Synthesis and crystal structures of silver(I) bridged tetra-phenyl-pyrylium complexes from tetraphenyl-cyclopentadiene

Article abstract of DOI:10.1016/j.ica.2005.01.009

Reactions of silver(I) perchlorate with tetraphenyl-cyclopentadiene (Ph₄H₂C₅) have isolated two novel silver(I) bridged tetraphenyl-pyrylium complexes: [Ag(ClO₄)(Ph ₄HC₅O⁺)](ClO₄)^- (1) and [Ag(ClO₄)(H₂O)(Ph₄HC₅O ⁺)](ClO₄^-) (2), depending on moisture-content of the reactants. Structure studies using single-crystal X-ray diffraction have showed that complex 1 contains a distorted tetrahedral metal center bridging two neighboring peripheral phenyl rings of one pyrylium cation and two perchlorate anions, whereas 2 involves a three-coordinate metal ion interacting with a pair of phenyl rings and one water molecule, leaving two perchlorate anions free from coordination. For both complexes, the precursor ligand Ph₄H ₂C₅ undergoes a ring-enlargement reaction, forming a six-membered pyrylium cation. The fundamentals of the synthesis, structure characterization and some properties are discussed.

Full text of DOI:10.1016/j.ica.2005.01.009

Inorganica Chimica Acta 358 (2005) 2355–2362
www.elsevier.com/locate/ica
Synthesis and crystal structures of silver(I) bridged
tetra-phenyl-pyrylium complexes from tetraphenyl-cyclopentadiene
a,
a
a
b
Gui Ling Ning *, Xin Cheng Li , Wei Tao Gong , Megumu Munakata ,
b
Masahiko Maekawa
a
State Key Laboratory of fine Chemicals, Dalian University of Technology, Zhongshan Road 158, Dalian 116012, PR China
b
Department of Chemistry, Kinki University, Osaka 577, Japan
Received 18 November 2004; accepted 11 January 2005
Available online 7 February 2005
Abstract
Reactions of silver(I) perchlorate with tetraphenyl-cyclopentadiene (Ph4H2C5) have isolated two novel silver(I) bridged tetraphe-
nyl-pyrylium complexes: [Ag(ClO4)(Ph4HC5O+)](ClO4)ꢀ (1) and ½AgðClO4ÞðH2OÞðPh4HC5OþÞꢁðClO ꢀÞ (2), depending on moisture-
4
content of the reactants. Structure studies using single-crystal X-ray diffraction have showed that complex 1 contains a distorted
tetrahedral metal center bridging two neighboring peripheral phenyl rings of one pyrylium cation and two perchlorate anions,
whereas 2 involves a three-coordinate metal ion interacting with a pair of phenyl rings and one water molecule, leaving two perchlo-
rate anions free from coordination. For both complexes, the precursor ligand Ph4H2C5 undergoes a ring-enlargement reaction,
forming a six-membered pyrylium cation. The fundamentals of the synthesis, structure characterization and some properties are
discussed.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Pyrylium; Silver(I) perchlorate; Complex; Tetraphenylcyclopentadiene
1. Introduction
paper, we exhibit two silver(I) bridged tetraphenyl-pyry-
lium complexes synthesized from tetra-phenyl-
cyclopentadiene.
Pyrylium salts have opened up broad prospects in
commercial applications owing to their fluorescence
and charge-transfer properties [1–4]. The peculiarities
in the photophysical and electrochemical characteristics
are attributable to the substitution patterns of the pyry-
lium ring [1,4–6]. Although a large number of differently
substituted pyrylium salts have been synthesized and
studied, almost all substitution species are composed
of organic groups or motifs [4–7]. The investigations
of introducing metal ions into the substitution system
for some potential properties are very limited [8]. In this
During the course of our exploration of silver(I) com-
plexes with polycyclic hydrocarbons for functional
materials [9,10], we found that the five-membered cyclo-
pentadiene ring of phenyl substituted cyclopentadienes,
such as tri-, tetra- and/or penta-phenyl-cyclopentadiene,
could be converted to six-membered pyrylium ring by
interacting with silver(I) perchlorate. The characteriza-
tions and formation mechanism of these pyrylium salts
have been published in our preliminary reports [11].
Interestingly, among these compounds, only tetra-phe-
nyl-pyrylium cation involved a silver(I) ion in its periph-
eral phenyl rings despite the same reaction condition
and process being followed. Furthermore, by changing
*
Corresponding author. Tel.:/fax: +86 41188993609.
E-mail address: ninggl@dlut.edu.cn (G.L. Ning).
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.01.009

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G.L. Ning et al. / Inorganica Chimica Acta 358 (2005) 2355–2362
the moisture-content of Ph4H2C5 1, another silver(I)
coordination pattern was also isolated. We report here,
in detail, the synthesis, structural characterizations and
some properties of these two complexes.
2.2.2. [Ag(ClO4)(H2O)(Ph4HC5Oþ)](ClO4 ꢀ) (2)
The brown column crystals of 2 were prepared in the
same way as 1, using Ph4H2C5 Æ nH2O (15 mg,
0.04 mmol) instead of Ph4H2C5. Ph4H2C5 is moisture-
adsorbing substance and Ph4H2C5 Æ nH2O can be easily
obtained by keeping the chemical in the air for 2–10
days. The increased moisture-content makes the reac-
tion much easier. X-ray quality crystals of 2 were ob-
tained after 2 weeksꢀ standing of the glass tube, 41% in
yield. IR, m/cmꢀ1: 1597s (pyrylium ring skeleton),
2. Experimental
2.1. General procedures
1
All reactions and manipulations were carried out un-
der an argon atmosphere using usual Schlenk tech-
niques. Solvents were dried and distilled by using
standard methods prior to use. Reagent grade 1,2,3,4-
tetraphenylcyclopentadiene was purchased from Tokyo,
Kasei Kogyou Co. Ltd., while silver(I) perchlorate
monohydrate was from Aldrich. IR spectra were re-
corded as KBr disks on a JASCO FT-IR 460 spectrom-
eter. 1H NMR spectra were obtained on INOVA 400 for
complex 1, GSX 270 FT for complex 2 and Ph4H2C5
precursor ligand. 13C NMR spectra were recorded on
INOVA 400. MS were measured on HP1100 for 1 and
JEOL LMS-HX 100 for 2. UV–Vis spectra were re-
corded on a Hitachi 150-20 spectrophotometer. Elemen-
tal analyses of complex 1 and 2 were performed by
Dalian Institute of Chemical Physics, China Academy
of Science and by the Department of Chemistry, Tokyo
Metropolitan University, Japan, respectively.
1112vs (mCl–O). H NMR [23 °C, (CD3)2CO, 270 MHz]:
d 9.89(1H, s, pyrylium ring). 13C NMR [23 °C,
(CD3)2CO, 400 MHz, d in ppm]: 209.97, 206.20,
173.61, 170.55, 164.03 (5 signals). Ms, m/z: 385. Anal.
Calc. for C29H23AgCl2O10 (2): C, 49.04; H, 3.26. Found:
C, 48.36; H, 3.25%.
2.3. X-ray crystallography
The single crystal suitable for X-ray measurement
was fixed on a glass fiber with adhesives. The diffraction
data for the two complexes were collected at room tem-
perature for 1 and 273.2 K for 2 on a Rigaku AFC7R
four-circle diffractometer equipped with graphite-mono-
chromated Mo Ka radiation. Space groups were se-
lected on the basis of systematic absences and intensity
statistics. Over the course of data collection, no decay
correction was applied for the complexes. All intensity
data were corrected for Lorentz and polarization effects.
The structures were solved by direct methods followed
by subsequent Fourier-difference calculation and refined
by a full-matrix least-squares analysis on F using the
TEXAN package [12]. Hydrogen atoms of all of the two
structures were introduced into their calculated posi-
tions; they were included, but not refined. Details of
the X-ray experiments and crystal data are summarized
in Table 1. Final atomic coordinates for all of the struc-
tures are given in the Supporting Information. The se-
lected bond distances and angles for the two
complexes are listed in Table 2.
Caution: Perchlorate salts of metal complexes with
organic ligands are potentially explosive! Only small
amounts of materials should be prepared and handled
with great care.
2.2. Synthesis
2.2.1. [Ag(ClO4)(Ph4HC5Oþ)]ClO4 ꢀ) (1)
To
a
solution of tetraphenyl-cyclopentadiene,
Ph4H2C5 (15 mg, 0.04 mmol), in a mixed solvent of
CH2Cl2/toluene (3/1 in volume, 4 ml) was added Ag-
ClO4 Æ H2O (46 mg, 0.2 mmol). After being stirred for
about 20 min, the resultant colorless solution was trans-
ferred to a 7-mm diameter glass tube and layered with n-
hexane as a diffusion solvent. The glass tube was sealed
under Ar and wrapped with aluminum foil. After stand-
ing at room temperature in the dark for about 6 weeks,
X-ray quality yellow plate crystals of 1 were obtained,
26% in yield. IR, m/cmꢀ1: 1594s (pyrylium ring skeleton),
3. Results and discussion
3.1. Synthesis, characterization and properties
The reactions of Ph4H2C5 with silver(I) perchlorate in
a mixed solvent of CH2Cl2/toluene afforded complexes 1
and 2, depending on the moisture-content of Ph4H2C5,
Footnote 1. The synthesis of the two organometallics
can be thought of as a type of combinatorial chemistry,
achieved by simultaneous ligand modification and metal
coordination reaction. It has been found in our studies
that phenyl substituted cyclopentadienes did not form
coordination complexes with silver perchlorate at nor-
mal conditions, although they proved a strong ability
1
1093vs and 1044vs (mCl–O). H NMR [23 °C, (CD3)2CO,
400 MHz]: d 9.96 (1H, s, pyrylium ring). Ms, m/z: 385.2.
Anal. Calc. for C29H21AgCl2O9 (1): C, 50.27; H, 3.03.
Found: C, 50.04; H, 3.08%.
1
For 2, Ph4H2C5 was exposed to the air with relative humidity
60–70% for more than 10 days at room temperature. While for 1, the
moisture-saturated Ph4H2C5 were put into a drying box for 2–3 days
before use.

G.L. Ning et al. / Inorganica Chimica Acta 358 (2005) 2355–2362
2357
Table 1
Crystallographic data
ture-content of Ph4H2C5, and thus complex 1 was ob-
tained. Scheme 1 gives the equation for the reaction of
Ph4H2C5 with AgClO4 in the presence of H2O, which
has been verified by our extensive study [11]. The reac-
tion shows that the original five-membered cyclopent-
adiene-ring of Ph4H2C5 is enlarged into six-membered
pyrylium-ring by inserting an oxygen atom, and mean-
while a silver(I) ion is coordinated to its peripheral phe-
nyl rings. Here, due to the fact that part of silver(I) ions
act as an oxidant, an excess amount of silver(I) perchlo-
rate has been used for the coordination. However, while
silver(I) perchlorate decreases, the silver(I) coordinated
pyrylium complex can also be obtained although part
of Ph4H2C5 remains. The bridged silver(I) ions in 1
and 2 cannot be removed by changing the amount of
1
2
Formula
C29H21AgCl2O9
692.25
C29H23AgCl2O10
710.27
Formula weight
Crystal system
Space group
monoclinic
P21/c
273.2
monoclinic
P21/n
296.2
Temperature (K)
Unit cell dimensions
˚
a (A)
10.567(1)
17.999(1)
14.7519(4)
99.4277(6)
2767.8(3)
4
12.030(3)
13.764(4)
17.662(6)
93.25(3)
2919(1)
4
˚
b (A)
˚
c (A)
b (°)
3
˚
V (A )
Z
F(0 0 0)
qcalc (g cmꢀ3
1392
1.661
1432
1.616
)
˚
2
Radiation, k(Mo Ka) (A)
0.7107
9.74
6313
0.7107
9.28
6699
silver(I) perchlorate, or by solvent extraction. In
l cmꢀ1
Number of data collected
contrast, while using bi-, tri- or penta-phenyl-cyclopent-
adiene instead of Ph4H2C5 in the reaction, only silver(I)-
free pyrylium cations have been obtained, regardless of
a large excess of silver(I) perchlorate used. The forma-
tion rate of the two complexes is dependent on the mois-
ture-content. If all reactants were deeply dried before
use, neither complex 1 nor 2 could be obtained. With
partially dried Ph4H2C5, in the case of 1, the complex
was formed very slowly, while for 2, in which Ph4H2C5
was exposed to the air with relative humidity 60–70%
for more than 10 days at room temperature, the crystals
were obtained much easier. However, if excess water
were dropped in the reaction solution, making organic/
inorganic phase separated, no crystals could be observed
anymore, probably due to the instability of pyrylium
cations in water [14]. On the other hand, without sil-
ver(I) ions, the reaction in Scheme 1 could not take
place. Several other metal ions, such as Cu(I), Cu(II)
and Au(I) ions, have been used in place of Ag(I) ion
to investigate the reaction. However, there has been no
pyrylium salt formed, although the reduced Cu/Au met-
als were observed. Here, silver(I) ion most likely func-
tions as both a Lewis acid catalyst and an oxidant. It
is noteworthy that the mixed solvent of CH2Cl2/toluene
has to be used in the synthesis. Toluene is used to dis-
solve silver(I) perchlorate, whereas the polar CH2Cl2
probably serves as an acceptor to dissolve the formed
pyrylium salts. Either of the solvents can make Ph4H2C5
dissolved.
Number of data in refinement
R1
3823
2423
0.059
0.0592
0.0845
2.255
wR2
0.170
1.785
GOF on F
ꢀ3
˚
qmax/qmin (e A
)
1.39/ꢀ0.85
0.8/ꢀ0.52
Table 2
˚
Selected bond lengths (A) and angles (°)
1
Ag(1)–O(1)
Ag(1)–C(14)
Ag(1)–C(15)
C(1)–O(9)
C(1)–C(2)
2.404(6) Ag(1)–O(5)
2.317(7)
2.593(6)
2.774(8)
1.319(6)
1.398(7)
1.388(7)
2.523(7) Ag(1)–C(20)
2.772(7) Ag(2)–C(21)
1.353(6) C(5)–O(9)
1.354(7) C(2)–C(3)
1.416(7) C(4)–C(5)
C(3)–C(4)
O(1)–Ag(1)–C(14)
O(5)–Ag(1)–C(14)
O(1)–Ag(1)–O(5)
C(1)–O(9)–C(5)
C(1)–C(2)–C(3)
C(3)–C(4)–C(5)
105.8(2)
118.3(3)
93.7(4)
O(1)–Ag(1)–C(20)
O(5)–Ag(1)–C(20)
C(14)–Ag(1)–C(20) 127.5(2)
114.7(2)
91.8(3)
122.1(4)
118.1(4)
119.5(4)
O(9)–C(1)–C(2)
C(2)–C(3)–C(4)
C(4)–C(5)–O(9)
121.9(4)
118.8(4)
119.3(4)
2
Ag(1)–O(2)
Ag(1)–C(21)
O(1)–C(1)
C(1)–C(2)
C(3)–C(4)
2.243(7) Ag(1)–C(16)
2.677(10)
2.61(1)
1.35(1)
1.37(1)
1.40(1)
Ag(1)–C(22)
O(1)–C(5)
C(2)–C(3)
C(4)–C(5)
2.53(1)
1.35(1)
1.39(1)
1.33(1)
O(2)–Ag(1)–C(16) 86.1(3)
O(2)–Ag(1)–C(22) 151.4(3)
C(16)–Ag(1)–C(22) 122.0(3)
O(2)–Ag(1)–C(21) 132.9(3)
C(16)–Ag(1)–C(21) 131.3(3)
C(21)–Ag(1)–C(22)
O(1)–C(1)–C(2)
C(2)–C(3)–C(4)
C(4)–C(5)–O(1)
31.1(3)
118.9(9)
119.6(8)
123.3(8)
These two complexes are soluble in common polar
organic solvents such as methanol, acetone or CH2Cl2.
They are very stable in the open laboratory environment
despite a little moisture-sensitivity at room temperature.
However, they decomposed below 150 °C forming black
powder.
C(1)–O(1)–C(5)
C(1)–C(2)–C(3)
C(3)–C(4)–C(5)
120.7(8)
120.1(8)
117.3(9)
to undergo simple g5-coordination with some transi-
tion-metal and lanthanide-metal ions, such as Gr, Fe,
Ru, Co, Mo, Rh, Ni, Pd, Ge, Sn, Pb, W and Lu [13].
Compound 2 was isolated occasionally by using the
moisture-adsorbed Ph4H2C5 and AgClO4 Æ H2O in the
mixed solvent. This motivated us to control the mois-
2
Water and benzene were selected as the extracting solvents. By
emerging these single crystals into either of the solvents for 24 h and
then undergoing a chemical analysis, the released silver(I) ion from the
crystals can be detected.

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G.L. Ning et al. / Inorganica Chimica Acta 358 (2005) 2355–2362
+
Ag
Ph
Ph
Ph
Ph
Ph
Ph
H
CH2Cl2 / toluene
Room temp.
Ph
Ph
H
H
+
+4Ag0 +3H+
+ 5Ag+ 2H2O
O
+
Scheme 1.
Characterization of the complexes was mainly based
on X-ray diffraction studies. Nevertheless, IR, NMR,
MS spectra and elemental analysis are good supplemen-
tary means to confirm incorporation of metal/perchlo-
rate ions and formation of pyrylium cations. The
strong absorption bands observed at 1093–1044 cmꢀ1
for 1 and 111ꢀ2 cmꢀ1 for 2 in IR spectra indicate the pres-
ence of ClO4 [9,10], which do not exist in the spectrum
of its precursor Ph4H2C5. The strong split absorption in
complex 1 at 1093–1044 cmꢀ1(mOCl) is consistent with
coordination of the perchlorate oxygen to metal ion
[10b,15]. According to the literature data [4a,18], the
skeleton vibrations of the pyrylium ring are 1594 cmꢀ1
for 1 and 1597 cmꢀ1 for 2, respectively, although they
exhibit obvious downfield shifts. The changed wave
numbers may be attributable to the substitution or coor-
dination pattern of the pyrylium ring [4a]. The 1H NMR
spectra of 1 and 2 together with their precursor ligand in
(CD3)2CO show that the original cyclopentadiene-ring
protons at 4.14 ppm shift to pyrylium-ring protons [7]
at 9.96 ppm for 1 and at 9.89 ppm for 2, respectively.
The chemical shifts of pyrylium-ring in the 13C NMR
spectrum were 209.97, 206.20, 173.61, 170.55 and
164.03 ppm. The mass spectra of 1 and 2 prove the exis-
tence of the intact cation at m/z 385 (Ph4HC5O+).
be attributable to the intramolecular charge-transfer
[17]. In contrast, complex 1 and/or 2 did not give such
absorption band, but tailed off into the visible region.
This could probably be interpreted as the effect of coor-
dinated Ag(I) ion, which changed the p-delocalization
length [17c].
3.2. Description of the structures
3.2.1. (Ph4HC5O+)[Ag(ClO4)2]ꢀ (1)
The molecular structure of complex 1 together with
atom-numbering scheme is shown in Fig. 2(a). The crys-
tallographic studies revealed that the original central
five-membered ring of precursor ligand Ph4H2C5 was
converted to a six-membered ring by insertion of an oxy-
gen atom. The O atom and the five C atoms in the newly
formed central ring are coplanar, with maximum devia-
˚
tion from the best plane being less than 0.025 A. Such
rings are iso-electronic with benzene and therefore show
aromatic character [17,18]. The C–C and C–O bond
lengths together with the bond angles in the central ring
˚
range from 1.319(6) to 1.416(7) A and 118.1(4) to
122.1(4)°, respectively, within the limits from 1.254(8)
˚
to 1.538(8) A and 108.6(5)° to 125.8(6)° in documented
pyrylium cations [19]. The coordination geometry
around silver(I) ion is pseudo-tetrahedral (taking the
C@C group as one ligand) [9,10], comprising two oxy-
gen atoms from two separate perchlorate anions and
two g2-carbon atoms from two neighboring phenyl
rings. The Ag–C distances range from 2.523(7) to
The UV–Vis absorption spectra of the two com-
pounds show completely different absorption features
from their precursor ligand Ph4H2C5. It is observed
from Fig. 1 that the precursor ligand Ph4H2C5 exhibits
a strong absorption band around 350 nm, which may
˚
2.774(8) A. The next closest contact between silver and
˚
carbon atoms is 2.948(6) A, well beyond the limits ob-
served in the reported silver(I)–aromatic complexes
[9,10,20]. The two Ag–O distances are 2.317(7) and
˚
2.404(6) A, respectively. The overall structure thus
formed is a discrete mononuclear complex. The posi-
tively charged central pyrylium ring exhibits a neutral
feature in its solid state by the static interaction with a
neighboring perchlorate anion shown in its cell packing,
Fig. 2(b).
3.2.2. [Ag(ClO4)(H2O)(Ph4HC5O+)](ClO4 ) (2)
-
By
using
water-adsorbed
precursor
ligand
Ph4H2C5 Æ nH2O in place of Ph4H2C5 in the above reac-
tion, a changed coordination framework, complex 2, was
isolated, whose molecular structure is given in Fig. 3(a).
Complex 2 also involves a central six-membered
Fig. 1. UV–Vis spectra of complexes 1, 2 and their precursor ligand in
toluene.

G.L. Ning et al. / Inorganica Chimica Acta 358 (2005) 2355–2362
2359
Fig. 2. Crystal structure with labeling of pyrylium cations in 1 (a), cell packing of 1 (b).
pyrylium ring. The C–C and C–O bond lengths of the
˚
pyrylium ring range from 1.33(1) to 1.40(1) A, and their
three-coordinate environment (taking the C@C group as
one ligand) [9,10]. Apart from the two bridging bonds
from the couple of phenyl rings, its third coordination
site is occupied by one oxygen atom from water, leaving
two perchlorate anions free from coordination. The
bond distances of Ag–C range from 2.53(1) to
bond angles are from 117.3(9)° to 123.3(8)°. The six
atoms in the pyrylium ring present the same coplanar
feature as those in 1. Furthermore, the silver(I) ion is
bonded by the same couple of phenyl rings as that in
1. However, unlike 1 where the metal ion exhibits a dis-
torted tetrahedral geometry, silver(I) ion in 2 displays a
˚
˚
2.677(10) A, and Ag–O is 2.243(7) A. The next closest
Ag–C and Ag–O distances are larger than 3.6 and

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G.L. Ning et al. / Inorganica Chimica Acta 358 (2005) 2355–2362
Fig. 3. Crystal structure with labeling of pyrylium cations in 2 (a), cell packing of 2 (b).
˚
2.762(9) A, respectively, which can be hardly
considered as an effective interaction [10]. The
tetraphenyl-pyrylium cation interacts with silver(I) ion
in an g1/g2 fashion, making the metal center in the cleft
between the two phenyl rings. The silver(I) bridged tet-
raphenyl-pyrylium moiety thus formed is a double-
charged cation. These cations keep neutral feature in
the solid state by incorporating perchlorate anions
between the pyrylium rings in their cell packing shown
in Fig. 3(b).
3.3. Modification of tetra-phenyl-cyclopentadiene ligand
Our frequent experiments have proved that
PhnH6 ꢀ nC5 (n = 2–5) did not form coordination com-
plexes with silver(I) ion in any normal solvents,

G.L. Ning et al. / Inorganica Chimica Acta 358 (2005) 2355–2362
2361
although Ph6C6 [9] and some phenylated alkenes [21]
displayed a strong coordination ability to the metal
ion. This implies that the central cyclopentadiene ring
(C5) of PhnH6 ꢀ nC5 ligands may dramatically affect
the interaction between its peripheral phenyl rings and
metal ions. Surprisingly, water molecules provide an
opportunity to change the ligand structure. It has been
proved by our extensive studies that the adsorbed water
molecules contribute to the formation of pyrylium ring
by providing inserted oxygen atom under the catalysis
and oxidation of silver(I) ion [11]. The water molecule
is added to the double bond of five-membered cyclo-
pentadiene-ring in a similar way to the strained ring sys-
tem [22] by a diene addition reaction [23]. Then, the
formed adduct undergoes a rearrangement process giv-
ing a six-membered neutral intermediate. According to
the literature [7], this intermediate is oxidized by silver(I)
ion to generate the six-membered pyrylium ring. Apart
from the verified pyrylium cation and silver(I) bridged
complex structures described above, the increased H+
concentration and reduced silver metal in Scheme 1
moisture-content of Ph4H2C5 leads to a three-coordinate
metal center. This implies that water molecule plays a key
role in controlling the architecture of silver(I) bridged
pyrylium complexes, probably due to the much stronger
interacting ability of water molecule with silver(I) ion. It
can be seen from Table 2 that the Ag–C bond distances
in 1 and 2 are all in normal ranges, being hardly to identify
the obvious differences (taking the C@C group as one li-
gand) [9,10,24]. However, the Ag–O bond distances are
quite different. In complex 1, each silver(I) ion links two
perchlorate anions with Ag–O distances of 2.404(6) and
˚
2.317(7) A, respectively, whereas in 2 the silver(I) ion is
bound to one oxygen from water at a distance of
˚
2.243(7) A. Such a short Ag–O distance, to the best of
our knowledge, has not been described in the aromatic
hydrocarbon system. There is only one report describing
a silver(I) bridged coordination polymer, where a water
molecule is bound to a tetrahedral silver(I) ion with Ag–
˚
O distance of 2.27(3) A [24]. In the present paper, the
strongly bridged water molecule makes the two perchlo-
rate counter-ions far from silver(I) ion, leading to a chan-
ged coordinate framework. As a consequence, the bond
lengths in the pyrylium ring of 1 and 2 are different. The
C–O and C–C bond lengths in 1 range from 1.319 to
3
are also identified [11].
3.4. Construction of a silver(I)-pyrylium complexes
˚
˚
1.416 A, while those in 2 are from 1.33 to 1.40 A. Complex
2 is unusual in the sense that the un-bridged perchlorate
anion from silver(I) ion has not been observed in the sil-
ver(I) complexes with polycyclic hydrocarbon ligand,
although various coordination modes of perchlorate ion
have been described in the literature [9,10,24,25].
Perhaps the most striking feature of this study is the
construction of silver(I) bridged tetra-phenyl-pyrylium
cation from tetraphenyl-cyclopentadiene. As seen in
the literature [3,7,8], a variety of substituted pyrylium
cations/salts have been synthesized and characterized.
However, very few studies concern organometallic sub-
stituents [8]. The silver(I)-bridged poly-phenyl-pyrylium
cation, to the best of our knowledge, has not been re-
ported before. Apart from the mild reaction conditions
and easy access of some precursors, the reaction path-
ways and its rationalization could be of broad interest
to chemists.
Probably due to the conjugated aromatic pyrylium
ring [7] which changed the steric configuration of the
original ligand, a pair of phenyl rings of the pyrylium
cation become vulnerable to the silver(I) attacking.
Thus, two g2–p orbitals from the phenyl groups of tet-
ra-phenyl pyrylium cation were bridged to a silver(I)
ion, forming a silver(I)-pyrylium complex. Nevertheless,
the positions of phenyl groups on the pyrylium ring may
dramatically affect the coordination behavior. Of all
these phenylate pyrylium salts synthesized, including
bi-, tri-, tetra- and penta-phenyl ones, only tetra-phenyl
pyrylium salt has proved to form coordination complex
with silver(I) perchlorate. Significantly, by changing the
reaction conditions such as the concentration of the
reactants, solvent, and ratios of silver(I) perchlorate to
precursor ligand, we cannot remove the bridged silver(I)
ions from 1 and 2, and cannot make the other phenylate
pyrylium cations coordinated by silver(I), either. This
may possibly be due to the proper orientations of the
adjacent phenyl rings, which provide a favorable dihe-
dral angle for silver(I) ion to incorporate [9].
4. Conclusion
On the other hand, water molecules can make the coor-
dination frameworks dramatically modified. In complex
1, where Ph4H2C5 was partially dried, the g2–p bridged
silver(I) ion is connected to two oxygen atoms from two
perchlorate anions to acquire a usual distorted tetrahe-
dral coordination geometry, whereas in 2, the increased
This study exemplifies two unprecedented silver(I)
bridged pyrylium complexes from tetra-phenyl cyclopent-
adiene. In the presence of silver(I) ion and trace amount of
water, phenylated cyclopentadienes undergo an oxida-
tion and ring-enlargement reaction to form phenylated
pyrylium ligands. The coordination of silver(I) ion to
the phenylated pyrylium group occurs only when
1,2,3,4-tetraphenyl cyclopentadiene was selected as pre-
cursor ligand. The coordination pattern of the complexes
is dependent on the moisture-content of the precursor li-
3
The H+ concentration was measured with pH meter in aqueous
solution by extracting the protic acid into water. Silver metal was
detected using XRD spectrometer.

2362
G.L. Ning et al. / Inorganica Chimica Acta 358 (2005) 2355–2362
(b) B. Caro, F. Robin-Le Guen, M. Salmain, G. Jaouen,
Tetrahedron 56 (2000) 257;
gand. With the increase of water adsorbed in Ph4H2C5,
the metal center in the pyrylium complexes changes from
distorted tetrahedral geometry to three-coordinate envi-
ronment. The results obtained here open an avenue to fu-
ture rational design of many other metallic pyrylium
compounds from cyclopentadiene derivatives.
(c) B. Caro, F. Robin-Le Guen, M.-C. Senechal-Tocquer, V.
Prat, J. Vaissermann, J. Organomet. Chem. 543 (1997) 87.
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Suenaga, T. Kuroda-Sowa, K. Sugimoto, Inorg. Chem. 38
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Acknowledgments
[10] (a) M. Munakata, G.L. Ning, Y. Suenaga, T. Kuroda-Sowa, M.
Maekawa, T. Ohta, Angew. Chem., Int. Ed. 39 (2000) 4555;
(b) G.L. Ning, L.P. Wu, K. Sugimoto, M. Munakata, T.
Kuroda-Sowa, Y. Suenaga, M. Maekawa, J. Chem. Soc., Dalton
Trans. (1999) 2529;
This work was partially supported by the National
Nature Science Foundation of China (No. 20072003)
and
a Grant-in-Aid for Science Research (No.
(c) M. Munakata, L.P. Wu, G.L. Ning, T. Kuroda-Sowa, M.
Maekawa, Y. Suenaga, J. Am. Chem. Soc. 121 (1999) 4968.
[11] (a) G.L. Ning, X.C. Li, M. Munakata, W.T. Gong, M. Maekawa,
T. Kamikawa, J. Org. Chem. 69 (2004) 1432;
10016743) from the Ministry of Education, Science, Cul-
ture and Sports in Japan.
(b) X.C. Li, G.L. Ning, L.P. Wu, Y. Lin, Chinese Chem. Lett. 13
(2002) 1141.
Appendix A. Supplementary data
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Supplementary data associated with this article can
be found, in the online version at doi:10.1016/
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