Effect of Anions on the Framework Formation of Novel AgI

Effect of Anions on the Framework Formation of Novel. AgI Coordination Polymers with Angular Bridging. Ligands. Zheng Huang, Miao Du, Hai-Bin Song, an...
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Effect of Anions on the Framework Formation of Novel AgI Coordination Polymers with Angular Bridging Ligands Zheng Huang, Miao Du, Hai-Bin Song, and Xian-He Bu*

CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 1 71-78

Department of Chemistry, Nankai University, Tianjin 300071, P. R. China Received June 30, 2003;

Revised Manuscript Received September 23, 2003

ABSTRACT: Coordination networks based on the organic ligand 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (L1) or 2,5bis(3-pyridyl)-1,3,4-oxadiazole (L2) and various inorganic silver(I) salts were prepared and characterized by singlecrystal X-ray analysis. Reaction of AgPF6 or AgClO4‚H2O and L1 in CH3OH/CHCl3 medium afforded a unique twodimensional coordination polymer {[Ag(L1)](PF6)}∞ (1) or {[Ag(L1)](ClO4)}∞ (2) with (2/4,3) topology. However, with the replacement of AgPF6 or AgClO4‚H2O with AgNO3 in the above reaction, an interesting three-dimensional coordination architecture {[Ag4(L1)4(NO3)2](NO3)2}∞ (3) constructed through weak interactions between nitrate ions and two different one-dimensional motifs was obtained. Furthermore, two one-dimensional coordination chains {[AgL1](CF3SO3)}∞ (4) and {[Ag(L2)] (CF3SO3)}∞ (5), with different structural geometries, were obtained by the reactions of AgCF3SO3 with L1 and L2, respectively. The structural diversities of these complexes demonstrate that counteranions play essential roles in the construction of such supramolecular frameworks. Introduction Crystal engineering of coordination polymers has attracted great attention in recent years due to their potential as functional materials as well as their interesting compositions and topologies.1-3 Although the general and precise principles for controlling the solid structures of the target products are still needed to be classified and established, many rational synthetic strategies have been brought forward and proved significant in the approach of the design of the metal-based coordination supramolecules. The selection of proper ligands as “building blocks” is undoubtedly a key point in manipulating the network structures. For instance, 4,4′-bipyridine has been widely used to construct a broad range of solid-state supramolecular architectures.4 Other factors such as metal ions with different coordination geometry5 or radius,6 counteranions with different bulk7 or coordination ability,8 solvent,9 metal/ligand ratio,10 and even pH value11 have also been found to highly influence the structural topologies of such coordination frameworks. In our attempt to investigate the design and control of the self-assembly of organic/inorganic supramolecular architectures with flexible or rigid bridging ligands,12,13 we have initiated a synthetic program for the construction of various supramolecular complexes with interesting extended frameworks based on the angular dipyridyl ligands, 2,5-bis(3- pyridyl)-1,3,4-oxadiazole (L2) and 2,5bis(4-pyridyl)-1,3,4-oxadiazole (L3).13 The roles of anions in construction of these novel coordination polymers or supramolecules were studied in detail. As a continuation of our work, in this contribution, we selected 2,5-bis(4pyridyl)-1,3,4-thiadiazole (L1) as the building block, and four new AgI complexes with three different topologies were obtained by varying the counteranions (PF6-, ClO4-, NO3-, and CF3SO3-). Furthermore, by using a * Corresponding author. E-mail: [email protected]. +86-22-23502458. Tel: +86-22-23502809.

Fax:

3,3′-N-donor ligand, L2, which has a different arrangement of the two pyridyl N-donors from that of L1, to react with AgCF3SO3, a new coordination polymer 5 was obtained. Experimental Section Materials and General Methods. All the solvents and reagents for synthesis were commercially available and used as received. The ligand L1 was commercially available and used without further purification and the ligand L2 was synthesized according to the literature procedure.14 FT-IR spectra (KBr pellets) were taken on a FT-IR 170SX (Nicolet) spectrometer, and elemental analyses were performed on a Perkin-Elmer 240C analyzer. Syntheses of the AgI Complexes. Colorless single crystals for complexes 1-5 suitable for X-ray analysis were obtained by the similar method as described below. {[AgL1](PF6)}∞ 1. A solution of AgPF6 (25 mg, 0.1 mmol) in CH3OH (15 mL) was carefully layered on top of a CHCl3 solution (10 mL) of L1 (24 mg, 0.1 mmol) in a test tube. After ca. two weeks at room temperature, colorless single crystals appeared at the boundary between CH3OH and CHCl3. Yield: 68%. Anal. Calcd for C12H8AgF6N4PS: C, 29.23; H, 1.64; N, 11.36. Found: C, 29.45; H, 1.49; N, 11.45. IR (KBr, cm-1): 3103m, 1607s, 1449m, 1434s, 1318m, 1187vs, 1005m, 890m, 846vs, 832vs, 706s, 615m, 558s, 541m. {[AgL1](ClO4)}∞ 2. Yield: 55%. Anal. Calcd. for C12H8AgClN4O4S: C, 32.20; H, 1.80; N, 12.52. Found: C, 32.41; H, 1.58; N, 12.61. IR (KBr, cm-1): 3094w, 3078w, 1592s, 1550m, 1426vs, 1412s, 1333s, 1262m, 1222m, 1143vs, 1108vs, 1087vs, 990m, 941m, 827s, 802m, 704s, 636m, 624s, 611s, 536m. {[Ag4L14(NO3)2](NO3)2}∞ 3. Yield: 72%. Anal. Calcd for C48H32Ag4N20O12S4: C, 35.14; H, 1.97; N, 17.07. Found: C, 35.45; H, 1.75; N, 17.37. IR (KBr, cm-1): 1591w, 1427w, 1383vs, 1332w, 1218w, 1097w, 989w, 826m, 736w, 694m, 610w. {[AgL1](CF3SO3)}∞ 4. Yield: 58%. Anal. Calcd for C13H8AgF3N4O3S2: C, 31.40; H, 1.62; N, 11.27. Found: C, 31.62; H, 1.51; N, 11.35. IR (KBr pellet, cm-1): 3050w, 3032w, 1626m, 1591m, 1551m, 1439m, 1427s, 1402m, 1332m, 1252vs, 1173s, 1097m, 1035s, 990m, 826s, 820s, 694s, 647s, 610m, 579m, 520m, 496m. {[AgL2](CF3SO3)}∞ 5. Yield: 63%. Anal. Calcd for C13H8AgF3N4O4S1: C, 32.45; H, 1.68; N, 11.64. Found: C, 32.70; H,

10.1021/cg0341095 CCC: $27.50 © 2004 American Chemical Society Published on Web 11/05/2003

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Table 1. Crystallographic Data and Structure Refinement Summary for Complexes 1-5 formula Mr crystal size/mm crystal system space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 D/g cm-3 Z T/K µ/mm-1 F(000) reflns collected unique reflns (Rint) parameters goodness of fit R1 [I >2σ(I)] wR2 (all data) max diff peak/e Å-3

1

2

3

4

5

C12H8AgF6N4PS 493.12 0.20 × 0.16 × 0.14 monoclinic P2(1)/c 6.7682(19) 27.871(8) 8.581(3) 90 98.400(6) 90 1601.4(8) 2.045 4 293(2) 1.557 960 6617 3218 226 1.069 0.0449 0.0918 0.358

C12H8AgCl N4O4S 447.60 0.26 × 0.22 × 0.18 monoclinic P2(1)/c 6.920(3) 28.322(14) 7.779(4) 90 102.234(8) 90 1489.9(13) 1.995 4 293(2) 1.697 880 6971 3057 237 0.998 0.0468 0.0972 0.718

C48H32Ag4N20O12S4 1640.66 0.24 × 0.20 × 0.18 triclinic P1 h 14.4598(2) 15.01760(10) 15.0598(2) 70.8670(10) 64.2750(10) 76.4070(10) 2766.81(6) 1.969 2 293(2) 1.628 1616 14421 9659 793 1.182 0.0564 0.1571 0.796

C13H8AgF3N4O3S2 497.22 0.24 × 0.18 × 0.12 triclinic P1 h 6.4369(19) 11.095(3) 11.422(3) 81.590(5) 88.922(5) 83.274(5) 801.4(4) 2.061 2 293(2) 1.574 488 4680 3246 238 1.087 0.0331 0.0888 0.375

C13H8 AgF3N4O4S 481.16 0.20 × 0.10 × 0.08 monoclinic P2(1)/c 5.536(4)) 16.555(8) 16.677(8) 90 95.475(13) 90 1521.6(15) 2.100 4 293(2) 1.527 944 8557 3108 235 1.014 0.0546 0.0919 0.477

1.44; N, 11.62. IR (KBr pellet, cm-1): 3062w, 2924w, 1629m, 1600m, 1558m, 1483m, 1464m, 1435m, 1337w, 1259vs, 1231s, 1194s, 1081m, 1034s, 962m, 811m, 729m, 696m, 646s, 578m, 519m. CAUTION! Perchlorate complexes of metal ions in the presence of organic ligands are potentially explosive. Only a small amount of material should be handled with care. X-ray Crystallography. Single-crystal X-ray diffraction measurements were carried out on a Bruker Smart 1000 CCD diffractometer equipped with a graphite crystal monochromator situated in the incident beam for data collection at room temperature. The determination of unit cell parameters and data collections were performed with Mo-KR radiation (λ ) 0.71073 Å). The program SAINT15 was used for integration of the diffraction profiles. All the structures were solved by direct methods using the SHELXS program of the SHELXTL package and refined with SHELXL (semiempirical absorption corrections were applied using SADABS program).16 Silver atoms in each complex were located from E-maps. The other non-hydrogen atoms were located in successive difference Fourier syntheses. The final refinement was performed by full matrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on F2. The hydrogen atoms were added theoretically and riding on the concerned atoms. Crystallographic data and experimental details for structural analyses are summarized in Table 1. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-211198 for 1, 211201 for 2, 211200 for 3, 211199 for 4, 211202 for 5. Copy of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: int. code +44(1223)336-033; E-mail: [email protected]].

Results and Discussion Preparation of Complexes 1-5. Both ligands L1 and L2 are very soluble in common polar organic solvents (such as CH2Cl2, CHCl3, CH3OH, and CH3CN), so that crystallization of their complexes with inorganic metal salts occurs readily. Complexes 1-5 were obtained as crystalline polymeric compounds in CH3OH/ CHCl3 mixed solvent system by combination of the corresponding ligand with different silver(I) salts through diffusion in satisfied yields (∼50-70%). In these specific reactions, the products do not depend on the ligand-to-

metal ratio. However, increasing the ligand-to-metal ratio resulted in somewhat higher yield and better crystal quality. Compounds 1-5 are air stable and can retain their structural integrity at room temperature for a considerable length of time. Description of Crystal Structures. {[AgL1](PF6)}∞ 1 and {[AgL1](ClO4)}∞ 2. The X-ray crystal structures of the silver(I) hexafluorophosphate salt 1 and perchlorate salt 2 of the ligand L1 show that they are isomorphous. Thus, here all figures concerning these two complexes are based on the crystal structure of complex 1. The polymeric structure of 1 has a unique noninterpenetrating two-dimensional (2/4,3) network containing three-coordinated AgI nodes. Each AgI center coordinates to two pyridyl N atoms and one thiadiazole N atom from three distinct ligands (Figure 1a). Two AgNpyridyl bond distances are equal (2.237(4) Å) and the Ag-Nthiadizole bond distance is 2.296(4) Å. The sum of bond angles around each AgI center [N(4)-Ag(1)-N(1) ) 127.36(15)°, N(1)-Ag(1)-N(2) ) 118.95(13)° and N(2)-Ag(1)-N(4) ) 113.67(14)°] is ca. 360°, indicating a slightly distorted trigonal planar coordination environment (see Table 2). In 1, each L1 ligand bridges three adjacent AgI centers in tridentate coordination fashion to generate a noninterpenetrating two-dimensional (2-D) network consisting of two types of metallacyclic grids (A and B) with different sizes. Two AgI centers are linked by one L1 using two pyridyl N atoms to form the longer edge of a parallelogram, the larger A grid, and its shorter edge is formed by another ligand using one pyridyl N atom and one thiadiazole N atom which simultaneously acts as the linked donor in the neighboring B grid to coordinate to two AgI centers. Thus, a centrosymmetric 40-membered tetrameric unit is constructed in which two pairs of ligand-bridged Ag‚‚‚Ag distances are 10.293 and 15.144 Å, respectively. In B grid, two L1 jointly coordinate to two AgI centers by using one pyridyl N atom and one thiadiazole N atom of each ligand to form a 14-membered dimeric unit. The distance between the two parallel pyridyl rings from two distinct ligands in

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Figure 1. For complex 1 (isostructural to 2): (a) ORTEP structure with 30% thermal ellipsoid probability. PF6- anions and hydrogen atoms are omitted for clarity. (b) 2-D (2/4,3) network including the inclusive anions. Hydrogen atoms are omitted for clarity. (c) Stacking diagram showing the channel cavities along the a direction. PF6- anions and hydrogen atoms are omitted for clarity.

this unit is ca. 3.22 Å (center-to-center separation ) 3.847 Å), suggesting the presence of significant edgeto-edge π-π stacking interaction,17 which presumably contributes to stabilizing the structure as depicted in Figure 1b. The Ag‚‚‚Ag nonbonding distance in grid B is 7.019 Å. The most striking feature of this structure is the formation of an unprecedented three-connected 2-D (2/4,3) net in which the “shortest circuits” formed around each connecting node are 2-gons and 4-gons. Two 4-gons and one 2-gons are adopted around each AgI node. On the other hand, if we regard each dimeric unit

(B grid) as one connecting node, this structure would be a (4,4) sheet. Another interesting point of complex 1 resides in the formation of a quasi-3-D network through interlayered π-π stacking interactions. The pyridyl rings which are constituent parts of dimeric units (B grid) are involved in the interlayer aromatic ring stacking with the closest separation of ca. 3.37 Å (center-to-center separation ) 3.566 Å). Therefore, the 2-D layers stack parallel along the a direction to form an open porous framework with rhombic channels (Figure 1c). The PF6- ions are filled

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Table 2. Selected Bond Lengths (Å) and Angles (°) for Complexes 1-5a (1) Ag(1)-N(4A) Ag(1)-N(2B) N(4A)-Ag(1)-N(1) N(1)-Ag(1)-N(2B) (2) Ag(1)-N(4A) Ag(1)-N(2B) N(4A)-Ag(1)-N(1) N(1)-Ag(1)-N(2B) (3) Ag(1)-N(2) Ag(1)-O(1) Ag(2)-N(6) Ag(3)-N(12) Ag(3)-O(5) Ag(4)-N(16) N(2)-Ag(1)-N(5) N(5)-Ag(1)-O(1) N(7)-Ag(2)-O(4) N(12)-Ag(3)-N(11) N(11)-Ag(3)-O(5) (4) Ag(1)-N(1) Ag(1)-N(1)-C(1) Ag(2)-N(4)-C(8) (5) Ag(1)-N(4A) N(4A)-Ag(1)-N(1)

2.237(4) 2.296(4) 127.36(15) 118.95(13)

Ag(1)-N(1)

2.239(4) 2.331(4) 131.50(17) 117.03(15)

Ag(1)-N(1)

2.179(2) 2.583(4) 2.204(3) 2.218(2) 2.515(2) 2.177(3) 160.04(10) 92.76(12) 87.94(12) 153.23(9) 85.03(10)

Ag(1)-N(5) Ag(2)-N(7) Ag(2)-O(4) Ag(3)-N(11) Ag(4)-N(15) N(2)-Ag(1)-O(1) N(7)-Ag(2)-N(6) N(6)-Ag(2)-O(4) N(12)-Ag(3)-O(5) N(15)-Ag(4)-N(16)

106.61(12) 158.16(9) 111.47(12) 115.33(10) 164.21(11)

2.162(3) 115.0(3) 119.6(3)

Ag(2)-N(4) Ag(1)-N(1)-C(5) Ag(2)-N(4)-C(12)

2.151(3) 128.0(2) 122.6(2)

2.157(4) 171.14(18)

Ag(1)-N(1)

N(4A)-Ag(1)-N(2B)

N(4A)-Ag(1)-N(2B)

2.237(4) 113.67(14) 2.247(4) 11.24(15) 2.187(3) 2.199(2) 2.494(4) 2.219(3) 2.173(2)

2.163(4)

a Symmetry codes: for 1: (A) -x + 1, y - 1/2, -z + 3/2; (B) -x, -y + 1, -z + 1; for 2: (A) -x, y + 1/2, -z + 3/2; (B) -x + 1, -y + 1, -z + 2; for 5: (A) -x - 1, y - 1/2, -z + 1/2.

in the cavities of the network and coordinate weakly to AgI ions (the Ag‚‚‚F separation is 2.910 Å). They probably act as templates for the formation of the network and consequently further stabilize this structure. As indicated above, the structure of 2 is similar to that of 1 except that the ClO4- ions replace PF6- ions to be included in the cavities. The ClO4- ions have weak interactions with AgI centers (the Ag‚‚‚O separation is 2.701 Å), and may also serve as templates for the formation of the network. {[Ag4L14(NO3)2](NO3)2}∞ 3. The structure of 3 is a more complicated and interesting framework consisting of stacks of two different 1-D coordination motifs. We define them as units A and B, respectively. In 3, each ligand takes bidentate coordination fashion and links two AgI centers with two pyridyl N atoms to form a nearly linear chain, which is the basal element of both units A and B. Unit A is made up of two antiparallel and equivalent 1-D ladders, each of which contains a pair of linked linear chains (Figure 2a). In these ladder chains, nitrate ions exist in two coordination modes. The nitrate ions taking the first coordination mode bridge AgI centers [Ag(2) and Ag(3)] from the pair of chains in bidentate coordination fashion to give the molecular ladder structure with rectangular cavities, in which the separation of Ag‚‚‚Ag across the nitrate ion is 6.675 Å and L1 is 15.060 Å. Thus, both AgI centers from the pair of chains have distorted trigonal planar geometries, each of which is comprised of two pyridyl N atoms and one anionic O atom. The three angles around the metal center are 158.16(9), 87.94(12), and 111.47(12)° for Ag(2), and 153.23(9), 115.33(10), and 85.03(10)° for the Ag(3) center. The Ag(2) and Ag(3) centers deviate from their corresponding coordination planes by 0.1647 and 0.2883 Å, respectively. All of the silver-donor bond

distances (see Table 2) are comparable with those of analogous complexes.18 The nitrate ions of the second coordination mode are located in the cavities of the ladder and have weak interactions with thiadiazole S atoms [S(3)‚‚‚N(19) ) 3.224 Å, S(2)‚‚‚N(19) ) 3.295 Å]. Interestingly, this type of nitrate ion also acts as bridges to link two antiparallel and equivalent ladders through weak interaction between one O atom of each anion located in one ladder and the Ag(3) center located in the other ladder (Ag-O ) 2.790 Å). Thus, two equivalent 1-D ladders are ligated together to form a doubleladder structure of unit A, in which the two ladders are related by an inversion center and have an offset by a half step with each other along the direction at which these ladders propagate. On the other hand, the structure of unit B is similar to that of unit A. There are also two coordination modes of nitrate ions and two different central AgI centers [Ag(1) and Ag(4)] (see Figure 2b). The differences between the two units (A and B) are illustrated as the following: (1) The first type of nitrate ion in unit B bridges two parallel linear chains through coordinating to AgI centers in one chain [O(1)-Ag(1) ) 2.583(4) Å], and weakly coordinating to AgI centers in the other chain [O(2)‚‚‚Ag(4) ) 2.742 Å] to form a ladder (the Ag‚‚‚Ag distance across nitrate ion is 6.724 and L1 is 15.018 Å); thus, the Ag(1) center has a distorted trigonal planar geometry comprised of two pyridyl N atoms and one anionic O atom. Two N-Ag-O and one N-Ag-N bond angles are 106.61(12), 92.76(12), and 160.04(10)°, respectively. The Ag(1) center deviates from the coordination plane by 0.0791 Å. The Ag(4) center is in a nearly linear coordination environment with two pyridyl N atoms with the N-Ag-N angle of 164.21(11)°. All of the silver-donor bond distances about Ag(1) and Ag(4) centers agree with the analogous complexes.18 (2) The second type of nitrate ion is located in the cavities of the ladder and exist as weak interactions with thiadiazole S atoms through one N and two O atoms (only through the N atom in unit A) [N(20)-S(4) ) 3.181 Å, O(8)-S(1) ) 3.285 Å, O(9)-S(1) ) 3.318 Å] as depicted in Figure 2b. (3) The O(1) atom of each nitrate ion of the first type located in one ladder weakly coordinates to the Ag(1) center located in the other ladder with a distance of 2.671 Å. Hence, different from unit A, two antiparallel ladders herein are linked by the first type of nitrate ion (by the second type of nitrate ion in unit A) to form a double-ladder structure, in which two ladders have no offset with each other along the direction at which these ladders propagate. As described above, the first type of nitrate ion in unit B plays an important role in construction of both the ladder and the double-ladder structures. However, the role of the second type of nitrate ion in unit B should not to be ignored because they contribute greatly to the linkage of units A and B, forming a 3-D supramolecular framework. As shown in Figure 2c, two O atoms [O(7) and O(9)] of each nitrate ion of this type coordinate weakly to the Ag(2) center in unit A, with the bond distances of 2.734 and 2.910 Å, respectively. In addition, one O(10) atom of each nitrate ion of the first type in unit A also weakly coordinates to the Ag(4) center in unit B with the Ag‚‚‚O separation of 2.977Å. All these

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Figure 2. For complex 3: (a) View of the molecular ladder in unit A. (b) View of the molecular ladder in unit B. (c) Unit A and unit B intercrossed by each other. Hydrogen atoms are omitted for clarity.

Ag‚‚‚O contacts link two types of neighboring ladders (from units A and B, respectively). {[AgL1](CF3SO3)}∞ 4. The structure of 4 consists of 1-D cationic chains and triflate counterions. There are two AgI centers [Ag(1) and Ag(2)] in the asymmetric unit. Each AgI center is in a linear coordination environment and binds to two pyridyl N atoms [Ag(1)-N(1) ) 2.162(3) Å, Ag(2)-N(4) ) 2.151(3) Å] from two ligands. In 4, each ligand links two AgI centers in bidentate bridging mode with two pyridyl N donors to form an infinite chain. The angle between the central thiadiazole ring and two N donors of the 4-pyridyl ring in the ligand molecule is 155.3°, resulting in a sinusoidal chain motif. The separation of the ligand-bridging Ag‚‚‚Ag contact is 14.795 Å. Of further interest, these

infinite chains are arranged in a parallel fashion, where the ligand molecules are relatively shifted to each other so that the shortest interchain Ag‚‚‚Ag distance is 6.437 Å. As shown in Figure 3a, all pyridyl rings around Ag(1) centers participate in aromatic interactions in two different ways. However, no aromatic interaction is observed for the pyridyl rings around Ag(2) centers. One of the two pyridyl rings around each Ag(1) center is involved in π-π stacking interaction in a “head-to-tail” fashion with one pyridyl ring in the other parallel chain (interplanar separation ) 3.386 Å, center-to-center separation ) 3.746 Å);18 the remaining pyridyl rings around AgI centers also exist in aromatic interaction with the thiadiazole rings in the other parallel chain with a dihedral angle of 3.4° (average interplanar

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Figure 3. For complex 4: (a) Two parallel chains linked through aromatic interactions. CF3SO3- anions and hydrogen atoms are omitted for clarity. (b) Stacking diagram. Hydrogen atoms are omitted for clarity.

separation ) 3.433 Å, center-to-center separation ) 3.709 Å). The stacks of these parallel chains form layers among which lie the CF3SO3- anions. In addition, weak interactions have also been found between the anions and the polycationic chains [O(3)‚‚‚Ag(1) ) 2.749 Å, O(1)‚‚‚Ag(2) ) 2.853 Å and F(3)‚‚‚S(1) ) 3.227 Å] as shown in Figure 3b. Despite their weakness, these interactions play an important role in linking the layers to generate a quasi-3-D framework. As each AgI center herein weakly coordinates to two centrosymmetric anionic O atoms, the Ag‚‚‚O weak contacts do not distort the perfect linear coordination geometry of the metal centers. {[AgL2](CF3SO3)}∞ 5. The structure of complex 5 again consists of 1-D cationic chains and triflate anions. Each crystallographically independent AgI center coordinates to two N atoms from two L2 ligands, and weakly coordinates to an anionic O atom with the Ag(1)‚‚‚O(2) length of 2.688 Å, showing a T-shaped coordination geometry with the N-Ag-N bond angle of 171.14(18)° (Figure 4a). The L2 ligands surrounding the AgI centers take trans-arrangement and each L2 links two AgI centers in cisoid form. The angle between the central oxadiazole ring and two N donors of the 3-pyridyl rings in the ligand molecule is 108.3°, resulting in a rectangular chain motif. The dihedral angles between the oxadiazole ring and two 3-pyridyl rings in each ligand are 6.1 and 5.1°, respectively, and the dihedral angle between the two 3-pyridyl rings is 5.8°, which agree well with the analogous complexes.13 The shortest intramolecular distance of Ag‚‚‚Ag contact is 8.304 Å, significantly shorter than that of 4 (14.795 Å). The crystal packing of 5 is shown in Figure 4b. The 1-D chains are stacked along the a direction to form

quasi-2-D wavelike layers with the average spacing between the aromatic rings being ca. 3.35 Å (center-tocenter separation ) 3.593 Å), indicating significant π-π stacking interactions. These layers are further linked together via weak interactions through triflate ions which are placed in the grooves of the layers. Two anions located in the neighboring layers are linked together through F‚‚‚F weak interaction (the separation is 2.813 Å), and each anion further presents a long contact with the AgI center as mentioned above. Hence, these two-linked anions serve as linkages between the adjacent layers and bring the layers to a quasi-3-D framework. Comparing the structures between 4 and 5 affords a good case for illuminating the effects of the pyridyl N position (4-4′ for L1 and 3-3′ for L2) on the frameworks of coordination polymers. The angle between the central thiadiazole/oxadiazole ring and two AgI centers bridged by the ligand is 153.2° for 4 and 80.5° for 5, resulting in different 1-D chain structures: sinusoidal in 4 and rectangular in 5. Recently, related studies on the ligand 1,2-bis(3-pyridyl)ethyne19 have been reported. To our interest, two different coordination fashions taken by L1, as well as its diverse structural geometries in complexes 1-4, give rise to different extended structures. In 1 and 2, the ligand L1 behaves in tridentate coordination fashion using two pyridyl N atoms and one thiadiazole N atom to bind three AgI centers. In 3 and 4, however, no thiadiazole N atom participates in the coordination; thus, each L1 takes a bidentate coordination mode with two pyridyl N atoms. In addition, the structural geometries of L1 are different in all the four complexes. In 1 and 2, the dihedral angles between the two 4-pyridyl rings are comparatively

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Figure 4. For complex 5: (a) The rectangular chain structure. (b) Stacking diagram. Hydrogen atoms are omitted for clarity. Table 3. Comparison of the Structural Parameters of the Ligand L1 in Complexes 1-4 N-L-N (deg)b φ (deg)c θ (deg)d

1

2

3 [Ag(1)]a

3 [Ag(2)]a

3 [Ag(3)]a

3 [Ag(4)]a

4

159.1 49.3 and 2.8 51.2

159.5 43.5 and 11.9 55.1

158.6 7.6 and 11.6 18.5

160.2 10.2 and 14.3 3.1

159.5 3.0 and 4.3 2.6

159.5 2.0 and 6.9 7.2

155.8 3.4 and 1.4 2.1

a Four ligands with different structural geometries which coordinate four types of AgI centers in complex 3. b The angle between the central thiadiazole ring and two N-donors of the 4-pyridyl ring. c The dihedral angles between the thiadiazole ring and two 4-pyridyl rings. d The dihedral angles between the two 4-pyridyl rings.

larger than those in 3 and 4, because such a conformation in 1 or 2 may reduce the steric crowding and takes advantage of generating π-π interactions between two pyridyl rings from two ligands. The details about the geometric data of L1 are listed in Table 3. Role of Anions in the Self-Assembly Process. From above results, the roles of the counteranions in determining the molecular structures of the coordination polymers have been clearly exhibited. The nature (coordinating ability, size, and shape) of the anions is the underlying reason behind the differences in the structures of this series of AgI complexes.7,8 The anions PF6- and ClO4- have similar size and both display poor coordination ability for usual transition metal ions, thereby in complex 1 or 2, the uncoordinated PF6- or

ClO4- only act as the counteranions to balance the charge and have a spacial templating effect in building up the coordination frameworks. For 3, the smaller NO3- anions possess stronger coordination or donor ability than PF6- or ClO4- ions, and serve as linkages to bridge the 1-D chains to 3-D framework with AgOnitrate contacts. For 4, the large bulk of the CF3SO3ions lying between the adjacent chains is the key factor that prevents the infinite chains from being linked through the Ag-Nthiadiazole bond to form a higher dimensional network, as is the case for complex 1 or 2. A recently reported complex of L3 with AgCF3SO3 shows the 1-D structure in which one AgI center coordinates to oxadiazole N atom and the other one does not.20 The shape and large volume of the CF3SO3- ions also inhibit

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themselves to link the neighboring chains effectively, like the NO3- ions in 3. Herein the uncoordinated CF3SO3- ions existing in weak interactions with cationic chains, probably act as templates for the formation of the network and consequently keep the structure stable. Conclusion and Comments A series of AgI complexes with the angular bridging ligands, 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (L1) and 2,5bis(3-pyridyl)-1,3,4-oxadiazole (L2), have been synthesized and structurally characterized. The molecular structures of these AgI complexes are profoundly influenced by the anions: from simple 1-D chains to novel noninterpenetrating 2-D (2/4,3) topology networks to 3-D frameworks containing two different 1-D motifs. This study clearly indicates that the coordination ability, mode, and/or bulk of the counteranions play important roles in crystal engineering.7,8 Acknowledgment. This work was financially supported by the Outstanding Youth Foundation of NSFC (No. 20225101). Supporting Information Available: Crystallographic information files (CIF) of compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

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