Thioether ligands as molecular rods in silver(I) coordination networks: 1,4-dithiane as an analogue of pyrazine Alexander J. Blake, Neil R. Brooks, Neil R. Champness,* John W. Cunningham, Peter Hubberstey and Martin Schröder* School of Chemistry, The University of Nottingham, University Park, Nottingham, UK NG7 2RD. E-mail: Neil.Champness@nottingham.ac.uk; m.schroder@nottingham.ac.uk Received 11th February 2000, Accepted 29th February 2000, Published 7th March 2000 The Ag(I) coordination networks, {[Ag(1,4-dithiane)]BF4}¥ and {[Ag2(1,4-dithiane)3](BF4)2}¥ have been prepared and structurally characterised, establishing the role of this simple thioether molecular rod in the construction of coordination networks. In the structure of {[Ag(1,4-dithiane)]BF4}¥ linear one-dimensional chains are formed, the arrangement of which is controlled by weak Ag···F2BF2 interactions [F···Ag = 2.886(2) Å].In {[Ag2(1,4-dithiane)3](BF4)2}¥ an unusual honeycomb network is observed. The synthesis of coordination networks is an area of crystal engineering which has been increasingly studied in recent years.1 Due to the potential of such materials as tuneable mesoporous materials, amongst other useful properties,2 much research has been focussed on the factors that control network structure and topology. Our ability to control the design of coordination networks arises from the management of the coupling of the coordination properties of individual metal ions with ligand functionality.1 We, and others, have also shown that the choice of anion3,4 and the crystallisation conditions can have a dramatic effect upon network structure and topology.5 Many of the reports to date have used bridging bidentate aromatic N-donors,1,3–8 such as pyrazine and 4,4�-bipyridyl, as divergent bridging ligands to propagate polymer growth. In contrast thioether bridging ligands have been significantly less studied,9,10 with the majority of studies focussed on macrocyclic ligands.11 These studies do include one example of the reaction of 1,4-dithiane with Ag(CF3CO2) which affords a two-dimensional polymeric array.9 We report herein the wider use of 1,4-dithiane as a molecular rod in the construction of coordination networks with Ag(I).There are significant parallels between 1,4-dithiane and pyrazine.Both ligands are bidentate donors which encourage bridging of metal centres and the separation of the two donor atoms (the ligand length) is similar in both cases (ca. 3.47 Å for 1,4-dithiane vs. ca. 2.76 Å for pyrazine). However, in addition to the presence of different donor atoms, there are also significant differences between the two systems. 1,4-Dithiane is saturated, and as a result has significantly more bulk, and some flexibility, although the chair conformation is preferred.12 In contrast, pyrazine is aromatic, flat and rigid. Thus whereas the N-donors of pyrazine are each monodentate with donation to a metal centre co-planar with the aromatic ring, the thioethers in 1,4-dithiane adopt an angle of ca.109° at the S-donor (Scheme 1a). This difference in angle allows what may be considered as syn- and anti-bridging (Scheme 1b) and metal-bridging by individual S-donors (Scheme 1c) can also lead to more complex connectivities. Therefore dithioether ligands such as 1,4-dithiane offer interesting features and potentially exploitable versatility. Scheme 1 Comparison of the possible bridging modes of pyrazine and 1,4-dithiane. (a) Illustrating the possible coordination sites on each ligand; (b) anti- and syn-bridging of the 1,4-dithiane unit; (c) bridging of metal centres at an individual S-donor. Reaction of AgBF4 with 1,4-dithiane† in a mixture of CH2Cl2 and MeOH gave colourless powders, the stoichiometry of which was found to be dependent on the ratios of starting materials used.Single crystals of {[Ag(1,4-dithiane)]BF4}¥ and {[Ag2(1,4-dithiane)3](BF4)2}¥ were grown by slow diffusion of solutions of AgBF4 in MeOH into solutions of the ligand in CH2Cl2, using the appropriate stoichiometries. CrystEngComm, 2000, 6Table 1 Crystal dataa Properties Formula MSpace group a/Å c/Å U/Å3 Zm (Mo-Ka)/mm–1 T/K Unique reflections [I >2 s (I)] (Rint) R1 13 0.0299 wR2 13 0.0769 a Click here for full crystallographic data (CCDC no. 1350/12). The structure determination on {[Ag(1,4-dithiane)]BF (Table 1) reveals the Ag(I) centre coordinated in a linear fashion by two thioether donors (S–Ag–S = 180°) (Fig. 1). The thioether ligand adopts an anti-bridging chair conformation to afford linear chains of alternating Ag(I) ions and thioether ligands.Longer interactions are also observed between the Ag(I) ions and the BF – anions [F···Ag = 2.886(2) Å] which form a chelating interaction with each Ag(I) centre and also bridge adjacent centres (Fig. 1). The overall arrangement around the Ag(I) ion is pseudo-square-planar with two trans thioether ligands and two trans BF4– ligands. Although these interactions are long, it has been confirmed previously that the arrangement of linear Ag(I) coordination polymers can be determined by weak anion–metal interactions.3 For example, the interaction between Ag(I) and the oxygen of a nitrate anion (Ag···O = 2.79 Å) results in the formation of a helical staircase structure in {[Ag(4-pytz)](NO3)}¥ instead of the simpler arrangement of linear chains observed for the analogous BF salt (Ag···F = 3.0–3.3 Å).3 – 4 In the case of {[Ag(1,4-dithiane)]BF4}¥ these weaker interactions determine the long-range ordering of the {[Ag(1,4-dithiane)]+}¥ chains.Considering the BF4– anion as a linear bridging ligand the overall structure can be Fig. 2 The overall network structure of {[Ag(1,4-dithiane)]BF4}¥ viewing each Ag(I) centre as a square-planar junction. [Ag—purple, S— yellow, B—gold, F—green.] {[Ag2(1,4-dithiane)3](BF4)2}¥ {[Ag(1,4-dithiane)]BF4}¥ C12H24Ag2B2F8S6 750.04 C4H8AgBF4S2 314.90 Tetragonal, P42/mbc (no.135) 2.292 220(2) 443 [435] (0.0255) Hexagonal, R 3m (no.166) 7.774(3) 11.036(2) 13.875(5) 16.485(6) 838.5(5) 1739.8(8) 4 3 2.904 150(2) 666 [484] (0.070) 0.0155 0.0346 4}¥ 4 Fig.1 View of the Ag(I) coordination environment in {[Ag(1,4- dithiane)]BF4}¥. Displacement ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles (°): Ag– S = 2.4999(11), Ag···F = 2.886(2), S–Ag–Si = 180, F–Ag– S = 82.88(3), Fi–Ag–S = 97.12(3). Symmetry codes: i = 1 – x, 2 – y, –z; ii = 1 – x, 2 – y, z; iii = x, y, –z. Click image or here to access a 3D representation.Scheme 2 Two of the possible coordination polymer topologies constructed from square-planar junctions. (a) (4,4) 2D grids, (b) the CdSO4 3D network observed in {[Ag(1,4-dithiane)]BF4}¥. thought of as a network of interconnected square-planar junctions (Fig.2). A number of structures are possible for such compounds including a simple (4,4) square-grid twodimensional sheet (Scheme 2a), and NbO, CdSO4 or the socalled ’dense-net’ three-dimensional structures.8 The structure observed here has a CdSO4 topology (Scheme 2b) and is also doubly-interpenetrated. 4 The single crystal X-ray structure determination of {[Ag2(1,4-dithiane)3](BF4)2}¥ (Table 1) reveals an entirely different polymeric structure. In this case, each Ag(I) centre is coordinated by three thioether donors in a distorted trigonal-planar arrangement (Fig. 3). Each 1,4-dithiane ligand bridges adjacent silver ions to afford a twodimensional sheet with a honeycomb (6,3) network structure (Fig.4). The hexagonal vacancies within each sheet are filled by BF – anions such that no interpenetration is required for space-filling (Fig. 5). As in {[Ag(1,4- dithiane)]BF dithiane) 4}¥, the BF4– counter-anion in {[Ag2(1,4- 3]BF4}¥ interacts with the Ag(I) ion, but at a Fig. 4 Honeycomb (6,3) network structe observed in {[Ag2(1,4-dithiane)3](BF4)2}¥. [Ag—purple, S—yellow, B—gold, F—green.] Click image or here to access a 3D representation. shorter distance of 2.637(3) Å. However, in this latter case, the interaction pulls the Ag(I) ion out of the trigonal plane of the three thioether donors by 0.55 Å [å(S–Ag– S) = 345.9°]. Since each counter-anion interacts with a single silver centre through one fluorine atom it is conceivable that they do not have a strong influence on the overall structure.Fig. 3 View of the Ag(I) coordination environment observed in {[Ag2(1,4-dithiane)3](BF4)2}¥. Displacement ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles (°): Ag–S = 2.5027(8), Ag···F(1) = 2.637(3), S–Ag–Si = 115.270(11). Symmetry codes: i = 1 – y, x – y, z; ii = 1 – x + y, 1 – x, z. Click image or here to access a 3D representation.Fig. 5 Overlapping of two "Ag6(1,4-dithiane)6 hexagons" illustrating the space-filling role of the BF4– anions. [Ag—purple, S—yellow, B—gold, F—green.] Click image or here to access a 3D representation. 4}¥ 4}¥ 4}¥ AgBF4 reacts with pyrazine to afford four different coordination polymers including one-, two- and threedimensional systems.7 Two of these, {[Ag(pyrazine)]BF and {[Ag2(pyrazine)3](BF4)2}¥, are closely related to the 1,4- dithiane complexes reported here.{[Ag(pyrazine)]BF consists of linear chains of alternating silver ions and bridging ligands in a similar manner to {[Ag(1,4- dithiane)]BF4}¥. The major topological difference between the {[Ag(pyrazine)]BF4}¥ and {[Ag(1,4-dithiane)]BF4}¥ is in the interaction between the BF4– anion and the Ag(I) centre. In {[Ag(pyrazine)]BF4}¥, the BF4– anions interact at long-range with two different Ag(I) ions at distances of ca. 2.72 Å, bridging adjacent {[Ag(pyrazine)]+}¥ chains to afford a two-dimensional (4,4) square-grid (Scheme 2a) in contrast to the structure of {[Ag(1,4-dithiane)]BF (Scheme 2b).The reaction of AgBF4 with pyrazine in a 2 : 3 metal : ligand ratio affords two different coordination polymers, one with an unusual a-ThSi2-like three-dimensional structure and one with a honeycomb (6,3) network similar to that observed for {[Ag2(1,4-dithiane)3](BF4)2}¥. However, the honeycomb sheet of {[Ag2(pyrazine)3](BF4)2}¥ is more 2(1,4-dithiane)3](BF4)2}¥, and distorted than that in {[Ag undulates significantly.7 In conclusion, we have shown that 1,4-dithiane can be used in an analogous manner to pyrazine for the construction of coordination polymers and have illustrated that the anion can be influential in determining the long-range order of these compounds. We anticipate that the rich chemistry observed for pyrazine complexes will be reflected in the development of dithioether coordination polymers.Acknowledgements We thank the EPSRC and the University of Nottingham for support. References 1 S. R. Batten and R. Robson, Angew. Chem., Int. Ed., 1998, 37, 1460; A. J. Blake, N. R. Champness, P. Hubberstey, W-S. Li, M. Schröder and M. A. Withersby, Coord. Chem. Rev., 1999, 183, 117; P. J. Hagrman, D. Hagrman and J. Zubieta, Angew. Chem., Int. Ed., 1999, 38, 2639. 2 O. M. Yaghi, H. Li, C Davis, D. Richardson and T. L. Groy, Acc. Chem. Res., 1998, 31, 474; W. B. Lin, Z. Y. Wang and L. Ma, J. Am. Chem. Soc., 1999, 121, 11249; O. R. Evans, R. G. Xiong, Z. Y. Wang, G. K. Wong and W. B. Lin, Angew. Chem., Int. Ed., 1999, 38, 536; W. B. Lin, O.R. Evans, R. G. Xiong and Z. Y. Wang, J. Am. Chem. Soc., 1998, 120, 13272; B. F. Abrahams, P. A. Jackson and R. Robson, Angew. Chem., Int. Ed., 1998, 37, 2657; D. M. L. Goodgame, D. A. Grachvogel and D. J. 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Chem. Soc., Dalton Trans., 1995, 2735. 13 SHELXL-97, G. M. Sheldrick, University of Göttingen, Germany, 1997. Footnote † {[Ag(1,4-dithiane)]BF4}¥. To a solution of AgBF4 (87 mg, 0.45 mmol) in MeOH (5 cm3) was added a solution of 1,4-dithiane (80 mg, 0.67 mmol) in CH2Cl2 (5 cm3). A colourless crystalline precipitate formed over a period of 5 min and the suspension was then stirred for a further 5 min. The product was filtered off and washed with diethyl ether and then dried in vacuo. Yield 73%. (Found: C, 15.26; H, 2.41%. Calc. for C4H8AgBF4S2: C, 15.26; H, 2.57%.) IR (KBr)/cm–1: 1406w, 1171w, 1152m, 1084s, 1053s, 892m. Single crystals suitable for X-ray diffraction studies were grown by slow diffusion between layered solutions of AgBF4 in MeOH and 1,4-dithiane in CH2Cl2. {[Ag2(1,4-dithiane)3](BF4)2}¥. To a solution of AgBF4 (103 mg, 0.53 mmol) in MeOH (3 cm3) was added a solution of 1,4-dithiane (100 mg, 0.80 mmol) in CH2Cl2 (6 cm3). A colourless crystalline precipitate formed over a period of 5 min and the suspension was then stirred for a further 5 min. The product was filtered off and washed with diethyl ether and then dried in vacuo. Yield 61%. (Found: C, 19.35; H, 3.13%. Calc. for C12H24Ag2B2F8S6: C, 19.21; H, 3.23%.) IR (KBr)/cm–1: 2960w, 2904w, 1414s, 1297m, 1132s, 1092s, 1001s, 966s, 909m, 890s, 759m, 658m, 517m. Single crystals suitable for X-ray diffraction studies were grown by slow diffusion between layered solutions of AgBF4 in MeOH and 1,4-dithiane in CH2Cl2 in the appropriate stoichiometries. Paper b001177k CrystEngComm © The Royal Society of Chemistry 2000