Solid channel structure and nanoscale drum-like Ag6 cluster constructed with pentafluorobenzenethiolate and triphenylphosphine ligands: The use of water-soluble silver(I) carboxylate as silver(I) source

Article abstract of DOI:10.1016/j.inoche.2005.10.003

A nanoscale drum-like hexanuclear silver(I) cluster [Ag(pfbt)(PPh ₃)]₆ 1 (Hpfbt = pentafluorobenzenethiol), which showed the arrays of channels based on its self-assembly in the solid, was obtained by the 1:1 molar-ratio reaction of

Full text of DOI:10.1016/j.inoche.2005.10.003

Inorganic Chemistry Communications 9 (2006) 60–63
www.elsevier.com/locate/inoche
Solid channel structure and nanoscale drum-like Ag6 cluster
constructed with pentafluorobenzenethiolate and
triphenylphosphine ligands: The use of water-soluble
silver(I) carboxylate as silver(I) source
*
Ryusuke Noguchi, Akihiro Hara, Akiyoshi Sugie, Kenji Nomiya
Department of Materials Science, Faculty of Science, Kanagawa University, Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan
Received 26 August 2005; accepted 2 October 2005
Available online 15 November 2005
Abstract
A nanoscale drum-like hexanuclear silver(I) cluster [Ag(pfbt)(PPh3)]6 1 (Hpfbt = pentafluorobenzenethiol), which showed the arrays
of channels based on its self-assembly in the solid, was obtained by the 1:1 molar-ratio reaction of the insoluble polymeric precursor
[Ag(pfbt)] 2 and PPh3 in chloroform. Synthetic yield and purity of 1 were strongly dependent on the purity of 2. Compound 2 with
1
higher purity was prepared in good yield using light-stable and water-soluble silver(I) carboxylate [Ag(Hpyrrld)]2 (H2pyrrld = 2-pyrrol-
idone-5-carboxylic acid) as the silver(I) source.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Nanoscale hexanuclear silver(I) cluster; Solid channel structure; Pentafluorobenzenethiol; Triphenylphosphine; 2-Pyrrolidone-5-carboxylic
acid
There is currently considerable interest in the coordina-
tion chemistry of coinage metals such as silver(I) and
gold(I) with biological and/or medicinal activities [1–3].
In the structural viewpoint, silver(I) complexes with thiol
ligands have shown a tendency to form cluster and polymer
structures [1,4], whereas the corresponding gold(I) com-
plexes have shown supramolecular arrangements of 2-coor-
dinate linear units [1,5–7].
It is known that the cooperation with electron-deficient
fluorinated aromatics and electron-rich aromatics can
induce electrostatic quadrupole stacking interaction and
contribute to the architecture of extended structures in the
crystal [8–13]. For example, the supramolecular dimer of
the triphenylphosphinegold(I) complex [Au(pfbt)(PPh3)]2
(Hpfbt = pentafluorobenzenethiol; Chart 1) through inter-
molecular quadrupole interactions between the fluorinated
phenyl ring (pfbtꢀ) and the phenyl ring of the neighboring
PPh3 molecule was realized in the solid state and in solution,
the molecular structure of which contained intramolecular
Auꢁ ꢁ ꢁF and H(phenyl of PPh3)ꢁ ꢁ ꢁF interactions as well as
2-coordinate P–Au–S bonding [14]. The related gold(I) com-
plex [Au(SPh)(PPh3)] with the unfluorinated aromatic thio-
late has shown a dimeric arrangement through the
aurophilic interaction [15]. On the other hand, the triphenyl-
phosphinesilver(I) complex with flurorine-free aromatic
ligand, [Ag(SPh)(PPh3)]4 (SPhꢀ = benzenethiolate), has
been reported as a tetranuclear silver(I) cluster with highly
distorted chair structure [16]. However, the structure of the
pfbtꢀ analogs of triphenylphosphinesilver(I) complex has
not been reported so far. Thus, we have aimed at preparing
such a complex and examining the effect of fluorinated and
unfluorinated aromatic thiolate ligands on the molecular
structure of the triphenylphosphinesilver(I) complexes.
Recently, we have found that the chiral and achiral sil-
ver(I) carboxylates, [Ag(R- or S-Hpyrrld)]2 and [Ag(R,S-
Hpyrrld)]2 (H2pyrrld = 2-pyrrolidone-5-carboxylic acid)
[17,18] are light-stable and water-soluble Ag–O bonding
*
Corresponding author. Tel.: +81463594111; fax: +81463589684.
E-mail address: nomiya@chem.kanagawa-u.ac.jp (K. Nomiya).
1387-7003/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.10.003

R. Noguchi et al. / Inorganic Chemistry Communications 9 (2006) 60–63
61
F
F
F
F
F
SH
Chart 1. Hpfbt (pentafluorobenzenethiol).
complexes. Their triphenylphosphine derivatives, e.g.,
[Ag2(R- or S-Hpyrrld)2(H2O)(PPh3)2] Æ H2O, [Ag(R- or S-
Hpyrrld)(PPh3)2]2, [Ag(R,S-Hpyrrld)(PPh3)]2 and [Ag(R,S-
Hpyrrld)(PPh3)2], showed different Ag–O bonding modes
depending on the number of PPh3 ligands and the chirality
of the Hpyrrldꢀ ligand [19]. The Ag–O bonding complexes
and the triphenylphosphinesilver(I) derivatives have been
recently used as useful precursors for formation of novel
silver(I) clusters such as [Ag(2-Hmba)(PPh3)]4 (2-H2mba =
2- mercaptobenzoic acid) with a three-leaves propeller (C3
symmetry)[20]and[Ag2(Himdc)(PPh3)2]2 (H3imdc = imidaz-
ole-4,5-dicarboxylic acid) with a ‘‘bivalve’’-like skeleton [21].
In this work, a nanoscale, S6 symmetry drum-like hexanu-
clear silver(I) cluster [Ag(pfbt)(PPh3)]6 1 was successfully
obtained in the 1:1 molar-ratio reaction ofthe insoluble poly-
meric precursor [Ag(pfbt)] 2 and PPh3 in chloroform
1
[22,23]. Complex 1 showed the arrays of channels resulting
from its self-assembly in the solid state. The water-solublesil-
ver(I) carboxylate [Ag(Hpyrrld)]2 was used as the silver(I)
source for preparation of 2 with higher purity. Herein, we
report the synthesis of 1 and 2, and the unequivocal charac-
terization of 1 with elemental analysis, TG/DTA, FTIR,
solution (1H and 31P) NMR and solid-state 31P CPMAS
NMR, and single-crystal X-ray crystallography.
Fig. 1. (a) Molecular structure of 1 (symmetry operation i = y + 2,
ꢀx + y + 1, ꢀz + 2; ii = ꢀx + y + 2, ꢀx + 1, z; iii = ꢀx + 2, ꢀy, ꢀz + 2;
iv = ꢀy + 1, x ꢀ y ꢀ 1, z; v = x ꢀ y, x ꢀ 1, ꢀz + 2) and (b) its skeleton
˚
representation with Ag, S, and P atoms. Selected interatomic distances (A)
and angles (ꢁ): Ag1–P1 2.4137(5), Ag1–S1 2.6062(5), Ag1–S1iv 2.6084(5),
Ag1–S1v 2.6930(5), Ag1ꢁ ꢁ ꢁAg1i separation 3.875 A; P1–Ag1–S1
˚
Compound 1 as colorless plate crystals was obtained in
79.0% (0.45 g scale) yield by the 1:1 molar-ratio reaction of
2 and PPh3 in chloroform. Pale yellow powder of 2 was
obtained in 95.3% (1.17 g scale) yield by the 1:2 molar-ratio
reaction of [Ag(R,S-Hpyrrld)]2 and Hpfbt in a 1:1 mixed
H2O/EtOH solvent. Instead of [Ag(R,S-Hpyrrld)]2, the sil-
ver(I) sources such as Ag2O and AgNO3 gave the impure
119.564(16), P1–Ag1–S1iv 115.210(16), S1–Ag1–S1iv 109.92(2), P1–Ag1–
S1v 134.069(17), S1–Ag1–S1v 85.798(15), S1iv–Ag1–S1v 85.751(15)ꢁ.
NMR are consistent with the solid-state structure revealed
by X-ray crystallography.
solid 2 contaminated with unreacted Ag2O and NOꢀ ion
Solution 31P NMR in CDCl3 of 1 showed one 31P reso-
nance at 9.30 ppm on the basis of coordination to the six
equivalent silver(I) atoms. The 1H NMR spectra of 1
showed multiplet peaks for aryl protons of the PPh3 ligand.
X-ray structure analysis revealed that an S6 symmetry
hexanuclear silver(I) cluster 1 was a micelle-like nanoscale
3
[22]. The synthetic reactions of 2 and 1 are shown in Eqs.
(1) and (2):
1=2½AgðR; S-HpyrrldÞꢂ2 þ Hpfbt ! 1½AgðpfbtÞꢂ2
þ R; S-H2pyrrld
ð1Þ
ð2Þ
6 ½AgðpfbtÞꢂ2 þ 6PPh3 ! ½AgðpfbtÞðPPh3Þꢂ 1
1
6
˚
object with an external diameter ca. 18 A and an internal
˚
diameter ca. 5 A (Fig. 1(a) and (b)), and it constructed
The composition and molecular formula of 1 were con-
sistent with elemental analysis, TG/DTA, FTIR, solution
(1H and 31P) NMR and solid-state 31P CPMAS NMR.
The solid-state 31P CPMAS NMR spectra of 1 showed
phosphorus resonance of doublet peaks (two lines) due to
1J(Ag–P) coupling for the PPh3 ligand coordinating to
the six equivalent silver(I) atoms. The solid-state 31P
nanoporous channel structures based on its self-assembly
in the solid state (Fig. 2) [24].
The molecular structure of 1, constructed with six 4-
coordinated Ag(l3-S)3P units (Ag1, Ag1i, Ag1ii, Ag1iii,
Ag1iv and Ag1v), was stabilized with many Ag–(l3–S)
and Ag–P bondings as well as several non-covalent, weak

62
R. Noguchi et al. / Inorganic Chemistry Communications 9 (2006) 60–63
Fig. 2. The solid-state packing of the Ag6 cluster 1, composed of Ag (blue), P (red), S (yellow), F (green) and C (gray) atoms, along the crystallographic c
axis. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
˚
and multiple intramolecular interactions, i.e., Fꢁ ꢁ ꢁH inter-
2.6084(5), 2.6930(5) A) in 1 are longer than those
i
˚
˚
˚
action (F6ꢁ ꢁ ꢁH112 2.574 A, F2ꢁ ꢁ ꢁH122 2.353 A), Fꢁ ꢁ ꢁC
(2.5245(7), 2.5147(8), 2.4925(7), 2.5593(8) A) in
ii
interaction (F2ꢁ ꢁ ꢁC122ii 3.169 A, F3ꢁ ꢁ ꢁC124 3.102 A)
[Ag(SPh)(PPh3)]4.
˚
˚
˚
and C(pfbt)ꢁ ꢁ ꢁC(Ph) interaction (C1ꢁ ꢁ ꢁC112 3.488 A,
The molecular structure of 1 is similar to that of the pre-
viously reported Ag6 cluster with a ‘‘drum’’-like skeleton,
˚
˚
C2ꢁ ꢁ ꢁC111 3.487 A, C2ꢁ ꢁ ꢁC112 3.367 A, C3ꢁ ꢁ ꢁC113
ii
˚
˚
˚
3.481 A, C3ꢁ ꢁ ꢁC114 3.419 A, C2ꢁ ꢁ ꢁC122 3.320 A), the dis-
[Ag{S2P(OPri)2}]6
(S2P(OPri)2 = diisopropyldithiophos-
tances of which were close to or slightly shorter than the
phine) [27], while that of 1 is quite different from those of
the previously reported Ag6 clusters formed with the S-
donor atom [28–33].
In summary, the nanoscale micelle-like Ag cluster 1 with
an S6 symmetry (an external diameter ca. 18 A and an
˚
˚
sum of the van der Waals radii (H 1.20 A, F 1.47 A, C
1.70 A). In 1, there was neither Ag–Ag interaction
(3.857 A) nor interaction between Ag and F atoms
˚
˚
˚
˚
(3.328 A).
˚
On the other hand, the external interactions among the
Ag6 clusters resulted in the self-assembly: one Ag6 unit was
linked to the neighboring six Ag6 units each other through
a dual mode of the intermolecular F5(F–Ph)ꢁ ꢁ ꢁH115(Ph)
internal diameter ca. 5 A), which showed solid channel
structure, was obtained using the separately prepared,
insoluble polymeric precursor 2 and PPh3. Using the
water-soluble silver(I) source [Ag(Hpyrrld)]2, compound 2
with higher purity was obtained in good yield. The present
silver(I) source would be useful for formation of novel sil-
ver(I) clusters, in the place of the traditional silver(I)
sources such as AgNO3, Ag2O, silver(I) acetate and so on
[20,21]. Also, novel nanoporous structures based on the sil-
ver(I) complexes would be built by using some fluorinated
aromatic thiolates (F–SPhꢀ) with the changed number and
site of F atom and changing the molar ratios of the precur-
˚
interaction (2.470 A) between the two Ag6 cluster units.
Thus, the aryl embraces through the dual Fꢁ ꢁ ꢁH interaction
significantly contribute to the packing and the arrays of
channels [25,26]. The unique pfbtꢀ ligand undoubtedly
contributes to the intramolecular and intermolecular, weak
multiple interactions which stabilize and drive the forma-
tion of the Ag6 cluster 1 and its self-assembly.
Complex 1 is in contrast to the triphenylphosphine-
gold(I) complex with the pfbtꢀ ligand, [Au(pfbt)(PPh3)]2,
which is a new class of supramolecular aggregation
through the intermolecular electrostatic quadrupole inter-
actions in the solid state and in solution [14]. Complex 1
can be also compared with the Ag4 cluster with the highly
distorted chair structure of [Ag(SPh)(PPh3)]4 with the fluo-
rine-free SPhꢀ ligand [16]: the Ag–S distances (2.6062(5),
sor [Ag(F–SPh)] and PPh3.
1
Acknowledgment
This work is supported by a High-tech Research Center
Project from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.

R. Noguchi et al. / Inorganic Chemistry Communications 9 (2006) 60–63
63
133 lL (1.00 mmol) of Hpfbt. To it, 1.0 mL of 1.0 M NaOH aqueous
solution (1.00 mmol) was added dropwise and the stirring continued
for 1 h. Pale yellow powder formed was collected on a membrane
filter (JG 0.2 lm), washed with water (50 mL · 2), EtOH (50 mL · 2)
and ether (50 mL · 2), and thoroughly dried in vacuo for 2 h. The
pale yellow powder obtained in 91.2% (0.28 g scale) yield was
contaminated with NOꢀ3 ion. Prominent IR bands at 1600–400 cmꢀ1
region (KBr disk): 1521m, 1479s, 1384vs (NOꢀ3 ), 1097m, 966s,
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NMR (substitution method with (NH4)2HPO4, 25.0 ꢁC ): d 5.76
(JAgꢀP 491 Hz).
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ꢀ
bohedral, space group R3, a = 27.6806(14), b = 27.6806(14),
3
˚
˚
c = 15.1191(15) A, c = 120ꢁ, V = 10032.5(12) A , Z = 3,
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[22] Compound 2: To 0.944 g (2.00 mmol) of [Ag(R,S-Hpyrrld)]2 dis-
solved in 40 mL of 1:1 (v/v) solvent mixture of H2O and EtOH was
added 432 lL (4.00 mmol) of Hpfbt, followed by stirring for 1 h. Pale
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ether (100 mL · 2), and thoroughly dried in vacuo for 2 h. The pale
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867m cmꢀ1. Synthesis of 2 using Ag2O instead of [Ag(R,S-Hpyrrld)]2:
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Hpfbt, followed by stirring for one day. The material obtained here
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[Ag(R,S-Hpyrrld)]2: To a solution of 0.169 g (1.00 mmol) of AgNO3
in 20 mL of 1:1 (v/v) solvent mixture of H2O and EtOH was added
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