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The Deposition of Metallopeptide-Based Coordination Polymers on Graphite Substrates Effects of Side-Chain Functional Groups and Local Surface Structure.

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Angewandte
Chemie
Coordination Polymers
The Deposition of Metallopeptide-Based
Coordination Polymers on Graphite Substrates:
Effects of Side-Chain Functional Groups and
Local Surface Structure**
Slobodan Novokmet, Mohammad S. Alam,
Viatcheslav Dremov, Frank W. Heinemann,
Paul Mller,* and Ralf Alsfasser*
Coordination polymers have attracted much attention in the
development of new functional materials[1] owing to their
many interesting properties such as zeolitic behavior,[2]
conductivity,[3] luminescence,[4] magnetism,[5] spin-crossover,[6]
and nonlinear optical effects.[7] Stimulated by possible applications, scientists have made impressive progress in the socalled crystal engineering of solid materials.[8] Yet the equally
important controlled assembly of metal-organic polymers on
solid surfaces is in its infancy.[9] A central focus of this
research must be the investigation of elementary structureformation processes on substrate surfaces. With a series of
structurally similar polymers containing different aromatic
amino acid building blocks, we were able to study both the
effects of substituents and local surface properties on the
deposition of coordination polymers on highly ordered
pyrolytic graphite (HOPG).
Scheme 1 illustrates our synthetic approach. Cleavage of
the methyl ester or benzyl ester protecting groups in zinc
complexes of dipicolylglycyl (Dpg) peptides results in the
formation of a free carboxylate function, which binds to the
metal ion under slightly acidic conditions. The coordination
polymers that form precipitate from aqueous solutions. We
have already reported on the synthesis and structure of
[{Zn(Dpg-Phe-O)}n] (CF3SO3)n (1; Phe = phenylalanine).[10]
Here we present two new compounds, [{Zn(Dpg-TyrO)}n] (CF3SO3)n (Tyr = tyrosine, 2) and [{Zn(Dpg-Nal-
Scheme 1. Synthesis of the homochiral helical coordination polymers 1?3.
[*] M. S. Alam, Dr. V. Dremov, Prof. Dr. P. Mller
Physikalisches Institut III
Universitt Erlangen-Nrnberg
Erwin-Rommel-Strasse 1, 91058 Erlangen (Germany)
Fax: (+ 49) 9131-15-249
E-mail: phm@physik.uni-erlangen.de
Priv.-Doz. Dr. R. Alsfasser
Institut fr anorganische Chemie
Universitt Freiburg
Albertstrasse 21, 79104 Freiburg (Germany)
Fax: (+ 49) 761-203-6012
E-mail: ralf.alsfasser@ac.uni-freiburg.de
S. Novokmet, Dr. F. W. Heinemann
Institut fr anorganische Chemie
Universitt Erlangen-Nrnberg
Egerlandstrasse 1, 91058 Erlangen (Germany)
[**] We gratefully acknowledge support from the SFB 583.
Angew. Chem. Int. Ed. 2005, 44, 803 ?806
O)}n] (CF3SO3)n (Nal = 2-naphthylalanine, 3). Ortep plots of
their structures are given in Figures 1 and 2. The cationic
polymers in 1?3 are very similar. In all cases right-handed
antiparallel-packed helices are found, in which three zinc
complex fragments make up each turn. Only the pitch
increases from 14.80 in 1 to 14.83 in 2 and 15.06 in 3,
most likely as a consequence of the larger aryl substituents.
The structural similarity of 1?3 was a desired feature since
it enabled us to compare the effects of different aromatic side
chains on the deposition of helical coordination polymers on
HOPG by scanning tunneling microscopy (STM). It turned
out that the phenylalanine and napthylalanine derivatives 1
and 3 do not form sufficiently stable patterns. Only the
tyrosine derivative 2 gave satisfactory results. The phenolic
tyrosyl OH groups seem to be necessary for a sufficient grip
on the substrate surface. Samples of 2 on HOPG were
DOI: 10.1002/anie.200461274
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
803
Communications
conveniently prepared by allowing 10 9 m aqueous solutions
of pH 5 to 6 to evaporate under air. Figure 3 shows that the
polymer adopts two different structures depending on the
local environment. A double-helical plait is formed on
Figure 1. Top: Ortep plot (ellipsoids at 30 % probability) of a single
cation in 2; shown is the second complex in the trimeric asymmetric
unit. Bottom: View along the 100 axis of the helical polymer.
Figure 3. STM topographies (HOPG) showing a) the formation of
double-helical superstructures on two different undisturbed surface
areas (left: 108 108 nm2 ; right: 42 42 nm2); b) a 10 10 nm2 detail
of a double-helix (left: 2D, right: 3D); and c) the aggregation of linear
polymer strands at steps on the surface (left: 2D, right: 3D;
100 100 nm2).
Figure 2. Top: Ortep plot (ellipsoids at 30 % probability) of a single
cation in 3; shown is the second complex in the trimeric asymmetric
unit. Bottom: View along the 100 axis of the helical polymer.
804
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
undisturbed flat surface areas (Figure 3 a and b). The distance
between two crossing points is approximately 6 nm. Each of
the two intertwined strands has a diameter of roughly 13.8 ,
indicating that it consists of a single helical coordination
polymer. Interestingly, the double-helical superstructure has a
left-handed chirality that is opposite to the right-handed
molecular helicity. Double helices most probably form
because a flat surface does not provide any means of
stabilization for the polymer, and intermolecular interactions
are dominant. However, the macromolecules show a preference for steps, which may be regarded as one-dimensional
distortions. Figure 3 c shows that the polymer 2 nicely
decorates a step and even follows a sharp kink. The structure
has changed drastically, presumably as a consequence of
stronger interactions with the distorted surface. Linearly
stretched polymer strands are formed. Single strands are not
resolved in Figure 3 c but the width of approximately 11 nm
indicates that roughly eight helices are packed together, most
likely in the same antiparallel fashion as that observed in the
crystal structure.
In a few cases we were able to map single linear polymer
strands with high magnification (Figure 4 a). Again, the width
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Angew. Chem. Int. Ed. 2005, 44, 803 ?806
Angewandte
Chemie
Figure 4. Topography and CITS image of a linear polymer strand
recorded simultaneously. V = 72.9 mV, tunneling current = 0.2 nA.
a) Topography (5 5 nm2), b) current image (5 5 nm2) at 135 mV.
of the structure conforms to the diameter of a single
molecular strand. Figure 4 b depicts a CITS image recorded
simultaneously. CITS (current imaging tunneling spectroscopy) records tunneling current?voltage characteristics at
every point of the topography map. The tip-to-sample
distance is defined by the topography parameters. CITS
reveals a three-dimensional data set of current and bias
voltage vs. position. Usually cross sections at some selected
bias points are plotted as current images. The current contrast
changes significantly when at certain bias values new molecular energy levels come into play, thus enhancing the
information obtained from topography alone. Figure 4 b is a
current image taken at a tunneling bias of 135 mV. One
clearly recognizes a periodicity along the strand which
conforms to the length of a single molecule (14.85 , see
the scale bar in Figure 4 b).
As a control, we prepared and investigated samples of the
amino acid ligand alone under conditions similar to those
employed with the polymer solution. The structures formed
are completely different from those of the coordination
polymer. Linear arrangements of single or multiple strands of
molecules are observed. Helical topologies are not detected.
For these low concentrations the surface is rather empty.
Effects resulting from the self-organization of dense molecular layers are certainly not expected.[11]
Scheme 2 summarizes our findings. On undisturbed
surfaces two right-handed homochiral helical coordination
polymers self-assemble to form a left-handed double-helical
superstructure. In contrast, steps on the surface induce the
formation of linearly stretched helical single strands which
aggregate to two-dimensional ribbons. The latter structure
resembles a two-dimensional slice through the three-dimensional crystal structure of 2 and indicates that crystal growth
starts at surface irregularities. These results shed first light on
some elementary steps during the pattern formation of metalorganic polymers on solid substrate surfaces.
Experimental Section
[Zn(Dpg-Nal-OBn)(H2O)](CF3SO3)2 and [Zn(Dpg-Tyr-OCH3)(H2O)](CF3SO3)2 : Solid Zn(CF3SO3)2 was added in one portion to a
stirred solution of the designated ligand in CH3CN. The solution was
stirred overnight and the solvent was removed under vacuum.
Addition of CH2Cl2 resulted in the formation of a cloudy solution,
which was left in a refrigerator at 20 8C overnight in order to
complete the precipitation of unchanged Zn(CF3SO3)2. Filtration and
Angew. Chem. Int. Ed. 2005, 44, 803 ?806
Scheme 2. Structure-formation processes in the coordination polymer
2. Linear strands are made up of from helical chains. On undisturbed
surfaces these strands coil to form a double-helical superstructure.
Steps in the surface result in an antiparallel aggregation of linear
strands. Layers of such sheets build a three-dimensional crystal.
removal of all solvent under vacuum provided the product as a white
solid.
1.56 g
(4.30 mmol)
[Zn(Dpg-Tyr-OCH3)(H2O)](CF3SO3)2 :
Zn(CF3SO3)2, 1.87 g (4.30 mmol) Dpg-Tyr-OCH3, 100 mL CH3CN,
50 mL CH2Cl2. Yield: 2.80 g, 3.43 mmol, 79.80 %. Elemental analysis
(%) calcd. for C26H28F6N4O11S2Zn (816.03 g mol 1): C 38.27, H 3.46, N
6.87, S 7.86; found: C 39.26, H 3.59, N 6.66, S 7.63; FAB-MS
(nitrobenzyl alcohol): m/z = 649 [M+ CF3SO3 H2O]; 1H NMR
(300 MHz, CD3OD): d = 2.58 (dd, 1 H, bCH2), 2.95 (dd, 1 H, bCH2),
3.58 (s, 3 H, OCH3), 3.61 (d, 1 H, C(O)CH2), 3.73 (d, 1 H, C(O)CH2),
4.39?4.54 (m, 5 H, pyCH2, aCH), 6.50 (m, 2 H, H2,6PhOH), 6.69 (m,
H3,5PhOH), 7.66 (m, 4 H, H3,5py), 8.13 (m, 2 H, H4py), 8.54 (m, 1 H,
H5py), 8.60 ppm (m, 1 H, H6py).
1.33 g
(3.67 mmol)
[Zn(Dpg-Nal-OBn)(H2O)](CF3SO3)2 :
Zn(CF3SO3)2, 2.00 g (3.67 mmol) Dpg-Nal-OBn, 100 mL CH3CN,
100 mL CH2Cl2. Yield: 3.00 g, 3.24 mmol, 88.26 %. Elemental analysis
(%) calcd. for C36H34F6N4O10S2Zn (926.19 g mol 1): C 46.68, H 3.70, N
6.05, S 6.92; found: C 46.82, H 3.36, N 6.27, S 7.63; FAB-MS
(nitrobenzyl alcohol): m/z = 757 [M+ CF3SO3 H2O]; 1H NMR
(300 MHz, CDCl3): d = 2.95 (m, 1 H, bCH2), 3.24?3.37 (m, 6 H,
b
CH2, C(O)CH2, n H2O), 3.53 (d, 1 H, pyCH2), 3.75?3.96 (m, 2 H,
pyCH2), 4.21 (d, 1 H, pyCH2), 4.96?5.07 (m, 3 H, aCH, CH2Bn), 6.80?
7.84 (m, 18 H, 5 HBn, 7 Hnaphtyl, H3,4,5py), 8.50 (d, 1 H, H6py), 8.70 (d,
1 H, H6py), 9.05 ppm (d, 1 H, NH).
2: [Zn(Dpg-Tyr-OCH3)(H2O)](CF3SO3)2 (1.00 g, 1.23 mmol) was
dissolved in 30 mL H2O. The pH was adjusted to 9.00 with 1m NaOH.
Consumption of base was monitored with a pH meter, and 1m NaOH
was used to keep the pH approximately constant at 9. The mixture
was stirred at room temperature until the pH remained constant (ca.
2 d). Lowering the pH to 4 with 0.2 m HCl was followed by the
immediate precipitation of the product 2�H2O, which was collected
on a sintered glass filter and dried under vacuum (0.50 g, 0.77 mmol,
62.35 %).
Elemental
analysis
(%)
calcd.
for
(C24H23F3N4O7SZn)3�H2O (1953.9 g mol 1): C 44.22, H 3.87, N 8.59,
S 4.92; found: C 44.15, H 3.75, N 8.54, S 4.96; FAB-MS (nitrobenzyl
alcohol): m/z = 483 [M+ CF3SO3]; 1H NMR (300 MHz, CD3OD):
d = 3.03 (dd, 1 H, bCH2), 3.24 (dd, 1 H, bCH2), 3.75 (s, 2 H, C(O)CH2),
3.95?4.39 (m, 4 H, pyCH2), 4.78 (m, 1 H, aCH), 6.63 (m, 2 H, H2,6PhOH),
7.11 (m, 2 H, H3,5PhOH), 7.41?7.56 (m, 4 H, H3,5py), 8.05 (m, 2 H, H4py),
8.22 (br. s, 1 H, 1 H6py), 8.81 ppm (d, 1 H, H6py).
3: [Zn(Dpg-Nal-OBn)(H2O)](CF3SO3)2 (1.68 g, 1.81 mmol) was
dissolved in 150 mL absolute CH3OH. Palladium/charcoal was added
as a catalyst. Hydrogen was passed over the stirred solution for 6 h at
70 8C. The mixture was filtered through celite and the solvent
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2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
805
Communications
removed by rotary evaporation. After the residue had been washed
with diethyl ether and dried under vacuum, the product 3�H2O was
obtained as a white powder (1.15 g, 1.68 mmol, 92.62 %). Elemental
analysis (%) calcd. for (C28H25F3N4O6SZn)3�H2O (2003.91 g mol 1):
C 48.60, H 4.03, N 8.10, S 4.63; found: C 48.67, H 3.96, N 8.14, S 4.48;
FAB-MS (nitrobenzyl alcohol): m/z = 667 [M+], 517 [M+ CF3SO3];
1
H NMR (300 MHz, CD3CN): d = 3.00 (dd, 1 H, bCH2), 3.36?3.68 (m,
4 H, bCH2, C(O)CH2, pyCH2), 3.95?4.23 (m, 3 H, pyCH2), 4.92 (m, 1 H,
a
CH), 7.27?7.69 (m, 11 H, Hnaphtyl, H3,5py), 7.96 (m, 1 H, H4py), 8.05 (m,
1 H, H4py), 8.22 (d, 1 H, NH), 8.38 (d, 1 H, H6py), 8.60 ppm (d, 1 H,
H6py).
X-ray structure analyses: Colorless needles of [{Zn(Dpg-TyrO)}3](CF3SO3)3�5 CH3OH稨2O (2) were obtained after slow diffusion of diethyl ether into a solution of the product in CH3OH over a
period of several weeks at room temperature. Colorless crystals of
[{Zn(Dpg-Nal-O)}3](CF3SO3)3�5 CH3OH (3) were obtained in an
analogous fashion. Suitable single crystals were embedded in
protective perfluoropolyether oil, and data were collected at 100 K
on a Bruker-Nonius KappaCCD diffractometer using MoKa radiation
(l = 0.71073 , graphite monochromator). Images were recorded
using f- and w-rotations with a rotation angle of 1.08 for 2 and 1.48 for
3, and an irradiation time of 100 s per frame for 2 and 210 s per frame
for 3. Lorentz, polarization, and semiempirical absorption corrections
(SADABS on the basis of multiple scans) were applied. The
structures were solved by direct methods and refined using fullmatrix least-squares procedures on F2 (SHELXTL NT 6.12). All nonhydrogen atoms were refined anisotropically (with the exception of
some disordered CH3OH molecules in 3 which were refined isotropically). All hydrogen atoms were geometrically positioned with
isotropic displacement parameters being 1.2 or 1.5 times U(eq) of
the corresponding C, N, or O atom. Compound 2 crystallizes with
8.5 molecules CH3OH and one H2O per formula unit. Some of the
CH3OH molecules in 2 are disordered and have been refined using
similarity restraints. Compound 3 crystallizes with 2.5 molecules
CH3OH per formula unit. These solvate molecules and two of the
CF3SO3 anions of 3 are disordered and were refined using a number of
restraints.
Selected
crystallographic
data
for
2:
C80.5H108F9N12O30.5S3Zn3 ; orthorhombic P212121 (no. 19), a =
14.834(2), b = 22.470(4), c = 29.320(4) ; Z = 4; V = 9773(3) 3 ;
1calcd = 1.492 g cm 3, m = 0.895 mm 1, Tmin = 0.743, Tmax = 1.000,
51 406 measured reflections (7.18 = 2q = 51.48), 16 501 unique reflections, 9940 observed reflections [I > 2s(I)], 1312 parameters, wR2 =
0.1727 (all data), R1 = 0.0764 [I > 2s(I)]. Selected crystallographic
data for 3: C86.5H85F9N12O20.5S3Zn3 ; monoclinic P21 (no. 4), a =
15.065(2), b = 13.053(2), c = 24.108(2) , b = 93.30(1)8, Z = 2; V =
4732.8(9) 3 ; 1calcd = 1.462 g cm 3, m = 0.912 mm 1, Tmin = 0.804,
Tmax = 1.000, 105 250 measured reflections (6.48 = 2q = 54.08), 20 414
unique reflections, 14 676 observed reflections [I > 2s(I)], 1305
parameters, wR2 = 0.1627 (all data), R1 = 0.0598 [I > 2s(I)]. CCDC
243711 (2) and CCDC 243712 (3) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: (+ 44) 1223-336-033; or deposit@
ccdc.cam.ac.uk)
STM measurements: The STM imaging was carried out under
ambient conditions using a home-built, low-drift microscope equipped with RHK1000 control electronics or with a commercial Nanoscope III system. A drop of the aqueous 10 9 m sample solution was
placed onto a freshly cleaved HOPG surface. Sections without
molecules clearly showed monoatomic resolution of the graphite
structure. Typically, tunneling currents between 10 and 200 pA were
employed. The bias voltage was 72.9 mV. The scan frequency was
varied between 2 to 5 Hz. Resolution was 256 256 points for
806
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
topography, and 128 128 in the CITS measurements. In most cases,
Pt/Ir(10 %) tips were used.
Received: July 12, 2004
Revised: September 28, 2004
Published online: December 28, 2004
.
Keywords: coordination polymers � materials science � peptides �
scanning probe microscopy � zinc
[1] C. Janiak, Dalton Trans. 2003, 2781.
[2] a) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, M. OKeeffe, O. M.
Yaghi, Science 2002, 295, 469; b) B. L. Chen, M. Eddaoudi, S. T.
Hyde, M. OKeeffe, O. M. Yaghi, Science 2001, 291, 1021; c) M.
Eddaoudi, D. Moler, H. Li, T. M. Reineke, M. OKeeffe, O. M.
Yaghi, Acc. Chem. Res. 2001, 34, 319; d) J. S. Seo, D. Whang, H.
Lee, S. I. Jun, J. Oh, Y. J. Jeon, K. Kim, Nature 2000, 404, 982.
[3] J. Hjelm, R. W. Handel, A. Hagfeldt, E. C. Constable, C. E.
Housecroft, R. J. Foster, J. Phys. Chem. B 2003, 107, 10 431.
[4] a) J.-C. Dai, X.-T. Wu, Z.-Y. Fu, C.-P. Cui, S.-M. Hu, W.-X. Du,
L.-M. Wu, H.-H. Zhang, R.-Q. Sun, Inorg. Chem. 2002, 41, 1391;
b) C. Seward, W.-L. Jia, R.-Y. Wang, G. D. Enright, S. Wang,
Angew. Chem. 2004, 116, 2993; Angew. Chem. Int. Ed. 2004, 43,
2933.
[5] L. Li, Z. Liu, S. S. Turner, D. Liao, Z. Jiang, S. Yan, Eur. J. Inorg.
Chem. 2003, 62.
[6] O. Sato, Acc. Chem. Res. 2003, 36, 692.
[7] O. R. Evans, W. Lin, Acc. Chem. Res. 2002, 35, 511.
[8] B. Moulton, M. J. Zaworotko, Chem. Rev. 2001, 101, 1629.
[9] a) D. Wouters, U. S. Schubert, Angew. Chem. 2004, 116, 2534;
Angew. Chem. Int. Ed. 2004, 43, 2480; b) C. Safarowsky, L. Merz,
A. Rang, P. Broekman, B. A. Hermann, C. A. Schalley, Angew.
Chem. 2004, 116, 1311; Angew. Chem. Int. Ed. 2004, 43, 1291;
c) U. S. Schubert, C. Eschbaumer, Angew. Chem. 2002, 114,
3016; Angew. Chem. Int. Ed. 2002, 41, 2892; d) A. Dmitriev, H.
Spillmann, N. Lin, J. V. Barth, K. Kern, Angew. Chem. 2003, 115,
2774; Angew. Chem. Int. Ed. 2003, 42, 2670; e) P. Messina, A.
Dmitriev, N. Lin, H. Spillmann, M. Abel, J. V. Barth, K. Kern, J.
Am. Chem. Soc. 2002, 124, 14 000; f) A. Semenov, J. P. Spatz, M.
Mller, 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.
[10] N. Niklas, F. Hampel, R. Alsfasser, Chem. Commun. 2003, 1586.
[11] Y. J. Zhang, M. Jin, R. Lu, Y. Song, L. Jiang, Y. Zhao, T. J. Li, J.
Phys. Chem. B 2002, 106, 1960.
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