Structure Elucidation DOI: 10.1002/anie.201203834 Design of Flexible Lewis Acidic Sites in Porous Coordination Polymers by using the Viologen Moiety** Masakazu Higuchi, Kohei Nakamura, Satoshi Horike, Yuh Hijikata, Nobuhiro Yanai, Tomohiro Fukushima, Jungeun Kim, Kenichi Kato, Masaki Takata, Daisuke Watanabe, Shinji Oshima, and Susumu Kitagawa* Considerable effort has been devoted to the design of metal– organic architectures and a variety of frameworks have emerged through self-assembly processes involving metal ions and organic linkers. [1] The synthesis of coordination polymers with a channel structure, polymers which have been called porous coordination polymers (PCPs) or metal– organic frameworks (MOFs), [2, 3] are of great interest because of their unique functions, such as gas storage, [4] separation, [5] and catalysis. [6, 7] Among the PCPs, frameworks having Lewis acidic sites have been highlighted because of their gas- capturing properties [8] or catalytic activities. [7] The main strategy for preparing the Lewis acidic sites is to introduce open metal sites (OMSs). In contrast, we have achieved the fabrication of charged organic surfaces (COSs) using a pyr- idinium moiety in the porous framework. [9] Because the guest- accessible interior of the pore is mainly organized by the organic moiety, these COSs interact effectively with guest molecules. Another noteworthy point of the introduction of COSs is flexibility, which is based on the flexible nature of the PCP framework. [3, 10] PCPs often show a flexible contraction/ expansion of the framework through guest accommodation, and if we could incorporate COSs onto the flexible network, the obtained framework would show induced-fit capture of guests at the COSs, a process which is difficult to achieve with the use of OMSs. For the purpose of the construction of flexible COSs, we employed a viologen derivative as an organic linker because of its intrinsic Lewis acidity [11] and the dynamic motion of the aromatic rings. [12] Herein we report the synthesis of a PCP bearing a viologen motif, the strength of the Lewis acidity, and the adsorption properties. The reaction of Zn(NO 3 ) 2 ·6 H 2 O with 1,4-naphthalenedi- carboxylic acid (1,4-H 2 ndc) and 1,1-bis(4-carboxybenzyl)- 4,4’-bipyridinium bis(hexafluorophosphate) (H 2 bcbpy·2 PF 6 ) in N,N’-dimethylformamide (DMF) affords the PCP {[Zn(1,4- ndc)(bcbpy)]·(0.5 DMF)(3.5 H 2 O)} n (10.5 DMF·3.5 H 2 O) (Scheme 1). The bcbpy, which is a zwitterionic ligand, acts as a neutral organic linker and 10.5 DMF·3.5 H 2 O does not include any counter anions. The crystal structure of 10.5 DMF·3.5 H 2 O was determined by single-crystal X-ray crystallography at 223 K. The Zn 2+ ion is tetrahedrally coordinated by two 1,4-ndc ligands and two bcbpy ligands (Figure 1 a) to give two-dimensional (2D) interpenetrated layers along the ac plane (Figure 1 b). The 2D layers are of the 4 4 -sql topology (see Figure S1 in the Supporting Information). The interpenetrated 2D layers are stacked along the b axis to form a 3D structure because of the p–p interaction between the 1,4-ndc and the viologen moiety of the bcbpy (Figure 1 c). The 10.5 DMF·3.5 H 2 O possesses 1D channels along the c axis with a cross-section of 4.7  4.1  2 (Figure 1d). The 0.5DMF and 3H 2 O sit in the cavity and the 0.5 H 2 O is between the 2D sheets. The pore surface is formed by bcbpy and 1,4-ndc ligands (Figure 1 e). The carbonyl oxygen atom of the DMF is located 2.48 and 2.64  from the two a-hydrogen atoms of the viologen moiety (Figure 2 a), and it forms a C  Scheme 1. Synthesis of 10.5 DMF·3.5 H 2 O. [*] Dr. M. Higuchi, Prof. Dr. S. Kitagawa Institute for Integrated Cell-Material Sciences, Kyoto University 69 Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501 (Japan) E-mail: kitagawa@icems.kyoto-u.ac.jp K. Nakamura, Dr. S. Horike, Dr. Y. Hijikata, Dr. N. Yanai, T. Fukushima, Prof.Dr. S. Kitagawa Department of Synthetic Chemistry & Biological Chemistry Graduate School of Engineering, Kyoto University Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan) Dr. J. Kim, Prof.Dr. M. Takata Japan Synchrotron Radiation Research Institute, RIKEN 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan) Dr. K. Kato, Prof.Dr. M. Takata Spring-8 Center, RIKEN 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan) D. Watanabe, S. Oshima Hydrogen & New Energy Research Laboratory, Research & Development Division, JX Nippon Oil & Energy Corporation 8, Chidoricho, Naka-ku, Yokohama 231-0815 (Japan) [**] The synchrotron radiation experiments were performed at the BL44B2 in the SPring-8 with the approval of the RIKEN (Proposal No. 20090066). This work was supported by the JX Nippon Oil & Energy Corporation, ERATO “Kitagawa Integrated Pores Project” of the Japan Science and Technology Agency (JST), and the New Energy and Industrial Technology Development Organization (NEDO). Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201203834. A ngewandte Chemi e 1 Angew. Chem. Int. Ed. 2012, 51,1–5  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü