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 containing ethynediide or alkyl and aryl ethynide, together with newly designed oligo-α-sulfanylpyrazinyl ligands, namely, [(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-2ylthio)pyrazine, 2), [(AgCC t Bu) 2 (AgCF 3 COO) 5 (L 3 )(DMSO)3(H2O)] (L3 = 2,6-bis(pyrazin-2-ylthio)pyrazine, 3), [(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O (4), and [(AgCCC6H4Cl-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.
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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 © 2013 American Chemical Society
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 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, 2,6bis(pyridin-2-ylthio)pyrazine (L1), 2-(pyrazin-2-ylthio)-6-(pyridin-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 5144
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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(η1DMSO) 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 μ4N,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). [(Ag 2C2)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. [(AgCC t Bu) 2 (AgCF 3 COO) 5 (L 3 )(DMSO) 3 (H 2 O)] (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 AgCCtBu dissolved in mixed trifluoroacetate/tetrafluoroborate, 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 C1C2 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, C7C8, 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 C1C2 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 CC triple bond lengths are 1.223(10) and 1.217(11) Å, being in good agreement with the values observed in other [AgCCtBu] complexes. 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− (O6containing) 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 μ2O,O′ bridging mode. The Ag7 segment is further strengthened by virtue of strong intramolecular hydrogen bonds of type
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 characterization of five new silver(I)−organic complexes based on Ln (n = 1, 2, 3) and ethynediide or ethynide: [(Ag 2 C 2 ) 2 (AgCF 3 COO) 11 (L 1 )(μ 2 -DMSO) 3 (DMSO) 5 ]· 1 / 4 H 2 O (1), [(Ag2C2)2(AgCF3COO)11(L2)(μ2-DMSO)5(DMSO)3]·1/4H2O (2), [(AgCCtBu)2(AgCF3COO)5(L3)(DMSO)3(H2O)] (3), [(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O (4), and [(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]· H2O (5).
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RESULTS AND DISCUSSION Description of Crystal Structures. [(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 embedded C22− species retains its triple-bond character, with a CC 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 interactions.8 The ethynide species C1C2 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, C3C4 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 reported that a pair of C22− 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 5145
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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]: C1C2 1.223(10), C3C4 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.
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). 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.
O12···O3 (2.693(11) Å) and weak ones (C6···O4 3.496(16) Å; C28···O2 3.256(14) Å) (Figure 2b). The flexible L3 exhibits the μ5-N,N′,N″,N‴,N⁗ pentadentatebridging 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) 5146
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Figure 2. (a) Coordination mode of the tBuCC− ligand in 3 with atom labeling (50% thermal ellipsoids). Selected bond lengths [Å]: C1C2 1.223(10), C7C8 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.
[(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O (4) and [(AgCCC6H4Cl-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 [AgCCtBu] in 3 with [AgCCPh] and [AgC CC6H4Cl-3], respectively, to yield nearly isostructural complexes 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 C1C2 and C23C24 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, C15C16 and C31C32, are each bound to a butterfly-shaped Ag4 5147
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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]: C1C2 1.200(10), C15C16 1.212(11), C23C24 1.202(10), C31C32 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) 5148
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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″ bidentatebridging 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). 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 adoption of the lower triclinic space group P1̅ 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 supramolecular 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
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. Conformational Adaptability of Oligo-α-sulfanylpyrazinyl 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 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 5149
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Table 2. Metric Parameters of Ligand Molecules L1−L3 in Complexes 1−5 complex
S atom
C−S−C bond angle (deg)
1
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)
2 3 4 5
short N···C distancea (Å)
dihedral angle δTTb (deg)
dihedral angle δCTc (deg)
torsion angle τd (deg)
71.2
76.8 88.9 78 89 89 55 71.4 121.3 62.0 53.4
−78.0(7) −114.6(6) −77.8(4) −114.8(5) 1.6(6) 32.7(6) −22.7(7) 24.8(8) −12.4(8) 19.0(7)
71.0 2.866 2.907 2.912 2.930 2.962 3.087
34.6 50.3 115.4
a Refers to the distance between the 1-positional N atom of the central ring and the 2-positional C atom of the terminal ring. bδTT refers to the dihedral angle between the two terminal rings. cδCT refers to the dihedral angle between the central ring and the terminal ring hitched by corresponding S atom. dτ 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.
taking a exo−exo configuration has relatively large N−C−S−C torsion angles (Table 2). 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 Bonding. 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 CC 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 CC−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. 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,
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
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SUMMARY Five new silver(I)−organic frameworks containing acetylenediide or alkyl and aryl ethynide, namely, [(Ag2C2)2(AgCF3COO)11(L1)(μ2-DMSO)3(DMSO)5]·1/4H2O (L 1 = 2,6-bis(pyridin-2-ylthio)pyrazine, 1), [(Ag 2 C 2 ) 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), [(AgCCPh)4(AgCF 3 COO) 2 (L 3 )(DMSO) 2 ]·DMSO· 1 / 2 H 2 O (4), and [(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]·H2O (5), have been synthesized and characterized by X-ray crystallography, 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 isostructural 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-αsulfanylpyrazinyl 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.
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EXPERIMENTAL SECTION
Reagents and Instruments. Reagents and solvents employed were commercially available and used as received. Polymeric [AgC CAg]n and [AgCCR]n (R = tBu, 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 spectrophotometer in the 4000−400 cm−1 region. 1H and 13C NMR spectra were measured on a 400 MHz Bruker spectrometer.
Figure 5. Fluorescent emission spectra of complexes 1−5 in the solid state at room temperature, excited at 280 nm. 5150
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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, νCC). 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. [(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, νCC); 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. [(AgCC tBu) 2 (AgCF3 COO) 5 (L 3 )(DMSO)3 (H 2O)] (3). Moist AgC2tBu (∼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, νCC). 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. [(AgCCPh)4(AgCF3COO)2(L3)(DMSO)2]·DMSO·1/2H2O (4). Complex 4 was synthesized in a similar manner to 3 except that AgC2Ph was used instead of AgC2tBu. Yellow crystals of 4 were obtained in ∼55% yield. IR: ν = 2002 cm−1 (s, νCC). 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. [(AgCCC6H4Cl-3)4(AgCF3COO)2(L3)(DMSO)]·H2O (5). Complex 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, νCC). 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 SHELX97 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.
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. 2-Mercaptopyrazine. Following a modified literature procedure,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 2,6dichloropyrazine (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 Al2O3 using ethyl acetate/CH2Cl2 (1:5) as an eluent. Yield: 1.93 g, 72%. 1H 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-Mercaptopyridine (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. 2,6-Bis(pyrazin-2-ylthio)pyrazine (L3). L3 was synthesized in the form of a yellow solid following the procedure for L1, using 2mercaptopyrazine (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;
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ASSOCIATED CONTENT
S Supporting Information *
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. 5151
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be those with C2C1−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 C2Cl−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. (21) Sheldrick, G. M. SHELXTL, Crystallographic Software Package, Version 5.1; Bruker-AXS: Madison, WI, 1998.
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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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.
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REFERENCES
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