From 2 2 to 8 8 Condensation Products of Diamine and Dialdehyde: Giant Container Shaped Macrocycles for Multiple Anion Binding.
The combination of 2,6 diformylpyridine and trans 1,2 diaminocyclopentane fragments results in 2 2, 3 3, 4 4, 6 6, and 8 8 macrocyclic imine condensation products. These imines can be reduced to the corresponding 2 2, 3 3, 4 4, 6 6, and 8 8 macrocyclic amines. The X ray crystal structures of their protonated derivatives show a rich variety of macrocycle conformations ranging from a stepped 2 2 macrocycle to a multiply folded 8 8 macrocycle of globular shape. These compounds bind anions via hydrogen bonds: two chloride anions are bound above and below the macrocyclic ring of the 2 2 amine, one chloride anion is bound approximately in the center of the 3 3 macrocycle, and two chloride anions are deeply buried inside a folded container shaped 4 4 macrocycle, while in the case of the previously reported 6 6 amine four chloride anions and two solvent molecules are buried inside a container shaped macrocycle. Yet another situation was observed for a multiply folded protonated 8 8 macrocycle which binds six sulfate anions; two of them are deeply buried inside the container structure while four anions interact with the clefts at the surface of the container.
The Journal of organic chemistry