Twofold fused concave hosts containing two phosphorus atoms: modules for the sandwich-type encapsulation of fullerenes in variable cavities

The design and synthesis of extended concave host P2 by fusion of two concave phosphorus-containing units is reported. Co-crystallization of P2 and the fullerene guests C(60) and C(70) afforded the 2 : 1 host–guest complexes (P2)(2) ⊃ C(60) and (P2)(2) ⊃ C(70), in which the two concave surfaces of P2 encapsulate the convex surface of the fullerenes in a sandwich fashion. Interestingly, the orientation of the two P2 molecules with respect to each other was observed to be flexible, resulting in the formation of a variety of cavity shapes. MALDI-TOF mass, NMR, and UV-vis absorption spectra supported the formation of host–guest complexes between P2 and the fullerenes in solution. The affinity of P2, containing two phosphorus atoms, towards fullerenes was significantly enhanced relative to P1 with one phosphorus atom.