Semirigid aromatic sulfone-carboxylate molecule for dynamic coordination networks: Multiple substitutions of the ancillary ligands

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′-carboxyphenylsulphonyl)benzene, which nicely balances shape persistence and flexibility to bring about the framework 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′-bipyridine and TCPSB and (2) ancillary ligands (AL) on the two terminal Co^II ions-these include DMF (N,N′-dimethylformamide), DMA (N,N′-dimethylacetamide), CH₃CN, and water. Most notably, the ancillary ligand sites are highly variable and undergo multiple substitution sequences while maintaining the solid reactants/products as single-crystals amenable to X-ray structure determinations. For example, when immersed in CH₃CN, the AL of an as-made single crystal of CoTCPSB-DMF (i.e., DMF being the AL) is replaced to form CoTCPSB-CH₃CN, which, in air, readily loses CH₃CN to form CoTCPSB-H₂O; the CoTCPSB-H₂O 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 ₃CN (to form CoTCPSB-CH₃CN) but NOT with water, methanol, ethanol, DMA, or pyridine; CoTCPSB-H₂O specifically pick outs DMF from a mixture of DMF, DMA, and DEF; an amorphous, dehydrated solid from CoTCPSB-H₂O 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. © 2011 American Chemical Society.