Double encapsulation of C₆₀, [6]CPP and Li⁺@C₆₀ inside a peropyrene-linked, CPP-based double nanohoop

The peculiar solid-state packing of a peropyrene-linked and CPP-based double nanohoop is known from earlier studies to hinder the desired formation of 1 : 2 complexes with C₆₀. In proof-of-concept experiments presented in this work, we provide evidence of the elusive 1 : 2 complex by employing electrospray ionization mass spectrometry. Additionally, for the first time, a binary 1 : 2 ring-in-ring complex of the double nanohoop with [6]CPP is observed. Most remarkably, we succeeded in generating a stable 1 : 2 complex accommodating the cationic endohedral metallofullerenes Li⁺@C₆₀ as guest molecules, only the second reported example of a 1 : 2 host-guest complex involving Li⁺@C₆₀ and the first within a CPP-based double nanohoop architecture. Evidently, the noncovalent attractive bonding exceeds the Coulomb repulsion of the two positive charges. These findings demonstrate that the intrinsic binding capability of the host is not fundamentally limited to 1 : 1 complexation but rather constrained by solid-state packing effects, suggesting that rational crystal engineering may enable access to such doubly occupied architectures in the condensed phase.