[(Benzimidazol-1-yl)methyl]benzamides as bifunctional reagents for reliable inorganic-organic supramolecular synthesis

Article abstract of DOI:10.1039/b504420k

A series of ligands that utilize five-membered N-heterocycles as coordination sites, and the self-complementarity of the carboxamide functionality, have been employed in the supramolecular synthesis of Ag(I)-based extended networks. The crystal structures

Full text of DOI:10.1039/b504420k

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F U L L P A P E R
[(Benzimidazol-1-yl)methyl]benzamides as bifunctional reagents for
reliable inorganic–organic supramolecular synthesis
Christer B. Aakero¨y,* John Desper, Michelle M. Smith and Joaquin F. Urbina
Department of Chemistry, Kansas State University, Manhattan, Kansas, 66506, USA.
E-mail: aakeroy@ksu.edu
Received 30th March 2005, Accepted 27th May 2005
First published as an Advance Article on the web 9th June 2005
A series of ligands that utilize five-membered N-heterocycles as coordination sites, and the self-complementarity of
the carboxamide functionality, have been employed in the supramolecular synthesis of Ag(I)-based extended
networks. The crystal structures of eight compounds are reported: bis[4-(2-methylbenzimidazol-1-
yl)methylbenzamide]silver(I) tetrafluoroborate hydrate methanol, 1; bis[3-(2-methylbenzimidazol-1-
yl)methylbenzamide]silver(I) tetrafluoroborate, 2; bis[4-(5,6-dimethylbenzimidazol-1-yl)methylbenzamide]silver(I)
tetrafluoroborate, 3; bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroarsenate methanol, 4;
bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroarsenate methanol0.5, 5; bis[4-(5,6-
dimethylbenzimidazol-1-yl) methylbenzamide]silver(I) hexafluoroarsenate, 6; bis[4-(2-methylbenzimidazol-1-
yl)methylbenzamide]silver(I) hexafluoroantimonate, 7; and bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I)
hexafluoroantimonate, 8. An analysis of motifs and structural patterns that result from the primary intermolecular
interactions in these structures, reveals that this family of ligands is capable of providing quite reliable means for
propagating the linear geometry of the complex ions into extended 1-D architectures via ligand–ligand, N–H · · · O,
hydrogen-bond interactions.
Introduction
The supramolecular synthesis of extended metal–ligand frame-
works with predetermined metrics and connectivities is a rapidly
expanding area of crystal engineering.1 Many of these architec-
tures are constructed from rigid linkers (multitopic ligands) and
can possess a high degree of structural integrity even though
they may display open structures with pores and channels.
Some of the most popular building blocks in the synthesis of
coordinationpolymers are ditopic ligands such as 4,4ꢀ-bipyridine
that can be combined in different stoichiometries with metal
ions of different coordination modes.2 Recently, a number of
coordination polymers built from flexible ditopic3 and tritopic4
N-substituted imidazole/benzimidazole ligands, Scheme 1, have
also been reported which demonstrates that such N-heterocycles
are also useful building blocks of extended metal-containing
networks.
Scheme 2 Comparison of C–N–C angles in (a) benzimidazol-1-yl- and
(b) pyridyl-containing ligands.
struction of porous networks in a more controlled manner; the
geometry of the metal node can be propagated simultaneously
in 3-D with only one type of ligand, thus reducing structural
interference.
Another supramolecular synthetic strategy for the con-
struction of extended metal-containing networks combines a
suitable ligand moiety (for metal coordination) with an ap-
propriate hydrogen-bond functionality (for the supramolecular
chemistry).5 An example of such a ligand is isonicotinamide,6,7
which typically produces a unit that is supramolecularly equiv-
alent to the ditopic 4,4ꢀ-(1,4-phenylene)bispyridine,8 Scheme 3.
Scheme 1 Ditopic and tritopic imidazol-1-yl/benzimidazol-1-yl lig-
ands used in the construction of coordination polymers.
Imidazol-1-yl and benzimidazol-1-yl-containing ligands may
turn out to be more versatile than their pyridyl counterparts
mainly due to their smaller C–N–C angles (108 vs. 120◦, respec-
tively) which alleviate steric crowding at the metal center upon
coordination. Consequently, five-membered N-heterocycles can
readily be accommodated in an octahedral geometry around a
suitable metal ion, an arrangement that is extremely rare for
pyridyl-based ligands, Scheme 2. Better access to symmetric
octahedral building blocks provides opportunities for the con-
Scheme 3 (a) Hydrogen-bond linked and (b) covalently-linked ex-
tended ligands.
The choice of hydrogen-bonding moiety is typically governed
by its ability to form consistent and predictable supramolecular
motifs but it is also important that it does not compete with
the N-heterocycle for the metal ion itself. The carboxamide
moiety frequently forms either dimeric or catemeric hydrogen-
bonded patterns in the presence of potentially disruptive species
2 4 6 2
D a l t o n T r a n s . , 2 0 0 5 , 2 4 6 2 – 2 4 7 0
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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(counterions, solvent molecules, etc.), and it is less likely to
coordinate directly to the metal ion than are pyridyl- or imidazol-
1-yl moieties. These attributes combine to make the carbox-
amide functionality a useful connector in inorganic–organic
supramolecular synthesis. Even though flexible [(imidazol-1-
yl)methyl]benzoic acid ligands have been employed in coordina-
tion chemistry,9 the carboxylic acid moiety is less reliable than
the carboxamide moiety due its propensity to bind directly to
the metal ion via one of many possible coordination modes in
which case the outcome is most likely a coordination polymer.
Based on the versatility of five-membered N-heterocycles as
coordination sites in inorganic supramolecular synthesis, cou-
pled with the robust self-complementarity of the carboxamide
functionality, we have previously synthesized a new family of
ligands for the directed assembly of extended metal-containing
networks,10 Scheme 4.
Synthesis of 4-[(5,6-dimethylbenzimidazol-1-
yl)methyl]benzonitrile
5,6-Dimethylbenzimidazole (1.04 g, 6.84 mmol) was dissolved
in 60 mL of dry THF with heat and stirring in a 250 mL round-
bottomed flask. To the clear, light brown-coloured solution was
added NaOH (2.74 g, 68.4 mmol) which turned milky-brown in
color. The mixture was stirred for 2 h at room temperature under
an N2 atmosphere. To this mixture was added a 30 mL solution of
dry THF containing a-bromo-p-tolunitrile (1.34 g, 6.84 mmol).
Stirring was continued for 16 h under an N2 atmosphere, after
which 7 mL of distilled water was added to dissolve the NaOH
pellets and NaBr. The two layers formed were separated using a
separatory funnel, and the THF layer was dried over anhydrous
MgSO4. The MgSO4 was filtered off by vacuum filtration, and
the filtrate was concentrated via rotary evaporation to produce
a pale yellow solid. Yield: 1.568 g (88.8%); mp 153–155 ◦C, 1H
NMR (CDCl3, 400 MHz): d 2.32 (s, 3H), 2.36 (s, 3H), 5.39 (s,
2H), 6.94 (s, 1H), 7.21 (d, 2H, J = 8.8 Hz), 7.59 (s, 1H), 7.62
(d, 2H, J = 8.4 Hz), 7.86 (s, 1H); IR (KBr pellet), m/cm−1: 2223
(C≡N).
Synthesis of 4-[(5,6-dimethylbenzimidazol-1-
yl)methyl]benzamide
4-[(5,6-Benzimidazol-1-yl)methyl]benzonitrile
(1.568
g,
3.83 mmol) was dissolved in 9 mL of DMSO with heat
and stirring in a 250 mL three-necked flask under an N2
atmosphere. The reaction flask was then cooled in an ice-water
bath and anhydrous K2CO3 (0.076 g, 0.547 mmol) was added
to the reaction mixture. 9 mL of 30 wt% H2O2 solution were
syringed dropwise into the reaction mixture, and a white solid
formed almost immediately. The reaction was then allowed
to warm to room temperature with continued stirring for 1 h
while covered in aluminum foil. 5 mL of distilled water was
added to the reaction mixture. A white solid was obtained upon
vacuum filtration, which was washed with two small portions
of distilled water and dried. Recrystallization of the solid
from hot acetonitrile afforded the product as colourless plates.
Scheme 4 (a) [(Benzimidazol-1-yl)methyl]benzamide ligands vs. (b)
nicotinamide.
In comparison with previously utilized nicotinamide and ison-
icotinamide, these ligands would provide greater space between
the nodes (metal ions) in the structure, which can increase
porosity. Furthermore, the conformational flexibility resulting
from the methylene bridge imparts an expanded solubility in
a wide range of solvents. How this added flexibility affects
the intended supramolecular assembly process is an important
consideration, which will be examined as part of this study.
In addition, a family of closely related ligands can be readily
prepared through common synthetic procedures, which allows
us to examine solid-state assembly and structure in a systematic
manner.
We will explore the inorganic–organic supramolecular chem-
istry of [(benzimidazol-1-yl)methyl]benzamide ligands by allow-
ing them to react with a variety of Ag(I) salts, to establish
how effectively they can propagate a linear geometry of a
complex ion into infinite 1-D chains with the aid of self-
complementary hydrogen-bond interactions. The presence of
various counterions also allows for an examination of the
structural complications that these units may present vis-a`-vis
the desired supramolecular assembly process. In this way, we will
be able to assess the supramolecular yield, the capacity of this
family of ligands to form specific and reproducible assemblies
through intermolecular interactions.
◦
1
Yield: 1.489 g (89%); mp 245–250 C; H NMR (DMSO-d6,
400 MHz): d 2.26 (s, 3H), 2.28 (s, 3H), 5.49 (s, 2H), 7.25 (s,
1H), 7.29 (d, 2H, J = 8.0 Hz), 7.34 (s, 1H), 7.43 (s, 1H), 7.81
(d, 2H, J = 8.0 Hz), 7.92 (s, 1H), 8.26 (s, 1H); IR (KBr pellet),
−1
=
m/cm :1672 (C O, s), 3167 (N–H, broad), 3332 (N–H, broad).
Synthesis of bis[4-(2-methylbenzimidazol-1-yl)methylbenza-
mide]silver(I) tetrafluoroborate hydrate methanol, 1. 4-[(2-Meth-
ylbenzimidazol-1-yl)methyl]benzamide (0.020 g, 0.075 mmol)
was dissolved in 3 mL of methanol with heat in a small beaker
and cooled to room temperature. To this solution was added
a methanolic solution containing silver(I) tetrafluoroborate
(0.007 g, 0.038 mmol) and the beaker with the resulting solution
covered in Al foil and stored in the dark. Pale-yellow needles
were obtained after five days; mp 172 ◦C (decomp.).
Synthesis of bis[3-(2-methylbenzimidazol-1-yl)methylbenza-
mide]silver(I) tetrafluoroborate, 2. 3-[(2-Methylbenzimidazol-
1-yl)methyl]benzamide (0.020 g, 0.075 mmol) was dissolved in
3 mL of methanol with heat in a small beaker and cooled
to room temperature. To this solution was added silver(I)
tetrafluoroborate (0.007 g, 0.038 mmol) in methanol and the
beaker containing the resulting solution covered in Al foil and
stored in the dark. Colorless plates were afforded after five days;
mp 264–266 ◦C (decomp.).
Experimental
Synthesis of bis[4-(5,6-dimethylbenzimidazol-1-yl)methylbenza-
mide]silver(I) tetrafluoroborate, 3. 4-[(5,6-Dimethylbenzi-
midazol-1-yl)methyl]benzamide (0.043 g, 0.155 mmol) was
dissolved in 3 mL of acetonitrile with 1 mL of ethanol with heat
in a 50 mL beaker. To it was added a solution of acetonitrile
containing silver(I) tetrafluoroborate (0.01 g, 0.05 mmol), upon
which the solution went cloudy. 1 mL of ethanol was added
The syntheses of [(2-methylbenzimidazol-1-yl)methyl]benzamide
ligands are reported elsewhere.10 Silver(I) tetrafluoroborate,
silver(I) hexafluoroarsenate, and silver(I) hexafluoroantimonate
were purchased from Aldrich and used without further purifica-
tion. Melting points were determined on a Fisher-Johns melting
point apparatus and are uncorrected.
D a l t o n T r a n s . , 2 0 0 5 , 2 4 6 2 – 2 4 7 0
2 4 6 3

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and the solution was heated until it was clear. The resulting
solution was covered in Al foil and stored in the dark. Colorless
prisms suitable for X-ray crystallography were obtained after
three days; mp >283 ◦C.
Unit cell constants and orientation matrix were improved
by least-squares refinement of reflections thresholded from the
entire dataset. Integration was performed with SAINT,12 using
this improved unit cell as a starting point. Precise unit cell
constants were calculated in SAINT from the final merged
dataset. Lorenz and polarization corrections were applied. Laue´
symmetry, space group, and unit cell contents were found with
XPREP. Data were reduced with SHELXTL.13 The structures
were solved in all cases by direct methods without incident. In
general, hydrogen atoms were assigned to idealized positions
and were allowed to ride. Where possible, the coordinates of the
amide hydrogen atoms were allowed to refine. Heavy atoms were
refined with anisotropic thermal parameters. Unless otherwise
noted, data were corrected for absorption. Crystallographic data
are given in Table 1, selected bond angles in Table 2, hydrogen-
bond geometries in Table 3, and thermal ellipsoids and labeling
schemes are shown in Fig. 1(a)–(h).
Synthesis of bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]-
silver(I) hexafluoroarsenate methanol, 4. 4-[(2-Methylbenzi-
midazol-1-yl)methyl]benzamide (0.030 g, 0.113 mmol) was
dissolved in 5 mL of methanol with heat in a small beaker
and cooled to room temperature. To this solution was added
a methanolic solution containing silver(I) hexafluoroarsenate
(0.017 g, 0.057 mmol) and the beaker with the resulting solution
covered in Al foil and stored in the dark. Colorless needles
appeared after two days; mp 195–197 ◦C.
Synthesis of bis[3-(2-methylbenzimidazol-1-yl)methylbenza-
mide]silver(I)hexafluoroarsenate–methanol (2/1), 5. 3-[(2-methyl-
benzimidazol-1-yl)methyl]benzamide (0.030 g, 0.113 mmol) was
dissolved in 5 mL of methanol with heat in a small beaker and
cooled to room temperature. To this solution was added silver(I)
hexafluoroarsenate (0.017 g, 0.057 mmol) in methanol and the
beaker containing the resulting solution covered in Al foil and
stored in the dark. Colorless microcrystals formed after one day,
which were too small for X-ray crystallography. The experiment
was repeated, this time adding a few microcrystals from the
previous experiment to the reaction mixture as seed crystals.
Colorless plates were obtained after one day; mp 248–250 ◦C
(decomp.).
Results
The crystal structure determination of 1 revealed that water
and methanol had been incorporated into the lattice. The
silver ion is coordinated to two 4-[(2-methylbenzimidazol-1-
yl)methyl]benzamide ligands in a linear fashion, Fig. 1(a), and
this geometry is propagated through symmetry-related head-to-
head R2 (8) carboxamide · · · carboxamide hydrogen bonds to
2
produce an infinite undulating one-dimensional chain, Fig. 2.
anti-N–H protons of carboxamide groups form N–H · · · O
hydrogen bonds with disordered methanol molecules, while the
tetrafluoroborate anions do not form any significant interactions
with the cationic chains. The shortest through space intra-chain
Synthesis of bis[4-(5,6-dimethylbenzimidazol-1-yl)methylbenza-
mide]silver(I) hexafluoroarsenate, 6. 4-[(5,6-Dimethylbenzimida-
zol-1-yl)methyl]benzamide (0.028 g, 0.102 mmol) was dissolved
in 3 mL of acetonitrile with 1 mL of ethanol with heat in a 50 mL
beaker. To it was added a solution of acetonitrile containing
silver(I) hexafluoroarsenate (0.01 g, 0.034 mmol). Amber prisms
suitable for X-ray crystallography were obtained after five days;
mp 265–270 ◦C (decomp.)
˚
distance between Ag(I) ions is approximately 23.6 A.
The asymmetric unit of 2 contains a disordered anion in
addition to two crystallographically unique molecules of 3-
[(2-methylbenzimidazol-1-yl)methyl]benzamide coordinated to
a central silver(I) cation in a near-linear fashion through their
benzimidazol-1-yl nitrogen atoms, Fig. 1(b). Neighboring com-
plexes are interconnected through self-complementary head-to-
Synthesis of bis[4-(2-methylbenzimidazol-1-yl)methylbenza-
mide]silver(I) hexafluoroantimonate, 7. 4-[(2-Methylbenzimida-
zol-1-yl)methyl]benzamide (0.030 g, 0.113 mmol) was dissolved
in 5 mL of methanol with heat in a small beaker and cooled to
room temperature. To this solution was added a methanolic
solution containing silver(I) hexafluoroantimonate (0.019 g,
0.057 mmol) and the beaker with the resulting solution covered
in Al foil and stored in the dark. Colorless plates formed after
two days; mp 238–241 ◦C.
head R2 (8) motifs as well as through catemeric C(4) N–H · · · O
2
motifs to produce an infinite one-dimensional ladder, Fig. 3.
N–H protons of the carboxamide moieties also display short
contacts to adjacent anions, thereby providing a bridge between
cationic ribbons Fig. 4. The shortest through space intra-chain
˚
distance between Ag(I) ions is approximately 21.5 A.
The crystal structure of 3 contains Ag(I) ions coordinated to
two ligands in a linear manner as well as a disordered [BF4]−
anion, Fig. 1(c). The ligands bind to the metal ion via the
benzimidazol-1-yl nitrogen atoms. The linear geometry of the
Synthesis of bis[3-(2-methylbenzimidazol-1-yl)methylbenza-
mide]silver(I) hexafluoroantimonate, 8. 3-[(2-Methylbenzimida-
zol-1-yl)methyl]benzamide (0.030 g, 0.113 mmol) was dissolved
in 5 mL of methanol with heat in a small beaker and cooled
to room temperature. To this solution was added silver(I)
hexafluoroantimonate (0.019 g, 0.057 mmol) in methanol and
the beaker containing the resulting solution covered in Al foil
and stored in the dark. Colorless plates were afforded after
two days; mp 235–238 ◦C (decomp.).
complex is propagated into infinite chains via a symmetric R2 (8)
2
carboxamide · · · carboxamide hydrogen motif. anti-N–H pro-
tons of the carboxamide groups are engaged in hydrogen-bond
interactions with [BF4]− anions. The through-space Ag · · · Ag
˚
separation within chains is 19.8 A. Adjacent chains interact
˚
through p · · · p stacking contacts (ca. 3.5 A) involving 5,6-
dimethylbenzimidazol-1-yl moieties, Fig. 5.
X-Ray crystallography
The crystal structure of 4 contains linear complex ions
composed of silver ions and two crystallographically unique
4-[(2-methylbenzimidazol-1-yl)methyl]benzamide ligands. The
counterions are disordered, and there is also a disordered
methanol molecule in the lattice, Fig. 1(d). Neighboring complex
ions are connected through catemeric C(4) N–H · · · O hydrogen
bonds to afford infinite undulating chains. Pairs of chains are
then linked through additional C(4) N–H · · · O hydrogen bonds
to produce one-dimensional ribbons. Neighboring ribbons are
X-Ray data were collected on a Bruker SMART 1000 four-
circle CCD diffractometer (1–3, 5 and 6) or SMART APEX
CCD diffractometer (4, 7, 8) using a fine-focus Mo-Ka tube.
Data were collected using SMART.11 Initial cell constants were
found by small widely separated “matrix” runs. Generally, an
entire hemisphere of reciprocal space was collected regardless of
Laue´ symmetry. Scan speed and scan width were chosen based
on scattering power and peak rocking curves. Datasets were
collected under an N2 stream at the temperature indicated in
Table 1.
˚
held together by p · · · p interactions (3.4 A) to generate a two-
dimensional sheet, Fig. 6.
CCDC reference numbers 267466–267473.
See http://www.rsc.org/suppdata/dt/b5/b504420k/ for cry-
stallographic data in CIF or other electronic format.
Hexafluoroarsenate anions are positioned inside the pores
of the sheet via interactions between syn-N–H protons of
carboxamide moieties and fluorine atoms. Methanol molecules
2 4 6 4
D a l t o n T r a n s . , 2 0 0 5 , 2 4 6 2 – 2 4 7 0

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D a l t o n T r a n s . , 2 0 0 5 , 2 4 6 2 – 2 4 7 0
2 4 6 5

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Fig. 1 Thermal ellipsoid plots (50% probabilities) and labeling scheme for 1–8 (a–h).
also interact with carbonyl oxygen atoms of the carboxamide
groups in the two-dimensional sheet.
there is also disordered methanol in the lattice, Fig. 1(e). The
geometry of the complex ion is propagated into an infinite one-
The crystal structure of
5
contains two crystallo-
dimensional chain by dimeric head-to-head R2 (8) N–H · · · O
2
graphically unique molecules of 3-[(2-methylbenzimidazol-1-
yl)methyl]benzamide coordinated in a linear geometry to a
central silver(I) cation through their benzimidazol-1-yl nitrogen
atoms. One of the carboxamide moieties is disordered and
hydrogen bonds between neighboring carboxamide moieties on
one side of the metal complex. In addition, there are O–H · · · O
hydrogen bonds between the O–H groups of methanol and
carbonyl oxygen atoms of carboxamide moieties to produce
2 4 6 6
D a l t o n T r a n s . , 2 0 0 5 , 2 4 6 2 – 2 4 7 0

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Table 2 Selected bond distances and angles for 1–8
N–Ag–N/◦
˚
Compound Ag–N/A
1
2
Ag1–N13 2.070(3)
N13–Ag1–N13 180
N13–Ag1–N33 173.38(9)
Ag1–N13 2.085(2)
Ag1–N33 2.086(2)
Ag1–N12 2.089(3)
Ag1–N13 2.073(2)
Ag1–N33 2.070(2)
Ag1–N13 2.102(3)
Ag1–N33 2.103(3)
3
4
N12−Ag1–N12 180
N13–Ag1–N33 173.67(7)
5
N13–Ag1–N33 171.38(13)
Fig. 3 Extended one-dimensional ladder motif in 2; [BF4]− anions
removed for clarity.
6
7
Ag1–N13 2.0707(19) N13–Ag1–N13 180
Ag1–N13 2.066(4)
Ag1–N33 2.086(4)
N13–Ag1–N33 173.97(13)
8
Ag1–N13 2.1025(17) N13–Ag1–N33 174.06(7)
Ag1–N33 2.0995(18)
Fig. 2 Linear cationic assembly in 1. Tetrafluoroborate anions and
solvent molecules are omitted for clarity.
Fig. 4 Interconnection of adjacent one-dimensional ladders in 2
through disordered tetrafluoroborate anions.
an alternating N–H · · · O/O–H · · · O hydrogen-bonded pattern,
Fig. 7.
carboxamide · · · carboxamide interactions extend the struc-
tural unit into an infinite 1-D assembly to yield an infinite chain,
Fig. 8.
syn- and anti-N–H protons of carboxamide groups on the
methanol side of the complex ion interact with anions.
In the crystal structure of 6, two 4-[(5,6-dimethylbenzi-
midazol-1-yl)methyl]benzamide ligands coordinate through
their benzimidazol-1-yl nitrogen atoms to each Ag(I) ion
Proximal chains are bridged through interactions between
anions and anti-N–H protons of carboxamide moieties to form
a 2-D framework, Fig. 9. The shortest through space Ag · · · Ag
in a linear fashion, Fig. 1(f). Self-complementary R2 (8)
distance within chains is 21.8 A.
˚
2
Table 3 Hydrogen-bond geometries for 1–8
D–H · · · A/◦
Generator for A
˚
˚
Compound
D–H · · · A
H · · · A/A
D · · · A/A
1
N27–H27A · · · O27
N27–H27B · · · O2S
2.03
2.46
2.911(5)
3.320(93)
173.9
164.3
−x + 1, −y − 1, −z + 1
2
N27–H27A · · · F12
N27–H27A · · · F16
N27–H27B · · · F11
N27–H27B · · · F15
N47–H47A · · · O47
N47–H47B · · · O27
2.02(4)
2.08(4)
2.26(3)
2.03(4)
2.10(3)
2.14(3)
2.918(4)
2.982(18)
3.090(4)
2.834(12)
2.881(3)
2.866(3)
166(3)
167(3)
160(3)
152(3)
177(3)
149(3)
−x + 1, −y + 1, −z
−x + 1, −y + 1, −z
x, y, z + 1
x, y, z + 1
−x + 1, −y, −z + 2
x, y + 1, z − 1
3
4
N27–H27A · · · O27
N27–H27B · · · F2
2.13(5)
2.20(5)
2.929(4)
2.902(11)
178(5)
148(5)
−x, −y, −z
x − 1/2, −y + 1, z − 1/2
N27–H27A · · · F3A
N47–H47A · · · F2B
N27–H27B · · · O47
N47–H47B · · · O27
O1S–H1S · · · O27
2.29
2.22
2.12
2.11
2.17
3.124(3)
3.027(18)
2.962(3)
2.977(3)
2.818(8)
158.3
152.7
159.4
166.2
134.1
x − 1, y − 1, z
x + 1, y, z
−x + 2, y − 1/2, −z + 1/2
x, y − 1, z
5
N27A–H27A · · · O27A
N27B–H27C · · · O27B
N47–H47A · · · F1
2.07
2.05
2.15
2.36
2.22
2.930(6)
2.88(2)
2.898(5)
3.181(6)
3.021(9)
172.0
159.2
143.6
157.9
162.3
−x + 1, −y + 1, −z + 2
−x + 1, −y + 1, −z + 2
−x + 1, −y, −z
N47–H47B · · · F3
x, y, z − 1
O1S–H1S · · · O47
6
7
8
N37–H37A · · · O37
N37–H37B · · · F1
2.06(4)
2.28(4)
2.944(3)
2.982(3)
173(3)
148(3)
−x, −y + 2, −z + 1
N27–H27B · · · O47
N47–H47B · · · O27
2.16
2.13
3.023(4)
2.969(4)
165.6
158.9
x, y − 1, z
−x + 2, y + 1/2, −z + 1/2
N27–H27A · · · O27
N47–H47A · · · F1
2.04(3)
2.15(4)
2.907(3)
2.959(3)
171(3)
165(3)
−x − 1, −y + 2, −z + 2
D a l t o n T r a n s . , 2 0 0 5 , 2 4 6 2 – 2 4 7 0
2 4 6 7

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˚
Adjacent ribbons interact via p · · · p interactions (3.3 A) between
benzimidazol-1-yl moieties to generate a two-dimensional sheet,
Fig. 10, similar to the extended structure in 4. The anions reside
within the pores of the sheet.
Fig. 5 An extended view of 3 showing p · · · p interactions between
adjacent 1-D chains; tetrafluoroborate anions are disordered.
Fig. 10 2-D sheet in 7 formed from N–H · · · O hydrogen bonds and
p · · · p interactions.
The crystal structure of 8 contains two crystallographi-
cally distinct 3-[(2-methylbenzimidazol-1-yl)methyl]benzamide
molecules coordinated to a silver(I) ion in a near-linear manner,
Fig. 1(h). Adjacent ions are interconnected through dimeric
head-to-head R2 (8) N–H · · · O hydrogen bonds on one side of
2
Fig. 6 Infinite two-dimensional sheet in 4 formed from catemeric
carboxamide · · · carboxamide hydrogen bonds and p · · · p interactions.
the metal complex, whereas the carboxamide moieties on the
other side are capped by interactions with hexafluoroantimonate
anions. Neighboring dimeric units interact through p · · · p inter-
˚
actions (3.6 A) between benzimidazol-1-yl moieties resulting in
a one-dimensional assembly, Fig. 11.
Fig. 7 Infinite 1-D chain in 5 formed from N–H · · · O/O–H · · · O
hydrogen bonds.
Fig. 11 Extended 1-D assembly in 8 held together by dimeric
carboxamide · · · carboxamide hydrogen bonds and p–p interactions.
Fig. 8 Infinite 1-D cationic chain in 6; [AsF6]− anions have been
removed for clarity.
Discussion
The crystal structure determination of 7 reveals the presence
of two crystallographically unique 4-[(2-methylbenzimidazol-1-
yl)methyl]benzamide ligands coordinated to a silver(I) cation
in a near-linear geometry via their benzimidazol-1-yl nitrogen
atoms, as well as a disordered hexafluoroantimonate anion,
Fig. 1(g). Adjacent units are held together by catemeric N–
H · · · O hydrogen bonds to produce an infinite undulating one-
dimensional chain. Neighboring chains are connected by cate-
meric N–H · · · O hydrogen bonds to generate an infinite ribbon.
Eight inorganic–organic coordination complexes with Ag(I)
ions and [(benzimidazol-1-yl)methyl]benzamide ligands were
characterized using single-crystal X-ray diffraction in order to
establish if this family of ligands is capable of facilitating high-
yielding supramolecular synthesis.
In each structure, 1–8, the Ag(I) ion is coordinated in a
linear manner by two ligands and the ligand–metal interaction
invariably takes place through the accessible nitrogen atom
of the benzimidazol-1-yl moiety. The amide moiety does not
Fig. 9 2-D framework formed in 6 through hydrogen bonds between neighboring 1-D chains and hexafluoroarsenate anions.
2 4 6 8
D a l t o n T r a n s . , 2 0 0 5 , 2 4 6 2 – 2 4 7 0

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bind directly to the metal ion in any case which leaves it open
to engage in the supramolecular assembly process. With eight
linear complexes there are sixteen amide moieties that need to
be classified according to the type of hydrogen-bond interac-
tions that they participate in. Ligand–ligand based hydrogen
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bonds (either R2 (8) or C(4) motifs) will lead to extended
2
assemblies, whereas hydrogen bonding to counterions and/or
solvent molecules represents loss of control and directionality
and is considered a failed assembly event. In this family of
compounds, adjacent amides produced nine R22s(8) motifs and
five C(4) motifs. Only on two occasions were the intended
supramolecular ligand · · · ligand interactions disrupted, once
by an [SbF6]− anion (in 8) and once by a methanol molecule
(in 5). The ligands are therefore capable of propagating the
inherent linear geometry of the metal complex in six of the eight
structures – a supramolecular yield of 75%. Since each structure
necessarily contains potentially disruptive counterions and, on
three occasions, included solvent molecules, a supramolecular
assembly strategy of extended metal-containing architectures
using this family of ligands is likely to be quite successful.
The fact that ligand-based amide · · · amide hydrogen bonds are
capable of maneuvering complex ions of substantial size, also
bodes well for the transferability and versatility of these ligands.
Since there was only one occasion when an anion disrupted
an intended recognition event it is not possible to rank the
potential structural interference from the anions used in this
structural study: [BF4]−, [AsF6]−, and [SbF6]−. Based upon
charge–size ratio one might expect the tetrafluoroborate anion to
be most likely to cause problems by competing as an alternative
hydrogen-bond acceptor, but that was not the case in 1–8.
It should be noted that these eight compounds represent all
the complexes in this family of compounds that have been
crystallographically characterized to date. With an increased
number of structural data points we do not expect to find any
marked deviations from the supramolecular yield that we have
found so far.
Secondary intermolecular interactions are responsible for
organizing 1-D assemblies with respect to each other, and
these forces can principally be classified as p · · · p contacts. The
asymmetric charge distribution in heterocyclic compounds can
strengthen such interactions, and there were several examples of
˚
short p–p distances (3.3–3.6 A) in these structures, indicative of
attractive forces that further stabilized the extended structures.
At this stage, it is clear that ligands, such as those described
herein, can be used effectively for the directed assembly of
complex ions into desired extended motifs even in the presence
of a variety of structurally disruptive counterions and solvent
molecules. At times, supramolecular ligands may provide some
advantages compared to their covalent counterparts as represen-
tatives from the latter group may require significant synthetic ef-
forts, and extended rigid aromatic ligands frequently suffer from
poor solubility, which can be a drawback during the synthesis
of the extended metal-containing network. We are currently
synthesizing 2-D and 3-D inorganic–organic hybrid systems
employing [(benzimidazol-1-yl)methyl]benzamide ligands and
metal ions with preferences for higher coordination numbers
in order to take advantage of the coordinating versatility
of five-membered N-substituted heterocyclic moieties for the
construction of open architectures. Furthermore, we are also
synthesizing even longer ligands, with the same coordinating and
hydrogen-bonding sites, to determine how the supramolecular
yield is affected by an increase in molecular weight of the
constituent building blocks in the assembly process.
5 (a) C. B. Aakero¨y, J. Desper and J. Valde´s-Mart´ınez, CrystEngComm,
2004, 6, 413–418; (b) C. B. Aakero¨y, A. M. Beatty, J. Desper,
M. O’Shea and J. Valde´s-Mart´ınez, DaltonTrans., 2003, 3956–3962;
(c) A. M. Beatty, CrystEngComm, 2001, 51; (d) C. B. Aakero¨y and
A. M. Beatty, Aust. J. Chem., 2001, 54, 409–421; (e) C. B. Aakero¨y,
A. M. Beatty and K. R. Lorimer, J. Chem. Soc., Dalton Trans.,
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CrystEngComm, 2000, 27, 1–6; (g) C. B. Aakero¨y, A. M. Beatty,
D. S. Leinen and K. R. Lorimer, Chem. Commun., 2000, 935–936;
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We are grateful for financial support from NSF (CHE-
0316479).
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