Article pubs.acs.org/crystal
Organosilver(I) Framework Assembly with Trifluoroacetate and Diethynyl-Functionalized Isomeric Stilbenes Sam C. K. Hau 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 S Supporting Information *
ABSTRACT: Single-crystal X-ray analysis of a series of six silver(I) trifluoroacetate complexes containing designed ligands each composed of a functionalized cis- or trans-stilbene skeleton bearing two terminal ethynyl groups at variable ring positions provided detailed information on the influence of ligand disposition and orientation, coordination preferences, and coexistence of different types of silver(I)−carbon bonding (silver−ethynide, silver−ethenyl and silver−aromatic) in the construction of a coordination network, which are consolidated by argentophilic and weak intra/ intermolecular interactions. The complex 3(Ag 2 L6)·14AgCF 3 CO 2 · [Ag 2 (CH 3 CN) 3 ](CF 3 CO 2 ) 2 ·4H 2 O·6CH 3 CN [H 2 L6 = (E)-1,2-bis(4ethynylphenyl)ethene] is the first reported example in which an ethynide terminal is bound by six silver(I) ions.
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INTRODUCTION Over the past decade, structurally diverse transition metal− ethynyl complexes1−3 have been widely employed as structure building units (SUBs) for constructing coordination polymers, which find potential application as photoluminescent materials,4 precursors of nonlinear optical materials,5 and rigid-rod molecular wires.6 Our group and others have made use of the silver(I) ethynide7 supramolecular synthon8 R−CC⊃Agn (R = alkyl, phenyl, heteroaryl, n = 3−5) as a versatile and robust SUB in the generation of various high-nuclearity clusters,3a,9,10,11a−c as well as two- and three-dimensional metal− organic frameworks (MOFs).11d−f,12. In addition, this multinuclear metal−ligand supramolecular synthon can be further combined with additional structural components such as carboxylate and ancillary ligands/anions. In a recent study, we reported new silver(I) trifluoroacetate complexes containing ligands each composed of an aromatic system functionalized with terminal and internal ethynyl groups and a vinyl substituent, yielding crystal structures involving different kinds of silver(I)−carbon bonding (silver−ethynide, silver−ethynyl, silver−ethenyl, and silver−aromatic).13 A subsequent investigation on silver(I) complexes generated with aromatic ligands bearing a terminal enediyne group showed that the well-shielded ethenyl group does not partake in silver-olefin binding.14 To extend our systematic investigation, we then turned our attention to stilbenoid compounds, which are well-known for their interesting photochemical and photophysical properties that find wide applications in materials science research.15 Three pairs of cis and trans isomers of diethynyl-functionalized stilbenes (H2L1,16 H2L2,16 H2L3, H2L4, H2L5,17 and H2L618), as shown in Scheme 1, have been employed as precursors for the generation of new MOFs © 2014 American Chemical Society
in combination with silver(I) trifluoroacetate, ancillary N-donor ligands, and cocrystallized solvent molecules. Herein we report our synthetic and structural studies of a series of six new silver−organic complexes: 2(Ag2L1)· 7AgCF3CO2·3CH3CN (1), 2(Ag2L2)·13AgCF3CO2·6H2O·1.5(4,4′-bpy) (2), (Ag2L3)·5AgCF3CO2·2H2O·CH3CN (3), (Ag2L4)·5AgCF3CO2·CH3CN·CH3OH·H2O (4), 2(Ag2L5)· 12.5AgCF3CO2·10H2O (5), and 3(Ag2L6)·14AgCF3CO2· [Ag2(CH3CN)3](CF3CO2)2·4H2O·6CH3CN (6). On the basis of our previous experience, we anticipated that the reaction of crude polymeric starting materials [Ag2L1]n (7), [Ag2L2]n (8), [Ag2L3]n (9), [Ag2L4]n (10), [Ag2L5]n (11), and [Ag2L6]n (12) with water-soluble silver salts would generate new MOFs consolidated by argentophilic and multinuclear silver(I)−ethynide bonding.11,13,14. Furthermore, the ethenyl group and N-donor ancillary ligands are potentially capable of partaking in silver(I)−olefin and π−π stacking interactions. Unfortunately, attempts to synthesis a well-defined crystalline sample of 10 using different silver(I) salts and polar solvents were unsuccessful.
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EXPERIMENTAL SECTION X-ray Crystallography. Selected crystals were used for data collection on a Bruker AXS Kappa Apex II Duo diffractometer at 173 K using frames of oscillation range 0.3°, with 2° < θ < 28°. An empirical absorption correction was applied using the SADABS program.19 The structures were solved by the direct method and refined by full-matrix leastsquares on F2 using the SHELXTL program package.20 The Received: April 10, 2014 Published: May 14, 2014 3567
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Scheme 1. Isomeric Pairs of Diethynyl-Functionalized Stilbenes Employed for the Assembly of Organosilver(I) Frameworksa
a
The syntheses of new stilbenes H2L3 and H2L4 are described in the Supporting Information.
Table 1. Crystallographic Data and Structure Refinement Parameters of Complex 1−6a complex
1
2
3
4
5
6
structural formula fw crystal system space group a (Å) b (Å) c (Å) α (Å) β (Å) γ (Å) V (Å)3 Z ρc (g cm−3) μ (mm−1) R1b (I > 2σ) wR2c (all data) GOF
C56H29Ag11F21N3O14
C77H44Ag17F39N3O32
C30H17Ag7F15NO12
C31H16Ag7F14NO12
C61H31Ag16.5F37.5O34
C104H66Ag22F48N9O36
2553.39 triclinic P1̅ (no. 2) 12.268(3) 12.301(3) 24.005(5) 81.779(4) 80.323(4) 70.373(4) 3348.8(14) 2 2.532 3.262 0.0246 0.0631 1.066
4097.94 monoclinic C2/c (no. 15) 24.205(3) 13.968(2) 61.649(7) 90.0 96.107(2) 90.0 20725(4) 8 2.627 3.279 0.0830 0.1939 1.197
1623.54 monoclinic P21/n (no. 14) 11.782(7) 13.594(8) 25.593(2) 90.0 94.723(1) 90.0 4085.0(4) 4 2.640 3.413 0.0308 0.0763 1.069
1615.54 monoclinic C2/m (no. 12) 27.072(2) 7.057(1) 22.571(2) 90.0 104.864(1) 90.0 4168.1(5) 4 2.574 3.341 0.1712 0.4892 1.986
7600.43 triclinic P1̅ (no. 2) 16.628(2) 17.478(2) 17.901(2) 73.796(2) 89.955(2) 82.319(2) 4947.4(8) 2 2.551 3.327 0.0710 0.2238 1.058
5302.80 triclinic P1̅ (no. 2) 11.304(7) 11.849(7) 27.655(2) 80.746(1) 87.808(1) 76.235(1) 3551.0(4) 1 2.491 3.092 0.0634 0.1715 1.066
a
Space group P21/n is equivalent to standard P21/c by an axial transformation. bR1 = Σ||Fo| − |Fc||/Σ|Fo|. cwR2 = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]}1/2.
Synthesis of Silver Trifluoroacetate Complexes Incorporating Diethynyl-Functionalized Stilbenes. 2(Ag2L1)·7AgCF3CO 2·3CH3CN (1). Silver salts AgCF3 CO2 (0.440 g, 2 mmoL) and AgBF4 (0.382 g, 2 mmoL) were first dissolved in a mixed solution of acetonitrile (1 mL) and deionized water (1 mL), to which complex 7 (∼15 mg) was then added. After stirring for about 30 min, the solution was filtered and left to stand in the dark at room temperature. After several days, yellow blocklike crystals of 1 were deposited in ca. 55% yield. Anal. Calcd (%) for C56H29Ag11F21N3O14: C, 26.34; H, 1.14; N, 1.65. Found: C, 26.30; H, 1.22; N, 1.55. IR spectrum (KBr): 2023 cm−1 (νCC, w). 2(Ag2L2)·13AgCF3CO2·6H2O·1.5(4,4′-bpy) (2). The previous preparative procedure was then repeated using complex 8 as a precursor, together with the addition of 4,4′-dipyridyl as an ancillary ligand, to form yellow blocklike crystals of 2 in ca. 50% yield. Anal. Calcd (%) for C77H44Ag17F39N3O32: C, 22.57; H, 1.08; N, 1.03. Found: C, 22.50; H, 1.05; N, 1.12. IR spectrum (KBr): 2037 cm−1 (νCC, w). (Ag2L3)·5AgCF3CO2·2H2O·CH3CN (3). The preparation of colorless blocklike crystals of 3 following the procedure used for 1 gave complex 9 in ca. 70% yield. Anal. Calcd (%) for C30H17Ag7F15NO12: C, 22.19; H, 1.06; N, 0.86. Found: C,
crystallographic data and structure refinement parameters are summarized in Table 1. Synthesis of Ligands H2L1−H2L6. Compounds H2L3 and H2L4 are newly synthesized for the present study. Reaction schemes and experimental procedures in the synthesis of H2L1−H2L6 are given in the Supporting Information. Preparation of Polymeric Silver Ethynides As Synthetic Precursors. Caution: Silver ethynides are potentially explosive and should be handled in small amounts with extreme care. Ligand H2L1 (1 mmoL) was first dissolved in acetonitrile (10 mL). Silver nitrate (1 mmoL) and triethylamine (1 mmoL) were added, and the mixture was subjected to vigorous stirring for 2 h in the dark. The resulting pale yellow slurry was diluted with methanol (20 mL) and filtered by suction filtration to collect a pale yellow precipitate of polymeric [Ag2L1]n (7), which was then washed thoroughly with methanol (3 × 10 mL) and stored in wet form at −10 °C in a refrigerator. Polymeric silver complexes of H2L2−H2L6 were prepared in the same manner. IR spectrum (νCC, w): [Ag2L1]n (7) 2018 cm−1, [Ag2L2]n (8) 2032 cm−1, [Ag2L3]n (9) 2034 cm−1, [Ag2L4]n (10) 2043 cm−1, [Ag2L5]n (11) 2033 cm−1, and [Ag2L6]n (12) 2031 cm−1. 3568
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Figure 1. (a) Perspective view of coordination geometry in double salt 2(Ag2L1)·7AgCF3CO2·3CH3CN (1). The argentophilic Ag···Ag distances shown as thick rods lie in the range of 2.70−3.40 Å. Silver atoms are drawn as thermal ellipsoids (50% probability level) with atom labeling. (b) Perspective view of Ag11 segments in 1 with an inversion center lying between Ag3 and Ag3A. Symmetry code: A, 2 − x, 1 − y, −z; B, 2 − x, 1 − y, 1 − z. In this and all other figures, the hydrogen and fluorine atoms are omitted for clarity.
Figure 2. (a) Perspective view of crystal packing in 1, showing all notable offset face-to-face π−π stacking interactions. (b) Perspective view of crystal packing showing all notable C−H···F hydrogen bonds between acetonitrile ligands and trifluoroacetate groups. Symmetry codes: A, −1 + x, y, z; B, x, 1 + y, z.
22.13; H, 1.13; N, 0.94. IR spectrum (KBr): 2028 cm−1 (νCC, w). (Ag2L4)·5AgCF3CO2·CH3CN·CH3OH·H2O (4). Silver salts AgCF3CO2 (0.440 g, 2 mmoL) were first dissolved in a methanol solution (1 mL). Complex 10 (∼20 mg) was then added to the solution. After stirring for about 30 min, the solution was filtered and left to stand in the dark at room temperature. After several days, colorless crystalline blocks of complex 4 were deposited in ca. 45% yield. Complex 10 contains trace amount of acetonitrile as contaminants. Anal. Calcd (%) for C31H16Ag7F14O12N: C, 23.05; H, 1.00. Found: C, 22.96; H, 0.93. IR spectrum (KBr): 2033 cm−1 (νCC, w). 2(Ag2L5)·12.5AgCF3CO2·10H2O (5). Silver salts AgCF3CO2 (0.660 g, 3 mmoL) and AgBF4 (0.382 g, 2 mmoL) were first dissolved in a mixed solution of acetonitrile (1 mL) and deionized water (0.5 mL). Complex 11 (∼20 mg) was then added to the solution. After stirring for about 30 min, the solution was filtered and left to stand in the dark at room temperature. After several days, colorless crystalline blocks of complex 5 were deposited in ca. 55% yield. Anal. Calcd (%) for C61H31Ag16.5F37.5O35: C, 19.20; H, 0.82. Found: C, 19.32; H, 0.88. IR spectrum (KBr): 2015 cm−1 (νCC, w). 3(Ag 2 L6)·14AgCF 3 CO 2 ·[Ag 2 (CH 3 CN) 3 ](CF 3 CO 2 ) 2 ·4H 2 O· 6CH3CN (6). AgCF3CO2 (0.440 g, 2 mmoL) was first dissolved in a mixed solution of THF (1 mL) and methanol (2 mL). Complex 12 (∼11 mg) was then introduced with vigorous stirring. Then the solution was filtered and left to stand
together with a beaker containing deionized water in a desiccator. Yellow needle-shaped crystals of 6 were deposited in ca. 35% yield through water diffusion. Anal. Calcd (%) for C53H33Ag11F24N4.5O18: C, 23.90; H, 1.25; N, 2.37. Found: C, 23.58; H, 1.11; N, 2.28. IR spectrum (KBr): 2026 cm−1 (νCC, w).
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RESULTS AND DISCUSSION
Crystallization. Double salts 1−6 were obtained from room-temperature crystallization of the corresponding crude polymeric compounds [Ag2L1]n (7), [Ag2L2]n (8), [Ag2L3]n (9), [Ag2L4] (10), [Ag2L5]n (11), and [Ag2L6]n (12) in a mixed water/methanol solution of AgCF3CO2/AgBF4 (2:1). AgCF3CO2 and AgBF4 were used, respectively, to provide the auxiliary CF3CO2− ligand and increase the silver(I) ion concentration. The high concentration of silver ions and their aggregation through argentophilicity ensure that the ethynide moiety mostly achieves a high ligation number of 4 or 5 within a butterfly-shaped Ag4 or square-pyramidal Ag5 basket,21,22 as opposed to most transition-metal alkyl and aryl ethynide complexes with ligation numbers ranging from 1 to 4; such baskets can undergo fusion to give larger aggregates or be mutually connected by bridging trifluoroacetate ligands to yield higher-dimensional MOFs.21 3569
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Figure 3. (a) Perspective view of the coordination geometry in double salt 2(Ag2L2)·13AgCF3CO2·6H2O·1.5(4,4′-bpy) (2). The argentophilic Ag··· Ag distances shown as thick rods lie in the range of 2.70−3.40 Å. Silver atoms are drawn as thermal ellipsoids (50% probability level) with atom labeling. (b) Perspective view of the Ag14 segments in 2, showing all notable silver-aryl interactions to form a coordination network structure. Symmetry codes: A, −0.5 + x, −0.5 + y, z; B, −0.5 + x, 0.5 + y, z.
Figure 4. (a) Perspective view of crystal packing in 2, showing all Ag−N bonds within the network structure. (b) Perspective view of the crystal packing in 2, showing notable H-bonding between aqua ligands and trifluoroacetate groups. Symmetry codes: A, 0.5 − x, 0.5 + y, 1.5 − z; B, 0.5 + x, 2.5 − y, −0.5 + z; C, −x, y, 1.5 − z; D, 0.5 − x, 0.5 − y, 2 − z; E, 0.5 + x, −0.5 + y, z; F, 1 − x, 1 − y, 2 − z; and G, −0.5 + x, −0.5 + y, z.
X-ray Crystallographic Study. The crystal structures of complexes 1−6 have been determined by single-crystal X-ray analysis (Table 1). 2(Ag2L1)·7AgCF3CO2·3CH3CN (1). Complex 1 contains two crystallographic independent ligands L1 with four ethynide moieties that exhibit different coordination modes: C1C2 and C19C20 taking the μ4−η1,η1,η1,η2 mode, with C17 C18 and C35C36 acting in the μ4−η1,η1,η2,η2 mode (Figure 1a). Such Ag4 segments coalesce to form a Ag11 aggregate through sharing of Ag1, Ag2, Ag5, Ag8, and Ag11 atoms by argentophilic interaction with observed Ag···Ag distances ranging from 2.80(1) to 3.32(1) Å, which are comparable to those reported in a wide variety of silver double and multiple salts.22 Furthermore, ethenyl carbon atom C10 is attached to silver atoms Ag5 at a bond distance of 2.852(3) Å, while silver atom Ag11 is μ1-coordinated by ethenyl carbon atoms C28 in L1 [2.703(4) Å], which are indicative of significant silverethenyl interaction.13 Three independent acetonitrile ligands are each μ1-coordinated to different silver atoms (N1−Ag3, N2−Ag8, and N3−Ag9) (Figure S1 in the Supporting Information). With successive inversion centers located between silver atom pairs (Ag3 and Ag3A; Ag9 and Ag9B), adjacent Ag11 aggregates are interconnected by four pairs of symmetry-related trifluoroacetate groups abbreviated as O1∧O2 and O1A∧O2A; O3∧O4 and O3A∧O4A; O9∧O10 and O9B∧O10B; and O11∧O12 and O11B∧O12B, respectively, to generate an infinite silver-organic coordination chain along the c axis (Figure 1b). Such chains are further associated together by offset face-to-face π−π stacking interaction [intercentroid
distance 3.618(8) Å] to form a supramolecular layer (Figure 2a). Neighboring layers are interconnected by weak H-bonding between acetonitrile ligands and trifluoroacetate groups [C56A−H···F14, 2.62(1) Å], leading to the formation of a supramolecular network (Figure 2b). 2(Ag2L2)·13AgCF3CO2·6H2O·1.5(4,4′-bpy) (2). In the crystal structure 2, the four ethynide moieties of two crystallographic independent L2 ligands are each capsulated by a butterflyshaped Ag 4 basket via different coordination modes (μ4−η1,η1,η1,η2 for C1C2, C17C18, and C19C20 and μ4−η1,η1,η2,η2 for C35C36) (Figure 3a). The four adjacent Ag4 segments are connected together by argentophilic interaction to yield a Ag13 aggregate, with Ag14 attached to it to give a Ag14 aggregate (Figure S2a in the Supporting Information). Three exterior silver atoms (Ag16, Ag17, and Ag18) are linked to the Ag14 segment through trifluoroacetate groups and aqua ligands in different ways (Ag16 by O3∧O4, O9∧O10, and O1W via μ4−η2,η2, μ3−η1,η2, and μ2−η1,η1; Ag17 by O19∧O20 and O3W via μ3−η1,η2 and μ2−η1,η1; Ag18 by O17∧O18 and O25∧O26 via μ3−η1,η2 and μ4−η2,η2). The two independent L2 ligands are held tightly through offset face-toface π−π stacking interaction [intercentroid distances: ring I··· ring III, 3.832(3) Å; ring II···ring IV, 3.959(3) Å; and Ccent of C9C10···Ccent of C27C28, 3.867(3) Å]. The remaining aqua ligands are each μ1-coordinated to a different silver atom (O2W to Ag16 and O4W to Ag17). Adjacent Ag14 aggregates are interconnected through argentophilic interaction between symmetry-related Ag14 and Ag4A to yield a coordination layer, which is orientated parallel to the bc plane (Figure S2b of the Supporting Information). 3570
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Figure 5. (a) Perspective view of coordination geometry in double salt (Ag2L3)·5AgCF3CO2·2H2O·CH3CN (3). Silver atoms are drawn as thermal ellipsoids (50% probability level) with atom labeling. The argentophilic Ag···Ag distances shown as thick rods lie in the range of 2.70−3.40 Å. (b) Perspective view of a portion of an infinite chain, showing all notable silver−aryl interactions that generate a coordination network. Symmetry codes: A, 3 − x, 1 − y, 1 − z; B, 0.5 + x, 0.5 − y, −0.5 + z; C, 2.5 − x, 0.5 + y, 1.5 − z.
Figure 6. (a) Perspective view of crystal packing in 3, in which adjacent silver chains are interconnected through the silver−ethynide interaction to yield a coordination layer. (b) Perspective view showing all notable H bonds between aqua ligands and trifluoroacetate groups. Symmetry codes: A, 3 − x, 1 − y, 1 − z; B, 0.5 + x, 0.5 − y, −0.5 + z; C, 2.5 − x, 0.5 + y, 1.5 − z; D, −1 + x, 1 + y, z; E, 2 − x, 2 − y, 1 − z; F, −0.5 + x, 1.5 − y, −0.5 + z; G, x, 1 + y, z.
Figure 7. (a) Perspective view of the coordination geometry in silver double salt (Ag2L4)·5AgCF3CO2·CH3CN·CH3OH·H2O (4). The argentophilic Ag···Ag distances shown as thick rods lie in the range of 2.70−3.40 Å. (b) Perspective view showing the planarity of the L4 ligand and end-on view of the infinite silver chain along the b axis. Symmetry codes: A, x, −y, z; B, x, 1 − y, z; C, 0.5 − x, 0.5 − y, −z; D, 0.5 − x, −0.5 + y, −z.
Notably, silver atom Ag16 is μ2-coordinated by an edge (C23A−C24A) of the phenyl ring from an adjacent chain at a bond distance of 2.379(1) Å, while Ag17A is bound by another edge (C14B−C15B) of the phenyl ring via a μ2 coordination mode [2.340(3) Å] (Figure 3b).13 In addition, the structure is stabilized by coordination of 2,2′bipridyl nitrogen atoms (N3 and N3C) to silver atoms (Ag3
and Ag3C). Adjacent silver layers in 2 are also associated by a pair of symmetry-related 2,2′-bipyridyl ligands (N1A∧N2A and N1B∧N2B), which are coordinated to silver atoms Ag13A, Ag15A, and Ag13B, with a 2-fold axis passing through Ag15A and Ag15C (see Figure 4). Such layers are interconnected by silver atom Ag18 through two pairs of inversion-related trifluoroacetate groups (O17∧O18 and O25∧O26), and the 3571
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Figure 8. (a) Perspective view of coordination geometry in double salt 2(Ag2L5)·12.5AgCF3CO2·10H2O (5). Silver atoms are drawn as thermal ellipsoids (50% probability level) with atom labeling. The argentophilic Ag···Ag distances shown as thick rods lie in the range of 2.70−3.40 Å. (b) Perspective view of silver(I) layer in 5 from the interconnection between types I and II silver chains. Symmetry codes: A, 1 − x, 1 − y, 1 − z; B, −1 − x, 2 − y, −1 − z; C, −x, 1 − y, −z.
Figure 9. (a) Perspective view of the crystal packing in 5, showing all notable H bonds between aqua ligands and trifluoroacetate groups. (b) Perspective view of the crystal packing in 5, showing H-bonding between aqua ligands and trifluoroacetate groups between coordination layers. Symmetry codes: A, −x, 2 − y, −z; B, −1 + x, 1 + y, −1 + z; C, 1 − x, 1 − y, −z; D, 1 − x, 2 − y, −z; E, x, 1 + y, z.
partial structural information can be derived from low-quality intensity data. As illustrated in Figure 7a, both terminal ethynide group C1C2 and C17C18 are each encapsulated to a Ag5 basket via the same μ5−η1,η1,η1,η2,η2 coordination mode with a crystallographic mirror plane bisecting the whole L4 ligand. Silver atoms Ag1 and Ag3 are hitched to the Ag5 segment through argentophilic interaction to yield a Ag7 aggregate. Such Ag7 aggregates linked with adjacent symmetric units through vertex sharing of Ag1 and Ag2 to generate an infinite silver chain along the b axis (Figure 7b). 2(Ag2L5)·12.5AgCF3CO2·10H2O (5). In complex 5, there are two crystallographic independent L5 ligands, in which each ethynide moiety is capped by a square-pyramidal Ag5 basket involving different coordination modes: μ5−η1,η1,η1,η2,η2 for C1C2 and C19C20 and μ5−η1,η1,η1,η1,η2 for C17C18 and C35C36 (Figure 8a). Two adjacent Ag5 baskets holding separate ethynide moieties C1C2 and C19C20 are fused together to form a Ag8 aggregate. Adjacent Ag8 aggregates are interconnected by two pairs of inversion-related trifluoroacetate groups (O1∧O2 and O1B∧O2B; O13B∧O14B and O13 ∧O14) to form a Ag16 segment, and cross-linkage of such segments by a pair of inversion-related [Ag0.5(μ3−η1,η2-CF3CO2)3(μ1− O5W)] units, in which the Ag17 atom exhibits half-site occupancy, and trifluoroacetate groups (O5 ∧ O6 and O5A∧O6A) produce an infinite silver(I)-organic coordination chain labeled type I, as shown in Figure S3a in the Supporting Information.
network structure is consolidated by weak H-bonding between trifluoroacetate and aqua ligands [O13···O2W, 2.72(1) Å; O2W···O5WG, 2.75(1) Å; O2W···O23G, 2.75(1) Å; and O5WG···O21G, 2.84(1) Å]. As a result, a complex, closely knitted three-dimensional silver(I)-organic coordination network structure is constructed. (Ag2L3)·5AgCF3CO2·2H2O·CH3CN (3). Both terminal ethynide groups C1C2 and C17C18 are each inserted into a Ag5 basket via the same μ5−η1,η1,η1,η2,η2 coordination mode; C1C2 is surrounded by Ag1−Ag5, whereas C17C18 is surrounded by Ag6, Ag7, and symmetry-related silver atoms Ag4A, Ag5A, and Ag2B from the adjacent Ag5 basket (Figure 5a). The acetonitrile ligand (N1) is attached to the Ag6 and Ag7 atoms via the μ2-coordination mode, and the aqua ligands are coordinated to different silver atoms (O1W−Ag3 and O2W−Ag7). Adjacent Ag5 segments are interlinked through argentophilic interaction to generate an infinite silver chain along the b axis (Figure 5b). Adjacent silver(I) chains are cross-linked via silver−ethynide bonding at both terminals of L3 to yield a coordination layer (Figure 6a), and weak hydrogen bonding between aqua ligands and trifluoroacetate groups [O1WC···O10, 2.97(1) Å; O1WC···O2WD, 2.84(1) Å] then generates a three-dimensional supramolecular network (Figure 6b). (Ag2L4)·5AgCF3CO2·CH3CN·CH3OH·H2O (4). The crystal structure of complex 4 cannot be fully resolved and defined due to the scarcity of high-angle diffraction spots; nevertheless, 3572
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Figure 10. (a) Perspective view of coordination geometry in double salt 3(Ag2L6)·14AgCF3CO2·[Ag2(CH3CN)3](CF3CO2)2·4H2O·6CH3CN (6). Silver atoms are drawn as thermal ellipsoids (50% probability level) with atom labeling. The argentophilic Ag···Ag distances shown as thick rods lie in the range of 2.70−3.40 Å. (b) Perspective view of crystal packing showing all notable π−π stacking interactions. Symmetry code: A, 2 − x, −y, 2 − z; B, 3 − x, −y, 2 − z. The acetonitrile ligands are omitted for clarity.
Figure 11. (a) Perspective view of crystal packing in 6, showing all notable H bonds between aqua ligands and trifluoroacetate groups. (b) Perspective view of the crystal packing showing all notable weak C−H···F bond between acetonitrile ligands and trifluoroacetate groups between layers. Symmetry code: A, 3 − x, −y, 2 − z; B, 2 − x, −y, 2 − z; C, 2 − x, −2 − y, 3 − z. The carbon atoms of acetonitrile ligands are omitted for clarity.
groups (O1∧O2 and O5∧O6 via μ4−η1,η2 and μ4−η2,η2 coordination modes, respectively) (Figure S4 in the Supporting Information). Through edge sharing of silver atoms Ag5 and Ag6, a Ag6 segment is fused with adjacent Ag5 to form a Ag9 aggregate through argentophilic interaction. Similarly, two adjacent Ag5 aggregates are coalesced to yield another Ag8 aggregate. The two independent ligands are held tightly to each other through offset face-to-face π−π stacking interaction [intercentroid distance ring I···ring III, 4.013(2) Å]. Besides this, such supramolecular synthons coalesce with adjacent units through argentophilic interaction with Ag···Ag bond distances ranging from 2.87(1) to 3.27(1) Å to yield a pair of symmetryrelated infinite silver chains along the direction of the a axis. Consequently, a distorted ladderlike silver double chain is produced, which is further stabilized by offset π−π stacking interaction between phenyl edges [Ccent of C4−C5···Ccent of C12A−C11A, 3.914(2) Å] (Figure 10b) and additional hydrogen bonding between aqua ligands and trifluoroacetate groups [O2W···O8, 2.70(2) Å; O2W···O14, 2.87(2) Å; O1WB···O2A, 2.71(1) Å; and O1WB···O4B, 2.78(1) Å] (Figure 11a). With a 2-fold axis passing through the midpoint between peripheral silver atoms Ag12 and Ag12C, which both are with a half-site occupancy, such dinuclear species are coordinated by three acetonitriles ligands, including a 2-fold orientationally disordered N4 via μ1 mode, and generates a trigonal-planar cationic species between silver double chains (Figure S4 of the
With a 2-fold axis passing through the midpoint between Ag11 and Ag11D, also that between Ag13A and Ag13C, two pairs of symmetry-related Ag5 segments bound to ethynide C17C18 and C35C36 coalesce to form different independent Ag8 aggregates (Figure S3b of the Supporting Information). Such Ag8 segments are interconnected through argentophilic interaction between Ag10 and Ag15C to generate a Type II infinite chain (Figure S3b of the Supporting Information). Bridged by the terminal ethynide groups of L5 ligands, the silver coordination chains I and II are interwoven into a two-dimensional coordination layer (Figure 8b). As illustrated in Figure 9a, each coordination layer is further stabilized by H-bonding between aqua ligands and trifluoroacetate groups in the range of 2.68(4)−2.98(2) Å. Adjacent metal−organic layers are then bridged by additional hydrogen bonding [O5WC···O26, 2.83(3) Å] to generate a 3D supramolecular structure (Figure 9b). 3(Ag 2 L6)·14AgCF 3 CO 2 ·[Ag 2 (CH 3 CN) 3 ](CF 3 CO 2 ) 2 ·4H 2 O· 6CH3CN (6). Complex 6 contains two crystallographic independent L6 ions, one of which being located at a crystallographic inversion center (Figure 10a). The three independent terminal ethynide moieties exhibit different coordination modes: μ 6 −η 1 ,η 1 ,η 1 ,η 1 ,η 1 ,η 2 for C1C2, μ5−η1,η1,η1,η1,η2 for C17C18, and μ5−η1,η1,η1,η1,η2 for C19C20. The peripheral silver atom Ag11, which exhibits half site-occupancy, is hitched to the Ag6 aggregate by a μ1coordinated aqua ligand and two pairs of trifluoroacetate 3573
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analysis of the complexes provided detailed information on the influence of ligand disposition and orientation, coordination preferences, and coexistence of different kinds of silver(I)− carbon bonding (silver−ethynide, silver−ethenyl, and silver− aromatic) in coordination network construction, as well as the roles played by weak interactions in supramolecular assembly. In 3(Ag2L6)·14AgCF3CO2·[Ag2(CH3CN)3](CF3CO2)2·4H2O· 6CH3CN (6), six silver(I) ions are found to be bound to a terminal ethynide group, which provides the first reported example of such a high ligation number for this carbon-rich ligand.
Supporting Information). Cross-linkage of adjacent silver double chains and cationic Ag12 species through weak C− H···F interaction between acetonitrile ligands and nearby trifluoroacetate groups [C53−H···F5C, 2.65(1) Å] yields a three-dimensional supramolecular network (Figure 11b). Silver-Ethynide Linkage Modes. The series of five complexes reported herein reaffirms the general utility of the silver-ethynide supramolecular synthon R−CC⊃Agn (n = 4, 5) in the coordination network assembly. In 6, an ethynide moiety (C1C2) of ligand L6 exhibits an unusually higher μ6−η1,η1,η1,η1,η1,η2 coordination mode. Among the five complexes in this study, only 1 is found to exhibit significant silver-ethenyl binding in a μ1-coordination mode. Notable silver-aromatic (Ag···Ar) interaction exists only in complex 2, and the coordination mode is μ1−η2. Structure-Correlation Relationship. As compared to L2, the Z configuration of the ethenyl group in L1 makes it more accessible to other silver atoms for significant silver−ethenyl interaction due to less steric congestion. On the other hand, formation of a coordination layer structure in 2 is dominated by silver−aromatic and aromatic π−π stacking interactions, which are facilitated by the relatively more planar structure of L2. In 4, the ethynide terminals of L4 are fully extended, so that fusion of their Ag5 envelops generates widely separated silver chains that disfavor the formation of π−π stacking between aromatic rings, and the entire stilbenoidal carbon skeleton retains its planarity. Comparing complexes 1, 3, and 5 that are based on the positional isomers of cis-stilbene, it is noted that the location of the outstretched ethynide terminals with respect to the internal ethenyl group has a dominant effect on the possible onset of the silver−ethenyl interaction. The terminal ethynides in L3 and L5 lie far apart from the central ethenyl group, which has no proximal Agn aggregates available for the silver−ethenyl interaction. On the other hand, in complex 6, the ligation mode of a terminal ethynide of L6 can be increased to μ6, being facilitated by the aromatic π−π stacking interaction arising from its nearly planar E-configuration. Role of Weak Intermolecular Interactions and Ancillary Ligands. The coordination modes of the trifluoroacetate groups vary from the common μ2−η2 kind to the μ2−η1,η1 and μ3−η1,η2 varieties. The trifluoroacetate ligand generally plays two important roles: one type spans an edge of the Agn basket to consolidate the [AgnCC](n−1)+ cationic moiety, whereas the other type bridges adjacent Agn baskets or Ag atoms coordinated by the olefin/aromatic moieties to generate an infinite chain or a layer-type structure. Aromatic π−π stacking interaction is more likely to occur in those complexes (2 and 5) that possess a stilbene ligand skeleton in a Z conformation. Complexes 1−6 all contain solvated water, methanol, or acetonitrile molecules in their crystalline lattices. In these complexes, hydrogen bonds (C− H···F or C−H···O) between solvent molecules and trifluoroacetate groups confer extra stability to a coordination network (2 and 5) or connect the metal−organic coordination chains into a three-dimensional supramolecular network (1, 3, 4, and 6).
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ASSOCIATED CONTENT
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AUTHOR INFORMATION
S Supporting Information *
CIF files, syntheses of ligands H2L1−H2L6 and their precursors, additional figures, and 1H and 13C NMR spectra data. This material is available free of charge via the Internet at http://pubs.acs.org. CCDC 989715 (1), 989716 (2), 989717 (3), 990164 (4), 989718 (5), 989719 (6), contain the crystallographic data for this paper, which can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We gratefully acknowledge financial support by the Hong Kong Research Grants Council (GRF CUHK 402710), the Wei Lun Foundation, and the award of a Postdoctoral Research Fellowship to S. C. K. Hau by The Chinese University of Hong Kong.
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REFERENCES
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CONCLUSIONS The present work reports the synthesis and structural characterization of a series of six silver(I) trifluoroacetate complexes containing carbon-rich ligands each composed of a functionalized cis- or trans-stilbene skeleton with two terminal ethynyl groups at variable positions. Single-crystal X-ray 3574
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