Computational characterization and modeling of buckyball tweezers: Density functional study of concave-convex π⋯π interactions

The geometries and binding energies of a recent buckyball tweezers (C ₆₀H₂₈) and its supramolecular complexes are investigated using recently developed density functionals (M06-L and M06-2X) that include an accurate treatment of medium-range correlation energy. The pincer part of the tweezers, corannulene, has a strong attractive interaction with C₆₀. However, due to the entropy penalty, the calculated gas-phase free energy of association of the C₆₀@corannulene supramolecule is positive 3.5 kcal mol^-1; and this entropy penalty explains why it is difficult to observe C₆₀@corannulene supramolecule experimentally. By using a π-extended tetrathiafulvalene (TTF), in particular 9,10-bis(1,3-dithiol-2- ylidene)-9,10-dihydroanthracene (TTFAQ or C₂₀H₁₀S ₄), as the pincer part, we modeled a new buckyball tweezers. The geometries and binding energies of the new buckyball tweezers and its supramolecular complexes are also calculated. Due to fact that the attractive interaction between TTFAQ and C₆₀ is weaker than that between corannulene and C₆₀, the gas-phase binding free energy in the C ₆₀@C₆₀H ₃₂S₈ supramolecular complex is smaller than that in the C₆₀@C₆₀H₂₈ supramolecule. We also discuss solvent effects.