Soluble silver acetylide for the construction and structural conversion of all-alkynyl-stabilized high-nuclearity homoleptic silver clusters

Article abstract of DOI:10.1021/acs.cgd.5b00286

Silver acetylide complex [Ag(ArC≡C)]_n (Ar = 3,5-di-tert-butylphenyl) with unprecedented high solubility in common organic solvents has been designed and synthesized. The high solubility is due to two bulky tert-butyl substituents on the phenyl

Full text of DOI:10.1021/acs.cgd.5b00286

Article
pubs.acs.org/crystal
Soluble Silver Acetylide for the Construction and Structural
Conversion of All-Alkynyl-Stabilized High-Nuclearity Homoleptic
Silver Clusters
†
‡
†
§
§
,†,∥
Rui Zhang, Xiang Hao, Xiumin Li, Zhengyang Zhou, Junliang Sun, and Rui Cao*
†
Department of Chemistry, Renmin University of China, Beijing 100872, China
‡
Center for Physicochemical Analysis and Measurement, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
§
∥
School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710119, China
*
S Supporting Information
ABSTRACT: Silver acetylide complex [Ag(ArCC)] (Ar = 3,5-di-tert-butyl-
n
phenyl) with unprecedented high solubility in common organic solvents has been
designed and synthesized. The high solubility is due to two bulky tert-butyl
substituents on the phenyl ring. This feature is significant to construct and isolate
single crystals of all-alkynyl-stabilized silver clusters, which are crucial to investigate
the intrinsic binding interaction and coordination modes between Ag(I) and
ethynide ligands. Crystallization of [Ag(ArCC)] under various conditions
n
resulted in three high-nuclearity homoleptic silver acetylide clusters, namely,
[
Ag (ArCC) ](OH) (1), [Ag (ArCC) ] (2), and [Ag (ArCC) ] (3).
21
20
16
16
15
15
Complex 1 has a [Ag ] cluster protected by twenty 3,5-di-tert-butyl-phenylethynide
21
ligands. Complexes 2 and 3 have neutral [Ag ] and [Ag ] clusters, respectively. In
1
6
15
addition to these homoleptic silver clusters, two new silver acetylides [Ag (ArC
20
C) (CH COO) ] (4) and [Ag (ArCC) (NO ) (CH CH OH) ](OH) (5)
16
3
4
22
16
3 4
3
2
4
2
were synthesized. The acetate and nitrate anions in these structures are more like
counterions instead of acting as critical building blocks or templates for cluster assembly. These results illustrated the significance
of 3,5-di-tert-butyl-phenylethynide ligands in the construction and stabilization of high-nuclearity silver clusters. Analysis of
structures of 1−5 revealed several novel coordination modes between Ag(I) and ethynide ligands, which contributed
considerably to our knowledge of Ag(I)−ethynide binding interactions.
2
1,29,33,36,38−42
INTRODUCTION
simple silver cluster or chain structures,
while in
■
1
the presence of coordinating oxoanions, such as triangular
nitrates and carbonates, tetrahedral sulfates and chromates, and
Silver acetylides are among the oldest organometallics known
and have attracted considerable attention recently because of
their unique catalytic features in alkyne activation
potential applications in a variety of areas, including organic
2
3,28,30−32,34,35,37
1
−7
polyoxometalates, large silver cages
can be
and
obtained with encapsulation of these anionic templates inside
silver cages.
8
−11
optoelectronics and photoluminescent materials.
On the
However, despite these achievements, structural character-
ization of homoleptic silver acetylides has been sparsely
demonstrated in the literature, because they are not soluble
and aggregate and precipitate immediately upon formation.
Homoleptic silver acetylides are synthons and fundamental
building blocks for the construction of various silver
other hand, it is of particular interest to investigate silver
acetylides from a structural point of view because of their
intriguing binding interactions and structural diversities and
1
2−18
properties.
More importantly, they provide a fascinating
1
9−22
system for self-assembly of polymers
and nanostruc-
through diverse coordination modes between
2
0,23−27
tures
1
7,23,25,26,31,32,34,35
clusters,
prepare silver nanomaterials.
and they are used as precursors to
Ag(I) and ethynide ligands abetted by metallophilic inter-
43−45
actions of d10 metal centers.
In addition, homoleptic silver
acetylides are candidates to study all-carbon-stabilized silver
clusters, although they have been rarely characterized in
comparison to silver clusters assembled by sulfur- and
As illustrated in Scheme 1, commonly known Ag(I)−
1
1
1 2
ethynide coordination modes include μ -η ,η (IIa), μ -η ,η
2
2
1
1
1
1
1
2
1 1 1 1
(
IIb), μ -η ,η ,η (IIIa), μ -η ,η ,η (IIIb), μ -η ,η ,η ,η (IVa),
3 3 4
46−56
1
1
2
2
phosphorus-based ligands.
and μ -η ,η ,η ,η (IVb). Substantial efforts have been made in
4
the past decade to explore Ag(I)−ethynide coordination for
28−38
self-assembly of various silver chains, clusters, and cages.
Received: February 28, 2015
Revised: April 10, 2015
In general, these studies demonstrated that in the absence of
templates, silver acetylides usually form relatively small and
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
Scheme 1. Coordination Modes between Phenylethynide
and Ag(I)
(IVc) coordination modes for Ag(I)−ethynide (Scheme 1)
have been illustrated in our structures. (4) Similar subcompo-
nents are found in these silver acetylides, which give new
insights into the self-assembly and conversion mechanism of
these clusters. (5) The high solubility of this silver acetylide is
useful in other silver chemistry. In addition to these key
findings, as silver nanoparticles will trace the shape and atomic
43
arrangement of the starting materials, our studies may
therefore provide a route for the preparation of all-carbon-
63−65
stabilized silver nanoparticles,
whose significant physical,
chemical, and biological properties can be controlled by size,
composition, and surface structures.
RESULTS AND DISCUSSION
■
In order to better understand the formation and conversion
mechanism of silver clusters, it is necessary to investigate the
structure of homoleptic silver acetylides, in which Ag(I)−
ethynide coordination is not interfered with or complicated by
other ligands and anions. However, due to their limited
solubility in solution, it is challenging to obtain crystals of
homoleptic silver acetylides with sufficient quality for single
crystal X-ray diffraction studies. By introducing two bulky tert-
butyl groups at the two meta positions of phenylacetylene, we
hypothesized that the resulting silver phenylacetylide would
have adequate solubility amenable for crystal growth using
traditional methods. As we expected, the reaction of 3,5-di-tert-
Because of the above-mentioned reasons, structural studies of
homoleptic silver acetylides are the subject of great significance.
By using X-ray powder diffraction and a model derived from its
copper congener, Che proposed a polymeric chain structure for
57
silver phenylacetylide. However, due to technical limitation of
X-ray powder diffraction, detailed structural information,
including accurate Ag(I)−ethynide bond distances and angles,
could not be obtained. Krossing and Scherer reported the
butyl-phenylacetylene and AgBF in the presence of triethyl-
amine as the base (Scheme 2) did not cause precipitation from
4
2
+
2
+
58
structural analysis of [Ag(η -C H ) ] and [Ag(η -C H ) ] ,
Scheme 2. General Synthetic Method for Silver 3,5-Di-tert-
butyl-phenylacetylide
2
2 3
2
2 4
but the ligands were acetylenes instead of ethynides. Zhao and
co-workers reported the structures of polynuclear silver carbide
59−61
clusters stabilized in polydentate macrocyclic ligands.
Although the silver clusters in these structures were surrounded
by macrocyclic ligands, this work provided an important
alternative way to stabilize such reactive units.
Recently, we developed a robust and accessible counter-
diffusion microfluidic device and used it to synthesize and grow
crystals of organometallic polymers that are not soluble for
dichloromethane/acetonitrile mixed solvent. Evaporation of
this solution at room temperature with stirring gave crystalline
white powders, which were collected by filtration, washed with
ethanol, and dried in vacuum. It was found that this silver
phenylacetylide powder was very soluble in nonpolar solvents,
such as dichloromethane, chloroform, toluene, and even diethyl
ether, but was barely soluble in polar solvents, such as ethanol,
acetonitrile, and dimethylformamide. The high solubility of this
homoleptic silver acetylide is unique, as in general, silver
acetylides are only soluble in solutions with concentrated Ag(I)
salts.
62
crystallization using traditional methods. By using this
technique, we were able to, for the first time, get X-ray
diffraction quality single crystals of silver phenylacetylide and
determine its structure unambiguously. Crystallographic studies
revealed its intriguing polymeric chain structure, and showed
that stronger Ag(I)−Ag(I) and Ag(I)−ethynide bonds and
tighter packing of polymeric chains were presented in this silver
62
phenylacetylide structure as compared to previous powder
5
7
sample by Che.
We reported herein the synthesis and structural character-
ization of five silver clusters using 3,5-di-tert-butyl-phenyl-
ethynide ligands. Unlike normal silver acetylides, with the
introduction of two bulky tert-butyl substituents on the phenyl
Recrystallization of this white precipitate from dichloro-
methane and ethanol afforded yellow crystals of 1. Crystallo-
graphic studies revealed that complex 1 crystallized in the
ring, the resulting silver acetylide [Ag(ArCC)] has high
monoclinic space group P2 /c with Z = 4 (other cell
parameters were summarized in Table 1). In the structure of
n
1
solubility in organic solvents, a feature that is crucial for the
synthesis and crystallization of homoleptic silver acetylides.
Several significant results are obtained in this work: (1)
Complexes [Ag (ArCC) ](OH) (1), [Ag (ArCC) ]
1, a [Ag ] cluster was found in the asymmetric unit with 20
21
phenylethynide ligands. No symmetry elements were found in
+
the structure of this [Ag ] cluster. The [Ag (ArCC) ]
21
20
16
16
21
21
20
(
2), and [Ag (ArCC) ] (3) are homoleptic silver
cation was charge balanced by one uncoordinated hydroxyl
anion, which was likely generated from the added base
1
5
15
acetylides. (2) Complexes 1−3 and [Ag (ArC
2
0
C ) ( C H C O O ) ] ( 4 ) a n d [ A g ( A r C 
triethylamine. As shown in Figure 1, the [Ag ] cluster was
1
6
3
4
2 2
21
C) (NO ) (CH CH OH) ](OH) (5) represent, to our
assembled through diverse Ag(I)−ethynide binding interac-
tions and Ag(I)−Ag(I) metallophilic interactions. From the
space-filling diagram, it can be noted that the bulky 3,5-di-tert-
1
6
3
4
3
2
4
2
knowledge, the largest silver acetylide clusters without
1
2
2
1 2 2 2
templates. (3) Very rare μ -η ,η ,η (IIIc) and μ -η ,η ,η ,η
3
4
B
DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
Table 1. Crystal Data and Structure Refinement Parameters for Complexes 1−5
Complex
formula
1
2
3
4
5
C320H421Ag O
C256H336Ag16
5139.17
150(2)
C240H315Ag15
4817.97
150(2)
C264H348Ag O8
C264H362Ag N O
22 4 18
21
20
fw (g mol−1)
6548.81
5806.82
150(2)
6252.72
T (K)
153(2)
153(2)
crystal system
space group
a (Å)
Monoclinic
Tetragonal
Orthorhombic
Ccca (#68)
35.961(4)
36.933(4)
40.933(5)
90
Tetragonal
Monoclinic
P2 /c (#14)
I4
̅
(#82)
I4
̅
(#82)
C2/c (#15)
80.349(10)
20.033(2)
40.226(5)
90
1
21.6397(16)
41.645(3)
41.752(3)
90
25.8070(9)
25.8070(9)
20.5657(10)
90
27.3816(7)
27.3816(7)
19.3573(6)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
99.8190(10)
90
90
90
90
112.8040(10)
90
90
90
90
3
Volume (Å )
37076(5)
4
13696.8(9)
2
54364(11)
8
14513.2(7)
2
59687(12)
8
Z
μ (mm−1)
1.121
1.158
1.094
1.360
1.456
F(000)
13344
5248
19680
5872
25216
θ range
2.20−26.45°
275045
75952
2.23−26.47°
158423
14097
2.17−26.38°
278541
27696
2.35−26.43°
44076
2.23−26.36°
191913
60246
reflections coll.
independent
reflections
14870
R(int) = 0.0701
1.034
R(int) = 0.0650
1.041
R(int) = 0.0581
1.034
R(int) = 0.0794
0.987
R(int) = 0.0439
1.037
Goof
a
a
a
a
a
final R indices [R > 2σ (I)]
R1 = 0.0733
R1 = 0.0681
R1 = 0.0967
R1 = 0.0541
R1 = 0.0820
b
b
b
b
b
wR = 0.1832
wR = 0.1889
wR = 0.2582
wR = 0.1173
wR = 0.2236
2
a
2
a
2
a
2
a
2
a
R indices (all data)
R1 = 0.1195
R1 = 0.0912
R1 = 0.1476
R1 = 0.1113
R1 = 0.1355
b
b
b
b
b
wR2 = 0.2058
wR2 = 0.2105
wR2 = 0.3043
wR2 = 0.1368
wR2 = 0.2687
a
b
2
o
2
c
2
2
o
2
0.5
R = ∑∥F | − |F ∥/|F |. wR = {∑[w(F − F ) ]/∑[w(F ) ]} .
1
o
c
o
2
There are several different Ag(I)−ethynide coordination
1
1
modes found in the structure of 1. These are five μ -η ,η , three
2
1
2
1
1
1
1 1 2
μ -η ,η , three μ -η ,η ,η , and nine μ -η ,η ,η (Table 2). In
2
3
3
these interactions, the Ag(I)−C bond distances are in the range
of 2.049(9)−2.706(8) Å, and the average value is 2.29(1) Å. As
the van der Waals radii of silver is 1.72 Å, Ag(I)−Ag(I)
interactions are considered to exist if the metal-to-metal
distance was less than 3.44 Å. In the structure of 1, the
Ag(I)−Ag(I) distances are between 2.8058(9) and 3.3370(9) Å
with an average value of 3.038(1) Å. In comparison to typical
silver acetylides, although no templates were presented, the
high-nuclearity of 1 was formed because of the relatively strong
and flexible Ag(I)−ethynide binding interactions that could
bridge several silver atoms together.
Figure 1. Crystal structure of complex 1. (a) Ball-and-stick
+
representation of the overall structure of [Ag (ArCC) ] cationic
21
20
cluster. All hydrogen atoms and tert-butyl moieties are omitted for
clarity. (b) [Ag ] core structure. (c) Space-filling diagram of the
2
1
+
[
Ag (ArCC) ] cluster, showing that the [Ag ] core is completely
21 20 21
protected by bulky 3,5-di-tert-butyl-phenylethynide ligands. Color
code: rose pink, silver; gray, carbon.
As shown in the crystal packing diagram of 1 (Figure 2),
owing to the large size of the cluster, the intermolecular spaces
were calculated to be 27% of the total volume in the single
crystal of 1. In addition, there are substantial amounts of
hydrophobic interactions between the tert-butyl groups on the
butylphenyl moieties formed a compact shell to protect the
[
Ag ] core structure. To the best of our knowledge, complex 1
represents the largest all-alkynyl-stabilized silver cluster.
21
Table 2. Coordination Modes of 3,5-Di-tert-butyl-phenylethynide Ligands Observed in the X-ray Structures of Complexes 1−5
Complex
1
2
3
4
5
Coordination mode
[Ag (ArCC) ]
[Ag (ArCC) ]
[Ag (ArCC) ]
[Ag (ArCC) ]
[Ag (ArCC) ]
2
1
20
16
16
15
15
20
16
22
16
1
1
2
1
μ -η ,η
5
4



4


2
2
1
μ -η ,η
3
8
7
2
1
1
2
2
1
μ -η ,η ,η
3


4

4
3
1
1
μ -η ,η ,η
9
8
10



4
3
1
2
μ -η ,η ,η




4



4
3
1
1
1
2
2
μ -η ,η ,η ,η






4
1
1 2
μ -η ,η ,η ,η
4
1
2 2
μ -η ,η ,η ,η
4
C
DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
Figure 3. Crystal structure of complex 2. (a) Ball-and-stick
Figure 2. Crystal packing structure of complex 1. Color code: rose
pink, silver; gray, carbon and hydrogen.
representation of the overall structure of [Ag (ArCC) ] cluster. All
16
16
hydrogen atoms and tert-butyl moieties are omitted for clarity. (b)
[
Ag ] core structure. (c) Schematic illustration showing the
1
6
assembling mechanism of the [Ag ] core by two [Ag ] clusters.
Color code: rose pink, silver; gray, carbon.
16
8
surface of the clusters, which are believed to help to prevent
free rotation of the clusters in the solid state. These interactions
are therefore essential to the successful formation of single
crystals of such large silver clusters without counteranions
compatible in size.
If toluene and dimethylformamide were used for the
crystallization of the white precipitate, a new silver cluster
structure was obtained. Single crystal X-ray structure analysis
determined that this silver acetylide complex is also homoleptic
with a [Ag ] core stabilized by sixteen phenylethynide ligands.
16
Therefore, the new [Ag (ArCC) ] silver cluster repre-
1
6
16
sented in the crystal structure of 2 is neutral in charge. Complex
2
crystallized in the tetragonal space group I4
̅
with Z = 2 (Table
1). The [Ag ] cluster was located at the special position with a
16
̅
crystallographically required 4 rotoinversion axis passing
through the four Ag atoms in the middle (Figure 3b). They
are Ag5−Ag1−Ag1−Ag5. As a result, in the asymmetric unit,
there are only five Ag atoms, in which two of them (Ag1 and
Ag5) generate two Ag atoms, and the other three (Ag2, Ag3
and Ag4) generate nine Ag atoms according to the symmetry
operation of the 4
As shown in Figure 3c, the [Ag ] cluster can be visualized as
constructed by two identical [Ag ] subcomponents, which have
̅
rotoinversion axis.
Figure 4. Crystal packing structure of complex 2. Color code: rose
pink, silver; gray, carbon and hydrogen.
1
6
8
∼
90° rotation from each other and connect together along the
rotoinversion axis. The very short Ag1−Ag1 distance at
.775(3) Å indicated a strong Ag(I)−Ag(I) bond. In the
4
̅
in the orthorhombic space group Ccca with Z = 8 (Table 1).
The X-ray structure of 3 consisted of a [Ag ] core surrounded
by 15 phenylethynide ligands (Figure 5). This homoleptic
neutral silver cluster was located at the special position with a
2
15
1
1
1 2
structure of 2, there are four μ -η ,η , eight μ -η ,η , and four
2
2
1
2 2
μ -η ,η ,η bridging phenylethynide ligands (Table 2). The μ -
3
3
1
2 2
η ,η ,η binding mode of ethynides is very rare in the literature.
The Ag(I)−C bond distances are in the range of 2.00(1)−
crystallographically required C rotation axis passing through
2
the three Ag atoms in the middle, that are Ag1−Ag6−Ag7
(Figure 5b). In each asymmetric unit, there are nine Ag atoms.
2
.69(1) Å with an average value of 2.29(1) Å, and the Ag(I)−
Ag(I) distances are between 2.775(3) and 3.091(1) Å with an
average value of 2.939(1) Å. Similar to 1, the crystal packing
diagram of 2 showed that hydrophobic interactions of the tert-
butyl groups played a crucial role in growing crystals of such
large and neutral silver clusters (Figure 4).
In addition to the three Ag atoms on the C rotation axis, the
2
other six generate six Ag atoms by the symmetry operation of
the C rotation axis. It is worth noting that one phenylethynide
2
ligand (C33−C48) was also located at the C axis. As a result,
2
this phenylethynide has a positional disorder in two sites, and
each component has an even 50% occupancy.
Attempts to recrystallize the white precipitate from toluene
and benzene gave another silver acetylide complex 3.
Crystallographic studies revealed that complex 3 crystallized
Similar to 2, the silver cluster of 3 can be divided to two
subcomponents, one [Ag ] and one [Ag ] cluster. They have
8
7
D
DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
Figure 6. Crystal structure of complex 4. (a) Ball-and-stick
Figure 5. Crystal structure of complex 3. (a) Ball-and-stick
representation of the overall structure of [Ag20(ArCC)16(OAc) ]
4
representation of the overall structure of [Ag (ArCC) ] cluster. All
hydrogen atoms and tert-butyl moieties are omitted for clarity. (b)
cluster. All hydrogen atoms, tert-butyl moieties and acetate ligands are
omitted for clarity. (b) Spindle-like [Ag20] core structure. (c)
Schematic illustration showing the assembling mechanism of the
15
15
[
Ag ] core structure. (c) Schematic illustration showing the
1
5
assembling mechanism of the [Ag ] core by a [Ag ] and a [Ag ]
[Ag20] core by an octahedral [Ag
] and two boat-like [Ag ] clusters.
6 7
15
8
7
clusters. Color code: rose pink, silver; gray, carbon.
Color code: rose pink, silver; gray, carbon.
∼
2
90° rotation from each other and connect together along the
between 2.886(1) and 3.375(1) Å with an average value of
3.072(1) Å.
C axis (Figure 5c). Interestingly, the [Ag ] clusters found in
8
both structures of 2 and 3 are almost identical. The skeleton of
In addition to phenylethynide ligands, four acetate groups
were also found in the X-ray structure of 4, which made the
silver cluster neutral in charge. The four acetate groups are all
symmetry equivalent, and each bridges two Ag atoms (Ag1 and
Ag2) through two Ag(I)−O bonds of 2.298(9) and 2.226(9) Å,
respectively. This bond distance is typical for a dative Ag(I)−O
bond. As no acetate ions were used in our synthesis, it was
believed that the acetate groups attached to the silver cluster
were derived from the hydrolysis of ethyl acetate molecules, a
reaction that might be catalyzed by silver clusters. It is necessary
to point out that the acetate groups are more like counter-
anions instead of acting as critical building blocks or templates
for the cluster assembly. Therefore, although the silver acetylide
4 is not homoleptic, it does highlight the significant role of
ligand 3,5-di-tert-butyl-phenylethynide in the construction and
stabilization of high-nuclearity silver clusters.
the [Ag ] cluster was parallel to that of [Ag ], but missed one
7
8
Ag atom at the spire position. In the structure of 3, seven
1
1
phenylethynide ligands have the μ -η ,η , four have the μ -
2
3
1
1
2
1 2 2
η ,η ,η , and four have the rare μ -η ,η ,η bridging modes
3
(
Table 2). The Ag(I)−C bond distances ranged from 2.04(1)
to 2.67(1) Å with an average value of 2.27(1) Å, and the
Ag(I)−Ag(I) distances ranged from 2.815(1) to 3.156(2) Å
with an average value of 3.006(1) Å. The many hydrophobic
interactions between the tert-butyl groups were also crucial for
the formation of high quality single crystals of 3.
In addition, we tried to grow crystals of this homoleptic silver
acetylide from tetrahydrofuran and ethyl acetate. To our
surprise, a new [Ag ] cluster of 4 with sixteen phenylethynide
2
0
and four acetate ligands was isolated (Figure 6a). Structural
analysis showed that, similar to 2, complex 4 crystallized in the
same tetragonal space group I4
̅
with Z = 2 (Table 1). The
Complexes 1−4 were all synthesized by using silver
tetrafluoroborate, whose BF4− counteranions were not found
in the X-ray structures. On the other hand, the reaction of 3,5-
di-tert-butyl-phenylacetylene and silver nitrate, and subsequent
recrystallization from dichloromethane and ethanol, gave silver
acetylide 5. Single-crystal X-ray structural analysis showed that
complex 5 crystallized in the monoclinic space group C2/c with
Z = 8 (Table 1). In each asymmetric unit, a [Ag ] cluster was
[
Ag ] cluster was also located at the special position with a
20
crystallographically required 4
̅
rotoinversion axis passing
through the four Ag atoms in the middle (Figure 6b). They
are Ag4−Ag3−Ag3−Ag4. Therefore, there are only six Ag
atoms in the asymmetric unit. Atoms Ag3 and Ag4 generate
two more Ag atoms, and the other four (Ag1, Ag2, Ag5, and
Ag6) generate twelve Ag atoms via the symmetry operation of
22
the 4
̅
rotoinversion axis.
coordinated by sixteen phenylethynide ligands and four nitrate
anions. The peanut-like silver cluster of 5 could be divided to
three subcomponents (Figure 7). Similar to 4, there is a
As shown in Figure 6c, the [Ag ] cluster of 4 can be divided
into three parts. In the center, there is a [Ag ] core, which has a
2
0
6
distorted octahedron geometry. This [Ag ] core is flanked by
distorted [Ag ] octahedron core, which is flanked by two
6
6
two boat-like [Ag ] clusters along the 4
̅
axis, and the two [Ag7]
crown-like [Ag ] clusters.
7
8
1
1 1
clusters have ∼90° rotation from each other. In the X-ray
For the sixteen phenylethynide ligands, two are μ -η ,η ,η ,
3
1
1
2
1 2 2 2
structure of 4, the sixteen phenylethynide ligands have four μ -
ten are μ -η ,η ,η , and four are very rare μ -η ,η ,η ,η binding
3 4
3
1
1
1
1
1
2
1
2
2
2
η ,η ,η , eight μ -η ,η ,η , and four very rare μ -η ,η ,η ,η
modes (Table 2). In these interactions, the Ag(I)−C bond
distances are in the range of 2.062(9)−2.69(1) Å with an
average value of 2.32(1) Å, and the Ag(I)−Ag(I) distances are
in the range of 2.807(1)−3.337(1) Å with an average value of
3
4
binding modes (Table 2). In these interactions, the Ag(I)−C
bond distances have a range of 2.08(1)−2.54(1) Å with an
average value of 2.30(1) Å, and the Ag(I)−Ag(I) distances are
E
DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
have an about 90° rotation from each other and connect
̅
together along the 4 and C2 axis, respectively. In both
structures, [Ag ] clusters were almost identical, and the [Ag ]
8
7
cluster missed one Ag atom at the spire position compared to
Ag ] (Figure 8). Therefore, these two clusters should be able
[
8
Figure 8. Schematic illustration showing the conversion between
Ag ] and [Ag ] cores via the loss of one Ag atom at the spire
[
16
15
position of a [Ag ] cluster.
8
to interconvert by losing/incorporating one Ag atom. We
characterized the bulk samples of complexes 2 and 3 by using
the powder X-ray diffraction (PXRD) method, which
confirmed the phase purity of both samples (Figure S10).
Similarly, in the structures of 4 and 5, the coordination modes
of phenylethynides are quite similar (Table 2). As shown in
Figure 7. Crystal structure of complex 5. (a) Ball-and-stick
2+
representation of the overall structure of [Ag (ArCC) (NO ) ]
22
16
3 4
cluster. All hydrogen atoms, tert-butyl moieties and nitrate ligands are
omitted for clarity. (b) Peanut-like [Ag ] core structure. (c)
2
2
Schematic illustration showing the assembly mechanism of the
Ag ] core by an octahedral [Ag ] and two crown-like [Ag ] clusters.
[
Figure 9, a [Ag ] octahedron core was found in both silver
22
6
8
6
Color code: rose pink, silver; gray, carbon.
3
.038(1) Å. The four nitrate anions were located at the middle
belt of the silver cluster. Each nitrate ion bridged two Ag atoms
through two Ag(I)−O bonds (ranged from 2.38(1) to 2.544(9)
Å). In addition to these anionic ligands, there were four ethanol
solvent molecules attached to the cluster through Ag(I)−O
bonds. As a result, the cluster was positively charged with a
2
+
formula of [Ag (C H ) (NO ) (CH CH OH) ] . The
2
2
16 21 16
3
4
3
2
4
positive charges were balanced by two uncoordinated hydroxyl
anions, which were also successfully located in the X-ray
structure of 5.
Figure 9. Schematic illustration showing the assembly of an octahedral
[
(
(
Ag ] core with two crown-like [Ag ] cores to form the [Ag ] cluster
6 8 22
left side) or with two boat-like [Ag ] cores to form the [Ag ] cluster
7
20
right side).
Structural analysis of these clusters might provide some new
insights into the formation and conversion of various silver
acetylides. Table 3 shows that Ag(I)−C and Ag(I)−Ag(I) bond
distances in the structures of 1−5 are comparable, indicating
that 3,5-di-tert-butyl-phenylethynide ligands played an essential
role for the assembly of high-nuclearity silver clusters. As
summarized in Table 2, the coordination modes of phenyl-
ethynide ligands represented in the structure of 2 and 3 are
clusters. In the structure of 4, this [Ag ] octahedron core was
6
flanked by two boat-like [Ag ] clusters, while in 5, it was
7
flanked by two crown-like [Ag ] clusters. The discovery of two
8
1
2 2
new Ag(I)−ethynide coordination modes, namely μ -η ,η ,η
and μ -η ,η ,η ,η , highlights the unique role of homoleptic
3
1
2 2 2
4
silver acetylides in the studies of binding interactions and
structural features of silver acetylides.
1
2 2
similar, and the rarely reported μ -η ,η ,η mode was found in
3
both structures. This similarity should be a result of the
structural resemblance between these two clusters. As we
discussed above, the [Ag ] cluster of 2 consists of two identical
In order to examine the potential of 3,5-di-tert-butyl-
phenylethynide to stabilize silver nanoparticles, we investigated
the reduction of silver acetylides. Addition of sodium
1
6
[
Ag ] subcomponents, while the [Ag ] cluster of 3 consists of
borohydride (NaBH ) to the dichloromethane/ethanol sol-
8
15
4
one [Ag ] and one [Ag ] cluster, and the two subcomponents
ution of silver phenylacetylide caused the color change from
8
7
Table 3. Bond Distance Information of Ag(I)−C and Ag(I)−Ag(I) of Complexes 1−5
complex
bonds
1
2
3
4
5
Ag−C (shortest) Å
Ag−C (longest) Å
Ag−C (average) Å
Ag−Ag (shortest) Å
Ag−Ag (longest) Å
Ag−Ag (average) Å
2.049(9)
2.706(8)
2.29(1)
2.00(1)
2.69(1)
2.29(1)
2.775(3)
3.091(1)
2.939(1)
2.04(1)
2.67(1)
2.27(1)
2.815(1)
3.156(2)
3.006(1)
2.08(1)
2.54(1)
2.30(1)
2.886(1)
3.375(1)
3.072(1)
2.062(9)
2.69(1)
2.32(1)
2.8058(9)
3.3370(9)
3.038(1)
2.807(1)
3.337(1)
3.038(1)
F
DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
colorless to deep purple (Figure S6). This process could be
monitored by spectroscopic methods. As shown in Figure S8,
the UV−vis absorbance in the range of 350−750 nm gradually
recrystallization from dichloromethane and ethanol, the white
precipitate was dissolved in toluene (5 mL) and dimethylformamide
(5 mL). Slow evaporation of the solution afforded complex 2 as yellow
crystals (136 mg, yield 85%). Anal. Calcd for [Ag (C H ) ]: C,
16
16 21 16
increased upon addition of NaBH , which was concomitant
4
5
9.83; H, 6.59; Ag, 33.58. Found: C, 59.96; H, 6.71; Ag, 33.51.
with the increase of the emission around 580 nm (excited at
Synthesis of Complex 3. Complex AgBF (20 mg, 0.1 mmol) was
4
550 nm, Figure S9). Importantly, after reaction with NaBH4,
dissolved in acetonitrile (1 mL). To this solution, 3,5-di-tert-butyl-
the solution particle size was analyzed by dynamic light
scattering, which showed the particle diameters were below 20
nm (Figure S7). This result suggested that silver clusters with
partially reduced Ag atoms were not likely to aggregate,
probably due to the steric hindrance of the 3,5-di-tert-butyl-
phenylethynide ligands. Although attempts to grow crystals of
silver clusters with mixed Ag(I) and Ag(0) oxidation states
were not successful at this stage, our studies confirmed that 3,5-
di-tert-butyl-phenylethynide was able to stabilize silver nano-
particles. Detailed reduction studies, including crystallization of
reduced species, are the subject of ongoing projects.
phenylacetylene (21 mg, 0.1 mmol) and triethylamine (0.03 mL) in
0
.5 mL of dichloromethane were added with vigorous stirring. After 12
h, the white precipitate that formed was collected by filtration, washed
with ethanol, and dried under vacuum. Recrystallization of this white
solid in toluene (1 mL) and benzene (1 mL) afforded complex 3 as
yellow crystals (28 mg, yield 88%). Anal. Calcd for [Ag (C H ) ]:
1
5
16 21 15
C, 59.83; H, 6.59; Ag, 33.58. Found: C, 60.11; H, 6.91; Ag, 33.40.
Synthesis of Complex 4. Compound 4 was synthesized using a
process similar to that employed for complex 1. Instead of
recrystallization from dichloromethane and ethanol, the white
precipitate was dissolved in tetrahydrofuran (2.5 mL) and ethyl
acetate (5 mL). Slow evaporation of the solution afforded complex 4
as crystalline yellow needles (132 mg, yield 91%). Anal. Calcd for
EXPERIMENTAL SECTION
[
Ag (C H ) (CH COO) ]: C, 54.60; H, 6.04; Ag, 37.15. Found:
20 16 21 16 3 4
■
C, 55.01; H, 6.33; Ag, 36.77.
General Methods and Materials. Manipulations of air- and
moisture-sensitive materials were performed under nitrogen gas using
standard Schlenk line techniques. All reagents were purchased from
commercial suppliers and used as received unless otherwise noted. Dry
solvents, acetonitrile, tetrahydrofuran, and dichloromethane, were
purified by passage through activated alumina. Electronic absorption
spectra were acquired on a Cary 50 spectrophotometer. Emission
Synthesis of Complex 5. Complex AgNO (340 mg, 2 mmol)
3
was dissolved in acetonitrile (5 mL). To this solution, 3,5-di-tert-butyl-
phenylacetylene (856 mg, 4 mmol) and triethylamine (0.3 mL) in 5
mL of dichloromethane were added with vigorous stirring. After the
evaporation of dichloromethane in 12 h, the white precipitate that
formed was collected by filtration, washed with ethanol, and dried
under vacuum. Recrystallization of this white solid in dichloromethane
(6 mL) and ethanol (12 mL) afforded complex 5 as yellow crystals
( 5 8 0 m g , y i e l d 9 0 % ) . A n a l . C a l c d f o r
spectra were obtained using a HORIBA JY Fluoromax-4 fluorometer.
1
̈
H NMR spectroscopic measurements were made on a Bruker
spectrometer operating at 400 MHz. Particle size analysis by dynamic
light scattering was performed using Malvern Nano ZS90. PXRD
patterns were recorded at room temperature on a PANalytical X’pert
diffractometer equipped with a PIXcel 1D detector (Cu Kα, 40 kV and
[Ag22(C16
H
)
21
16(NO
)
(CH
CH OH) ](OH) : C, 50.71; H, 5.84;
3 2 4 2
3
4
Ag, 37.95. Found: C, 51.01; H, 6.01; Ag, 37.59.
X-ray Diffraction Studies. Complete data sets for 1−5 were
collected. Single crystals suitable for X-ray analysis were each coated
with Paratone-N oil, suspended in a small fiber loop, and placed in a
cooled gas stream on a Bruker D8 Venture X-ray diffractometer.
Diffraction intensities were measured using graphite monochromated
Mo Kα radiation (λ = 0.71073 Å) at 150(2) K and a combination of φ
and ω scans. Data collection, indexing, data reduction, and final unit
4
0 mA).
Synthesis of Ligand 3,5-Di-tert-butyl-phenylacetylene. A
mixture of 2.10 g (7.80 mmol) of 1-bromo-3,5-di-tert-butylbenzene,
.392 g (0.56 mmol) of (PPh ) PdCl and 0.052 g (0.27 mmol) of CuI
0
3
2
2
in 36 mL of triethylamine was stirred at room temperature under
nitrogen for 40 min. To this solution, 1.60 mL (11.2 mmol) of
trimethylsilylacetylene was added, and the resulted solution was
refluxed for 3 h under nitrogen with stirring. After filtration, the filtrate
was evaporated under reduced pressure and the residue was purified by
column chromatography on silica gel with hexane to give 1-
6
6
cell refinements were carried out using APEX2; absorption
6
7
corrections were applied using the program SADABS. All structures
68
were solved with direct methods using SHELXS and refined against
2
69
F on all data by full-matrix least-squares with SHELXL, following
(
7
trimethylsilyl)ethynyl-3,5-di-tert-butylbenzene in 97% yield (2.17 g,
established refinement strategies.
1
.56 mmol) as yellow prisms. H NMR (CDCl ): δ 0.26 (s, 9H), 1.31
3
In all structures, non-hydrogen atoms were refined anisotropically.
All hydrogen atoms binding to carbon were included into the model at
geometrically calculated positions and refined using a riding model.
Coordinates for hydrogen atoms on oxygen were taken from the
difference Fourier synthesis and those hydrogen atoms were
subsequently refined freely. The isotropic displacement parameters
of all hydrogen atoms were fixed to 1.2 times the U value of the atoms
they are linked to (1.5 times for methyl groups). Details of the data
quality and a summary of the residual values of the refinements are
listed in Table 1.
(
s, 18H), 7.32 (d, J = 1.7 Hz, 2H), 7.38 (t, J = 1.7 Hz, 1H).
Complex 1-(trimethylsilyl)ethynyl-3,5-di-tert-butylbenzene (2.17 g,
7.56 mmol) was dissolved in 100 mL of THF. After adding 12 mL (12
mmol) of 1.0 M (Bu N)F in THF, the mixture was stirred for 30 min.
4
The resulting solution was then evaporated under reduced pressure,
and the residue was purified by column chromatography on silica gel
with hexane to give 3,5-di-tert-butyl-phenylacetylene in 95% yield
1
(
1.54 g, 7.18 mmol) as white prisms. H NMR (CDCl ): δ 1.32 (s,
3
1
8H), 3.03 (s, 1H), 7.36 (d, J = 1.6 Hz, 2H), 7.43 (t, J = 1.6 Hz, 1H).
Synthesis of Complex 1. Complex AgBF (98 mg, 0.5 mmol) was
4
Automatic structure evaluation performed with PLATON as
implemented in the CheckCIF routine resulted in a few level A alerts.
dissolved in acetonitrile (3 mL). To this solution, 3,5-di-tert-butyl-
phenylacetylene (214 mg, 1 mmol) and triethylamine (0.075 mL) in 5
mL of dichloromethane were added with vigorous stirring. After the
evaporation of dichloromethane in 12 h, the white precipitate that
formed was collected by filtration, washed with ethanol, and dried
under vacuum. Recrystallization of this white solid in dichloromethane
(
1) The alert concerning large nonsolvent H U (max)/U (min): in
iso iso
our structures, there are many tert-butyl units. Because of the free
rotation of the C−C single bonds, the methyl groups on tert-butyl
units usually have large thermal movements, which cause the U
iso
values of their hydrogen atoms to be large (the isotropic displacement
parameters of hydrogen atoms on methyl groups are fixed to 1.5 times
the U value of the C atoms they are linked to). (2) The alert
concerning short Intra XH3.. XHn: this issue is also caused by the
positional disorder of many tert-butyl units in the structure. (3) The
alert concerning torsion calc: the standard uncertainty of torsion
angles estimated by SHELXL is different from that by CheckCIF.
(
1.5 mL) and ethanol (4 mL) afforded complex 1 as crystalline yellow
blocks (148 mg, yield 92%). Anal. Calcd for [Ag (C H ) ](OH):
21
16 21 20
C, 58.69; H, 6.48; Ag, 34.59. Found: C, 59.03; H, 6.81; Ag, 34.15.
CAUTION! Silver acetylides are potentially explosive and should be
handled with care and in small amounts.
Synthesis of Complex 2. Compound 2 was synthesized using a
process similar to that employed for complex 1. Instead of
G
DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
(
8) Yam, V. W. W.; Lo, K. K. W.; Wong, K. M. C. J. Organomet.
CONCLUSION
■
Chem. 1999, 578, 3−30.
9) Powell, C. E.; Humphrey, M. G. Coord. Chem. Rev. 2004, 248,
25−756.
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41−272.
(11) Teo, B. K.; Xu, Y. H.; Zhong, B. Y.; He, Y. K.; Chen, H. Y.;
In summary, by introducing two bulky tert-butyl groups to the
two meta positions of phenylacetylene, we considerably
increased the solubility of silver phenylacetylide. This improve-
ment is significant for the synthesis and structural studies of
homoleptic silver acetylides. With this new ethynide ligand,
three unprecedented homoleptic silver acetylides, [Ag (ArC
(
7
(
2
2
1
Qian, W.; Deng, Y. J.; Zou, Y. H. Inorg. Chem. 2001, 40, 6794−6801.
(12) Wang, Q. M.; Mak, T. C. W. Angew. Chem., Int. Ed. 2001, 40,
1130−1133.
C) ](OH) (1), [Ag (ArCC) ] (2), and [Ag (ArC
2
0
16
16
15
C) ] (3), and two new silver acetylide complexes,
1
5
(
13) Zhao, L.; Mak, T. C. W. J. Am. Chem. Soc. 2004, 126, 6852−
853.
14) Zhao, L.; Mak, T. C. W. J. Am. Chem. Soc. 2005, 127, 14966−
4967.
15) Zhao, L.; Wong, W. Y.; Mak, T. C. W. Chem.Eur. J. 2006, 12,
865−4872.
16) Zhao, L.; Wan, C. Q.; Han, J.; Chen, X. D.; Mak, T. C. W.
Chem.Eur. J. 2008, 14, 10437−10444.
17) Xie, Y. P.; Mak, T. C. W. Angew. Chem., Int. Ed. 2012, 51, 8783−
786.
(18) Martín-Lasanta, A.; de Cienfuegos, L. A
D.; Mota, A. J.; Orte, A.; Ruedas-Rama, M. J.; Ribagorda, M.;
Cardenas, D. J.; Carreno, M. C.; Echavarren, A. M.; Cuerva, J. M.
[
Ag (ArCC) (CH COO) ] (4) and [Ag (ArC
2
0
16
3
4
22
6
(
1
(
4
(
C) (NO ) (CH CH OH) ](OH) (5), were isolated and
16 3 4 3 2 4 2
structurally characterized. Although the silver clusters of
complexes 4 and 5 contain acetate and nitrate anions, they
are more like counterions instead of acting as critical building
blocks or templates for cluster assembly. Therefore, complexes
1
−5 represent, to the best of our knowledge, the largest silver
acetylide clusters without templates. Structural analysis of 1−5
contributed significantly to the understanding of the intrinsic
binding interaction between Ag(I) and ethynide ligands, and
provided crucial insights into the construction and conversion
of all-alkynyl-stabilized silver clusters. Preliminary results
showed that silver clusters with mixed Ag(I) and Ag(0)
oxidation states could be stabilized by phenylethynide ligands,
which might provide an alternative way for the preparation of
all-carbon-stabilized silver nanoparticles.
(
8
́
.; Johnson, A.; Miguel,
́
̃
Chem. Sci. 2014, 5, 4582−4591.
(19) Zhao, L.; Zhao, X. L.; Mak, T. C. W. Chem.Eur. J. 2007, 13,
5
927−5936.
(
20) Gruber, F.; Jansen, M. Z. Anorg. Allg. Chem. 2011, 637, 1676−
679.
21) Cheng, P. S.; Marivel, S.; Zang, S. Q.; Gao, G. G.; Mak, T. C. W.
1
(
ASSOCIATED CONTENT
■
Cryst. Growth Des. 2012, 12, 4519−4529.
*
S
Supporting Information
(22) Li, B.; Huang, R. W.; Yao, H. C.; Zang, S. Q.; Mak, T. C. W.
CrystEngComm 2014, 16, 723−729.
Figures S1−S10. Tables S1−S5. X-ray data as CIF files for
complexes 1−5 have been deposited at the Cambridge
Crystallographic Data Centre (CCDC), under deposition
number CCDC 1044527 (1), 1044528 (2), 1044529 (3),
044530 (4), and 1044531 (5). This material is available free of
charge via the Internet at http://pubs.acs.org.
(
23) Gao, G. G.; Cheng, P. S.; Mak, T. C. W. J. Am. Chem. Soc. 2009,
1
(
1
(
4
(
31, 18257−18259.
24) Gruber, F.; Schulz-Dobrick, M.; Jansen, M. Chem.Eur. J. 2010,
6, 1464−1469.
25) Gruber, F.; Jansen, M. Angew. Chem., Int. Ed. 2010, 49, 4924−
926.
26) Hau, S. C. K.; Cheng, P. S.; Mak, T. C. W. J. Am. Chem. Soc.
1
AUTHOR INFORMATION
■
*
2012, 134, 2922−2925.
Corresponding Author
E-mail: ruicao@ruc.edu.cn.
(27) Zhou, K.; Geng, Y.; Yan, L. K.; Wang, X. L.; Liu, X. C.; Shan, G.
G.; Shao, K. Z.; Su, Z. M.; Yu, Y. N. Chem. Commun. 2014, 50, 11934−
1
1937.
Notes
(
28) Rais, D.; Yau, J.; Mingos, D. M. P.; Vilar, R.; White, A. J. P.;
Williams, D. J. Angew. Chem., Int. Ed. 2001, 40, 3464−3467.
29) Wang, Q. M.; Mak, T. C. W. Angew. Chem., Int. Ed. 2002, 41,
The authors declare no competing financial interest.
(
ACKNOWLEDGMENTS
4135−4137.
■
(
30) Bian, S. D.; Wang, Q. M. Chem. Commun. 2008, 5586−5588.
31) Bian, S. D.; Wu, H. B.; Wang, Q. M. Angew. Chem., Int. Ed.
We are grateful for the financial support from the “Thousand
Talents Program” of China, the National Natural Science
Foundation of China (No. 21101170), the Fundamental
Research Funds for the Central Universities and the Research
Funds of Renmin University of China.
(
2
(
3
(
009, 48, 5363−5365.
32) Bian, S. D.; Jia, J. H.; Wang, Q. M. J. Am. Chem. Soc. 2009, 131,
422−3423.
33) Wu, H. B.; Huang, Z. J.; Wang, Q. M. Chem.Eur. J. 2010, 16,
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DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.cgd.5b00286
Cryst. Growth Des. XXXX, XXX, XXX−XXX