Square-Planar Silver(I)-Containing Polymers Formed from π-Stacked Entities Lyall R. Hanton* and Aidan G. Young Department of Chemistry, UniVersity of Otago, P.O. Box 56, Dunedin, New Zealand ReceiVed NoVember 24, 2005; ReVised Manuscript ReceiVed February 15, 2006
CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 4 833-835
ABSTRACT: The flexible ligand 4,6-bis(3′-pyridylmethylsulfanyl)dibenzofuran (L) was synthesized in a three-step reaction sequence. This new ligand was complexed with both AgClO4 and AgNO3, in a 1:2 metal-to-ligand ratio. The isomorphous structures were onedimensional coordination polymers each containing a rare square-planar Ag(I) connector. The X-ray structures showed numerous π interactions. The design of coordination polymers based on flexible ligands provides many challenges. Normally when flexible ligands are employed in coordination polymer synthesis the geometrical requirements of the metal tend to dominate the structure, as the ligand has many degrees of freedom and hence few conformational restraints. However, when metals such as silver that have plastic coordination spheres are combined with ligands that have conformational flexibility, it is possible that unusual structures will occur. In coordination polymer chemistry, Ag(I) is found to adopt a wide variety of coordination geometries ranging from two to six coordinate. Possibly the most uncommon stereochemistry is squareplanar with few previously reported examples.1,2 About the same number of examples exist for this stereochemistry with Ag(I) ions in discrete coordination complexes.3 As crystal engineering develops, more examples are being reported. Square-planar nodes are useful building blocks in crystal engineering.1d Silver offers an advantage over palladium and platinum because of its increased lability, which is more suited to self-assembly processes. Recently, we reported the synthesis of both rigid and flexible ligands based on a dibenzofuran spacer with exodentate thiopyridine arms and successfully used these ligands to form metallamacrocyclic rectangles.4 These ligands offer various possibilities for the way in which they can be derivatized. For example, the length and flexibility of the thio-pyridine arms can be varied, as can the position of those arms on the dibenzofuran spacer, and finally the donor nitrogen position can be altered. In metallomacrocyclic rectangles, the arms of the ligands were found to fold inward, facilitating the formation of discrete molecular rectangles.4 The system we report below has 3-substituted pyridine donors and thio-pyridine arms intermediate in flexibility between the systems Scheme 1.
Synthetic Route for L with NMR Numbering Scheme
we previously investigated (Scheme 1). Surprisingly, it was found that, upon complexation, the thio-pyridine arms folded outward * To whom correspondence should be addressed. Fax: (+64) 3-4797906. Phone: (+64) 3-479-7918. E-mail:
[email protected].
Figure 1. Comparison of (a) calculated pattern from single-crystal X-ray data for {[Ag(L)2]ClO4}∞ to (b) experimental PXD data for bulk preparation of {[Ag(L)2]ClO4}∞.
leading to the formation of an unusual coordination polymer instead of forming the expected discrete rectangle. The ligand 4,6-bis(3′-pyridylmethylsulfanyl)dibenzofuran (L) was prepared in a three-step process (Scheme 1) in low yield by treatment of dilithiated dibenzofuran with 2 equiv of disulfide 1.5 The disulfide was prepared from 3-picolyl chloride hydrochloride via 3-sulfanylmethylpyridine in good yield.6 The equimolar reaction of L with AgClO47 or AgNO38 gave offwhite solids. For AgClO4, analysis was consistent with a 1:2 metalto-ligand ratio for the complex. The AgNO3 complex was only ever isolated in low yield. Despite many attempts, a microanalytically pure sample could not be obtained perhaps due to the presence of amorphous material. Powder X-ray diffraction (PXD) patterns were recorded for the materials prepared by bulk reaction, and there was good agreement with the patterns generated from the single-crystal structural studies (Figures 1 and 2).9 The few intensity differences that were observed may have been due to preferred orientation of the powder samples caused during sample preparation. The X-ray structures of {[Ag(L)2]X}∞ (X ) ClO4, NO3) were isomorphous.10 They revealed that the complexes were onedimensional (1D) polymers (Figure 3), and the asymmetric units each consisted of one ligand, half a Ag(I) ion, and half a counteranion disordered over a center of symmetry. Interestingly, the Ag(I) ions adopted a rare square-planar arrangement in which the Ag(I) ions sat on centers of symmetry. For each structure, this generated a strictly planar arrangement for the silver and four nitrogen donors around it (Figure 3). A Cambridge Structural database (CSD Version 5.26) search showed that for each structure one Ag-N distance fell within the normal range for four coordinate Ag-N distances (2.20-2.46 Å), while the other distance was at the higher end of the upper quartile.11 Interestingly, many of the
10.1021/cg0506267 CCC: $33.50 © 2006 American Chemical Society Published on Web 03/01/2006
834 Crystal Growth & Design, Vol. 6, No. 4, 2006
Communications
Figure 4. View in the (0 1 1) plane showing the one-dimensional chains of {[Ag(L)]ClO4}∞ and the positions of one of the disordered ClO4- anions. H atoms are omitted for clarity.
Figure 2. Comparison of (a) calculated pattern from single-crystal X-ray data for {[Ag(L)2]NO3}∞ to (b) experimental PXD data for bulk preparation of {[Ag(L)2]NO3}∞.
Figure 3. View of one of the isomorphous complexes, {[Ag(L)2]ClO4}∞, showing square-planar Ag(I) ions with anions omitted for clarity (50% probability ellipsoids). Selected bond lengths (Å) and angles (°) for {[Ag(L)2]X}∞ (ClO4-, NO3-): Ag(1)-N(1) 2.578(2), 2.5059(14), Ag(1)-N(2A) 2.308(2); 2.3062(15); N(1)-Ag(1)-N(2B) 95.28(7), 94.21(4) (symmetry codes: A -x, 1 - y, -z; B x - 1, y - 1, z - 1; C -x - 1, -y, -z - 1; D -x, y + 1, -z).
previously reported square-planar silver complexes display two long and two short bonds.1-3 The bond valence sum (BVS) model12 has been used to show that all four N atoms are required to satisfy the Ag(I) valence, in a reported square-planar Ag-N system.2 A BVS of 1.00 ( 0.20 units represents complete valence satisfaction for a Ag(I) ion. For {[Ag(L)2]ClO4}∞ assuming linear coordination, a BVS of 0.59 units was calculated with two Ag-N distances of 2.308(2) Å. This value was outside the stipulated error limit of (0.20 units for valence satisfaction. Conversely, a BVS of 0.88 ( 0.20 units was calculated when all four Ag-N distances were included. For {[Ag(L)2]NO3}∞, the linear BVS and square-planar BVS were calculated at 0.60 ( 0.20 units and 0.95 ( 0.20 units, respectively. The ligand adopted a helical type of conformation in which the pyridyl arms were on opposite sides of the plane of the furan ring, at approximate right angles to both each other and the furan ring. The ligands sat over each other and formed a 32-membered metallamacrocyclic ring. The dibenzofuran moieties were π-stacked with distances between the furan planes of 3.67 and 3.64 Å for the ClO4- and NO3- complexes, respectively.13 The centroid-to-centroid distances of the central furan rings were 3.89 and 3.91 Å, respectively. The Ag(I) ions in the rings were 18.1 and 17.69 Å apart, respectively. The metallamacrocycles were linked together through the square-planar Ag(I) ions such that all furan rings in the chain were parallel to each other. The 1D chains ran along the [1 1 1] axis. It was unexpected that the two structures would be isomorphous. Coordinating anions such as NO3- often give rise to coordination polymers with different architectures to those arising
from noncoordinating anions such as ClO4-.14 It suggested that this motif, with overlaying of the dibenzofuran rings coupled with the outwardly splayed thio-pyridine arms, was favored and was most likely responsible for Ag(I) adopting this geometry. The chains in the (0 1 1) plane formed sheets through axial interactions between the square-planar Ag(I) ions and disordered counteranions (Figure 4). This gave rise to a tetragonally distorted arrangement around the Ag(I) ions. The anions were disordered over centers of symmetry, and this disorder gave axial Ag‚‚‚O distances of 2.93 and 3.01 Å for {[Ag(L)2]ClO4}∞ and 2.93 Å for {[Ag(L)2]NO3}∞. A CSD search showed those values to be at the very extreme of Ag‚‚‚O-Cl and Ag‚‚‚O-N distances.11 However, consideration of the van der Waals radii [sum of the van der Waals radii ) 3.91 Å]15 suggested a weak interaction between the Ag(I) ion and the counterion may exist. That both ClO4- and NO3counterions were disordered in the structures further supported the argument that any Ag‚‚‚O axial interactions present were very weak and that square-planar coordination for Ag(I) was a valid assignment. The sheets were joined to each other to form a three-dimensional array through two different types of π interactions. First, the N(2) containing pyridine rings in adjacent sheets were involved in π-π stacking interactions [centroid-centroid distance ) 3.75 and 3.62 Å for the ClO4- and NO3- complexes, respectively].13 Second, the pyridine rings were involved in complementary C(pyridine)-H‚‚‚ π(pyridine) interactions with C-H(perp)‚‚‚π distances of 2.66 and 2.60 Å16 for the ClO4- and NO3- complexes, respectively. Finally, the structures contained no solvent-accessible volume.17 The ligand L was designed to facilitate the formation of discrete supramolecular species. Surprisingly, the X-ray structures revealed 1D polymers containing rare square-planar Ag(I) geometry. We surmised that the ligand conformation combined with its π-stacking nature thwarted our attempt at forming a discrete structure. This points to the usefulness of flexible ligands in supramolecular synthesis by providing access to unusual stereochemistries. The cooperative effects of ligand flexibility and π-bonding propensity have provided a linking moiety with few available binding options leading to formation of this square-planar silver node. This robust arrangement even overcomes the influence of counterions in these coordination polymers. By the use of ligands with these properties, such unusual nodes can be engineered, at least in 1D polymers. Acknowledgment. We thank Prof. Ward T. Robinson and Dr. Jan Wikaira (University of Canterbury) for X-ray data collection, Mr. Damian Walls (Department of Geology) for PXD data collection, and the University of Otago Research Committee for a University of Otago Research Grant. Supporting Information Available: An X-ray crystallographic file in CIF format for the structure determination of {[Ag(L)]ClO4}∞ and {[Ag(L)2]NO3}∞. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Suenaga, Y.; Kitamura, K.; Kuroda-Sowa, T.; Maekawa, M.; Munakata, M. Inorg. Chim. Acta 2002, 328, 105. (b) Patra, G. K.; Goldberg, I. J. Chem. Soc., Dalton Trans. 2002, 1051. (c) Ino, I.;
Communications
(2) (3)
(4) (5)
(6)
Zhong, J.; Munakata, M.; Kuroda-Sowa, T.; Maekawa, M.; Suenaga, Y.; Kitamori, Y. Inorg. Chem. 2000, 39, 4273. (d) Hong, M.; Zhao, Y.; Su, W.; Cao, R.; Fujita, M.; Zhou, Z.; Chan, A. S. C. Angew. Chem., Int. Ed. 2000, 39, 2468. (e) Smith, G.; Cloutt, B. A.; Byriel, K. A.; Kennard, C. H. L. Aust. J. Chem. 1997, 50, 741. (f) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Sironi, A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1895. (g) Bing, X.; Dong, C.; Wenxia, T.; Kaibei, Y.; Zhongyuang, Z. Acta Crystallogr. 1991, C47, 1805. Chowdhury, S.; Drew, M. G. B.; Datta, D. New J. Chem. 2003, 27, 831. (a) Hou, L.; Li, D.; Yin, Y.; Wu, T.; Ng, S. W. Acta Crystallogr. 2004, E60, m1106. (b) Reger, D. L.; Gardinier, J.; Smith, M. D. Polyhedron 2004, 23, 291. (c) Reger, D. L.; Gardinier, J. R.; Smith, M. D. Inorg. Chem. 2004, 43, 3825. (d) Constable, E. C.; Housecroft, C. E.; Kariuki, B. M.; Kelly, N.; Smith, C. B. Inorg. Chem. Comm. 2002, 5 199. (e) Carmona, D.; Viguri, F.; Lahoz, F. J.; Oro, L. A. Inorg. Chem. 2002, 41, 2385. (f) Heyduk, A. F.; Krodel, D. J., Meyer, E. E.; Nocera, D. G. Inorg. Chem. 2002, 41, 634. (g) Chen-jie, F.; Chun-ying, D.; Hong, M.; Cheng, H.; Qing-jin, M.; Yong-jiang, L.; Yu-hua, M.; Zhe-ming, W. Organometallics 2001, 20, 2525. (h) Chen, Z.; Wang, R.; Dilks, K. J.; Li, J. J. Solid State Chem. 1999, 147, 132. (i) Constable, E. C.; Edwards, A. J.; Haire, G. R.; Hannon, M. J.; Raithby, P. R. Polyhedron 1998, 17, 243. (j) Arduengo, A. J. III; Dias, H. V. R.; Calabrese, J. C. J. Am. Chem. Soc. 1991, 113, 7071. (k) Fritchie, C. J. Jr. J. Biol. Chem. 1972, 247, 7459. Caradoc-Davies, P. L.; Hanton, L. R. Dalton Trans. 2003, 1754. Preparation of L. Under a N2 atmosphere, a solution of dibenzofuran (0.800 g, 5.23 mmol) and TMEDA (1.83 g, 15.7 mmol) in dry distilled diethyl ether (100 mL) was cooled to -78 °C. A solution of n-BuLi (9.80 mL of 1.6 M solution in hexane, 15.7 mmol) was added dropwise over 1 h, causing the solution to turn golden yellow. The reaction was allowed to warm slowly to room temperature and was stirred under a N2 atmosphere for 18 h. The reaction was cooled to -78 °C, and a solution of 1 (2.65 g, 10.7 mmol) in dry distilled benzene (75 mL) was added in short bursts over 1 h. The reaction was allowed to warm slowly to room temperature causing a thick creamy precipitate to form and was stirred under a N2 atmosphere for 12 h. The removal of solvent by rotary evaporation yielded a cream/yellow solid that was dissolved in water (100 mL) and washed with CH2Cl2 (2 × 100 mL). The organic extracts were dried (MgSO4) and reduced by rotary evaporation to yield a brown oil (2.24 g). This was purified on a column (10% hydrated silica gel) eluted with an 80% chloroform 20% ethyl acetate solvent mix, to give L as a yellow oil. Yield: 0.337 g (16%). Anal. Calc. for C24H18N2S2O‚1/4H2O: C, 68.79; H, 4.45; N, 6.68; S, 15.30. Found: C, 68.77; H, 4.38; N, 7.02; S, 15.44%. 1H NMR (500 MHz, CD2Cl2) δ(TMS): 8.41 (2H, s, H2), 8.36 (2H, dd, 3J ) 4.5 Hz, 4J ) 1.5 Hz, H6), 7.85 (2H, dd, 3J ) 7.5 Hz, 4J ) 1 Hz, H11)*, 7.60 (2H, dd, 3J ) 8 Hz, 4J ) 1.5 Hz, H4), 7.39 (2H, dd, 3J ) 7.5 Hz, 4J ) 1 Hz, H9)*, 7.26 (2H, t, 3J ) 8 Hz, H10), 7.13 (2H, m, H5), 4.31 (4H, s, H7) ppm (*assignments may be reversed). 13C NMR (500 MHz, CD2Cl2) δ(TMS): 155.5 (q, C13), 150.1 (C2), 148.7 (C6), 136.4 (C4), 133.7 (q, C3), 130.9 (C9)∼, 124.7 (q, C12), 123.9 (C10), 123.5 (C5), 120.6 (C11)∼, 118.5 (q, C8), 35.63 (C7) ppm (∼assignments may be reversed). High-resolution ES-MS (CH3CN) found: MH+ 415.0941, 12C 1H 14N 32S 16O requires MH+, 415.0939. IR (KBr disc): 3489, 24 18 2 2 1574, 1477, 1417, 1399, 1188, 1074, 1026 cm-1. Preparation of 1. A 30% aqueous H2O2 solution (5.61 mL, 84.0 mmol) was injected into a solution of 3-sulfanylmethylpyridine (5.60 g, 44.7 mmol) in methanol (100 mL). After the sample was stirred for 20 min, sodium sulfite (5.00 g, 39.6 mmol) was added to destroy excess peroxide. The removal of solvent by rotary evaporation yielded a yellow/brown solid that was dissolved in CH2Cl2 (150 mL) and was washed with water. The removal of solvent provided 1 as a cream
Crystal Growth & Design, Vol. 6, No. 4, 2006 835
(7)
(8)
(9) (10)
(11) (12) (13) (14) (15) (16)
(17)
oil, which crystallized as a tan solid while being dried in vacuo for 48 h. Yield: 4.40 g (80%). Anal. Calc. for C12H12N2S2: C, 58.03; H, 4.87; N, 11.27. Found: C, 57.80; H, 4.75; N, 11.44%. 1H NMR (300 MHz, CDCl3) δ(TMS): 8.54 (2H, d, J ) 4.8 Hz, Py-H), 8.47 (2H, s, Py-H), 7.56 (2H, d, J ) 7.8 Hz, Py-H), 7.28 (2H, m, Py-H), 3.59 (4H, s, -CH2-). ES-MS (CH3CN): m/z 249 [1H]+, 125 [(1)2H]2+. Preparation of {[Ag(L)2]ClO4}∞ AgClO4 (27.4 mg, 0.132 mmol) in degassed MeCN (20 mL) was added to L (109.5 mg, 0.264 mmol) in degassed CHCl3 (20 mL). The resulting solution was stirred under a N2 atmosphere overnight and was reduced by rotary evaporation until a white precipitate began to form. n-Butanol (20 mL) was added to assist with flocculation, and the solution was reduced until a precipitate formed in the remaining solvent. The off-white powder was collected by filtration and washed with diethyl ether. Yield: (95.0 mg) (69.5%). Colorless X-ray quality crystals were obtained from the slow diffusion and subsequent evaporation of a CHCl3 solution of L layered with neat ethyl acetate and a MeCN solution of AgClO4 layered with neat MeCN. Anal. Calc. for C48H36N4S4O6AgCl: C, 55.62; H, 3.50; N, 5.41; S, 12.37. Found: C, 55.32; H, 3.68; N, 5.45; S, 12.24%. IR (KBr disc): 1587, 1480, 1417, 1398, 1347, 1184, 1147, 1116, 1072, 1026 cm-1. Preparation of {[Ag(L)2]NO3}∞ This was prepared in an analogous manner to {[Ag(L)2]ClO4}∞ using AgNO3 (18.2 mg, 0.107 mmol) and L (89.0 mg, 0.214 mmol). Yield: (18.4 mg) (17.2%). Colorless X-ray quality crystals were obtained from the slow diffusion and subsequent evaporation of a CHCl3 solution of L layered with neat MeCN and a MeCN solution of AgClO4. POWDERCELL 2.0 Nolze, G.; Kraus, W. Powder Diffract. 1998, 13, 256. X-ray diffraction data were collected on a Bruker SMART CCD for {[Ag(L)2]ClO4}∞ and a Bruker Apex II for {[Ag(L)2]NO3}∞. For {[Ag(L)2]ClO4}∞: C48H36AgClN4O6S4 FW ) 1036.41, triclinic, P1h, a ) 8.082(5), b ) 8.805(5), c ) 15.276(5) Å, R ) 94.905(5), β ) 94.934(5), γ ) 91.290(5)°; V ) 1078.6(10) Å3, Z ) 1. Dc ) 1.596 g cm-3, µ ) 0.780 mm-1, T ) 168(2) K, F(000) ) 528, 13 954 collected, 4297 unique (Rint ) 0.0259) and 3203 observed [I > 2σ(I)] reflections, 310 parameters, final R1 [I > 2σ(I)] ) 0.0324, wR2 (all data) ) 0.0812. For {[Ag(L)2]NO3}∞: C48 H36AgN5O5S4 FW ) 998.93, triclinic, P1h, a ) 7.891(5), b ) 8.746(5), c ) 15.204(5) Å, R ) 96.326(5), β ) 96.211(5), γ ) 90.670(5)°; V ) 1036.5(9) Å3, Z ) 1. Dc ) 1.600 g cm-3, µ ) 0.745 mm-1, T ) 85(2) K, F(000) ) 510, 27 994 collected, 8696 unique (Rint ) 0.0257) and 7005 observed [I > 2σ(I)] reflections, 301 parameters, final R1 [I > 2σ(I)] ) 0.0329, wR2 (all data) ) 0.0733. The structures were solved with direct methods (SHELXS) and refined on F2 using all data, by full-matrix least-squares procedures (SHELXL 97). The counterions were disordered across centers of symmetry. Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, O.; Kennard, O.; Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J. M.; Watson, D. G.; J. Chem. Inf. Comput. Sci. 1991, 31, 187. Brown, I. D.; Altermatt, D. Acta Crystallogr. 1990, B41, 244. Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885. Hannon, M. J.; Painting, C. L.; Plummer, E. A.; Childs, L. J.; Alcock, N. W. Chem. Eur. J. 2002, 8, 2225. Bondi, A. J. Phys. Chem. 1964, 68, 441. (a) Nishio, M. CrystEngComm 2004, 6, 130. (b) Nishio, M.; Honda, K.; Tsuboyama, S.; Umezawa, Y.; Uzawa, J. Bull. Chem. Soc. Jpn. 1998, 71, 1207. (c) Malone, J. F.; Murray, C. M.; Charlton, M. H.; Docherty, R.; Lavery, A. J. J. Chem. Soc., Faraday Trans. 1997, 93, 3429. Spek, A. L. Acta Crystallogr. 1990, A46, 194.
CG0506267
