Noncovalent Interactions and Properties of Host-Guest Systems Based on C82/C82Gd Bucky-Balls and Symmetry Broken Nanohoop TP-[11]CPP.

The nanoscale host-guest interactions between a symmetry broken carbonaceous nanohoop TP-[11]cycloparaphenylene (TP-[11]CPP) and endohedral metallofullerene (EMF) C82Gd were explored by using density functional theory calculations. The geometry mutual-matching between TP-[11]CPP and C82Gd is perfect, and the two main configurations of TP-[11]CPP@C82Gd host-guest complexes could be formed spontaneously with high binding energies. Interestingly, the position of the Gd atom in the C82 cage can be adjusted by its external host molecule. The binding strength depends on the structure of the host, but the binding thermodynamics is decided by the structure of the fullerene cage. The selective binding of empty cage C82 from its mixture with EMF C82Gd is discussed by using a standard Boltzmann expression of statistical thermodynamics. In addition, the FT-IR and UV-visible spectra are simulated, host-guest noncovalent interaction regions are investigated based on the electron density and reduced density gradient, and magnetic susceptibility is preliminarily investigated, which may be helpful for a deep understanding of the present host-guest systems in the future. It is anticipated that such a theoretical calculation regarding to carbonaceous nanosize host-guest structures would be a driven force for the developments of novel nanohoop@EMF systems in functional materials, nonchromatographic separation and even nano single molecular electret devices.