Nanosized Silver(I) Coordination Networks of Mixed Bix-Diphosphine

The structures are influenced by the cooperative effect of different conformations of bix and the syn- and anti-form of Lpp. Possible formation proces...
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Nanosized Silver(I) Coordination Networks of Mixed Bix-Diphosphine (Bix ) 1,4-Bis(imidazol-1-ylmethyl)benzene) Li Zhang, Xing-Qiang Lu¨, Chun-Long Chen, Hai-Yan Tan, Hua-Xin Zhang, and Bei-Sheng Kang*

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 1 283-287

School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, China Received March 28, 2004;

Revised Manuscript Received June 1, 2004

ABSTRACT: Assembly of silver(I) salts and bix in the presence of diphosphines provided four polymeric complexes [Ag(bix)(dppe)]n‚nBF4 (1), [Ag(bix)(dppp)]n‚nPF6 (2), [Ag(bix)(dppe)]n‚nPF6‚nCH3OH (3), and [Ag(bix)(dppe)]n‚nSbF6‚ nCH3OH (4). X-ray diffraction analyses reveal that both 1 and 2 have a two-dimensional network composed of nanosized metallocyles, and the [Ag(bix)]n chains in 2 show alternate left and right helices. Complexes 3 and 4 are isomorphous, and they have 3D open frameworks of diamondoid topology with the size of 13 × 13 Å2 along the b-axis. Possible formation processes were interpreted by ESI-MS results. Introduction Metal-organic assemblies continue to be of current interest owing to the propensity of incorporating interesting functions such as zeolitic, magnetic, electronic, and nonlinear optical (NLO) properties, and the diversity of their structural motifs varying from extended coordination polymers to discrete molecular entities such as cages, metallomacrocycles, and many others.1 Ditopic ligands with an arene core have been widely used as building blocks for constructing composite organic/inorganic supramolecular architectures.2-5 These ligands are usually utilized alone to react with transition metals without the addition of auxiliary ligands. It has been reported that the structures of the resulting complexes depend on the nature of the ditopic ligand and the metal ions as well as the counteranions.2-5 However, what will happen to the reaction system when a second ligand is added? Herein, we report the construction of two 2D nanosized networks of [Ag(bix)(dppe)]n‚nBF4 (1) and [Ag(bix)(dppp)]n‚nPF6 (2), and two 3D nanoporous frameworks of [Ag(bix)(dppe)]n‚nPF6‚nCH3OH (3) and [Ag(bix)(dppe)]n‚nSbF6‚nCH3OH (4) by the reactions of Ag(I) salts and 1,4-bis(imidazol-1-ylmethyl)benzene (bix) in the presence of diphosphines Lpp (Ph2P(CH2)nPPh2, n ) 2, dppe; n ) 3, dppp). Construction Approach. High dimensional coordination frameworks can be derived from low dimensional building blocks by the linkage of organic ligands through metal-to-ligand bonds. A related concept of the second building unit (SBU) has been conveyed by Yaghi,6 and it has been proven to be helpful in directing the construction of a given structure.7 In this report, the Ag2(bix)2 ring was constructed as SBU I. According to the literature, the [Ag(bix)]n polymeric chain, designated as SBU II, would be formed by the ring-opening polymerization of the Ag2(bix)2 rings (SBU I).8 Since the coordination numbers of Ag(I) can vary from two to six, SBU I and SBU II might serve as the building blocks * Corresponding author. E-mail: [email protected].

to construct new networks by the occupation of the additional coordination sites at the Ag(I) ion by other ligands, such as diphosphines Lpp. The participation of Lpp might result in new extended networks. Results and Discussion Synthesis. The four complexes 1-4 were prepared by similar procedures: Ag(I) salts and bix reacted in CH3OH first to form a precipitate, which then reacted with Lpp in DMF, with the molar ratio of Ag(I) salt, bix, and Lpp of 1:1:1. The DMF solution of the precipitate obtained from the reaction of bix‚2H2O and AgX (X ) BF4-, PF6-, or SbF6-) showed a similar high peak at m/z 779 (92%), 837 (82%), or 929 (66%) corresponding to {Ag2(bix)2(BF4)}+, {Ag2(bix)2(PF6)}+, or {Ag2(bix)2(SbF6)}+, respectively. The appearance of the {Ag2(bix)2(X)}+ peaks indicates the formation of the dinuclear Ag2(bix)2 in solution, which has been observed in numerous complexes obtained from the reactions of transition metal (M) salts with ditopic ligands (L).9 The peak corresponding to the monomer {Ag(bix)}+ (m/z 345, 100%) was the highest one in the three solutions, which can dimerize to form the dimeric Ag2(bix)2 (SBU I) or further polymerize to produce the oligomeric or polymeric chain [Ag(bix)]n (SBU II), while the latter can be also formed by the ring-opening polymerization of the former as reported previously.8 It might be proposed that, in the DMF solution of bix‚2H2O and AgX, there exist interconversions among the monomer Ag(bix)X, the dinuclear Ag2(bix)2X2 ((SBU I)X2), and oligomer or polymer [Ag(bix)]nXn. On the addition of Lpp, the assembly of SBUs and Lpp lead to the networks of 1-4. As shown in the next sections, with the same Ag(I) salt used, the networks are built from the same SBUs. Structure of [Ag(bix)(dppe)]n‚nBF4 (1). Complex 1 is composed of a two-dimensional polymeric cation [Ag(bix)(dppe)]nn+ and BF4- anions. The tetrahedrally coordinated Ag(I) ion in the N2P2 environment from two bix and two dppe ligands is shown in Figure 1. The 2D network of the cation is constructed by the Ag2(bix)2

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Figure 1. View of two asymmetric units of [Ag(bix)(dppe)]nn+ in 1 with atomic labeling, atoms are drawn with 30% probability ellipsoids. Phenyl rings of dppe and hydrogen atoms were omitted for clarity.

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Figure 3. View of two asymmetric units of [Ag(bix)(dppp)]nn+ in 2 with atomic labeling, atoms are drawn with 30% probability ellipsoids. Phenyl rings of dppp and hydrogen atoms were omitted for clarity.

Figure 2. View of the 2D network of [Ag(bix)(dppe)]nn+ in 1 (Ag(I), purple; bix, blue; dppe, yellow): (a) along the c-axis; (b) along the b-axis.

Scheme 1. Schematic View of the Syn- and Anti-Conformations of Bix

Figure 4. View of the 2D network of [Ag(bix)(dppp)]nn+ in 2 (Ag(I), purple; bix, blue; dppe, yellow): (a) along the c-axis; (b) along the b-axis.

rings whose Ag(I) atoms are further coordinated by antiform dppe ligands linking them to four other rings (Figure 2a). The chair-form Ag2(bix)2 ring is formed by two anti-conformation bix ligands (Scheme 1) bridging two Ag(I) atoms end-to-end with the Ag‚‚‚Ag distance of 12.75 Å. The dihedral angle of the two imidazolyl rings (Im) coordinated to the same Ag(I) and that of the Im rings in the same bix are both 167°. The network can be also viewed this way: the dppe ligands link the Ag(I) atoms longitudinally (Figure 2a) forming the zigzag polymeric chains [Ag(dppe)]n with the Ag‚‚‚Ag distances of 8.20 or 7.40 Å across a dppe ligand, while two adjacent chains are stuck together at the Ag atoms by the double bridging bix to construct a series of 46membered Ag6C24N8P8 metallocycles from Ag6(bix)4-

(dppe)4 (R1) with the BF4- anions located inside. When viewed from the b-axis, there exists a series of open channels formed by the Ag2(bix)2 units (Figure 2b). Structure of [Ag(bix)(dppp)]n‚nPF6 (2). Complex 2 consists of an 2D cationic network [Ag(bix)(dppp)]nn+ and PF6- anions. Each tetrahedral Ag(I) atom is again coordinated by N2P2 from two bix and two dppp (Figure 3). Interestingly enough, although the composition of the cation is similar to that in 1 with the proportion of Ag:bix:Lpp being 1:1:1, the 2D structure in Figure 4a shows a reverse pattern when compared to 1: here the cyclic Ag2(dppp)2 rings are bridged by bix, contrary to that in 1 where the rings Ag2(bix)2 are bridged by dppe. The bix ligands are also of the anti-conformation forming the helical [Ag(bix)]n polymeric chains containing alternate left (Λ)- and right (∆)- handed helices as

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Scheme 2. Schematic View of the Metallomacrocyclic Rings Ag6(bix)4(Lpp)4 in Complexes 1 (R1) and 2 (R2)a

a

Ag(I), sphere; bix, solid line; Lpp, hollow line.

Figure 6. View of the 3D network of the [Ag(bix)(dppe)]nn+ cation in 3 (Ag(I), purple; bix (A), blue; bix (B), cyan; dppe, yellow): (a) along the b-axis; (b) along the c-axis.

n+

Figure 5. View of a fragment of [Ag(bix)(dppe)]n in 3 with atomic labeling showing the metal coordination environment, atoms are drawn with 30% probability ellipsoids. Phenyl rings of dppe and hydrogen atoms were omitted for clarity.

shown in Figure 4a with the pitch of 18.68 Å. The difference of 2 from 1 is also shown in the comparison of the conformation of bix: the dihedral angle of the two Im rings varies from 72.5° for those coordinated to the same Ag(I) atom to 140° for those in the same bix, thus resulting in the helical structure. The dppp in the 64membered Ag6C38N16P4 rings from Ag6(bix)4(dppp)4 (R2) shows the syn-form with the Ag‚‚‚Ag distance of 6.21 Å across the dppp. Viewed from the b-axis, each [Ag(bix)]n helix forms an infinite channel as shown in Figure 4b, and its voids are partially occupied by the PF6- anions and a few of the phenyl rings of dppp. The metallomacrocyclic rings Ag6(bix)4(Lpp)4 designated as R1 (Lpp ) dppe) or R2 (Lpp ) dppp) as shown in Scheme 2 are present in 1 or 2, respectively. In the rings, there exist two kinds of disilver loops Ag2(bix)2 and Ag2(Lpp)2, and two types of pillars Lpp-Ag-Lpp and bix-Ag-bix. The sizes of the metallocycles calculated by the distance between the two loops (Ag1‚‚‚Ag5 or Ag2‚‚‚Ag4) and that between the two pillars (Ag3‚‚‚Ag6) are 11.56 × 22.79 (R1) and 18.68 × 19.01 Å2 (R2). Structures of [Ag(bix)(dppe)]n‚nPF6‚nCH3OH (3) and [Ag(bix)(dppe)]n‚nSbF6‚nCH3OH (4). Complexes 3 and 4 are isomorphous, and only the structure of 3 will be discussed. Complex 3 contains an 3D cationic network [Ag(bix)(dppe)]nn+ of diamondoid topology and PF6- anions. Each tetrahedrally coordinated silver(I) ion is connected with other four Ag(I) ions by two bix and two dppe ligands (Figure 5), which is different from the three-connected silver(I) ion in 1 or 2, and thus resulting in the higher dimensionality. Figure 6a shows the zigzagging polymeric chains [Ag(bix)]n in the molecule

connected by the dppe ligands, which are situated in the direction perpendicular to the plane of the alternately arranged [Ag(bix)]n chains with the Ag‚‚‚Ag distance across dppe of 7.28 Å. Figure 6 shows the 3D channels in [Ag(bix)(dppe)]nn+, which are partially occupied by the PF6- anions and the phenyl rings of dppe. The size of the channels along the b-axis is 13.53 × 13.20 Å2 calculated by the Ag‚‚‚Ag distances across bix(A) (blue in Figure 6) and bix(B) (cyan in Figure 6), where A and B represent different anti-conformations of bix ligands with the dihedral angle 0 (A) or 86.7° (B) of the two Im rings in a bix ligand. The dihedral angle of the two Im rings coordinated to the same Ag(I) atom is 55.1°. Coordination Chemistry of Bix. As we can see in complexes 1-4, bix bridges Ag(I) ions exclusively by the anti-conformation. In fact, the flexible ligand bix is capable of adopting either the syn- or the anti-conformation depending on the orientation of the two Im arms (Scheme 1), which will lead to different structures. The M2(bix)2 metallocycle with bix of the syn-conformation was observed in the complexes with M ) Ag, Zn, and Co.4a,4b,4d When bix adopts the anti-conformation, the resulted structures are shaped by the relative orientation (as estimated by the dihedral angle) of the two Im rings. In diphosphino-complexes 1-3, bix bridges Ag(I) ions with varied dihedral angle of 167° in 1, 140° in 2, and 87 or 0° in 3. Caused by such large variations, the architectures of the molecules resulted from the combinations of bix and Ag(I) contain structural units ranging from the closed Ag2(bix)2 rings, the helical [Ag(bix)]n chains including Ag(bix) half rings, to the zigzaging [Ag(bix)]n chains. In addition, bix may exhibit both syn- and anti-conformations in the same molecule such as in complexes Ag2(bix)3(NO3)2, [Zn(bix)2(NO3)2]‚ 4.5H2O, and [Co(bix)2(H2O)2](SO4)‚7H2O.4a,4b,4d As for most of the reported 2D or 3D coordination polymers constructed only with bix, interpenetration is a common

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Table 1. Crystallographic and Data Collection Parameters for 1-4 complex

1

2

3

4

formula fw cryst syst space group a, Å b, Å c, Å β, ° V, Å3 Z Fcalcd, g m-3 µ, mm-1 R wRa

C40H38AgBF4N4P2 831.36 monoclinic P21/n 16.729(3) 11.559(2) 20.933(3) 104.578(2) 3917.6(10) 4 1.410 0.649 0.0484 0.1266

C41H40AgF6N4P3 903.55 monoclinic P21/n 13.850(5) 18.677(7) 15.719(6) 99.893(6) 4006(2) 4 1.498 0.686 0.0479 0.1308

C41H42AgF6N4OP3 921.57 monoclinic C2/c 27.514(9) 14.252(4) 24.004(7) 113.521(5) 8631(5) 8 1.418 0.640 0.0551 0.1546

C41H42AgF6N4OP2Sb 1012.35 monoclinic C2/c 27.881(9) 14.252(4) 24.059(8) 111.799(5) 8877(5) 8 1.515 1.182 0.0463 0.1509

a w ) [σ2(F 2) + (0.0738P)2 + 4.1714P]-1. P ) (F 2 + 2F 2)/3 (1); w )[σ2(F 2) + (0.1000P)2 + 0.0000P]-1. P ) (F 2 + 2F 2)/3 (2), (3), o o c o o c and (4).

feature in their structures, suggesting that bix has the ability to cause entanglements.4a-d But in complexes 1-4, the interpenetrating ability of bix ligands is disabled. Complexes 1-4 are all noninterpenetrating, and the presence of the phenyl rings of Lpp and counterions may play a key role in the generation of such structures. Conclusion In summary, by the introduction of the auxiliary ligand Lpp, complexes of varied molecular architectures without interpenetration can be constructed from silver salts and the flexible ditopic imidazolyl-containing ligand bix. With the cooperative effect of different conformations of bix, supplemented by the syn- and antiform of Lpp, a variety of new polymeric complexes can be formed. The participation of the secondary ligands in the reaction of Ag-bix will be pursued further to find the rational way to construct new noninterpenetrating architectures which might find application in material sciences, catalysis, or separation. Experimental Procedures Materials and General Methods. All reagents and chemicals were purchased from commercial sources and used as received. The ligand bix was synthesized according to the methods in the literature.4a Elemental analysis for C, H, and N was carried out on an Elementar Vario EL elemental analyzer. Infrared spectra were taken from 4000 to 400 cm-1 on a Bruker EQUINOX 55 FT-IR spectrophotometer. ESI-MS was performed on a Finnigan LCQDECAXP HPLC-MSn mass spectrometer with a mass to charge (m/z) range of 2000 using a standard electrospray ion source. Syntheses of Complexes. Complexes [Ag(bix)(dppe)]n‚ nBF4 (1), [Ag(bix)(dppp)]n‚nPF6 (2), [Ag(bix)(dppe)]n‚nPF6‚nCH3OH (3), and [Ag(bix)(dppe)]n‚nSbF6‚nCH3OH (4) were prepared by a similar procedure. A solution of 0.1 mmol of bix‚2H2O (0.027 g) in 5 mL of MeOH was added dropwise to a stirred solution of 0.1 mmol of silver(I) salt (0.019 g of AgBF4 for 1; 0.025 g of AgPF6 for 2 and 3; 0.034 g of AgSbF6 for 4) in 5 mL of MeOH at room temperature. White precipitate formed immediately, and the solution was filtered after stirring for 0.5 h. The precipitate collected was then added to 5 mL of DMF, and then to the solution was added 0.1 mmol of diphosphine (0.040 g of dppe for 1, 3 and 4; 0.041 g of dppp for 2) with stirring for another 0.5 h. It was filtered again, and Et2O was diffused into the filtrate slowly over several weeks at room temperature to give colorless cubic crystals of the products.

Table 2. Selected Atomic Distance (Å) and Angles (°) for 1-4 Ag1-N1 Ag1-N4 Ag1-P1 Ag1-P2 N1-Ag1-N4 N1-Ag1-P1 N1-Ag1-P2 P1-Ag1-N4 P1-Ag1-P2 P2-Ag1-N4 N-C(methylene)C(phenyl)

1

2

3

4

2.346(3) 2.399(3) 2.436(1) 2.449(1) 104.7(1) 105.6(1) 101.9(9) 109.6(1) 131.60(3) 100.8(1) 112.3(3) 113.2(3)

2.327(4) 2.460(3) 2.454(1) 2.468(1) 100.8(1) 110.85(9) 107.55(9) 96.87(9) 131.24(4) 104.31(9) 111.5(3) 114.9(4)

2.399(5) 2.345(4) 2.447(1) 2.446(1) 104.9(2) 102.3(1) 97.3(1) 108.0(1) 130.10(5) 110.4(1) 112.4(6) 109.7(4)

2.385(4) 2.343(4) 2.443(1) 2.444(1) 103.7(2) 98.6(1) 102.8(1) 109.72(9) 130.24(4) 107.94(9) 112.1(5) 111.0(4)

[Ag(bix)(dppe)]n‚nBF4 (1). Yield: 75%. Anal. Calc. for C40H38AgBF4N4P2: C, 57.79; H, 4.61; N, 6.74. Found: C, 57.49; H, 4.73; N, 6.78%. IR (cm-1, KBr): 3050m, 1655m, 1520m, 1434m, 1393m, 1355m, 1283m, 1238m, 1058s (BF4-), 833m, 746m, 718m, 696m, 654m. [Ag(bix)(dppp)]n‚nPF6 (2). Yield: 80%. Anal. Calc. for C41H40AgF6N4P3: C, 54.50; H, 4.46; N, 6.20. Found: C, 54.17; H, 4.36; N, 6.11%. IR (cm-1, KBr): 3050m, 1513m, 1434m, 1235m, 1107m, 1081m, 838s (PF6-), 741m, 697m, 658m. [Ag(bix)(dppe)]n‚nPF6‚nCH3OH (3). Yield: 70%. Anal. Calc. for C41H42AgF6N4OP3: C, 53.44; H, 4.59; N, 6.08. Found: C, 53.84; H, 4.47; N, 6.25%. IR (cm-1, KBr): 3429m, 3055m, 1509m, 1435m, 1229m, 1105m, 1083m, 840s (PF6-), 748m, 730m, 696m, 660m. [Ag(bix)(dppe)]n‚nSbF6‚nCH3OH (4). Yield: 80%. Anal. Calc. for C41H42AgF6N4OP2Sb: C, 48.64; H, 4.18; N, 5.53. Found: C, 49.01; H, 3.91; N, 5.81%. IR (cm-1, KBr): 3423m, 3055m, 1509m, 1435m, 1230m, 1105m, 1084m, 750m, 731m, 697m, 659s (SbF6-). X-ray Crystallography. The single-crystal X-ray diffractionl data were collected at room temperature (298 K) on a Bruker Smart 1000 CCD diffractometer using graphite monochromated Mo-KR radiation (λ ) 0.71073 Å). The structures were solved by direct methods using the SHELXS-97 program10a and refined with SHELXL by full-matrix least-squares methods.10b The coordinates of all the non-hydrogen atoms were refined anisotropically, while the hydrogen atoms were located geometrically and refined isotropically. The crystallographic data, data collection parameters, and refinements of 1-4 are listed in Table 1. Selected atomic distance and bond angles of 1-4 are given in Table 2. Additional crystallographic details and complete listings have been deposited at the Cambridge Crystallographic Data Center (CCDC) as supplementary publication reference number CCDC-215681 for 1, 234615 for 2, 234616 for 3, and 234617 for 4. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336-033; E-mail: [email protected] or http://www.ccdc.cam.ac.uk).

Silver(I) Coordination Networks

Acknowledgment. This work was supported by NNSF of China and FDRP of Higher Education of China. References (1) (a) Tominaga, M.; Tashiro, S.; Aoyagi, M.; Fujita, M. Chem. Commun. 2002, 2038. (b) Jouaiti, A.; Hosseini, M. W.; Kyritsakas, N. Chem. Commun. 2003, 472. (c) Prior, T. J.; Bradshaw, D.; Teat, S. J.; Rosseinsky, M. J. Chem. Commun. 2003, 500. (2) (a) Su, C. Y.; Cai, Y. P.; Chen, C. L.; Kang, B. S. Inorg. Chem. 2001, 40, 2210. (b) Su, C. Y.; Cai, Y. P.; Chen, C. L.; Zhang, H. X.; Kang, B. S. J. Chem. Soc., Dalton Trans. 2001, 359. (c) Cai, Y. P.; Su, C. Y.; Zhang, H. X.; Zhou, Z. Y.; Zhu, L. X.; Chan, A. S. C.; Liu, H. Q.; Kang, B. S. Z. Anorg. Allg. Chem. 2002, 628, 2321. (3) (a) Tan, H. Y.; Zhang, H. X.; Ou, H. D.; Kang, B. S. Inorg. Chim. Acta 2004, 357, 869. (b) Liu, H. K.; Su, C. Y.; Qian, C. M.; Liu, J.; Tan, H. Y.; Kang, B. S. J. Chem. Soc., Dalton Trans. 2001, 1167. (c) Liu, J.; Liu, H. K.; Feng, X. L.; Zhang, H. X.; Zhou, Z. Y.; Chan, A. S. C.; Kang, B. S. Inorg. Chem. Commun. 2001, 4, 674. (4) (a) Hoskins, B. F.; Robson, R.; Slizys, D. A. J. Am. Chem. Soc. 1997, 119, 2952. (b) Hoskins, B. F.; Robson, R.; Slizys, D. A. Angew. Chem. Int. Ed. 1997, 36, 2336. (c) Abrahams, B. F.; Hoskins, B. F.; Robson, R.; Slizys, D. A. CrystEngComm 2002, 4, 478. (d) Carlucci, L.; Ciani, G.; Proserpio, D. M. Chem. Commun. 2004, 380. (e) Shen, H. Y.; Liao, D. Z.; Jiang, Z. H.; Yan, S. P.; Wang, G. L.; Yao, X. K.; Wang, H. G. Acta Chem. Scand. 1999, 53, 387.

Crystal Growth & Design, Vol. 5, No. 1, 2005 287 (5) (a) Fei, B. L.; Sun, W. Y.; Zhang, Y. A.; Yu, K. B.; Tang, W. X. J. Chem. Soc., Dalton Trans. 2000, 2345. (b) Sui, B.; Fan, J.; Okamura, T.; Sun, W. Y.; Ueyama, N. New J. Chem. 2001, 25, 1379. (c) Zhu, H. F.; Zhao, W.; Okamura, T.; Fei, B. L.; Sun, W. Y.; Ueyama, N. New J. Chem. 2002, 26, 1277. (6) (a) Eddaoudi, M.; Kim, J.; Wachter, J. B.; Chae, H. K.; Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2001, 123, 4368. (b) Vodak, D. T.; Braun, M. E.; Kim, J.; Eddaoudi, M.; Yaghi, O. M. Chem. Commun. 2001, 2534. (7) (a) Brammer, L.; Burgard, M. D.; Rodger, C. S.; Swearingen, J. K.; Rath, N. P. Chem. Commun. 2001, 2468. (b) Sun, D.; Cao, R.; Sun, Y.; Bi, W.; Yuan, D.; Shi, Q.; Li, X. Chem. Commun. 2003, 1528. (c) Dan, M.; Udayakumar, D.; Rao, C. N. R. Chem. Commun. 2003, 2212. (d) Wang, X.; Qin, C.; Wang, E.; Li, Y.; Hu, C.; Xu, L. Chem. Commun. 2004, 378. (e) Bu, X. H.; Chen, W.; Lu, S. L.; Zhang, R. H.; Liao, D. Z.; Bu, W. M.; Shionoya, M.; Brisse, F.; Ribas, J. Angew. Chem. Int. Ed. 2001, 40, 3201. (8) (a) Brandys, M. C.; Puddephatt, R. J. Chem. Commun. 2001, 1508. (b) Burchell, T. J.; Eisler, D. J.; Jennings, M. C.; Puddephatt, R. J. Chem. Commun. 2003, 2228. (c) Shin, D. M.; Lee, I. S.; Lee, Y. A.; Chung, Y. K. Inorg. Chem. 2003, 42, 2977. (9) (a) Li, J. R.; Zhang, R. H.; Bu, X. H. Cryst. Growth Des. 2003, 3, 829. (b) Zou, R. Q.; Li, J. R.; Xie, Y. B.; Zhang, R. H.; Bu, X. H. Cryt. Growth Des. 2004, 4, 79. (c) Xie, Y. B.; Zhang, C.; Li, J. R.; Bu, X. H. Dalton Trans. 2004, 562. (d) Su, C. Y.; Cai, Y. P.; Chen, C. L.; Smith, M. D.; Kaim, W.; Loye, H. C. zur J. Am. Chem. Soc. 2003, 125, 8595. (10) (a) G. M. Sheldrick, SHELXTL-PC; Siemens Analytical X-ray Instruments, Inc.: Madison, WI, 1990. (b) SHELXTL PC, SHELXTL 5.10 Bruker AXS Inc., Madison, WI, 1998.

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