Assembly of silver(i)-organic frameworks from flexible supramolecular synthons with pendant ethynide arm attached to biphenyl and phenoxybenzene skeletons

Article abstract of DOI:10.1039/c3ce40230d

A series of six silver(i) complexes bearing terminal ethynide moiety attached via pendant arm to biphenyl and phenoxybenzene skeletons of two new ligands have been synthesized. In these compounds, the invariable appearance of the μ₃-, μ₄- and μ₅-ligation modes of the ethynide moiety reaffirms the general utility of the silver-ethynide supramolecular synthons L ? Ag_n (n = 3-5) in coordination network assembly. In complexes 1, 2, 4, and 5, silver(i)-aromatic interactions play important roles in assembling a series of silver-organic frameworks. Notably, an unusual π...Ag₄...π sandwich unit makes it appearance in complex 2, which is the first example in silver-ethynide complexes. An argentophilic layer is found in complex 3. In addition, a two-fold interpenetrating 3D supramolecular framework based on discrete Ag₈ aggregate is found in complex 6. In the solid state, their luminescence behaviors have been studied.

Full text of DOI:10.1039/c3ce40230d

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Assembly of silver(I)–organic frameworks from flexible
supramolecular synthons with pendant ethynide arm
attached to biphenyl and phenoxybenzene skeletons3
Cite this: DOI: 10.1039/c3ce40230d
Bo Li,a Ren-Wu Huang,a Shuang-Quan Zang*a and Thomas C. W. Makab
A series of six silver(I) complexes bearing terminal ethynide moiety attached via pendant arm to biphenyl
and phenoxybenzene skeletons of two new ligands have been synthesized. In these compounds, the
invariable appearance of the m3-, m4- and m5-ligation modes of the ethynide moiety reaffirms the general
utility of the silver–ethynide supramolecular synthons L [ Agn (n = 3–5) in coordination network assembly.
In complexes 1, 2, 4, and 5, silver(I)–aromatic interactions play important roles in assembling a series of
Received 3rd February 2013,
Accepted 18th March 2013
…
…
silver–organic frameworks. Notably, an unusual p Ag4 p sandwich unit makes it appearance in complex
2, which is the first example in silver–ethynide complexes. An argentophilic layer is found in complex 3. In
addition, a two-fold interpenetrating 3D supramolecular framework based on discrete Ag8 aggregate is
found in complex 6. In the solid state, their luminescence behaviors have been studied.
DOI: 10.1039/c3ce40230d
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flexible ones can change their conformations to meet the
coordination requirement of the metal ion, which facilitates
the formation of silver(I)–aromatic interactions and other
intermolecular interactions.
Introduction
Silver(I)–ethynide complexes have attracted much interest
owing to their structural diversity1–3 and promising applica-
tion as luminescent materials.4 The diverse coordination
modes of the alkynyl moiety together with argentophilic
interaction lead to the formation of giant silver clusters,2 or
extended solid-state architectures.3 In the past decade, our
group has engaged in the designed construction of coordina-
tion networks based on new silver–ethynide supramolecular
synthons. By utilizing them, a series of silver(I)–organic
networks stabilized by argentophilic and silver–ethynide (s,
p and mixed s, p) interactions have been obtained.3,5–7
Recently, Zhang and co-workers have studied the bonding
and structures of silver–ethynide complexes incorporating
pyridyl, pyrimidyl and carboxylate groups.3i With the aim of
constructing unusual architectures, we have explored the
employment of several ligands with one or more ethynyl
groups attached to a phenyl, biphenyl, or naphthyl skeleton via
In continuation of our research program and with the aim
of constructing silver(I)–organic networks stabilized by both
silver–ethynide, silver–aromatic and argentophilic interac-
tions, we have designed two new conformational flexible
ligands, 1-phenyl-4-(prop-2-ynyloxy)benzene (HL1), and 1-phe-
noxy-4-(prop-2-ynyloxy)benzene (HL2), with one substituent
bearing terminal ethynyl group on the aromatic ring, and the
phenyl ring is potentially capable of partaking in p–p and
silver–aromatic interactions. The reaction of crude starting
materials [AgL]n with water, water–acetonitrile, methanol–
soluble silver trifluoroacetate–tetrafluoroborate generated six
new metal–organic networks, namely, [(AgL1)?(AgCF3CO2)2]n
(1),
[(AgL1)?(AgCF3CO2)5?(CH3CN)?(H2O)]n
(3), [(AgL2)?(AgCF3CO2)4]n
(2),
(4),
[(AgL1)4?(AgNO3)2]n
[(AgL2)2?(AgCF3CO2)3]n (5), and [(AgL1)?(AgCF3CO2)3?(bpy)2]n
(6), which are expected to be stabilized by silver(I)–ethynide
and argentophilic interactions.
a
flexible –CH2–O– link for the construction of MOFs
consolidated by both silver(I)–ethynide and silver(I)–aromatic
interactions. Indeed, compared to rigid organic ligands,
aThe College of Chemistry and Molecular Engineering, Zhengzhou University,
Zhengzhou 450001, People’s Republic of China. E-mail: zangsqzg@zzu.edu.cn;
Fax: +86-371-67780136
bDepartment 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
Experimental section
Materials and physical measurements
Commercially available 4-phenylphenol, 4-phenoxyphenol,
propargyl bromide (80% in toluene), and K2CO3 were used
without further purification. All synthetic reactions yielding
organic ligands and polymeric starting materials were carried
out under a nitrogen atmosphere. Elemental analysis for C, H,
Electronic supplementary information (ESI) available: Solid-state excitation
3
and emission spectra for compounds 1–6. CCDC 910770–910775. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3ce40230d
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and N were performed on a Perkin-Elmer 240 elemental
analyzer. The FT-IR spectra were recorded from KBr pellets in
the range from 4000 to 400 cm21 on a Bruker VECTOR22
spectrometer. Luminescence spectra for the solid samples
were recorded on a FluoroMax-4 fluorescence spectrophot-
ometer.
Caution! Silver ethynide complexes are highly potentially
explosive in the dry state when subjected to heating or
mechanical shock, and should be handled in small amounts
with extreme care.
Anal. calcd for C36H22Ag5F9O10: C, 32.64; H, 1.67. Found: C,
32.67; H, 1.61. IR spectrum: 2109 cm21 (w, nCMC).
Synthesis of [(AgL1)?(AgCF3CO2)3?(bpy)2]n (6). [AgL1]n (0.011
g, 0.035 mmol) was dissolved in methanol solution (1.5 mL) of
AgCF3CO2 (0.22 g, 1 mmol). To the resulting solution bpy
(0.008 g, 0.05 mmol) was added, a clear solution was obtained,
which was evaporated slowly in the air. Colorless crystals were
isolated in ca. 63% yield. Anal. calcd for C82H54Ag8F18N8O14: C,
38.17; H, 2.11; N, 4.34. Found: C, 38.11; H, 2.08; N, 4.40. IR
spectrum: 2069 cm21 (w, nCMC).
X-ray crystallographic analysis
Selected crystals were used for data collection on an OXFORD
Diffraction Gemini Single Crystal diffractometer. An empirical
absorption correction was applied using the SADABS pro-
gram.8 The structures were solved by the direct methods and
refined by full-matrix least-squares on F2 using the SHELXTL
Results and discussion
Syntheses
The neutral ligands HL1 and HL2 were synthesized according
to the literature method.10 Reaction of 4-phenylphenol and
4-phenoxyphenol, respectively, with propargyl bromide in
acetone in the presence of K2CO3 afforded 1-phenyl-4-(prop-
2-ynyloxy)benzene (HL1) and 1-phenoxy-4-(prop-2-ynyloxy)ben-
zene (HL2). Polymeric starting materials [AgL]n were prepared
according to the literature method.11 While sufficiently
crystalline materials of 1, 2, 4–6 have been obtained by slow
evaporation of crude polymeric compounds [AgL]n in a
concentrated aqueous, water–acetonitrile, or methanol solu-
tion of AgBF4/AgCF3CO2, respectively, growing crystals of 3 in a
size and quality suitable for single-crystal X-ray diffraction
required us to run precipitation under diffusion control. The
program package.9 Most of the CF3 moieties of CF3CO2
2
groups in these compounds were disordered, and the SADI
command was used to fix them in the refinements. In 6, silver
atom Ag4 is located in two disordered positions with
occupancy ratios of 0.82 : 0.18. The crystallographic data and
selected bond lengths and angles for 1–6 are listed in Tables
S1–S3, ESI.
3
Synthesis of [(AgL1)?((AgCF3CO2)2]n (1). AgCF3CO2 (0.22 g, 1
mmol) and AgBF4 (0.382 g, 2 mmol) were dissolved in 1 mL of
water. Then, [AgL1]n (0.025 g, 0.083 mmol) solid was added to
the solution. After stirring for about 1 h, the solution was
filtered. After several days, colorless block crystals of 1 were
deposited in about 60% yield. Anal. calcd for C19H11Ag3F6O5:
C, 30.15; H, 1.46. Found: C, 30.21; H, 1.54. IR spectrum: 2065
cm21 (w, nCMC).
Synthesis of [(AgL1)?(AgCF3CO2)5?(CH3CN)?(H2O)]n (2). The
procedure is similar to the synthesis of 1 except that
acetonitrile (0.2 mL) was added. After several days, colorless
needle crystals of 2 were deposited in about 55% yield. Anal.
calcd for C27H16Ag6F15NO12: C, 21.93; H, 1.09; N, 0.95. Found:
C, 21.87; H, 1.14; N, 1.02. IR spectrum: 2069 cm21 (w, nCMC).
Synthesis of [(AgL1)4?(AgNO3)2]n (3). AgNO3 (0.34 g, 2 mmol)
was dissolved in 1 mL DMSO. [AgL1]n (0.020 g, 0.066 mmol)
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. After several days,
pale yellow needle crystals of 3 were obtained in about 45%
yield. Anal. calcd for C60H44Ag6N2O10: C, 45.03; H, 2.77; N,
1.75. Found: C, 45.09; H, 2.83; N, 1.83. IR spectrum: 2066 cm21
(w, nCMC).
tetrafluoroborate ion was employed to provide
a high
concentration of silver ions, which enhanced aggregation
through argentophilicity such that the ethynide moiety is
embraced within a trigonal Ag3, butterfly-shaped Ag4 or
square-pyramidal Ag5 basket. All of the complexes 1–6 are
stable at room temperature in the solid state.
Description of crystal structures
[(AgL1)?(AgCF3CO2)2]n (1). In the crystal structure of 1, the
ethynide moiety C1 and C2 taking the m4-g1,g1,g2,g2 coordina-
tion mode lies perpendicular to the plane comprising silver
atoms Ag1#1, Ag2, and Ag3, pointing almost linearly at Ag1
(C2–C1–Ag1 177.05(5)u) to give rise to a butterfly-shaped Ag4
basket (Fig. 1). In 1, the anionic ligand L1 adopts a non-planar
conformation, in which the torsion angel C4–O1–C3–C2 is
270.01(1)u, which facilitate to the formation of silver(I)–
Synthesis of [(AgL2)?(AgCF3CO2)4]n (4). The procedure is
similar to the synthesis of 1 except that [AgL2]n (0.020 g, 0.060
mmol) was added instead of [AgL1]n. After several days,
colorless block crystals of 4 were deposited in about 65% yield.
Anal. calcd for C23H11Ag5F12O10: C, 22.74; H, 0.91. Found: C,
22.79; H, 0.99. IR spectrum: 2112 cm21 (w, nCMC).
Synthesis of [(AgL2)2?(AgCF3CO2)3]n (5). The procedure is
similar to the synthesis of 2 except that [AgL2]n (0.020 g, 0.060
mmol) was added instead of [AgL1]n. After several days,
colorless block crystals of 5 were deposited in about 60% yield.
Fig. 1 Atom labeling and coordination mode of L1 in 1 (50% thermal ellipsoids
2
are drawn for silver atoms). All hydrogen atoms and CF3 moieties of CF3CO2
are omitted for clarity. Symmetry codes: #1 2x, 2y, 2 2 z; #2 2x, y, 1.5 2 z.
Atom color codes: Ag purple, C gray, O red.
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hexagonal array are interconnected by face-to-face p–p stack-
ing interactions between adjacent phenyl rings I with the
distances of 3.686(2) Å to form a three-dimensional supramo-
lecular network (Fig. 2c).
[(AgL1)?(AgCF3CO2)5?(CH3CN)?(H2O)]n (2). The asymmetric
unit of 2 contains six crystallographically independent Ag(I)
ions, five trifluoroacetate ions, one coordinated acetonitrile
molecule, and one coordinated water molecule. In 2, there are
one independent anionic ligand L1, adopting a non-planar
conformation, in which the torsion angle C3–O1–C25–C2 is
296.47(7)u. The ethynide group composed of C1 and C2 is
capped by
a square-pyramidal Ag5 basket in the m5-
g1,g2,g2,g2,g2 coordination mode, as shown in Fig. 3.
Utilizing two m3-g1,g2 and m2-g1,g1 trifluoroacetate groups
(O2–O3 and O10–O11) as linkage components, together with
…
the argentophilic interactions (Ag3 Ag6 2.938(2) Å), the
external silver atom Ag6 is hitched to the Ag5 basket, within
which the argentophilic Ag–Ag distances vary from 2.787(2) to
3.324(2) Å, being shorter than twice the van der Waals radius
of silver ions (3.44 Å)13 and suggesting the presence of
significant argentophilic interactions. The Ag6 atom coordi-
nates to two carbon atoms (C4 and C5) of phenyl ring I in the
g2 mode with bond lengths of 2.893(8) and 2.908(7) Å (Fig. 3).
Phenyl ring II takes a m2-g1,g1 mode to coordinate to two
independent silver atoms (Ag3#1 and Ag6#1) with bonds
Fig. 2 (a) Ag6 aggregate in 1. (b) Ag6 aggregates are fused together through
two pairs of trifluoroacetate groups and argentophilic interactions to produce a
silver column in 1. (c) 3D supramolecular structure of 1 linked by face-to-face p–
2
p stacking interactions. All hydrogen atoms and CF3 moieties of CF3CO2 are
omitted for clarity. Symmetry codes: #1 2x, 2y, 2 2 z; #2 2x, y, 1.5 2 z; #3 x,
2y, 0.5 + z. Atom color codes: Ag purple, C gray, O red.
…
…
aromatic interaction. Phenyl ring I takes g1 and g2 modes to
lengths of 2.776(9) (Ag3#1 C12) and 3.026(8) Å (Ag6#1 C14),
respectively. Through such Ag–aromatic interactions, adjacent
anionic ligands sandwich multiple silver atoms to produce a
coordinate to two independent silver atoms (Ag2 and Ag3#2)
…
with bond lengths of 2.989(9)
…
ing the presence of significant Ag(I)–p interaction.12 Such
Å
(Ag2 C9), 2.498(8)
Å
…
…
…
p
Ag4 p structure, which is also consolidated by trifluoroa-
(Ag3#2 C5), and 2.690(8) Å (Ag3#2 C6), respectively, imply-
cetate groups, as shown in Fig. 4a. Although metal–organic
macrocycle has been obtained,14 the p Ag4 p sandwich unit
is still rarely constructed with flexible supramolecular syn-
thons. These moieties are further associated together through
coordination interactions between silver atoms and trifluor-
oacetate groups (O4–O5, O6–O7, O4#2–O5#2 and O6#2–O7#2),
affording a silver column with the m4-O,O9,O9,O9 and m3-
…
…
…
butterfly-shaped Ag4 baskets share one edge (Ag1 Ag1#1
3.134(8) Å) to produce a Ag6 aggregate, and further united
through two pairs of trifluoroacetate groups (O2–O3, O2#2–
O3#2, O4–O5 and O4#2–O5#2) via m3-g1,g2 and m4-g1,g3
coordination modes with the assistance of argentophilic
…
…
interactions Ag1 Ag1#2 (3.250(1) Å), Ag1 Ag2#2 (3.108(9) Å),
…
…
…
Ag3 Ag2#2 (3.268(1) Å), Ag2 Ag1#2 (3.108(9) Å), Ag2 Ag3#2
(3.268(1) Å), respectively, to form a silver column along the c
axis (Fig. 2a and b). The infinite columns arranged in a
Fig. 3 Atom labeling and coordination mode of L1 in 2 (50% thermal ellipsoids
2
…
…
are drawn for silver atoms). All hydrogen atoms and CF3 moieties of CF3CO2
Fig. 4 (a) p Ag4 p sandwich structure in 2. (b) 2D network of 2. Symmetry
codes: #1 2 2 x, 2 2 y, 2z; #2 1 2 x, 1 2 y, 1 2 z; #3 1 2 x, 2 2 y, 1 2 z. Atom
color codes: Ag purple, C gray, O red, N blue.
are omitted for clarity. Symmetry code: #1 2 2 x, 2 2 y, 2z. Atom color codes:
Ag purple, C gray, O red.
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C32, C49–O4–C48–C47 are 173.67(5)u, 174.03(6)u, 169.84(6)u,
175.39(6)u, respectively. These silver columns are further
associated together through the linkage of Ag3, Ag6, their
symmetry-related atoms to generate an infinite double chain
along the b axis. Such double chains are linked together
…
through Ag Ag interaction (Ag1–Ag5#3) to form a 2D silver
layer parallel to the ab plane with the anion ligand protruding
on both sides (Fig. 6b). Owing to the phenyl ring appended on
both sides of this silver(I) layer, there is no obvious
intermolecular interaction between layers. To the best of our
knowledge, this is the first silver layer in flexible silver–
ethynide complexes although there are several examples in
rigid ones.3b,h,i,k
Fig. 5 Atom labeling and coordination mode of L1 in 3 (50% thermal ellipsoids
are drawn for silver atoms). All hydrogen atoms are omitted for clarity.
Symmetry codes: #1 x, 1 + y, z; #2 2 x, 2 2 y, 2z; #3 1 2 x, 2 2 y, 2z; #4 21 + x,
y, z; #5 2x, 1 2 y, 2z. Atom color codes: Ag purple, C gray, O red, N blue.
[(AgL2)?(AgCF3CO2)4]n (4). The asymmetric unit of 4 con-
tains five crystallographically independent Ag(I) ions and four
trifluoroacetate ions. In the crystal structure of 4, the anionic
ligand L2 adopts a non-planar conformation, in which the C3
and O1 atoms nearly lie in the plane of the corresponding
phenyl ring, and the torsion angle C4–O1–C3–C2 is 65.34(8)u.
As shown in Fig. 7, the ethynide group (C1MC2) is enveloped by
a square-pyramidal Ag5 basket in the m5-g1,g1,g2,g2,g2 mode.
The peripheral Ag5 atom is hitched to the Ag5 basket by a pair
of m3-O,O,O9 trifluoroacetate groups (O5, O5, O6 and O9, O10,
O10). Adjacent square-pyramidal Ag5 baskets coalesce together
O,O9,O9 modes, respectively. The infinite silver columns are
also interconnected together by trifluoroacetate groups (O8–
O9 and O8#2–O9#2) to engender a two-dimensional network
via the m3-O,O9,O9 mode (Fig. 4b). There is no obvious
intermolecular interaction between layers.
[(AgL1)4?(AgNO3)2]n (3). The asymmetric unit of 3 contains
six crystallographically independent Ag(I) ions, and two
coordinated nitrate anions. As shown in Fig. 5, the ethynide
groups (C1MC2, C16MC17, C31MC32 and C46MC47) are envel-
oped by three trigonal Ag3 aggregate in the m3-g1,g2,g2
coordination modes and two butterfly-shaped Ag4 baskets in
the m4-g1,g1,g2,g2 coordination modes, respectively. Such
aggregates share Ag2 and their symmetry-related atoms to
produce an infinite silver column, as illustrated in Fig. 6a.
Different from complexes 1 and 2, there is no silver–aromatic
interaction, which is possibly due to each of four independent
L1 anions adopting a nearly planar conformation, in which the
torsion angels C4–O1–C3–C2, C19–O2–C18–C17, C35–O3–C33–
…
by sharing one edge (Ag2 Ag2#3 2.820(1) Å) to give rise to a
Ag8 aggregate, and such aggregates are further united together
through trifluoroacetate groups (O3–O4, O7–O8 and O9–O10)
and their symmetry-related atoms via m3-g1,g2 and m4-g1,g3
coordination modes, respectively, to form a silver column
along the a axis (Fig. 8a and b). Moreover, the phenyl rings I
and II of the independent anionic L2 ligand are both attached
to silver atoms though the g2 mode. The Ag4#1 atom
coordinates to two carbon atoms (C5 and C6) of phenyl ring
I with bond lengths of 2.683(7) and 2.955(8) Å. Silver atom
Ag5#4 coordinates to two carbon atoms (C13 and C14) of
phenyl ring II with bond lengths of 2.505(2) and 2.503(2) Å,
which extended the silver column to lead to the formation of a
three-dimensional supramolecular architecture along the b
and c directions (Fig. 8c).
[(AgL2)2?(AgCF3CO2)3]n (5). In the crystal structure of 5,
anionic ligand L2 also adopts a non-planar conformation, in
Fig. 7 Atom labeling and coordination mode of L2 in 4 (50% thermal ellipsoids
2
are drawn for silver atoms). All hydrogen atoms and CF3 moieties of CF3CO2
are omitted for clarity. Symmetry codes: #1 1 + x, y, z; #2 2x, 2 2 y, 1 2 z; #3 1 2
Fig. 6 (a) View of silver column in 3 along the b axis. (b) 2D network of 3 parallel
to the ab plane. Symmetry codes: #1 x, 1 + y, z; #2 2x, 2 2 y, 2z; #3 1 2 x, 2 2 y,
2z. Atom color codes: Ag purple, C gray, O red, N blue.
x, 2 2 y, 1 2 z; #4 1 + x, 3/2 2 y, 1/2 + z. Atom color codes: Ag purple, C gray, O
red.
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Fig. 10 (a) Silver column formed from Ag6 aggregates, and further consolidated
by the trifluoroacetate groups and Ag–aromatic interaction in 5. (b) 2D
structure of 5 linked by face-to-face p–p stacking interactions. All hydrogen
2
atoms and CF3 moieties of CF3CO2 are omitted for clarity. Symmetry code: #1
1/2 2 x, 21/2 + y, 1/2 2 z. Atom color codes: Ag purple, C gray, O red.
…
2.821(1) Å (Ag4 C20), respectively. Adjacent Ag3 and Ag4
baskets coalesce together by sharing one vertex (Ag2) to yield a
Ag6 aggregate, within which the argentophilic Ag–Ag distances
vary from 2.901(2) to 3.323(2) Å. Such aggregates connected
together by sharing the Ag5 and its symmetry-related atoms to
give rise to a silver column along the b axis direction, which is
further consolidated by the trifluoroacetate groups and Ag–
aromatic interaction (Fig. 10a). Finally, association of chains
through face-to-face p–p stacking interactions between adja-
cent phenyl rings with the distances of 3.732(2) Å furnishes a
2D network (Fig. 10b). There is no obvious intermolecular
interaction between layers.
Fig. 8 (a) Ag8 aggregates in 4. (b) Silver column formed from Ag8 aggregates
through sharing one edge in 4. (c) 3D supramolecular structure of 4. All
hydrogen atoms and CF3 moieties of CF3CO22 are omitted for clarity. Symmetry
codes: #1 1 + x, y, z; #2 2x, 2 2 y, 1 2 z; #3 1 2 x, 2 2 y, 1 2 z; #4 1 + x, 3/2 2 y,
1/2 + z; #5 2x, 1/2 + y, 1/2 2 z. Atom color codes: Ag purple, C gray, O red.
which the C3 and O3, C18 and O1 atoms nearly lie in the plane
of the corresponding phenyl ring, and the torsion angles C4–
O3–C3–C2 and C19–O1–C18–C17 are 77.87(2) and 60.45(2)u,
respectively. As shown in Fig. 9, the ethynide groups (C1MC2
and C16MC17) are enveloped by a trigonal Ag3 aggregate in the
m3-g1,g2,g2 coordination mode and a butterfly-shaped Ag4
basket in the m4-g1,g1,g2,g2 coordination mode, respectively.
Notably, the silver atom Ag3#2 coordinates to two carbon
atoms (C8 and C9) of phenyl ring I via the g2-mode with bond
lengths of 2.780(2) and 2.887(2) Å. Phenyl ring III takes a m2-
g1,g1 mode to coordinate two independent silver atoms (Ag2
[(AgL1)?(AgCF3CO2)3?(bpy)2]n (6). In addition, we have
carried out exploratory studies on structural control by
introducing nitrogen-donor ancillary ligands to direct the
assembly process, which led to the formation of supramole-
cular structure 6. The asymmetric unit of 6 contains four
crystallographically independent Ag(I) ions, one anionic L1
ligand, three trifluoroacetate ions and two bpy molecules. In 6,
anionic ligand L1 adopts a non-planar conformation, in which
the C3 and O1 atoms nearly lie in the plane of the phenyl ring,
and the torsion angle C4–O1–C3–C2 is 71.92(4)u. As shown in
Fig. 11, the ethynide group (C1MC2) is bound to the butterfly-
shaped Ag4 basket in the m4-g1,g1,g2,g2 coordination mode.
Two bpy molecules are associated to the Ag4 basket with Ag1
and Ag4, respectively. Such butterfly-shaped Ag4 baskets are
…
and Ag4) with bond lengths of 2.957(2) Å (Ag2 C24) and
…
…
fused by argentophilic interaction Ag3 Ag2#1, Ag2 Ag3#1
(3.091(4) Å) to yield a Ag8 aggregate, additional consolidation
being provided by two pairs of trifluoroacetate groups (O2–O3,
O2#1–O3#1, O4–O5 and O4#1–O5#1) through the m2-O,O9 and
m3-O,O9,O9 mode, respectively. Adjacent Ag8 aggregates are
…
united together through weak p p stacking (centroid–centroid
distance 4.073(3) Å) interaction to furnish a one-dimensional
chain along the c axis. Notably, the infinite chains are
…
interconnected by hydrogen bond C14#3–H14#3 F3
…
(H14#3 F3 2.589(3) Å) to yield a three-dimensional supramo-
Fig. 9 Atom labeling and coordination mode of L2 in 5 (50% thermal ellipsoids
2
lecular architecture with a hole (ca. 16.24 6 17.65 Å2), as
shown in Fig. 12b. Notably, the presence of the large voids in
this supramolecular framework facilitate the formation of
are drawn for silver atoms). All hydrogen atoms and CF3 moieties of CF3CO2
are omitted for clarity. Symmetry codes: #1 1/2 2 x, 21/2 + y, 1/2 2 z; #2 1/2 2
x, 1/2 + y, 1/2 2 z. Atom color codes: Ag purple, C gray, O red.
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Fig. 11 Atom labeling and coordination mode of L1 in 6 (50% thermal
ellipsoids are drawn for silver atoms). All hydrogen atoms and CF3 moieties of
2
CF3CO2 are omitted for clarity. Symmetry code: #1 2x, 2y + 1, 2z + 1. Atom
color codes: Ag purple, C gray, O red, N blue.
interpenetrations. The channels are filled by another identical
framework in
(Fig. 12c).
a typical 2-fold interpenetration fashion
Photoluminescence properties
Compared to gold–ethynide and copper(I)–ethynide com-
plexes, the photoluminescence properties of silver(I)–ethynide
complexes are relatively less well investigated, and their
emissions mainly originate from intraligand n A p* and p
A p* transitions.3i,4e,15 Therefore, in the present work, the
luminescent properties of the free ligands and complexes 1–6
were investigated in the solid state at room temperature (Fig.
S1–S8, ESI ). As shown in Fig. S3–S8, ESI, all of the complexes
…
Fig. 12 (a) One-dimensional chain of 6 linked by p p stacking interaction. All
2
3
3
hydrogen atoms and CF3 moieties of CF3CO2 are omitted for clarity. (b) The
in this work displayed weak luminescence in the solid state at
room temperature, and the maximum excitation and emission
chains are also further interconnected through inter-chain hydrogen bonds to
give a 3D network. (c) A space-filling view of the 2-fold interpenetration
framework. Symmetry codes: #1 2x, 2y + 1, 2z + 1; #2 2x + 1, y 2 1/2, 2z + 5/
2 for 6.
wavelengths are listed in Table S4, ESI. The emission spectra
3
of complexes 1–6 display maxima peaks at 396 nm (1), 373 nm
(2), 367 nm (3), 396, 415 nm (4), 438 nm (5), and 373 nm (6),
respectively. Complexes 1, 4, and 5 show red shifts, while
others (2, 3, and 6) show no shifts or slight blue shifts. In
Weak intermolecular interactions
…
complexes 1, 4 and 5, there are strong Ag p interactions,
In the construction of solid-state frameworks, coordinate
covalent bonding and noncovalent interactions are two well-
established essentials of crystal engineering. Indeed, the latter
one lays the foundation of an enormous family of supramo-
lecular synthons. The new metallo–ligand supramolecular
synthon R–C6H4OCH2CMC [ Agn (R = C6H5 or C6H5O, n = 3, 4,
5) offers a good opportunity to introduce silver(I)–aromatic
and p–p interactions in the construction of metal–organic
networks of variable dimensions. Silver(I)–aromatic interac-
tions provide a powerful tool for the building of novel
molecular architectures. As we reported in this work, common
…
while complexes 3 and 6 show no Ag p interactions and
…
complex 2 shows a relatively longer Ag p distance. This fact is
clear that the absorption bands of complexes 1–6 mainly
…
originate from ligand-centered excited states and Ag
interactions within the complexes.
p
Influence of solvent and neutral ligands
It should be noted that the solvent molecules affect the
coordination ability of the anionic component, and lead to the
diversity of the final structures. For example, the structural
differences of 1–3 and 4, 5 are mainly caused by changes of the
solvent. Polymeric starting material [AgL]n dissolves in a
concentrated aqueous solution of silver salts. To improve the
solubility of [AgL]n, a mixed solvent of water and acetonitrile
was used. In complex 3, we even use DMSO in place of water
and acetonitrile. When the ancillary ligand 2,29-bpy was
employed, the steric effect of the chelating 2,29-bpy is reflected
in the generation of a discrete molecular cluster, which is
further associated by the intermolecular interaction to form a
2-fold interpenetrated 3D framework in complex 6.
…
weak intermolecular interactions such as Ag p (1, 2, 4 and 5),
…
p
p (1 and 5) and hydrogen bonding (6) have been employed
as available cohesive forces in the consolidation of such
supramolecular architectures.
Conclusions
In summary, two flexible supramolecular synthons are herein
employed to construct silver(I)–organic frameworks by virtue
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Paper
Q. Zang, R. Liang, Y.-J. Wu and T. C. W. Mak,
Organometallics, 2011, 30, 1710; (k) P.-S. Cheng,
S. Marivel, S.-Q. Zang, G.-G. Gao and T. C. W. Mak, Cryst.
Growth Des., 2012, 12, 4519.
of changing the groups from phenyl ring to phenoxy group. In
the series of six complexes, the invariable appearance of the
m3-, m4- and m5-ligation modes of the ethynide moiety are
obtained. The diversities of the present structures indicate that
controlled synthesis by adjusting the silver–ethynide supra-
molecular synthons, silver salts or synthetic methods is a facile
and effective approach to the designed construction of new
supramolecular assemblies with distinct structural features.
Silver(I)–aromatic interaction was successfully introduced into
the silver–ethynide system, which play important roles in
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assembling
a
series of silver–organic frameworks.
…
…
Interestingly, it is the first example of an unusual p Ag4
p
interaction in silver–ethynide complexes. In the solid state, all
the complexes synthesized in this work are emissive at room
temperature, which mainly originates from intraligand n A p*
and p A p* transitions.
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We gratefully acknowledge financial support by the National
Natural Science Foundation of China (No. 20901070),
Zhengzhou University, and the Hong Kong Research Grants
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