A Triple-Stranded Ladder-Type Coordination Polymer - Crystal Growth

Jun 26, 2012 - (14) Reflecting this, only five triple-rail ladders have been reported until now. .... for the construction of new related architecture...
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A Triple-Stranded Ladder-Type Coordination Polymer Eunji Lee, Joobeom Seo, Shim Sung Lee,* and Ki-Min Park* Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, S. Korea S Supporting Information *

ABSTRACT: Stepwise synthesis and structural characterization of one-dimensional coordination polymers whose topologies depend on the anions are reported. A simple ladder-type precursor, {[Ag2(L)2](ClO4)2}n (1), was prepared by the reaction of bis(4pyridylmethyl)sulfide (L) with AgClO4. Treatment of 1 with potassium thiocyanate and potassium cyanide afforded a twisted ribbon-type chain of type [Ag(L)SCN]n (2) and a triple-rail ladder of type [Ag3(L)2(CN)3]n (3), respectively. The result demonstrates that replacement of the noncoordinated perchlorate anions by pseudohalide ions in the coordination sphere of 1 plays a crucial role in determining the structures of the resulting species.

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ver the past two decades, much effort has been given to the construction of new supramolecular architectures, involving self-assembled coordinative frameworks due to their interesting network topologies1 and applicable properties as nanomaterials.2,3 Among diverse types of supramolecular architectures, ladder-shaped species4 adopting normal,5 quasi,6 twist,7 undulating,8 alternate,9 and rope-type10,11b arrangements have received much attention due to their intriguing structural features and their often unusual magnetic, electronic, and optical properties.11−13 Among ladder-type architectures, the preparation of triple-rail ladder-type coordination polymers has proved difficult because it demands metal ions with two kinds of geometries that are located on the middle rail and the outer rails, respectively. In 2001, Schröder reviewed a range of crystal engineering studies on dipyridyl derivative-based one-dimensional (1D) Ag(I) coordination polymers, in which the triple ladder was excluded.14 Reflecting this, only five triple-rail ladders have been reported until now.15 Furthermore all these known triple-rail ladders incorporate rails consisting of linear metal-ditopic organic ligand structures, with acetates as the rungs. Recently, we reported two-dimensional (2D) Ag(I) coordination networks constructed from bis(4-pyridylmethyl)sulfide (L)16 and bridging coligands such as 4,4′-bipyridine and terephthalate using a stepwise approach starting from the 1D network precursor [Ag2(L)2](ClO4)]n (1).16 This work showed that the replacement of perchlorate ions in the precursor 1 by the above coligands leads to isolation of higher dimensional open frameworks free of any interpenetration. Motivated by this result and as an extension of our studies employing stepwise assembly toward achieving higher dimensionality, we have coupled this approach with employing the pseudohalides cyanide and thiocyanate as alternating inorganic bridging coligands. Thus, in this work we have explored the effect of such inorganic bridging ions on the © 2012 American Chemical Society

assembly of coordination polymers of the present type (Scheme 1). Scheme 1. Precursor-Mediated Stepwise Approach toward Obtaining Double-stranded Chain (2) and Triple-Rail Ladder (3) Assemblies

Herein we report the preparation and crystal structures of two coordination polymers, 2 and 3, with different 1D networking patterns using a stepwise assembly approach. Both products serve to illustrate the major change in structure that can arise from a simple change in the counterion available to the system. In particular, the utility of these results is highlighted by the formation of a triple-rail ladder structure in the case of cyanide. It needs to be noted that the attempted Received: May 21, 2012 Revised: June 20, 2012 Published: June 26, 2012 3834

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preparation of both new products from one-pot reactions of L with silver(I) cyanide or thiocyanate was not possible, suggesting the importance of the proposed stepwise assembly approach. Ligand L was prepared according to our previously published method.16 First, the ladder-type precursor 1 (Scheme 1) was obtained from the reaction of L with AgClO4 in methanol as an off-white precipitate in quantitative yield. Precursor 1 was identified by comparison of the powder X-ray diffraction (XRD) patterns of the synthesized sample with the corresponding single-crystal data (Figure S1a).16 Framework 1 was then employed in further reactions with the above potassium salts. First, the reaction of KSCN with 1 in water/DMSO yielded the colorless crystalline product 2. X-ray analysis17 revealed that 2 is a twisted-ribbon, double-stranded 1D chain with the formula [Ag(L)(SCN)]n (Figure 1). In 2, a

Figure 1. Twisted ribbon-like coordination polymer 2, [Ag(L)(SCN)]n, showing the π−π interactions (dashed lines). [Symmetry codes: (i) 1 − x, −y, 1 − z; (ii) 1 − x, −y, −z]. Figure 2. Triple-rail ladder structure of 3, [Ag3(L)2(CN)3]n: (a) top view, (b) side view, and (c) packing structure viewing along the b axis. X denotes either C or N atoms of the disordered CN group. [Symmetry codes: (i) x, −1 + y, z; (ii) 1 − x, 1 − y, z; (iii) 1 − x, 2 − y, z].

simple −(AgL)n− chain is formed that involves binding of two pyridine nitrogen atoms from two L to the Ag atom [Ag1−N 2.337(2) and 2.358(2) Å]; adjacent parallel chains are crosslinked by Ag−S bonds [2.5597(8) Å], resulting in the twistedribbon structure. The distorted tetrahedral coordination sphere of the Ag atom is completed by an S atom from one terminal thiocyanato ion which was also confirmed by its IR stretching vibration at 2082 cm−1 (Figure S2a). In the double-stranded chain, face-to-face π−π interactions [interplane separations: 3.481(8) Å and 3.234(3) Å, and centroid···centroid distances: 4.12 Å and 4.00 Å] exist between pyridine rings. Moreover, face-to-face π−π interactions are present between adjacent double-stranded chains with interplane and centroid···centroid distances of 3.66(1) Å and 4.12 Å, respectively, linking the 1D double-strand chains into a pseudo 2D sheet structure. Contrary to our expectation, the thiocyanate in 2 acts as a terminal ligand which replaces the perchlorate ion in precursor 1. In parallel with the formation of 2, it is noted that we recently reported a nitrato coordination polymer of type [Ag(L)(NO3)]n, having a similar connectivity pattern.16 Having obtained the twisted ribbon-type 1D chain 2, we then proceeded to undertake the identical reaction involving KCN instead of KSCN (CAUTION! Metal cyanides and most cyanometalates are toxic and should be handled and disposed of accordingly.). KCN reacts with 1 in water/DMSO to yield the colorless crystalline product 3 that was suitable for X-ray analysis.17 Very interestingly, the crystal structure of 3 shows an unusual 1D arrangement, adopting the triple-rail ladder topology, with the formula [Ag3(L)2(CN)3]n (Figure 2). In this structure, three parallel polymeric −(AgCN)n− chains

acting as the rails are linked by two L forming the rungs to form the triple-stranded ladder arrangement. In the rearrangement process, notably, the Ag−S bonds in precursor 1 are cleaved when the Ag atoms are bridged by the cyanide ions. The asymmetric unit of 3 contains one L, one and a half Ag atoms, and one and a half cyanide ions. Importantly, two Ag atoms (Ag1 and Ag2) show very different coordination environments (Figure 2a). The three-coordinate Ag1 atom that lies on the outside of the triple-rail ladder structure connects to two bridging cyanide ions to form the outer strands, with the third coordination site occupied by one of the pyridine nitrogens of L. The Ag1 atom is considerably distorted from regular trigonal planar to give a T-shaped geometry: the bond angles for C13−Ag1−N1, C13i−Ag1−N1, and C13− Ag1−C13i are 88.95(16)°, 106.64(19)°, and 161.2(2)°, respectively. The Ag2 atom locates at the cross-point of the rungs and the central rail, connecting the cyanide ions vertically and L horizontally. Accordingly, the Ag2 atom is fourcoordinate being bound to two pyridine nitrogens and two cyanide ions, with the coordination bond angles falling in the range 80.0(3)−157.7(3)°  far from regular polyhedron angles. The triple-rail ladder arrangement in 3 is generated by the presence of two crystallographic 2-fold symmetry axes at Ag2 and at the center of the C≡N bond in the central strand. The Ag···Ag distance in each strand is 5.35 Å, while their separation 3835

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between two neighboring strands is 13.46 Å (Figure 2a,b). Thus, the width of 3 is ca. 24.7 Å, which corresponds to the widest separation among the triple-rail ladders so far reported.15 In fact, the triple-rail ladders reported previously have narrow widths because they use acetate ions as the rungs between the rails. In the packing structure, the 1D triple-rail ladder structure propagates along the b axis (Figure 2b,c), and adjacent triplerail ladders interact through the pyridyl groups to form a “waved” pseudo 2D sheet sustained by intermolecular Ag···S interactions [3.0193(2) Å]. Weak C−H···π interactions (H···centroid distance: 2.72 Å) also exist between superimposed pyridyl groups (Figure S6). Unlike the thiocyanate ion in 2, in 3 the cyanide acts as a bridging ion to give two types of -(AgCN)n- backbones: one forms part of the central rail and is present as a fourcoordinated Ag2 atom and the second type is in the outer rails and is present as a three-coordinated atom (Ag1). Such a rearrangement appears to be mainly induced by the stronger dicoordinating ability of the cyanide ion. In IR spectrum of 3, the signal at 2131 cm−1 indicates the bridging CN− vibration which is consistent with that of the crystal structure (Figure S2b). The alternative one-pot reaction of L with AgCN or AgSCN, however, gave no equivalent product under the same conditions. Thermogravimetric analysis indicates that 2 and 3 are stable up to 185 and 170 °C, respectively (Figure S3). Above these temperatures, the observed multistep weight loss corresponds to the decomposition of the organic ligands and loss/ decomposition of the pseudohalide anions. The remaining weight loss corresponds to the formation of Ag2O [for 2; 31.4% (calcd. 30.3%) and for 3; 42.0% (calcd. 41.6%)]. In summary, the precursor-mediated stepwise appoach has allowed the construction of two anion-dependent 1D coordination polymers that include a rare triple-rail ladder structure exhibiting the greatest width yet reported. In this approach, the thiocyanate ion replaces the perchlorate ion in the precursor and simply acts as a terminal ligand to give the twisted-ribbon structure. However, the cyanide ion functions not only as a strong bridging coligand but also induces the rearragement of the precuror to give the unusual triple-rail ladder structure. Further investigations based on the present approach for the construction of new related architectures are in progress.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

Details of the experimental procedures, PXRD, IR spectra, TGA, additional figures, crystal data (PDF format), and X-ray crystallographic files (CIF format) for 2 and 3, and PXRD for 1 are included. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (K.M.P.); [email protected] (S.S.L.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by WCU project (R32-20003) and NRF (2011-0026744). 3836

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(15) (a) Peedikakkal, A. M. P.; Vittal, J. J. Inorg. Chem. 2010, 49, 10. (b) Sun, B.-W.; Gao, S.; Wang, Z.-M. Chem. Lett. 2001, 30, 2. (c) Ghoshal, D.; Mostafa, G.; Maji, T. K.; Zangrando, E.; Lu, T.-H.; Ribas, J.; Chaudhuri, N. R. New J. Chem. 2004, 28, 1204. (d) Woodward, J. D.; Backov, R. V.; Abboud, K. A.; Talham, D. R. Polyhedron 2006, 25, 1605. (e) Phuengphai, P.; Youngme, S.; Kongsaeree, P.; Pakawatchai, C.; Chaichit, N.; Teat, S. J.; Gamezf, P.; Reedijk, J. CrystEngComm 2009, 11, 1723. (16) Park, K.-M.; Seo, J.; Moon, S.-H.; Lee, S. S. Cryst. Growth Des. 2010, 10, 4148. (17) The X-ray data were collected on a Bruker SMART CCD diffractometer with graphite monochromated Mo Kα (λ = 0.710673 Å) radiation source at room temperature. The data were processed to give structure factors using SAINT-plus.18 Semiempirical absorption corrections were applied to the data sets using the SADABS.19 The structures were solved by direct methods and refined by full matrix least-squares methods on F2 for all data using SHELXTL software.20 In 3, judging from the difference in the displacement parameters and the site occupancies, discrimination of C and N atoms was possible for the CN group (C13N13) of the outer rails. However the C and N atoms of the CN groups are crystallographically indistinguishable. Therefore, the C or N atoms were named X and treated as disordered with the site occupancies of 0.5. The thermal parameters of C and N on the same site constrained to be equal. The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed in calculated positions and refined with a riding model. The figures were prepared using the Diamond program.21 Crystal data for 2: C13H12AgN3S2, Mr = 382.25, colorless, 0.30 × 0.50 × 0.50, triclinic, space group P1̅, a = 8.1645(8), b = 8.2253(8), c = 12.3145(12) Å, α = 83.306(2), β = 80.590(2), γ = 63.071(2)o, V = 726.54(12) Å3, Z = 2, μ = 1.663 mm−1, θmax = 26.00°, 172 parameters, 2792 independent reflections, 2792 with I > 2σ(I). R = 0.0274, wR = 0.0647 (R = 0.0357, wR = 0.0695 for all data), GOF = 1.021. Crystal data for 3: C27H24Ag3N7S2, Mr = 834.26, colorless, 0.10 × 0.20 × 0.40, orthorhombic, space group P21212, a = 36.150(3), b = 5.3476(4), c = 7.3795(5) Å, V = 1426.59(18) Å3, Z = 2, μ = 2.216 mm−1, θmax = 28.31°, 178 parameters, 3482 independent reflections, 3482 with I > 2σ(I). R = 0.0374, wR = 0.0756 (R = 0.0639, wR = 0.0939 for all data), GOF = 1.023. (18) SMART (ver. 5.625) and SAINT-plus (ver. 6.22): Area Detector Control and Integration Software; Bruker AXS Inc.: Madison, WI, 2000. (19) Bruker, SADABS (ver. 2.03): Empirical Absorption and Correction Software; Bruker AXS Inc.: Madison, WI, 1999. (20) SHELXTL (ver. 6.10): Program for Solution and Refinement of Crystal Structures; Bruker AXS Inc.: Madison, WI, 2000. (21) Brandenburg, K. DIAMOND; Crystal Impact GbR: Bonn, Germany, 1998.

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