
http://dx.doi.org/10.1080/10610278.2012.699052
http://www.tandfonline.com

628
M. Abdul-Kadir et al.
A new ligand L5, with chelating di-2-pyridylmethyl donor
(a)
2+
groups, was prepared. Three compounds were studied in
solution by 1D and DOSY NMR spectroscopy and all were
investigated by mass spectrometry, while X-ray crystal-
lography was used to obtain the structures of three new
metallo-macrocyclic complexes and three related coordi-
nation polymers. This enabled the consequences of
competing supramolecular synthons to be investigated by
comparing the solution and solid-state behaviour of each
metal–ligand combination.
M
A–
M
O
N
N
O
N
N
Ag
Ag
NH
NH
HN
HN
N
N
O
O
(b)
M
A–
M
(c)
A–
A–
2. Experimental section
M
M
2.1 General experimental
n
Melting points were measured on a Gallenkamp melting
point apparatus and are uncorrected. Elemental analyses
were performed by the Campbell Microanalytical
Laboratory at the University of Otago. Infrared spectra
were collected on a PerkinElmer Spectrum BX FTIR
spectrometer as KBr discs or on a PerkinElmer 100S FTIR
spectrometer using a universal attenuated total reflectance
(UATR) accessory. NMR spectra were recorded on a
Varian Gemini 300 MHz or a Varian 600 MHz NMR
spectrometer at 238C using a 5 mm probe. 1H NMR spectra
recorded in CDCl3 were referenced relative to the internal
standard Me4Si, while those recorded in DMSO-d6 and
CD3CN were referenced to the solvent peak. Electrospray
(ES) mass spectra were obtained using a Finnigan LCQ
mass spectrometer. Unless otherwise stated, all chemicals
were obtained from commercial sources and used as
received. Dichloromethane was dried by standard
literature procedures (53) and freshly distilled from
calcium hydride. Compounds L1–L4 were prepared
according to the methods described in the literature (47).
Figure 1. Schematic representations of the targeted metallo-
supramolecular assemblies containing (a) one type of ligand or
(b) a mixture of ligands. (c) An alternative, ring-opened
coordination polymer form of structure (a).
species have been employed as anion sensors (39). In this
latter context, we have directed our attention towards two
major types of organic ligands, namely electron-deficient
[3]radialene compounds (40–44) and heterocyclic amide
ligands (45–47), in an effort to generate simple metallo-
supramolecular assemblies and coordination polymers that
encapsulate anions. Flexible bis-amide-containing ligands
(Diagram 1) were chosen to probe the effects of having two
different and potentially competing, orthogonal, supramole-
cular synthons in the same component, namely metal donor
sites and hydrogen bond donor/acceptor moieties. Pudde-
phatt has observed the effect of similar multiple supramo-
lecular synthons in more rigid bis-amide compounds
(48–51) and also for an isomer of L1 (52). In two cases in
the current work, L4 and L5, the hydrogen bond donors are
pre-organised to lessen the ability of the diamide compounds
to form self-assembled hydrogen-bonded tapes (47).
2.2 Synthesis of 2,6-[N,N0-bis(di-(pyridin-2-yl)methyl)
pyridine]-2,6-dicarboxamide hydrate (L5 H2O)
Herein, we investigate the competing syntheses of
discrete self-assembled metallo-macrocyclic compounds
(Figure 1(a)) and coordination polymers (Figure 1(c)) of
the diamide compounds L1–L5 with silver(I) metal salts.
2,6-Pyridinedicarboxylic acid (1.06 g, 5.85 mmol) was
suspended in dichloromethane (20 ml). Freshly distilled
SOCl2 (5 ml) and dry N,N0-dimethylformamide (DMF)
X
X
N
N
Y
Y
H
N
H
N
H
N
H
N
N
O
O
O
O
O
O
L4
X = N, Y = CH L1
X = CH, Y = N L2
H
N
O
H
N
N
N
N
N
N
H
H
N
N
N
N
O
L3
L5
Diagram 1. The diamide ligands used in this study.

Supramolecular Chemistry
629
(100 ml) were added and the reaction mixture was heated at
reflux for 1 h. After cooling to room temperature, the
solvent was removed in vacuo to give a white solid that
was dried under high vacuum for 30 min. The solid was re-
dissolved in CH2Cl2 (40 ml), di-(2-pyridyl)methylamine
(0.58 g, 6.2 mmol) and NEt3 (0.81 ml, 5.9 mmol) were
added and the solution was heated at reflux for 24 h. The
solvent was removed in vacuo to give a brown oil, and the
residue was redissolved with dichloromethane (100 ml),
washed with saturated sodium bicarbonate solution
(2 £ 100 ml) and chlorinated solvent layer dried over
magnesium sulfate. The residue was purified by column
chromatography, eluting with a methanol:dichloromethane
(1:9) solvent system, to give L5·H2O as an off-white solid
(1.70 g, 51%). Mp 180–1838C. Anal found. C, 67.3; H,
4.7; N, 18.8. C29H25N7O3 requires C, 67.0; H, 4.9; N,
2256 (w, CuN stretch), 1659 (s, CvO stretch), 1629, 1592,
1543, 1352, 1298, 842 (s, PZF stretch), 709, 560.
2.3.2 {[Ag(L2)](NO3)·(H2O)]}n (7)
A solution of L2 (35.1 mg, 0.101 mmol) in warm methanol
(4 ml) was combined with an acetonitrile solution (2 ml) of
AgNO3 (17.1 mg, 0.101 mmol). Slow evaporation over a
period of 2–3 weeks gave large colourless blocks. The
solutionwas decanted fromthecrystals, whichwerewashed
with acetone and then with diethyl ether and dried (25.5 mg,
49%). m/z (ES-MS, CH3CN) 453.1 ([107Ag(L2)]þ, 73%),
455.1 ([109Ag(L2)]þ, 66%), 798.6 ([107Ag(L2)2]þ, 75%),
800.6 ([109Ag(L2)2]þ, 60%), 967.5 ([107Ag2(NO3)(L2)2]þ,
6%), 969.6 ([107Ag109Ag(NO3)(L2)2]þ, 7%), 971.6
([109Ag2(NO3)(L2)2]þ, 5%). Found: C, 47.0; H, 3.6; N,
13.6. C20H18N5O5Ag requires C, 46.5; H, 3.5; N, 13.6%.
SelectedIR bands (KBr disc, cm21): 3294 (s, NZH stretch),
3066, 2925 (m, CZH stretches), 1655 (s, CvO stretch),
1611, 1549, 1425, 1383, 1315 (s, NZO stretches), 851, 693.
1
18.8%. H NMR (300 MHz; CDCl3; Me4Si) d 6.54 (2H,
CH), 7.14 (4H, m, pyH50), 7.60 (8H, m, pyH30, pyH40),
8.02 (1H, t, pyH4), 8.37 (2H, d, pyH3 and pyH5), 8.50
(4H, 2d, pyH60) and 10.32 (2H, d, NH); (600 MHz;
DMSO-d6) d 6.43 (2H, d, CH), 7.29 (4H, dd, pyH50), 7.62
(4H, d, pyH30), 7.78 (4H, t, pyH40), 8.25 (3H, m, pyH3,
pyH4, pyH5), 8.45 (4H, d, pyH60), 8.50 (4H, 2d, pyH60)
and 10.07 (2H, d, NH). 13C (75.1 MHz; CDCl3; Me4Si)
d ¼ 177.98, 149.57, 141.11, 137.19, 122.74, 122.31,
120.23, 103.87, 59.82. m/z (ES-MS) 501.6, (MHþ, 15%),
523.4, (MNaþ, 40%). Selected IR bands (KBr disc, cm21):
3378 (s), 3354 (s), 1724 (m), 1671 (s), 1587 (m), 1503 (s),
1436 (s) and 997 (s). Crystals of L5 were obtained by slow
evaporation of a methanol–acetonitrile solution.
2.3.3 {[Ag2(CF3CO2)2(L2)2][Ag2(m2-CF3CO2)2(L2)2]} (8)
A methanol solution (4 ml) of L2 (34.9 mg, 0.100 mmol)
was combined with an acetonitrile solution (4 ml) of
AgCF3CO2 (22.6 mg, 0.100 mmol). Slow evaporation over
a period of 1 week gave large colourless blocks. The
solutionwas decanted fromthecrystals, whichwerewashed
with acetone and then with diethyl ether and dried (42.4 mg,
75%). m/z (ES-MS, CH3CN) 453.1 ([107Ag(L2)]þ, 69%),
455.1 ([109Ag(L2)]þ, 61%), 493.3 ([107Ag(L2)(CH3CN)]þ,
14%), 495.4 ([109Ag(L2)(CH3CN)]þ, 9%), 672.6
([107Ag(CF3COO)(L2 þ Hþ)]þ, 18%), 674.6 ([109Ag(CF3-
COO)(L2 þ Hþ)]þ, 31%), 798.6 ([107Ag(L2)2]þ, 70%),
800.6 ([109Ag(L2)2]þ, 60%), 904.8 ([107Ag2(L2)2]þ, 5%),
906.8 ([107Ag109Ag(L2)2]þ, 9%), 908.8 ([109Ag2(L2)2]þ,
5%), 1018.5 ([107Ag2(CF3COO)(L2)2]þ, 15%), 969.6
([107Ag109Ag(CF3COO)(L2)2]þ, 31%), 971.6 ([109Ag2(-
CF3COO)(L2)2]þ, 15%). Found: C, 46.9; H, 3.3; N 9.9.
C22H18N4O4F3Ag requires C, 46.7; H, 3.2; N, 9.9%.
Selected IR bands (UATR disc, cm21): 3307 (m, NZH
stretch), 3074 (w, CZH stretch), 1738 (w, CvO stretch),
1643 (s, CvO stretch), 1541, 1421, 1184, 1127.
2.3 Syntheses of Ag(I) compounds
2.3.1 {[Ag(L1)(CH3CN)](PF6)}n (6)
A solution of L1 (35.6 mg, 0.103 mmol) in methanol (3 ml)
was combined with an acetonitrile solution (1.5 ml) of
AgPF6 (25.9 mg, 0.102 mmol). Slow evaporation over a
period of 2–3 weeks gave large colourless needles that had
grown as clumps. The crystals were collected by filtration,
washed with acetone and then with diethyl ether and dried
under suction (30.0 mg, 46%). 1H NMR (600 MHz,
CD3CN) d 4.56, (d, 4H, CH2), 7.25 (d, 2H, aryl H4 and
H6), 7.31 (1H, t, aryl H5), 7.38 (1H, s, aryl H2), 7.47 (2H,
dd, pyH5), 7.85 (bs, 2H, NH), 8.16 (2H, d, pyH4), 8.67 (2H,
d, pyH6) and 8.96 (2H, s, pyH2). m/z (ES-MS, CH3CN)
453.1 ([107Ag(L1)]þ, 67%), 455.1 ([109Ag(L1)]þ, 61%),
798.7 ([107Ag(L1)2]þ, 100%), 800.7 ([109Ag(L1)2]þ, 40%),
904.9 ([107Ag2(L1)2]þ, 5%), 906.9 ([107Ag109Ag(L1)2]þ,
2.3.4 {[AgNO3(L3)]·(CH3OH)]}n (9)
A solution of L3 (17.7 mg, 0.051 mmol) in methanol (3 ml)
was combined with an acetonitrile solution (1 ml) of AgPF6
(8.6 mg, 0.051 mmol). Slow evaporation over aperiod of 2–
3 weeks gave colourless rods. The crystals of 9 were
collected by filtration, washed with acetone and then with
diethyl ether and dried under suction (11.0 mg, 39%). m/z
(ES-MS, CH3CN) 453.1 ([107Ag(L3)]þ, 100%), 455.1
([109Ag(L3)]þ, 90%), 798.6 ([107Ag(L3)2]þ, 86%), 800.6
([109Ag(L2)2]þ, 75%), 967.4 ([107Ag2(NO3)(L3)2]þ, 7%),
8%),
908.8
([109Ag2(L1)2]þ,
5%),
1050.7
([107Ag2(PF6)(L1)2]þ, 24%), 1052.7 ([107Ag109Ag(PF6)(-
L1)2]þ, 42%), 1054.7 ([109Ag2(PF6)(L1)2]þ, 21%). Found:
C, 41.4; H, 3.4; N, 10.8. C22H21N5O2F6PAg requires C,
41.3; H, 3.3; N, 10.9%. Selected IR bands (KBr disc, cm21):
3268 (s, NZH stretch), 3052, 2920 (m, CZH stretches),

630
M. Abdul-Kadir et al.
969.6 ([107Ag109Ag(NO3)(L3)2]þ, 9%), 971.6 ([109Ag2
(NO3)(L3)2]þ, 5%). Found: C, 46.4; H, 3.9; N 13.2.
C21H22N5O6Ag requires C, 46.0; H, 4.1; N 12.8%. Selected
IR bands (KBr disc, cm21): 3355 (s, NZH stretch), 3062,
2948 (m, CZH stretches), 1635 (s, CvO stretch), 1593,
1540, 1384 (s, NZO stretch), 1300, 755, 703.
2.3.6 [Ag2(L5)2](NO3)2·2(CH3OH)·2H2O (11)
AgNO3 (0.046 g, 0.27 mmol) was dissolved in methanol
(5 ml), heated for a few minutes, before being added
dropwise to a solution of L5 (0.068 g, 0.135 mmol) which
was dissolved in hot methanol–acetonitrile (15 ml). The
resulting solution was heated for 45 min and left to
evaporate at room temperature. After 1 month, the solution
afforded [Ag2(L5)2](NO3)2 as colourless rod-shaped
1
2.3.5 [Ag2(NO2)2(L4)2] (10)
crystals (20.0 mg, 21%). H NMR (600 MHz, DMSO-d6)
d 6.48 (2H, d, CH), 7.35 (4H, dd, pyH50), 7.72 (4H, d,
pyH30), 7.85 (4H, t, pyH40), 8.22 (3H, m, pyH3, pyH4,
pyH5), 8.48 (4H, d, pyH60), 8.50 (4H, 2d, pyH60) and
10.01 (2H, d, NH). m/z (ES-MS, DMSO/methanol) 608.1
([107Ag(L5)]þ, 100%), 610.1 ([109Ag(L5)]þ, 95%), 713.9
([107Ag2(L5ZH)]þ, 9%), 715.9 ([107Ag109Ag(L5ZH)]þ,
18%), 717.9 ([109Ag2(L5ZH)]þ, 8%), 1214.6 ([107Ag2(-
L5)(L5ZH)]þ, 3%), 1216.8 ([107Ag109Ag(L5)(L5ZH)]þ,
5%), 1218.8 ([109Ag2(L5)(L5ZH)]þ, 3%). Selected IR
bands (UATR, cm21): 3256 (w), 1654 (m), 1598 (m), 1527
(m), 1382 (s, NZO stretch), 1155 (m).
A solution of L4 (17.7 mg, 0.051 mmol) in methanol (2 ml)
was combined with an acetonitrile solution (2 ml) of
AgNO2 (8.2 mg, 0.053 mmol). Slow evaporation over a
period of 2–3 weeks gave colourless needles. The crystals
were collected by filtration, washed with diethyl ether and
1
dried under suction (19.5 mg, 76%). H NMR (600 MHz,
CD3CN) d 4.67, (d, 4H, CH2), 7.36 (dd, 2H, pyH50), 7.80
(2H, d, pyH40), 8.11 (1H, t, pyH4), 8.21 (1H, d, pyH3 or
pyH5), 8.29 (1H, d, pyH3 or pyH5), 8.43 (2H, d, pyH60),
8.61 (2H, s, pyH20) and 9.07 (2H, bs, NH). m/z (ES-MS,
CH3CN) 454.2 ([107Ag(L4)]þ, 95%), 456.1 ([109Ag(L4)]þ,
83%), 800.6 ([107Ag(L4)2]þ, 100%), 802.7 ([109Ag(L4)2]þ,
86%), 906.7 ([107Ag2(L4)(L4ZH)]þ, 2%), 908.7
([107Ag109Ag(L4)(L4ZH)]þ, 4%), 910.8 ([109Ag2(-
L4)(L4ZH)]þ, 5%). Found: C, 45.7; H, 3.5; N, 16.8.
C38H34N12O8Ag2 requires C, 45.5; H, 3.4; N, 16.8%.
Selected IR bands (UATR, cm21): 3345, 3267 (w, NZH
stretches), 3047 (w, CZH stretch), 1673 (s, CvO stretch),
1530, 1207, 1189, 1166, 709.
2.4 X-ray crystallography
In general, crystals were mounted under oil onto a plastic
loop and X-ray data collected at low temperatures with
˚
Cu-Ka (l ¼ 1.5418 A, L5; Table 1) or Mo-Ka radiation
˚
(l ¼ 0.71073 A, 6–11; Tables 1 and 2). Data were
collected on (i) a Bruker Apex II CCD diffractometer or
Table 1. Crystal data and X-ray experimental data for L5–L8.
Compound
L5
L6
L7
L8
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C29H23N7O2
501.54
150(2)
Monoclinic
P21/c
11.0268(4)
14.7568(5)
15.3369(6)
105.767(4)
2401.73(15)
4
1.387
0.740
1048
C22H21AgF6N5O2P
640.28
89(2)
Monoclinic
P21/c
9.5304(10)
15.3420(19)
16.846(2)
99.527(6)
2429.1(5)
4
1.751
0.973
1280
C20H20AgN5O6
534.28
89(2)
Orthorhombic
P212121
8.0073(5)
9.7288(5)
25.8930(16)
C22H18AgF3N4O4
567.27
89(2)
Monoclinic
C2/m
16.128(3)
28.894(6)
11.672(2)
125.381(7)
4434.6(15)
8
1.699
0.972
2272
˚
a (A)
˚
b (A)
˚
c (A)
b (8)
Volume (A )
3
˚
2017.1(2)
4
1.759
1.050
1080
0.18 £ 0.16 £ 0.05
2.24–32.32
15,525
Z
Dcalc (mg/m3)
Absorption coefficient (mm21
F(0 0 0)
)
Crystal size (mm3)
Theta range for data (8)
Reflections collected
0.24 £ 0.15 £ 0.06
9.51–71.33
12,405
0.45 £ 0.09 £ 0.06
1.81–27.00
26,786
0.68 £ 0.40 £ 0.05
1.41–27.67
25,788
Independent reflections [R(int)]
Completeness to theta max (%)
Observed reflections [I . 2s(I)]
Data/restraints/parameters
Goodness of fit on F 2
4526 [0.0430]
96.8
2792
4526/0/343
0.784
0.0345
5298 [0.0279]
99.9
4847
5298/1/352
1.042
0.0349
6824 [0.0347]
96.8
5820
6824/0/289
1.026
0.0390
0.0897
0.885 and 20.808
20.04(2)
5136 [0.0282]
98.2
4614
5136/0/415
1.134
0.0440
R1 [I . 2s(I)]
wR2 (all data)
0.0689
0.161 and 20.143
0.0853
1.216 and 21.037
0.1286
1.298 and 21.106
23
˚
Largest diff. peak and hole (e.A
Absolute structure parameter
)

Supramolecular Chemistry
Table 2. Crystal data and X-ray experimental data for 9–11.
631
Compound
9
10
11
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C21H22AgN5O6
548.31
89(2)
Triclinic
P 2 1
9.2220(9)
9.5374(9)
13.5591(13)
75.528(4)
87.210(5)
67.492(4)
1065.30(18)
2
1.709
0.997
556
0.21 £ 0.16 £ 0.04
1.55–27.79
21,188
C19H17AgN6O4
501.26
89(2)
Triclinic
P 2 1
8.0086(2)
9.3538(2)
13.5170(3)
100.812(1)
100.476(1)
99.552(1)
956.81(4)
2
1.740
1.095
504
0.28 £ 0.08 £ 0.03
1.57–27.00
16,659
C60H58Ag2N16O14
1442.96
150(2)
Orthorhombic
Pbca
10.0396(3)
23.0612(8)
25.4876(7)
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
Volume (A )
Z
5901.0(3)
4
1.624
0.747
2944
0.15 £ 0.10 £ 0.07
2.35–29.66
29,891
Dcalc (mg/m3)
Absorption coefficient (mm21
F(0 0 0)
)
Crystal size (mm3)
Theta range for data (8)
Reflections collected
Independent reflections [R(int)]
Completeness to theta max (%)
Observed reflections [I . 2s(I)]
Data/restraints/parameters
Goodness of fit on F 2
4906 [0.0424]
97.2
4578
4906/0/300
1.051
0.0446
4168 [0.0255]
100.0
3871
4168/0/271
1.086
0.0194
7666 [0.0553]
100.0
4365
7666/2/425
0.877
0.0394
R1 [I . 2s(I)]
wR2 (all data)
0.1367
3.209 and 21.445
0.0518
0.370 and 20.268
0.0772
1.181 and 20.683
23
˚
Largest diff. peak and hole (e.A
)
(ii) an Oxford Diffraction X-Calibur diffractometer. Data
were corrected for polarisation and Lorenztian effects,
and absorption corrections applied using a multi-scan
method. Structures were solved by direct methods using
SHELXS-97 (54) and refined by full-matrix least squares
on F 2 by SHELXL-97 (55). Unless otherwise stated, all
non-hydrogen atoms were refined anisotropically and
hydrogen atoms were included as invariants at geome-
trically estimated positions. Diagrams were generated
using the program X-Seed (56) as an interface to POV-
Ray (57). Additional refinement details for individual
structures are described below. CCDC numbers 873856–
873862 contain the full crystal data for these structures.
These data can be obtained from the Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.
ac.uk/data_request/cif.
Compound 11: Two DFIX commands were used to
maintain chemically sensible OZH bond lengths for the
water solvate molecule.
3. Results and discussion
3.1 Ligand synthesis
Following the approach previously used to prepare related
diamide ligands (47, 58, 59), di-(2-pyridyl)methylamine,
which was synthesised in two steps using literature
procedures (60–62), was reacted with 2,6-dimethylpyr-
idine dichloride to give L5 as a cream solid in ca 51% yield.
Elemental analysis suggested that this product was obtained
as the hydrate, L5·H2O. This compound was characterised
1
by H NMR spectroscopy with the expected number of
resonances for a symmetrical di-substituted derivative. The
NH signal was observed significantly downfield at
10.32 ppm and the IR spectra of L5 exhibit several
characteristic strong bands, including a CvO stretching at
approximately 1671 cm21, a strong band at 3354 cm21 that
is attributed to the NZH stretching vibration, and a band at
1503 cm21 that is due to aromatic CvN stretches. ESI-MS,
conducted in a mixture of methanol–acetonitrile solution,
showed the expected positively charged ion of [L5 þ H]þ at
m/z 501.6 (40%). Compound L5 was recrystallised by
dissolution in hot methanol–acetonitrile and on standing at
room temperature for 5 days yielded colourless crystals
2.5 Additional refinement details
Compound 6: The hexafluorophosphate anion in 6 is
disordered over two positions (77:23), and a DFIX
restraint was used to maintain a sensible geometry for
Part 2.
Compound 8: The pendant pyridyl rings of the two
half-ligand moieties in the asymmetric unit are disordered
over two positions (with approximately 50% occupancy).
Both trifluoroacetate anions are disordered across mirror
planes in the structure.

632
M. Abdul-Kadir et al.
3.2 Coordination chemistry
Compounds L1–L5 are all ditopic ligands that, under
appropriate conditions, would be expected to form discrete
metallo-macrocycles capable of encapsulating anions in
the cavity formed within the macrocyclic structure.
However, due to their inherent flexibility, it is also
possible that coordination polymers may form. To
understand the types of structures that can be obtained
with compounds L1–L5, they were reacted with a range of
silver salts (AgX where X ¼ NO2, NO3, CF3COO and
PF6). This yielded crystalline samples of six silver
complexes displaying either the desired discrete metallo-
macrocyclic structures or 1D coordination polymers
(Scheme 1), the latter of which are, in turn, assembled
into 2D and 3D hydrogen-bonded networks. However, it
was suspected that all compounds may form discrete
structures in solution, and thus attempts were made to
characterise all materials in solution by a combination of
1H NMR spectroscopy, diffusion-ordered spectroscopy
and mass spectrometry. In the solid state, all compounds
were studied by IR spectroscopy, elemental analysis and
single-crystal X-ray diffraction.
Figure 2. A view of the structure of compound L5. The weak
pre-organising hydrogen bonds involving the 2,6-pyridine
dicarboxamide core are shown but the hydrogen bonding
involving the pendant pyridine rings is not shown.
with a plate morphology which were suitable for structure
analysis using single crystal X-ray crystallography.
Compound L5 crystallises in the monoclinic space
group P21/c, with one complete molecule in the
asymmetric unit. In the crystal structure, the two di-2-
pyridylmethyl arms have quite different arrangements: one
arm has the two 2-substituted pyridine rings directed either
side of the plane of the 2,6-pyridine dicarboxamide core,
while the second arm has one pyridine ring almost in the
plane of the 2,6-pyridine dicarboxamide core and the other
ring nearly perpendicular to the 2,6-pyridine dicarbox-
amide core. In the case of the second di-2-pyridylmethyl
arm, the in-plane pyridine ring (N31) is involved in a weak
3.2.1 Synthesis of 1D coordination polymers
Reaction of AgPF6 with L1 in a mixture of acetonitrile and
methanol followed by slow evaporation of the solvent
mixture yielded colourless block-shaped crystals of
{[Ag(L1)(CH3CN)](PF6)}n (6) in moderate 46% yield.
In the solid state, the formulation of 6 was supported by
elemental analysis and the observation of CuN triple
bond stretch at 2256 cm21 and a PZF stretch at 842 cm21
Similarly, 1D coordination polymer of L2,
.
a
{[Ag(L2)](NO3)·(H2O)]}n (7), was also obtained by the
reaction of this compound with AgNO3 in 49% yield. This
formulation for the bulk sample was confirmed by IR
spectroscopy which revealed NZO stretches of the nitrate
at 1383 cm21 and a good match between the calculated
and the found C, H and N values. Finally, reaction of L3
with AgNO3 gave another 1D coordination polymer,
{[Ag(L3)](NO3)·(CH3OH)]}n (9), which was also structu-
rally characterised by X-ray crystallography. The IR
spectrum revealed NZO stretches of the nitrate anion at
1384 cm21 and NZH, CZH and CvO stretches consistent
with the ligand at 3355, 2948 and 1635 cm21, respectively.
To ascertain the behaviour of these compounds in
solution, we investigated the 1H and DOSY NMR
spectroscopy and electrospray mass spectrometry (ES-
MS) of all three compounds. ES-MS for 6 and 7 revealed
molecular ions [Ag2(X)(L)2]þ (where X ¼ anion) that
were consistent with the formation of either a [2 þ 2]
metallo-macrocycle or an oligomeric structure in solution.
The corresponding molecular ions were not observed for
compound 9, as L3 has a more divergent structure,
˚
˚
hydrogen bond (NZH· · ·N: d ¼ 2.268 A, D ¼ 2.638 A,
angleNHN ¼ 105.148) with one of the NH donors of the
2,6-pyridine dicarboxamide core. The other di-2-pyridyl-
methyl arm (N41) makes a similar weak electrostatic
hydrogen bond with the other amide NH donor despite
being twisted out of the plane. In a similar manner to the
other diamide compounds investigated (47, 58, 59), the
structure of compound L5 demonstrates that the 2,6-
pyridine dicarboxamide core pre-organises the amide
moieties by weak intramolecular hydrogen bonding
˚
interactions (NZH· · ·N: d ¼ 2.241 and 2.312 A,
˚
D ¼ 2.663 and 2.699 A, angleNHN ¼ 109.128 and
109.658; Figure 2). In solution, the di-2-pyridylmethyl
moieties are able to freely rotate about the CZN single
bond to allow various coordination modes for L5. Aside
from the intramolecular hydrogen bonding involving the
pre-organised amide moiety and one of the pendant
pyridine arms, the packing diagram does not reveal any
other significant hydrogen bonding interactions.

Supramolecular Chemistry
633
NCCH3
Ag
N
N
AgPF6
H
N
H
N
N
O
N
H
N
NH
O
O
PF6
L1
O
6
n
Ag
AgNO3
N
N
H
N
H
N
N
N
O
O
L2
NH
HN
O
O
AgCF3COO
NO3.H2O
n
CF3
7
O
O
O
N
N
Ag
N
O
O
O
N
Ag
N
O
NH
NH
HN
NH
HN
CF3
O
O
O
O
+
F3C
HN
NH
HN
O
Ag
O
N
O
N
Ag
N
O
O
8a
8b
CF3
O
Ag ONO2
N
O
AgNO3
N
H
H
N
N
H
N
N
H
N
O
N
L3
O
CH3OH
n
9
O
N
O
N
Ag
NH
HN
HN
N
N
AgNO2
ONO
H
N
H
N
N
N
ONO
Ag
N
NH
O
O
O
N
N
O
L4
10
N
N
N
N
O
O
Ag
H
N
H
N
NH
HN
AgNO3
N
N
N
N
N
O
O
N
N
NH
O
HN
Ag
O
N
N
N
L5
N
(NO3)2.2CH3OH.2H2O
11
Scheme 1. The synthesis of discrete metallo-macrocycles and coordination polymers from L1–L5.

634
M. Abdul-Kadir et al.
2+
O
O
N
N
O
O
N
N
Ag
Ag
NH
NH
HN
HN
Diagram 2. A generic representation of a dinuclear metallo-
macrocycle.
Figure 3. (a) A view of the 1D zigzag coordination polymer in
the structure of {[Ag(L1)(CH3CN)](PF6)}n. (b) The 2D
hydrogen-bonded sheet formed from the 1D zigzag
coordination polymer 6. The 2D network lies in the ab-plane of
the unit cell.
although peaks corresponding to [Ag(L)2]þ and [AgL]þ
were observed.
Compound 6 was soluble at suitable concentrations for
NMR spectroscopy in CD3CN, such solutions could be
prepared by mixing appropriate ratios of AgPF6 and L1 or
re-dissolving crystals of 6. Limited coordination-induced
shifts (CIS) were observed for this compound in CD3CN,
whichcombinedwiththenumberofchemicalenvironments
observedfor the protons indicated that the product observed
in solution was twofold symmetric. Despite the minimal
CIS, DOSY revealed that the species present in solution had
a diffusion coefficient of 4.95 ^ 0.05 £ 10210 m2/s; the
diffusion coefficient of L1 under the same conditions was
6.73 ^ 0.06 £ 10210 m2/s. As experimental diffusion rates
obtained for two different spherical molecules in the same
environment have been shown to be inversely proportional
to the ratio of their radii (63–67), this indicates that the
species formed from AgNO3 and L1 is larger than the
original ligand. Such analysis has been utilised to estimate
the relative size of a molecule from a comparison of the
diffusion rates and is more readily applied than establishing
a Stokes–Einstein relation for this type of system (68). The
calculated ratio D6/DL1 is 0.74, which is in agreement with
the theoretical ratio of 0.72–0.75 expected for a dimeric
structure (Diagram 2) (63–65, 68). Unfortunately, despite
using both approaches to prepare NMR solutions,
compounds 7 and 9 were not soluble in CD3CN at suitable
concentrations nor appear to be maintained in dimethyl-
sulfoxide (DMSO) solution, and thus the corresponding
analysis could not be completed.
structure consists of a simple 1D zigzag coordination
polymer that is hydrogen bonded to adjacent polymers
through NZH· · ·OvC hydrogen bonds. Unlike the syn or
‘U’-shaped structure of L1 in the solid state (46), here L1
adopts an alternate conformation in this structure and
connects two T-shaped, but two-connecting silver cations
˚
(AgZNpy bond distances 2.167(2) and 2.178(2) A;
˚
AgZNCCH3 distance 2.450(3) A) to create a zigzag motif
(Figure 3(a)). These 1D coordination polymers (which
extendalongthe b-axisoftheunitcell)arehydrogenbonded
to adjacent polymers to create a hybrid coordination and
hydrogen-bonded 2D network (Figure 3(b)) that has (4,4)-
connectivity. The NZH· · ·OvC amide hydrogen bonding
˚
interactions are typical (NZH· · ·O: d ¼ 2.011 and 2.088 A,
˚
D ¼ 2.857 and 2.932 A); thus, within the 2D network
the ligand acts as a four-connecting centre. The self-
complementary NZH· · ·OvC amide hydrogen bonds are
rigorously maintained in this structure, preventing any
interactions with anionic (or otherwise) guests.
Crystals of {[Ag(L2)](NO3)·(H2O)}n (7) were also
obtained by slow evaporation, as colourless needles. The
compound crystallises in the chiral orthorhombic space
group P212121, with one molecule of L2, a silver atom, a
weakly coordinated nitrate anion and a solvate water
molecule in the asymmetric unit. In this structure, the ligand
adopts a ‘U’-shaped conformation not dissimilar to that
observedinthesolidstateforL2(46). However, asobserved
in the structure of L1, the amide hydrogen bond donors are
not directed into the cavity that is formed. Each molecule of
the ligand coordinates to two silver atoms leading to the
formation of a 1D coordination polymer. The polymeric
structure is a helix (Figure 4(a)) that, whenviewed down the
helical axis (b-axis), has been contracted in one dimension
and extended in the other (Figure 4(b)). The silver atoms
have a linear geometry and are coordinated by two pyridyl
Therefore, it appears that in solution compound 6 forms
an [Ag2(L1)2] complex (Diagram 2) while it is unclear as to
whether compounds 7 and 9 form oligomeric precursors to
their solid-state structures or discrete metallo-macrocyclic
entities. Nonetheless, in the solid state, all three compounds
form 1D coordination polymers that are self-assembled into
2D and 3D hydrogen-bonded networks. {[Ag(L1)(CH3-
CN)](PF6)}n, compound 6, crystallises in the monoclinic
space group P21/c, with an asymmetric unit containing one
molecule of L1, a silver atom, a coordinated acetonitrile
solvent molecule and a hexafluorophosphate anion (with
minor disorder of the equatorial fluorine atoms). The
˚
donors (2.188(2) and 2.199(2) A) of two different ligands; a
nitrate makes a long contact with the silver atoms through a
˚
single oxygen atom (2.745(4) A). A complete turn of the

Supramolecular Chemistry
635
Figure 6. (a) A view of the 1D zigzag coordination polymer in
the crystal structure of {[AgNO3(L3)]·(CH3OH)}n (9). (b) The
2D hydrogen-bonded network in 9. Individual chains are shown
in different colours.
Figure 4. Two views of the helical 1D coordination polymer in
the structure of 7: (a) a side-on view of the helical polymer and
(b) a representation looking down the helical axis.
give a 1D coordination polymer (Figure 6(a)). The AgZN
˚
distancesare 2.159(3)and2.164(3) A, while theAgZONO2
helix, two repeating units of the polymer, equates to the
˚
length of the b-axis cell length of 9.73(1) A.
˚
distance is comparatively longer at 2.681(4) A. The 1D
coordination polymer has a zigzag structure, akin to that
observed for L1 in the structure of 6, where the nitrate anion
coordinates in a similar manner to the acetonitrile solvate
molecule in the previous structure. Despite L3 having a
para-substitution pattern in the central xylene ring, the Ag–
˚
Ag separation is shorter (16.00 A) than observed in 6 where
the xylene is meta-substituted.
In a similar manner to the structure of 6, the amide
functional groups of L2 are involved in inter-polymer
hydrogen bonding. Each helix is interdigitated by four
other helices which form typical hydrogen bonds with one
of the four amide functional groups in a repeating unit of
the helix. Two views of this interdigitation are shown in
Figure 5(a),(b). This bundling of the helices by hydrogen
bonding leads to an apparently robust 3D M–L covalent
and hydrogen-bonded network structure. Helical hydro-
gen-bonded chains of nitrate anions and water solvate
molecules extend along the b-axis of the unit cell in the
small channels, adjacent to the metal centre and between
the coordination polymers (Figure 5(c)).
Onceagain, the 1D coordination polymersare hydrogen
bonded to give a 2D network structure (Figure 6(b)). Within
the 2D network, the 1D coordination polymers are stacked
almost directly on top of one another with the amide
functionality twisted out of the plane of the coordination
polymer. The hydrogen bonding distances between
adjacent polymers are reasonably short (NZH· · ·O:
˚
˚
Complex {[AgNO3(L3)]·(CH3OH)}n (9) crystallises in
the triclinic space group P 2 1 with one silver atom, one
nitrate anion, a methanol solvate molecule and two half-
molecules of the ligand in the asymmetric unit. The
centroids of the ligands lie on centres of inversion. Each
ligand coordinates two different T-shaped silver atoms,
which in turn are coordinated by two ligand molecules to
d ¼ 1.994 and 2.073 A, D ¼ 2.774 and 2.889 A). Each
ligand molecule is hydrogen bonded to two other molecules
of L3 in adjacent coordination polymers and coordinated to
two further molecules by the silver atoms. Thus, L3 is a 4-
connecting centre in this structure resulting in a (4,4)-
connected network structure as observed for 6. The packing
within the crystal is completed by close packing of the 2D
Figure 5. (a, b) Two views of the interdigitated bundles of helices in the structure of {[Ag(L2)](NO3)·(H2O)}n. (c) The helical
hydrogen-bonded chains of nitrate anions and water solvate molecules in the channels of 7.

636
M. Abdul-Kadir et al.
networks with the coordinated nitrate anions in channels
between the 2D layers. The methanol molecules, also
located in these channels, are hydrogen bonded to an
oxygen atom of an adjacent nitrate anion (OZH· · ·O:
molecular ions were observed that correspond to [Ag2(-
L5)(L5ZH)]þ. The 1H NMR spectra of compounds 10 in
CD3CN and 11 in DMSO-d6 indicated that the complexes
remained intact in solution, with small CIS at the pyridyl
protons being observed upon coordination to a silver atom.
Once again, despite the minimal CIS observed for 10
and 11, DOSY was employed to examine the complexes in
solution. In CD3CN, 10 had a diffusion coefficient of
4.65 ^ 0.06 £ 10210 m2/s, while the diffusion coefficient
of L4 under the same conditions was 5.69 ^ 0.05 £
10210 m2/s. The metallo-macrocycle 10 has a very similar
diffusion rate and thus size to the solution species 6
(4.95 ^ 0.05 £ 10210 m2/s), although interestingly the
diffusion rates for L1 and L4 differ more significantly.
ThisperhapspointstothedifferingconformationsofL1and
L4 in solution as comparing the calculated ratio of the
˚
˚
d ¼ 2.024 A, D ¼ 2.834 A).
Despite forming a range of solution products, reaction of
L1, L2 and L3 with silver(I) salts all form 1D coordination
polymers that are self-assembled into 2D and 3D hydrogen-
bonded networks in the solid state. It appears that in solution
the competitive environment of the polar, hydrogen bond
accepting solvents enables the formation of small oligomeric
and metallo-macrocyclic structures, as confirmed in the case
of 6, yet as the solid-state structures form, ringopening of the
metallo-macrocycles can occur to generate the 1D
coordination polymers and to maximise the complementary
hydrogen bonding between the orthogonal amide moieties.
Such ring-opening polymerisation of metallo-macrocycles
has been observed for other systems (42, 43, 48–52, 69, 70).
In this case, the ring-opening polymerisation is favoured by
the formation of complementary hydrogen-bonded tapes of
the 1D coordination polymers.
diffusion rates of the complex versus the ligand, D10/DL4
,
gave a value of 0.82. This is a little outside the theoretical
ratio of 0.72–0.75 expected for a dimeric structure (63–65,
68), perhaps as a consequence of the slower diffusion rate of
L4, butstill provides qualified support for the formation of a
dinuclear metallo-macrocycle. The theoretical ratios of the
diffusion constants of 0.72–0.75 are calculated for hard
sphere dimers, and thus will be lower than might be
expected for metallo-macrocycles like the ones under
consideration here. A comparison with the ratio of the radii
(R) for 10 and L4, calculated from thevolume of the species
in their crystal structures, R10/RL4 ¼ 0.76, also provides a
value lower than the ratio obtained experimentally from
DOSY measurements. The corresponding analysis con-
ducted for 11 in more viscous DMSO-d6, the only common
NMR solvent that 11 is soluble in, provided diffusion
coefficients of 0.63 ^ 0.01 £ 10210 m2/s for 11 and a
diffusion coefficient under the same conditions of
0.75 ^ 0.03 £ 10210 m2/s for L5. No direct comparison
of the results obtained for 11 to those attained for 6 and 10
can be made as the measurements were undertaken in
different solvents. However, the ratio of diffusion
coefficients, D11/DL5 was 0.84 and similar to the
corresponding ratio for 10, which provided evidence for
maintenance of the solid-state structure in solution.
The tightly packed nature of 11 (see Figure 10) means
that the diffusion rate for this species may be faster than
expected due to its smaller hydrodynamic volume, and thus
the D11/DL5 ratio is correspondingly higher.
3.2.2 Synthesis of the Ag(I) metallo-macrocycles
A second silver(I) complex (8) obtained with L2 and
AgCF3COO in 75% yield has a rather complicated structure
that consists of two related [Ag2(L2)2] metallo-macro-
cycles. In the solid state, the formulation of 8 was supported
by elemental analysis and the observation of amide NZH
stretch at 3307 cm21 and a amide CvO stretch at
1643 cm21 in the IR spectrum. Like coordination polymers
7 and 9, compound 8 was not appreciably soluble in a single
solvent and this prevented NMR studies from being
conducted. The other two ligands investigated, L4 and L5,
possess one important difference over compounds L1–L3,
specifically a central pyridine core that should pre-organise
their conformation and favour the formation of discrete
metallo-macrocycles in solution. This was initially
confirmed in the solid state for both L4 and L5. Reaction
of L4 with AgNO2 gave crystals of a [2 þ 2] metallo-
macrocycle, [Ag2(NO2)2(L4)2] (10) in 76% yield. Simi-
larly, reaction of L5 with AgNO3 gave colourless rod-like
crystals ofcomplex[Ag2(L5)2](NO3)2·2CH3OH·2H2O(11)
in 21% yield from slow evaporation of the methanol–
acetonitrile reaction medium. The formation of compounds
10 and 11 was supported by elemental analysis and IR data
confirming the presence of the ligands (CvO stretches: 10,
1673 cm21; 11, 1654 cm21) and for 11, nitrate anions with
The crystal structure of 8 is composed of two closely
related [2 þ 2] dimetallo-macrocyclic complexes,
specifically [Ag2(CF3CO2)2(L2)2] (8a) and [Ag2(m2-
CF3CO2)2(L2)2] (8b) (Figure 7). The major difference
between these two complexes is the presence of a
trifluoroacetate anion that acts as a bidentate chelating
ligand in one metallo-macrocycle (8a) and a m2-bridging
ligand in the other (8b). The asymmetric unitconsistsof two
independent half-ligand moieties, two silver atoms (both on
a mirror plane) and two trifluoroacetate anions (also on a
an NZO stretch at 1382 cm21
.
The behaviour of the dinuclear metallo-macrocycles 10
and 11 in solution was investigated using ES-MS and NMR
spectroscopy. The ES-MS of 10 revealed peaks for
[Ag2(L4)(L4ZH)]þ although these were in low relative
abundance. In the ES-MS spectrum of compound 11,
dissolved in a mixture of DMSO and methanol, equivalent

Supramolecular Chemistry
637
˚
(Ag1) and 3.66(1) A (Ag2), and ligand conformations in the
two metallo-macrocycles differ markedly. In the species
involving Ag1, the ligand is severely twisted and while the
AgZAg separation is larger, the silver atoms are actually
pinched together but splayed apart in an orthogonal
direction. Conversely, L2 in the species involving Ag2
adopts a more typical conformation. The extent of the
twisting can be seen by the comparison of the torsion angles
for NHZCH2ZC1arylZC2aryl about the central phenyl ring;
in the first instance this twist is 29.18 where typically, and
in the second macrocycle, it is 3.48. No useful cavities are
present in either metallo-macrocycle, and as a consequence
of the ligand conformation, the amide hydrogen bond
donor/acceptor moieties are directed away from the
metallo-macrocyclic core.
In the packing of the two metallo-macrocycles, there
˚
are weak AgZAg contacts (AgZAg distance 3.138 A) that
are well within the sum of the van der Waal’s radii for
silver(I) (71, 72). Due to the conformation of L2, both
macrocycles form a number of hydrogen bonding
interactions that generate a 3D hydrogen-bonded network.
The formation of the 3D hydrogen-bonded network begins
with the formation of hydrogen-bonded tapes of the
two alternating metallo-macrocycles along the c-axis
(Figure 8(a)). A total of eight intra-tape hydrogen bonds
Figure 7. Perspective views of the metallo-macrocycle based
on (a) Ag1 (8a) and (b) Ag2 (8b) showing the distinct
conformations observed in the solid state.
mirror plane). The pendant pyridyl rings of both half-ligand
moieties are disordered. As a consequence of the different
coordination mode of the trifluoroacetate anions, the silver
atoms adopt slightly different coordination environments,
albeit with the same mix of donors. Ag1 has a very distorted
four coordinate geometry with a 131.95(16)8 angle between
˚
˚
(NZH· · ·O: d ¼ 2.090 A, D ¼ 2.941 A, angleNHO 169.948
˚
˚
and CZH· · ·O: d ¼ 2.202 A, D ¼ 3.122 A, angleCHO
169.848) connect each metallo-macrocycle to two others.
Each hydrogen-bonded tape is then bound to four other
tapes through hydrogen bonds (Figure 8(b)). These inter-
tape hydrogen bonds are relatively strong, NZH· · ·O:
˚
the pyridine donors and a AgZN bond length of 2.262(3) A.
The AgZO bond lengths to the chelating trifluoroacetate
˚
anions are 2.534(7) and 2.645(7) A. In comparison, Ag2 has
˚
AgZN bond lengths of 2.126(7) and 2.274(7) A (for the
disorder components) and AgZO bond lengths of 2.530(4)
and 2.544(4) for the bridging trifluoroacetate.
The NZAgZN angle is more linear for the macrocycle
involving Ag2 with bond angles in the range 155.5(5)8–
172.2(4)8, depending on the interpretation of the disorder
model.
˚
˚
d ¼ 1.862 A, D ¼ 2.693 A, angleNHO 161.958. This pack-
ing is reminiscent of the packing observed in compound 7,
whereby individual 1D coordination polymers are inter-
digitated with four others.
The metallo-macrocycle formed from L4 and AgNO2
(10) adopts a comparatively simpler structure in the solid
state. Crystallisation of 10, as colourless crystals, was
achieved by slow evaporation of an acetonitrile–methanol
solution of the complex. Compound 10 crystallises in the
As a consequence of the two modes of trifluoroacetate
coordination, the macrocycles have two quite different
˚
conformations. The AgZAg separations are 6.37(1) A
Figure 8. (a) A perspective view of the hydrogen-bonded tapes in 8. (b) The crystal packing of 8 showing the inter-tape hydrogen
bonding (in the ab-plane). The disorder components and the trifluoroacetate anions have been omitted for clarity; the void space observed
in the figure is occupied predominantly by the anions.

638
M. Abdul-Kadir et al.
Figure 9. (a) Two perspective views of the [Ag2(NO2)2(L4)2]
metallo-macrocycle 10. (b) A view of the 1D hydrogen-bonded
tapes in 10.
triclinic space group P 2 1 with a single molecule of L4,
one silver atom and a coordinated nitrite anion in the
asymmetric unit. The [Ag2(NO2)2(L4)2] metallo-macro-
cycle is generated by the operation of a centre of inversion
(Figure 9). The silver centres are distorted tetrahedral with
Figure 10. Two perspective views of the discrete metallo-
macrocycle complex 11.
˚
AgZN bond lengths of 2.2209(14) and 2.2423(14) A, and
In this dimer, the ligand acts as a bridge that provides a
˚
Ag–Ag distance of 8.170 A. This complex has a similar
˚
AgZO bond lengths of 2.4547(13) and 2.604(1) A. As
shown in Figure 9(a), the metallo-macrocycle is far from
planar and one 2,6-pyridine dicarboxamide unit is inclined
up and the second down. The Ag–Ag separation within 10
structure to a discrete [2 þ 2] metallo-macrocyclic silver
complex incorporating 1,2-bis(di-2-pyridylaminomethyl)-
benzene as a bridging ligand (73). Thus, it seems that the
amide moieties do not play a significant role in favouring
the formation of such entropically driven [2 þ 2]
assemblies. However, it is worth noting that the previously
reported complex has a more open metallo-macrocyclic
structure compared with complex 11 and is stabilised by
Ag–p interactions. No such interactions are observed in
this complex as the pyridyl donors saturate the
coordination requirements of the metal centres. Although
the amide NH donors point into the centre of the complex,
the resulting cavity is too small for guest inclusion and,
due to the steric bulk of the ligand, not accessible (Figure
10(b)). Due to this internalisation of the hydrogen bond
donors in the crystal packing, no significant hydrogen
bond interactions between the complex and the solvents or
anion were identified.
˚
is 13.36 A.
Despite being pinched in the centre, the metallo-
macrocycle is far more open than the structure of 8 and acts
as a host for two coordinated nitrite anions of two adjacent
molecules of 10. Each nitrite anion forms two moderately
strong hydrogen bonds with a 2,6-pyridine dicarboxamide
˚
˚
unit (NZH· · ·O: d ¼ 2.192 A, D ¼ 2.990 A, angleNHO
˚
˚
154.378 and NZH· · ·O: d ¼ 2.200 A, D ¼ 2.982 A,
angleNHO 151.18). These two hydrogen bonds are supported
by several other weak hydrogen bonds involving the pyridyl
hydrogens of L4. This results in the assembly of the
molecules of 10 into hydrogen-bonded tapes (Figure 9(b)).
As noted, compound 11, [Ag2(L5)2], is also a [2 þ 2]
dimetallo-macrocyclic complex with L5 acting as a
bridging ligand. Compound 11 crystallises in the orthor-
hombic space group Pbca with an asymmetric unit
comprising one molecule of ligand L5, half of a silver
atom, one non-coordinated nitrate, and non-coordinated
water and methanol solvate molecules. A perspective view
of 11 is shown in Figure 10 with the silver atoms in the
structure coordinated by two ligand entities through the
chelating pyridine donors, which results in a distorted
tetrahedral geometry at each silver centre (bond angles in
the range 82.20(8)8 2 140.29(8)8). The AgZN bond
In contrast to the preferential formation of coordi-
nation polymers by ligands L1–L3 in the solid state,
notwithstanding the result obtained for complex 8, L4 and
L5 appear to favour the formation of discrete metallo-
macrocycles both in solution and in the solid state. This
facility is a consequence of the pre-organising effect of the
2,6-pyridine dicarboxamide moiety as noted by others (74,
75), but presumably also the resulting hydrogen bond
donor–acceptor mismatch that occurs by having one
hydrogen bond donor region and two separate hydrogen
bond acceptor carbonyl moieties. This disfavours the
˚
lengths, in the range 2.315(2)–2.423(2) A, are typical for
tetrahedral silver(I) with four nitrogen heterocyclic donors.

Supramolecular Chemistry
639
formation of hydrogen-bonded tapes or networks that
support the crystal packing in the structures of the
coordination polymers encountered with L1–L3. The
effect of pre-organisation was previously observed in
solid-state structures of L1–L4 alone (47).
currently looking at several approaches to limit the
propensity of these compounds to form the hydrogen-
bonded networks observed in 6, 7 and 9. These include
continuing to utilise pre-organised binding pockets (like
L4) and synthesising the thioamide analogues of L1–L3.
Acknowledgements
4. Conclusion
C.J.S. thanks the Australian Research Council for an Australian
Post-doctoral Fellowship and a Future Fellowship (FT0991910),
and supporting this research through a Discovery Project
(DP0773011). M.A.K. thanks the Ministry of Higher Education,
Malaysia, and the University Malaysia Terengganu for financial
support. The University of Otago is acknowledged for providing
access to facilities for X-ray crystallography.
In this work, we have examined the self-assembly of five
flexible heterocyclic diamide ligands with silver(I) metal
salts with the intention of forming discrete metallo-
supramolecular structures with anion-complexing ability.
From this work, the structures of three new metallo-
macrocyclic complexes and three related coordination
polymers were obtained. It was observed that compounds
L1–L3, which lack the pre-organising effect of a central
2,6-pyridine dicarboxamide core, appear to preferentially
form 1D coordination polymers, {[Ag(L1)(CH3-
CN)](PF6)}n (6), {[Ag(L2)](NO3)·(H2O)]}n (7) and
{[AgNO3(L3)]·(CH3OH)]}n (9), which in turn form 2D
and 3D hydrogen-bonded networks stabilised through
orthogonal hydrogen bonding interactions. This precludes
the formation of the desired hydrogen bond donor pockets
to selectively complex anions. This is despite the
observation that at least one system, L1, appears to form a
discrete metallo-macrocyclic structure in solution. Thus, in
solution, where solvent molecules are capable of acting as
hydrogen bond acceptors, discrete structures for L1–L3
can be obtained. This contrasts with the behaviour
encountered for the structurally similar diamide ligand L4
that possess the pre-organising central 2,6-pyridine
dicarboxamide core; the structure of [Ag2(NO2)2(L4)2]
(10) in solution and in the solid state is a dinuclear metallo-
macrocycle. This was confirmed by ES-MS and DOSY
NMR spectroscopy in solution and X-ray crystallography in
the solid state. A fifth ligand, L5, with two chelating di-2-
pyridylmethyl donor groups, was also prepared to further
favour discrete metallo-macrocyclic species in solution.
The resulting silver(I) complex, [Ag2(L5)2](NO3)2·2CH3-
OH·2H2O (11), forms such a structure in solution and in the
solid state but unfortunately lacks any internal cavity due to
its steric bulk. In one instance, L2 gives rise to a dinuclear
metallo-macrocycle that in the solid state exists as
supramolecular isomers, namely [Ag2(CF3CO2)2(L2)2]
and [Ag2(m2-CF3CO2)2(L2)2].
Note
1. Current address: Department of Chemical Sciences, Faculty
of Science and Technology, University Malaysia
Terengganu, 21030 Terengganu, Malaysia.
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