Silver-organic frameworks containing ethynediide or ethynide with ancillary oligo-α-sulfanylpyrazinyl and dimethylsulfoxide ligands

Article abstract of DOI:10.1021/om400706d

Five new silver(I)-organic frameworks containing ethynediide or alkyl and aryl ethynide, together with newly designed oligo-α-sulfanylpyrazinyl ligands, namely, [(Ag₂C₂)₂(AgCF ₃COO)₁₁(L₁)(μ₂-DMSO) ₃(DMSO)₅]·¹/₄H₂O (L₁ = 2,6-bis(pyridin-2-ylthio)pyrazine, 1), [(Ag₂C ₂)₂(AgCF₃COO)₁₁(L ₂)(μ₂-DMSO)₅(DMSO)₃] ·¹/₄H₂O (L₂ = 2-(pyrazin-2-ylthio)-6-(pyridin-2-ylthio)pyrazine, 2), [(AgCi - C ^tBu)₂(AgCF₃COO)₅(L ₃)(DMSO)₃(H₂O)] (L₃ = 2,6-bis(pyrazin-2-ylthio)pyrazine, 3), [(AgCi - CPh)₄(AgCF ₃COO)₂(L₃)(DMSO)₂] ·DMSO·¹/₂H₂O (4), and [(AgCi - CC₆H₄Cl-3)₄(AgCF ₃COO)₂(L₃)(DMSO)]·H₂O (5), have been synthesized and characterized by X-ray crystallography. Isomorphous complexes 1 and 2 feature an infinite coordination chain composed of (C ₂)₂Ag₁₅ clusters alternatively linked by L ₁ or L₂ ligands; weak intermolecular C- H···F hydrogen bonding between adjacent infinite chains results in a three-dimensional supramolecular network. Complex 3 exhibits a coordination layer structure composed of (^tBuC₂) ₂Ag₇ aggregates. Compounds 4 and 5 are nearly isostructural, each possessing a ladder-like chain with a centrosymmetric (arylC₂)₈Ag₁₂ cluster as its structure building unit. With the assistance of weak intermolecular hydrogen bonds, three-dimensional and two-dimensional supramolecular architectures were generated in 4 and 5, respectively. The diverse coordination modes of oligo-α-sulfanylpyrazinyl ligands L_n (n = 1, 2, 3) account for the variable framework dimensionalities observed for 1-5. Notably, complexes 3-5 provide the first examples of extended, conformationally flexible N-donor ancillary ligands incorporated into silver alkyl and aryl ethynide systems. In addition, complexes 1-5 display ligand-based photoluminescence.

Full text of DOI:10.1021/om400706d

Article
pubs.acs.org/Organometallics
Silver−Organic Frameworks Containing Ethynediide or Ethynide with
Ancillary Oligo-α-sulfanylpyrazinyl and Dimethylsulfoxide Ligands
Li-Li Wen,†,‡ Han Wang,† Chong-Qing Wan,§ 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, Central China Normal University, Wuhan 430079, People’s Republic of China
§Department of Chemistry, Capital Normal University, Beijing 100048, People’s Republic of China
S
* Supporting Information
ABSTRACT: Five new silver(I)−organic frameworks con-
taining ethynediide or alkyl and aryl ethynide, together with
newly designed oligo-α-sulfanylpyrazinyl ligands, namely,
[ ( A g 2 C 2 ) 2 ( A g C F 3 C O O ) 1 1 ( L 1 ) ( μ 2 - D M S O ) 3 -
(DMSO)5]·1/4H2O (L1 = 2,6-bis(pyridin-2-ylthio)pyrazine, 1),
[ ( A g 2 C 2 ) 2 ( A g C F 3 C O O ) 1 1 ( L 2 ) ( μ 2 - D M S O ) 5 -
(DMSO)3]·1/4H2O (L2 = 2-(pyrazin-2-ylthio)-6-(pyridin-2-
ylthio)pyrazine, 2), [(AgCCtBu)2(AgCF3COO)5(L3)-
(DMSO)3(H2O)] (L3 = 2,6-bis(pyrazin-2-ylthio)pyrazine, 3),
[(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O
(4), and [(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]·H2O (5), have been synthesized and characterized by X-ray
crystallography. Isomorphous complexes 1 and 2 feature an infinite coordination chain composed of (C2)2Ag15 clusters
alternatively linked by L1 or L2 ligands; weak intermolecular C−H···F hydrogen bonding between adjacent infinite chains results
in a three-dimensional supramolecular network. Complex 3 exhibits a coordination layer structure composed of (tBuC2)2Ag7
aggregates. Compounds 4 and 5 are nearly isostructural, each possessing a ladder-like chain with a centrosymmetric
(arylC2)8Ag12 cluster as its structure building unit. With the assistance of weak intermolecular hydrogen bonds, three-dimensional
and two-dimensional supramolecular architectures were generated in 4 and 5, respectively. The diverse coordination modes of
oligo-α-sulfanylpyrazinyl ligands Ln (n = 1, 2, 3) account for the variable framework dimensionalities observed for 1−5. Notably,
complexes 3−5 provide the first examples of extended, conformationally flexible N-donor ancillary ligands incorporated into
silver alkyl and aryl ethynide systems. In addition, complexes 1−5 display ligand-based photoluminescence.
various ancillary ligands may induce the Agn cluster at each
ethynyl terminus to change its configuration, within which the
silver−ethynide interactions can be classified into three types:
σ, π, and mixed (σ, π).7
INTRODUCTION
■
Recent interest in the study of rational design of discrete
molecules and coordination frameworks of different dimensions
based on multinuclear silver(I)−ethynyl aggregates is spurred
by their structural diversity1,2 and potential application as
materials with desirable photoluminescent and nonlinear
optical properties.3 Over the past dozen years, our systematic
investigation on the synthesis and structural characterization of
double, triple, and quadruple salts of silver ethynediide
(Ag2C2),4 silver 1,3-butadiyne-1,4-diide (Ag2C4),5 and silver
1,5-hexadiyne-1,6-diide (Ag2C6H4)6 has resulted in successful
examples of controlling structure diversity through the
introduction of various extended bi/multidentate N-, O-, or
mixed N,O-donor ancillary ligands. In contrast to plentiful
studies employing rigid linkers such as 4,4′-bipyridine,
imidazole, cyanobenzoate, nicotinate, and pyrazinecarboxylate,
the incorporation of flexible bridging ligands into silver
ethynediide and homologous systems remains underdeveloped.
Moreover, to the best of our knowledge, hitherto no attempt to
employ conformationally flexible, multidentate N-donor ligands
for the linkage of RC2⊃Agn (n = 3−5; R = alkyl, aryl)
aggregates has been documented. Notably, fine-tuning with
The above considerations stimulated us to carry out further
studies on silver(I) complexes containing ethynediide, alkyl and
aryl ethynides, and flexible extended linkers. Accordingly, we
have designed three oligo-α-sulfanylpyrazinyl ligands, 2,6-
bis(pyridin-2-ylthio)pyrazine (L1), 2-(pyrazin-2-ylthio)-6-(pyr-
idin-2-ylthio)pyrazine (L2), and 2,6-bis(pyrazin-2-ylthio)-
pyrazine (L3), which can be viewed as one central pyrazinyl
and two pendant pyrazinyl (or one pyridyl and one pyrazinyl,
or two pyridyl) rings interlinked by two bridging sulfur atoms
(Scheme 1). Obviously, with the rotatable C(sp2)−S bonds and
the variable C(sp2)−S−C(sp2) angle (∼100°), this series of
flexible ligands can be expected to exhibit variable ligation
modes through conformational change. Employment of these
three multidentate N-donor ligands as structure-directing
components, each with its rich coordination bonding sites
Received: July 18, 2013
Published: September 9, 2013
© 2013 American Chemical Society
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molecules, forming a hydrophobic coat around the (C2)2@Ag15
core (Figure 1b). In comparison to mean Ag−O(μ2-DMSO)
distances in the range 2.329(6)−2.477(5) Å, Ag−O(η1-
DMSO) has one much shorter bond of 2.298(5) Å and one
much longer of 2.565(6) Å. In addition, the Ag15 skeleton is
also stabilized by weak intramolecular hydrogen bonds C47−
H47C···O13 (C47···O13 3.376(11) Å), C48−H48A···O13
(C48···O13 3.431(11) Å), C50−H50C···F16 (C50···F16
3.211(10) Å), and C54−H54A···F33 (C54···F33 3.067(12)
Å). The flexible L1 ligand coordinates to four silver(I) in the μ4-
N,N′,N″,N‴,S tetradentate chelating/bridging mode, further
linking adjacent Ag15 skeletons into a ribbon-like infinite chain
along the b axis, with Ag−N bond lengths of 2.326(6)−
2.518(6) Å and a Ag2−S1 bond distance of 2.671(2) Å (Figure
1c). Finally, weak CL1−H···Ocarboxylate and CL1(or DMSO)−H···F
hydrogen bonds interconnect neighboring coordination chains
to generate a three-dimensional supramolecular network
(Figure 1d).
Scheme 1
and hydrogen-bonding capacity, overrides Coulombic and
argentophilic interactions to construct diverse organo-silver(I)
architectures with interesting properties.
Herein we report the synthesis and structural character-
ization of five new silver(I)−organic complexes based on Ln (n
= 1, 2, 3) and ethynediide or ethynide: [(Ag2C2)2-
(AgCF3COO)11(L1)(μ2-DMSO)3(DMSO)5]·1/4H2O (1),
[(Ag2C2)2(AgCF3COO)11(L2)(μ2-DMSO)5(DMSO)3]·1/4H2O
(2), [(AgCCtBu)2(AgCF3COO)5(L3)(DMSO)3(H2O)] (3),
[(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O
(4), and [(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]·
H2O (5).
[(Ag2C2)2(AgCF3COO)11(L2)(μ2-DMSO)5(DMSO)3]·1/4H2O
(2). Compound 2 is isomorphous with 1, with L2 replacing L1
(Supplementary Figure S1). The corresponding atoms in this
pair of complexes have matching atomic coordinates, but two
monodentate DMSO ligands in 1 function in the bidentate
mode in 2.
[(AgCCtBu)2(AgCF3COO)5(L3)(DMSO)3(H2O)] (3).
Although silver ethynides have been effectively employed for
the construction of coordination networks,10 the introduction
of extended, conformationally flexible N-donor bridges into a
reaction system containing AgC2R (R = alkyl and aryl) to
achieve multidimensional architecture has not been reported
until now due to their poor solubility in aqueous solution.
Herein, by adding newly synthesized oligo-α-sulfanylpyrazinyl
ligand L3 into a concentrated DMSO solution containing
AgCCtBu dissolved in mixed trifluoroacetate/tetrafluorobo-
rate, compound 3 was isolated. Its crystal structure contains
two independent tert-butylethynide anions each attached to a
Ag4 basket in different coordination modes. The ethynide
moiety C1C2 acting in the μ4-η2, η1, η1, η1 coordination
mode inserts into a barblike Ag4 unit to form three σ/π-type
silver−ethynide bonds with distances in the range 2.145(7)−
2.421(6) Å and a π bond (Ag4−Ccent = 2.3152(7) Å), whereas
the other ethynide terminus, C7C8, adopts the μ4-η1, η1, η1,
η1 mode, being embraced by a butterfly-shaped Ag4 through
four Ag−C σ/π bonds with bond lengths in the range
2.148(7)−2.382(7) Å. Interestingly, ethynide C1C2 lies
perpendicular to the plane comprising silver(I) atoms Ag1, Ag3,
and Ag4, pointing almost linearly toward Ag7 at a C2−C1−Ag7
angle of 159.5(6)°. By sharing one silver atom (Ag3), two Ag4
clusters coalesce to form an irregular Ag7 aggregate (Figure 2a).
The two measured CC triple bond lengths are 1.223(10) and
1.217(11) Å, being in good agreement with the values observed
in other [AgCCtBu] complexes.
RESULTS AND DISCUSSION
■
D e s c r i p t i o n o f C r y s t a l S t r u c t u r e s .
[(Ag2C2)2(AgCF3COO)11(L1)(μ2-DMSO)3(DMSO)5]·1/4H2O (1).
In the crystal structure of 1, the building block is a (C2)2@
Ag15 aggregate composed of 15 silver(I) atoms and a pair of
encapsulated ethynediide anions. The Ag15 cluster can be
visualized as two partially opened Ag8 polyhedra (labeled A and
B) that share a common vertex, Ag5 (Figure 1a). Each of the
2−
embedded C2 species retains its triple-bond character, with a
CC bond length of 1.233(10) Å. The Ag···Ag distances
within the Ag15 aggregate range from 2.9074(8) to 3.3118(8) Å,
suggesting the existence of significant argentophilic inter-
actions.8
The ethynide species C1C2 located in cage A is stabilized
by six Ag···C σ/π bonds in the range 2.165(7)−2.384(7) Å and
two π-bonding interactions with Ag−Ccent bond lengths of
2.3786(7)−2.4878(5) Å in the μ8-η2, η1, η1, η1, η2, η1, η1, η1
mode. In cage A, the mean deviations are less than 0.0122 Å for
atoms constituting the upper square (Ag1Ag2Ag4Ag5) and
bottom triangle (Ag6Ag7Ag8), making a dihedral angle of
23.4°. Similarly, C3C4 encapsulated in cage B is stabilized by
five Ag···C σ/π bonds varying from 2.135(7) to 2.258(7) Å and
three π-bonding interactions with Ag−Ccent bond lengths of
2.3729(6)−2.4596(5) Å in the μ8-η1, η2, η1, η2, η2, η1, η1, η1
mode. In cage B, the two atom sets (Ag11Ag12Ag13Ag14) and
(Ag5Ag9Ag10) are essentially each coplanar, with mean
deviations less than 0.0148 Å, and they are nearly parallel to
each other, with a dihedral angle of 7.3°. Notably, we have
Each of four μ2-O,O′ trifluoroacetate groups bridges one
edge of the Ag7 aggregate to stabilize the cationic [Ag7(C
CtBu)2]5+ moiety. In addition, the remaining CF3COO− (O6-
containing) acts in the simple η1 mode, and three DMSO and
one aqua ligand (O12) are peripherally coordinated to silver
atoms to hold the cluster together. The Ag2−O6 distance is
2.255(5) Å, which is markedly shorter than other Ag−O bonds
(2.331(6)−2.578(6) Å) of the trifluoroacetate anions in a μ2-
O,O′ bridging mode. The Ag7 segment is further strengthened
by virtue of strong intramolecular hydrogen bonds of type
2−
reported that a pair of C2 dianions can be trapped inside an
irregular Ag15 double cage composed of a triangulated
dodecahedron and a monocapped square antiprism that share
a common edge,9 but the (C2)2@Ag15 moiety found here is
assembled in a different way.
The overall cluster skeleton is additionally coordinated by 10
μ2-O,O′ and one μ3-O,O′,O″ (O11−O12) trifluoroacetate
moieties, plus three μ2-O,O (O24, O25, and O26) bridging
and five η1-O (O23, O27, O28, O29, and O30) DMSO ligand
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Figure 1. (a) Atom labeling and coordination mode of independent ethynediide ligands encapsulated in a Ag15 double cage in complex 1. Selected
bond lengths [Å]: C1C2 1.223(10), C3C4 1.233(10), Ag···Ag 2.9074(8)−3.3118(8). (b) Neutral silver(I) cluster stabilized by trifluoroacetate
and DMSO ligands. The turquoise dotted lines represent intramolecular hydrogen bonds. (c) Ribbon-like coordinate chain along the b axis formed
by linkage of (C2)2@Ag15 units by bridging L1 ligands. (d) Three-dimensional supramolecular network with green dotted lines representing
intermolecular hydrogen bonds. All irrelevant hydrogen and fluorine atoms are omitted for clarity.
O12···O3 (2.693(11) Å) and weak ones (C6···O4 3.496(16) Å;
C28···O2 3.256(14) Å) (Figure 2b).
Å; C38···F1e 3.466(18) Å; symmetry codes: c 1−x, −y, 1−z; d
x, 1+y, z; e x, −1+y, z) consolidate the layer framework (Figure
2d).
The flexible L3 exhibits the μ5-N,N′,N″,N‴,N⁗ pentadentate-
bridging mode, further connecting the Ag7 skeleton along the a
and b axes to generate a coordination layer structure, with Ag−
N bond lengths of 2.230(6)−2.381(6) Å (Figure 2c).
Moreover, stronger intermolecular hydrogen bonds (O12···
O11a 2.823(11) Å; C16···O10b 2.962(9) Å; symmetry codes: a
2−x, 1−y, 1−z; b 1−x, 1−y, 1−z) and weaker intermolecular
hydrogen bonds (C17···O8b 3.297(9) Å; C17···O9b 3.326(9)
Å; C20···O12a 3.173(11) Å; C21···O7a 3.113(9) Å; C25···
O14c 3.100(10) Å; C28···O5d 3.343(14) Å; C37···F2e 3.38(3)
Attractive intramolecular N···C interactions (defined as the
distance between the 1-positional N atom of the central ring
and the 2-positional C atom of the terminal ring) in the range
2.866−2.907 Å are found in 3, which are well below the sum of
their van der Waals radii (3.220 Å) based on Pauling’s values
(C 1.72, N 1.50 Å).11 Apparently, the N···C affinity mainly
involves electrostatic interaction between nucleophile and
electrophile,12,13 which facilitates adoption and stabilization of
the endo−endo conformation of L3.
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t
Figure 2. (a) Coordination mode of the BuCC− ligand in 3 with atom labeling (50% thermal ellipsoids). Selected bond lengths [Å]: C1C2
1.223(10), C7C8 1.217(11), Ag···Ag 2.8504(8)−3.2429(8). (b) Neutral silver(I) cluster stabilized by surrounding ligands. The turquoise dotted
lines represent intramolecular hydrogen bonds. (c) Coordination layer almost parallel to the ab plane with H-bonding interactions omitted. (d)
Layer stacking viewed down the b axis with intermolecular hydrogen bonds denoted by green dotted lines. All irrelevant hydrogen and fluorine atoms
are omitted for clarity.
[(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O (4)
and [(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]·H2O (5).
To explore the effect of varying the R group on the structures
of silver aggregates and the resulting network, we subsequently
replaced [AgCCtBu] in 3 with [AgCCPh] and [AgC
CC6H4Cl-3], respectively, to yield nearly isostructural com-
plexes 4 (Figure 3) and 5 (Supplementary Figure S2).
In the crystal structure of 4, there are four independent
phenylethynide anions exhibiting two different coordination
modes. The ethynide moieties C1C2 and C23C24 are
each capped by a Ag3 basket in the μ3-η1, η1, η1 mode, with
Ag···C σ/π bonds in the range 2.293(7)−2.340(7) Å and
2.168(6)−2.393(7) Å, respectively, as well as a Ag3−C1 σ bond
(2.145(7) Å). The other two ethynide terminals, C15C16
and C31C32, are each bound to a butterfly-shaped Ag4
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Figure 3. (a) Atom labeling and coordination modes of the phenylethynide ligands in 4. The silver(I) and ethynide carbon atoms are drawn as 50%
thermal ellipsoids. Symmetry codes: a −x, 2−y, −z. Selected bond lengths [Å]: C1C2 1.200(10), C15C16 1.212(11), C23C24 1.202(10),
C31C32 1.206(10), Ag···Ag 2.8470(7)−3.1261(8). (b) Centrosymmetric neutral Ag12 cluster in 4. The turquoise dotted lines represent
intramolecular hydrogen bonds. Symmetry code: a −x, 2−y, −z. (c) Coordination ladder chain in the crystal structure of 4. The red dotted lines
represent π−π interactions. (d) 3D supramolecular network constructed by connecting ladder chains through hydrogen bonds (green dotted lines).
All irrelevant hydrogen and fluorine atoms are omitted for clarity. Symmetry code: b 1/2+x, 5/2−y, −1/2+z.
basket in the μ4-η1, η1, η1, η1 mode, forming three σ/π bonds
(2.409(6)−2.467(6) Å, 2.391(6)−2.583(7) Å) and a Ag···C σ
bond (2.120(7) and 2.131(7) Å, respectively) (Figure 3a). As
shown in Figure 3b, the silver atoms are united together
through an argentophilic interaction to form a Ag12 aggregate
with an inversion center located midway between Ag4 and
Ag4a, which is based on the cross-linkage of a twisted Ag6
triangular antiprism (Ag1, Ag2, Ag3, Ag4, Ag5a, and Ag6) and
its inversion-related counterpart (Ag1a, Ag2a, Ag3a, Ag4a, Ag5,
and Ag6a) by three pairs of Ag···Ag linkage (Ag4−Ag6a and
Ag4a−Ag6, Ag5−Ag6 and Ag5a−Ag6a, Ag4−Ag5 and Ag4a−
Ag5a). Apart from four trifluoroacetate moieties each spanning
a Ag···Ag edge by the μ2-O,O′ mode, there are four η1-DMSO
molecules that stabilize the Ag12 core. Additional intramolecular
hydrogen bonds (C10···O5, 3.293(12) Å; C13···O2, 3.389(18)
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Å; C14···O2, 3.300(15) Å; C38···O1, 3.204(12) Å) exist in the
Ag12 cluster.
The flexible L3 ligand functions in the μ2-N,N′,N″ bidentate-
bridging mode to form a metallacyclic structure featuring
parallel double bridges, further linking adjacent Ag12 skeletons
into a ladder chain directed along the a axis, with Ag−N
distances of 2.518(6)−2.520(6) Å (Figure 3c). Neighboring
phenyl rings of ethynide ligands arranged along the a direction
are involved in pairwise offset face-to-face π−π contacts
(intercentroid distance, 3.464 Å), which fall within the normal
range of π−π stacking interactions. Such π-type interactions
further stabilize the silver-chain structure. The silver(I)−
organic ladder chains in 4 are further interconnected by
intermolecular hydrogen bonds C34−H34···O5a (C34···O5a
3.276(10) Å) and C44−H44···S3b (C44···S3b, 3.380(9) Å) to
produce a three-dimensional supramolecular architecture
(Figure 3d).
Figure 4. Coordination modes of Ln ligands in silver ethynediide and
ethynide complexes: (a) terminal rings in exo−exo configuration in 1
and 2, (b) endo−endo in 3, (c) endo−endo in 4 and 5.
L1−L3 enables them to take diverse coordination modes in
bridging discrete Agn aggregates associated with ethynediide or
ethynide to form higher-dimensional architectures.
A notable finding is that both 4 and 5 feature ladder-chain
structures based on very similar Ag12 clusters. However, the two
complexes belong to different crystal systems, with 4
crystallizing in the monoclinic space group P21/c, whereas
Conformational Adaptability of Oligo-α-sulfanylpyr-
azinyl Ligands. In isomorphous complexes 1 and 2, the
flexible L1 ligand adopts the exo−exo configuration (see torsion
angle τ in Table 2) to exhibit a μ4-N,N′,N″,N‴,S tetradentate
chelating/bridging mode that involves all four N atoms and one
S atom of the L1 ligand (Figure 4a). The terminal heterocyclic
rings make a dihedral angle of 71.2° in 1 and 71.0° in 2; with
respect to the central pyrazinyl ring, the terminal pyridyl rings
are tilted at 76.8° and 88.9° for 1 and 78° and 89° for 2.
In complex 3, the flexible L3 ligand adopts the endo−endo
conformation to bridge five silver(I) centers (Figure 4b); the
pair of terminal pyrazinyl rings make a dihedral angle of 34.6°,
and they are tilted with respect to the central pyrazinyl ring at
89° and 55°. Unlike the case in 1, the N atom at position 1 of
the central pyrazinyl ring does not partake in coordination
bonding.
Interestingly, although L3 in both 4 and 5 also takes the
endo−endo conformation, it forms a metallacycle with both
terminal pyrazyl rings coordinated to the same silver(I) ion,
and the central pyrazyl ring only makes use of its outer N atom
to coordinate to a second silver(I) ion (Figure 4c). The
terminal pyrazinyl rings make a dihedral angle of 50.3° in 4 and
115.4° in 5. The angles between the terminal rings and the
central pyrazyl motif are ca. 71.4° and 121.3° for 4, which are
much larger than those in 5 (ca. 62.0° and 53.4°). In addition,
significant intramolecular N···C interactions are also found in 4
and 5 (Table 2). Obviously, the shorter N···C contacts
engender the smaller C(sp2)−S−C(sp2) angle for both
compounds. For example, N···C contacts of complex 4 show
the shortest distance of 2.912 Å and the smallest C(sp2)−S−
C(sp2) angle of 101.8(4)°. The variation trend is consistent
with that observed in a series of silver(I) complexes of semirigid
di-2-pyrimidyl sulfide.12
adoption of the lower triclinic space group P1 by 5 could be
̅
associated with introduction of the chloro substituent in the
phenyl ring.
For complex 5, a similar pairwise offset face-to-face π−π
interaction (intercentroid distance, 3.552 Å) was also found
between neighboring 3-chlorophenyl rings of ethynide ligands
oriented along the a axis. The ladder chains in 5 are
interconnected by intermolecular hydrogen bonds C16−
H16···Cl1b (C16···Cl1b 3.508(11) Å) and C42−H42···O5c
(C42···O5c 3.357(10) Å) to yield a two-dimensional supra-
molecular architecture (Figure S2).
Role of DMSO in Synthesis and Crystallization. In
contrast to the solubility behavior of Ag2C2, silver(I) alkyl and
aryl ethynides are sparingly soluble in a concentrated aqueous
solution of water-soluble silver(I) salts such as AgNO3 and
AgF. Hence we had to use mixed water/DMSO as a reaction
medium in this work. For example, AgC2R (∼100 mg)
dissolved completely in 1 mL of DMSO containing silver
trifluoroacetate (1 mmol)/tetrafluoroborate (2 mmol) to give a
clear solution; in contrast, Ag2C2 (∼100 mg) was only partially
soluble in 1 mL of the same mixed solution. It is noteworthy
that DMSO enhances solubility and crystallization by
functioning as a coligand for compounds 1 and 2, acting in
the unusual μ2-bridging mode with an Ag−O−Ag angle within
the expected range of 75.2(1)° to 115.3(2)°, which may be
predominantly ascribed to the more compact assembly of
silver(I) centers around each ethynediide species in the solid
state. A similar μ2-bridging fashion of DMSO has been
observed in two supramolecular silver polyoxometalate
architectures.14 In complexes 3−5, the coordinated DMSO
molecules act only as terminal ligands.
Ancillary Role of L1−L3 Ligands in Coordination
Framework Assembly. In crystalline complexes 1−5, the
series of multidentate oligo-α-sulfanylpyrazinyl ligands adopt
three distinctly different coordination modes: μ4-N,N′,N″,N‴,S
(L1 and L2 for 1 and 2, respectively), μ5-N,N′,N″,N‴,N⁗ (L3
for 3), and μ2-N,N′,N″ (L3 for both 4 and 5) (Figure 4), which
connect the multinuclear silver aggregates to form three types
of extended coordination architectures: a ribbon-like infinite
chain for complexes 1 and 2, a layer structure for complex 3,
and ladder chains for complexes 4 and 5. Apparently, the
conformational flexibility of oligo-α-sulfanylpyrazinyl ligands
For compounds 3−5, attractive intramolecular N···C
distances (2.866−3.087 Å) occur between the 1-positional N
atom of the central ring and the 2-positional C atom of the
terminal ring; such common dominant contact drives and
stabilizes the endo−endo configuration of the L3 ligand. Careful
scrutiny also reveals that the variation trend of the N···C
contacts correlates with that of the N−C−S−C torsion angles
in complexes 3−5: the shorter the N···C distance, the smaller
the N−C−S−C torsion angle observed for each complex
(Table 2). In contrast, the N···C distances in complexes 1 and 2
span from 3.288 to 3.593 Å, and accordingly ligand L1 or L2
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Table 2. Metric Parameters of Ligand Molecules L1−L3 in Complexes 1−5
a
b
c
d
complex S atom C−S−C bond angle (deg) short N···C distance (Å) dihedral angle δTT (deg) dihedral angle δCT (deg) torsion angle τ (deg)
1
2
3
4
5
S1
S2
S1
S2
S1
S2
S1
S2
S1
S2
98.7(4)
97.6(4)
98.2(3)
97.0(3)
101.0(3)
99.8(3)
101.8(4)
102.3(4)
103.3(4)
105.0(4)
71.2
76.8
88.9
78
−78.0(7)
−114.6(6)
−77.8(4)
−114.8(5)
1.6(6)
71.0
89
2.866
2.907
2.912
2.930
2.962
3.087
34.6
89
55
32.7(6)
50.3
71.4
121.3
62.0
53.4
−22.7(7)
24.8(8)
115.4
−12.4(8)
19.0(7)
a
b
Refers to the distance between the 1-positional N atom of the central ring and the 2-positional C atom of the terminal ring. δTT refers to the
c
dihedral angle between the two terminal rings. δCT refers to the dihedral angle between the central ring and the terminal ring hitched by
corresponding S atom. τ refers to the N−C−S−C torsion angle where N is the 1-positional atom of the central pyrazinyl ring, and the first and
second C atom individually belong to the central and terminal ring hitched by the corresponding S atom.
d
taking a exo−exo configuration has relatively large N−C−S−C
torsion angles (Table 2).
374, 388 nm for 5. The emissions are neither metal-to-ligand
charge transfer (MLCT) nor ligand-to-metal charge transfer
(LMCT) in nature, and they can be assigned to a combination
of the charge transfer process and intraligand emission states
(π*−n or π−π*) since very similar emissions have been
observed for the free ligands L1−L3 (Supplementary Figure S3)
and ethynediide,16 as well as alkyl and aryl ethynide.17
It is noteworthy that the variation trend of the intramolecular
N···C distances in L3 for complexes 3, 4, and 5 is also
consistent with that of the dihedral angles between two endo−
endo terminal rings (Table 2). The short N···C contact deceases
as the dihedral angle between the terminal rings decreases. For
example, complex 3 has the shortest N···C interactions of
2.866−2.907 Å and the smallest tilt angle of 34.6°.
Argentophilic Interaction and Silver−Ethynide Bond-
ing. The Agn aggregates in complexes 1−5 are stabilized by
argentophilic interactions in the range 2.8470(7)−3.3501(10)
Å. The variation in their shapes may be ascribed to diverse
silver−ethynide bonding interactions resulting from the
different μn coordination modes of the terminal CC units.
The silver−ethynide interactions in these complexes can be
broadly classified into three types, σ, π, and mixed (σ,π),
according to criteria based on the observed Ag−C bond
distances and CC−Ag bond angles.15 The measured σ, π,
and mixed (σ,π) Ag−C bond distances in complexes 1−5 are
listed in Table S2 for comparison.
SUMMARY
■
Five new silver(I)−organic frameworks containing acetylene-
d i i d e o r a l k y l a n d a r y l e t h y n i d e , n a m e l y ,
[(Ag2C2)2(AgCF3COO)11(L1)(μ2-DMSO)3(DMSO)5]·1/4H2O
(L1 = 2,6-bis(pyridin-2-ylthio)pyrazine, 1), [(Ag2C2)2-
(AgCF3COO)11(L2)(μ2-DMSO)5(DMSO)3]·1/4H2O (L2 = 2-
(pyrazin-2-ylthio)-6-(pyridin-2-ylthio)pyrazine, 2), [(AgC
CtBu)2(AgCF3COO)5(L3)(DMSO)3(H2O)] (L3 = 2,6-bis-
(pyrazin-2-ylthio)pyrazine, 3), [(AgCCPh)4 -
(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O (4), and
[(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]·H2O (5),
have been synthesized and characterized by X-ray crystallog-
raphy, elemental analysis, FT-IR spectra, and luminescence
measurement. Isomorphous complexes 1 and 2 feature a
ribbon-like infinite chain based on a composite (C2)2Ag15
cluster, while complex 3 exhibits a coordination layer structure
constructed from a (tBuC2)2Ag7 aggregate. In nearly isostruc-
tural compounds 4 and 5, a ladder-like chain is achieved with an
(arylC2)8Ag12 segment as its basic building unit. The diverse
coordination modes and flexible conformation of oligo-α-
sulfanylpyrazinyl ligands are responsible for the different
network dimensionalities manifested by 1−5, and complexes
3−5 provide the first examples of extended N-donor ancillary
ligands incorporated into silver alkyl and aryl ethynide systems.
Moreover, with the assistance of weak intermolecular hydrogen
bonds, three-dimensional supramolecular architectures are
found for 1, 2, and 4, in contrast to the two-dimensional
supramolecular networks in 3 and 5.
Fluorescence Properties. The solid-state luminescence
properties of complexes 1−5 have been investigated at room
temperature (Figure 5). Broad emission bands were observed at
373, 416, 434 nm for 1; 356, 370, 402, 425, 442 nm for 2; 362,
372, 402, 439 nm for 3; 361, 372, 407, 426 nm for 4; and 364,
EXPERIMENTAL SECTION
■
Reagents and Instruments. Reagents and solvents employed
were commercially available and used as received. Polymeric [AgC
t
CAg]n and [AgCCR]n (R = Bu, Ph, C6H4Cl-3) were prepared
according to the literature method.18 Elemental C, H, and N
microanalyses were carried out with a Perkin-Elmer 240 elemental
analyzer. IR spectra were recorded on KBr discs on a Bruker Vector 22
1
Figure 5. Fluorescent emission spectra of complexes 1−5 in the solid
state at room temperature, excited at 280 nm.
spectrophotometer in the 4000−400 cm−1 region. H and 13C NMR
spectra were measured on a 400 MHz Bruker spectrometer.
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Fluorescence measurements were recorded with a Hitachi 850
fluorescence spectrophotometer. All synthetic reactions yielding
organic ligands and polymeric starting materials were carried out
under a nitrogen atmosphere.
CAUTION! Silver−ethynediide and silver−ethynide complexes are
potentially explosive in the dry state when subjected to heating or
mechanical shock and should be handled in small quantities with extreme
care.
143.01; 144.87; 147.40; 151.53; 153.03. Anal. Calcd (%) for
C12H8N6S2: C 47.98, H 2.68, N 27.98. Found: C 47.92, H 2.69, N
27.94.
[(Ag2C2)2(AgCF3COO)11(L1)(μ2-DMSO)3(DMSO)5]·1/4H2O (1).
Moist Ag2C2 (∼100 mg) was added to 1 mL of a concentrated
DMSO solution of AgCF3COO (0.45 g, 2 mmol) and AgBF4 (0.38 g,
2 mmol) in a beaker, and the mixture was stirred until the solution
reached saturation. The excess Ag2C2 was filtered off, and 1 mL of a
concentrated DMSO solution of L1 (0.015 g, 0.05 mmol) was added.
After stirring for about 30 min, the solution was filtered. Pale yellow
crystals of 1 (∼45%) were obtained by diffusion of H2O into the
filtrate after several days. IR: ν = 1805 cm−1 (w, νCC). Anal. Calcd
(%) for C56H58.50Ag15F33N4O30.25S10 (Mr = 3837.32): C 17.53, H 1.54,
N 1.46. Found: C 17.45, H 1.71, N 1.61.
2-Mercaptopyrazine. Following a modified literature proce-
dure,19 NaHS (68−72%, 11.7 g, ca. 150 mmol) was dissolved in 50
mL of DMF, to which 2-chloropyrazine (5.727 g, 50 mmol) was
added. After refluxing for 3 h at 100 °C, DMF was removed under
vacuum. The residue was dissolved in water and then acidified with
CH3COOH to give a yellow precipitate, which was thereafter extracted
with 2 M NaOH. After removal of the insoluble material, acidification
of the filtrate gave the product as a yellow solid. Yield: 4.20 g, 85%. 1H
NMR (300 MHz, DMSO-d6): δ 7.61 (q, 1H); 7.78 (d, 1H); 8.51 (s,
1H); 14.33 (br, 1H).
2-Chloro-6-(pyrazin-2-ylthio)pyrazine. 2-Mercaptopyrazine
(2.24 g, 20 mmol) and KOH (1.24 g, 22 mmol) were added to 50
mL of acetone precooled in an ice/acetone bath. After stirring for 1 h,
a solution of 2,6-dichloropyrazine (2.98 g, 20 mmol) in 50 mL of
acetone was added dropwise. Thereafter, the mixture was allowed to
warm to room temperature, stirred for another hour, and then refluxed
overnight. Rotary evaporation gave a yellow residue, which was then
redissolved in 50 mL of CH2Cl2, washed successively with water and
brine, and dried over Na2SO4. A yellow solid was isolated by removal
of the solvent, and the product was further purified by column
chromatography on silica gel using CH2Cl2 as an eluent. Yield: 4.04 g,
90%. 1H NMR (300 MHz, CDCl3): δ 8.43 (s, 1H); 8.49 (s, 2H); 8.58
(s, 1H); 8.75 (s, 1H).
2,6-Bis(pyridin-2-ylthio)pyrazine (L1). A solution of 2,6-
dichloropyrazine (1.34 g, 9 mmol) in 25 mL of acetone was added
dropwise into a mixture of 2-mercaptopyridine (2.22 g, 20 mmol) and
KOH (1.24 g, 22 mmol) in 50 mL of acetone precooled in an ice/
acetone bath. Then the mixture was stirred for an hour in the ice/
acetone bath before being allowed to warm to room temperature and
subsequently refluxed overnight. A yellow residue was obtained by
rotary evaporation. It was then redissolved in 50 mL of CH2Cl2,
washed successively with water and brine, and dried over Na2SO4. L1
was obtained as a yellow solid by removal of the solvent, and the
product was further purified by column chromatography on Al21O3
using ethyl acetate/CH2Cl2 (1:5) as an eluent. Yield: 1.93 g, 72%. H
NMR (400 MHz, CDCl3): δ 7.18 (t, 2H); 7.44 (d, 2H); 7.59 (t, 2H);
8.40 (s, 2H); 8.50 (d, 2H). 13C NMR (100 MHz, CDCl3): δ 122.6;
126.9; 137.4; 142.5; 150.4; 154.4; 154.5. Anal. Calcd (%) for
C14H10N4S2: C 56.35, H 3.38, N 18.78. Found: C 56.30, H 3.43, N
18.72.
2-(Pyrazin-2-ylthio)-6-(pyridin-2-ylthio)pyrazine (L2). 2-Mer-
captopyridine (1.11 g, 10 mmol) and KOH (0.62 g, 11 mmol) were
added to 50 mL of acetone and stirred for 1 h in an ice/acetone bath.
Then a solution of 2-chloro-6-(pyrazin-2-ylthio)pyrazine (2.25 g, 10
mmol) in 25 mL of acetone was added dropwise. The mixture was
stirred for another hour in an ice/acetone bath and then refluxed
overnight. A yellow residue was obtained by rotary evaporation. It was
then redissolved in 30 mL of CH2Cl2, washed successively with water
and brine, and dried over Na2SO4. Solvent removal yielded L2 as a
yellow solid, which was further purified by column chromatography on
silica gel using ethanol/CH2Cl2 (1:100) as an eluent. Yield: 2.45 g,
82%. H NMR (400 MHz, CDCl3): δ 7.22 (d, 1H); 7.23 (d, 1H); 8.30
(s, 1H); 8.39 (t, 1H); 8.41 (d, 2H); 8.44 (d, 1H); 8.45 (d, 1H); 8.59
(d, 1H). 13C NMR (100 MHz, CDCl3): δ 124.89; 126.61; 140.89;
141.52; 141.96; 143.33; 144.86; 148.10; 150.13; 150.39; 150.98;
153.46; 153.90. Anal. Calcd (%) for C13H9N5S2: C 52.16, H 3.03, N
23.39. Found: C 52.11, H 3.05, N 23.35.
[(Ag2C2)2(AgCF3COO)11(L2)(μ2-DMSO)5(DMSO)3]·1/4H2O (2).
The synthetic procedure for 1 was repeated using L2 instead of L1,
and dark yellow crystals of 2 (∼30%) were isolated. IR: ν = 1806 cm−1
(w, νCC); Anal. Calcd (%) for C55H57.50Ag15F33N5O30.25S10 (Mr =
3838.31): C 17.21, H 1.51, N 1.82. Found: C 17.28, H 1.73, N 1.91.
[(AgCCtBu)2(AgCF3COO)5(L3)(DMSO)3(H2O)] (3). Moist
t
AgC2 Bu (∼100 mg) was added to 1 mL of a concentrated DMSO
solution of AgCF3COO (0.22 g, 1 mmol) and AgBF4 (0.38 g, 2 mmol)
in a beaker, and the mixture was stirred for 30 min to obtain a clear
solution. Next, 1 mL of a concentrated DMSO solution of L3 (0.015 g,
0.05 mmol) was added. After stirring for another 30 min, the mixture
was filtered. Yellow crystals of 3 (∼50%) were obtained by diffusion of
H2O into the filtrate after several days. IR: ν = 2023 cm−1 (w, νCC).
Anal. Calcd (%) for C40H46Ag7F15N6O14S5 (Mr = 2035.27): C 23.61,
H 2.28, N 4.13. Found: C 23.67, H 2.35, N 4.21.
[(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O (4).
Complex 4 was synthesized in a similar manner to 3 except that
t
AgC2Ph was used instead of AgC2 Bu. Yellow crystals of 4 were
obtained in ∼55% yield. IR: ν = 2002 cm−1 (s, νCC). Anal. Calcd (%)
for C212H172Ag24F24N24O28S18 (Mr = 7125.89): C 35.73, H 2.43, N
4.72. Found: C 35.80, H 2.54, N 4.76.
[(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]·H2O (5). Com-
plex 5 was synthesized in a similar manner to 4 except that
AgC2PhCl-3 was used instead of AgC2Ph. Yellow crystals of 5 were
obtained in ∼55% yield. IR: ν = 2027 cm−1 (m, νCC). Anal. Calcd
(%) for C50H30Ag6Cl4F6N6O6S3 (Mr = 1810.03): C 33.18, H 1.67, N
4.64. Found: C 33.21, H 1.78, N 4.70.
Single-Crystal Structure Determination. Crystal data were
collected on a Bruker Smart Apex II CCD diffractometer with Mo Kα
radiation (λ = 0.71073 Å) at 173(2) K. The intensities were corrected
for Lorentz and polarization factors, as well as for absorption by the
multiscan method.20 The structures were solved by the direct method
and refined by full-matrix least-squares fitting on F2 using the SHELX-
97 program,21 and all non-hydrogen atoms were refined with
anisotropic thermal parameters. For complex 2, the terminal pyridyl
and pyrazinyl rings of ligand L2 were indistinguishable, and the
corresponding pair of C and N atoms opposite to the coordinated N
atoms were each refined as (C+N)/2. For 3, a trifluoroacetate group
exhibits orientational disorder, and the fluorine atoms (F4, F5, F6, F4′,
F5′, F6′) were each refined with half site-occupancy. For 4, a
disordered trifluoroacetate group is handled in a similar manner. The
phenyl ring (C17−C18−C19−C20−C21−C22) is disordered at two
positions with a ratio of 0.5:0.5. The free oxygen atom O1W is
disordered with an assigned site-occupancy ratio of 0.5, and its
hydrogen atoms were not located. For 5, the H atoms of the free water
molecule (O6) could not be located.
ASSOCIATED CONTENT
■
S
* Supporting Information
2,6-Bis(pyrazin-2-ylthio)pyrazine (L3). L3 was synthesized in the
form of a yellow solid following the procedure for L1, using 2-
mercaptopyrazine (2.24 g, 20 mmol) instead of 2-mercaptopyridine as
a reactant. 1H NMR (400 MHz, CDCl3): δ 8.44 (d, 2H); 8.47 (t, 2H);
8.51 (s, 2H); 8.60 (d, 2H). 13C NMR (100 MHz, CDCl3): δ 142.86;
X-ray crystallographic data and refinement parameters (Table
S1) and selected bond lengths and angles (Table S2) for
complexes 1−5, and Figures S1−S3. This material is available
free of charge via the Internet at http://pubs.acs.org.
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be those with C2C1−Ag angles less than 90°, are generally the
longest among all Ag−C bonds, whereas the remaining mixed (σ,π)-
type bonds correspond to those with C2Cl−Ag angles lying
between a right angle and 160°.
(16) Che, C.-M.; Chao, H.-Y.; Miskowski, V. M.; Li, Y.-Q.; Cheung,
K.-K. J. Am. Chem. Soc. 2001, 123, 4985−4991.
(17) Li, B.; Huang, R.-W.; Zang, S.-Q.; Mak, T. C. W. CrystEngComm
2013, 15, 4087−4093.
(18) (a) Wang, Q.-M.; Mak, T. C. W. J. Am. Chem. Soc. 2001, 123,
1501−1502. (b) Zhao, L.; Zhao, X.-L.; Mak, T. C. W. Chem.Eur. J.
2007, 13, 5927−5936.
(19) Lee, J. W.; Lee, B. Y.; Kim, N. D. Arch. Pharm. Res. 2001, 24,
16−20.
(20) CrystalClear, Version 1.3.5; Rigaku Corp.: Woodlands, TX,
1999.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tcwmak@cuhk.edu.hk.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work is support by the Hong Kong Research Grants
Council (GRF CUHK 402710) and the Wei Lun Foundation.
We thank The Chinese University of Hong Kong for the award
of a Postdoctoral Research Fellowship to L.-L.W. and a
Postgraduate Studentship to H.W.
(21) Sheldrick, G. M. SHELXTL, Crystallographic Software Package,
Version 5.1; Bruker-AXS: Madison, WI, 1998.
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