Molecular Self-Assembly: Solvent Guests Tune the Conformation of a Series of 2,6-Bis(2-anilinoethynyl)pyridine-Based Ureas

The conformations of 2,6-bis(2-anilinoethynyl)pyridine-based urea receptors were studied by single crystal X-ray diffraction methods and revealed a rich conformational flexibility influenced by solvents. Whereas receptor L 1 in DMSO prefers an “S” conformation, receptor L 1 crystallizes in an “O” conformation from a DMSO/CH3OH binary solvent system, and a “W” conformation in the ternary solvent mixture DMSO/toluene/1,4-dioxane. In the case of L 2 , the molecule adopts an “S” conformation where water molecules are sandwiched between two molecules of L 2 to form a dimer. Similar to L 2 , L 3 also forms a dimer in which water molecules are sandwiched between L 3 molecules, which are capped with two molecules of DMSO. Such a capping DMSO solvate is lacking in the case of L 2 . Taken together, these results demonstrate that the conformation of 2,6-bis(2-anilinoethynyl) pyridine-based urea receptors can be dramatically manipulated and tuned by the choice of crystallization solvents.