Molecular tectonics on surfaces: Bottom-up fabrication of 1D coordination networks that form 1D and 2D arrays on graphite

Article abstract of DOI:10.1002/anie.200603558

(Figure Presented) Nanopatterning of multifunctional architectures, that is, 1D or 2D arrays on surfaces, can be achieved through bottom-up fabrication of 1D coordination networks by self-assembly processes. A coordinating tecton bearing both monodentate and tridentate coordination poles is combined with suitable metal centers (see scanning tunneling microscopy image).

Full text of DOI:10.1002/anie.200603558

Angewandte
Chemie
DOI: 10.1002/anie.200603558
Supramolecular Chemistry
Molecular Tectonics on Surfaces: Bottom-Up Fabrication of 1D
Coordination Networks That Form 1D and 2D Arrays on Graphite**
Mathieu Surin, Paolo Samorì,* Abdelaziz Jouaiti, Nathalie Kyritsakas, and Mir Wais Hosseini*
In memory of Guy Ourisson
Molecular networks are periodic architectures formed upon
mutual bridging between molecular construction units called
As stated above, although considerable effort has been
devoted to the design and formation of 3D crystals composed
of organic tectons and metal centers, the use of a molecular
[
1–4]
[13]
tectons.
Such molecular assemblies are generated in the
crystalline phase by self-assembly through molecular recog-
nition processes, which take place between tectons bearing
complementary interaction sites within their structure. So far,
molecular tectonics has been mainly focused on the design
and generation of molecular architectures in the crystalline
phase. However, the control of spatial arrangements of
molecular units on substrate surfaces is also a field of current
tectonics approach for the generation of 2D crystalline
metalloorganic patterns and arrays at surfaces has so far not
been explored. Herein, we describe the design and the STM
study of 1D coordination networks that form either 1D or 2D
nanoscale arrays at surfaces. This bottom-up patterning is
generated by self-assembly processes upon combining a
directional, rigid, organic coordinating tecton bearing two
differentiated coordination poles with suitable metal centers.
We focused on 1D coordination networks, which present
translational symmetry in one direction of space of an
assembling node that results from the formation of coordi-
nation bonds between organic units and metal centers. The
design of such an arrangement may be based on the use of
noncentric tectons bearing two coordination poles that offer
different denticities. In particular, a combination of tectons
which expose one monodentate and one tridentate coordina-
tion pole with metal centers offering four free coordination
sites that occupy the corners of a square would match the
requirement for the formation of directional 1D coordination
networks (Figure 1). As concerns the metal center, one may
envisage the use of either octahedral dicationic metals
associated with two coordinating anions occupying the
apical positions (Figure 1, top) or square-planar metal centers
[
5]
interest. In particular, the self-assembly of metal–ligand-
based architectures at surfaces is a promising and versatile
[
6,7]
method for the fabrication of 2D metal-ion arrays.
Indeed,
the correct choice of the ligand–metal pair made it possible to
fabricate various thermodynamically stable nanoscale pat-
[
8]
terns of bipyridine-based complexes adsorbed on surfaces.
Scanning tunneling microscopy (STM) and spectroscopy can
provide direct and quantitative insight into the nanoscale
properties of supramolecular architectures by addressing and
[
9]
manipulating assemblies with a submolecular resolution. Up
to now, STM characterizations of metal–ligand self-assembly
of terpyridine-based architectures have been focused on the
study of single-molecule complexes that form self-organized
[
10]
[6,11]
monolayers, gridlike assemblies,
cycles.
or hexameric macro-
[
12]
(
Figure 1, bottom). In the crystalline phase, this strategy has
[
14–16]
been proven to be operational in the case of CoCl2.
[*] Dr. M. Surin,Dr. P. Samorì
Nanochemistry Laboratory
ISIS/CNRS 7006,UniversitØ Louis Pasteur
allØe Gaspard Monge,67083 Strasbourg (France)
8
Fax: (+39)516-399-844
E-mail: samori@isis-ulp.org
Dr. P. Samorì
Istituto per la Sintesi Organica e la Fotoreattività
Consiglio Nazionale delle Ricerche
via Gobetti 101,40129 Bologna (Italy)
Dr. A. Jouaiti,Dr. N. Kyritsakas,Prof. Dr. M. W. Hosseini
Laboratoire de Chimie de Coordination Organique
UMR CNRS 7140,UniversitØ Louis Pasteur
4
rue Blaise Pascal,67000 Strasbourg (France)
Fax: (+33)390-241-325
E-mail: hosseini@chimie.u-strasbg.fr
[
**] This work was supported by the UniversitØ Louis Pasteur,the
Institut Universitaire de France,the CNRS,the Ministry of
Education and Research,the ERA-Chemistry project SurConFold,
and the EU-Marie Curie EST project SUPER (MEST-CT-2004-
Figure 1. Schematic representation of the formation of directional 1D
networks,based on the combination of an organic tecton bearing a
monodentate and a tridentate coordination pole and either a neutral
octahedral metal complex (top) or square-planar dicationic metal
center (bottom),which offers four free coordination sites.
0
08128).
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2007, 46, 245 –249
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
245

Communications
chloroform molecules. All CÀC and CÀN bond lengths are in
agreement with expected and reported values. Compound 6
exhibits an almost flat conformation (Figure 2a). The pyri-
dine ring is almost coplanar with the anthracene unit (0.78 tilt
angle). The central pyridine unit of the terpyridine moiety is
also coplanar with the anthracene spacer. However, the other
two pyridine units are in a trans conformation and tilted with
Scheme 1. Synthesis of tecton 6.
The design of the tecton 6 (Scheme 1) was based on the
use of an anthracene moiety as a platform, and pyridine and
terpyridine units as the two different coordination poles. Both
the pyridine and terpyridine units were connected to the
backbone at their 4-positions. The linkage between the
monodentate and tridentate coordination poles and anthra-
cene was achieved at positions 9 and 10 by ethenyl groups.
This connectivity pattern was chosen because it leads to an
inline disposition of the two coordinating poles. The choice of
the ethenyl spacer was motivated by the fact that such a unit,
by avoiding atropoisomerism, would lead to a flat yet p-
conjugated construction unit well-suited to physisorption
within self-assembled architectures on a graphite surface.
The synthesis of compound 6 was sequential and based on
two palladium-catalyzed C–C coupling reactions. The starting
material was 9,10-dibromoanthracene (2; Scheme 1). The
condensation of 2 with 4-ethynylpyridine (3), prepared
Figure 2. a) A portion of the solid-state structure of tecton 6 (black N,
gray C) and b) packing of consecutive units. Hydrogen atoms are not
represented for clarity. For bond distances and angles,see text.
respect to the central pyridine (NCCC dihedral angle of
À178). Molecules of compound 6 are packed along the b axis
with the same orientation, thus leading to arrangement along
this direction. The lateral packing of molecules in the XOY
plane is achieved in syn-parallel mode, thus affording a polar
sheet. As a result of the antiparallel packing of molecules
along the c axis, the overall arrangement is apolar. Conse-
quently, the head-to-tail-type disposition of molecules along
the c axis leads to parallel and face-to-face packing of the
pyridine and terpyridine units, with a centroid-to-centroid
distance between consecutive units of approximately 3.93 Š
(Figure 2b).
[
17]
according to published procedures, in Et N in the presence
3
of Pd(OAc) and PPh afforded compound 1 in 34% yield. As
2
3
expected, this reaction also led to the formation of the
[
18]
symmetrical double-condensation product 4 (25% yield).
Figure 3 shows ordered 2D monolayers formed by assem-
bly of the tecton 6 onto a graphite surface. The monolayer
displays a polycrystalline structure (Figure 3a), which consists
of hundreds of nanometer-wide domains that are stable over
several minutes. Bright rods, tilted by about 358 with respect
to the b axis of the unit cell (see black arrows in Figure 3b),
are observed. The unit cell dimensions, estimated from the
smaller-scale image (Figure 3b), are a = (3.2 Æ 0.2) nm, b =
(2.60 Æ 0.15) nm, and a = (89 Æ 3)8, which lead to an area A =
The latter, based on the anthracene core and bearing two
pyridine moieties, is a bis(monodentate) unit and might also
be of interest for the generation of either discrete or infinite
networks when combined with appropriate metal centers. The
reaction between compound 1 and 4-ethynylterpyridine (5),
[
19]
synthesized according to the literature,
in Et N with
3
Pd(OAc) and PPh as catalysts afforded the desired com-
2
3
pound 6 in 80% yield.
The solid-state structure of the free tecton 6 was inves-
tigated by X-ray diffraction on a single crystal. The crystal
2
(8.32 Æ 1.0) nm . In the inset of Figure 3b, the Corey–Paul-
ing–Koltun (CPK) molecular structure has been added on top
of the STM zoom image, thus providing evidence for a zigzag
(
monoclinic, C2/c) is composed of 6 and two disordered
2
46
www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 245 –249

Angewandte
Chemie
II
(1.70 Æ 0.15) nm. Given the high electron densities of the Co
metal centers, it is most likely that these spots correspond to
the Co ions complexed by tecton 6. However, such spots are
not laterally correlated. In fact, these 1D nanostructures grow
either as single anisotropic nano-objects or as tightly packed
parallel wires separated by a variable distance (see white
arrows in Figure 5a). Time-resolved STM mapping made it
possible to highlight a dynamic exchange between the 1D
nanostructures and a 2D monolayer adsorbed at the solid/
liquid interface, the latter consisting most probably of the
pure ligand 6. In particular, on the several seconds timescale,
the neutral 1D networks formed upon mutual bridging
Figure 3. a,b) STM images of the pure ligand 6. Tip bias
(V )=745 mV; average tunneling current (I )=36.0 pA. The inset in
tip t
between tectons 6 and CoCl complexes (indicated by white
2
(
b) shows a zoom image. See text for further details.
arrows in Figure 4) disassemble into the 2D monolayer. This
disappearance of the 1D nanostructure can be a consequence
packing motif that may result from a
different orientation of molecule 6 on
the XOY plane with respect to the
surface underneath. The two different
rows are marked by solid and dashed
white arrows (Figure 3b, inset). As
expected from p–p interactions between
the rather flat conjugated compound 6
and the substrate, in both cases the
molecules are adsorbed preferentially
parallel to the basal plane of the under-
lying graphite plane. The observed
Figure 4. a–c) Time-resolved STM images of the uncharged network formed by ligand 6 and CoCl . The
2
packing of unit cells containing two arrows indicate a given 1D network that disassembles over time. Vtip =705 mV; I =13.0 pA.
t
molecules is probably favored by both
intra- and intermolecular weak N···HÀC
[
20]
hydrogen bonds. The lower contrast
of the molecules along the dotted lines, if compared to those
along the solid lines, can be a result of either different
positioning of molecules along the z axis (that is, different
distances from the surface) or different conformers of 6 that
[
21]
possess a lower degree of planarity.
In both cases, the
overlap between the p orbitals of compound 6 and the
substrate varies, thus leading to changes in the detected
tunneling currents.
According to previous observations on the crystalline
[
14–16]
phase of structurally related tectons,
the combination of
the neutral tecton 6 with CoCl should lead to the formation
2
Figure 5. STM images of the network generated upon combining
of neutral 1D coordination networks on the graphite surface.
The generation of the network results from the binding of the
II
tecton 6 with a) CoCl and b) Pd . Image (a) shows the formation of
2
laterally uncorrelated 1D nanostructures,while (b) displays the parallel
packing of 1D networks that leads to the generation of a 2D nanoscale
array. a) Vtip =705 mV; I =13 pA; b) V =983 mV; I =13.6 pA.
II
Co center, which adopts the octahedral coordination geom-
etry and offers four free coordination sites occupying the
corners of a square (the two apical positions being occupied
t
tip
t
À
by two Cl anions), with one terpyridine and one pyridine
coordinating pole belonging to consecutive tectons
6
of either its desorption in the supernatant solution or a
disassembly process occurring directly at the surface. Given
the different spacing between repeating motifs, that is, (1.70 Æ
0.15) nm intermetal distance along the 1D network, and the
b axis of the unit cell for the pure tecton 6 mentioned above
(b = (2.60 Æ 0.15) nm), it is most likely that a desorption–
readsorption process takes place during the disappearance of
1D networks. The high shape persistence of the 1D nano-
structures is determined by the directionality of the coordi-
nation bonds formed between the Co metal center and tecton
(
Figure 1, top). This coordination mode defines the assem-
bling node, which, upon translation into one direction of
space, leads to the 1D network.
Figures 4 and 5a show STM images of a film prepared by
physisorption of a solution containing the neutral tecton 6 and
neutral CoCl complex on graphite. Perfectly straight nano-
2
structures with a length up to 400 nm were observed. At a
smaller scale (Figure 5a), these 1D nanostructures are made
of aligned and regularly spaced circular spots separated by
Angew. Chem. Int. Ed. 2007, 46, 245 –249
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
247

Communications
6
and the rigidity of the latter. The parallel packing of the 1D
persistent 1D coordination networks in the presence of
metal cations. Depending on the overall charge of the
network and thus on the nature of the tectons used, either
1D or 2D arrays that expose metal centers in preprogrammed
locations, with an Šngstrom resolution, may be obtained. We
are currently investigating the generation of molecular net-
works on surfaces using the molecular building block reported
here, and its analogues, with a variety of other metal centers.
Finally, given the multifunctional character of these architec-
tures, which incorporate a metal center and an optically active
unit (that is, anthracene), future studies will be addressed
toward the exploitation of their unique optical properties.
networks might suggest that the graphite substrate lattice or
step edges dictate the relative orientation of the networks
assembled at the surface. This is a well-known behavior,
which has been ascribed to the greater reactivity of step edges
of graphite. Notably, grid-type architectures based on bis-
(
terpyridine) ligands combined with cobalt also adsorb on
[
11c]
graphite step edges.
As a result of the nonplanarity of the
octahedral assembling node, the ligand backbones cannot be
fully planar to the graphite surface, thus leading to partial
overlap of the p orbitals of tecton 6 and the graphite. As a
consequence, it is most likely that the 1D networks are
stabilized by interactions with the step edges of graphite
rather than by side-to-side packing interactions.
Received: August 31, 2006
Published online: November 30, 2006
II
On the other hand, the use of the Pd cation, by design,
yields a polycationic 1D network. Indeed, because of the
dicationic nature of palladium, its binding by the neutral
tecton 6 generates a charged square-planar assembling node
formed by the palladium center and one terpyridine and one
pyridine unit belonging to consecutive tectons 6. Figure 5b
shows a STM image of the straight, laterally correlated,
Keywords: coordination modes · nanostructures ·
scanning probe microscopy · supramolecular chemistry · tectons
.
[
1] a) M. Simard, D. Su, J. D. Wuest, J. Am. Chem. Soc. 1991, 113,
696; b) J. D. Wuest, Chem. Commun. 2005, 5830.
4
parallel 1D networks obtained by self-assembly of the ligand 6
[
2] S. Mann, Nature 1993, 365, 499.
II
with Pd on graphite. As in the case of CoCl , the spots
2
[
3] a) M. W. Hosseini, Acc. Chem. Res. 2005, 38, 313; b) M. W.
Hosseini, Chem. Commun. 2005, 5825.
observed along the rows can be attributed to the metal centers
as a result of their high electron density. The spots form a 2D
crystalline layer characterized by the unit cell a = (4.0 Æ
[4] M. W. Hosseini, CrystEngComm 2004, 6, 318.
[5] J. Huskens, M. A. Deij, D. N. Reinhoudt, Angew. Chem. 2002,
114, 4647; Angew. Chem. Int. Ed. 2002, 41, 4467.
0
.2) nm, b = (2.00 Æ 0.15) nm, and a = (91 Æ 3)8, which leads
2
[6] M. Ruben, J. Rojo, F. J. Romero-Salguero, L. H. Uppadine, J. M.
to a surface area A = (8.0 Æ 1.0) nm (see black rectangle in
Figure 5b). Each unit cell contains one molecule of tecton 6
and one Pd cation. The 1D cationic networks are formed
Lehn, Angew. Chem. 2004, 116, 3728; Angew. Chem. Int. Ed.
2004, 43, 3644.
II
[
7] a) M. A. Lingenfelder, H. Spillmann, A. Dmitriev, S. Stepanow,
N. Lin, J. V. Barth, K. Kern, Chem. Eur. J. 2004, 10, 1913; b) S.
Stepanow, M. Lingenfelder, A. Dmitriev, H. Spillmann, E.
Delvigne, N. Lin, X. B. Deng, C. Z. Cai, J. V. Barth, K. Kern, Nat.
Mater. 2004, 3, 229; c) P. Zell, F. Mogele, U. Ziener, B. Rieger,
Chem. Eur. J. 2006, 12, 3847.
along the b axis through interconnection of palladium cations
by neutral tectons 6. The lateral correlation between the 1D
networks forming the crystalline layer suggests a cooperative
process that takes place during the generation of 1D networks
assembled on graphite. The unit cell area (normalized for a
single unit composed of one tecton 6 and one palladium
[
8] a) M. M. S. Abdel-Mottaleb, N. Schuurmans, S. De Feyter, J.
Van Esch, B. L. Feringa, F. C. De Schryver, Chem. Commun.
2
cation) of approximately 8.0 nm is larger than that deter-
2002, 1894; b) S. De Feyter, M. M. S. Abdel-Mottaleb, N.
2
mined for the free tecton 6 (about 4.16 nm ), which suggests
Schuurmans, B. J. V. Verkuijl, J. H. van Esch, B. L. Feringa,
F. C. De Schryver, Chem. Eur. J. 2004, 10, 1124.
À
possible packing within the monolayer of BF4 counterions
between polycationic 1D networks. This packing mode seems
reasonable because it avoids repulsive interactions between
positively charged 1D networks. Furthermore, the formation
of a 2D monolayer made of parallel and regular dispositions
of the 1D networks on the graphitic surface may also be
attributed to the planar disposition of the assembling node,
and thus the 1D networks favoring p-stacking interactions
between the polycationic 1D networks and the surface.
Notably, in both cases shown above, the STM character-
ization of physisorbed metal–ligand complexes at the solid/
liquid interface reveals 1D coordination networks with
lengths over a few hundreds of nanometers. Such lengths
are comparable to those observed on straight structures made
of dry metallo-supramolecular complexes of bis(terpyridine)
[9] a) P. Samorꢀ, J. Mater. Chem. 2004, 14, 1353; b) S. De Feyter,
F. C. De Schryver, J. Phys. Chem. B 2005, 109, 4290.
10] a) E. Figgemeier, L. Merz, B. A. Hermann, Y. C. Zimmermann,
C. E. Housecroft, H. J. Gꢁntherodt, E. C. Constable, J. Phys.
Chem. B 2003, 107, 1157; b) B. A. Hermann, L. J. Scherer, C. E.
Housecroft, E. C. Constable, Adv. Funct. Mater. 2006, 16, 221.
[
[11] a) A. Semenov, J. P. Spatz, M. Mꢂller, J. M. Lehn, B. Sell, D.
Schubert, C. H. Weidl, U. S. Schubert, Angew. Chem. 1999, 111,
2701; Angew. Chem. Int. Ed. 1999, 38, 2547; b) U. Ziener, J. M.
Lehn, A. Mourran, M. Mꢂller, Chem. Eur. J. 2002, 8, 951; c) M. S.
Alam, S. Strꢂmsdꢂrfer, V. Dremov, P. Mꢁller, J. Kortus, M.
Ruben, J. M. Lehn, Angew. Chem. 2005, 117, 8109; Angew.
Chem. Int. Ed. 2005, 44, 7896.
[
12] G. R. Newkome, P. Wang, C. N. Moorefield, T. J. Cho, P. P.
Mohapatra, S. Li, S. H. Hwang, O. Lukoyanova, L. Echegoyen,
J. A. Pallagalo, V. Lancu, S.-W. Hla, Science 2006, 312, 1782.
[13] a) S. R. Batten, R. Robson, Angew. Chem. 1998, 110, 1558;
Angew. Chem. Int. Ed. 1998, 37, 1460; b) A. J. Blake, N. R.
Champness, P. Hubberstey, W.-S. Li, M. A. Withersby, M.
Schrꢂder, Coord. Chem. Rev. 1999, 193, 117; c) M. W. Hosseini,
NATO ASI Ser. C 1999, 538, 181; d) G. F. Swiergers, T. J.
Malefetse, Chem. Rev. 2000, 100, 3483; e) B. Moulton, M. J.
Zawortko, Chem. Rev. 2001, 101, 1629; f) C. Janiak, Dalton
II
derivatives with Fe stabilized by alkane lamellae ( ꢀ 200 nm
long) self-assembled on graphite, as revealed by atomic force
[
22]
microscopy investigations.
In conclusion, by STM studies at the graphite/solution
interface, we have demonstrated the possibility of designing
flat, coordinating construction units capable of forming
2
48
www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 245 –249

Angewandte
Chemie
Trans. 2003, 2781; g) L. Carlucci, G. Ciani, D. M. Proserpio,
Coord. Chem. Rev. 2003, 246, 247; h) S. Kitagawa, Angew. Chem.
[17] L. Della Ciana, A. Haim, J. Heterocycl. Chem. 1984, 21, 607.
[18] T. M. Fasina, J. C. Collings, D. P. Lydon, D. Albesa-Jove, A. S.
Batsanov, J. A. K. Howard, P. Nguyen, M. Bruce, A. J. Scott, W.
Clegg, S. W. Watt, C. Viney, T. B. Marder, J. Mater. Chem. 2004,
14, 2395.
[19] V. Grosshenny, F. M. Romero, R. Ziessel, J. Org. Chem. 1997, 62,
1491.
2004, 116, 2388; Angew. Chem. Int. Ed. 2004, 43, 2334; i) G.
Fꢃrey, C. Mellot-Draznieks, C. Serre, F. Millange, Acc. Chem.
Res. 2005, 38, 218; j) D. Bradshaw, J. B. Claridge, E. J. Cussen,
T. J. Prior, M. J. Rosseinsky, Acc. Chem. Res. 2005, 38, 273;
k) S. L. James, Chem. Soc. Rev. 2003, 32, 276.
[
[
[
14] A. Jouaiti, M. W. Hosseini, A. De Cian, Chem. Commun. 2000,
[20] D. Wouters, S. Hꢂppener, R. Lunkwitz, L. F. Chi, H. Fuchs, U. S.
Schubert, Adv. Funct. Mater. 2003, 13, 277.
[21] P. Samorꢄ, A. Fechtenkꢂtter, T. Bꢂhme, F. Jꢅckel, K. Mꢁllen, J. P.
Rabe, J. Am. Chem. Soc. 2001, 123, 11462.
[22] D. G. Kurth, N. Severin, J. P. Rabe, Angew. Chem. 2002, 114,
3833; Angew. Chem. Int. Ed. 2002, 41, 3681.
1863.
15] A. Jouaiti, V. Jullien, J.-M. Planeix, M. W. Hosseini, A. De Cian,
Chem. Commun. 2001, 1114.
16] A. Jouaiti, M. W. Hosseini, N. Kyritsakas, Chem. Commun. 2002,
1898.
Angew. Chem. Int. Ed. 2007, 46, 245 –249
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
249