A mixed-valent silver(I, II) complex containing a self-assembled silver(I) cluster dimer with encapsulated acetylide dianion

Article abstract of DOI:10.1039/b202709g

A new mixed-valent silver complex [Ag^II(tmc)][Ag^II(tmc)- (H₂O)]₂·[Ag^I₁₁ (C₂)(CF₃CO₂)₁₂(H₂O) ₄]₂ (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) was synthesized by adding tmc to a concentrated aqueous solution of silver trifluoroacetate containing dissolved silver acetylide. Single-crystal X-ray analysis revealed that the resulting [Ag^II(tmc)]²⁺ and [Ag^II(tmc)(H₂O)]²⁺ complex cations induce the self-assembly of a centrosymmetric anionic cluster dimer from the Ag(I), C₂^2- and CF₃CO_2- species. A new type of cluster core [C₂@Ag₈]Ag was observed, which takes the form of a bicapped trigonal prism with a pendant silver atom attached to one edge.

Full text of DOI:10.1039/b202709g

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A mixed-valent silver(I, II) complex containing a self-assembled
silver(I) cluster dimer with encapsulated acetylide dianiony
Quan-Ming Wang, Hung Kay Lee and Thomas C. W. Mak*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong SAR, P. R. China. E-mail: tcwmak@cuhk.edu.hk; Fax: +852 2603 5057;
Tel: +852 2609 6279
Received (in New Haven, CT, USA) 7th February 2002, Accepted 6th March 2002
First published as an Advance Article on the web 18th April 2002
II
new mixed-valent silver complex [Ag (tmc)][Ag (tmc)-
II
A
I
(
H
2
O)]
2
Á[Ag 11(C
2
)(CF
3
CO
2
)
12(H
2
O)
4
]
2
(tmc ¼ 1,4,8,11-tetra-
methyl-1,4,8,11-tetraazacyclotetradecane) was synthesized by
adding tmc to a concentrated aqueous solution of silver trifluoro-
acetate containing dissolved silver acetylide. Single-crystal
II
2+
X-ray analysis revealed that the resulting [Ag (tmc)]
and
complex cations induce the self-assembly
of a centrosymmetric anionic cluster dimer from the Ag(I),
II
2+
[
Ag (tmc)(H O)]
2
2
À
À
C
C
2
and CF
@Ag ]Ag was observed, which takes the form of a bicapped
3
CO
2
species. A new type of cluster core
[
trigonal prism with a pendant silver atom attached to one edge.
2
8
1
A large number of mixed-valent systems have been studied in
the decades since the structure of the first man-made example,
2
Prussian Blue, was elucidated over 30years ago. Despite the
fact that compounds such as Ag
(
2
F(0, I), AgO(I, III) and Ag-
Ag )NO (I, III) are known, mixed-valent silver complexes
6
O
8
3
are rarely reported in the literature mainly due to the powerful
oxidizing nature of silver in higher oxidation states. Our recent
study on the chemistry of silver acetylide (Ag
demonstrated that Ag(I) and Ag(II) co-exist in the complex
2 2
C ) has
II
Ag (tmc)(BF
I
[
4
)][Ag
6
(C
2
)(CF CO
3
2
)
5
(H
2
O)]ÁH O (tmc ¼ 1,4,8,-
2
11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), and an
II
infinite [Ag (tmc)(BF
+1
)]
4
1
cationic column induces the
assembly of an anionic zigzag chain constructed from edge-
sharing of silver(I) triangulated dodecahedra each enclosing a
2À
3
C2 species. It is of interest to establish the generality of the
generation of this kind of mixed-valent complex via dis-
proportionation of silver(I) in the presence of a nitrogen
macrocycle. In addition, we would like to investigate the
effect of disruption of the cationic column on the assembly
process. Herein we report the synthesis and crystal struc-
II
2+
Fig. 1 (a) RSSR (Type III) [Ag (tmc)] cation at a site of symmetry
+
ꢀ
1
. Selected bond lengths (A): Ag12–N1, 2.187(5); Ag12–N2, 2.185(5).
II
2+
(
b) Aqua ligated RSRS (Type I) [Ag (tmc)]
cation. Selected bond
lengths (A): Ag13–N3, 2.195(6); Ag13–N4, 2.194(7); Ag13–N5,
.193(6); Ag13–N6, 2.224(7); Ag13–O5W, 2.684. Thermal ellipsoids
+
II
II
ture of the new complex [Ag (tmc)] [Ag (tmc)(H O)]
2
2
2
I
[
Ag 11(C
2 3 2 2 4 2
)(CF CO )12(H O) ] , 1.
are drawn at the 30% probability level.
Complex 1 was obtained by adding tmc ligand to a con-
centrated aqueous solution of silver trifluoroacetate containing
dissolved silver acetylide. The tmc ligand readily induces dis-
proportionation of Ag(I) to elemental silver and Ag(II), and the
higher oxidation state is stabilized by formation of the
co-planar as Ag12 is located at an inversion center. But for the
RSRS cation shown in Fig. 1(b), four N atoms and Ag13 are
II
2+
[
Ag (tmc)]
complex cation. X-Ray structure analysis reve-
+
folded into two planes, N3N4N5Ag13 (deviation 0.015 A) and
+
aled that there are two crystallographically distinguishable tmc
ligands in the unit cell: one located at an inversion center with
the RSSR (Type III) configuration while the other is in the
N3N6N5Ag13 (deviation 0.016 A), making a dihedral angle of
ꢀ
2
(
2
6.0 , due to coordination of an additional axial aqua ligand
Ag13–O5W: 2.684 A). The Ag–N bond lengths in the range
+
4
RSRS (Type I) form. An ORTEP drawing of these two kinds
+
+
.185(5)–2.224(7) A are in agreement with the 2.195 A found
5
in [Ag (tmc)](ClO ) .
4 2
II
of [Ag (tmc)] cations is illustrated in Fig. 1. For the RSSR
cation shown in Fig. 1(a), four N atoms and Ag12 are strictly
II
The presence of divalent silver has been confirmed by the
ESR spectrum of compound 1, which elicits a distinct signal
9
y In memory of Dr Richard K. McMullan (1929–2002).
(g ¼ 2.05) due to the d electronic configuration of silver(II).
DOI: 10.1039/b202709g
New J. Chem., 2002, 26, 513–515
513
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2002

2
À
Interestingly, overall charge balance with respect to the sil-
ver(II) complex cations is provided not by a simple counter-
encapsulated C
that carry a pendant silver atom. The lengths of the edges of
the [C @Ag ]Ag cage in 1 lie in the range of 2.8693(7)–
2
species represent the only kno wV ni e we x Aa mr ti cp l le e Os nline
I
ion but by a novel silver(I) cluster dimer {[Ag 11(C
2
)-
. The basic polyhedral unit of this
2
8
6À
+
(
CF
3
CO
2
)12(H
2
O)
4
]
2
}
3.3236(7) A (within twice the van der Waals radius of the silver
atom), except for three considerably longer ones at
cluster anion is shown in Fig. 2, which can be described as a
bicapped trigonal prism with one additional silver atom (Ag9)
Ag1Á Á ÁAg4 ¼ 4.156, Ag2Á Á ÁAg3 ¼ 3.683 and Ag5Á Á ÁAg6 ¼
+
attached to one edge. This is a new kind of C
cage, although a similar bicapped trigonal prism has been
found in 2Ag CO O where
2
@Ag
8
single
3.689 A. This is suggestive of the significance of argentophi-
8
licity, namely the d -d closed-shell attraction that pro-
10 10
9
2
C
2
Á3AgCNÁ15CF
3
2
AgÁ2AgBF
4
Á9H
2
motes the aggregation of silver(I) centers.
2À
6
two such prisms share a triangular face to give a double cage.
In the present case, the trigonal prism comprises two triangles,
Ag1Ag2Ag3 and Ag4Ag5Ag6, while Ag7 and Ag8 each caps a
rectangular face. The mean deviation of the atoms constituting
A C
2
species is accommodated in the bicapped trigonal
cage and retains its triple bond character with a
prismatic Ag
C–C bond length 1.212(8) A. This is in accordance with the
8
+
1
0,11
previous findings in a variety of C
ferent from the case of interstitial C
2
@Ag
n
cages,
units in organometallic
but dif-
the three rectangular faces of the trigonal prism lies in the
range 0.046–0.195 A. A pendant atom Ag9 is attached to
2
+
compounds where much longer C–C bond distances are found,
2À
+
+
an edge of the trigonal prism with bond distances of
Ag2Á Á ÁAg9 ¼ 3.0654(9) and Ag5Á Á ÁAg9 ¼ 3.0897(9) A. The
such as 1.39(2) A in [Co
12,13
9
(C
2
)(CO)19
]
and 1.48(2) A in
+
[Rh (C )(CO) ].
1
2
2
25
silver cage [C
2
@Ag
9
]Ag in Ag
2
C
dant silver atom, but it is attached to one vertex (the capping
2
Á8AgF also contains a pen-
There are two silver(I) atoms (Ag10and Ag11) linked to this
À
[C @Ag ]Ag system via carboxylate groups of the CF CO
2 8 3 2
atom) of a monocapped square antiprism with an AgÁ Á ÁAg
ligands. A pair of aqua ligands of type O1W bridge two sil-
ver(I) atoms of type Ag10to generate a centrosymmetric
cluster dimer. Additional aqua ligands are terminally coordi-
nated (O2W on Ag10, O3W and O4W on Ag11) to complete
the tetrahedral coordination geometry around Ag10and Ag11,
+
7
distance of 3.0632(5) A. These two types of silver cages with
I
giving rise to the supermolecular anion [Ag (C )(CF CO ) -
1
1
2
3
2 12
6À
( shown in Fig. 3. Intermolecular hydrogen bonds
are formed between the aqua ligands on Ag11 and carboxylate
H
2
O)
4
]
2
groups of the neighboring cluster with bond distances O3W–
O101 (À1 + x, y, z) ¼ 2.698 A, O3W–O31 (À1 + x, y, z) ¼
+
+
+
2
structure is constructed through these hydrogen bonds along
.869 A and O4W–O22 (À1 + x, y, z) ¼ 2.738 A. A ladder-like
the a direction.
It is noteworthy that in [Ag (tmc)(BF
II
I
4
)][Ag
6
(C
2
)-
À
(
CF CO ) (H O)]ÁH O, the BF anions provide a weak axial
3
2 5
2
2
4
II
linkage between adjacent [Ag (tmc)] moieties to form a
cationic column, inducing the assembly of a parallel polymeric
anionic chain from the Ag(I), C
compound 1, lacking the participation of BF4 ions, the Ag(II)
cations do not line up in a one-dimensional array and instead a
dimeric supermolecular Ag(I) cluster anion is generated.
The unique capability of tetraaza macrocyclic ligands such
as tmc to generate and stabilize a higher oxidation state of
2À
À
3
species. In
2
and CF
3
CO
2
À
2
À
an-
Fig. 2 Silver(I) bicapped trigonal prism with encapsulated C
ion and an extended arm (Ag9). In this [C @Ag ]Ag cluster core,
2
2
8
+
AgÁ Á ÁAg distances longer than 3.4 A (twice the van der Waals radius of
1
4
silver plays a key role in the formation of the present mixed-
valent system. It is noteworthy that a quite different result was
obtained when a crown ether was employed, which serves as a
capping ligand directly coordinated to a vertex of the silver
silver) are represented by broken open lines. Thermal ellipsoids are
drawn at the 30% probability level. Selected bond distances A: C1–C2
+
1.212(8), Ag1–C1 2.534(6), Ag3–C1 2.531(6), Ag4 –C1 2.242(6), Ag6–
C1 2.285(6), Ag7–C1 2.202(6), Ag1–C2 2.410(6), Ag2–C2 2.138(6),
Ag3–C2 2.563(6), Ag5–C2 2.380(6), Ag8–C2 2.309(6), Ag1Á Á ÁAg2
15
cage.
3.0535(7), Ag1Á Á ÁAg3 3.2758(8), Ag1Á Á ÁAg7 2.9901(7), Ag2Á Á ÁAg5
3.3236(7), Ag2Á Á ÁAg8 2.8767(7), Ag2Á Á ÁAg9 3.0654(9), Ag3Á Á ÁAg6
2.9397(7), Ag3Á Á ÁAg7 3.1807(7), Ag3Á Á ÁAg8 2.9964(7), Ag4Á Á ÁAg5
2.8693(7), Ag4Á Á ÁAg6 2.8841(7), Ag4Á Á ÁAg7 2.8832(6), Ag5Á Á ÁAg8
2.9889(7), Ag5Á Á ÁAg9 3.0897(9), Ag6Á Á ÁAg7 3.1676(7), Ag6Á Á ÁAg8
2.9721(7).
This work has established the generality of the dis-
proportionation reaction to incorporate both Ag(II) and Ag(I)
in a crystalline complex. While Ag(II) ions are stabilized by tmc
ligands to form complex cations, anionic clusters are assem-
2À
À
species.
bled from the Ag(I), C
2
and CF
3
CO
2
Fig. 3 Perspective view of the structure of the dimeric supermolecular anion in 1. The silver(I) cages are highlighted by solid lines (only short
AgÁ Á ÁAg distances are shown). Aqua ligands are depicted in cross-hatched shading. The F atoms of the CF
À
3
CO
2
ligands are omitted for clarity.
5
14
New J. Chem., 2002, 26, 513–515

1
7
View Article Online
Experimental
the SHELXTL program package. Hydrogen atoms of tmc
ligands were included with a riding mode, but no attempt was
made to locate the H atoms of aqua molecules. The crystal-
lographic data and structure refinement details are summari-
zed in Table 1, and selected bond distances and angles are
listed in captions for Fig. 1 and 2.
7
Ag C2 was prepared as described previously. AgCF CO
2
2
3
(
98%, ACROS) and tmc (99%, Aldrich) were used as pur-
chased without further purification. Infrared spectrum was
recorded on a Nicolet Impact 420FT-IR spectrometer using
À1
KBr pellet over the range 4000–400 cm . EPR spectrum
(
CCDC reference number 178881. See http:==www.rsc.org=
suppdata=nj=b2=b202709g= for crystallographic data in CIF
or other electronic format.
aqueous solution in capillary) was recorded at room tem-
perature on a Bruker EMX X-band spectrometer equipped
with an ER 4102ST TE102 rectangular cavity.
II
Preparation of {[Ag (tmc)] [Ag (tmc)(H
II
2
O)]
2
}-
Acknowledgements
I
{
[Ag 11(C
Ag C was added to an aqueous solution (1 ml) of AgCF CO
2
2 3 2 2 4 2
)(CF CO )12(H O) ] }
We acknowledge financial support from the Research Grants
Council of the Hong Kong Special Administrative Region
(Project No. CUHK 4268=00P) and a Postdoctoral Fellowship
to Q.-M. Wang from The Chinese University of Hong Kong.
2
2
3
(
442 mg, 2 mmol) in a plastic beaker with stirring until satu-
rated. The excess amount of Ag C was filtered off, and tmc
2
2
(
26 mg, 0.1 mmol) was added to the filtrate. The colorless
solution turned rapidly dark red along with the precipitation
of black metallic silver, which was removed by filtration. The
filtrate was allowed to stand without disturbance, and dark-red
prismatic crystals of 1 were obtained in ca. 70% yield (based
on tmc) after several days. Compound 1 is relatively stable in
the dark but readily decomposes in common solvents such as
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water and ethanol. Anal. calcd for C94
H
116Ag25
7.6; H, 1.8; N, 2.6. Found: C, 16.9; H, 1.5; N, 2.3. IR (cm ):
F
72
N
12
O
58 : C,
and G.-D. Zhou, Crystallography in Modern Chemistry:
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1
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2
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2 2
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Data collection was performed at 293 K on a Bruker SMART
ꢀ
1
000 CCD diffractometer using a 0.3 frames of oscillation
ꢀ
ꢀ
range with 1.5 < y < 28 . An empirical absorption correction
was applied using the SADABS program. The structure was
solved by direct methods and all non-hydrogen atoms were
1
501.
1
6
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2
anisotropically refined by full-matrix least-squares on F using
3
2
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Table 1 Crystallographic data for 1
Chemical formula
Formula weight
Crystal system
94 72 12 58
C H116Ag25F N O
6406.74
Triclinic
P1(no. 2)
9
¨
P. Pyykko, Chem. Rev., 1997, 97, 597; M. Jansen, Angew. Chem.,
Int. Ed. Engl., 1987, 26, 1098.
-
Space group
+
a=A
+
12.7452(6)
13.4695(6)
25.324(1)
87.885(1)
81.162(1)
78.936(1)
4215.8(3)
1
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1130.
16 G. M. Sheldrick, SADABS, Program for Empirical Absorption
Correction of Area Detector Data., University of Gottingen,
Germany, 1996.
b=A
+
c=A
ꢀ
a=
b=
g=
ꢀ
ꢀ
+
3
U=A
Z
T= C
ꢀ
20
+
l=A
0.71073
29.88
28 164
19 834
0.0208
À1
m(Mo-Ka)=cm
Total reflect.
Unique reflect.
R
R
wR
int
a
1
(obs. reflns)
(all reflns)
0.0469
0.1449
b
2
1
7
G. M. Sheldrick, SHELXTL 5.10for Windows NT, Structure
Determination Software Programs, Bruker Analytical X-Ray
Systems, Inc., Madison, WI, USA, 1997.
a
b
2
o
2
c
2
2 2 1=2
) ]}
R
1
¼ SkF j À jF
o
c
k=SjF
o
j. wR
2
¼ {S[w(F
À F
) ]=S [w(F
o
.
New J. Chem., 2002, 26, 513–515
515