Argentophilic infinite chain, column, and layer structures assembled with the multinuclear silver(I)-phenylethynide supramolecular synthon

Article abstract of DOI:10.1021/cg300691n

Nine silver(I) complexes bearing the phenylethynide ligand and different ancillary anions, namely, double salts AgC≡CPh?AgNO₃ (1), 2AgC≡CPh?AgNO₃ (2), [Ag₅(C≡CPh) ₄(DMSO)₂]X [X = BF₄ (3A), ClO₄ (3B), PF₆ (3C), AsF₆ (3D), SbF₆ (3E)], 2AgC≡CPh?5AgO₂CCF₃?4DMSO (4), and a triple salt 10AgC≡CPh?2AgOTf?AgNO₃?3DMSO (5), have been synthesized and shown to possess coordination frameworks that are assembled with the supramolecular synthon Ph-C≡C?Ag_n (n = 3, 4, 5). Different argentophilic layers are found in nitrate complexes 1 and 2, which are crystallized from water and mixed water/DMSO, respectively. Difficulty was encountered in growing quality crystals of complexes 3A-3E, 4, and 5 bearing weakly coordinating anions, but DMSO proved to be a good solvent for crystallization by functioning as a coligand. The isostructural compounds 3A-3E exhibit the same type of pseudohexagonal packing of infinite silver columns, with the ancillary anionic component filling the intervening space and linking adjacent columns via weak hydrogen bonds. Three-dimensional supramolecular frameworks based on similar packing of silver chains and columns, respectively, are found in double salt 4 and triple salt 5.

Full text of DOI:10.1021/cg300691n

Article
pubs.acs.org/crystal
Argentophilic Infinite Chain, Column, and Layer Structures
Assembled with the Multinuclear Silver(I)−Phenylethynide
Supramolecular Synthon
Published as part of the Crystal Growth & Design virtual special issue In Honor of Prof. G. R. Desiraju
Ping-Shing Cheng,† Samipillai Marivel,† Shuang-Quan Zang,‡ Guang-Gang Gao,§
and Thomas C. W. Mak*,†
†Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, New
Territories, Hong Kong SAR, People’s Republic of China
‡Department of Chemistry, Zhengzhou University, Zhengzhou, 450001, People’s Republic of China
§Heilongjiang Engineering Technical Centre of Irradiation Cross-linking Materials, 3 World Road, Jiamusi, 154004, People’s Republic
of China
S
* Supporting Information
ABSTRACT: Nine silver(I) complexes bearing the phenylethynide ligand and different
ancillary anions, namely, double salts AgCCPh·AgNO3 (1), 2AgCCPh·AgNO3 (2),
[Ag5(CCPh)4(DMSO)2]X [X = BF4 (3A), ClO4 (3B), PF6 (3C), AsF6 (3D), SbF6 (3E)],
2AgCCPh·5AgO2CCF3·4DMSO (4), and a triple salt 10AgCCPh·2AgOTf·Ag-
NO3·3DMSO (5), have been synthesized and shown to possess coordination frameworks
that are assembled with the supramolecular synthon Ph−CC⊃Agn (n = 3, 4, 5). Different
argentophilic layers are found in nitrate complexes 1 and 2, which are crystallized from water
and mixed water/DMSO, respectively. Difficulty was encountered in growing quality crystals of
complexes 3A−3E, 4, and 5 bearing weakly coordinating anions, but DMSO proved to be a
good solvent for crystallization by functioning as a coligand. The isostructural compounds 3A−
3E exhibit the same type of pseudohexagonal packing of infinite silver columns, with the
ancillary anionic component filling the intervening space and linking adjacent columns via weak hydrogen bonds. Three-
dimensional supramolecular frameworks based on similar packing of silver chains and columns, respectively, are found in double
salt 4 and triple salt 5.
charges omitted for simplicity. In view of their frequent
occurrence and robustness, such structural patterns can be
regarded, in accordance with Desiraju’s seminal definition of
supramolecular synthon in the context of crystal engineering,8 as
novel multinuclear metal−ligand supramolecular synthons9 for
the designed construction of a wide variety of organosilver(I)
compounds composed of discrete molecules, including large-
nuclearity clusters,10 as well as one- to three-dimensional
networks.11
INTRODUCTION
■
The study of metal−ethynide complexes has drawn consid-
erable interest due to their structural diversity1 and potential
application as photoluminescent materials,2 precursors of
nonlinear optical materials,3 and rigid-rod molecular wires.4
Diverse coordination modes of the ethynide moiety to the
coinage metal center (Cu, Ag, and Au) facilitate the onset of
metallophilic interactions,5 usually leading to the formation of
clusters, multinuclear aggregates, or extended solid-state
architectures.6
In contrast to the chemical behavior of Ag2C212 and Ag2C4,13
silver(I) aryl ethynide is sparingly soluble in a concentrated
aqueous solution of a soluble silver(I) salt, so that its double
and multiple silver(I) salts cannot be readily obtained in
crystalline form. Hitherto most of the reported silver(I) aryl
ethynide complexes have been synthesized with the incorpo-
ration of phosphine14 or carboxylate-supporting ligands,15
except for four aryl or heteroaryl ethynide complexes with
silver(I) nitrate16 and one with silver(I) triflate.17 Notably, both
Over a dozen years ago, we initiated a systematic
investigation on the synthesis and structural characterization
of crystalline silver(I) complexes containing various ethynide-
2−
containing ligands, including the all-carbon dianions C2 and
2−
−
C4 and carbon-rich monoanions of the type R−C2 (R =
alkyl, aryl, heteroaryl).7 In such complexes, the terminal carbon
atom of the ethynide ligand that carries a formal negative
charge is invariably surrounded by three to six Ag(I) atoms.
The corresponding polynuclear cationic silver(I)-ethynediide,
-1,3-butadiene-1,4-diide, and -ethynide aggregates may be
designated as C2@Agn (n = 6−8), Ag4⊂C≡C−C≡C⊃Ag4,
and R−C≡C⊃Agn (n = 3−6), respectively, with the overall
Received: May 20, 2012
Revised: July 16, 2012
Published: July 19, 2012
© 2012 American Chemical Society
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Table 1. Crystallographic Data for Compounds 1−5
compound
empirical formula
1
2
3A
3B
C8H5Ag2NO3
378.87
orthorhombic
Pca21 (No. 29)
21.936(1)
16.025(1)
7.604(1)
90
C16H10Ag3NO3
587.86
monoclinic
P21/c (No. 14)
16.918(1)
6.513(1)
13.605(1)
90
C36H20Ag5BF4O2S2
1174.80
C36H20Ag5ClO6S2
1187.44
monoclinic
P21/n (No. 14)
8.545(1)
26.880(1)
17.597(1)
90
formula weight
crystal system
space group
a [Å]
triclinic
P1 (No. 2)
̅
8.580(1)
14.894(1)
16.645(1)
67.43(1)
85.22(1)
82.42(1)
1945.8(2)
2
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V [Å3]
Z
90
92.96(1)
90
103.51(1)
90
90
2672.9(2)
12
1497.1(1)
4
3930.0(3)
4
D
calc (g/cm3)
2.824
2.608
2.005
2.007
μ(Mo−Kα) (mm−1
F(000)
)
4.369
3.897
2.628
2.663
2136
1112
1120
2272
reflections collected
independent reflections
observed reflections [I > 2σ(I)]
parameters
42026
32799
48456
7655
112525
9431
5664
3601
4827
3343
6480
6768
416
209
443
463
goodness-of-fit
0.933
1.038
1.426
1.068
R1 [I > 2σ(I)]
0.0272
0.0603
0.0225
0.0625
3E
0.0421
0.1200
4
0.0387
0.0974
5
wR2 (all data)
3C
3D
C36H20Ag5F6O2PS2
1232.96
monoclinic
P21/c (No. 14)
8.505(1)
27.457(2)
17.857(1)
90
C36H20Ag5AsF6O2S2
1276.91
monoclinic
P21/c (No. 14)
8.462(1)
27.714(4)
17.932(2)
90
C36H15Ag5F6O2SbS2
C68H68Ag14F30O28S8
1834.94
C86H50Ag13F6NO11S4
2917.82
monoclinic
C2/c (No. 15)
35.168(7)
14.390(3)
19.492(4)
90
1318.70
triclinic
triclinic
P1 (No. 2)
̅
P1 (No. 2)
̅
8.413(1)
16.722(1)
16.746(1)
114.11(1)
99.08(1)
94.42(1)
2096.9(2)
2
14.146(1)
16.183(1)
23.228(2)
90.74(2)
95.36(2)
105.89(2)
5087.9(8)
4
103.080(1)
90
102.69(3)
90
109.19(4)
90
4061.9(5)
4
4102.4(10)
4
9316(3)
4
2.016
2.067
2.088
2.395
2.080
2.568
3.304
3.079
2.916
2.822
2352
2424
1238
3512
5560
136681
7574
24429
43059
8059
154060
18340
117068
11480
5721
6340
3378
6258
16293
8232
472
462
420
1354
599
1.065
1.031
1.224
1.140
5.973
0.0423
0.0521
0.0763
0.1614
0.0504
0.1319
0.0340
0.1108
0.1132
0.1078
nitrate and triflate belong to the class of strongly coordinating
ligands for the synthesis of metal complexes.
(3D), SbF6 (3E)], 2AgCCPh·5AgO2CCF3·4DMSO (4), and
the triple salt 10AgCCPh·2AgOTf·AgNO3·3DMSO (5), in
which the anionic component plays a vital role in dictating the
assembly of argentophilic and coordination networks.
In the present study, we have developed a modified
crystallization method to obtain new complexes of silver(I)
phenylethynide in combination with various ancillary silver(I)
salts in order to address two issues: (a) the influence of various
weakly coordinating inorganic anions on supramolecular
assembly with the multinuclear synthon Ph−CC⊃Agn (n =
4, 5); and (b) the factors that favor the generation of
argentophilic silver(I) columns and layers. Herein we report the
synthesis and structural characterization of a series of nine
silver(I) phenylethynide complexes, namely, double salts
AgCCPh·AgNO3 (1), 2AgCCPh·AgNO3 (2), [Ag5(C
CPh)4(DMSO)2]X [X = BF4 (3A), ClO4 (3B), PF6 (3C), AsF6
EXPERIMENTAL SECTION
■
General Comments. In general, crystalline silver double and
multiple salts containing phenylethynide as a component can be
obtained from slow evaporation of crude polymeric silver(I)
phenylethynide [AgCCAr]n in a concentrated aqueous or water/
acetonitrile solution of AgNO3/AgBF4/AgCF3CO2. However, silver(I)
phenylethynide is sparingly soluble in a concentrated aqueous solution
of AgWCA, where WCA represents a weakly coordinating inorganic
anion. Therefore we used DMSO to replace water or water/
acetonitrile as a reaction medium in combining polymeric silver(I)
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phenylethynide with various water-soluble silver salts (AgNO3, AgBF4,
AgClO4, AgPF6, AgAsF6, AgSbF6, AgO2CCF3, and AgOTf) to yield
new double and triple salts. After filtration, the filtrate was transferred
to a test tube, and water was layered over it for crystallization via slow
liquid diffusion.
Reagents. All chemicals and solvents were commercially available
and used without further purification. Polymeric [AgCCPh]n was
prepared according to the literature method.18,19
data and parameters for X-ray structure analysis are summarized in
Table 1.
RESULTS AND DISCUSSION
■
Description of Crystal Structures. AgC≡CPh·AgNO3 (1).
In the crystal structure of 1, there are three independent
phenylethynide anions each attached to a butterfly-shaped Ag4
basket in different coordination modes. The ethynide moieties
C1C2 and C17C18 act in the μ4-η1,η1,η2,η2 coordination
mode, and the other ethynide group C9C10 adopts the μ4-
η1,η2,η2,η2 mode (Figure 1).
Caution! Silver-ethynide complexes are potentially explosive in the dry
state when subjected to heating or mechanical shock and should be used in
small quantities with extreme care.
Syntheses and Characterization. [AgCCPh·AgNO3] (1).
AgNO3 (0.510 g, 3 mmol) was dissolved in deionized water (1
mL), and [AgCCPh]n (≈ 30 mg) solid was added to the solution.
After stirring for about half an hour, the solution was filtered. After a
few days, colorless plate-like crystals were collected in ca. 40% yield.
Compound 1 melts at 178.1−179.9 °C. Elemental analysis for
C8H5O3NAg2, found (calcd): C, 25.69 (25.36); H, 1.71 (1.33); N,
3.38 (3.70). IR spectrum: 2012 cm−1 (w, ν CC).
[2AgCCPh·AgNO3] (2). [AgCCPh]n (≈ 100 mg) was added to
1 mL of a concentrated DMSO of AgNO3 (0.510 g, 3 mmol) in a
beaker. After stirring for about half an hour, the solution was filtered
and transferred to a test tube. Next, water was layered over the
solution, and the test tube was left undisturbed in the ambient
environment. After several days, colorless plate-like crystals were
obtained in ca. 80% yield. Compound 2 decomposes above 170 °C.
Elemental analysis for C16H10O3NAg3, found (calcd): C, 32.79
(32.69); H, 1.73 (1.71); N, 2.34 (2.38). IR spectrum: 2012 cm−1
(w, ν CC).
[Ag5(PhCC)4(DMSO)2]X [X = BF4 (3A), ClO4 (3B), PF6 (3C), AsF6
(3D), SbF6 (3E)]. AgX (1 mmol) was dissolved in DMSO (1 mL), and
[AgCCPh]n (≈ 0.1 g) was then added to the solution. After stirring
for 1 h, the solution became clear and was transferred to a test tube.
Water was layered over the solution. After one week, yellow needle-
shaped crystals were obtained in ca. 75% yield. All compounds
decompose above 120 °C. 3A, C36H32BF4O2S2Ag5, elemental analysis
found (calcd): C, 36.69 (36.43), H, 2.78 (2.72). IR spectrum: 2006
cm−1 (w, ν CC); 3B, C36H32ClO6S2Ag5, found (calcd): C, 36.49
(36.05), H, 2.71 (2.69). IR spectrum: 2011 cm−1 (w, ν CC); 3C,
C36H32PF6O2S2Ag5, found (calcd): C, 34.79 (34.73), H, 2.56 (2.59).
IR spectrum: 2018 cm−1 (w, ν CC); 3D, C36H32AsF6O2S2Ag5,
found (calcd): C, 33.69 (33.54), H, 2.71 (2.50). IR spectrum: 2009
cm−1 (w, ν CC); 3E, C36H32SbF6O2S2Ag5, found (calcd): C, 32.54
(32.37), H, 2.30 (2.41). IR spectrum: 2009 cm−1 (w, ν CC).
[2AgCCPh·5AgCF3CO2·4DMSO] (4). AgCF3CO2 (0.440 g, 2
mmol) was dissolved in 1 mL of DMSO. [AgCCPh]n (≈ 50 mg)
was added to the solution. After stirring for about half an hour, the
solution was filtered and transferred to a test tube. And then, water was
layered over the solution and the test tube was stored in a refrigerator
at 4 °C. After several days, pale yellow needle-shaped crystals of 4 were
obtained in ca. 25% yield. Compound 4 melts from 136.0 to 137.7 °C.
Elemental analysis for C34H34O14F15S4Ag7, found (calcd): C, 22.51
(22.26); H, 1.79 (1.87). IR spectrum: 2014 cm−1 (vw, ν CC).
[10AgCCPh·2AgOTf·AgNO3·3DMSO] (5). AgNO3 (0.085 g, 0.5
mmol) and AgOTf (0.514 g, 2 mmol) were dissolved in DMSO (1
mL) in a beaker. [AgCCPh]n (≈ 100 mg) was then added to the
solution. After stirring for about half an hour, the solution was filtered
and transferred to a test tube. Next, water was layered over the
solution, and the test tube was stored in a refrigerator at 4 °C. After
several days, pale yellow needle-like crystals of 5 were obtained in ca.
20% yield. Compound 5 decomposes above 120 °C. Elemental
analysis for C88H68F6O12NS5Ag13, found (calcd): C, 34.89 (35.14); H,
2.34 (2.28); N, 0.58 (0.47). IR spectrum: 2008 cm−1 (w, ν CC).
X-ray Crystallographic Analysis. Selected crystals were used for
data collection on a Bruker SMART APEX−II CCD diffractometer at
293 K (for 1, 2, 3A−3E, and 5) and 150 K (for 4) using frames of
oscillation range 0.5°, with 2° < θ < 28°. An empirical absorption
correction was applied using the SADABS program.20 The structures
were solved by the direct method and refined by full matrix least-
squares on F2 using the SHELXTL program package.21 The crystal
Figure 1. Atom labeling and coordination modes of independent
phenylethynide ligands in AgCCPh·AgNO3 (1) (50% thermal
ellipsoids). Hydrogen atoms and nitrate anions are omitted for clarity.
Symmetry codes: a 1 − x, − y, 0.5 + z; b 0.5 − x, y, 0.5 + z. Selected
bond lengths [Å]: C1C2 1.24(1), C9C10 1.22(1), C17C18
1.21(1), Ag···Ag 2.860(1)−3.268(1).
An argentophilic silver(I) layer in the crystal structure of 1 is
formed from the cross-linkage of an alternating arrangement of
parallel double (colored red; composed of Ag1, Ag2, and Ag3)
and single (colored purple; Ag5 and Ag6) zigzag chains, with
silver(I) atoms of type Ag4 (colored green) strengthening the
layer through additional Ag···Ag interaction (Figure 2).
Figure 2. Argentophilic layer in the crystal structure of 1. Color codes
for atoms: normally purple is used for Ag in all figures, but different
colors are used as required to facilitate description of structural
features: Ag1, Ag2, and Ag3 red; Ag4, green; Ag5 and Ag6, purple.
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Unusually short cationic contacts between adjacent d10 Ag(I)
centers in the range 2.80−3.30 Å (less than 3.40 Å, twice the
van der Waals radius of metallic silver) that give rise to layer-
type structures are known to exist in many crystalline silver(I)
oxo-salts such as KAgCO3, Ag2CO3, and AgBO2 for well over a
half-century, although such layers were not referred to as
argentophilic in the early literature.22 In contrast, the
occurrence of silver(I) layers in organometallic compounds is
rare, the few reported examples being Ag2C2·2AgClO4·2H2O,23
3[Ag2(o-CCC6H4CC)]·14AgCF3CO2·2CH3CN·9H2O,24
and Ag2(2,5-CCpyCC)·3AgNO3.25 Compound 1 provides
the first example of a corrugated, thick silver(I) layer stabilized
by argentophilicity.
Figure 4. Atom labeling and coordination modes of the phenyl-
ethynide and nitrate ligands in 2AgCCPh·AgNO3 (2) (50% thermal
ellipsoids). Hydrogen atoms are omitted for clarity. Symmetry codes: a
1 − x, −0.5 + y, 0.5 − z; b x, 0.5 − y, −0.5 + z; c 1 − x, −0.5 + y, 0.5 −
z. Selected bond lengths [Å]: C1C2 1.22(1), C9C10 1.22(1),
Ag···Ag 2.895(1)−3.359(1).
The corrugated silver(I)-layer structure is additionally
stabilized by nitrate ions exhibiting different coordination
modes: (O1−O2−O3) μ2-O,O′, (O4−O5−O6) μ2-O,O′ and
(O7−O8−O9) μ-O. As shown in Figure 3, the phenyl ethynide
Figure 3. (a) Side view of the corrugated silver(I)-phenylethynide
layer in 1 assembled by argentophilic interaction and nitrate ligands.
(b) Weak interactions (π−π: green dotted line; C−H···O hydrogen
bond: turquoise dotted line) contributing to stabilization of the
silver(I)- phenylethynide layer structure. Color codes for atoms: Ag,
purple; C, gray; H, turquoise; O, green; N, blue.
groups arranged on both sides of the thick silver(I) layer are
involved in pairwise offset face−to−face π−π interaction (inter-
centroid distance, 4.169 Å) and weak C−H···O(nitrate)
hydrogen bonds (C4···O8, 3.279 Å; C8···O1, 3.278 Å;
C16···O9 3.301 Å; C20···O1, 3.233 Å).
2AgC≡CPh·AgNO3 (2). Compound 2 was obtained from the
crystallization of [AgCCPh]n in a DMSO solution of AgNO3,
instead of an aqueous solution of AgNO3 as in the formation of
complex 1. In the crystal structure of 2, there are two
independent phenylethynide anions (C1C2) and (C9
C10), which are bound to Ag3 baskets in the μ3-η1,η1,η2 and μ3-
η1,η2,η2 coordination modes, respectively (Figure 4).
Figure 5. (a) Herringbone silver(I) layer of 2 formed from
argentophilic interaction between chairlike Ag6 aggregates. Symmetry
codes: (b) side view of argentophilic layer in 2 assembled by π−π
stacking, C−H···O hydrogen bonding and bridging nitrate ligands on
both sides. Color scheme for atoms: Ag, purple; C, gray; H, turquoise;
O, orange; N, blue. Green and turquoise dotted lines represent π−π
and C−H···π interactions, respectively.
corner-linkage of chairlike Ag6 aggregates formed by the double
linkage between two inversion-related silver(I) triangles (Ag1,
Ag2, Ag3; Ag1d, Ag2d, Ag3d; colored blue to facilitate
visualization).
As shown in Figure 5a, the silver atoms are united together
through argentophilic interaction to form a herringbone
silver(I) layer on the bc plane, which is constructed by the
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Figure 6. (a) Atom labeling and coordination modes of the phenylethynide ligands in 3A. The silver(I) and ethynide carbon atoms are drawn as 30%
thermal ellipsoids, and hydrogen atoms are omitted for clarity. Selected bond lengths [Å]: C1C2 1.23(1), C9C10 1.21(1), C17C18 1.20(1),
C25C26 1.22(1), Ag···Ag 2.904(1)−3.377(1). (b) Characteristic cationic silver(I) column in the isostructural series of complexes 3A to 3E
formed from the linkage of a linear array of centrosymmetric Ag8 rhombic prisms (colored purple) by atoms Ag3 and Ag3b (colored yellow). (c)
Coordination of silver(I) column by surrounding phenylethynide anions and DMSO ligands. Symmetry codes: a 1 − x, 1 − y, 1 − z; b 2 − x, 1 − y, 1
− z.
As shown in Figure 5b, the nitrate ligand adopts the μ2-O,O′
mode to consolidate the silver(I) layer. Adjacent phenyl rings
of ethynide ligands arranged on both sides of the silver(I) layer
interact through both offset face-to-face π−π interaction (inter-
centroid distance 3.603 Å) and edge-to-face C−H···π
interaction (H···center, 2.859 Å with a C−H···centroid angle
of 115°), the latter being shorter than the normal C−H···π
interaction of 3.05 Å [1.05 times the sum of accepted van der
Waals radii of hydrogen (1.20 Å) and carbon (1.70 Å)].26 Such
π-related interactions further stabilize the silver(I)-layer
structure.
common, weakly coordinating inorganic ions constitute an
isostructural series of complexes that exhibit essentially the
same type of crystal structure. In particular, 3C and 3D are
isomorphous as both belong to space group P21/c with very
similar unit-cell dimensions.
The crystal structure of compound 3A, which contains the
−
BF4 anion, is described as a representative example. Here the
ethynide moieties C1C2 and C25C26 are each capped by
a butterfly-shaped Ag4 basket in the μ4-η1,η1,η1,η2 coordination
mode, whereas ethynides C9C10 and C17C18 adopt the
μ3-η1,η1,η1 and μ3-η1,η2,η2 coordination modes, respectively
(Figure 6a). The four independent silver(I) atoms (Ag1, Ag2,
Ag4, Ag5) and their inversion-related counterparts form a Ag8
[Ag5(PhC≡C)4(DMSO)2]X [X= BF4 (3A), ClO4 (3B), PF6
(3C), AsF6 (3D), SbF6 (3E)]. Complexes 3A−3E bearing
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Figure 7. Packing of silver(I) columns (viewed end-on) in complexes (a) 3A and (b) 3E, which are linked by weak hydrogen bonds to give a three-
dimensional supramolecular network. In the case of 3A, face-to-face π−π interaction of phenyl rings occurs between adjacent silver columns in the b
direction.
rhombic prism, and fusion of a linear array of such polyhedra
via bridging atoms Ag3 and Ag3b yields an infinite cationic
silver(I) column directed along the a-axis (Figure 6b). This
silver column is coordinated by the surrounding phenyl-
ethynide and DMSO ligands (Figure 6c).
Table 2. Comparison of Three-Dimensional Supramolecular
Structures of 3B, 3C, and 3D
The crystal structure of 3A consists of a hexagonal packing of
parallel coordinated silver columns, with the BF4− ion playing a
space-filling role as well as linking neighboring columns via
weak C−H···F hydrogen bonds (C5···F2, 3.316 Å; C30···F4,
−
3.407 Å). In view of the small size of the BF4 ligand, face-to-
face π−π interaction (4.087 Å) of phenyl rings of adjacent silver
columns also occurs (Figure 7a).
The infinite cationic silver(I) column found in 3A also exists
in the crystal structures of 3B to 3E. Despite the large
difference in steric bulk of the BF4− and SbF6− anions, they play
the same role in linking the infinite silver(I) columns in 3A and
3E, respectively, by weak hydrogen bonds to form a
pseudohexagonal network (Figure 7).
In a like manner, when AgClO4, AgPF6, and AgAsF6 are used
in turn to generate 3B, 3C, and 3D, respectively, a similar
hexagonal array of infinite silver(I) columns are interconnected
by weak hydrogen bonds to form a three-dimensional
supramolecular network. The crystal structures of 3B and the
isomorphous pair 3C and 3D are displayed in Table 2.
Notably, the mode of crystal packing and closest separation
between the cationic silver(I) columns can be fine-tuned by
varying the size of the ancillary inorganic anion. With a steady
increase in the size of WCAs, the separation between adjacent
silver(I) columns increases (Table 3).
2AgC≡CPh·5AgO2CCF3·4DMSO (4). In the crystal structure
of 4, there are four independent phenylethynide anions which
are consolidated into a Ag15 aggregate via different coordination
modes. The ethynide moieties C1C2 and C17C18 are
each capped by a butterfly-shaped Ag4 basket in the μ4-
η1,η1,η1,η2 mode, and the other two ethynide groups C9C10
and C25C26 are each bound to a square-pyramidal Ag5
basket in the μ5-η1,η1,η1,η1,η2 mode, as shown in Figure 8a. This
Ag15 aggregate is stabilized by continuous π−π stacking of
phenyl rings (intercentroid distances (I)···(II) 4.120 Å,
(II)···(III) 3.874 Å, (III)···(IV) 4.087 Å) lying on one side.
All trifluoroacetate groups each spans a Ag···Ag edge by the μ2-
O,O′ mode (Figure 9a).
Adjacent Ag14 aggregates are further fused together through a
shared silver atom (Ag14) and a bridging μ2-DMSO molecule
to generate an infinite silver(I) chain along the b axis (Figure
9a). The remaining DMSO molecules are each coordinated to
the silver chain (three in μ1 and four in μ2 mode) at intervals
between segments of four phenyl rings. Because of the steric
effect of the bridging DMSO molecule, complex 4 exhibits
segmented π−π interactions rather than infinite continuous
π−π stacking among parallel phenyl rings in AgC
CPh·3AgO2CCF3·CH3CN.18
As shown in Figure 9b, the infinite silver(I) chains are
interconnected by two kinds of weak hydrogen bonds, that is,
C6−H6A···F9 (C14−F9 3.11 Å) and C61−H61B···F22 (C61−
F22 3.38 Å), to form a three-dimensional supramolecular
structure.
10AgC≡CPh·2AgOTf·AgNO3·3DMSO (5). In the crystal
structure of complex 5, independent atoms Ag1, Ag2, Ag5,
Ag6, and Ag7 together with their inversion-related counterparts
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Table 3. Variation of Separation between Nearest Silver(I) Columns in Isostructural Complexes 3A−3E with the Presence of
Different Ancillary Inorganic WCAs
[Ag5(PhCC)4(DMSO)2]X
shortest center to the center distance between adjacent silver(I) columns (Å)
3A
3B
3C
3D
3E
X
BF4
ClO4
16.06
PF6
AsF6
SbF6
14.89
16.37
16.51
16.72
Figure 8. (a) Atom labeling and coordination modes of four independent phenylethynide units in 2AgCCPh·5AgO2CCF3·4DMSO (4) (50%
−
thermal ellipsoids). The DMSO and CF3CO2 ligands and all hydrogen atoms are omitted for clarity. Symmetry code: a − x, −1 + y, z. Selected
bond lengths [Å]: C1C2 1.20(1), C9C10 1.22(1), C17C18 1.23(1), C25C26 1.24(1), Ag···Ag 2.896(1)−3.170(1). (b) Side view of
silver(I) chain in 4 surrounded by trifluoroacetate ligands and DMSO molecules.
This silver(I) column is stabilized by formation of a π−π
interaction cycle which consists of an offset face-to-face π−π
interaction (center-to-center distance 3.913 Å), a C−H···π-
(ethynide) interaction (H4···midpoint of C9 and C10 = 3.016
Å with a C4−H4···midpoint of C9 and C10 angle 158°, and
two edge−to−face C−H···π interactions (H31 to center of (II)
distance = 2.836 Å with a C−H···centroid angle 143°; H40 to
center of (IV) distance = 2.944 Å with a C−H···centroid angle
140°) (Figure 11).
In the crystal structure of 5, the infinite silver(I) columns
arranged in a hexagonal array are interconnected by C30−
H30···F2 (C30−F2 3.520 Å) hydrogen bonds to form a three-
dimensional supramolecular structure (Figure 12).
DISCUSSION
■
Crystallization Procedure. Polymeric silver(I) phenyl-
ethynide readily dissolves in a concentrated aqueous solution of
AgNO3, but it has very low solubility in a saturated solution of a
soluble silver(I) salt AgX in water, where X represents an
Figure 9. (a) Silver(I) chain in complex 4 connected by sharing the
inorganic anion in the weakly coordinating series composed of
Ag14 atom and bridging DMSO ligand. All hydrogen atoms and CF3
−
−
−
−
−
BF4 , ClO4 , PF6 , AsF6 , and SbF6 (henceforth abbreviated
as WCAs). In our attempted preparation of new crystalline
silver(I) complexes containing phenylethynide and a mono-
anion in this series, we explored mixed-solvent systems by
employing a water-miscible cosolvent such as methanol,
ethanol, acetone, THF, DMF, and DMSO. Subsequently, we
found that the solubility of silver(I) phenylethynide can be
greatly increased using DMSO as a cosolvent. We therefore
modified the crystallization method by layering water over a
concentrated DMSO solution of a variety of silver(I) salts,
thereby resulting in a high phenylethynide/X molar ratio in the
product complexes (see Table 4).
Influence of Solvent and Ancillary Anion. Double salts
1 and 2, which bear different molar ratios, are obtained from
crystallization in water and water/DMSO, respectively. DMSO
proved to be a good solvent for crystallization of complexes 3−
5 by functioning as a ligand. From the available structural data
presented in Table 4, it appears that the coordination ability of
phenylethynide is weakened when the complex has a high
−
moieties of CF3CO2 are omitted for clarity. (b) Adjacent silver(I)
chains (viewed end-on) in complex 4 are linked by weak hydrogen
bonds C6−H6A···F9 (C14−F9 3.11 Å) and C61−H61B···F22 (C61−
F22 3.38 Å) to give a three-dimensional network.
constitute an argentophilic Ag10 incomplete double cubane. An
infinite silver(I) column is constructed by fusion of such
incomplete double cubanes with a bent Ag3 unit (Ag3, Ag4,
Ag3b) with C2 symmetry (Figure 10a).
Complex 5 features a neutral silver(I) coordination column
stabilized by phenylethynide, triflate, and nitrate anions
oriented along the c-axis (Figure 10b). All the phenylethynide
anions are each capped by three silver atoms. The ethynide
moieties C1C2, C9C10, and C25C26 act in the μ3-
η1,η1,η2 coordination mode, and ethynides C17C18 and
C33C34 adopt μ3-η1,η1,η1 and μ3-η1,η2,η2 coordination
modes, respectively. The triflate and nitrate anions adopt μ-O
and μ2-O,O′ coordination modes, respectively, to act as
effective counteranions to balance the charge.
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Figure 10. (a) Argentophilic column in 5 formed by fusion of centrosymmetric Ag10 incomplete double cubanes (yellow) and C2 bent Ag3 unit
(purple). (b) The silver(I) polyhedron column in complex 5 surrounded by phenylethynide ions, whose phenyl rings are engaged in π−π, C−
H···π(phenyl) and C−H···π(ethynide) weak interactions. Hydrogen atoms, nitrates, triflates, and DMSO molecules are omitted for clarity. Selected
bond lengths [Å]: C1C2 1.202(8), C9C10 1.210(5), C17C18 1.198(1), C25C26 1.22(1), C32C33 1.22(1), Ag···Ag 2.905(1)−
3.311(1). Symmetry codes: a: 1 − x, 1 − y, 1 − z; b: 1 − x, y, 1.5 − z.
Figure 11. π−π Interaction cycle in compound 5. Green dotted line
indicates π−π stacking; turquoise dotted line represents C−H···π
interaction.
Figure 12. Hexagonal array of coordination columns in complex 5
cross-linked by C30−F2 weak hydrogen bonds to form a three-
dimensional supramolecular structure. Other ligands are omitted for
clarity.
molar ratio of silver(I) phenylethynide to ancillary silver(I) salt.
Moreover, the nature of the ancillary anion also affects the
coordination mode of the phenylethynide anion. In DMSO,
when AgO2CCF3 was used, the ligation number27 of phenyl-
ethynide is 4 and 5. It decreases to 3 and 4 when a weakly
coordinating inorganic anion (WCA) is used. In the presence of
the nitrate anion, only three silver atoms are bonded to the
ethynide moiety.
Crystal growth from DMSO and H2O gives compounds 1
and 2 of different stoichiometry, indicating that the solvent
molecule affects the coordination ability of the anionic
component. When DMSO is used in place of water, fewer
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Table 4. Effect of Solvent and Ancillary Anion X on the Ligation Number of Phenylethynide and AgC2Ph/AgX Molar Ratio
complex
4
2
5
3A to 3E AgCCPh·3AgO
1
2CCF3·CH3CN18
a
silver(I) salt
solvent
AgO2CCF3
DMSO
4 and 5
1:2.5
AgNO3 AgNO3 + AgOTf WCA
AgO2CCF3
AgNO3
H2O
4
H2O + CH3CN
b
ligation number of phenylethynide
3
3
3 and 4
4:1
5
ratio of silver(I) phenylethynide to component silver
salt
2:1
10:3
1:3
1:1
a
b
WCA = weakly coordinating inorganic anion. Ligation number defined as number of metal ions consolidated by the ligand.
silver(I) ions are bound to the ethynide moiety, thereby
lowering the molar ratio of silver(I) phenylethynide to the
ancillary silver(I) salt, as well as the ligation number of
phenylethynide.
draws neighboring Ag(I) atoms together to facilitate the onset
of argentophilicity, such that the binding interaction that
consolidates the multinuclear metal−ligand aggregate is
considered to be mainly ionic with minor contribution from
covalent σ and π components. Accordingly we have adopted
the term “silver(I)-ethynide” in preference to “silver(I)-ethynyl”
and consistently used it in all our publications. To date,
formation of the multinuclear metal−ligand supramolecular
synthons is restricted to silver(I), as no analog has yet been
found for the other two coinage metals and the transition
elements. The fact that analogous multinuclear metal−ligand
supramolecular synthons are not formed by copper(I) and
gold(I) presumably arises from the insolubility of their salts in
common solvents.
When the ancillary silver salt AgO2CCF3 was employed, the
steric effect of the trifluoromethyl group is reflected in the
generation of an infinite silver(I) coordination chain. In
contrast, AgNO3 induces assembly of silver(I)-phenylethynide
to form an argentophilic layer. Upon addition of a silver(I) salt
of WCA to silver(I)-phenylethynide, the silver layer is rolled up
to yield a silver column composed of fused Agn polyhedra. The
nitrate ions in 1, DMSO molecules, and the corresponding
counterions in 3A−3E and 5 were found to exhibit positional/
orientational disorder, which was properly addressed in
structure refinement.
π−π Interaction. In our previous studies of silver(I) aryl
ethynide complexes, π−π interaction has been demonstrated to
play an important role in crystal formation by inducing the
assembly of Ar−CC⊃Agn building units to form a silver(I)
layer, column, chain, or bridged aggregate.17 As expected, the
aromatic ring of phenylethynide invariably partakes in
continuous or discontinuous π−π interaction to give an infinite
columnar structure in 4 and layer-type structures in 1 and 2.
However, when WCA is added, π−π interaction is interrupted,
and the phenyl rings only surround the silver(I) column to
form a hydrophobic shield. The WCA tends to force the
silver(I) phenylethynide together to form thick argentophilic
columns in 3 and 5.
Argentophilicity and Silver(I)-Ethynide Supramolecu-
lar Synthons. It is well-established that metallophilic
attractions5 are roughly comparable in strength with typical
hydrogen bonds. A well-known example is aurophilicity, the
propensity for aggregation of Au(I) centers in dinuclear or
polynuclear complexes,28 for which ab initio calculations
showed that such cohesive d10-d10 interaction, together with
significant relativistic effects, can be attributed mainly to
dispersion forces.5 For analogous Ag(I) and Cu(I) complexes,
presumably dispersion plays a dominant role while relativistic
effects are absent or negligible. Theoretical treatments of
dimeric models of linear two-coordinate group 11 complexes at
the MP2 level have suggested that metallophilicity decreases in
the order Au(I) > Ag(I) > Cu(I),29 which agrees with chemical
intuition. However, later theoretical studies at higher level
(CCSD and CCSD(T)) showed that argentophilicity may even
exceed aurophilicity in strength.30
There is as yet no definitive theoretical study on multinuclear
metal−ligand aggregates such as the silver(I)-ethynide supra-
molecular synthons, which we and other groups have employed
to assemble a wide variety of inorganic and organometallic
oligomers, high-nuclearity clusters, infinite chains, layers, and
three-dimensional frameworks.7,10 In our working model, the
terminal ethynyl carbon atom bearing the negative charge
CONCLUSION
■
On the basis of the multinuclear metal−ligand supramolecular
synthon Ph−CC⊃Agn (n = 3, 4, 5), the present work reports
the synthesis and structure of a series of silver(I) complexes
containing phenylethynide and inorganic ligands that include
the nitrate ion and a series of weakly coordinating anions
(WCAs). Crystallization of complexes containing WCAs is
made possible only using DMSO as a solvent, which plays the
role of an ancillary ligand. A systematic investigation of the
effect of variation of the anionic component on supramolecular
assembly showed that, to a certain extent, the dimension and
pattern of argentophilic aggregation can be controlled by using
different ancillary anions, yielding silver(I) layers in 1 and 2
with the nitrate ion, and isostructural complexes 3A−3E that
exhibit a three-dimensional supramolecular host network
composed of a hexagonal array of infinite silver(I) columns
that accommodate the WCA guests. With the incorporation of
organic ligand trifluoroacetate and triflate in 4 and 5,
respectively, an infinite silver(I) chain and a thick neutral
silver(I) column are obtained.
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray structure analysis results of 1−5 in CIF format. CCDC
reference numbers 865513−865521. This information is
available free of charge via the Internet at http://pubs.acs.
org/.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tcwmak@cuhk.edu.hk; fax: (852) 26035057.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We gratefully acknowledge financial support by the Hong Kong
Research Grants Council (GRF CUHK 402408 and 402710)
■
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(9) These persistent structural patterns serve as versatile structure
building units in crystal engineering, but logically they should be
regarded as multinuclear metal−ligand supramolecular synthons to
conform to the classical definition of Desiraju, since each cationic
aggregate is held together by weak interatomic/molecular attractive
interactions rather than conventional coordination bonding.
(10) (a) Bian, S.-D.; Wu, H.-B.; Wang, Q.-M. Angew. Chem., Int. Ed.
2009, 48, 5363−5365. (b) Bian, S.-D.; Jia, J.-H.; Wang, Q.-M. J. Am.
Chem. Soc. 2009, 131, 3422−3423. (c) Qiao, J.; Shi, K.; Wang, Q.-M.
Angew. Chem., Int. Ed. 2010, 49, 1765−1767. (d) Gao, G.-G.; Cheng,
P.-S.; Mak, T. C. W. J. Am. Chem. Soc. 2009, 131, 18257−18259.
(e) Gruber, F.; Jansen, M. Angew. Chem., Int. Ed. 2010, 49, 4924−
4926. (f) Putaj, P.; Lefebvre, F. Coord. Chem. Rev. 2011, 255, 1642−
1685. (g) Xie, Y.-P.; Mak, T. C. W. J. Am. Chem. Soc. 2011, 133,
3760−3763. (h) Hau, S. C. K.; Cheng, P.-S.; Mak, T. C. W. J. Am.
Chem. Soc. 2012, 134, 2922−2925. (i) Xie, Y.-P.; Mak, T. C. W. Chem.
Commun. 2012, 1123−1125.
(11) (a) Zhao, L.; Wong, W.-Y.; Mak, T. C. W. Chem.Eur. J. 2006,
12, 4865−4872. (b) Zhao, L.; Wan, C.-Q.; Han, J.; Chen, X.-D.; Mak,
T. C. W. Chem.Eur. J. 2008, 14, 10437−10444. (c) Zang, S.-Q.;
Mak, T. C. W. Inorg. Chem. 2008, 47, 7094−7105. (d) Zang, S.-Q.;
Han, J.; Mak, T. C. W. Organometallics 2009, 28, 2677−2683.
(12) (a) Guo, G.-C.; Zhou, G.-D.; Wang, Q.-G.; Mak, T. C. W.
Angew. Chem., Int. Ed. Engl. 1998, 37, 630−632. (b) Guo, G.-C.; Zhou,
G.-D.; Mak, T. C. W. J. Am. Chem. Soc. 1999, 121, 3136−3141.
(13) (a) Zhao, L.; Mak, T. C. W. J. Am. Chem. Soc. 2004, 126, 6852−
6853. (b) Zhao, L.; Du, M.; Mak, T. C. W. Chem. Asian J. 2007, 2,
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and the Wei Lun Foundation for postdoctoral fellowships to
Guang-Gang Gao, Shuang-Quan Zang, and Samipillai Marivel,
and the award of a Postgraduate Studentship to P.-C. Cheng by
The Chinese University of Hong Kong.
DEDICATION
■
Dedicated to Prof. Gautam R. Desiraju on the occasion of his
60th birthday.
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