Controlled assembly of silver(I)-pyridylfullerene networks

Article abstract of DOI:10.1002/anie.200700769

Stack them up! Ag^I ions combined with functionalized fullerenes (C₆₀) form either discrete binuclear metallacycles or extended polymeric networks (see structure), depending on the geometry of the functional groups on the fullerene an

Full text of DOI:10.1002/anie.200700769

Angewandte
Chemie
DOI: 10.1002/anie.200700769
Supramolecular Chemistry
Controlled Assembly of Silver(I)-Pyridylfullerene Networks**
Jian Fan, Yu Wang, Alexander J. Blake, Claire Wilson, E. Stephen Davies,
Andrei N. Khlobystov,* and Martin Schröder*
Fullerene-containing supramolecular architectures[1] are
attracting attention because of their unusual physicochemical
properties and potential applications as superconductors[2]
and ferromagnetic materials,[3] in optical and quantum
devices,[4] and for inhibition of HIV protease.[5] Controlling
the positions and orientations of fullerenes in the solid-state
and on surfaces has been addressed by various methods, such
as encapsulation of fullerenes within carbon nanotubes,[6]
adsorption on nanopatterned surfaces,[7] and cocrystallization
with a variety of organic,[8] metal–porphyrin,[9] organometal-
lic,[10] and inorganic molecules.[11] Although fullerene chemis-
try has been of major interest for the past 20 years,
supramolecular structures based upon metal coordination to
functionalized fullerenes are still quite rare, and very few such
systems have been unambiguously structurally character-
ized.[12,13] The majority of examples are based on porphyrin
architectures, which assemble by apical coordination of an
nitrogen donor of the functionalized fullerene to a metal ion
bound equatorially to the porphyrin.[12] To date no examples
of polymeric aggregates of functionalized fullerenes with
transition-metal ions and coordinate bonding have been
structurally characterized, and the nature of complexation
within such a system remains unknown. The assembly of
fullerenes within coordination-polymer frameworks will
afford flexible control of interfullerene distances and inter-
actions in the solid-state, and will allow utilization of the
structural and stereochemical diversity of coordinate bonding
to construct optically and electronically active fullerene
structures. We describe herein the control of fullerene–
fullerene separations and orientations by coordination to
metal ions, and report the first example of a chain coordina-
tion polymer containing a fullerene-functionalized ligand.
Diederich and co-workers have reported[13] the first
example of a binuclear cyclophane-fullerene using a metal-
directed self-assembly procedure in which only one type of
structure can be formed, which is partly due to the rigidity of
the ligand employed. We have adopted an alternative
approach in which greater ligand flexibility and ligand-
donor angularity have been incorporated within two exo-
bidentate ligands, bis(pyridin-4-ylmethyl)-3’H-cyclopropa-
[1,9](C60-Ih)[5,6]fullerene-3’,3’-dicarboxylate (1), and bis(pyr-
idin-3-ylmethyl)-3’H-cyclopropa[1,9](C60-Ih)[5,6]fullerene-
3’,3’-dicarboxylate (2; Scheme 1). The ligands 1 and 2 are
isomers and may be expected to exhibit diverse structural
behavior when binding to metal ions as a consequence of the
Scheme 1. Ligands 1 and 2.
ꢀ
ꢀ ꢀ
conformational flexibility of the CH2
O group linking the
fullerene cage with the pyridyl donor. We chose AgI salts to
react with 1 and 2 since these metal centers are sufficiently
labile and have relatively controllable coordination chemistry
in supramolecular assembly.[14]
Ligands 1 and 2 were synthesized by the Bingel cyclo-
propanation method.[15] Complexes 3–5 were obtained by
[*] Dr. J. Fan, Y. Wang, Prof. Dr. A. J. Blake, Dr. C. Wilson, Dr. E. S. Davies,
Dr. A. N. Khlobystov, Prof. Dr. M. Schröder
School ofChemistry
½ðAg-1Þ2ŠðPF6Þ2 Á 5 C6H6 Á 6 CH3CN 3
The University ofNottingham
University Park, Nottingham, NG7 2RD (UK)
Fax: (+44)115-9513563
E-mail: Andrei.Khlobystov@nottingham.ac.uk
Martin.Schroder@nottingham.ac.uk
f½Ag-1ŠPF6 Á C6H6 Á C6H5CNg1
½ðAg-2Þ2ŠðPF6Þ2 Á 5 C6H6
4
5
reaction of AgPF6 and the ligands 1 and 2 by solution-layering
methods at ambient temperature. The dark red crystals of the
products are stable in air, insoluble in common organic
solvents and have been characterized by single crystal X-ray
diffraction.[16]
The reaction of AgPF6 with 1 in a mixture of benzene and
acetonitrile affords the binuclear metallacycle 3. In the single
crystal X-ray structure (Figure 1), each AgI ion is bound to
two nitrogen donors, each coming from two different ligands 1
[**] We thank the EPSRC-funded synchrotron crystallography service
and its director Professor W. Clegg for collection of single-crystal
diffraction data at the Daresbury SRS. We also thank the EPSRC
National Mass Spectrometry Service at the University ofWales,
Swansea (UK) for mass spectra. M.S. gratefully acknowledges
receipt ofa Royal Society Wolsfon Merit Award and ofa Royal
Society Leverhulme Trust Senior Research Fellowship. A.N.K.
gratefully acknowledges receipt of a Royal Society University
Research Fellowship, and thanks EPSRC and ESF for a EURYI Award.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
ꢀ
ꢀ
ꢀ
(Ag N 2.151(9) and 2.150(9) Š, < N Ag N 166.1(4)8). The
Angew. Chem. Int. Ed. 2007, 46, 8013 –8016
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Communications
ꢀ
Figure 1. a) The binuclear cation in 3; b) View of 3 with the C H···p
interactions indicated by dashed lines. Atoms labeled with the suffix A
are related to the corresponding unsuffixed atoms by inversion
(symmetry operation A: 11= ꢀx, 1= ꢀy, 1ꢀz). O red, N blue, Ag pink.
2
2
two pyridyl groups of one ligand extend on the same side of
the fullerene cage with a dihedral angle between these two
rings of 51.08. Thus, the bis(pyridine)fullerene ligand in 3
adopts a cisoid-conformation, which is essential for the
formation of the discrete 2+2 metallacycle (Figure 1). Fur-
thermore, each AgI ion is bound by one acetonitrile molecule
Figure 2. a) A one-dimensional zigzag chain in compound 4; b) View
ofthe chains in 4 propagating along the [101] direction. Ag···C24
ꢀ
located on either side of the macrocycle (Ag N 2.653(9) Š),
to give a distorted T-shaped coordination environment at AgI
1
(1= +x, = ꢀy, 1= +z) interactions are shown as dashed lines linking
2
2
2
ions. The binuclear metallacyclic structure is further stabilized
the zigzag chains into two-dimensional sheets. Coordinated benzoni-
trile ligands have been removed for clarity. O red, N blue, Ag pink,
P orange, F green.
[17]
ꢀ
ꢀ
by intramolecular end-on C H···p interactions (aC H···X
1368, H···X 3.08, Ag···Ag 4.190 Š, where X is centroid of the
pyridyl group).
In contrast to 3, reaction of AgPF6 with 1 in a mixture of
benzene, methanol, and benzonitrile results in the formation
of the one-dimensional chain polymer 4 (Figure 2) with the
chain propagating through the operation of the n-glide along
the [101] direction (Ag···Ag 14.101 Š). The asymmetric unit
of 4 contains one AgI ion, a PF6ꢀ ion and one molecule each of
coordinated ligand, benzene, and benzonitrile with each AgI
ion bound in a linear fashion to two nitrogen donors from two
a mixed solution of benzene, methanol, and acetonitrile. The
asymmetric unit of compound 5 contains one AgI ion
ꢀ
coordinated by one ligand molecule, one PF6 ion, and two-
and-a-half benzene molecules. In 5, the cisoid conformation
of the ligand, the coordination environment at AgI, and the
binuclear structure are similar to those found in compound 3
ꢀ
ꢀ
ꢀ
(Ag N 2.131(7), 2.108(8) Š, aN Ag N 178.7(3)8). The two
I
ꢀ ꢀ
Ag centers are clipped together by two F P F units from two
ꢀ
ꢀ
ꢀ
different fullerene ligands (Ag N 2.157(5), 2.163(4) Š, aN
PF6 ions (Figure 3a; Ag···F 2.820, 2.951 Š, Ag···Ag separa-
I
ꢀ
Ag N 176.6(2)8). Planar coordination at Ag is completed by
tion 3.769 Š). The main difference between complexes 3 and
5 is that pyridyl donor groups in the ligand 2 are more angular
ꢀ
interaction with a fluorine atom from the PF6 ion (Ag···F
ꢀ ꢀ
ꢀ
2.637(9) Š) and from a nitrogen donor from a benzonitrile
with respect of the O CH2 linker-group to the fullerene
cage, compared to the pyridyl donors in ligand 1 which are
more linear. As a result, the binuclear metallacycle in 5 is
more puckered than in 3 and there is a significant shortening
of the distance between the fullerene cages within complex 5,
which has a center-to-center interfullerene distance of
22.027 Š compared to 26.839 Š in the structural isomer 3.
Also, in 5, the dihedral angle between the adjacent pyridine
rings in the ligand is reduced to 22.08 compared to 51.08 in 3,
and the centroid–centroid distance of the pyridine rings is
3.827 Š, suggesting possible long-range p···p interaction
(Figure 3b).[19]
I
ꢀ
molecule (Ag N 2.776(5) Š) with cis angles at Ag ranging
from 88.3(2) to 93.3(2)8. In contrast to 3, the two pyridyl
groups in 4 are directed to opposite sides of the fullerene cage.
More interestingly, an interaction between AgI and the
fullerene cage is seen in 4, with a shortest intermolecular
1
Ag···C(fullerene) distance of 2.801 Š at C24 (1= + x, = ꢀy,
2
2
1
= + z). This situation is comparable to complexes of AgI with
2
aromatic systems (2.47–2.92 Š),[18] and is reminiscent of the
interactions in adducts of AgNO3 with C60 reported by Balch
and co-workers.[11] It is, therefore, tempting to rationalize the
formation of 4 as being driven in part by the AgI···fullerene
interactions which template inter-chain contacts leading to
the formation of a 2D sheet structure (Figure 2b) from 1D
chains.
The complexes 3–5 appear to be virtually insoluble in
most organic solvents, which precluded characterization of
their solution properties by conventional spectroscopic meth-
ods. For complex 3 the limited solubility in benzonitrile did
allow cyclic voltammetry (CV) studies to be carried out,
which indicated that in solution, the AgI complexes either
dissociate into free ligand and AgI ions, or undergo dissoci-
To determine what effect the disposition of donor groups
attached to the fullerene cage have on the geometry of
resultant complexes, binding of ligand 2 to AgI was explored.
The complex 5 was obtained by the reaction of AgPF6 and 2 in
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3-ylmethyl)malonate was synthesized by the similar procedure as
bis(pyridin-4-ylmethyl)malonate, with
a yield of 32% (3.25 g).
1H NMR (270 MHz, CDCl3): d = 8.56 (m, 4H), 7.63 (m, 2H), 7.27
(m, 2H), 5.16 (s, 4H), 3.47 (s, 2H) ppm; 13C NMR (68 MHz, CDCl3):
d = 166.0, 150.0, 149.8, 136.2, 130.8, 123.6, 64.8, 41.3 ppm. ESI-MS:
m/z 287 (M++H).
1: A solution of C60 (0.100 g, 0.14 mmol), bis(pyridin-4-ylme-
thyl)malonate (0.040 g, 0.14 mmol), and iodine (0.035 g, 0.14 mmol)
in toluene (200 cm3) was stirred at room temperature for 30 min.
DBU (1,8-diazabicyclo[5.4.0]undec-7-ene; 0.021 g, 0.14 mmol) was
then added and the mixture stirred for a further 2 days. Column
chromatography (SiO2; toluene, then chloroform/acetone 7:3, v/v)
gave 1 as a dark brown powder. Yield 0.032 g, 23%. 1H NMR
(270 MHz, CDCl3): d = 8.65 (m, 4H), 7.35 (m, 4H), 5.51 (s, 4H) ppm;
13C NMR (68 MHz, CDCl3): d = 163.14, 150.44, 145.43, 145.34, 145.08,
145.01, 144.83, 144.59, 144.57, 143.98, 143.22, 143.17, 143.13, 143.11,
142.28, 141.86, 141.15, 139.16, 122.57, 77.29, 71.09, 66.99 ppm.
MALDI-MS: m/z 1004 (M+). Elemental analysis (%) calcd for
C75H12N2O4 : C 89.64, H 1.19, N 2.79; found: C 89.53, H 1.14, N 2.74.
2 was synthesized by a procedure similar to that for 1. Yield
Figure 3. a) The binuclear cation in 5 with the Ag···F interactions
indicated by dotted lines; O red, N blue, Ag pink, P orange, F green.
b) View of 5 showing aromatic p···p interactions as dashed lines.
Atoms labeled with the suffix A are related to the corresponding
unsuffixed atoms by inversion (symmetry operation A: 2ꢀx, ꢀy, 1ꢀz).
1
0.029 g, 21%. H NMR (270 MHz, CDCl3): d = 8.72 (d, J = 1.81 Hz,
2H), 8.64 (dd, J1 = 4.82, J2 = 1.67 Hz, 2H), 7.76 (m, 2H), 7.34 (m, 2H),
5.49 (s, 4H) ppm; 13C NMR (68 MHz, CDCl3): d = 163.25, 150.45,
150.34, 145.38, 145.29, 145.04, 144.78, 144.76, 144.70, 144.58, 143.95,
143.18, 143.12, 143.08, 142.27, 141.85, 141.08, 139.08, 136.73, 130.24,
123.68, 77.29, 71.19, 66.43 ppm. MALDI-MS: m/z 1004 (M+).
Elemental analysis (%) calcd for C75H12N2O4: C 89.64, H 1.19, N
2.79; found: C 89.56, H 1.14, N 2.74.
3: A solution of AgPF6 (0.003 g, 0.01 mmol) in acetonitrile
(3 cm3) was carefully layered over a solution of 1 (0.010 g, 0.01 mmol)
in benzene (10 cm3). Dark red crystals suitable for X-ray crystallo-
graphic studies were isolated by filtration after several weeks. Yield
0.013 g, 83%; elemental analysis (%) calcd for C96H36AgF6N5O4P: C
73.15, H 2.28, N 4.44; found: C 73.07, H 2.20, N 4.36.
4: A solution of AgPF6 (0.003 g, 0.01 mmol) in methanol/
benzonitrile (4 cm3, 1:3, v/v) was carefully layered over a solution of
1 (0.010 g, 0.01 mmol) in benzene (10 cm3). Dark red crystals suitable
for X-ray crystallographic studies were isolated by filtration after
several weeks. Yield 0.011 g, 78%; elemental analysis (%) calcd for
C88H23AgF6N3O4P: C 73.39, H 1.60, N 2.92; found: C 73.45, H 1.47, N
2.84.
5: A solution of AgPF6 (0.003 g, 0.01 mmol) in methanol/
acetonitrile (3 cm3, 1:2, v/v) was carefully layered over a solution of
2 (0.010 g, 0.01 mmol) in benzene (10 cm3). After several weeks the
reaction mixture contained single crystals of 5 and an unknown solid
which were collected by filtration. The bulk sample did not give
satisfactory results by elemental analysis.
ation upon reduction (Supporting Information). Elemental
and XPS (X-ray photoelectron spectroscopy) analysis of AgI–
fullerene complexes confirmed that the composition and the
metal/ligand ratio in bulk products of complexes are the same
as in single crystals used for X-ray diffraction.
We have shown that pyridyl-functionalized fullerenes can
act as efficient tectons with AgI cations to form polymeric and
metallacyclic products. The arrangement of fullerenes in these
supramolecular coordination systems can be controlled by
conditions of synthesis and by the structure of the functional
group on the fullerene with either AgI···C60 interactions as in
ꢀ
4, or possible end-on C H···aromatic interactions as in 3, and
face-to-face aromatic–aromatic interactions as in 5 stabilizing
the structures. The structural difference between compounds
3 and 4 also reveals the importance of solvent mediation in
the formation of discrete molecular or polymeric structures,
with the latter templated by AgI···C60 interactions. Also,
complexes 3–5 incorporate a significant amount of solvent in
the cavities created by the loose-packing of fullerene cages,
suggesting that, by replacing AgI with 5- or 6-coordinate metal
ions, such as ZnII or CuII, highly porous two- and three-
dimensional fullerene frameworks should be formed for
potential gas storage[20] as well as for the generation of
unusual optoelectronic properties. Work in these areas is now
in progress.
Received: February 20, 2007
Revised: July 2, 2007
Published online: September 17, 2007
Keywords: fullerenes · N ligands · self-assembly · silver ·
.
supramolecular chemistry
Experimental Section
Bis(pyridin-4-ylmethyl)malonate. A solution of malonyl dichloride
(5.00 g, 35.5 mmol) in dichloromethane (50 cm3) was added dropwise
into a solution of 4-pyridylcarbinol (7.73 g, 71.0 mmol) and triethyl-
amine (5 cm3) in dichloromethane (100 cm3) at room temperature.
The mixture was stirred overnight, and then washed with water (3 ”
50 cm3). The organic phase was dried over anhydrous Na2SO4,
separated by filtration, and the filtrate evaporated to dryness. The
residue was purified by column chromatography (SiO2; acetone as
eluent) to afford the product as a brown oil. Yield 3.65 g, 36%.
1H NMR (270 MHz, CDCl3): d = 8.57 (m, 4H), 7.20 (m, 4H), 5.17 (s,
4H), 3.58 (s, 2H) ppm; 13C NMR (68 MHz, CDCl3): d = 165.8, 150.1,
144.1, 121.9, 65.3, 41.2 ppm. ESI-MS: m/z 287 (M++H). Bis(pyridin-
[1] a) G. Orlandi, Photochem. Photobiol. Sci. 2006, 5, 1121; b) J. M.
Ashcroft, D. A. Tsyboulski, K. B. Hartman, T. Y. Zakharian,
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Communications
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1.638 gcmꢀ3, m(MoKa) = 0.428 mmꢀ1, 11698 unique reflections
measured and used in all calculations. Final R1 (6303 F ꢁ
4s(F)) = 0.113 and wR(all F2) was 0.261. Crystal data for 4.
Mr = 1438.93, monoclinic, a = 23.927(2), b = 9.9394(7), c =
25.538(2) Š, b = 113.721(1)8, U = 5560.3(11) Š3, T= 150(2) K,
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,
m(MoKa) = 0.482 mmꢀ1, 10380 unique reflections measured and
used in all calculations. Final R1 (5125 F ꢁ 4s(F)) = 0.0571 and
wR(all F2) was 0.149. Crystal data for 5. Mr = 2905.9, triclinic, a =
10.012(3), b = 10.188(3), c = 27.931(8) Š, a = 99.213(3), b =
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ꢀ
ꢀ ꢀ
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[16] Crystal data for 3. Mr = 3152.3, monoclinic, a = 17.189(2), b =
9.9375(14), c = 75.236(11) Š, b = 96.089(2)8, U = 12779(5) Š3,
T= 150(2) K, space group C2/c (No. 15), Z = 4, 1calcd
=
8016 www.angewandte.org
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