Varying the Frameworks of Novel Silver(I) Coordination Polymers with

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CRYSTAL GROWTH & DESIGN

Varying the Frameworks of Novel Silver(I) Coordination Polymers with Thioethers by Altering the Backbone or Terminal Groups of Ligands

2002 VOL. 2, NO. 4 303-307

Xian-He Bu,*,†,‡ Wen-Feng Hou,† Miao Du,† Wei Chen,† and Ruo-Hua Zhang† Department of Chemistry, Nankai University, Tianjin 300071, P. R. China, and The State Key Laboratory of Structural Chemistry, Fuzhou 350002, P. R. China Received March 12, 2002;

Revised Manuscript Received April 29, 2002

ABSTRACT: A series of novel silver-thioether metal-organic supramolecular architectures forming different frameworks are constructed by the direct reactions of AgI perchlorate with a series of di- or trithioether ligands which are closely related in structure. In the crystal structures of the four complexes, a variety of coordination modes of the AgI centers due to the conformation freedom or steric hindrance have been observed, indicating that the nature of the ligands is a determining factor in controlling the structural topology of the metal-organic supramolecular architectures. Introduction The rational design of coordination polymer networks based on multitopic ligands and metal centers represents one of the most exciting and rapidly developing field in current coordination and supramolecular chemistry due to their potential applications in many areas.1-3 There has been rapid development of multidimensional networks based primarily on linking metal centers with rigid bridging components such as 4,4′-bipyridine,4 and some extended architectures or networks constructed from flexible bridging units have also been reported, although such examples are still comparatively rare.5 AgI is a favorable and fashionable building block or connecting node for coordination polymers,6 and thioether ligands possess unusual potential for the construction of coordination architectures.7 However, fully characterized examples of the coordination complexes of thioether ligands with AgI ions are mainly restricted to macrocylic thioethers, and a small number of examples with acyclic thioethers are reported.8 We report herein the construction of novel AgI coordination polymers forming different networks, by using di- and trithioether ligands (see Chart 1) as building blocks. The four thioether ligands we chose in this study, 1,3-bis(propylthiomethyl)benzene (L1), 1,3-bis(phenylthiomethyl) benzene (L2), 1,5-bis(benzythio)pentane (L3), and 1,3,5-tri(phenylthiomethyl)benzene (L4), are structurally closely related to each other. We are attempting to examine the influence of sterichindrance or the conformation freedom of the ligands on the resultant structures of their metal complexes. The crystal structures of the AgI complexes were elucidated by X-ray diffraction analyses, and the distinction of their coordination modes was illuminated. Experimental Procedures Materials and General Methods. All the reagents for syntheses were obtained commercially and purified by standard methods prior to use. Elemental analyses were performed * To whom correspondence should be addressed. Fax: +86-2223530850. E-mail: [email protected]. † Nankai University. ‡ The State Key Laboratory of Structural Chemistry.

Chart 1

on a Perkin-Elmer 240C analyzer. IR spectra were measured on a 170SX (Nicolet) FT-IR spectrometer with KBr pellets. 1H NMR spectra were recorded on a Bruker AC-P500 spectrometer (400 MHz) at 25 °C in CDCl3 with tetramethylsilane as the internal reference. Synthesis of Ligands. The dithioether ligands, 1,3-bis(propylthiomethyl)benzene (L1), 1,3-bis (phenylthiomethyl)benzene (L2), and 1,5-bis(benzythio)pentane (L3) were prepared according to the reported procedures under an argon atmosphere.8,9 The trithioether ligand 1,3,5-tri(phenylthiomethyl)benzene (L4) was synthesized by the similar method along with the minor modification as described below.9 Thiophenol (630 mg, 5.7 mmol) was added to a stirred solution of KOH (320 mg, 5.7 mmol) in ethanol (50 mL). The mixture was refluxed for 30 min and a solution of 1,3,5-tri(bromomethyl)benzene10 (500 mg, 1.9 mmol) in THF (15 mL) was slowly added to it. The mixture was refluxed for 3 h more. The KBr precipitate was filtered off, and the filtrate was evaporated to obtain a white solid in 50% yield. Anal. Calcd for C27H24S3, C, 72.93; H, 5.44. Found: C, 72.76; H, 5.62. 1H NMR (400 MHz, CDCl3), 3.95 (s, 6H, S-CH2-Ph), 7.00-7.44 (m, 18H, Ph). Syntheses of the Complexes 1-4. Colorless single crystals suitable for X-ray analyses for all complexes were obtained by the similar method. All reactions were carried out in the absence of light with 1:1 molar ratio for AgI/ligand species. [AgL1]2(ClO4)2 1. AgClO4 (21 mg, 0.1 mmol) in acetone (5 mL) was slowly added to the solution of L1 (26 mg, 0.1 mol) in chloroform (5 mL). The mixture was refluxed for 30 min and

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Table 1. Summary of Crystallographic Data for Complexes 1-4 formula Mr crystal size (mm) crystal system space group T (K) a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) D (g cm-3) F (000) Z µ (cm-1) measured reflections unique reflections parameters refined Rint R Rw S largest diff. peak (e Å-3)

1 C28H44Ag2Cl2O8S4 923.51 0.40 × 0.30 × 0.20 monoclinic P21/n 293(2) 11.342(3) 13.087(4) 12.982(4) 90 95.930(6) 90 1916.7(10) 1.600 936 2 1.420 7794 3387 199 0.0557 0.0588 0.1445 1.048 0.744

2 C20 H18AgClO4S2 529.78 0.20 × 0.15 × 0.25 monoclinic P21/c 298(2) 10.674(3) 23.490(6) 8.452(2) A 90 91.790(5) 90 2118.1(9) 1.661 1064 4 1.298 8782 3736 253 0.1362 0.0434 0.0793 0.808 0.440

allowed to stand at room temperature. Colorless single crystals were obtained by slow evaporation of the solvent in 52% yield (24 mg). Anal. Calc. for C28H44Ag2Cl2O8S4: C, 36.41; H, 4.80. Found: C, 36.16; H, 4.92. IR (KBr pellet, cm-1): 2997w, 2922w, 1578m, 1480s, 1441s, 1425m, 1240m, 1161m, 1129s, 1093vs, 1024s, 1002m, 743s, 711m, 623s. [AgL2ClO4]∞ 2. Yield: 48%. Anal. Calc. for C20H18AgClO4S2: C, 45.34; H, 3.42. Found: C, 45.29; H, 3.75. IR (KBr pellet, cm-1): 2961s, 2929m, 1589m, 1487m, 1454s, 1340m, 1296m, 1244m, 1095vs, 711s, 624vs. {[Ag(L3)2](ClO4)}∞ 3. Yield: 57%. Anal. Calc. for C34H40AgClO4S4: C, 52.07; H, 5.14. Found: C, 52.31; H, 5.00. IR (KBr pellet, cm-1): 2929s, 2855m, 1584s, 1481s, 1438s, 1142vs, 1093vs, 1024m, 738vs, 690s, 628s. {[Ag(L4)2](ClO4)}∞ 4. Yield: 39%. Anal. Calc. for C27H24AgClO4S3: C, 49.74; H, 3.71. Found: C, 49.98; H, 3.60. IR (KBr pellet, cm-1): 3049m, 2993w, 1600m, 1580m, 1479s, 1440s, 1422m, 1334m, 1155m, 1100vs, 1067vs, 1023s, 743s, 719m, 689s, 621s. CAUTION: Although we have met no problems in handling perchlorate salts through this work, these should be treated with great caution due to their potentially explosive nature. X-ray Crystallography. Single-crystal X-ray diffraction measurements for complexes 1-4 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. Determination of unit cell parameters and data collections were performed with Mo-KR radiation (λ ) 0.71073 Å), and unit cell dimensions were obtained with least-squares refinements. The program SAINT11 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.12 AgI atoms in each complex were located from E-maps, and 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 and refined with fixed thermal factors. Crystallographic data and experimental details for structural analyses are summarized in Table 1.

Results and Discussion [AgL1]2(ClO4)2 1. The structure of 1 consists of two AgI centers related by a C2 symmetric axis and spanned

3 C34 H40AgClO4S4 784.22 0.20× 0.15× 0.10 monoclinic Pn 298(2) 9.2013(14) 10.1824(17) 19.267(3) 90 103.533(3) 90 1755.0(5) 1.484 808 2 0.924 7059 4776 397 0.0306 0.0306 0.0832 1.045 0.673

4 C27H24AgClO4S3 651.96 0.25× 0.20× 0.20 triclinic P-1 293(2) 10.514(16) 10.514(16 15.58(3) 70.75(3) 70.75(3) 62.15(2) 1406(4) 1.540 660 2 1.066 5751 4831 325 0.0575 0.0575 0.1373 0.965 0.908

Table 2. Selected Bond Lengths (Å) and Angles (°) for Complexes 1-4 1 Ag(1)-S(2) Ag(1)‚‚‚O(1) S(2)-Ag(1)-S(1) 2 Ag(1)-S(1) Ag(1)-O(1) S(1)-Ag(1)-S(2A) S(2A)-Ag(1)-O(1) 3 Ag(1)-S(1) Ag(1)-S(3) S(4)-Ag(1)-S(2) S(2)-Ag(1)-S(1) S(2)-Ag(1)-S(1) 4 Ag(1)-O(1) Ag(1)-S(1) O(1)-Ag(1)-S(2A) S(2A)-Ag(1)-S(1) S(2A)-Ag(1)-S(3B)

2.416(3) 2.807 160.81(8)

Ag(1)-S(1) Ag(1)‚‚‚O(2)

2.430(3) 2.889

2.454(3) 2.556(10) 159.61(9) 101.4(2)

Ag(1)-S(2A) Ag(1)‚‚‚O(3) S(1)-Ag(1)-O(1)

2.457(3) 2.719(4) 91.7(3)

2.6726(11) 2.6255(12) 122.20(4) 120.93(4) 99.60(3)

Ag(1)-S(2) Ag(1)-S(4) S(4)-Ag(1)-S(3) S(4)-Ag(1)-S(1) S(3)-Ag(1)-S(1)

2.5935(11) 2.5863(12) 105.25(4) 98.27(3) 106.62(14)

2.424(11) 2.538(4) 99.5(5) 119.86(8) 121.13(10)

Ag(1)-S(2A) Ag(1)-S(3B) O(1)-Ag(1)-S(1) O(1)-Ag(1)-S(3B) S(1)-Ag(1)-S(3B)

2.534(4) 2.548(3) 101.9(4) 95.2(4) 111.95(14)

by two ligands to form a unique 16-membered macrocyclic box-like dimeric unit. In this boxlike macrocycle, the four S atoms are approximately coplanar. Each AgI center can be regarded as quasi-tetracoordinated with two sulfur atoms in two distinct ligands and two weak contacts with two perchlorate oxygens. As shown in Table 2, the bond distances of Ag(1)-S(1) and Ag(1)-S(2) are 2.430(3) and 2.416(3) Å, respectively, which are almost equivalent. They are both comparable to the bond distances of other known thioether AgI complexes.9 In the dinuclear box-like complex unit, the two phenyl rings are paralleled with a separation of approximately 5.3 Å. Between two macrocycles units, each perchlorate anion is oriented to two silver(I) centers of two distinct units and makes a close contact. The vertical distance between the adjacent macrocycle plane is 0.5532 Å, and there is a small difference in the distances between Ag and O atoms (2.807 and 2.889 Å, respectively), indicating the presence of weak Ag-O contacts,13 and via this interaction, an infinite quasi-one-dimensional chain

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Figure 1. One-dimensional linear arrangement of complex 1 bridged by perchlorate anions.

Figure 2. Two-dimensional coordination network along the xy plane in complex 2.

array was formed, and this may stabilize the complex in the crystal. The Ag‚‚‚Ag nonbonding distance in one dimeric box unit is 6.854 Å, and the Ag‚‚‚Ag separation between the adjacent dimeric units is 4.511 Å, which are comparable to those of other known linear AgI complexes.14 [AgL2ClO4]∞ 2. The crystal structure of 2 shows tetrahedrally coordinated AgI ions ligated via two sulfur donors from two distinct L2 ligands and two oxygen donors from two perchlorate anions. The Ag-S bond distances are almost equivalent (2.454(3) and 2.457(3) Å, respectively), but the Ag-O bond distances are slightly different (2.556(10) and 2.719(4) Å). The two S-Ag-O bond angles are 91.7(3) and 101.4(2)°, respectively. In 2, one L2 ligand bridges two AgI centers with two distinct S donors to form a -Ag-S-C-Ph-C-S-Aglinear structural unit along the a-direction. These chains are also linked by two oxygen atoms of the perchlorate anions through relatively weaker coordination interactions to form an infinite noninterpenetrating two-dimensional grid as depicted in Figure 2. It should be noted that L1 and L2 just differ in their terminal groups, but their complexes form very different structures, probably due to the larger phenyl groups of L2 prevents the formation of a face-to-face box unit. The ligand-bridged Ag‚‚‚Ag nonbonding distance is 10.674 Å, and the adjacent Ag‚‚‚Ag nonbonding distance through the perchlorate anion is 5.007 Å. The distance between the parallel neighboring aromatic rings of the distinct planes is ca. 3.5 Å, indicating the presence of significant face-to-face π-π stacking interactions15 along c-direction, and via this interactions, the two-dimensional planes are fused together into a quasi-threedimensional structure. {[Ag(L3)2](ClO4)}∞ 3. The structure of 3 shows a tetrahedrally coordinated AgI ions ligated via four S donors of four distinct L3 ligands, with the other S donor

Figure 3. View from the c-direction showing the twodimensional square grid of 3.

of each ligand linking adjacent AgI ions to give an infinite two-dimensional structure (Figure 3). This may be ascribed to the fact that the pentane backbone of L3 is more flexible than the phenyl groups of other three ligands and the aryl skeleton can rotate freely to reduce the steric hindrance so that four ligands could coordinate to one metal center. The four Ag-S bond distances in 3 are slightly longer than those in 2, probably because each AgI center coordinates to four distinct L3 ligands, and the longer bond distances could reduce the steric hindrance. All the angles around AgI are in the range 98.27(3)-122.20(4)°. Each L3 ligand links two AgI centers to form a 32membered rectangular macrocycle where two pairs of Ag‚‚‚Ag distances are 10.28 and 9.20 Å, respectively, and four AgI atoms are approximately coplanar. The ligands adopt two different conformations, A and B (Figure 3), in the macrocycle and each emerges in the unit alternately. In type A, the ligand shows a cis form with two Ag-S bonds approximately coplanar with the ligand skeleton. Two phenyl rings of one ligand are located at the same side of the macrocycle and the dihedral angle between them is 31.1°. In B conformation, the ligand presents a trans form and two phenyl rings reside at the different side with a dihedral angle of 94.9°. The pseudo-torsion angle between two Ag-S bonds is 151.4° in A and 100.2° in B. Discrete noncoordinating ClO4anions occupy the voids in the cationic network and neutralized the charge. The macrocycles extend along the a- and b- directions to form a two-dimensional lattice-like structure. It is worth noted that the backbones of L2 and L3 are very similar, but their complexes form quite different structures, probably because the phenyl group in the backbone of L2 increases the rigidity of the ligand.

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Figure 4. View of the (6,3) topological net of 4.

Scheme 1

{[Ag(L4)2](ClO4)}∞ 4. The structure of 4 reveals an infinite honeycomb unit, in which each metal center is tetrahedrally coordinated to three sulfur atoms of three distinct L4 ligand groups and the fourth coordination is accomplished with one oxygen atom of the perchlorate anion. Each ligand links three adjacent AgI centers with its three sulfur atoms to form a nearly hexagonal 24membered macrocycle that consists of three metal ions and three ligand groups. This repeating unit possesses a crystallographic C3 symmetry axis passing through its center to form a (6,3) net. In the macrocycle, the shortest Ag‚‚‚Ag adjacent distance is 10.514 Å, and three phenyl rings of three distinct ligands partially filled the macrocycle cavity to sustain it. Each of the aromatic rings between the adjacent planes is parallel to each other and separated by ca. 3.4 Å, indicating the presence of significant face-to-face π-π stacking interactions. Via these π-π interactions a twodimensional bilayer structure is formed (the AgI atoms in two adjacent layers are arranged staggered), and this may stabilize the complex in the crystal16 as depicted in Scheme 1. The structure of 4 has a unique lamellar structural motif. In all the four complexes, the di- or trithioether ligands act as bridging ligands, regardless the rigid (L1, L2, and L4) or flexible (L3) nature of the ligands. The coordination environment of AgI in complex 3 is different from that of the other three in which each silver center coordinates to four distinct ligands because the aryl skeleton of the ligand can rotate freely to reduce the steric hindrance. In addition, the perchlorate anions play different roles in the four complexes. In compounds 1, 2, and 4, there exist weak interactions between the perchlorate anions and the AgI centers: in complex 4,

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the perchlorate anions coordinate to the AgI centers as monodenate ligands; however, in complexes 1 and 2, the perchlorate anions further act as bridges to link the repeating units to form a one-dimensional chain or twodimensional sheet structure, respectively. While in 3, each AgI center coordinates to four distinct ligands, and the perchlorate anion resides in the cavity to balance the charge and keep the structure stable. However, there is also small difference in the coordination fashions of 1, 2, and 4, showing the influences of the terminal groups. And in the three complexes, long-range Ag-S contacts and π-π interactions play an important role in the formation of networks. In conclusion, four silver-thioether metal-organic supramolecular architectures forming quite different frameworks have been constructed by the direct reactions of AgI perchlorate with a series of well chosen dior trithioether ligands which are closely related in structure, and a variety of coordination modes of the AgI centers due to the conformation freedom or steric hindrances has been observed, indicating that the nature of the ligands is a determining factor in controlling the structural topology of the metal-organic supramolecular architectures, and this offers us opportunity in controlling the coordination networks by ligand modifications. Further studies using other new ligands for construction of novel networks and systematic studies on such ligands by varying their backbones, as well as studies on the properties and functionality of such complexes are under way in our lab. Acknowledgment. This work was financially supported by NSF of China (No. 29971019) and the Natural Science Foundation of Tianjin (China). Supporting Information Available: Four X-ray crystallographic files in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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