Phenoxyaluminum(salophen) Scaffolds: Synthesis, Electrochemical Properties, and Self-Assembly at Surfaces of Multifunctional Systems

Article abstract of DOI:10.1002/chem.201801118

Salophens and Salens are Schiff bases generated through the condensation of two equivalents of salicylaldehyde with either 1,2-phenylenediamines or aliphatic diamines, respectively. Both ligands have been extensively exploited as key building blocks in coordination chemistry and catalysis. In particular, their metal complexes have been widely used for various catalytical transformations with high yield and selectivity. Through the modification of the phenol unit it is possible to tune the steric hindrance and electronic properties of Salophen and Salen. The introduction of long aliphatic chains in salicylaldehydes can be used to promote their self-assembly into ordered supramolecular structures on solid surfaces. Herein, we report a novel method towards the facile synthesis of robust and air-stable [Al(Salophen)] derivatives capable of undergoing spontaneous self-assembly at the graphite/solution interface forming highly-ordered nanopatterns. The new synthetic approach relies on the use of [MeAl^III(Salophen)] as a building unit to introduce, via a simple acid/base reaction with functionalized acidic phenol derivatives, selected frameworks integrating multiple functions for efficient surface decoration. STM imaging at the solid/liquid interface made it possible to monitor the formation of ordered supramolecular structures. In addition, the redox properties of the Salophen derivatives functionalized with ferrocene units in solution and on surface were unraveled by cyclic voltammetry. The use of a five-coordinate aluminum alkyl Salophen precursor enables the tailoring of new Salophen molecules capable of undergoing controlled self-assembly on HOPG, and thereby it can be exploited to introduce multiple functionalities with subnanometer precision at surfaces, ultimately forming ordered functional patterns.

Full text of DOI:10.1002/chem.201801118

A Journal of
Accepted Article
Title: Phenoxy Al(Salophen) Scaffolds: Synthesis, Electrochemical
properties, and Self-Assembly at Surfaces of Multifunctional
Systems
Authors: Paolo Samori, Luca Mengozzi, Mohamed El Garah, Andrea
Gualandi, Matteo Iurlo, Andrea Fiorani, Artur Ciesielski,
Massimo Marcaccio, Francesco Paolucci, and Pier Giorgio
Cozzi
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To be cited as: Chem. Eur. J. 10.1002/chem.201801118
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Chemistry - A European Journal
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Phenoxy Al(Salophen) Scaffolds: Synthesis, Electrochemical
properties, and Self-Assembly at Surfaces of Multifunctional
Systems
[
a]
[b]
[a]
[a]
[a]
Luca Mengozzi, Mohamed El Garah, Andrea Gualandi, Matteo Iurlo, Andrea Fiorani, Artur
[
b]
[a]
[a]*
[b]
[a]
Ciesielski, Massimo Marcaccio, Francesco Paolucci, Paolo Samorì, * and Pier Giorgio Cozzi *
[
2]
Abstract: Salophens and Salens are Schiff bases generated
through the condensation of two equivalents of salicylaldehyde with
either 1,2-phenylenediamines or aliphatic diamines, respectively.
Both ligands have been extensively exploited as key building blocks
in coordination chemistry and catalysis. In particular, their metal
complexes were widely used for various catalytical transformations
with high yield and selectivity. Through the modification of the phenol
unit it is possible to tune the steric hindrance and electronic
properties of the salophen and salen. The introduction of long
aliphatic chains in salicylaldehydes can be used to promote their
self-assembly into ordered supramolecular structures on solid
surfaces. Herein we report a novel method towards the facile
synthesis of robust and air stable Al(salophen) derivatives capable to
undergo spontaneous self-assembly at the graphite/solution
interface forming highly-ordered nanopatterns. The new synthetic
approach relies on the use of MeAl(III)(salophen) as building unit to
introduce, via a simple acid-base reaction with functionalized acidic
phenol derivatives, selected frameworks integrating multiple
functions for efficient surface decoration. Scanning tunneling
microscopy (STM) imaging at the solid/liquid interface made it
possible to monitor the formation of ordered supramolecular
structures. In addition, the redox properties of the salophen
derivatives functionalized with ferrocene units in solution and on
surface were unraveled by cyclic voltammetry. The use of a five
coordinate aluminum alkyl salophen precursor enables the tailoring
of new salophen molecules capable of undergoing controlled self-
assembly on HOPG, and thereby it can be exploited to introduce
multiple functionalities with a sub-nanometer precision at surfaces,
ultimately forming ordered functional patterns.
unique propensity to bind different metal ions. In their dianionic
form these ligands can display two covalent and two
coordinative binding sites located in a planar array. The resulting
metal complexes are ad-hoc building blocks as catalysts in
organic synthesis due to their ability to efficiently transfer chiral
[
3]
information.
Salen metal complexes are also considered
[
4]
privileged catalysts,
as demonstrated by their successful
application in many challenging asymmetric reactions. The
modular structure of these ligands enables a wide structural
modification (Scheme 1), paving the way to a straightforward
development of numerous asymmetric transformations. In
particular, a large number of catalytic reactions using metallo-
[
5]
salens, including the hydrolytic kinetic resolution and the
[
6]
asymmetric ring opening of epoxides, or Lewis acid promoted
[
7]
activation of carbonyl compounds, have been developed.
Moreover, because of their unique properties, Salen metal
complexes are capable of activating both the nucleophiles and
[
8]
the electrophiles in the transition state of
Furthermore, salen metal complexes show
a
reaction.
bifunctional
a
character, as the ligand is able to assemble a Lewis acidic metal
[
9]
with an electron rich periphery. In addition, M(salen) (M = Ni,
Co) complexes were also recently reported to form intriguing
[
10]
supramolecular two-dimensional (2D) networks.
Achiral salophen ligands, which are obtained when aromatic
diamines are used in the condensation reaction with
salicylaldehydes, can be considered being strictly correlated to
the salen ligands. Achiral salophen are capable of binding a
metal center resulting in nearly perfectly planar configuration of
the complex, enabling their interaction via strong π-
π
[
11]
stacking.
From the point of view of coordination, salophen
metal complexes are penta- or hexa-coordinated, with additional
axial coordination sites available on the axis perpendicular to the
Introduction
[12]
salophen plane. Salophen ligands offer a unique platform for
[
11]
molecular recognition
and have been used to prepare
In particular, subtle modifications of the
[
1]
Salen are well established tetradentate ligands exhibiting a
[12]
effective complexes.
monomeric chemical structure strongly influence the self-
assembly on a surface from different environments thus allowing
to control the formation of different secondary structures.
[
a]
b]
Dr. L. Mengozzi, Dr. A. Gualandi, Dr. M. Iurlo, Dr. A. Fiorani, Prof.
M. Marcaccio, Prof. F. Paolucci, Prof. P. G. Cozzi
Dipartimento di Chimica “G. Ciamician”
ALMA MATER STUDIORUM Università di Bologna
Via Selmi 2, 40126, Bologna,Italy.
E-mail: piergiorgio.cozzi@unibo.it; francesco.paolucci@unibo.it
Dr. M. El Garah, Dr. A. Ciesielski, Prof. P. Samorì
University of Strasbourg, CNRS, ISIS UMR 700
[
8
alleé Gaspard Monge, F-67000 Strasbourg, France
E-mail: samori@unistra.fr
Supporting information for this article is given via a link at the end of
the document.
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Results and Discussion
Synthesis of Al(salophen) building blocks
The direct reaction of MeAl(salophen) complex 4 with acidic
[
16]
functionalities was used to introduce a ferrocene unit. Inspired
by Atwood’s demonstration of the successful reaction of
[
17]
complex 4 with phenols,
we have combined 4 with p-
ferrocenephenol 5 by refluxing the two compounds in 1:1 ratio in
[
18]
toluene for 8 h. This reaction enabled the efficient introduction
of the ferrocene moiety into a salophen scaffold.
Scheme 1. Multiple functions played by salen or salophen metal complexes.
The planar conformation of metal-salens and salophens makes
them ideal platforms to be physisorbed at surfaces and
interfaces to form ordered self-assembled structures. The STM
sub-nanometer resolved imaging of salen and salophen metal
complexes immobilized at surfaces, may be used to cast light at
molecular level onto their rich coordination chemistry and
catalysis. However, very few reports can be found in literature
[
13]
on STM studies on metal-salen complexes. Recently, Kleij et
al. described the metallo-supramolecular behavior of Ni and Zn
[
14]
metal-salophens at the liquid/solid interface:
while
Ni(salophen) were found to form monolayers, the Zn complex
assembled into bilayers, via complex dimerization. This bilayer
formation was shown to be reversible when a coordinating
ligand as pyridine was added. Although the pyridine ligand could
not be directly viewed in the STM image, its presence is
accompanied by an indirect evidence: the addition of pyridine to
Zn(salophen) led to a reduction of the dimensionality in the self-
assembled structure at surfaces, from bilayer to monolayer.
The salophen complexes ability to form ordered supramolecular
assemblies at surfaces along with their functionalization in the
apical positions with functional moieties render them powerful
scaffolds to nanopattern surfaces and interfaces with functional
moieties with a high spatial resolution. However, one of the
major limitations of Zn(salophen) complexes is the labile nature
of the complexes with coordinating basic molecules at apical
position.
Scheme 2. Synthesis of ferrocene functionalized Al(salophen) complex 6
To promote the molecular physisorption on graphite at the
solid/liquid interface, the salophen molecule was decorated in
the para position with long alkyl chains by grafting the
commercially available 2-methyl-4-n-dodecyl-phenol in the
salophen moiety (see SI for the details). The desired salophen
[
19]
ligand 7 was obtained in 33% yield,
after chromatographic
Atwood and co-workers designed and synthesized a variety of
salen and salophen aluminum complexes, and studied their
purification. The corresponding MeAl(salophen) 8, a moisture
sensitive solid, was produced by a minor modification of the
conditions used for the synthesis of 6 (see SI for details). The
[
15]
coordination chemistry. The authors thoroughly described the
ability of aluminium(III) derivatives to form stable
1
completion of the reaction was proven by H NMR analysis.
pentacoordinated complexes with an additional ligand in the
axial position, a characteristic that differ them from Zn(salophen)
complexes. The increased stability of the Al(salophen)
molecules could be therefore a clear advantage for the tailored
introduction of moieties into ordered pattern at surfaces.
In this paper, we report for the first time the use Al(salophen)
metal complexes to generate ordered self-assembled
monolayers at surfaces and we demonstrate that the facile
introduction of desired moieties as apical ligands on the
Al(salophen) is a viable route to simultaneously position multiple
functional units such as ferrocenes and chiral phosphines at
surfaces with a sub-nm precision.
Traces of moisture in the solvent or in the reaction mixture can
considerably reduce the yields. In these cases variable amounts
of unreacted Salophen ligand were detected together with non-
identified species, probably due to formation of aluminum-oxo
[
15a,b]
derivatives.
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possible as ferrocenyl alcohols are capable of forming stabilized
carbenium ions, and phenol, being less nucleophilic than pyrrole
towards the generated carbenium ions, is not reactive,
[
26,27]
guaranteeing the absence of by-products.
To prove the
robustness of this chemistry, also the crowded compound 12
was reacted in the general conditions (toluene, reflux) for the
direct reaction with 8, to give pure compound 13 in 94% yield.
However, as chiral ferrocene ethanol 12 was used as racemic
mixture, the complex 13 was obtained as an inseparable mixture
of different diastereoisomers.
Scheme 3. Preparation of the Al(salophen) complex 9.
In order to broaden our approach and exploit further the
potential of ferrocene functionalized MeAl(salophen) as scaffolds
to pattern multiple functions on solid surfaces, we have tethered
MeAl(salophen) to an enantioenriched and functionalized chiral
ferrocene moiety. The possibility to decorate the graphite
surface with chiral enantioenriched ferrocene phosphine ligands
is extremely appealing for exploiting the rich catalytic chemistry
of phosphines which are one of the most important and widely
Complex 8 is more sensitive to hydrolysis and to decomposition
compared to complex 4, which is probably protected by the
bulky tert-butyl substituent from adventitious traces of water.
In order to explore the properties of salophene scaffolds
decorated with multiple ferrocene units, we have expanded our
synthetic effort to the complexation of MeAl(salophen) 8 with the
bis-ferrocenyl compound 12. The pyrrole moiety was chosen
[
28]
used chiral ligands.
because it can be easily functionalized with electrophiles in S
N
1-
[
20]
Unfortunately, the protocol that was pursued to successfully
type or Friedel-Crafts reactions,
or used for cross-coupling
[
21]
[22]
produce 12 “on water” gave very low yields in this case. Instead,
reactions,
or in direct CH activation.
We have therefore
when the reaction was performed in CH
2 2
Cl in presence of
opted to use N-(4-hydroxyphenyl)pyrrole 10 derivative because
of its stability along with its ability to graft to Al(salophen)
complexes via its phenol group.
In(OTf) the desired product was detected albeit conversion was
3
low probably because the Lewis acid was strongly complexed by
the reaction product. Indeed, using a stoichiometric amount of
3
In(OTf) at 0°C, afforded the complete conversion of acetate 14
after several hours to give a mixture of di- and mono-alkylated
products, unreacted phenol 10 and several unidentified side-
products. The formation of aluminum complex 16 was obtained
again using the standard reaction conditions in high yield and
high purity by refluxing the pure compounds 15 and 8 in 1:1
ration in toluene for 8 h (Scheme 5). Complexes 6, 9, 13, and 16
were found completely soluble in DCM, toluene, and CHCl
while a low solubility in hexane was observed.
3
,
Scheme 4. Preparation of the pyrrole derivative 12 and its reaction with the
MeAl(Salophen) complex 8.
Compound 10 was obtained by a simple reaction (see SI for
detail) from commercially available 4-aminophenol. Although
[
23]
many Friedel-Crafts reactions with pyrrole in the presence of a
variety of Lewis acid and many nucleophiles have been widely
exploited, we have found that compound 11 was sensitive to the
presence of Lewis acids. However, due to the high
Scheme 5. Preparation of the pyrrole derivative 15 and its reaction with the
MeAl(salophen) complex 8.
[
24]
nucleophilicity of pyrrole
N
it was possible to perform the S 1
[
25,26]
reaction of 11 “on water”
without the need of Lewis acids.
Upon a simple stirring of the two reagents suspended “on water”
at 80 °C for 21 h, the dialkylated product 12 was obtained as a
mixture of diastereoisomers in a statistic ratio. Such reaction is
Electrochemistry of salophen derivatives
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The electrochemical properties of salophens were investigated
in DCM solutions, under ultra-dry conditions, while salophen
complexes spin-coated on highly oriented pyrolytic graphite
mV compared to the case in solution. In this case, a higher value
for 16 is rather unexpected and this would indicate that
ferrocenyl cations do not benefit from the carbon surface
stabilization or from the aqueous solvent. The salophen films
showed a remarkable stability under the conditions used in the
voltammetric experiments, where the reversible behavior was
still observed after several cycles. Moreover, no significant aging
of the film was observed and the current did not exhibit any
significant decrease with respect to the original measurement
after several (10) days (Figure S2 in SI).
(
HOPG) were studied in aqueous solutions in order to avoid their
desorption from the surface.
Figure portrays the cyclic voltammograms of salophen
1
complexes 9, 13 and 16 either in solution and spin-coated on
HOPG. The salophen ligand 7, investigated in DCM solution
(
Figure S1), shows two reductions and two oxidations, and the
cyclic voltammetry response can be rationalized in terms of
salophen molecular orbitals. The HOMO is localized on phenol
moieties, while the LUMO resides substantially on imine
Table 1. Electrochemical data of salophen complexes 9, 13 and 16: E1/2 / V vs
[
29,30]
+
moieties.
The two non-reversible reductions are therefore
Ag/AgCl (KCl, 3M). [a] Anodic peak potential. Fc/Fc HOPG is E1/2 / V of Fc on
centered on the imine moieties. On the other hand, the two
oxidations are ascribed to phenolic moiety: the first one is non-
reversible likely due to a follow-up deprotonation reaction,
according to an EC mechanism. The second oxidation could be
attributed to the oxygen radical oxidation to ketone. From
HOPG.
9
13
16
I
-1,61
0,43
1,65
0,36
-1,61
0,42
1,48
0,39
-1,69
0,50
1,43
0,61
+
Fc/Fc
[
31]
deconvolution analysis of the CV curves,
compared to the
a
II
+
mono-electronic Fc /Fc, the valence of each redox step was
estimated to be one electron for both reductions, two electrons
for the first and one for the second oxidation. Salophen
complexes (9, 13, and 16) follow approximately the same
behavior of ligand 7. A single one-electron reduction was only
observed while the second is likely occurring outside the solvent
potential window. Oxygen-centered oxidations take place in a
single non-reversible peak, probably associated to complex
break up. Noteworthy, the presence of a cathodic peak in the
backward oxidation scan of complexes 13 and 16 is attributed to
the pyrrole moiety of the capping ligand. Likely, the redox
process ascribed to pyrrole is overlapped to that of the oxygen.
Since in complex 16 the two peaks are less overlapping, with a
light evidence of an anodic peak around 1 V in the forward scan,
we attributed the oxidation peak of pyrrole at E1/2= 0.92 V, from
deconvolution analysis.
+
Fc/Fc HOPG
The ferrocene moieties give one oxidation peak at 0.43 V (9),
0
.42 V (13) and 0.50 V (16). While the addition of pyrrole (13)
does not affect the ferrocene centered oxidations, the electro-
withdrawing phenyl phosphine groups, directly bound to
[
32,33]
ferrocene (16) increase the E1/2 value.
The ferrocene moieties are the only one capable of providing an
electrochemical response when the complexes are deposited on
HOPG due to the narrower potential window of water. Salophen
adsorption onto HOPG electrode surfaces brings about changes
in ferrocene oxidation energetics. The half wave potential of
ferrocene in 9, 13 and 16 is 0.36 V, 0.39 V and 0.61 V,
respectively.
As previously showed, HOPG surface can stabilize radical
[
34]
cations.
In this case, ferrocenyl radical cations stabilization
would likely take place via the phenyl rings, with the salophen
ligand adsorbed onto the HOPG surface. In addition, a lower
potential could be ascribed to the different solvent: in water the
Figure 1. Cyclic voltammetry measurements of salophen complexes in
solution (left side) and salophen spin coated on HOPG (right side). In solution:
scan rate 500mV/s. On surface: scan rate: 10 mV/s (black), 20 mV/s (red), 50
mV/s (blue) and 100 mV/s (green). All the potentials referred to Ag/AgCl,
KCl(3M); T=298K.
+
potential of Fc /Fc couple is lower compared to organic solvents
[
35,36]
such as DCM.
These two factors can account for potentials
of 9 and 13, which are lower compared to those measured in
solution of 70 mV and 30 mV, respectively. Conversely,
ferrocene potential of complex 16 is 0.61 V, being higher of 110
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Surface modification studies with Salophen
derivatives.
salophen complexes containing ferrocenes units. Figure
displays STM height images of the crystalline patterns formed by
salophen derivatives 9, 13 and 16 onto HOPG/solution interface.
The STM height image of 9 monolayers on HOPG is displayed
in Figure 2a. It shows a monocrystalline monolayer featuring a
2D lamellar motif with the 9 molecules being physisorbed flat on
the graphite surface. Within the lamella, the aromatic cores of
salophens appears as a bright protrusion. Such high contrast of
salophen cores in the STM image is related to their high
electronic density. Moreover, a notable features centered in the
core of salophens can be seen, and can be attributed to
ferrocene groups adsorbed immobilized as a second molecular
2
Scanning tunneling microscopy (STM) was used to probe the
self-assembly of different salophene derivatives at graphite-
solution interface. The comparative study was carried out by
applying a drop of a 1.0 ± 0.1 mM solution of the chosen
salophen derivative in 1-phenyloctane on freshly cleaved highly
oriented pyrolytic graphite (HOPG). All the images were
recorded in constant current mode. Initially, we have focused our
attention on the study of the self-assembly of the organic ligand
7
and the metallic 8 at the solid/liquid interface. Figure S2
[
37]
displays the poor order within the monolayer of 7, which is in line
layer (Figure 2a). The molecular model of 9 presented in the
Figure 2b exhibits the spatial distribution of the ferrocene units
(in blue color) matching to the molecular packing portrayed from
STM image. Furthermore, based on the spacing between the
lamellas, we conclude that the alkyl chains are physisorbed flat
on HOPG and interdigitated between the lamellas.
[
14a]
with previous reports on similar salophen derivatives.
On the
other hand, 8 performs also a 2D crystalline lamellar structure at
the phenyloctane/HOPG interface (Figure S3)
We have extended our investigation to the salophen derivative
incorporating two ferrocene groups, i.e. 13. The STM image in
Figure 2c reveals that the packing of 13 at the solution-graphite
interface is nearly identical with that of 9, yet in the self-
assembled monolayer of 13 two bright features are visible on the
salophen cores. Similarly to 9, the molecular packing of 13 is
highly dense and therefore there is no enough space to
accommodate the ferrocene units on the basal surface. The dark
parts of the image are attributed to interdigitated assembled
alkyl chains of the molecule. A molecular packing model of 13 is
presented in the Figure 2d.
STM image in the Figure 2e shows the molecular packing of the
derivative 16. The alkyl chains can be resolved and appear
interdigitated with darker contrast compared to the cores of the
molecules. The aromatic core of 16 appears with four bright
protrusions (Figure 2e). These protrusions represent the
positions of ferrocene groups together with ferrocenyl phosphine
units. These latter are adsorbed as a top layer, similar case as
for the previous derivatives, i.e. 9 and 16. Figure 2f displays the
corresponding molecular model of 16.
For all the crystalline 2D patterns, the unit cells parameters, i.e.
the length of the vectors a and b, the angle between the vectors
(
(
(
α), the unit cell area (A), the number of molecules in the unit cell
mol) and the area occupied by a single molecule in the unit cell
mol) are summarized in the Table 2.
N
A
Table 2. Experimental unit cell parameters of Salophen derivatives structures
9, 13 and 16)
(
2
Structure
a [nm]
b [nm]
α [º]
A [nm ]
N
mol
A
mol
2
[
nm ]
9
2.4 ± 0.1
2.4 ± 0.1
2.4 ± 0.1
1.1 ± 0.1
1.2 ± 0.1
1.1 ± 0.1
75 ± 2
75 ± 2
76 ± 2
2.5±0.2
2.5±0.2
2.5±0.2
1
1
1
2.5±0.2
2.5±0.2
2.5±0.2
Figure 2. STM images showing the molecular packing of salophen derivatives
at 1-phenyloctane/HOPG interfaces. Tunneling parameters: average current
1
1
3
6
2
5–30 pA, average bias: 500–650 mV. a) Self-assembly and b) molecular
packing motif of 9. c) Self-assembly d) molecular packing motif of 13. e) Self-
assembly and f) molecular packing motif of 16.
While the derivatives 9, 13 and 16 exhibit an identical unit cell
and occupied area by single molecule (see the Table 2), the
difference can be clearly seen on the contrast of their cores
The degree of order at the supramolecular level as obtained
within the monolayers was found to be much higher for the
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(
Figure 2a, 2c and 2e). In particular, this contrast strongly
molecules were applied to the basal plane of the surface. For STM
measurements, the substrates were glued to a magnetic disk and an
electric contact was made with silver paint (Aldrich Chemicals). The STM
tips were mechanically cut from a Pt/Ir wire (80/20, diameter 0.25 mm).
The raw STM data were processed through the application of
background flattening and the drift was corrected using the underlying
graphite lattice as a reference. The lattice was visualized by lowering the
bias voltage to 20 mV and raising the current up to 65 pA. STM imaging
was carried out in constant height mode. Monolayer pattern formation
was achieved by applying onto freshly cleaved HOPG 4µL of a solution.
The STM images were recorded at room temperature once achieving a
negligible thermal drift. Solutions of all salophen molecules were
depends on the number of the functional groups exposed on the
Salophen scaffold being one ferrocene for 9, two for 13, and two
plus two additional ferrocenyl phosphines for 16. Linear arrays of
single group and doublets are respectively performed by the
self-assembly of
9 and 13 into HOPG whereas complex
architecture is resulted from the adsorption of 16 into the surface.
This latter is due to the presence of diphenyl phosphine units
together with the ferrocene groups. Since 16 lies flat to the
surface forming dense molecular packing, all the functional
groups point away from the surface.
prepared by dissolving them in CHCl
give 1.0 ± 0.1 mM solution (solvent composition 90 % 1-phenyloctane +
0 % CHCl ). All the molecular models were minimized with MMFF and
3
and diluting with 1-phenyloctane to
Conclusions
1
3
In summary, we have designed and synthesized a new family
Al(salophen) metal complexes bearing long aliphatic chains to
processed with QuteMol visualization software.
promote
the
molecular
self-assembly
into
ordered
supramolecular structures at the graphite/solution interface.
Following a bottom-up approach we have constructed ordered
nano-patterned surfaces by using of MeAl(III)(salophen) as
molecular scaffold. Different functional groups (Ferrocene, chiral
ferrocenyl phosphines) were introduced, via a simple acid-base
reaction, with tailored phenol units. The ordered structures were
investigated by employing scanning tunneling microscopy (STM)
imaging at the solid/liquid interface, and the redox properties of
compounds fully investigated by cyclic voltammetry. Our simple
and modular approach based on the chemical functionalization
of salophen scaffolds enables to decorate surfaces and
interfaces with multiple functions with a sub-nanometer precision,
for potential applications in material chemistry and catalysis.
Acknowledgements
Bologna University, Fondazione Del Monte, SLAMM project are
acknowledged for financial support to Andrea Gualandi and
Luca Mengozzi. This work was supported by the European
Community through the project EC FP7 ICT-MOLARNET
(318516) and the European Research Council project
SUPRAFUNCTION (GA-257305) the Agence Nationale de la
Recherche through the LabEx project Chemistry of Complex
Systems (ANR-10-LABX-0026_CSC) and the International
Center for Frontier Research in Chemistry.
Experimental Section
Keywords: Salophen• HOPG• Self-assembly• Cyclic
voltammetry• STM microscopy
Electrochemistry: cyclic voltammetry was conducted in a three electrodes
cell where the working electrode is Pt disc (Ø=125 µm), counter is Pt
spiral and quasi-reference electrode is Ag spiral. Ferrocene-salophen
molecules were dissolved in dry dichloromethane (0,1 mM) with
tetrabutylammonium hexafluorophosphate (80 mM). Before and
throughout the CV experiments, the electrochemical cell is kept free from
water and oxygen. Decamethylferrocene was used as internal standard
at the end of every measurement. Details have been provided
[
[
1]
2]
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
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Salen witches! Functionalized HOPG
surfaces can be obtained by
L. Mengozzi, M. El Garah, A. Gualandi,
M. Iurlo, A. Fiorani, A. Ciesielski, M.
Marcaccio, F. Paolucci, P. Samorì, and
P. G. Cozzi
ROAl(Salophen) molecules (RO =
phenol substituted derivatives) by self
-
assembly. Phosphines or ferrocene
moieties can be simply introduced by
this technique on graphitic surface,
and fully characterized by STM and
electrochemistry.
Page No. – Page No.
Phenoxy Al(Salophen) Scaffolds:
Synthesis, Electrochemical
properties, and Self-Assembly at
Surfaces of Multifunctional Systems
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