A Peanut‐Shaped Polyaromatic Capsule: Solvent‐Dependent Transformation and Electronic Properties of a Non‐Contacted Fullerene Dimer

Abstract

Synthesis of molecular containers capable of incorporating multiple fullerenes remains challenging. Reported here is that room-temperature mixing of metal ions with W-shaped bispyridine ligands featuring polyaromatic panels results in the quantitative formation of apeanut-shaped M 2 L 4 capsule.T he capsule reversibly converts into two molecules of an ML 2 double tube in response to changes in the solvent. Notably,t he capsule allows the incorporation of two fullerene molecules into the connected two spherical cavities at room temperature.T he close proximity yet noncontact of the encapsulated C 60 molecules,with aseparation of 6.4 ,w as revealed by X-ray crystallographic analysis.T he resultant, unusual fullerene dimer undergoes sequential reduction within the capsule to generate (C 60 C À ) 2 ,C 60 C À ·C 60 2À ,a nd (C 60 2À ) 2 species.Furthermore,temperature-controlled stepwise incorporation of two C 60 molecules into the capsule is demonstrated.Fullerenes themselves provide unique spherical nanostructures as well as advanced redox activities so that their finite and infinite assemblies have been gathering much attention for the development of functional nanocarbon-based devices and materials. [1] Regarding the finite system, there are many reports on covalently linked fullerene assemblies in dumbbell ( Figure 1a) [2] and dendrimer fashions, [3] as well as transitionmetal-directed fullerene assemblies. [4] In contrast, encapsulation of fullerene molecules within molecular containers is another promising method to efficiently prepare discrete fullerene assemblies through noncovalent interactions. [5] Nevertheless,o wing to the large and bulky structures (ca. 1nmi no uter diameter), the synthesis of host compounds capable of selectively binding two or more fullerene guests in the cavity still remains challenging, [6, 7] even though several host structures possess cavities whose sizes are larger than those of ac ouple of fullerenes. [8] Nitschke and co-workers succeeded recently in the preparation of fullerene (C 60 ) n assemblies (n = 2-4, Figure 1b), in which the fullerenes tightly contact each other,u tilizing porphyrin-based coordination cages. [9] However,t he detailed electrochemical characters of fullerene assemblies are still obscure and the redox properties of non-contacted, discrete fullerene assemblies, which are expected to display unique electronic communication, have not been recorded to date.H ere we present as traightforward synthesis of ap eanut-shaped polyaromatic capsule,b yt he self-assembly of metal ions and W-shaped bispyridine ligands (1)w ith embedded polyaromatic panels, and it allows the selective incorporation of two fullerene C 60 molecules with an intermolecular separation of 6.4 (Figure 1c). Then ovel non-contacted fullerene dimer generates (C 60 C À ) 2 ,C 60 C À ·C 60 2À,and (C 60 2À ) 2 species upon electrochemical reduction in the isolated cavity of the capsule.We have proven that W-shaped polyaromatic ligands 2 with three pyridine coordination sites (Figure 1d)q uantitativ...

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