A molecular Popeye: Li + @C 60 and its complexes with [ n ]cycloparaphenylenes.

In this work, we compare for the first time the stability of [ n ]cycloparaphenylene ([ n ]CPP)-based host-guest complexes with Li + @C 60 and C 60 in the gas and the solution phase. Our gas-phase experiments reveal a significant increase in stability for the complexes featuring [9-12]CPP with Li + @C 60 . This increased interaction strength is also observed in solution. Isothermal titration calorimetry shows for the formation of [10]CPP⊃Li + @C 60 a two orders of magnitude larger association constant than that for the C 60 analog. Additionally, an increased binding entropy is observed. This study contributes to a better understanding of host-guest complexes between [ n ]CPPs and endohedral metallofullerenes at a molecular level, which is the prerequisite for future applications.