Rigid-Strut-Containing Crown Ethers and [2]Catenanes for Incorporation into Metal-Organic Frameworks

Abstract

To introduce crown ethers into the struts of metal-organic frameworks (MOFs), general approaches have been developed for the syntheses of dicarboxylic acid dibenzo[30]crown-10 (DB30C10DA), dicarboxylic acid di-2,3-naphtho[30]crown-10 (DN30C10DA), dicarboxylic acid bisparaphenylene[34]crown-10 (BPP34C10DA), and dicarboxylic acid 1,5-naphthoparaphenylene[36]crown-10 (NPP36C10DA). These novel crown ethers not only retain the characteristics of their parent crown ethers since they can 1) bind cationic guests and 2) serve as templates for making mechanically interlocked molecules (MIMs), such as catenanes and rotaxanes, but they also present coordination sites to connect with secondary building units (SBUs) in MOFs. The binding behavior of BPP34C10DA with 1,1'-dimethyl-4,4'-bipyridinium bis(hexafluorophosphate) (DMBP.2PF(6)) has been investigated by means of UV/Vis, fluorescence, and NMR spectroscopic techniques. The crystal superstructure of the complex DMBP.2PF(6)subset of BPP34C10DA was determined by X-ray crystallography. The NPP36C10DA-based [2]catenane (H(2)NPP36C10DC-CAT.4PF(6)) and the BPP34C10DA-based [2]catenane (H(2)BPP34C10DC-CAT.4PF(6)) were prepared in DMF at room temperature by the template-directed clipping reactions of the planarly chiral NPP36C10DA and BPP34C10DA with 1,1'-[1,4-phenylenebis(methylene)]di-4,4'-bipyridin-1-ium bis(hexafluorophosphate) and 1,4-bis(bromomethyl)benzene, respectively. The crystal structure of the dimethyl ester (BPP34C10DE-CAT.4PF(6)) of the [2]catenane H(2)BPP34C10DC-CAT-4PF(6) was investigated by X-ray crystallography, which revealed racemic R and S isomers with planar chirality present in the crystal in a 1:1 ratio. These crown ether based struts serve as excellent organic ligands to bind with transition metal ions in the construction of MOFs: the crown ethers BPP34C10DA and NPP36C10DA in the presence of Zn(NO(3))(2)center dot 4H(2)O afforded the MOF-1001 and MOF-1002 frameworks, respectively. The crystal structures of MOF-1001 and MOF-1002 are both cubic and display Fm (3) over barm symmetry. The unit cell parameter of the metal-organic frameworks is a=52.9345 A. Since such MOFs, containing electron-donating crown ethers are capable of docking incoming electron-accepting substrates in a stereoelectronically controlled fashion, the present work opens a new access to the preparation and application of MOFs.