Supramolecular silver(I) complexes with highly strained polycyclic aromatic compounds

Article abstract of DOI:10.1021/ja981483y

Four organosilver(I) complexes of polycyclic aromatic hydrocarbons (PAHs) have been investigated crystallographically. The aim was to establish whether a favorable combination of cation-π interactions and aromatic stackings might produce functional organometallic solid materials with novel networks. Complete structures of the silver(I) perchlorate with 9,10- diphenylanthracene (L¹), rubrene (L²), benzo[a]pyrene (L³), and coronene (L⁴) were determined by X-ray diffraction. All compounds are organometallic species based on cation-π interactions. While complex 1 with L¹ revealed a discrete mononuclear structure, complex 2 with rubrene displayed a π-bonded 3-D polymer. Complexes 3 and 4 can be regarded as both coordination polymer and stacking polymer, and the detailed differences in the geometries and the stacking patterns of L³ and L⁴ gave helical and triple-decker networks, respectively. The ESR spectroscopic results and conductivity of the compounds are also discussed. The present findings may serve as a basis for understanding specific interactions responsible for self-assembly of multinuclear aggregates involving PAHs.

Full text of DOI:10.1021/ja981483y

8610
J. Am. Chem. Soc. 1998, 120, 8610-8618
Supramolecular Silver(I) Complexes with Highly Strained Polycyclic
Aromatic Compounds
Megumu Munakata,* Liang Ping Wu, Takayoshi Kuroda-Sowa, Masahiko Maekawa,
Yusaku Suenaga, Gui Ling Ning, and Toshiyuki Kojima
Contribution from the Department of Chemistry, Kinki UniVersity, Kowakae, Higashi-Osaka,
Osaka 577-8502, Japan
ReceiVed April 30, 1998
Abstract: Four organosilver(I) complexes of polycyclic aromatic hydrocarbons (PAHs) have been investigated
crystallographically. The aim was to establish whether a favorable combination of cation-π interactions and
aromatic stackings might produce functional organometallic solid materials with novel networks. Complete
structures of the silver(I) perchlorate with 9,10-diphenylanthracene (L1), rubrene (L2), benzo[a]pyrene (L3),
and coronene (L4) were determined by X-ray diffraction. All compounds are organometallic species based on
cation-π interactions. While complex 1 with L1 revealed a discrete mononuclear structure, complex 2 with
rubrene displayed a π-bonded 3-D polymer. Complexes 3 and 4 can be regarded as both coordination polymer
and stacking polymer, and the detailed differences in the geometries and the stacking patterns of L3 and L4
gave helical and triple-decker networks, respectively. The ESR spectroscopic results and conductivity of the
compounds are also discussed. The present findings may serve as a basis for understanding specific interactions
responsible for self-assembly of multinuclear aggregates involving PAHs.
Introduction
further dramatic influence on the reactive properties of the fused
polyaromatic solid surfaces.8-10 Despite these achievements,
the potential of PAHs for building macromolecules and forming
supramolecular assemblies with helical, cylindrical, and host-
guest topologies has only recently been explored.11-14 The
study includes linkage of the macrocycles through the multiple
hydrogen bonding sites and a variety of van der Waals contacts,
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in solution.3-7 Incorporation of metal ions into the PAHs
systems through cation-π interactions has meanwhile brought
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S0002-7863(98)01483-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/12/1998

Supramolecular SilVer(I) Complexes with PAHs
J. Am. Chem. Soc., Vol. 120, No. 34, 1998 8611
including π-π and related dipole-dipole-induced interactions
associated with arene-arene interactions.
The development of methods for the efficient synthesis of
polynuclear PAHs offers exciting prospects in the field of
supramolecular chemistry. Modern supramolecular chemistry
is currently dominated by the biomimetic motive of weak
interactions such as hydrogen bonding and π-π stackings.
Interactions between aromatic molecules represent an important
class of intermolecular forces in chemistry, which have been
well-characterized both experimentally and theoretically.15 They
control a range of molecular recognition and self-assembly
phenomena such as the packing of aromatic molecules in the
crystalline state and, hence, the material properties. While being
involved in a research program aimed at designing new
assemblies of copper(I) and silver(I) complexes with macrocy-
clic polyhapto organic ligands for the development of functional
supramolecular materials,16 we became interested in the mo-
lecular and crystal structures of complexes between Ag(I) and
very large PAH compounds. With their unique shape, size, and
a large number of closely spaced molecular orbitals, large
polycyclic aromatics are promising to act favorably as prototype
compounds for a wide range of functional solid materials.17
Relevant silver(I) complexes with smaller aromatics such as
benzene,18 cyclophane,19 indene,20 acenaphthene,21 naphtha-
lene,22 and anthracene23 are known. The study of these
compounds is mainly concerned with the nature of π bonding,
packing, and steric effects. Recently, we have reported
polymeric silver(I) complexes of pyrene and perylene in which
both aromatic compounds display an unusual symmetric tetra-
η2-coordination, linking four metal atoms forming W-type
sandwich polymeric chain and sheets.24 Here, we continue our
exploration on the construction of supramolecular architectures
of metal ions linked by π macrocycles including 9,10-diphe-
nylanthracene (L1), rubrene (L2), benzo[a]pyrene (L3), and
coronene (L4). These aromatics have been so far used in
donor-acceptor compounds with alkali metal ions4-6 or as
model studies.25 Extensive Chemical Abstracts Service (CAS)
and Cambridge Structural Database searches gave no hint of
known structures of π-hydrocarbon coordinative compounds.
Our results have shown that employment of π macrocycles as
precursors incorporating metal-ligand interactions and π-π
stackings as recognition motifs has been proved to be a new
approach for the generation of novel molecular and supramo-
lecular architectures with potential electrical properties.
Experimental Section
General Procedures. All reactions and manipulations were carried
out under an argon atmosphere by using the standard Schlenk vacuum
line techniques. Solvents were dried using standard procedures and
distilled under an argon atmosphere prior to use. Reagent grade 9,-
10-diphenylanthracene and coronene were purchased from Tokyo, Kasei
Kogyou Co. Ltd. while rubrene, benzo[a]pyrene, and silver(I) perchlo-
rate were purchased from Aldrich. AgClO4‚H2O was dried at 40 °C
under reduced pressure for 5 h before use. All other chemicals were
purchased from Wako Pure Chemical, Inc. and used without further
purification. Microanalyses were performed by the Department of
Chemistry, Tokyo Metropolitan University. IR spectra were recorded
as KBr disks on a JASCO 8000 FT-IR spectrometer. ESR spectra were
obtained on JEOL JES-TE200 ESR spectrometer. Electrical resistivities
of compacted pellets were measured by the conventional two-probe
technique. CAUTION: The following preparations use AgClO4‚H2O,
which is potentially explosive.
Syntheses. [Ag(L1)(ClO4)(C6H6)2] (1). A solution of AgClO4‚H2O
(22.5 mg, 0.1 mmol) in 10 mL of benzene was added to 9,10-
diphenylanthracene (33.0 mg, 0.1 mmol). After being stirred for 10
min, the resultant light-yellow solution was filtered. The filtrate was
introduced into a 7-mm diameter glass tube and layered with 2 mL of
n-pentane as a diffusion solvent. The glass tube was sealed under Ar
and wrapped with tin foil. After the filtrate was allowed to stand at
room temperature in a dark room for 3 d, light-yellow brick crystals
of 1 were obtained. Anal. Calcd for C38H30AgClO4: C, 65.71; H,
4.32. Found: C, 65.52; H, 4.29.
[Ag4(L2)(ClO4)4(H2O)4] (2). The red brick crystals of 2 were
prepared in the same way as 1, using rubrene (13.3 mg, 0.025 mmol)
instead of 9,10-diphenylanthracene, and n-hexane was used as the
diffusion solvent. Anal. Calcd for C42H36Ag4Cl4O20: C, 35.18; H,
2.53. Found: C, 35.91; H, 2.36.
[Ag4(L3)2(ClO4)4(C6H5CH3)2] (3). Mixing of AgClO4‚H2O (67.5
mg, 0.3 mmol) and benzo[a]pyrene (37.9 mg, 0.15 mmol) in 10 mL of
toluene produced a light-yellow solution which was stirred and filtered.
The filtrate was introduced into a glass tube and layered with n-hexane.
After the filtrate was allowed to stand at room temperature in a dark
room for 7 d, light-yellow plate crystals of 3 were obtained. Anal.
Calcd for C40H24Ag4Cl4O16: C, 35.98; H, 1.81. Found: C, 35.92; H,
1.94.
(15) (a) Hunter, C. A. Chem. Soc. ReV. 1994, 101. (b) Hunter, C. A.;
Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525.
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Yamamoto, M.; Kuroda-Sowa, T.; Maekawa, M. J. Chem. Soc., Dalton
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Poupko, R.; Rabinovitz, M. J. Am. Chem. Soc. 1983, 105, 2164.
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Rundle, R. E. J. Am. Chem. Soc. 1958, 80, 5075.
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Angew. Chem., Int. Ed. Engl. 1986, 25, 1089. (b) Kang, H. C.; Hanson, A.
W.; Eaton, B.; Boekelheide, V. J. Am. Chem. Soc. 1985, 107, 1979.
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Y.; Sugimoto, K. Inorg. Chem. 1997, 36, 4903.
(25) (a) Goddard, R.; Haenel, M. W.; Herndon, W. C.; Kru¨ger, C.;
Zander, M. J. Am. Chem. Soc. 1995, 117, 30. (b) Herndon, W. C. J. Am.
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D. A.; Lin. P. J. Am. Chem. Soc. 1992, 114, 41.
[Ag4(L4)3(ClO4)4] (4). This compound was prepared by vapor
diffusion. To a saturated solution (10 mL) of coronene in benzene
(less than 1.5 mmol/L) was added AgClO4‚H2O (22.5 mg, 0.1 mmol).
The resultant light-yellow solution was introduced into one compartment
of an h-shaped glass tube. The second compartment was filled with
n-hexane. The glass tube was sealed, and after standing for 7 d yellow
prism single crystals of 4 were isolated. Anal. Calcd for C36H18Ag2-
Cl2O8: C, 49.93; H, 2.10. Found: C, 49.64; H, 2.06.

8612 J. Am. Chem. Soc., Vol. 120, No. 34, 1998
Munakata et al.
Table 1. Crystallographic Data
1
2
3
4
formula
fw
C38H30AgClO4
693.97
C42H36Ag4Cl4O20
1434.00
C54H40Ag4Cl4O16
1518.18
C36H18Ag2Cl2O8
865.18
crystal color, habit
crystal size, mm
crystal system
space group
a, Å
b, Å
c, Å
yellow, brick
0.20 × 0.20 × 0.25
triclinic
red, brick
yellow, plate
0.30 × 0.30 × 0.30
orthorhombic
Pca21
15.662(4)
13.037(8)
yellow, prisms
0.20 × 0.20 × 0.20
triclinic
P1h
12.771(4)
11.224(2)
10.894(3)
89.43(2)
65.25(2)
79.57(2)
1391(8)
2
0.20 × 0.28 × 0.16
orthorhombic
Fddd
16.638(5)
34.949(3)
P1h
9.516(1)
10.671(1)
7.8315(7)
92.131(8)
103.812(7)
91.283(9)
771.4(3)
1
14.634(3)
25.434(3)
R, deg
â, deg
γ, deg
V, Å3
8509(2)
8
2.239
5632
5193(4)
4
1.942
2992
Z
D
calcd, g cm-3
1.494
354
2.066
852
F(000)
diffractometer
radiation
Rigaku AFC5R
Mo KR(λ ) 0.71069 Å)
7.79
ω - 2θ
16.0 (in ω)
6-55
3748
2355
374
0.055
0.062
2.12
Rigaku AFC5R
Cu KR(λ ) 1.54178 Å)
179.92
ω - 2θ
32.0
6-120
1762
1127
181
Rigaku AFC7R
Mo KR
17.60
ω - 2θ
16.0
6-55
6593
4306
697
0.043
0.050
2.01
Rigaku AFC7R
Mo KR
16.58
ω - 2θ
16.0
6-55
6714
4974
433
µ, cm-1
scan type
scan rate, deg min-1
2θ range, deg
no. of reflns measd
no. of obsd data (I > 3.00σ(I))
no. of params
Ra
0.075
0.091
2.90
0.036
0.045
1.56
b
Rw
goodness of fit
2
a R ) ∑(|Fo - Fc)|/∑|Fo|. b Rw ) {∑w(|Fo| - |Fc|)2/∑w|Fo| }1/2
.
X-ray Data Collection, Structure Solution, and Refinement. The
single-crystal X-ray diffraction experiments for complexes 1, 3, and 4
were performed at room temperature on a Rigaku AFC-7R or Rigaku
AFC-5R four-circle diffractometer equipped with a 12-kW rotating
anode Mo X-ray source (λ (KR) ) 0.71069 Å), while that for 2 was
carried out with graphite monochromated Cu KR radiation (λ ) 1.54178
Å). In each case, a suitable single crystal was mounted on a glass
fiber or enclosed in a glass capillary. Unit cell parameters were obtained
from a least-squares analysis of the setting angles of 25 high-angle
reflections in which the appropriate cell angles were constrained to
their ideal values. Intensity data were collected by using standard scan
techniques (ω - 2θ). Space groups were selected on the basis of
systematic absences and intensity statistics which, in all cases, led to
satisfactory refinements. In each case, the intensities of three standard
reflections, monitored at 150-reflection intervals throughout data
collection, remained constant within experimental error, indicating
crystal and electronic stability. Thus, no decay correction was applied.
usual sources.28 Hydrogen atoms were assumed to be isotropic. All
crystallographic computations were performed on a VAX computer
by using the program system TEXSAN.29 Details of the X-ray
experiments and crystal data are summarized in Table 1. Final atomic
coordinates for all of the structures are given in the Supporting
Information. Important bond lengths and bond angles for four
complexes are given in Table 2.
Results and Discussion
Characterization and IR Spectra of the Products. The
reactions of four aromatics with silver(I) perchlorate under mild
conditions readily afforded the complexes 1-4. Compounds
1, 2, and 4 are reasonably stable at room temperature under
ambient light for several days. However, great care is needed
to get satisfactory elemental analyses for 3. The product cannot
be dried in vacuo, and even trying to remove excess toluene
with a slow stream of dry argon resulted in the loss of
coordinated toluene and the loss of transparency of the crystals
at room temperature. Therefore, the theoretical value for the
elemental analysis of 3 is based on the formula without toluene
molecules. The crystal used for X-ray structure determination
was enclosed in a glass capillary. Infrared spectroscopy is a
good indicator of incorporation of metal ions into the PAH
system. The infrared spectra were recorded in the region 4000-
400 cm-1 on KBr disks. PAHs have several very distinctive
signals, including the region from 3030 to 3065 cm-1, which
contains the C-H stretching absorptions. A second region, from
1314 to 1620 cm-1, consists of three or four quite intense
signals, corresponding to the in-plane vibrations of the CdC
bonds. All of these are present in the infrared spectrum of 1-4.
In addition, each complex exhibits strong absorptions of υ(OCl)
at 1086-1100 cm-1. The corresponding strong absorption of
For complex 2, an empirical absorption correction based on azimuthal
scans of several reflections was applied which resulted in transmission
factors ranging from 0.63 to 1.00. For the rest, azimuthal scans of
several reflections indicated no need for an absorption correction. The
diffracted intensities were corrected for Lorentz and polarization effects.
The structures were solved by a direct method26 and expanded using
Fourier techniques.27 All non-hydrogen atoms were refined with
anisotropic thermal parameters, except for some disordered O atoms
in 1-3. The positions of all the hydrogen atoms were determined from
difference electron density maps and were included but not refined.
For 1-3, the hydrogen atoms for benzene, H2O and toluene molecules
are excluded. Final refinements for all the structures were performed
on these data having I > 3σ(I) and included anisotropic thermal
parameters for non-hydrogen atoms. Reliability factors are defined as
2
R ) Σ(|Fo - Fc)|/Σ|Fo| and Rw ) {Σw(|Fo| - |Fc|)2/Σw|Fo| }1/2. Atomic
scattering factors and anomalous dispersion terms were taken from the
(26) SIR88: Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.;
Polidori, G.; Spagna, R.; Viterbo, D. J. Appl. Crystallogr. 1989, 22, 389.
(27) DIRDIF94: Direct Methods for difference structures-an automatic
procedure for phase extension and refinement of difference structure factors.
Beurskens, P. T. Technical Report; Crystallographic Laboratory: University
of Nijimegen, The Netherlands, 1994; Vol. 1.
(28) Keller, H. J.; Noethe, D.; Pritzkow, H.; Wehe, D.; Werner, M. Mol.
Cryst. Liq. Cryst. 1980, 62, 181.
(29) TEXSAN-TEXRAY Structural Analysis Package. Molecular Struc-
ture Corp.: The Woodlands, TX, 1985.

Supramolecular SilVer(I) Complexes with PAHs
J. Am. Chem. Soc., Vol. 120, No. 34, 1998 8613
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg)
1
Ag-O(2)
Ag-C(7)
Ag-C(30)
2.67(3)
2.57(1)
2.49(1)
Ag-C(6)
Ag-C(29)
Ag-C(34)
2.68(1)
2.62(1)
2.57(1)
O(2)-Ag-C(6)
O(2)-Ag-C(29)
O(2)-Ag-C(34)
C(6)-Ag-C(29)
C(6)-Ag-C(34)
C(7)-Ag-C(30)
C(29)-Ag-C(30)
C(30)-Ag-C(34)
102.7(7)
103.1(7)
84.4(8)
113.9(4)
96.3(4)
142.0(4)
32.3(5)
115.1(5)
O(2)-Ag-C(7)
O(2)-Ag-C(30)
C(6)-Ag-C(7)
C(6)-Ag-C(30)
C(7)-Ag-C(29)
C(7)-Ag-C(34)
C(29)-Ag-C(34)
74.1(7)
118.5(8)
29.6(4)
129.2(4)
113.0(4)
101.2(4)
145.7(5)
2
Ag-O(1)
Ag-C(1)
Ag-C(9)
2.46(2)
2.40(1)
2.54(2)
Ag-O(5)
Ag-C(2)
2.27(3)
2.68(1)
O(1)-Ag-O(5)
O(1)-Ag-C(2)
O(5)-Ag-C(1)
O(5)-Ag-C(9)
C(1)-Ag-C(9)
95.6(8)
91.2(5)
142.3(9)
98.9(8)
107.3(5)
O(1)-Ag-C(1)
O(1)-Ag-C(9)
O(5)-Ag-C(2)
C(1)-Ag-C(2)
C(2)-Ag-C(9)
97.4(5)
114.7(6)
114.5(8)
30.3(4)
135.6(6)
3
Ag(1)-O(1)
Ag(1)-C(1)
Ag(1)-C(33)
Ag(2)-O(5)
Ag(2)-C(9)
Ag(2)-C(43)
Ag(3)-O(9)
Ag(3)-C(14)
Ag(3)-C(22)
Ag(4)-O(13)
Ag(4)-C(29)
2.51(1)
2.36(1)
2.39(1)
2.52(2)
2.44(1)
2.44(2)
2.49(1)
2.73(1)
2.54(1)
2.71(2)
2.50(1)
Ag(1)-O(14)
Ag(1)-C(2)
Ag(2)-O(2)
Ag(2)-C(8)
Ag(2)-C(42)
Ag(3)-O(6)
Ag(3)-C(13)
Ag(3)-C(21)
Ag(4)-O(10)
Ag(4)-C(28)
Ag(4)-C(49)
2.53(1)
2.56(1)
2.40(1)
2.51(1)
2.56(2)
2.59(1)
2.41(1)
2.40(1)
2.42(1)
2.55(1)
2.53(2)
Figure 1. Structure and labeling of 1.
υ(OH) for complex 2 appeared at 3540 cm-1, confirming the
presence of water molecule in the compound.
Monomeric Structure of [Ag(L1)(ClO4)(C6H6)2] (1). The
crystallographic studies of 1 revealed a discrete mononuclear
structure shown in Figure 1. The coordination sphere around
the silver atom is pseudotetrahedral, being made up of two
crystallized solvate benzene molecules, one oxygen atom from
the perchlorate ion, and one carbon-carbon π interaction from
η2-diphenylanthracene. The Ag-C distances for L1 are unequal,
being 2.68(1) and 2.57(1) Å for C(6) and C(7), respectively.
The silver-benzene π interaction is asymmetrical, having
Ag-C distances of 2.49(1) and 2.62(1) Å for one benzene and
of 2.57(1) Å for the other. The remaining silver-carbon
interactions are greater than 2.93 Å, well beyond the limits from
2.47 to 2.76 Å observed in the reported silver(I)-aromatic
complexes.18-24 Thus, using the shortest Ag-C distances, the
two benzene moieties are best considered to involve different
coordination modes, one with η2 and the other with η1 bonding.
Complex 1 is a rare example of monomeric silver compound
with benzene and its derivatives. Normally, the arenes are found
to be η2-coordinated to the metal ions, and each benzene
molecule is associated with two metal ions lying above and
below the ring.18,30 With perchlorate ions acting as spacers,
such a connection sometimes can generate an infinite chain
structure as observed in the silver perchlorate complex of
benzene.18 Least-squares plane calculation indicates that the
polycycle in 1 has no molecular constraint and the maximum
deviation from the anthracene plane is 0.02 Å. The two phenyl
groups are also essentially planar and lie almost perpendicular
to the anthracene with dihedral angles of 77° and 81°,
respectively, between the anthracene and Ph planes. The
structure with the metal atoms interacting with only one
localized CdC bond of the benzene molecule explains the
distortion of the ring. Compared with the average CdC distance
of 1.399 Å for the uncoordinated benzene molecule, the donation
of electrons from the benzene π system to Ag results in the
lengthening of C(29)-C(30) bond to 1.42(2) Å, while the
remaining five distances of the ring average 1.38(2) Å.
O(1)-Ag(1)-O(14)
O(1)-Ag(1)-C(1)
O(1)-Ag(1)-C(2)
O(1)-Ag(1)-C(33)
O(14)-Ag(1)-C(1)
O(14)-Ag(1)-C(2)
O(14)-Ag(1)-C(33)
C(1)-Ag(1)-C(2)
C(1)-Ag(1)-C(33)
C(2)-Ag(1)-C(33)
O(2)-Ag(2)-O(5)
O(2)-Ag(2)-C(8)
O(2)-Ag(2)-C(9)
O(2)-Ag(2)-C(42)
O(2)-Ag(2)-C(43)
O(5)-Ag(2)-C(8)
O(5)-Ag(2)-C(9)
O(5)-Ag(2)-C(42)
O(5)-Ag(2)-C(43)
C(8)-Ag(2)-C(9)
C(8)-Ag(2)-C(42)
C(8)-Ag(2)-C(43)
C(9)-Ag(2)-C(42)
C(9)-Ag(2)-C(43)
C(42)-Ag(2)-C(43)
78.9(3)
115.3(4)
124.4(4)
86.5(4)
93.3(5)
24.0(4)
98.7(5)
31.8(4)
156.9(4)
129.2(4)
90.8(6)
119.6(5)
102.2(5)
128(1)
O(6)-Ag(3)-C(13)
O(6)-Ag(3)-C(14)
O(6)-Ag(3)-C(21)
O(6)-Ag(3)-C(22)
O(9)-Ag(3)-C(13)
O(9)-Ag(3)-C(14)
O(9)-Ag(3)-C(21)
O(9)-Ag(3)-C(22)
C(13)-Ag(3)-C(14)
C(13)-Ag(3)-C(21)
C(13)-Ag(3)-C(22)
C(14)-Ag(3)-C(21)
C(14)-Ag(3)-C(22)
C(21)-Ag(3)-C(22)
O(10)-Ag(4)-O(13)
O(10)-Ag(4)-C(28)
O(10)-Ag(4)-C(29)
O(10)-Ag(4)-C(49)
O(13)-Ag(4)-C(28)
O(13)-Ag(4)-C(29)
O(13)-Ag(4)-C(49)
C(28)-Ag(4)-C(29)
C(28)-Ag(4)-C(49)
C(29)-Ag(4)-C(49)
O(1)-Cl(1)-O(2)
105.9(5)
135.8(4)
87.7(4)
117.0(4)
85.9(5)
86.7(4)
113.8(4)
121.3(4)
30.4(5)
157.9(4)
131.1(5)
135.5(4)
105.6(5)
29.9(4)
69.8(4)
111.6(4)
96.6(4)
97.4(6)
144.0(5)
112.7(5)
94(1)
106(1)
111.6(5)
87.5(4)
85.9(7)
102(1)
31.2(4)
109.4(8)
121.4(7)
129.1(9)
150.1(7)
27.3(8)
32.3(4)
120.3(9)
152.6(9)
106.9(8)
4
Ag(1)-O(1)
Ag(1)-C(1)
Ag(1)-C(25)
Ag(2)-O(2)
Ag(2)-C(4)
Ag(2)-C(28)
2.456(3)
2.517(4)
2.455(4)
2.483(3)
2.402(4)
2.478(4)
Ag(1)-O(5)
Ag(1)-C(2)
Ag(1)-C(26)
Ag(2)-O(6)
Ag(2)-C(5)
Ag(2)-C(29)
2.425(4)
2.499(4)
2.448(4)
2.452(4)
2.516(4)
2.456(4)
O(1)-Ag(1)-O(5)
O(1)-Ag(1)-C(2)
O(1)-Ag(1)-C(26)
O(5)-Ag(1)-C(2)
O(5)-Ag(1)-C(26)
C(1)-Ag(1)-C(25)
C(2)-Ag(1)-C(25)
C(25)-Ag(1)-C(26)
C(4)-Ag(2)-C(29)
O(2)-Ag(2)-C(5)
O(2)-Ag(2)-C(29)
O(6)-Ag(2)-C(5)
O(6)-Ag(2)-C(29)
C(4)-Ag(2)-C(28)
C(5)-Ag(2)-C(29)
81.5(1)
O(1)-Ag(1)-C(1)
O(1)-Ag(1)-C(25)
O(5)-Ag(1)-C(1)
O(5)-Ag(1)-C(25)
C(1)-Ag(1)-C(2)
C(1)-Ag(1)-C(26)
C(2)-Ag(1)-C(26)
O(2)-Ag(2)-O(6)
O(2)-Ag(2)-C(4)
O(2)-Ag(2)-C(28)
O(6)-Ag(2)-C(4)
O(6)-Ag(2)-C(28)
C(4)-Ag(2)-C(5)
C(5)-Ag(2)-C(28)
C(28)-Ag(2)-C(29)
93.2(1)
00.6(1)
117.8(2)
118.1(2)
31.6(1)
136.3(1)
131.7(1)
89.4(1)
118.1(1)
106.6(1)
97.5(1)
86.1(1)
32.6(1)
143.3(1)
32.5(1)
106.5(1)
121.7(1)
91.0(2)
94.4(2)
123.7(1)
142.8(1)
32.7(1)
136.3(1)
96.0(1)
91.7(1)
123.3(1)
115.1(1)
135.1(1)
121.0(1)
(30) (a) Schier, A.; Wallis, J. M.; Mu¨ller, G.; Schmidbaur, H. Angew.
Chem., Int. Ed. Engl. 1986, 25, 757. (b) Frank, W.; Schneider, J.; Mu¨ller-
Becker, S. J. Chem. Soc., Chem. Commun. 1993, 799.

8614 J. Am. Chem. Soc., Vol. 120, No. 34, 1998
Munakata et al.
Figure 2. Structure and labeling of 2 with twisted conformation of
the naphthacene skeleton shown at the bottom.
3-D Polymeric Structure of [Ag4(L2)(ClO4)4(H2O)4] (2).
The X-ray analysis of 2 showed that the unit cell contains eight
rubrenes, whose structure is depicted in Figure 2 together with
atom numbering scheme. The complex consists of a 3-D
framework of the metal ions bridged by the polycyclic aromatics.
The molecular center of the rubrene coincides with the crystal-
lographic inversion center; thus, each aromatic molecule is
symmetrically π bonded to eight crystallographically equivalent
Ag atoms. Each metal center interacts asymmetrically with two
rubrenes, one with η2 bonding at C(1) and C(2) positions with
Ag-C distances of 2.40(1) and 2.68(1) Å, respectively, and
the other with η1 coordination at C(9) with Ag-C separation
of 2.54(2) Å. The tetrahedral coordination sphere around the
silver cation is completed by one water molecule and one
perchlorate ion with Ag-O separations of 2.27(3) and 2.46(2)
Å, respectively. Repeating the connection generates an infinite
3-D framework of metal ions linked by rubrene groups as shown
in Figure 3. To achieve π interactions with eight metal atoms,
the naphthacene skeleton of the bulky rubrene is no longer
planar; instead, it is severely twisted against the central C(5)-
C(5′) bond resulting in a dihedral angle of 30.5° between the
two halves of the ring.
Figure 3. Packing diagram of 3-D polymer 2. Top: showing eight
Ag atoms (red) bound to one rubrene; ClO4- and H2O are not shown.
Bottom: schematic presentation of the twisted rubrene molecules in
the cell.
Helical Structure of [Ag4(L3)2(ClO4)4(C6H5CH3)2] (3). The
structure of 3 displays formation of double helical arrangement
of polycyclic molecules and perchlorate ions. The compound
can be regarded as both a coordination polymer and a stacking
polymer. The structure of the compound contains an extraor-
dinary tetranuclear silver building block as shown in Figure 4.
While there are four crystallographically distinct Ag(I) cations,
these have a similar pseudotetrahedral environment comprising
two perchlorate oxygen atoms and one carbon-carbon π bond
with the polyaromatic. The fourth coordination site for both
Ag(1) and Ag(3) is completed by η1 coordination to the second
polycycle, while Ag(2) and Ag(4) are further π bonded to one
toluene molecule with η2 and η1 bonding, respectively. The
Ag-C distances range from 2.36(1) to 2.56(1) Å, and Ag-O
distances range from 2.40(1) to 2.71(2) Å. Within the building
block, the four silver atoms are linked by two benzo[a]pyrene
Figure 4. Structure and partial labeling of 3.
to the rigid conformation of L3, the two independent polycyclic
moieties are essentially planar and inclined with each other by
18.34°. The two toluene molecules act as complementary
spacers to accommodate Ag atoms for a tetrahedral coordina-
tion. The total structure is arranged in a spiral fashion with
the strand of polycycles and the strand of perchlorate ions
interwound around the silver atoms, leading to the two strands
of the double helical superstructure as illustrated in Figure 5.
-
molecules and three bridging ClO4 ions. The two adjacent
building blocks are bridged by the fourth perchlorate ion,
resulting in an infinite chain structure of the metal cations. Due

Supramolecular SilVer(I) Complexes with PAHs
J. Am. Chem. Soc., Vol. 120, No. 34, 1998 8615
Figure 5. Double-helical structure of 3, toluene and uncoordinated oxygen atoms of perchlorates are omitted for clarity. (a) Ball-and-stick model
(red: Ag, blue: O, yellow: Cl, black: C). (b) Space-filling model.
Figure 6. Intermolecular π-π interactions in 3.
Even the strands of polycycles are arranged in an unusual
fashion. The packing diagram shows that the aromatic rings
of two adjacent strands stack on top of each other, with an
interplanar separation of 3.46 Å. This results in extended
Figure 7. Structure and partial labeling of 4.
interweaved strands of polycycles associated by aromatic π-π
interactions, Figure 6.
carbon-carbon π bonds from two different coronene molecules
with Ag-C bond distances ranging from 2.402(4) to 2.517(4)
Å. The next closest contacts between silver and carbon atoms
are 3.076(4) and 3.103(5) Å for Ag(1) and Ag(2), respectively.
The two dimeric subunits are bridged by the second perchlorate
ion with Ag-O bond distances of 2.456(3) Å for Ag(1) and
2.483(3) Å for Ag(2). Each coronene moiety exhibits a tetra-
η2-coordination, bridging sequentially four metal centers and
resulting in a unique triple-decker polymeric structure shown
in Figure 8.
Triple-Decker Polymeric Structure of [Ag4(L4)3(ClO4)4]
(4). The compound 4 can also be regarded as both a coordina-
tion polymer and a stacking polymer. The structure exists in
the solid state as an aromatic-linked polymer of dimers lying
approximately on the ab plane as shown in Figure 7. Within
the dimer, there are two independent Ag(I) ions coupled by one
bridging perchlorate with Ag(1)‚‚‚Ag(2) separation of 3.9798-
(5) Å. The tetrahedral metal center is coordinated to two

8616 J. Am. Chem. Soc., Vol. 120, No. 34, 1998
Munakata et al.
Figure 8. Triple-decker structure of 4.
outward by 0.25 Å. This phenomenon is certainly striking for
a rigid polycyclic aromatic compound!
Molecular Planarity and Aromatic Stackings. An under-
standing of the relationship between molecular structure and
physicochemical properties would provide insight into the design
of solids with properties that depend on the arrangement of
molecules in crystals. Planarity is often presumed to be the
significant geometric characteristic of the molecular structures
of PAHs. Upon PAHs coordinating with metal ions, however,
this planarity may no longer exist. As discussed earlier, in
complexes 1 and 3, both 9,10-diphenylanthracene (L1) and
benzo[a]pyrene (L3) are found to possess essentially planar
molecular frameworks. The average deviation of carbon atoms
from the mean plane is less than 0.027 Å, which is insignificant
in both cases. In contrast to the planarity of L1 and L3, both
rubrene (L2) in 2 and coronene (L4) in 4 exhibit nonplanarity.
The average deviation of carbon atoms from the mean plane is
0.53 Å for L2 and 0.087 Å for L.4 In fact, due to the octafold
π coordination of L2 and the strong intermolecular interactions
of L,4 the two polycyclic aromatics exist with highly nonplanar,
even twisted and bent, conformations, Table 3. It is immediately
apparent that topological constrains resulted from cation-π
bonding and that π-π interactions are the structural features
responsible for nonplanarity of aromatics in their coordination
compounds.
The polycyclic aromatics L1, L2, and L4 have been previously
reported to form π-hydrocarbon anions with alkali metals.4-6
Although crystal structural determination and elemental analysis
as well as infrared spectroscopy in the present work are
consistent with characteristic neutral aromatics, the formation
of organic radicals was corroborated by an ESR measurement
at room temperature. All complexes were found to exhibit a
well-resolved intense resonance. The characteristic g values
in Table 3 are attributable to the organic radicals,17,31 indicative
of partial electron transfer between Ag(I) and the aromatics.
The spin densities for the organic radicals, estimated from the
comparison with the DPPH (diphenylpicrylhydrazyl) standard,
were measured. The significantly higher spin density of 0.18%
for 2 is consistent with the highly strained molecular conforma-
tion of rubrene in the complex, indicating easy electron transfer
between Ag(I) and the highly twisted polycyclic aromatics.
Molecular constraint may assist the interaction by putting the
interacting groups closer to each other in the coordination sphere
and enhance the charge transfer between the donor and acceptor
through the reduction of the electron density on the coordinated
aromatics. Indeed, the formation of Ag(II) or Ag(0) ac-
companied by the electron transfer was observed by a broad
ESR signal at g ) 2.1 for 2 and 4, whereas the corresponding
signal was not observed for 1 or 3 because of the low sensitivity.
Associated with the distortion of molecular planarity of
aromatics is the distance between the two carbon atoms and
Figure 9. Intermolecular π-π interactions in 4.
The packing diagram shows that the compound involves both
intramolecular and intermolecular π-π interactions, which
constitutes columnar aromatic stacks as shown in Figure 9. The
interplanar distances are unequal, ranging from 3.23 to 3.5 Å.
It is noted that the intermolecular π-π interactions are
significantly stronger as evidenced by the unusually close
contacts of 3.23 Å between the two intermolecular coronene
planes, much shorter than 3.4 Å for the modeled porphrin-
porphrin interactions in solution.15b The unique stacking pattern
in 4 can be a structure-determining factor. A closer insight into
the intermolecular aromatic ring stacking may be obtained from
studying the conformational changes accompanying the interac-
tion. Each triple-decker unit consists of a centrosymmetric
middle metallomacrocycle, an outer metallomacrocycle, and its
centrosymmetric pair. The middle plane is essentially planar,
having a maximum deviation of 0.018 Å from the best least-
squares plane. The outer unit shows greater deviation from
planarity with a maximum deviation of 0.087 Å. In this outer
unit, the C(2) and C(4) atoms and the C(11) and C(13) atoms
(see Figure 7), in particular, are displaced 0.1654 and 0.1311
Å and 0.1421 and 0.1974 Å, respectively, from the plane in a
direction away from the middle plane. The total result is that
the strong intermolecular interactions cause the two outer
coronene planes in the triple-decker unit to severely bend
(31) (a) Davies, A. G.; McGuchan, D. C. Organometallics 1991, 10,
329. (b) Courtneidge, J. L.; Davies, A. G. Acc. Chem. Res. 1987, 20, 90.
(c) Davies, A. G.; Shields, C. J. Chem. Soc., Perkin Trans. II 1989, 1001.

Supramolecular SilVer(I) Complexes with PAHs
Table 3. Physicochemical Properties
J. Am. Chem. Soc., Vol. 120, No. 34, 1998 8617
1
2
3
4
coordinated aromatic CdC bond distance (Å)
noncoordinated aromatic C-C bond distance (av) (Å)
presence of molecular constraint
presence of π-π stackings
1.35
1.39
no
no
2.002
1.37
1.40
yes
no
1.35 (av)
1.41
no
yes (not column)
2.003
1.38 (av)
1.41
yes
yes (column)
2.001
ESR g values
2.003
2.146
2.118
spin density
σ
0.18%
0.00024%
0.01%
25 °C (S cm-1)
0
1.9 × 10-6
1.0 × 10-5
3.1 × 10-3
interior angles on the ring. In all cases, the CdC bond lengths
in the polycyclic ring coordinated to the silver atoms are
significantly shortened by about 0.03-0.06 Å compared with
the averaged distances of the noncoordinated C-C bonds, Table
3, indicative of large electron density accumulated on the
π-bonded carbon atoms. A similar finding was reported for
the coordinated benzene molecule in [Ag(C6H6)(ClO4)] where
the distances between the two carbon atoms in the ring nearest
to the silver atoms is 1.35 Å, while the neighboring carbon-
carbon distance is 1.43 Å.18(d) These observations are surprising
since in either case, whether silver(I) acts as an electron acceptor
or as a donor of electrons from a filled d orbital to an empty
molecular orbital of the aromatic, it would change the coordi-
nated carbon-carbon distances in the opposite direction to that
observed. It is not clear whether the polarization of the mobile
π electrons by the positive silver ions would increase the
electron density in the bonds closest to the positive silver ion.
The lack of detailed understanding of electron effects affecting
these bond distances precludes any discussion of the significance
of these variations.
Aromatic stacking is a common feature of PAH compounds
regardless of considerable variations in the coordinative interac-
tions. Complex 1 is a monomer, and there is no aromatic
stackings observed in the structure. Likewise, intermolecular
π interactions are not involved in the coordination of polymer
2. Structure analysis confirmed the presence of strong aromatic
interactions in 3 and 4, which result in the assembly of
coordination polymers into π-π interacted supramolecular
structures. Complex 4, in particular, involves both intermo-
lecular and intramolecular columnar aromatic stacks. The
stacking interaction contributes not only to the stability of the
complex but also to its electrical conducting behaviors. It is
known that hydrocarbons form conducting radical salts.32 The
room-temperature conductivities for 1-4 were measured, and
the results are listed in Table 3. Complex 1 is an insulator,
whereas 2-4 exhibit semiconductivity. Although compound
2 has a relatively higher spin density, it exhibits low conductivity
due to the lack of aromatic π-π stackings. The value for 4 is
3 orders of magnitude greater than that of 2 and is comparable
to the values for intrinsic atomic semiconductors, such as silicon.
The semiconducting behavior can be rationalized when the
nature of the conducting stacks is considered. The stacking
interaction generally arises from the interaction between the
π-orbitals of two aromatic rings, especially between the highest
occupied molecular orbital (HOMO) of the donor ring and the
lowest unoccupied orbital (LUMO) of the acceptor ring. Strong
intermolecular as well as intramolecular aromatic stackings in
4 obviously offer the most effective electron-transfer pathway
among four complexes.
the structures of the present four organosilver compounds,
together with those of pyrene and perylene,24 provide an
excellent illustration of the unique coordinative versatility of
the large aromatic compounds. To accommodate the most
favorable pseudotetrahedral stereochemistry of the silver(I) ion,
each polycycle adjusts its conformation accordingly with all
coordination modes occurring through molecular recognition.
They can display a usual symmetric tetra-η2-coordination,
linking four metal atoms forming triple-decker molecular stacks
as observed for coronene, and a W-type sandwich of polymeric
chain and sheets as found in pyrene and perylene systems.24
They can also exhibit symmetric tetra-η1 and tetra-η2-bonding,
linking eight metals as described for rubrene. Furthermore,
asymmetric coordination of η2 and η1, linking three metal ions
for benzo[a]pyrene, or just η2 bonding to one metal center as
characterized for 9,10-diphenylanthracene is even unique. The
conformation of these macrocycles is not necessarily coplanar
in complexation with metal ions, and they can be significantly
twisted or slightly bent as observed in rubrene and coronene,
respectively. By the use of metal-containing molecular building
blocks, the achievement of electron-transfer processes and
unusual electroproperties looks promising. The power and
versatility of these large aromatic hydrocarbons in complexing
metal ions will undoubtedly offer considerable advantages over
the planned synthesis of polynuclear aromatic molecules with
defined form and function. We are presently working toward
this direction.
Conclusions
Using perchlorate anions as complementary bridging ions and
the crystallized solvent molecules such as benzene and toluene
as spacers, the reactions of silver(I) perchlorate and four
polycyclic aromatics afforded unique monomer and polymeric
complexes based on cation-π interactions. Incorporation of
transition metal ions into polycyclic aromatics has a dramatic
influence on the physical properties of the resultant multidi-
mensional π system of the aromatics. In each case, the silver
ions are coordinated to the short CdC bond moiety by cation-π
interactions, and large electron densities on the carbons close
to the metal ions and molecular constraints are responsible for
the observed high spin densities of the organic radicals.
Formation of functional aromatic stack columns is essential for
the characteristic conductivity of this type of compound.
Although the X-ray structural data for four polycyclic com-
pounds comprise the main results of this paper, the precise data
confirmed our initial belief that, based on cation-π bonding and
noncovalent aromatic stackings, the large aromatic compounds
have the potential as possible components for the self-assembly
of multinuclear functional organometallics with novel networks.
Using PAHs for Multinuclear Aggregates. Although there
is long-standing structural evidence for the efficacy of an
aromatic compound as a ligand toward all types of metal ions,
Acknowledgment. This work was partially supported by a
Grant-in-Aid for Science Research [Nos. 09554041, 10440201,
and 10016743 (priority areas)] from the Ministry of Education,
Science, Culture and Sports in Japan.
(32) Lempka, H. J.; Oberland, S.; Schmidt, W. Chem. Phys. 1985, 96,
349.

8618 J. Am. Chem. Soc., Vol. 120, No. 34, 1998
Munakata et al.
Supporting Information Available: Tables of crystal data,
intensity measurements, structure solution and refinement,
atomic coordinates and thermal parameters, intramolecular bond
lengths and angles, and least-squares planes for 1-4 (38 pages,
print/PDF). See any current masthead page for ordering
information and Web access instructions.
JA981483Y