A Stable Hemicarceplex With an Encapsulated Cationic Guest

A hemicarcerand first reported by Quan and Cram in 1991 was prepared and characterized by X‐ray crystallography. It incorporates CoCp 2 + PF 6 − with an equilibrium constant of ~220 M −1 at 120°C and apparently is indefinitely stable at room temperature. This potential weakly coordinating cation's structure was also determined by X‐ray analysis, and the cation is located on the inside and the counteranion on the outside of the cage through one of its four potential openings. Computations model these results and suggest that the imine linker needs to be modified to reduce the electrostatic attraction of the oppositely charged ions by physically separating them further.