Published: July 07, 2011 r2011 American Chemical Society 7142 dx.doi.org/10.1021/ic2007292 | Inorg. Chem. 2011, 50, 7142–7149 ARTICLE pubs.acs.org/IC Semirigid Aromatic SulfoneCarboxylate Molecule for Dynamic Coordination Networks: Multiple Substitutions of the Ancillary Ligands Xiao-Ping Zhou, † Zhengtao Xu,* ,† Matthias Zeller, ‡ Allen D. Hunter, ‡ Stephen Sin-Yin Chui, § and Chi-Ming Che § † Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, China ‡ Department of Chemistry, Youngstown State University, One University Plaza, Youngstown, Ohio 44555, United States § Department of Chemistry and HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong, China b S Supporting Information ’ INTRODUCTION Porous coordination networks (PCNs, or metal organic frame- works, MOF), 1 constructed by using metal ions and organic linkers through coordination bonds, are attracting much attention for their remarkable porous features and potential application in sorption/ separation, 2 catalysis, 2h,3 and sensing. 2e, 4 Compared with the more rigid inorganic zeolites or metal oxides, the inherent suppleness of the organic building blocks tends to impart to the resultant coordination networks significant structural flexibility in the solid state, giving rise to dynamic behaviors in guest absorption and transport (e.g., guest molecules traversing a host net without open channels, 1f,5 sorption hysteresis), as well as in the conversions between different framework structures via external stimulus (e.g., heat, guest molecules) 5m,6 or solution/solvent-mediated processes. 7 On the other hand, the study of these dynamic behaviors can be greatly facilitated by the availability of crystallographical data, for example, single-crystal to single-crystal (SCSC) transformations can be monitored by X-ray crystal diffraction to unveil the relevant structural and mechanistic details. 5g Among the increasing number of reported SCSC transfor- mations of coordination networks, 5g,6a6h,8 most are based on guest-dependent dynamic behaviors. To achieve reactions on the coordination spheres of the metal centers, heating is often needed to displace the volatile ancillary ligands (e.g., H 2 O) by other donor species (e.g., carboxyl, pyridyl/MeOH, or NO 3  ). 6ae In these cases, the substituting donors often originate from the host network and they are usually preassembled around the metal center. By contrast, it remains a challenge to engage externally introduced guest ligands to effect substitution processes at the metal center, even though progress along this direction has recently been made by the groups of Bharadwaj 6h and Zeng. 6g Received: April 8, 2011 ABSTRACT: We report dynamic, multiple single-crystal to single-crystal transformations of a coordination network system based on a semirigid molecule, TCPSB = 1,3,5-tri(4 0 -carboxyphenylsulphonyl)benzene, which nicely balances shape persistence and flexibility to bring about the frame- work dynamics in the solid state. The networks here generally consist of (1) the persistent core component (denoted as CoTCPSB) of linear Co II aqua clusters (CoOCoO-Co) integrated into 2D grids by 4,4 0 - bipyridine and TCPSB and (2) ancillary ligands (AL) on the two terminal Co II ions—these include DMF (N,N 0 -dimethylformamide), DMA (N,N 0 - dimethylacetamide), CH 3 CN, and water. Most notably, the ancillary ligand sites are highly variable and undergo multiple substitution se- quences while maintaining the solid reactants/products as single-crystals amenable to X-ray structure determinations. For example, when immersed in CH 3 CN, the AL of an as-made single crystal of CoTCPSBDMF (i.e., DMF being the AL) is replaced to form CoTCPSBCH 3 CN, which, in air, readily loses CH 3 CN to form CoTCPSBH 2 O; the CoTCPSBH 2 O single crystals, when placed in DMF, give back CoTCPSBDMF in single-crystal form. Other selective, dynamic exchanges include the following: CoTCPSBDMF reacts with CH 3 CN (to form CoTCPSBCH 3 CN) but NOT with water, methanol, ethanol, DMA, or pyridine; CoTCPSBH 2 O specifically pick outs DMF from a mixture of DMF, DMA, and DEF; an amorphous, dehydrated solid from CoTCPSBH 2 O regains crystalline order simply by immersion in DMF (to form CoTCPSBDMF). Further exploration with functional, semirigid ligands like TCPSB shall continue to uncover a wider array of advanced dynamic behaviors in solid state materials.