Noncovalent encapsulation of cobaltocenium inside resorcinarene molecular capsules

The encapsulation of cobaltocenium (Cob+) inside hexameric molecular capsules of two different resorcinarenes was investigated in dichloromethane solution. Both 1H NMR spectroscopic and voltammetric experiments clearly reveal that Cob+ experiences encapsulation. Diffusion coefficient measurements obtained from PGSE NMR experiments indicate that the molecular capsules exist in dichloromethane solution in the absence of any cations. Bound and free Cob+ ions undergo slow exchange on the NMR time scale, but the bound Cob+ ions rotate and/or tumble freely inside the molecular capsules. Under experimental conditions suitable for voltammetry the encapsulation of Cob+ depends on the nature of the supporting electrolyte. Tetraalkylammonium hexafluorophosphate, tetrafluoroborate, and perchlorate supporting electrolytes prevent the encapsulation of Cob+, while tetraalkylammonium chloride and bromide salts allow it. The nature of the tetraalkylammonium cation plays a smaller role in the encapsulation. Finally, the structure of the resorcinarene also factors into the overall stability of the molecular assembly.