Two morphologies of stable, highly ordered assemblies of a long-chain-substituted [2 × 2]-grid-type FeII complex adsorbed on HOPG

Article abstract of DOI:10.1002/ejic.200500064

The programmed self-assembly of a multimetallic grid-type supramolecular architecture and its hierarchical organization on graphite are described. The doubly functionalized 4,6-bis(2,2′-bipyridyl-6-yl)-2-phenylpyrimidine derivative 1, equipped with CH₂OC₁₆H₃₃ moieties at the terminal pyridine rings, was designed as a new bis(tridentate) ligand and synthesized using Stille-type coupling reactions. Treatment of ligand 1 with Fe(BF₄)₂·6H₂O in CHCl ₃/CH₃CN led to the spontaneous formation of a [2 × 2]-grid-type Fe^II complex 2 in quantitative yield. The self-assembled tetranuclear complex 2 was adsorbed onto highly oriented pyrolytic graphite (HOPG) and studied by scanning tunneling microscopy (STM), which showed two morphologies of highly ordered two-dimensional arrays of the metallo-supramolecular archi tectures. The resulting monolayers of the grid-type complex 2 are much more stable than that obtained from the corresponding unsubstituted grid-type complex owing to the additional attractive forces between the hexadecyl moieties in 2 and the HOPG surface. Moreover, the reproducibility of the STM images of the hexadecyl-substituted grid 2 was strongly improved compared to the unsubstituted one. These results suggest that the introduction of long alkyl chains into metallo-supramolecular architectures would have general advantages for their organization and STM investigation on HOPG. Details of the preparation and the STM investigation of ligand 1 are also presented. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejic.200500064

FULL PAPER
Two Morphologies of Stable, Highly Ordered Assemblies of a Long-Chain-
Substituted [2×2]-Grid-Type FeII Complex Adsorbed on HOPG
Ahmed Mourran[a][‡]Ulrich Ziener,[a] Martin Möller,*[a][‡] Esther Breuning,[b]
Masakazu Ohkita,[b,c] and Jean-Marie Lehn*[b]
Keywords: Iron / Long alkyl chains / Scanning tunneling microscopy / Highly oriented pyrolytic graphite / Nanopatterning /
Self-assembly
The programmed self-assembly of a multimetallic grid-type
supramolecular architecture and its hierarchical organization
on graphite are described. The doubly functionalized 4,6-
bis(2,2Ј-bipyridyl-6-yl)-2-phenylpyrimidine derivative 1,
equipped with CH2OC16H33 moieties at the terminal pyridine
rings, was designed as a new bis(tridentate) ligand and syn-
thesized using Stille-type coupling reactions. Treatment of li-
gand 1 with Fe(BF4)2·6H2O in CHCl3/CH3CN led to the spon-
taneous formation of a [2×2]-grid-type FeII complex 2 in
quantitative yield. The self-assembled tetranuclear complex
2 was adsorbed onto highly oriented pyrolytic graphite
(HOPG) and studied by scanning tunneling microscopy
(STM), which showed two morphologies of highly ordered
two-dimensional arrays of the metallo-supramolecular archi-
tectures. The resulting monolayers of the grid-type complex
2 are much more stable than that obtained from the corre-
sponding unsubstituted grid-type complex owing to the ad-
ditional attractive forces between the hexadecyl moieties in
2 and the HOPG surface. Moreover, the reproducibility of the
STM images of the hexadecyl-substituted grid 2 was strongly
improved compared to the unsubstituted one. These results
suggest that the introduction of long alkyl chains into
metallo-supramolecular architectures would have general
advantages for their organization and STM investigation on
HOPG. Details of the preparation and the STM investigation
of ligand 1 are also presented.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
dinative interactions) as well as weak, nondirectional inter-
actions (such as van der Waals force and hydrophobic inter-
action). In this study we examined the hierarchical organi-
zation of a self-assembled multimetallic supramolecular
architecture on graphite.
We have previously shown that the self-assembly of bi-
s(tridentate) ligands, based on terpyridine-like binding sites,
with octahedrally coordinated metal ions such as FeII, CoII,
and ZnII leads to [2×2]-grid-type complexes.[2–4] These
complexes present interesting electronic, redox, and mag-
netic properties such as electronic interactions between the
metal centers,[2] multilevel electrochemical reduction up to
10 reversible steps,[5] antiferromagnetic transition at low
temperatures,[6] and spin crossover phenomena triggered by
temperature, pressure, and light.[7] For technological appli-
cation a further 2D or 3D ordering of these supramolecular
complexes is required. Several strategies have been exam-
Introduction
The design and formation of ordered nanoscaled struc-
tures with functional properties have attracted considerable
attention in materials science and nanotechnology.[1] A bot-
tom-up approach based on the self-assembly of simple
building units to nanometric-size objects is expected to be
a powerful tool, instead of microfabrication as a top-down
approach, for producing functional materials with great
technological advantages. Especially interesting is a sequen-
tial application of different self-organization principles for
the preparation of hierarchically structured materials. This
would be realized by the controlled use of relatively strong,
directional interactions (such as hydrogen bonds and coor-
[a] Organische Chemie III/Makromolekulare Chemie, Universität
Ulm,
Albert-Einstein-Allee 11, 89081 Ulm, Germany
[b] Laboratoire de Chimie Supramoléculaire, ISIS, Université ined to obtain such ordered arrangement of the grid-type
Louis Pasteur 8,
supramolecular architectures, including self-assembly at the
Allée Gaspard Monge, B. P. 70028, 67083 Strasbourg cedex,
air-water interface,[8] hydrogen-bonded crystal formation,[9]
France
and adsorption on graphite.[10,11] An excellent method to
Fax: +33-3-90245140
E-mail: lehn@isis.u-strasbg.fr
visualize such assemblies with submolecular resolution on
[c] Department of Applied Chemistry, Nagoya Institute of Tech-
for example highly ordered pyrolytic graphite (HOPG) is
represented by scanning tunneling microscopy (STM).[12]
However, the stabilities of the monolayers obtained from
unsubstituted [2×2]-grid-type complexes[10] and its pyridyl-
nology,
Nagoya 466-8555, Japan
[‡] Present address: Deutsches Wollforschungsinstitut, RWTH
Aachen,
Pauwelsstraße 8, 52056 Aachen, Germany
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DOI: 10.1002/ejic.200500064
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A. Mourran, U. Ziener, M. Möller, E. Breuning, M. Ohkita, J.-M. Lehn
FULL PAPER
substituted derivatives[11] are low, and thus their STM
images are obtained only with low reproducibility. To ad-
dress these problems, we have designed as a new ligand 4,6-
bis(2,2Ј-bipyridyl-6-yl)-2-phenylpyrimidine (1), equipped
with CH2OC16H33 moieties at the terminal pyridine rings.
The long alkyl chains are expected to result in better ad-
sorption on graphite.[13] Herein, we describe the details of
the nanopatterning of HOPG by the long-chain-substituted
[2×2]-grid-type complex 2, together with the preparation
and STM investigation of ligand 1.
Results and Discussion
Synthesis of Ligand 1 and Self-Assembly of [2×2]-Grid-
Type FeII Complex 2
The synthesis of the long-chain-substituted ligand 1 is
outlined in Scheme 1. Deprotonation of 2-bromo-5-(hy-
droxymethyl)pyridine (3), which was readily accessible from
commercially available 2-hydroxy-5-pyridinecarboxylic
acid,[14] with sodium hydride in DMF followed by treat-
ment with hexadecyl iodide afforded ether 4 in 66% yield.
Stannylation of 4 with a hexamethyldistannane/Pd(PPh3)4
system in refluxing toluene produced 5, which was in turn
coupled with 2,6-dibromopyridine in the presence of
Pd(PPh3)4 to afford bipyridine derivative 6 in 52% yield.
Twofold Stille coupling of 4,6-dichloro-2-phenylpyrimi-
dine[15] with 2 equiv. of 7, which was prepared by stan-
nylation of 6 with a hexamethyldistannane/Pd(PPh3)4 sys-
tem, in refluxing toluene in the presence of Pd(PPh3)4 gave
the desired ligand 1 in 57% yield.
Scheme 2. Formation of the [2×2]-grid-type FeII complex 2, i)
Fe(BF4)2·6H2O, CHCl3/CH3CN (1:1).
.
STM Investigation of Ligand 1 Adsorbed on HOPG
Self-assembly of ligand 1 on HOPG results in a highly
ordered structure; the representative STM image of 1 is
shown in Figure 1. Brighter and darker lamellae alternate
within the image, where a bright color represents higher
electron density. The periodicity of the lamellae is 55 Å. The
brighter moiety exhibits a width of 25 Å and the darker
moiety a width of 30 Å. The bright stripe shows a struc-
tured pattern with numerous small bright spots and is at-
tributed to the aromatic rings. The darker stripe presents
Scheme 1. Synthesis of ligand 1, i) NaH, DMF, then C16H33I; ii)
Me3SnSnMe3, Pd(PPh3)4, toluene; iii) 2,6-dibromopyridine,
Pd(PPh3)4; iv) Me3SnSnMe3, Pd(PPh3)4, toluene; v) 4,6-dichloro-
2-phenylpyrimidine, Pd(PPh3)4.
Reaction of 1 with Fe(BF4)2·6H2O in acetonitrile/chloro-
form (1:1) proceeded smoothly and cleanly to yield the cor-
responding [2×2]-grid-type complex 2 in quantitative yield,
as similarly shown earlier for the formation of related com-
plexes (Scheme 2).[2–4] The electrospray mass spectrum of 2
confirms its [2×2]-grid-like structure in solution.[16]
Figure 1. STM image of 1 on HOPG from 1,2,4-trichlorobenzene:
Lamellar widths: 25 and 30 Å; Vbias = –362 mV, Iset = 23.8 pA.
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Two Morphologies of an FeII Complex Adsorbed on HOPG
FULL PAPER
Scheme 3. Proposed model for the conformation and ordering of 1 on graphite.
.
an additional pattern of linear arrays of spots, which form ily distinguished from the features of ligand 1 (Figure 1).
an angle of 50° with the ribbons. These linear arrays are Hence, we assume that 2 forms at the solution/HOPG inter-
assigned to the alkyl chains in 1. The image can be interpre- face at least two different morphologies. The formation of
ted as a flat arrangement of the aromatic rings on the sur- (pseudo)polymorphs[20] in 2D monolayers – sometimes de-
face, which is expected for optimal contact between the pending on the solvent[21] – is known but the grid-like com-
monolayer and the basal plane of graphite. The alkyl chains plexes of HOPG polymorphism were only observed in the
in 1 are ordered commensurately with the graphite lat- case of different substituents in the periphery and in the
tice.[13] The conformation of the aromatic units of 1 on the center of the complexes, respectively.[10]
surface would be analogous to those observed for related
A detailed view of domain A (Figure 2b) shows that the
compounds both in solution and in the solid state, i.e., a brighter stripes are built from square-like entities with an
transoid conformation of the NC–CN bonds connecting the edge length of 22 to 24 Å whereas the darker ribbons are
heterocycles, as indicated in our previous studies.[11,17–19] In structured by more narrow and broader stripes perpendicu-
the lower left corner of the STM image (Figure 1Ͻyigr1Ͼ) lar to the ribbon direction. Because of the differences in
a defect can be observed.
electron density we attribute the brighter ribbons to the
A plausible model for the arrangement of 1 on the sur- grid-like structure of the aromatic part of 2 and the darker
face is shown in Scheme 3. In this model, the bright stripes bands to the alkyl substituents.
are formed by the aromatic part of two rows of molecules
Regarding a reasonable model for the arrangement of 2
of 1, which may be stabilized by weak intramolecular C– in domain A the fourfold symmetry of the square-like enti-
H···N interactions.[11,17–19] The alkyl chains form an angle ties in Figure 2b gives hints for an arrangement of 2 with
of 50° with this stripe. From geometrical estimations the the C4 axis perpendicular to the substrate surface
expected widths of the ribbons fit very well with the experi- (Scheme 4c). In Scheme 4a the geometrical dimensions of
mental values. The tilt angle of the alkyl chains with the the grid core of 2 show that we expect an edge length for
main axis of the lamellae allows the optimal contact of ca. the squares without the alkyl chains of 18 Å. The larger size
4.5 Å between neighboring chains.[11] The comparison of of the square-like shapes in Figure 2b suggests that each
the length of the alkyl chains in 1 and the observed width of grid-like complex is rotated along the C4 axis so that the
the darker stripes in the image suggests a noninterdigitated ligands are no longer parallel and orthogonal, respectively,
assembly of the alkyl chains.
to the main direction of the bright stripes but form an angle
of 20–30° and 110–120°, respectively (Scheme 4c). A further
stripy fine structure of the square-like bright areas in the
direction of one set of two parallel ligands per complex
molecule with the above given angles supports this assump-
tion. There is no optimal contact possible between the alkyl
chains and the graphite surface due to the nonplanar struc-
ture of 2. We suggest that the chains adopt a conformation
similar to that shown in Scheme 4b, which exhibits the side
view of one ligand molecule 1 in its conformation in com-
plex 2. Such conformation allows close contact between a
part of an alkyl chain and graphite. The width of the darker
ribbons of 18 Å is too small for a noninterdigitated arrange-
STM Investigation of [2×2]-Grid-Type FeII Complex 2
Assembled on HOPG
Representative STM images of the [2×2]-grid-type FeII
complex 2 on HOPG are shown in Figure 2. The large scan
area exhibits two domains of alternating brighter and
darker ribbons (Figure 2a). On the first glimpse both do-
mains seem to represent the same structure with changing
preferred directions. A closer look reveals that the periodici-
ties of the ribbons differ between 42 Å (domain A) and
23 Å (domain B), respectively, but both domains can be eas-
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A. Mourran, U. Ziener, M. Möller, E. Breuning, M. Ohkita, J.-M. Lehn
FULL PAPER
Scheme 4. Proposed model for the arrangement of 2 on HOPG in
domain A: top view of one grid-like complex along the C2 axis (a,
left), side view of one grid-like complex (a, right), side view of one
ligand 1 with the proposed conformation of the alkyl chains ensur-
ing close contact between the surface and the alkyl chains (b), top
view of the arrangement of the grid-like complexes on HOPG (c).
A detailed view of domain B shows lamellae which are
built from a bright and a dark band, the dark formed by
fine stripes with an angle of 40° with respect to the ribbons
(Figure 2c). Theses stripes are assigned to the alkyl chains.
The bright parts are attributed to the high electron density
aromatic moieties of complex 2 showing an additional fine
structure with a periodicity of 17 Å.
Comparing with the much larger periodicity of the rib-
bons in domain A (42 Å, Figure 2b), we suggest an edge-
on arrangement of the complexes on the graphite in domain
Figure 2. STM images of 2 on HOPG from 1,2,4-trichlorobenzene:
Large-scan-area image with two different domains A and B (Vbias B (periodicity 23 Å, Figure 2c), though we cannot assign
= –651 mV, Iset = 39.4 pA) (a), detailed view of domain A with a
unambiguously the fine structure of the bright parts to the
lamellar structure (periodicity: 42 Å) and a periodic fine structure
structure of the grid-like complex. The edge-on arrange-
within each lamella (periodicity: 22 Å), a stripy fine structure with
ment of the complexes on the graphite may be accompanied
an angle of ca. 115° with respect to the lamella axis is visible, too
by a tilt angle of up to 70° which would lead to a projected
area of 17×18 Å (Scheme 5). This arrangement should lead
to an improved contact between the two alkyl chains next
to the graphite and the graphite surface at the expense of
the other six alkyl chains which are bent to come at least
(Vbias = –410 mV, Iset = 36.6 pA) (b), detailed view of domain B
with a lamellar structure (periodicity: 23 Å) and a periodic fine
structure within each lamella (periodicity: 17 Å; Vbias = –344 mV,
Iset = 44.1 pA) (c).
ment of the alkyl chains despite the above suggested confor- partially into contact with the graphite surface. An ad-
mation. Hence, we assume interdigitation which on the ditional consequence of such an arrangement is a stacking
other side would lead, with the assumed orientation of the of the complexes which should be advantageous due to
grid-like complexes, to a partial bumping of the alkyl chains their highly charged character. Within one ribbon the com-
(see Scheme 4c). Though the resolution of the STM image plexes are assumed to be parallel to each other. Comparing
in Figure 2b does not give enough information on the exact adjacent ribbons a shift between two neighboring molecules
ordering of the alkyl chains we suppose that at these posi- of ca. 6 Å can be found which might be caused by the pack-
tions the alkyl chains are approximately on top of each ing of the alkyl chains.
other. This might cause the contrast of brighter stripes
within the darker ribbons in Figure 2b because of the top- (see Figure 2a) but we do not yet know how the formation
ography and not primarily due to higher electron density. of one or the other morphology can be controlled. The
The two arrangements of complex 2 coexist on HOPG
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Two Morphologies of an FeII Complex Adsorbed on HOPG
FULL PAPER
under ambient conditions; chemical shifts are given in ppm using
TMS as reference. 13C NMR spectra were recorded with a Bruker
AC200 spectrometer in CDCl3 at 50 MHz, also under ambient con-
ditions; chemical shifts are given in ppm using the solvent peak as
reference. Fast atom bombardment (FAB) mass spectra were re-
corded with a ZAB-HF VG spectrometer with m-nitrobenzyl
alcohol as the matrix. Electrospray (ES) mass spectra were re-
corded with a triple quadrupole mass spectrometer Quattro II. The
microanalyses were carried out at the Service Central de Microana-
lyse du CNRS, Faculté de Chimie, Strasbourg. Column chromatog-
raphy was carried out on Merck silica gel 60 or Merck alumina
activity II–III. 2-Bromo-5-(hydroxymethyl)pyridine (3)[14] and 4,6-
dichloro-2-phenylpyrimidine[15] were prepared according to known
procedures.
2-Bromo-5-(hexadecyloxymethyl)pyridine (4): To a suspension of so-
dium hydride (128 mg, 5.32 mmol, 60% dispersion in oil) in anhy-
drous DMF (6 mL) was added 2-bromo-5-(hydroxymethyl)pyridine
(3)[14] (500 mg, 2.7 mmol) and the reaction mixture was stirred at
room temperature for 1 h. The suspension was cooled to 0 °C and
hexadecyl iodide (1.06 g, 3.0 mmol) was added to it. The mixture
was then allowed to warm to room temperature and stirred for
44 h. After evaporation of the solvent, the residue was subjected to
chromatography on silica gel eluting with hexane/EtOAc (4:1, v/v)
to afford 4 as a colorless powder (723 mg, 66%). M.p. 47 °C. 1H
NMR (200 MHz, CDCl3): δ = 0.84 (t, J = 6.7 Hz, 3 H, CH3), 1.22
(m, 26 H, CH2), 1.57 (quint, J = 6.7 Hz, 2 H, OCH2CH2), 3.44 (t,
J = 6.4 Hz, 2 H, OCH2), 4.42 (s, 2 H, CpyCH2O), 7.41 (d, J =
8.2 Hz, 1 H, 4-H), 7.51 (dd, J = 8.2 and 2.4 Hz, 1 H, 3-H), 8.28
(d, J = 1.8 Hz, 1 H, 6-H). 13C NMR (50 MHz, CDCl3): δ = 14.0,
22.6, 26.1, 29.3, 29.4, 29.6, 31.9, 69.4, 71.0, 127.8, 133.5, 137.8,
141.1, 149.2. MS (FAB): m/z (%) = 412.1 (100) [M + H]+. IR (KBr):
Scheme 5. Proposed model for the arrangement of 2 on HOPG in
domain B: top view of the arrangement of the grid-like complexes
(top), side view of the arrangement of the grid-like complexes par-
allel to the graphite surface with an angle of 70° resulting in a
projected area of 17×18 Å (bottom). Only the grid cores are
shown, the alkyl chains are omitted for clarity.
forms are stable enough not to be transformed into each
other by the STM tip or any other external trigger present
in the course of our STM experiments.
ν = 2954, 2916, 2851, 1586, 1566, 1473, 1458, 1388, 1110, 1089,
˜
1026, 842, 824, 716, 630 cm–1. C22H38BrNO (412.46): calcd. C
64.20, H 9.31, N 3.41; found C 64.07, H 9.46, N 3.38.
Conclusions
The doubly functionalized ligand 1, having CH2OC16H33
moieties at the terminal pyridine rings, was designed as a
new bis(tridentate) ligand and synthesized. Treatment of 1
with Fe(BF4)2·6H2O in CHCl3/CH3CN led to the spontane-
ous formation of a [2×2]-grid-type FeII complex 2 in a
quantitative yield. The STM investigations of both ligand 1
and the FeII complex 2 on graphite revealed their stable,
regular arrangements on the surfaces. Complex 2 shows two
different morphologies – a flat and an edge-on assembly of
the grid-like complexes on HOPG. We do not yet know
the factors determining the formation of one or the other
arrangement. Importantly, stability of the monolayers of
the long-chain-substituted complex 2, and thus, reproducib-
ility of their STM images have been significantly enhanced
compared to the corresponding unsubstituted complex.
Therefore, the present results suggest that the introduction
of long alkyl chains into the ligand would be a useful strat-
egy for the STM investigations of the related grid-type com-
plexes as well as other metallo-supramolecular architectures
on HOPG surfaces.
2-Bromo-6-[5Ј-(hexadecyloxymethyl)pyrid-2Ј-yl]pyridine (6): A mix-
ture of
4 (1 g, 2.42 mmol), hexamethyldistannane (880 mg,
2.66 mmol), and Pd(PPh3)4 (70 mg, 0.060 mmol) in toluene
(16 mL) under argon was refluxed for 4 h. 2,6-Dibromopyridine
(1.26 g, 5.32 mmol) and Pd(PPh3)4 (120 mg, 0.11 mmol) were
added to the mixture and the reaction mixture was further refluxed
under argon for 20 h. After evaporation of the solvent, the residue
was subjected to chromatography on silica gel eluting with hexane/
EtOAc (9:1, v/v) to afford 6 as a colorless powder (620 mg, 52%).
1
M.p. 67 °C. H NMR (200 MHz, CDCl3): δ = 0.88 (t, J = 6.1 Hz,
3 H, CH3), 1.25 (m, 26 H, CH2), 1.56–1.72 (m, 2 H, OCH2CH2),
3.50 (t, J = 6.4 Hz, 2 H, OCH2), 4.57 (s, 2 H, CpyCH2O), 7.47 (dd,
J = 7.9 and 1.2 Hz, 1 H, 3Ј- or 5Ј-H), 7.65 (t, J = 7.9 Hz, 1 H, 4Ј-
H), 7.79 (dd, J = 8.2 and 2.4 Hz, 1 H, 3-H), 8.37 (dd, J = 7.6 and
0.9 Hz, 1 H, 3Ј- or 5Ј-H), 8.38 (d, J = 8.2 Hz, 1 H, 4-H), 8.62 (d,
J = 2.1 Hz, 1 H, 6-H). 13C NMR (50 MHz, CDCl3): δ = 14.0, 22.6,
26.1, 29.3, 29.4, 29.6, 31.8, 70.0, 70.8, 119.5, 120.9, 127.7, 134.7,
136.0, 139.0, 141.4, 148.3, 153.6, 157.1. MS (FAB): m/z (%) = 489.4
(100) [M + H]+. IR (KBr): ν = 2953, 2916, 2849, 1600, 1570, 1545,
˜
1470, 1434, 1387, 1124, 1026, 988, 801, 777, 754, 718, 672 cm–1.
C27H41BrN2O (489.54): calcd. C 66.25, H 8.44, N 5.72; found C
66.17, H 8.32, N 5.74.
4,6-Bis{6Ј-[5ЈЈ-(hexadecyloxymethyl)pyrid-2ЈЈ-yl]pyrid-2Ј-yl}-2-phen-
ylpyrimidine (1): A mixture of 6 (300 mg, 0.61 mmol), hexamethyl-
distannane (221 mg, 0.64 mmol), and Pd(PPh3)4 (21 mg,
0.018 mmol) in toluene (4 mL) under argon was refluxed for
25 min. After evaporation of the solvent, the resultant crude stan-
nylated product 7 was used for the following coupling reaction
Experimental Section
General: Melting points were measured with a digital Electro-
therma apparatus and are uncorrected. H NMR spectra were re-
corded with a Bruker AC200 spectrometer in CDCl3 at 200 MHz
1
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A. Mourran, U. Ziener, M. Möller, E. Breuning, M. Ohkita, J.-M. Lehn
these determinations is estimated below 5% for distances and
FULL PAPER
without further purification. 1H NMR (200 MHz, CDCl3): δ = 0.39
[s, 9 H, Sn(CH3)3], 0.89 (t, J = 6.1 Hz, 3 H, CH3), 1.26 (m, 26 H, angles.
CH2), 1.63 (quint, J = 6.7 Hz, 2 H, OCH2CH2), 3.50 (t, J = 6.4 Hz,
2 H, OCH2), 4.57 (s, 2 H, CpyCH2O), 7.44 (dd, J = 7.3 and 1.5 Hz,
Acknowledgments
1 H, 3Ј- or 5Ј-H), 7.64 (t, J = 7.3 Hz, 1 H, 4Ј-H), 7.80 (dd, J = 8.2
and 2.4 Hz, 1 H, 3-H), 8.27 (dd, J = 7.9 and 1.2 Hz, 1 H, 3Ј- or
5Ј-H), 8.54 (d, J = 7.9 Hz, 1 H, 4-H), 8.62 (d, J = 1.5 Hz, 1 H, 6-
H). A mixture of 7 (334 mg, 0.58 mmol), 4,6-dichloro-2-phenylpyr-
imidine (8)[15] (66 mg, 0.29 mmol), and Pd(PPh3)4 (34 mg,
0.029 mmol) in toluene (5 mL) under argon was refluxed for 21 h.
After evaporation of the solvent, the residue was taken up in CHCl3
and filtered through a short pad of alumina. The solvent was evap-
orated, the residue was taken up in MeOH/acetone (1:1, v/v), and
the precipitate formed was centrifuged off, washed with MeOH/
acetone and dried in vacuo. The crude product thus obtained was
further purified by column chromatography on alumina eluting
with hexane/CHCl3 (1:1, v/v) to afford 1 as a colorless powder
(162 mg, 57%). M.p. 141 °C. 1H NMR (200 MHz, CDCl3): δ =
0.87 (t, J = 5.8 Hz, 6 H, CH3), 1.24 (m, 52 H, CH2), 1.67 (quint,
J = 7.0 Hz, 4 H, OCH2CH2), 3.56 (t, J = 6.4 Hz, 4 H, OCH2), 4.64
(s, 4 H, CpyCH2O), 7.56–7.65 (m, 3 H, m- and p-H), 7.87 (d, J =
6.7 Hz, 2 H, 3Ј- or 5Ј-H), 8.05 (t, J = 7.9 Hz, 2 H, 4Ј-H), 8.60 (d,
J = 7.9 Hz, 2 H, 3Ј- or 5Ј-H), 8.71–8.80 (m, 8 H, o-, 3ЈЈ-, 4ЈЈ- and
6ЈЈ-H), 9.62 (s, 1 H, 5-H). 13C NMR (50 MHz, CDCl3): δ = 14.1,
22.7, 26.2, 29.3, 29.5, 29.6, 29.6, 29.6, 29.7, 29.8, 31.9, 70.3, 70.9,
111.5, 120.8, 121.7, 122.4, 128.4, 128.4, 130.6, 134.4, 136.0, 137.9,
137.9, 148.5, 153.8, 155.3, 155.4, 163.9, 164.1. MS (FAB): m/z (%)
We thank the Ministry of Education, Science, Sports, and Culture
of Japan (M. O.), Université Louis Pasteur (M. O.), and the Min-
istère de l’Education Nationale, de la Recherche et de la Technolo-
gie (E. B.). The work was further supported by the Deutsche For-
schungsgemeinschaft within the framework of the Sonderfor-
schungsbereich 569 at the University of Ulm and is part of the
Marie Curie Research Training Network program BioPolySurf,
which is financially supported by the EU under contract no.
MRTN-CT-2004-005516. We also thank P. Maltèse (NMR) and H.
Nierengarten (ES MS) for their spectroscopic measurements.
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= 973.7 (100) [M + H]+. IR (KBr): ν = 3060, 2918, 2850, 1720,
˜
1556, 1540, 1471, 1377, 1263, 1115, 1022, 994, 814, 50, 718, 690,
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[2×2]-Grid-Type FeII Complex (2): A mixture of 1 (5 mg, 5.14
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1116.4 [M – 4 BF4]4+, 876.3 [M – 5 BF4]5+
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STM Investigations: STM measurements were carried out under
ambient conditions with a low-current RHK 1000 control system.
STM imaging of the adlayers was performed at the internal inter-
face between HOPG and a concentrated solution of the ligand 1,
dissolved in 1,2,4-trichlorobenzene, according to the procedure of
Rabe.[13a] A drop of the solution was placed on a freshly cleaved
HOPG surface, while the surface had already been scanned by
STM under the conditions that allowed atomic resolution of the
graphite surface structure. A potential of U = 1 V was applied to
the substrate. The scan rate was varied between 0.2 and 0.6 μms–1.
The tunneling current set point was 8–20 pA. All images presented
were obtained at constant current mode using a Pt/Ir (90:10) tip,
which was mechanically sharpened. Complex 2 was dissolved in
acetonitrile at a concentration less than 1 wt.-%. A drop of the
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substrates were dried in the presence of acetonitrile vapor over 1 h
(in a covered Petri dish with a few mL of acetonitrile next to the
sample). Then the sample was taken out of the Petri dish and dried
fully under ambient conditions. The molecular structure of the ad-
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2646
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 2641–2647

Two Morphologies of an FeII Complex Adsorbed on HOPG
FULL PAPER
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Published Online: May 27, 2005
Eur. J. Inorg. Chem. 2005, 2641–2647
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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